Quarterly Notes Geological Survey of New South Wales
August 2016 No 147
Outcomes of the Nymagee mineral system study — an improved understanding of the timing of events and prospectivity of the central Lachlan Orogen Abstract The Nymagee mineral system study in central New South Wales provides a new framework for understanding the Cobar Basin and adjacent areas including the Mount Hope Trough, Kopyje Shelf (Canbelego–Mineral Hill Volcanic Belt) and Mouramba Shelf. This summary reports 22 new U–Pb SHRIMP dates and a cassiterite U–Pb LA-ICPMS date. In addition, the palaeontology of key units was reviewed to better define time–space relationships and to support the interpretation of the U–Pb dating program. Other significant aspects include a study of the volcanic facies present in the Mount Hope Group and Kopyje Group based on their petrology; collection of new sulfur- and lead-isotope data to characterise inputs of basement and basin-derived sulfur and metals into a range of mineral systems; the spectral scanning of 41 diamond drillholes using the HyLogger™ to map the mineralogical response of host rocks to alteration and metamorphism; and mapping of the former May Day gold mine open cut. The new dating shows that there was a general age progression of S-, I- and A-type magmatism in the area and, together with a review of palaeontology, showed that units of the Mount Hope Group, Amphitheatre Group and Kopyje Group are of latest Silurian to earliest Devonian age. Other important outcomes include: the stratigraphy of the Mount Hope Group can be simplified with six lava types recognised and that a number of volcanic centres are present within the area; the majority of the southern Cobar Superbasin underwent sub-greenschist to lowest greenschist facies metamorphism and only late diagenetic conditions existed for the Winduck Shelf; and the area was deformed during the Middle Devonian Tabberabberan Orogeny. For structurally controlled high-sulfide zones, it is proposed that sulfur- and lead-isotope data indicate that hot fluids leached sulfur and/or base metals from the basement to the Cobar Basin (e.g. Hera, Mallee Bull, Nymagee) in addition to contributions from basinal sequences, and that those fluids deposited their metals by fluid mixing with possible cooling of these fluids to trigger sulfide precipitation. Keywords: Nymagee, Lachlan Orogen, Cobar Basin, Mount Hope Trough, Kopyje Shelf, Canbelego–Mineral Hill Volcanic Belt, Mouramba Shelf, mineralisation, dating, sulfur isotope, lead isotope, volcanic facies, alteration, metamorphism
AUTHORS Peter M. Downes, 1Phil L. Blevin, 2 Richard Armstrong, 3Carol J. Simpson, 1 Lawrence Sherwin, 1David B. Tilley and 1Gary R. Burton 1
Geological Survey of New South Wales, Research School of Earth Sciences, Australian National University ,3Consultant 1
2
© State of New South Wales through Department of Industry, Skills and Regional Development 2016. Papers in Quarterly Notes are subject to external review. External reviewer for this issue was Martin Scott. His assistance is appreciated. Quarterly Notes is published to give wide circulation to results of studies in the Geological Survey of New South Wales. Papers are also welcome that arise from team studies with external researchers. Contact:
[email protected] ISSN 0155-3410 (print) ISBN 2204-4329 (online)
Introduction
Contents Abstract 1 Introduction 2 Geological setting
3
Previous studies
7
Results 10 Age dating
10
Palaeontological review
11
HyLogger metamorphism and alteration study
14
Petrographic volcanic facies review of the Mount Hope Group and Canbelego–Mineral Hill Volcanic Belt 17 Isotopic studies
22
Other studies
25
Discussion
27
Conclusions 31 Acknowledgements 32 References 32 Technical editing:
Richard Facer
Production co-ordination and general editing :
Simone Meakin and Geneve Cox
Geospatial information:
Kate Holdsworth
Layout:
Nicole Edwards
Cover image: Pyrrhotite–chalcopyrite filled fractures in drillhole 4MCD008 (415170E, 6413390N, Zone 55) at the Mallee Bull deposit. Field of view is about 4 cm wide. (Photographer P.M. Downes).
Disclaimer
The information (and links) contained in this publication is based on knowledge and understanding at the time of writing (March, 2016). However, because of advances in knowledge, users are reminded of the need to ensure that the information upon which they rely is up to date and to check the currency of the information with the appropriate officer of the Department of Industry, Skills and Regional Development or the user’s independent adviser. The product trade names in this publication are supplied on the understanding that no preference between equivalent products is intended and that the inclusion of a product name does not imply endorsement by the department over any equivalent product from another manufacturer.
Copyright
© State of New South Wales through Department of Industry, Skills and Regional Development 2016. You may copy, distribute and otherwise freely deal with this publication for any purpose, provided that you attribute the Department of Industry, Skills and Regional Development as the owner.
The Nymagee mineral systems study (Nymagee Project) was undertaken to update the geological, geochronological, geochemical and mineral occurrence framework for the Nymagee 1:250 000 map sheet area and adjacent areas (Figure 1). The project area is located in the centre of New South Wales; covers a key part of the Central Subprovince of the Lachlan Orogen and includes parts of the late Silurian–Early Devonian Cobar Basin as well as the adjacent Mount Hope Trough, Rast Trough, Winduck Shelf, Mouramba Shelf and Kopyje Shelf (which also hosts the Canbelego– Mineral Hill Belt). These units are part of the ‘Cobar Superbasin’ which a number of workers, including David and Glen (David & Glen 2004; David 2006, 2010) have used to group these deep water and adjacent shallow water palaeogeographic units. The Nymagee area covers a complex geological environment with different mineralisation styles and multiple mineralising events. Many companies are exploring in the area. A number of new mineral deposits/zones have recently been discovered (e.g. Gundaroo, Mallee Bull). There is recognised potential for the presence of strategic metals, including tin and tungsten. However, little work had been undertaken by the Geological Survey of New South Wales since the completion of the Nymagee metallogenic project in the early 1990s (Suppel & Gilligan 1993; Suppel & Pogson 1993). The need for an improved understanding of the area had been identified when compiling the 1:1 500 000 scale metallogenic map of New South Wales (Downes et al. 2011). The project aims for the Nymagee study have been described in Downes et al. (2013). Key elements of the project included: the dating of volcanic units, granites and mineralisation to better understand the timing of events; investigating potential sources of metals and mineralising fluids by using sulfur- and lead-isotopes; reviewing the petrology of the Mount Hope Group and Canbelego–Mineral Hill Volcanic Belt to better understand the distribution of volcanic facies — and to identify possible volcanic centres; and to map alteration associated with mineralisation, using the HyLogger™ spectral scanner at Londonderry. Other work undertaken as part of the project included a structural investigation of the May Day mine area, an updated mineral occurrence dataset, a revised basement interpretation for the Nymagee 1:250 000 map sheet area and an improved whole rock geochemistry dataset.
QUE EN SLAN D
Bourke BOURKE
LOUTH
SO U TH AU STR AL I A
Wilcannia
BARNATO
WALGETT
COBAR
NYNGAN Nyngan
COBAR
Dubbo
Nymagee
Broken Hill IVANHOE
NYMAGEE Mount Hope
NARROMINE
Newcastle
BOOLIGAL
Lake Cargelligo CARGELLIGO
FORBES
SYDNEY SOUTH PACIFIC OCEAN Wollongong
Hay Wagga Wagga
REFERENCE
Canberra
Nymagee project area
A.C.T
Central Lachlan Orogen Cobar Basin Kopyie Shelf
VICTO R IA
Mount Hope Trough
0
100
200 km
Mouramba Shelf Rast Trough Eastern Lachlan Orogen 1:250 000 map sheet 2016_05_020
Figure 1. Location of the Nymagee project area.
The aim of this paper is to present new U–Pb (SHRIMP and LA-ICPMS) dating for the Nymagee project area, summarise key findings of individual studies carried out as part of the Nymagee project and to discuss the major project outcomes. Details of individual studies and results are being made available as papers published in refereed journals, as Geological Survey of New South Wales open file reports and/or as updated datasets available through the department’s online data warehouse. For this project the absolute dating time scale of Gradstein et al. (2012) was used to compare stratigraphic ages to radiometric ages. A number of studies are ongoing and include 40Ar/39Ar dating of mineralisation and mapping of thermal (metamorphic) isograds through the area. The results of these studies will be reported separately. The results of this study are being integrated into the 1:500 000 metallogenic map for the Cobar area (Fitzherbert et al. in press) that is planned for publication later in 2016.
Geological setting The Lachlan Orogen is part of the >1500 km-wide Tasmanides that developed along the Pacific margin of the Australian craton during Palaeozoic time (Foster et al. 1999; Glen 2005). The Tasmanides developed as a series of tectonic cycles consisting of periods of prolonged crustal extension, in response to slab rollback at the leading edge of the palaeo-Pacific oceanic plate and a retreating subduction boundary (Collins 2002; Collins & Richards 2008) followed by regional-scale deformation events. The Lachlan Orogen in New South Wales includes three major cycles — the Benambran Cycle (490–433 Ma), which was terminated by the earliest Silurian Benambran Orogeny; the Tabberabberan Cycle (433–380 Ma), which was terminated by the Middle Devonian Tabberabberan Orogeny and the Kanimblan Cycle (380–~340 Ma) that was terminated by the Early Carboniferous Kanimblan Orogeny (Glen 2005, 2013; Collins & Richards 2008).
Quarterly Notes
3
145°30′E 31°26′S
147°12′E 31°27′S
COBAR Hermidale Canbelego
Pipeline Ridge
Cobar Basin
Nymagee Igneous Complex Gundaroo (De Nardi, Ridge)
4
1
Crowl Creek South Shuttleton
2
Winduck Shelf
R7 prospect
Manuka
3
Hera
Canbelego–Mineral Hill Volcanic Belt
Sandy Creek
6
Gilgunnia Granite Thule Granite
Ordovician basement
Nymagee Nymagee
May Day
Mallee Bull
Mouramba Shelf Yellow Mountain
5
MD 2-Siegals
Erimeran Granite
Mineral Hill
Fountaindale
Boolahbone Granite
Wagga Tank
Blind Calf
BMW
Melrose Tallebung
Mount Allen
Mount Hope Trough
Winduck Shelf
Mount Hope Great Central mine area Mount Solar
Ordovician basement
Rast Trough
Walters Range Shelf
Derrida Granite
Condobolin Condobolin
Euabalong
33°09′S 145°28′E
33°10′S 147°12′E
REFERENCE Ordovician Girilambone Group Wagga and Bendoc groups Fifield Suite Silurian to Early Devonian (Cobar Superbasin) Cobar Basin Amphitheatre Group Mount Hope Trough Mount Hope Group Broken Range Group Bootheragandra Group Rast Trough
Kopyje Shelf
Faults
Kopyje Group
1
Jackermaroo Fault
Mine or prospect
Ootha Group
2
Buckwaroon Fault
Locality
3
Blue Mountain Fault
Highway
Mouramba Group
4
Crowl Creek Fault
Major road, sealed
Walters Range Group
5
Scotts Craig Fault
Major road, unsealed
6
Rookery Fault
Unit boundary
Mouramba Shelf
Winduck Shelf Mulga Downs Group
Fault
Winduck Group
Project area
Yarra Yarra Creek Group Silurian to Early Devonian Granites S-, I- and A-type granites (undifferentiated)
Rast Group
0
15
30 km
2016_05_021
Figure 2. Generalised geology and major tectonic units for the Nymagee project area. The map shows the location of major mineralised zones and geological units at group level (only). Individual formations referred to in the text are not shown unless they do not belong to a formal group. Note: based on geophysical and whole-rock geochemical data the Derrida Granite (Derrida Phase — Meakin 2005) is now interpreted to be part of the Ungarie Granite (this study, Fitzherbert et al. in press).
4
August 2016
The focus of the present study is the Nymagee 1:250 000 map sheet area and environs which lies in the Central ‘Subprovince’ (Glen 2005) of the Lachlan Orogen (Figure 1). Basement to that area includes Ordovician turbiditic sedimentary rocks of the Girilambone and Wagga groups (Figure 2). The Wagga Group is of Lancefieldian to early Gisbornian age (Colquhoun, Hendrickx & Meakin 2005). By contrast, the age of that part of the Girilambone Group which lies within the study area is poorly constrained with, as yet, no fossils identified. Late Ordovician conodonts have been identified to the east of the study area — 20 km north of Condobolin (Percival 1999) whilst Early to Middle Ordovician conodonts have been identified by Percival (2006, 2007) in the Sussex and Byrock 1:100 000 map sheet areas (see Burton et al. 2012) — to the north of the study area. Also associated with the Girilambone Group are minor mafic units, including the Break O’Day Amphibolite (not shown — note: individual formations and members are not shown in figures unless otherwise stated due the scale and available space). These Ordovician sequences were deformed and metamorphosed during the Benambran Orogeny in the early Silurian (443–433 Ma — Glen 2005; supported by 40Ar/39Ar dates (on deformationrelated mica) of 440.2 ± 2.6 Ma, 435.2 ± 2.6 Ma and 434.3 ± 3.5 Ma — Fergusson et al. 2005). Following the Benambran Orogen the area underwent extension which resulted in extensive granitic plutonism and the development of a series of north-trending shallow- to deep-water basins/ rifts during the late Silurian to Early Devonian. These palaeogeographic units include the Mount Hope Trough in the western part of the study area, the Cobar Basin and the poorly exposed Rast Trough in the central part of the area (Figure 2). Flanking these is the Mouramba Shelf and shallow marine Kopyje Shelf (which hosts the Canbelego–Mineral Hill Volcanic Belt) to the east of the Cobar Basin whilst the Winduck Shelf formed to the west of the Cobar Basin (Figure 2, Glen et al. 1985). The major plutons that were emplaced during the late Silurian include the Derrida Granite (Derrida Phase — Meakin 2005, now interpreted to be part of the Ungarie Granite based on geophysical and whole rock geochemical data — this study, Fitzherbert et al. in press), Erimeran Granite, Thule Granite and the mount hope Granite. The timing of this plutonism will be discussed later in this paper. The Mount Hope Trough, which hosts mineralisation in the Great Central mine area (Browns lode, Comet, Quarry Hill, Great Central–Hodge lode, Great Central South), Wagga Tank, Mount Allen (Au) and Mount Solar, is dominated by felsic volcanic and derived sedimentary rocks of the late Silurian to earliest Devonian (Sherwin 2013; this study) Mount Hope
Group (Figure 2). The Mount Hope Group includes the Mount Halfway Volcanics, Mount Kennan Volcanics, Double Peak Volcanics and Regina Volcanics (individual units not shown in Figure 2) and similar age fine- to coarse-grained clastic rocks of the Broken Range Group (MacRae 1987a; Scheibner 1987) that David (2005) suggested formed the sag phase of the Mount Hope Trough. East of the Mount Hope Trough is the deep water late Silurian to earliest Devonian (Sherwin 2013; this study) Cobar Basin, which dominates the central part of the study area. The Cobar Basin, which hosts mineralisation at Mallee Bull, May Day and South Shuttleton, is dominated by fine-to medium-grained turbidites (MacRae 1987a, b) of the Amphitheatre Group (Figure 3). The Amphitheatre Group can be subdivided into the informal lower Amphitheatre Group and upper Amphitheatre Group which are separated by the Shume Formation (not shown in Figures 2 & 3). Both the lower and upper Amphitheatre units include a sequence of quartz-rich to quartz–lithic sandstones and siltstones whilst the Shume Formation also includes minor felsic volcanic and volcaniclastic rocks (MacRae 1987b). To the east of the Cobar Basin is the shallow to deep water Mouramba Shelf which hosts the Hera and Nymagee deposits (Figure 2). This Shelf includes the late Silurian to earliest Devonian (Sherwin 2013) Mouramba Group (Figure 2) which is dominated by the Burthong Formation (not shown). Both MacRae (1987b) and Pogson (1991a) noted that the Burthong Formation includes a sequence of very fine- to mediumgrained interbedded sandstones and siltstones with minor basal conglomeratic units and minor localised felsic volcanic/volcaniclastic horizons. Paterson (1974) noted the presence of slumping, cross-bedding, graded bedding and soft-sediment deformation in the Burthong Formation at the Nymagee mine and MacRae (1987b) recorded current-generated ripple marks and flutes — all of which support the interpretation that the Burthong Formation represented an outwash fan to marine shelf sequence. Separated from the Cobar Basin area by outcropping sequences of the Ordovician Girilambone Group is the Canbelego–Mineral Hill Volcanic Belt (also known as the Mineral Hill Rift — see Scheibner & Basden 1998). This late Silurian to earliest Devonian volcanic package is part of the Kopyje Shelf (Suppel & Gilligan 1993) and is host to mineralisation at Mineral Hill and Yellow Mountain (Figure 2). Units forming the Canbelego– Mineral Hill Volcanic Belt are grouped as part of the Kopyje Group (Figure 2) (MacRae 1987b; Pogson 1991a,b) which includes the Babinda Volcanics, Majuba Volcanics and Mineral Hill Volcanics (individual units not shown). The Mineral Hill Volcanics, which Blevin
Quarterly Notes
5
145°30′E 31°26′S
147°12′E 31°27′S
COBAR Hermidale Canbelego
Baledmund Formation (Pipeline Ridge)
Thule Granite
Nymagee Igneous Complex
Nymagee Cu mine
Nymagee felsic dykes
Nymagee
Hera
Thule Granite
R7 unnamed granite Erimeran Granite
Gilgunnia Granite
Tarran Volcanics Thule Granite Boolahbone Granite
Mount Allen Granite
Mount Halfway Volcanics Fountaindale (Mo) Nombiginni Volcanics
Blind Calf Urambie Granite Tallebung
Derrida Granite
Regina Volcanics
Ural Volcanics (Shepherds Hill Volcanics)
Condobolin
Euabalong 33°09′S 145°28′E
33°10′S 147°12′E
REFERENCE Dating carried out as part of the Nymagee project
Ordovician
Kopyje Shelf
Girilambone Group
Kopyje Group
Locality
Ar39/Ar40
Wagga and Bendoc groups
Ootha Group
Highway
SHRIMP
Fifield Suite
SHRIMP (monazite) LA-ICPMS (cassiterite) Dating from other studies LA-ICPMS (Norman 2004) Re–Os (molybdenite) (Creaser 2003)
Silurian to Early Devonian (Cobar Superbasin) Cobar Basin Amphitheatre Group Mount Hope Trough Mount Hope Group
SHRIMP (Black 2007)
Broken Range Group
SHRIMP (Isaacs 2000)
Bootheragandra Group
SHRIMP (Spandler 1998) LA-ICPMS (Bull et al. 2008)
Rast Trough
Mouramba Shelf
Major road, sealed
Mouramba Group
Major road, unsealed
Walters Range Group
Unit boundary
Winduck Shelf
Fault
Mulga Downs Group
Project area
Winduck Group Yarra Yarra Creek Group Silurian to Early Devonian Granites S-, I- and A-type granites (undifferentiated)
Rast Group
0
15
30 km 2016_05_022
Figure 3. Location for the U–Pb SHRIMP geochronology and LA-ICP-MS U–Pb geochronology samples dated as part of the Nymagee study. Also shown in this figure are the locations of samples dated by other workers (Table 1). All dating was done on zircon unless otherwise stated.
6
August 2016
and Jones (2004) suggest is part of the I-type Majuba “Supersuite”, includes felsic volcanic and related sedimentary rocks, together with minor dolomites whilst the Babinda Volcanics and Majuba Volcanic are two thick felsic volcanic units that interfinger with fine-grained terrigenous to shallow marine sedimentary rocks of the Baledmund Formation (Pogson 1991a). South of the Cobar Basin is the Early Devonian (Colquhoun, Meakin & Cameron 2005) Rast Trough (Figure 2) which hosts the Browns Reef deposit (not shown — located at 33.322S, 146.326E). The trough includes a broadly transgressive sequence with a basal syn-rift succession of coarse, basement-derived sedimentary rocks, quartz-rich sandstones, basal siliclastic and volcaniclastic rocks and finally A-type (transitional to I-type) submarine to ?subaerial felsic volcanic rocks of the Ural Volcanics (Figure 2) (Colquhoun & Cameron 2005; Bull et al. 2008). Deposition in the Rast Trough commenced in the late Silurian, with the majority of the trough fill being deposited during the Lochkovian, although, deposition probably continued until late in the Early Devonian (early Emsian — Colquhoun, Meakin & Cameron 2005). North of the Mount Hope Trough and west of the Cobar Basin is the Winduck Shelf which is represented by the Early Devonian Winduck Group (Figure 2). Within that area carbonate- and sandstone-hosted base metal–silver mineralisation (Manuka — formerly Wonawinta; Gundaroo — Figure 2) is hosted by the Pragian to early Emsian (Sherwin 2013) Gundaroo Sandstone (not shown). Both Scheibner (1987) and MacRae (1987a) noted that the Gundaroo Sandstone includes thinly to thickly bedded sandstones and siltstones. MacRae (1987a) also noted the presence of minor limestone units, including the Booth Limestone Member which is now exposed at the Manuka silver mine. In the mine area the exposed limestone unit shows development of a ‘tower karst’-like weathering surface which interfingers with and is draped by pyritic black shales. Many significant faults dissect the area (Figure 2). These include the Rookery Fault and adjacent structures on the eastern side of the Cobar Basin, the Blue Mountain Fault and Jackermaroo Fault on the western edge of the basin. Cross-cutting structures including the Crowl Creek Fault which trends northwest and the Buckwaroon Fault which trends northeast. The timing of basin inversion and deformation of the late Silurian to earliest Devonian sequences, which host the majority of mineralisation, is poorly constrained. Glen et al. (1992) proposed that the initial deformation of the Cobar Basin occurred between 395 and 400 Ma (i.e. the Cobar deformation — Scheibner & Basden 1998) while Sun et al. (2000) proposed a somewhat
later timing at around 385 to 389.2 Ma — essentially correlating this event with the Tabberabberan Orogeny. Mineralisation styles within the project area include massive to colloform and crustiform banded gold– base metal epithermal systems (Mineral Hill, Pipeline Ridge); carbonate-hosted silver–lead–zinc “Mississippi Valley”-type mineralisation (Manuka); structurally controlled low sulfide gold (‘orogenic gold’ — May Day); high sulfide gold–base metal ‘Cobar-type’ deposits (Hera, Nymagee, Mallee Bull); possible volcanic associated massive sulfide (VAMS)-type base metal systems (Great Central); and intrusion-related tin, tungsten and molybdenum mineralisation (e.g. Tallebung) (Figure 2).
Previous studies The Nymagee area has been the focus of many studies since the discovery of copper, gold, lead–zinc–silver and tin–tungsten in the late nineteenth century. Important early studies include those by Carne (1908, 1911, 1912), with the majority of the project area initially being mapped at 1:250 000 scale during the late 1960s (Adamson et al. 1968). Furthermore, detailed mapping, supported by explanatory notes were completed in the 1980s and early 1990s (e.g. MacRae & Pogson 1985; MacRae 1987a, b, 1988, 1989; Pogson 1991a, b; Scheibner 1985, 1987; Trigg 1987, 1988). This 1:100 000 scale mapping project culminated in the 1:250 000 Nymagee metallogenic map and explanatory notes that were completed in 1993 (Suppel & Gilligan 1993, Suppel & Pogson 1993). Major regional studies completed since the completion of the Nymagee metallogenic study (Suppel & Gilligan 1993) include the pmd*CRC Cobar project in the mid-2000s — the results of which went largely unpublished, and a PhD project by David (2005, 2006) on the structural setting of the Cobar Basin. However, the timing of magmatic events and mineralisation, and the nature of the ore forming fluids, was still poorly constrained. Previous dating studies undertaken since the completion of metallogenic mapping project include those by Spandler (1998), Isaacs (2000), Blevin (2003), Norman (2004), Black (2007) and Bull et al. (2008). In total there are 13 U–Pb dates for zircons for volcanic rocks and plutons and a single Re–Os date for molybdenite (from the Fountaindale prospect). Table 1 summarises past dating results. Prior to this the timing of geological events was largely based on palaeontological data, field unit relationships and K–Ar and Rb–Sr dating. Few isotope data are available for the Nymagee area. Previous S-isotope data include those from: Rayner (1969 — single analyses for Blackfellow Dam, Mount
Quarterly Notes
7
Table 1. Summary of previous U–Pb and Re–Os dating results carried out in the Nymagee project area since the late 1990s. Unit/prospect dated*
Sample no. (where available)
Dating technique
Age (Ma)
Reference
Boolahbone Granite
TRI-53
SHRIMP
420.0 ± 2.5
Black (2007)
Erimeran Granite
TRI-44
SHRIMP
427.1 ± 2.4
Black (2007)
Erimeran Granite
Ermeran
SHRIMP
434 ± 4
Isaacs (2000)
Fountaindale Granodiorite
TYM-063
LA-ICP-MS
420 ± 2
Norman (2004)
Fountaindale prospect
DDH AOG 8A
Re–Os
424.7 ± 1.5
Creaser pers. comm. (2003) in Blevin (2003)
Mineral Hill Volcanics
CA01
SHRIMP
422.2 ± 3.7
Spandler (1998)
Mineral Hill Volcanics
CA120
SHRIMP
428.2 ± 3.9
Spandler (1998)
Mount Hope Volcanics
KB511B–MHV: MHup
LA-ICP-MS
409 ± 4
Bull et al. (2008)
Mount Hope Volcanics
KB502–MHV: Mhcd
LA-ICP-MS
409 ± 7
Bull et al. (2008)
Mount Hope Volcanics
KB426–MHV: MHmv
LA-ICP-MS
415 ± 5
Bull et al. (2008)
Nymagee Igneous Complex
NIC
SHRIMP
~425
Isaacs (2000)
Tarran Volcanics
Tarran
SHRIMP
433.1 ± 4.4
Isaacs (2000)
Wilmatha Granite
CA05
SHRIMP
421.1 ± 3.4
Spandler (1998)
Yellow Mountain Granite
TRI-24
SHRIMP
420.6 ± 2.8
Black (2007)
*Units and deposits are arranged in alphabetical order Table 2. Summary of results for the U–Pb SHRIMP dating of zircons and monazite and U–Pb LA-ICP-MS dating of cassiterite carried out as part of the Nymagee project.
8
Unit dated
Sample no.
S-, I- or A-typea
Mineral dated
Age (Ma)
Baledmund Formation
PCN092 226.75–227.95 m
?
zircon
419.3 ± 2.8
Pipeline Ridge volcaniclastic sandstone
Bodorkos et al. (2015)
Blind Calf felsic dyke
PB-12-DBC-01
?
zircon
413.9 ± 3.2
rhyolite volcanic rock
this study
Boolahbone Granite
TRI-52
A-type
zircon
415.8 ± 3.1
very felsic granite
this study
Derrida Granite (now Ungarie Granite)
PB_11 NYM_04
S-type
zircon
426.3 ± 3.3
medium grained granite
this study
Erimeran Granite
PB_11_NYM_02
S-type
zircon
424.5 ± 2.6
medium grained granite
this study
Gilgunnia Granite
TRI-47
?S-type
zircon
422.5 + 3.6
medium grained ?S-type
this study
Mineral Hill Volcanics
TRI-58
I-type
zircon
417.6 ± 3.2
rhyolite — Freytag Dome
this study
Mount Allen Granite
PB_11 NYM_05
S-type
zircon
422.8 ± 2.7
medium grained granite
this study
Mount Halfway Volcanics
ZFXDD1 408.9m
S-type
zircon
422.8 ± 2.6
Mount Halfway Volcanics
Chisholm et al. (2014)
Nombiginni Volcanics
PB_11_NYM_14
S-type
zircon
419.1 ± 3
rhyolite adjacent to this study quarry
August 2016
Comment and rock type
Reference
Unit dated
Sample no.
S-, I- or A-typea
Mineral dated
Age (Ma)
Comment and rock type
Nymagee felsic dykes
PDNY 12.002
I-type
zircon
415 ± 2.7
Nymagee felsic dyke swarm
this study
Nymagee Igneous Complex
PB_11_NYM_03
S-type
zircon
nr
foliated portion
this study
Nymagee Igneous Complex
TRI-39
S-type
zircon
nr
massive phase
this study
Nymagee Igneous Complex
TRI-39
S-type
monazite
428.1 ± 4.3
massive phase
this study
R7 prospect (unnamed granite)
DD09NV0005 278.80–280.70 m
S-type
zircon
422.8 ± 4.9
R7 Prospect, unnamed granite
Chisholm et al. (2014)
Regina Volcanics PB-12-REG-01
S-type
zircon
418.7 ± 3.1
Great Central mine this study
Tallebung
mineralisation
cassiterite
418 ± 6
Tallebung mine
this study
Reference
Tarran Volcanics
TRI-37
A-type
zircon
415 ± 3.9
porphyritic dyke member
this study
Thule Granite
CCRC 535 28 m
S-type
zircon
425.7 ± 2.4
‘Wonawinta Anticline’
Chisholm et al. (2014)
Thule Granite
CCR 144 366.68–370.00 m
S-typev
zircon
427.2 ± 3.1
De Nardi prospect — Thule Granite intersected in drilling
Chisholm et al. (2014)
Thule Granite
TRI-54
S-type
zircon
424.1 ± 2.9
main body (southern end)
this study
Ural Volcanics (formerly Shepherds Hill Volcanics)
PDNY 12.003
A-type
zircon
412.2 ± 2.6
Shepherds Hill quarry
this study
Urambie Granodiorite
GRB-MO-04
S-type
zircon
428.0 ± 1.7
porphyritic granodiorite
Bodorkos et al. (2015)
Notes a Compositional type based on Blevin (2002) and present study. All samples except that for Tallebung were analysed using the U–Pb SHRIMP technique. The Tallebung sample was analysed using LA-ICP-MS.
Quarterly Notes
9
Hope and Nymagee), Bush (1980 — Mineral Hill); Northcott (1986 — Anomaly 3 in the Great Central mine area); Ryan (1987 — Wagga Tank); Spandler (1998 — Mineral Hill); David (2005); Mernagh (2008 — Hera, Mineral Hill, Fountaindale, Sandy Creek); and Downes (2009). For Pb-isotopes, previous studies include the unpublished data in the CSIRO Pb-isotope database (92 analyses — many from samples supplied by David Suppel and Peter Downes as part of GSNSW/CSIRO collaborative studies) together with those by David (2005 — Wagga Tank, 6 analyses), Mernagh (2008 — Hera, Mineral Hill, Sandy Creek, 7 analyses) and Huston (2016 — Mallee Bull, Nymagee, 2 analyses).
Results Age dating To better define the timing of magmatism and mineralising events across the project area 22 samples from igneous-related units (granites — 13; volcanic rocks —7; felsic dykes — 2) were analysed using the U–Pb SHRIMP dating technique (Table 2) with an additional sample of cassiterite, from the Tallebung mine being analysed using the U–Pb LA-ICP-MS dating technique. The majority of analyses were carried out at the Research School of Earth Sciences, Australian National University (Canberra — this study) with the remaining analyses being carried out at Geoscience Australia (GA — see Chisholm et al. 2014; Bodorkos et al. 2015). The location of samples is shown on Figure 3, with sample locations included in Appendix 1. The focus of the U–Pb SHRIMP dating program was to better understand the timing of magmatic events and unit correlations across the project area. Based on our results, the units dated for this study can be grouped into three distinct populations: an older group of S-type granites that formed between ~428 and ~424 Ma; a group of S- and I-type granites and volcanic rocks that formed between ~423 and ~418 Ma, and a younger group of A- and I-type intrusions and volcanic units that formed between ~416 and ~412 Ma. The age of the Nymagee Igneous Complex which has multiple structural fabrics and is interpreted to predate the middle to late Silurian sequences in the Nymagee area has been resolved. Two samples (TRI-39, PB_11_ NYM_03) analysed by U–Pb SHRIMP dating on zircons contained populations of inherited zircons with no apparent magmatic overgrowths. However, a second attempt using U–Pb SHRIMP dating of monazite from TRI-39 gave a date of 428.1 ± 4.3 Ma, which is interpreted to be the magma crystallisation. This result is discussed later.
10
August 2016
Four S-type granitoids — the Derrida, Erimeran, Thule and Urambie plutons, included in the present study — have ages between ~428 and ~424 Ma that are within error. The Derrida Granite (now Ungarie Granite — this study) gave a 426 ± 3.3 Ma date, the Erimeran Granite yielded a 424.5 ± 2.6 Ma date (supported by a date of 427.1 ± 2.4 Ma by Black 2007 — Table 1). The Thule Granite gave dates of 427.2 ± 3.1 Ma (Chisholm et al. 2014 — intersected by drilling at the De Nardi prospect), 425.7 ± 2.4 Ma (Chisholm et al. 2014 — exposed in the ‘Wonawinta Anticline’) and 424.1 ± 2.9 Ma (southern part of the main body) whilst the Urambie Granodiorite yielded a date of 428.0 ± 1.7 Ma (Bodorkos et al. 2015) (Table 2). A previous SHRIMP date for zircon for the Erimeran Granite by Isaacs (2000) of 434 ± 4 Ma is not supported by the present study. A feature of these granites is that they intrude Ordovician basement units and clearly predate the late Silurian to Early Devonian felsic volcanic and sedimentary units that host the majority of mineralisation associated with the Cobar Superbasin, as noted by previous workers. Several of the volcanic units and intrusions dated as part of the present study yielded ages between ~423 and ~418 Ma. On the western side of the study area they include the Gilgunnia Granite (422.5 ± 3.6 Ma), the Mount Allen Granite (422.8 ± 2.7 Ma) (both S-type — Blevin 2002, this study) and an unnamed intrusion related to mineralisation at the R7 prospect (422.8 ± 4.9 — Chisholm et al. 2014) that is also S-type. Similar dates have been obtained for units of the Mount Hope Group (Mount Hope Trough — Figure 2), including the Mount Halfway Volcanics (422.8 ± 2.6 — Chisholm et al. 2014) (S-type — Blevin 2002), the Nombiginni Volcanics (419.1 ± 3 Ma) and the Regina Volcanics (418.7 ± 3.1 Ma) (both S-type — this study). Furthermore, the dates for the Mount Halfway Volcanics and Gilgunnia Granite are almost identical — supporting the previous interpretation by Blevin (1999) that they are coeval and co-magmatic. Similarly, Scheibner (1987) described the Mount Allen Granite as intruding and having a gradational contact with the Double Peak Volcanics (Mount Hope Group) — again supporting a late Silurian to earliest Devonian age for the Mount Hope Group and related intrusions. However, the proposed timing for volcanic units of the ‘Mount Hope Volcanics’ (Mount Halfway Volcanics) by Bull et al. (2008) using U–Pb LA-ICP-MS dating of zircons (reported results — 409 ± 4 Ma, 409 ± 7 Ma and 415 ± 5 Ma) is not supported by the present study. On the eastern side of the Cobar Basin is the Canbelego–Mineral Hill Volcanic Belt. There, two units were dated as part of the present study. They are the Baledmund Formation, which yielded a date of 419.3 ± 2.8 Ma (Bodorkos et al. 2015) for a
volcaniclastic sandstone at the Pipeline Ridge prospect and the felsic I-type (Blevin 2003, Blevin & Jones 2004) Mineral Hill Volcanics which yielded a date of 417.6 ± 3.2 Ma for a rhyolite from the unmineralised Freytag Dome (just outside the Mineral Hill mine). The age for the Baledmund Formation, which interfingers with the felsic I-type (Blevin 2003; Blevin & Jones 2004) Florida Volcanics to the north, is supported by a U–Pb SHRIMP date for zircon from the Florida Volcanics of 421.7 ± 2.3 Ma (Black 2005) and by the latest Silurian to earliest Devonian brachiopod and conodont assemblages found elsewhere in the Baledmund Formation (MacRae 1987b). Our age for the Mineral Hill Volcanics (Freytag Dome, Table 2) is only slightly younger than the date from Spandler (1998) for a quartz–feldspar porphyry intruding the Mineral Hill Volcanics which yielded a U–Pb SHRIMP date for zircons of 422.2 ± 3.7 Ma — and is supported by the latest Silurian fossil assemblages associated with the Mineral Hill Volcanics (see palaeontology review — this study) and by 40Ar/39Ar dating on white micas from mineralised zones at Mineral Hill (Downes & Phillips in prep.). Five units yielded significantly younger U–Pb SHRIMP dates for zircon than those discussed above and formed between ~416 and ~412 Ma. They include: the felsic A-type (Blevin 2003; Blevin & Jones 2004) Boolahbone Granite (415.8 ± 3.1 Ma); the felsic A-type (this study) Tarran Volcanics and the Ural Volcanics (formerly Shepherds Hill Volcanics) which yielded ages of 415 ± 3.9 Ma and 412.2 ± 2.6 Ma (respectively); the Nymagee felsic dyke swarm (southeast of Nymagee), interpreted to be I-type, yielded a 415 ± 2.7 Ma age; and the felsic dykes intruding Ordovician age metasedimentary rocks at the Blind Calf copper prospect (near Mineral Hill) gave an age of 413.9 ± 3.2 Ma. The timing of mineralisation in the Nymagee area is poorly constrained. As part of the present study cassiterite from the Tallebung tin system, was dated using the U–Pb LA–ICP-MS technique. The sample yielded a date of 418 ± 6 Ma. Although the uncertainty on this age is large, the age suggests that it is unlikely that Tallebung is related to the ~428 to 424 Ma magmatic event (which includes the Erimeran Granite) but is part of the ~423 to 418 Ma or younger magmatic events. There are possible issues with the dating for the Boolahbone Granite (415.8 ± 3.1 Ma) and the Tarran Volcanics (415 ± 3.9 Ma). The Boolahbone Granite was interpreted by Scheibner (1987) to be co-magmatic with the Mount Kennan Volcanics (supported by Blevin 1999; Blevin & Jones 2004). In addition, there is a U–Pb SHRIMP age for zircon by Black (2007) of 420.0 ± 2.5 Ma. However, Scheibner (1987) noted the presence of significant hornfelsing and contact
metamorphism in sedimentary rocks of the Mount Kennan Volcanics which is intruded by this granite — implying that those units had lithified. That supports the interpretation that the granite was emplaced after the Mount Kennan Volcanics and that the previous dating from Black (2007) was in error. Similarly, the age for the Tarran Volcanics is significantly younger than that proposed by Isaacs (2000) of 433.1 ± 4.4 Ma. Blevin and Jones (2004) noted that the Tarran Volcanics overlies the Erimeran Granite and that the dating results by Isaacs (2000) for both units have different populations based on their morphologies and their U and Th contents. Given that the data for the Erimeran Granite by both Black (2007) and the present study are within error and are significantly younger than that proposed by Isaacs (2000) there is confidence in the new results.
Palaeontological review As part of the present study a review was undertaken on the palaeontology of key units to better define time– space relationships and to support the interpretation of the U–Pb SHRIMP dating of zircons for volcanic units. Three major areas of focus of the present study were: the age constraints of the Mineral Hill Volcanics; the Mount Hope Group; and the Mulga Downs Group — particularly with respect to the Winduck Group–Mulga Downs Group boundary. The full results are included in Sherwin (2013) and summarised in Figure 4. Figure 4 shows that the stratigraphic units in the lower part of the Cobar Supergroup range in age from late Silurian (Pridolian to possibly as old as the late Ludlow crispa conodont zone) to the Early Devonian (early Lochkovian). Furthermore, for the central part of the Nymagee area, there are no younger strata preserved that clearly overlie the deep water part of the Cobar Basin. There is a distinct hiatus between the lower and upper parts of the Cobar Supergroup to the east of the Cobar Basin in the Mineral Hill area where there is marked discordance between early Lochkovian and late Lochkovian units (Sherwin 1995). However, no similar time-break was recognised to the west of the Cobar Basin for the Winduck Shelf area. A key change to the stratigraphy of the area is the recognition that there is no significant time-break, if any, between the Winduck Group and the overlying Mulga Downs Group. The base of the Mulga Downs Group is now regarded to be close to Pragian–Emsian boundary whilst the upper age limit is less constrained but believed to be no younger than the mid-Eifelian (early Middle Devonian). In addition, Sherwin (2016) suggested that the Cocoparra Group, which lies to the south in the adjacent Cargelligo 1:250 000 map sheet area is very likely to be a stratigraphic equivalent to the Mulga Downs Group and possibly even partly time
Quarterly Notes
11
Ma
CARBONIFEROUS
360
365
FAMENNIAN
LATE
370
375 FRASNIAN 380
385 MIDDLE
DEVONIAN
390
T
GIVETIAN
400
EMSIAN
?
?
?
?
Bundycoola Formation
?
?
EARLY
Gundaroo Sandstone
E
R
A
N
O
R
O
G
E
N
Y
?
LUDLOW
Thule Granite
MOUNT HOPE GROUP
AMPHITHEATRE GROUP
Gilgunnia Granite Mount Allen BROKEN RANGE GROUP Granite
Tarran Roset Volcanics Sandstone MOURAMBA GROUP Hathaway Conglomerate Kruge Conglomerate Member Member
Whitlock Conglomerate Member
Erimeran Granite
Urambie Granodiorite Ungarie Granite
WENLOCK
Inverleith Sandstone
Daalboro Sandstone
Nymagee felsic dykes
RAST GROUP
?
Babinda Volcanics
?
?
Mount Knobby Formation
Boothumble Fm
Myamley Sandstone Gwando Siltstone
Ewolong Formation
Ural Volcanics Crossleys Tank Formation
?
?
?
Majuba Volcanics
Baledmund Formation
KOPYJE GROUP
AMPHITHEATRE GROUP
YARRA YARRA CREEK GROUP
Talingaboolba Formation Wilmatha Granite
Mount Walton porphyry
COBAR SUPERGROUP
Shume Formation
Jerula Limestone Member
Gleninga Formation
Lumga Siltstone
Buckambool Sandstone
?
SILURIAN
B
Whoey Tank Formation
Yar Sandstone
WALTERS RANGE GROUP
?
PRIDOLI
430
B
Later Devonian cover in this region either removed by erosion or never deposited
Booth Limestone Member
?
Sawmill Tank Siltstone
?
425
A
?
Boolahbone Granite 420
R
Bulgoo Formation
WINDUCK GROUP
LOCHKOVIAN
E
?
?
Meadows Tank Formation
410
B
?
Merrimerriwa Formation
PRAGIAN
415
?
B
Crowl Creek Formation
MULGA DOWNS GROUP
395
405
?
EIFELIAN
A
?
Tollingo Kooranjie Fifteen Mile Tank Cauldwell Vale Yellow Mineral Hill granodiorite Conglomerate Mountain Conglomerate Conglomerate Volcanics Member Member Granite Ulinbawn Conglomerate Wirrilah Member Mount Susannah Conglomerate Conglomerate Member Nymagee Igneous Complex
2016_05_023a
440
SILURIAN
435
B
E
N
A
M
B
R
A
N
O
R
O
G
E
N
Y
LLANDOVERY
445 BOLINDIAN ?
?
LATE
450 EASTONIAN
Currawalla Shale (BENDOC GROUP)
455 GISBORNIAN
?
Alandoon Chert MIDDLE
465
ORDOVICIAN
460
DARRIWILIAN
?
Undifferentiated mafic unit
YAPEENIAN CASTLEMAINIAN
470
Break O’Day Amphibolite
CHEWTONIAN
WAGGA GROUP
BENDIGONIAN
475
?
?
?
GIRILAMBONE GROUP
EARLY 480
?
LANCEFIELDIAN
485
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
?
? 2016_05_023b
Figure 4. Time–space plot for the Nymagee project area, updated by Fitzherbert et al. (in press), incorporating the new data from U–Pb SHRIMP dating and the review to the palaeontological controls for stratigraphy by Sherwin (2013). The time scale used is from Gradstein et al. (2012).
12
August 2016
equivalent to the upper Winduck Group. The main findings are summarised below. • Mineral Hill Volcanics — fossils from the Mineral Hill Volcanics are abundant but generally poorly preserved. Morrison et al. (2004) proposed a Wenlock to Ludlow age for the volcanics, but this is likely to be too old. The shelly fauna from this unit most closely compares with the Ludlovian– Pridolian fauna of the Yass Basin and is also supported by a Pridolian conodont fauna noted by Pickett and McClatchie (1991) for the Mineral Hill Volcanics. Also the unit unconformably overlies the Forbes Group (Forbes 1:250 000 map sheet area) which has a late Wenlock graptolite fauna (Sherwin 2010). A Pridolian (423.0 ± 2.3 Ma to 419.2 ± 3.2 Ma) age for the Mineral Hill Volcanics overlaps with and is within error of the U–Pb SHRIMP dating results of 422.2 ± 3.7 Ma (Spandler 1998) and 417.6 ± 3.2 Ma (this study). • Mount Hope Group and Broken Range Group — Scheibner (1987) considered that the Broken Range Group is locally interbedded with the Mount Hope Group to the east (Nombiginni Volcanics) and in the Great Central mine area (Mount Halfway Volcanics/Regina Volcanics). The age for both units depends on poorly preserved brachiopods in the Broken Range Group that were previously identified as late Lochkovian to Pragian. However, a similar but better preserved fauna of Pridolian to early Lochkovian age that has been identified in units near Bogan Gate can be used to constrain the age of the Broken Range Group. Hence the Broken Range Group is now interpreted to be Pridolian to early Lochkovian in age. This is supported by the U–Pb SHRIMP dating results for the Mount Halfway Volcanics (422.8 ± 2.6 — Chisholm et al. 2014), Nombiginni Volcanics (419.1 ± 3 Ma) and Regina Volcanics (418.7 ± 3.1 Ma) (both this study). • Winduck Group — this unit is locally rich in marine fossils indicative of an Early Devonian (Lochkovian to Pragian) age (Sherwin 1995; Sherwin & Meakin 2010). A possible late Silurian (Pridolian) age cannot be discounted, based on fossils known from a typical Winduck Group sandstone unit near Cobar, although that outcrop may possibly be a sandy member of the mostly underlying Amphitheatre Group . The upper age limit of the Winduck Group is well constrained by latest Pragian conodonts in the Booth Limestone Member, just below the contact with the overlying Mulga Downs Group (J.A. Talent pers. comm., 25-8-2013 in Sherwin 2013). This is a slight revision of a previous early Pragian age suggested by Pickett (1984, 1986). • Winduck Group–Mulga Downs Group boundary — the boundary between these units was field checked in a number of places as part of the present
study. Although the outcrop is patchy there is sufficient to suggest that the boundary is marked by lenticular beds of pebbly conglomerate (possibly Meadows Tank Formation — Mulga Downs Group) but no other obvious lithological changes were noted. For the adjacent Wrightville 1:100 000 scale map sheet area (to the north) Glen et al. (1987) noted that the Mulga Downs Group was generally paraconformable with the overlying Winduck Group but noted a number of localised areas where there were apparent local disconformable or angular unconformable relationships. For the Nymagee project area the boundary is interpreted to be transitional/conformable. This is supported by: David (2005), who noted that the boundary between the units was conformable in both outcrop and in drillholes in the Manuka (Wonawinta) area; and data from seismic line 09GA-RS2 (Survey 188 — data available at Geoscience Australia website: http://www.ga.gov.au/metadata-gateway/metadata/ record/gcat_69989). That seismic line trends east– west across the Yathong Trough–southern Cobar Basin area (central part of the Nymagee 1:250 000 map sheet area) and shows that there is no major or apparent disruption to deposition of the basin sedimentary units identified as the Winduck Group and overlying Mulga Downs Group (S. Dick pers. comm. 27/08/2015). It is suggested that the Winduck Group–Mulga Downs Group boundary is close to the Pragian–Emsian boundary, based on latest Pragian conodonts in the Booth Limestone Member (J.A. Talent pers. comm., 25-8-2013 in Sherwin 2013) and the presence of disarticulated fish plates of Wuttagoonaspis and Groendlandaspis, possibly indicative of Emsian to Eifelian age but known to occur in South Australia in erratics derived from the Winduck Group (see below). • Mulga Downs Group — fossil control for this unit is poor. However, disarticulated fish plates of Wuttagoonaspis and Groenlandaspis from the lower part of the Merrimerriwa Formation (stratigraphically overlying the basal Meadows Tank Formation) have been identified by Ritchie (Alex Ritchie, pers. comm. 1977 — quoted in Glen 1982; Glen et al. 1987). Ritchie also suggested that the fossils indicated a possible Emsian to Eifelian age (see Ritchie 1969, 1973), but cautioned that the age range for these fossils was poorly understood. Furthermore, Flint et al. (1980) illustrated erratic blocks from South Australia of fossiliferous Winduck Group lithology with Wuttagoonaspis on the same bedding plane as typical Winduck Group shelly faunas, i.e. Lochkovian (Sherwin 1995; Sherwin & Meakin 2010). It may be that the slab with Wuttagoonaspis was originally sourced from outcrop of the Mulga Downs Group. However, the
Quarterly Notes
13
photograph from Flint et al. (1980, figure 6) also showed a gastropod known from the Winduck Group, possibly Straparollus culleni, on the slab with the Wuttagoonaspis plate. The upper age limit of Wuttagoonaspis is less certain, although Young (1995) shows a limit at about the mid-Emsian. This was subsequently extended to the mid-Eifelian (Young 2006). Given that Pragian marine fossils are known from the Booth Limestone Member (Winduck Group) from just below the Mulga Downs Group boundary it is very likely that the Winduck–Mulga Downs boundary is very close to the Pragian–Emsian boundary. The upper age for the Mulga Downs Group is much less well constrained but is believed to be no younger than Eifelian (Middle Devonian).
HyLogger metamorphism and alteration study Core from 41 diamond drill holes from 14 mineralised zones/deposits (Figure 5) were scanned using the HyLogger™ spectral scanner located at the WB Clarke Geoscience Centre, Londonderry, New South Wales. This instrument generates high-resolution semi-continuous visible near-infrared (VNIR), shortwave infrared (SWIR) and thermal infrared (TIR) data which were then analysed using The Spectral Geologist (TSG™) software to infer the mineralogy of host sequences, mineralised zones and associated alteration. The study focused on characterising the mineral assemblages distal to, within and proximal to mineralised zones. The results from the study are being published in the Australian Journal of Earth Sciences (see Downes et al. submitted) and summarised below. Downes et al. (submitted) found that the mineral assemblages for zones distal to mineralisation in the Mount Hope Trough, southern Cobar Basin, Mouraramba Shelf, Canbelego–Mineral Hill Volcanic Belt (Kopyje Shelf) and Rast Trough are consistent with sub- to lowest greenschist facies metamorphic conditions. By contrast, the mineral assemblages for zones distal to mineralisation in the Winduck Shelf are consistent with very low grade, probable late diagenetic zone conditions — supported by temperatures of less than 150°C from fluid inclusion data at Manuka (Giles 1993). It was suggested that these findings have important implications for the burial and basin inversion models in the southern Cobar Superbasin. The genetic model for the Cobar Superbasin from David (2005) involves increased subsidence, elevated geotherms and substantially thicker basinal sequences on the eastern side of the basin. Presumably, the inversion of the basin has resulted in the exposure of the deeper and hotter (middle greenschist) units along the eastern margin of the Cobar Basin. However, based
14
August 2016
on this study and excluding the Winduck Shelf, there is no evidence for a change in regional thermal field from sub- to lowest greenschist facies to hotter levels across the entire southern Cobar Basin. For zones proximal to mineralisation there are significant changes in the abundance, species and presence of minerals identified within the spectral data. With the exception of Yellow Mountain, where changes are subtle, these responses were interpreted to be largely alteration-related. For several of the zones included in the present study there are systematic changes in chlorite composition from Fe- and/or Fe– Mg-chlorites to more Mg-rich varieties. These include: Browns Reef, Great Central, Hera, May Day, Mount Allen, Mount Solar, Nymagee and South Shuttleton (Crowl Creel–South Shuttleton zone) (Figure 6 — Browns Reef deposit not shown, located at 33.322S, 146.326E). In addition, talc was noted for May Day, Mineral Hill and South Shuttleton. Downes et al. (submitted) suggested that this change in chlorite composition could be due to either scavenging of Fe to form Fe-bearing sulfides (e.g. pyrrhotite, pyrite, chalcopyrite, sphalerite) and/or an abundance of Mg in the ore-forming fluids — suggesting that these fluids were undersaturated with respect to iron and supporting the interpretation that many of the oreforming fluids are of basinal and/or sea water origin. However, for Mineral Hill Fe-chlorite abundance correlates with the mineralised (sulfide-rich) zones, suggesting that there has been significant addition of Fe to the central part of that system. The available S-isotope data for Mineral Hill (Downes 2009) suggests that these ore-forming fluids were derived from a magmatically derived reservoir. The study found that there was no systematic variation in observed white mica abundance and chemistry for many of the mineralised zones. White mica abundance did not systematically change, with Hera and Yellow Mountain having increased abundance, Browns Reef and Mineral Hill having decreased abundance and other zones having only localised (non-systematic) changes. A change from muscovitic to more phengitic compositions was noted at Great Central, Hera (Figure 7), May Day and Wagga Tank — whereas the reverse trend (phengitic to more muscovitic compositions) was noted at Mount Solar and Yellow Mountain. By contrast, for the SOZ (Southern Ore Zone — G and H Lode area) at Mineral Hill there appeared to be a change in the composition and/or type of white mica as evidenced by a noticeable shortening of the 2200nm Al-OH absorption feature away from more muscovitic compositions adjacent to the mineralised zone. However, no systematic changes in white mica composition were noted for several zones, including Lowan North, Mount Allen and South Shuttleton.
145°30′E 31°26′S
147°12′E 31°27′S
COBAR Hermidale Canbelego
Cobar Basin
Nymagee Igneous Complex Ordovician basement
Nymagee Nymagee Hera
Crowl Creek South Shuttleton
Winduck Shelf
Blue Mountain
Manuka
Canbelego–Mineral Hill Volcanic Belt
Lowan North
Gilgunnia Granite Mouramba Shelf
Thule Granite
May Day Yellow Mountain
Erimeran Granite
Mineral Hill
Boolahbone Granite
Wagga Tank
Ordovician basement
Mount Allen
Mount Hope Trough Great Central mine area Mount Solar
Winduck Shelf
Rast Trough
Walters Range Shelf
Derrida Granite Condobolin
Euabalong
33°10′S 147°12′E
33°09′S 145°28′E
REFERENCE Ordovician
Kopyje Shelf
Girilambone Group
Kopyje Group
Mine or prospect
Wagga and Bendoc Groups
Ootha Group
Locality
Fifield Suite Silurian to Early Devonian (Cobar Superbasin) Cobar Basin Amphitheatre Group Mount Hope Trough Mount Hope Group Broken Range Group Bootheragandra Group Rast Trough
Mouramba Shelf
Highway
Mouramba Group
Major road, sealed
Walters Range Group
Major road, unsealed
Winduck Shelf Mulga Downs Group
Unit boundary
0
15
30 km
Project area
Winduck Group Yarra Yarra Creek Group Silurian to Early Devonian Granites S-, I- and A-type granites (undifferentiated)
Rast Group 2016_05_024
Figure 5. The location of deposits and prospects included in the HyLogger™ study (from Downes et al. submitted). Notes: Browns Reef deposit not shown — located at 33.322S, 146.326E); based on geophysical and whole-rock geochemical data the Derrida Granite (Derrida Phase — Meakin 2005) is now interpreted to be part of the Ungarie Granite (this study, Fitzherbert et al. in press).
Quarterly Notes
15
Drillhole NMD053W1
Drillhole NMD047
Scope 1:46972; 5180 Points, r=0.626; Aux: FeatEx Depth, 2255 +- 10
Scope 1:46972; 4895 Points, r=-0.799; Aux: FeatEx Depth, 2255 +- 10
2260 2256
0.0175 0.0155 0.0134
2252
0.0113 0.0093
Wavelength (nm)
0.0217 0.0196
0.0175 0.0155 0.0134 0.0113 0.0093
1 378
2
Mg-chlorite
369
360
351
342
Depth (m)
333
0.0051 0.0031 0.001 279
1
2
Mg-chlorite 270
261
252
Depth (m)
1 Quartzo-feldspathic unit
2248
0.0031 0.001
Fe-chlorite
0.0217 0.0196
0.0072
0.0051
2248
0.0072
0.0258 0.0237
2260 2264
0.0279
Fe-chlorite
0.0258 0.0237
2256
0.0279
East
0.032 0.0299
2264
0.032 0.0299
West
Wavelength (nm)
East
2252
West
243
234
Mineralised zone
2 Metamorposed clay-rich unit
2016_05_025
Figure 6. Changes in chlorite composition in response to alteration associated with mineralisation — an example from the Nymagee copper mine (drill holes NMD053W1 and NMD047) (from Downes et al. 2016). The chlorite becomes more magnesium-rich in the vicinity of the main mineralised zone. The colour legend on the Y axis shows the depth of the 2255 ± 10 nm wavelength Fe-OH absorption feature (as % reflectance). NMD053W1 was drilled from west to east and NMD047 was drilled east to west, with both interesting the mineralised zone in about the same area. Cu (ppm)
Drillhole HRD003
3300
Northeast
Southwest 2214
3080 3080 2860 2860 2640 2640
White mica wavelength
2420 2420 2200 2200
2211
1980 1980 1760 1760 1540 1540 1320 1320
2208
11001100
Figure 7. Changes in white mica composition in response to alteration associated with mineralisation — an example from Hera (HRD003). The white mica becomes more phengitic (Mg– Fe being substituted for Al in the muscovite–phengite series) in the vicinity of copper mineralisation — as shown by the change of white mica Al–OH absorption feature wave length on the Y-axis. The colour legend shows the copper abundance in ppm.
880 880 660 660 440 440
2205
220 220 0
340
350
360
370
380
390
Depth (m)
400
410
420
430
0 NULL 2016_05_026
Whilst minor K-feldspar and plagioclase (particularly Na-rich varieties) were noted in the TIR data for many of the drillholes included in Downes et al. (submitted), those authors noted that changes to feldspar abundance and composition were only observed at Mineral Hill, Hera, May Day and Lowan North. At Mineral Hill (Parkers Hill) and at Hera there is an increase in the abundance of K-feldspar proximal to mineralisation, whereas at May Day the mineralising fluids were interpreted to be locally feldspar-destructive. For Lowan North, those authors noted an apparent increase in Na-rich plagioclase which was closely correlated with the extent of the Fe-chlorite zone and interpreted to be alteration-related. Widespread carbonate alteration was not a dominant alteration type identified by Downes et al. (submitted) with the exception of the carbonate-hosted base metal systems at Manuka and Blue Mountain (Figure 5). Minor zones of Fe–Mg carbonate were noted at Great Central (Great Central mine), May Day, Mineral Hill (Parkers Hill) and South Shuttleton. However, whilst certainly recorded in many drillholes, alteration-
16
August 2016
related carbonate was not identified in the spectral data for other zones included in the present study — probably due to the low overall carbonate abundance and disseminated nature of any carbonate present. At Manuka and Blue Mountain the mineralised zones are associated with carbonate-rich (calcite, ankerite, dolomite) units that appear to have been dolomitised (Mg-alteration) but not all dolomite-rich zones were mineralised. Also at Manuka there is a basal arkosic unit with a strong dolomitic response indicating that this unit may have also been dolomitised. Minor elevated base metal values are also associated with this zone, and Downes et al. (submitted) suggested that metalliferous Mg-carbonate-bearing fluids infilled the available pore space during the mineralising event. An important finding from the study was the need to obtain spectral data for several holes from the same zone/deposit in order to systematically assess lateral and vertical changes in the composition and abundance of minerals within each assemblage. However, it must be emphasised that the spectral resolution of the current generation of HyLogger™ scanners may result in fine-grained, dark or lowabundance minerals being overlooked and/or not detected within a mineral assemblage.
Petrographic volcanic facies review of the Mount Hope Group and Canbelego–Mineral Hill Volcanic Belt Office-based petrographic reviews of the Mount Hope Group and the Canbelego–Mineral Hill Volcanic Belt were undertaken as part of the Nymagee project to better understand the geological setting and the distribution of volcanic facies within these two areas. This study utilised approximately 980 thin sections from the extensive GSNSW collection, initially focused on the Mount Halfway Volcanics — the most areally extensive unit of the Mount Hope Group. However, the Ambone Volcanics, Coando Volcanics, Goona Volcanics, Mount Kennan Volcanics, Nombiginni Volcanics and Regina Volcanics were also included. Subsequently the review was extended to include volcanic-dominated units of the Canbelego–Mineral Hill Volcanic Belt, on the eastern side of the project area (the Florida Volcanics, Babinda Volcanics, Majuba Volcanics, Baledmund Formation, Mineral Hill Volcanics, Talingaboolba Formation — Kopyje Group; and Yarnel Volcanics — Ootha Group). The aims of the project were to: identify major coherent volcanic and volcaniclastic facies; up-date the volcanic terminology and interpretation from that used by previous workers (such as Felton 1981; MacRae 1987a, b; Scheibner 1987; Pogson 1991a); and to identify possible volcanic centres. Details of this petrographic review (Simpson 2014, 2015) include the supporting thin section descriptions, photomicrographs and digital data (.txt) files. The key results are summarised below. Note that the Florida Volcanics, Yarnel Volcanics and parts of the Mineral Hill Volcanics and Talingaboolba Formation lie outside the Nymagee project area but are included for completeness for this study.
Mount Hope Group Mount Halfway Volcanics
Six compositionally and texturally distinct coherent rhyolitic/dacitic units (four of these shown on Figure 8) and three major volcaniclastic facies were identified by the petrographic review for the Mount Halfway Volcanics. In addition, less voluminous lavas, volcaniclastic rocks (including pumice breccias and peperites) and older syn-volcanic intrusive rocks were distinguished. Two of the rhyolites (Types 2 and 4 — Figure 8, Photographs 1 and 2 respectively) have strike lengths that are very extensive (>26 km and >18 km, respectively) and compositionally uniform. These units are interpreted to be large, mainly intrusive bodies (sills or lava-sill complexes). An additional two coherent rhyolites (Type 1 in the north, Photograph 3,
146°09′E 32°02′S
145°35′E 32°02′S
NYMAGEE
LACHLAN DOWNS
Type 4 Rhyolite
Gilgunnia Granite
Thule Granite
Gilgunnia
Boolahbone Granite
Type 5 Rhyolite MOUNT ALLEN
Type 3 Rhyolite
Type 2 Rhyolite
Mount Allen Granite KILPARNEY Type 2 Rhyolite
Mount Hope Type 3 Rhyolite
Matakana 33°02′S 145°34′E
CARGELLIGO
HILLSTON
33°02′S 146°08′E
REFERENCE Coherent volcanic units (based on petrography)
Locality Major road, sealed
Type 2 rhyolite
Major road, unsealed
Type 3 rhyolite
Minor road, unsealed
Type 4 rhyolite
1:100 000 map sheet
Type 5 rhyolite
Unit boundary
Outcropping stratigraphic units Ambone Volcanics Coando Volcanics Double Peak Volcanics Goona Volcanics Mount Halfway Volcanics Mount Kennan Volcanics
0
10
20 km
Nombiginni Volcanics Regina Volcanics
2016_05_027
Figure 8. Distribution of mappable compositionally and texturally distinct coherent units within the Mount Halfway Volcanics of the Mount Hope Group (modified from Simpson 2014). Note: two coherent rhyolite units (Type 1, Type 6) are not shown on the figure as they are complexly intercalated with coarse- and fine-grained volcaniclastic facies and hence do not form mappable units at this scale.
Quarterly Notes
17
18
Photograph 1. Type 2 rhyolite with phenocrysts of embayed quartz, altered plagioclase (top right), alkali feldspar (left base) and chlorite/white mica-replaced ferromagnesian phenocrysts (top left) set in a coarsely microcrystalline groundmass. A small vesicle in lower right corner is in-filled with quartz and biotite. Photomicrograph in cross-polarised light. Slide T35925a: x2 lens; red scale is 1 mm (Photographer C.J. Simpson).
Photograph 2. A moderately crystal-rich coherent, biotitebearing Type 4 rhyolite with phenocrysts of plagioclase, quartz, biotite (near top and lower left corner) and pale, phyllosilicate-replaced phenocrysts set in a micropoikilitic to borderline granophyric groundmass. Photomicrograph in cross-polarised light. T46087b: x2 lens (Photographer C.J. Simpson).
Photograph 3. One of the least altered samples of Type 1 rhyolite. It is moderately crystal-rich and contains quartz, plagioclase and less abundant alkali feldspar (base of photo), chlorite- and phyllosilicate-replaced ferromagnesian phenocrysts (top and base of photo, respectively) set in a massive, finely microcrystalline groundmass. Minor fine-grained secondary phyllosilicates and metamorphic biotite are in the groundmass and associated with chlorite. Photomicrograph in cross-polarised light. T88877a, x2 lens (Photographer C.J. Simpson).
Photograph 4. Typical Type 3 rhyolite, containing phenocrysts of embayed quartz, altered plagioclase (lower right), alkali feldspar (left side) and phyllosilicate-replaced ferromagnesian minerals (top of photo) in this view. The groundmass is coarsely microspherulitic and micropoikilitic. Photomicrograph in cross-polarised light. T35148b: x2 lens (Photographer C.J. Simpson).
and Type 6 in the south) are also areally extensive but are not shown on Figure 8, as they are complexly intercalated with coarse- and fine-grained volcaniclastic facies suggesting that they are part of large, subaqueous, effusive and explosive volcanic centres (Gilgunnia Range eruptive centre and Nombinnie–Regina eruptive centre, respectively — Figure 9).
The major volcaniclastic facies recognised in the Mount Halfway Volcanics include: crystal-lithic volcanic breccia; vitric-crystal volcanic sandstone; vitric volcanic siltstone/mudstone and less abundant pumice breccia (Photograph 5) and peperites (Photograph 6). The crystal-lithic volcanic breccias contain abundant rhyolite lava fragments, as well as tiny oval clasts of perlitic groundmass referred to as
August 2016
146°09′E 32°02′S
145°35′E 32°02′S
NYMAGEE
LACHLAN DOWNS
Bedooba EC
Gilgunnia Granite
Thule Granite
Gilgunnia
Gilgunnia Range EC
Mount Kennan Volcanics feldspar-phyric dacite EC
Boolahbone Granite
Mount Victor EC
Mount Kennan Volcanics quartzphyric dacite EC Mt Kennan Volcanics quartz-phyric rhyolite EC MOUNT ALLEN
Nombinnie-Regina EC
Nombiginni EC
Double Peak EC
Mount Allen Granite KILPARNEY
Mount Allen EC Mount Hope
‘pearls’, 26 km strike length) may be related to this proposed centre. Mount Allen eruptive centre (Mount Halfway Volcanics) — this proposed centre is based on the diversity of lithologies represented in thin sections from the area. Nombinnie–Regina eruptive centre (Mount Halfway Volcanics) — this proposed centre is the southernmost eruptive centre in the Mount Halfway Volcanics and broadly encompasses the distribution of coarse-grained Type 3 rhyolite but also includes intercalated volcaniclastic rocks, particularly within the previously mapped Regina Volcanics (Great Central mine area). Mount Kennan Volcanics — three possible lavadominated eruptive centres, each with slightly different compositions, occur within this unit. They are: feldspar-phyric dacite near “Salt Creek”; quartzbearing feldspar-phyric dacite near Boolahbone; and, quartzo-feldspathic rhyolite near Mount Kennan. Double Peak eruptive centre — this possible centre is based on the diversity of lithologies within a relatively small area (predominantly rhyolite and dacite lava), previously mapped volcaniclastic rocks, the associated Mount Allen Granite and mineralisation.
• Nombiginni eruptive centre — this possible centre is developed in the upper part of Nombiginni Volcanics and represents a possible source for the extensive plagioclase-phyric dacite in this area.
147°11′E 31°28′S
146°13′E 31°28′S
Mount Boppy
Canbelego
Pipeline Ridge
Depositional environments
This petrographic study supports previous interpretations (e.g. Bull 2006) that the Mount Hope Group formed in a relatively deep marine environment for both eruption and emplacement of the various units. Petrographic observations supporting this interpretation include the presence of normal size grading and planar lamination in volcanic sandstones, a general lack of abrasion of delicate pyroclasts in the volcaniclastic facies and abundance of bead-like clasts (‘pearls’), derived from quench-fragmented glassy lavas, in coarse-grained volcaniclastic rocks that are in close proximity to these lavas. In addition, the identification of possible replaced fayalite phenocrysts in some coherent units of the Mount Halfway Volcanics (and correlatives Ambone Volcanics and Regina Volcanics) suggests that the magmas producing these rocks were hightemperature and relatively anhydrous.
Hermidale
CANBELEGO
HERMIDALE
NYNGAN
Nymagee
NYMAGEE
BOBADAH Overflow
TOTTENHAM
Yellow Mountain
Mineral Hill
KILPARNEY
GINDOONO
BOONA MOUNT
Canbelego–Mineral Hill Volcanic Belt From north to south, the Canbelego–Mineral Hill Volcanic Belt includes units of the Kopyje Group (Florida Volcanics, Babinda Volcanics, Majuba Volcanics, Baledmund Formation, Mineral Hill Volcanics, Talingaboolba Formation) and the Ootha Group (Yarnel Volcanics — which lies outside the Nymagee project area) (Figure 10). In contrast with the original mapping and petrographic work carried out in the Canbelego–Mineral Hill Volcanic Belt during the 1980s and 1990s, which identified abundant welded tuffs attributed to pyroclastic flow emplacement, lavas appear to be a major part of all formations in the belt aside from the Baledmund Formation, Talingaboolba Formation and Yarnel Volcanics. In addition, evidence for welding was not identified in this petrographic study. The two major characteristics of the rhyolitic and dacitic lavas in the belt, that distinguish them from primary pyroclastic rocks, include the presence of predominantly intact phenocrysts and abundant evidence that the groundmass was originally volcanic glass. This includes devitrification textures such as micropoikilitic and microspherulitic textures, and perlitic textures formed by the hydration of glass. Two main lava facies were identified, based on mineral proportions rather than geochemistry. These are: (i) a relatively crystal-rich rhyolite characterised by quartz, alkali feldspar, plagioclase and a small number of biotite phenocrysts; and (ii) aphyric to mainly sparsely
Euabalong CARGELLIGO
Condobolin Condobolin TULLIBIGEAL
CONDOBOLIN 33°13′S 147°11′E
33°13′S 146°12′E
REFERENCE Stratigraphic unit Babinda Volcanics
Locality
Baledmund Formation
Highway
Florida Volcanics
Major road, sealed
Majuba Volcanics
Major road, unsealed
Mineral Hill Volcanics
Minor road, sealed
Talingaboolba Formation
Minor road, unsealed
Yarnel Volcanics
1:100 000 map sheet
Deposit
Unit boundary
2016_05_029
0
20
40 km
Figure 10. Distribution of volcanic units within the Canbelego–Mineral Hill Volcanic Belt that were included in the petrographic study by Simpson (2015). From north to south they are: Florida Volcanics, Babinda Volcanics, Majuba Volcanics, Baledmund Formation, Mineral Hill Volcanics, Talingaboolba Formation and Yarnel Volcanics. Also shown are the index 100 000 map sheets for the project area. Distribution of volcanic units modified from the Cobar 1:500 000 metallogenic map (Fitzherbert et al. in press). Note that the Florida Volcanics and the Yarnel Volcanics lie outside the Nymagee study area.
Quarterly Notes
21
plagioclase-phyric (to approximately 15% of rock) dacite. In addition, there is compelling evidence that the rhyolites were erupted first with a change to dacitic composition occurring at a higher stratigraphic level. There is also a close association between samples of coherent rhyolite and/or dacite with mainly coarsegrained proximal volcaniclastic rocks, including crystal-lithic and crystal-vitric volcanic sandstones and rare lithic breccia. This supports the presence of previously proposed volcanic centres coincident with the main outcrop of the Florida Volcanics, Majuba Volcanics and Mineral Hill Volcanics. In these formations the crystal and lithic component of the coarse-grained volcaniclastic rocks is clearly derived from rhyolitic explosive eruptions and disaggregation of rhyolitic lava. By contrast, the Babinda Volcanics is dominated by dacitic lavas, which may be a lava/ sill complex, although abundant pumiceous volcanic sandstone in the lower part of this unit also supports the interpretation that there was some early explosive volcanism in this area. In some of these formations (e.g. Florida Volcanics) samples of the finer-grained, more distal volcaniclastic facies — such as vitricrich volcanic siltstone and fine pumiceous volcanic sandstone — are concentrated at a distance from the proximal facies, which also lends support to the presence of discrete volcanic centres. The Florida Volcanics and the Badinda Volcanics, together with the vast majority of Baledmund Formation, are essentially undeformed aside from minor faulting, fracturing and/or weak cleavage development and have not undergone significant regional or contact metamorphism. It was also noted that the interfingering relationships between the Baledmund Formation and a number of units (including the Florida, Babinda and Majura volcanics) are more complex than previously mapped. Coherent lava and other proximal units of the Baledmund Formation (i.e. rhyolites and crystal-lithic volcanic sandstone lithologies/units) are better included in other volcanic units. It is noted that the Mineral Hill Volcanics and Talingaboolba Formation are also undeformed and have a low metamorphic grade. However, many of the samples included in the present study have been affected by silica–sericite ± albite alteration with smaller amounts of iron oxides (some after pyrite?), chlorite, epidote, clay and carbonate. By contrast, samples from the Yarnel Volcanics are typically silicified with disseminated iron oxides, some probably after pyrite, and a small amount of sericite, clay and carbonate.
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Summary There were many similarities in the rock types and character of the volcanic facies associations observed in samples from the Canbelego–Mineral Hill Volcanic Belt and those of the Mount Hope Group; however, there was a key compositional difference. Some of the rhyolite lavas in the Mount Hope Group contain phenocrysts of probable olivine and pyroxene — suggesting unusually high magma temperatures and relatively anhydrous compositions were associated with the Mount Hope Group but no similar textures/ minerals were identified in similar units of the Canbelego–Mineral Hill Volcanic Belt — where the rhyolites contain only biotite phenocrysts and trace amphibole (or replaced phenocrysts thereof).
Isotopic studies Regional sulfur and lead isotope studies combined with insights from the deposits and geological setting can provide constraints as to the sources of metals, fluids and ore-forming process at both deposit and district scales. These inputs are important for understanding how the mineral system formed and the triggers to oreforming processes. As part of the present study over 300 sulfide-rich samples, from 27 separate deposits/ zones, were analysed for sulfur isotopes and 43 Pb-rich samples from 13 deposits/zones were analysed for lead isotopes. Additional samples were also analysed from non-mineralised igneous rocks and sulfides distal to mineralisation to characterise potential background Pb- and S-isotope reservoirs. The new data build upon 114 S-isotope analyses and 107 Pb-isotope analyses from earlier studies — including those in the CSIRO Pb-isotope database and subsequent pmd*CRC Cobar Basin study (Mernagh 2008) and several theses (Bush 1980; David 2005; Northcott 1986; Ryan 1987; Spandler 1998). This study is ongoing and will be published separately (see Downes & Poulson in prep.).
Sulfur isotopes Preliminary analysis of the available S-isotope data indicates that there are significant variations between unit/setting and deposit types. Three deposits/ systems included in the present study have average S-isotope values close to zero (Group 1). These are the Condobolin Au–Ag–base metal system (average = 2.9‰), Fountaindale (Au — average = -2.1‰) and Tallebung (Sn–W — average = -0.9‰) (Figure 2). S-isotope values close to zero suggest that the majority of sulfur in these deposits was sourced from reservoirs containing significant magmatic sulfur. A second group of deposits have average S-isotope values that lie between 4 and 8 per mil (Group 2), which suggests that significant sulfur in these deposits was sourced from reservoirs containing both magmatic
and reduced seawater sulfate and/or that mixing occurred between these two end-member reservoirs. They include: Anomaly 3 (Great Central mine area — Au–Ag–(Pb)); Hera (Au–Cu–Zn–Pb); Mineral Hill (Cu–Au–(Ag–Pb–Zn–Bi)); Mount Hope (Cu–(Ag–Au) — limited data); Mount Solar (Au — limited data); and Nymagee (Cu–(Pb–Zn–Ag)) (Figure 2). Group 3 deposits have average S-isotope signatures that lie between 8 and 12 per mil. These values suggest that the sulfur was derived dominantly from reservoirs containing sulfur derived from Ordovician to earliest Devonian reduced seawater sulfate sources (i.e. derived from basinal fluids). They include: Blind Calf (Cu) (Photograph 8); BMW (Pb–Zn–(Cu–Au)); Great Central (Cu); Pipeline Ridge (Zn–Cu–Pb–(Au–Ag) (Photograph 9); R7 (Cu–Zn); Sandy Creek (Pb–Zn); South Shuttleton (Cu–(Pb–Zn–Ag)); and Wagga Tank (Zn–Pb–Cu–(Au–Ag)) (Figure 2). Many of the deposits included in this group are enriched in a range of metals, including copper, lead, zinc, silver and/or gold. Several deposits have average d34S values greater than 12 per mil (Group 4). They include: Gundaroo (Ag– Zn–Pb–(Cu) — average = 12.2‰); Mallee Bull (Cu– Au–(Pb–Zn– Ag) (cover photograph); — two apparent signatures of 12.9‰ and 19.8‰); MD2–Siegals (Zn– (Pb–Cu–Ag) — average = 12.6‰); Mount Allen (Au– Fe — average =12.2‰); Manuka (Wonawinta; Pb–Zn– Ag — wide range of values with 2 possible signatures of ~11 and ~19); and Yellow Mountain (Cu–Pb–Zn– Ag–(Au) — average = 15.1‰) (Figure 2). The range of S-isotope values for these deposits suggests that sulfur for these systems came from reduced seawater sulfate reservoirs with some deposits also having a contribution of sulfur from reservoirs containing unfractionated seawater/basinal fluids (i.e. primary basinal fluids). Both Mineral Hill and Pipeline Ridge have a wide range of S-isotope values, with the data for both deposits suggesting that sulfur was sourced from both magmatic and reduced seawater sulfate reservoirs. The data support the interpretation that fluid mixing was an important part of the ore-forming process and that these deposits are zoned epithermal systems. (As noted above Pipeline Ridge is dominated by a reduced seawater sulfate signature but values as low as 4.8‰ are present). Several of the copper and/or gold-rich structurally controlled high sulfide “Cobar” type deposits (e.g. Hera, Nymagee, Mount Hope) have S-isotope values which suggest that at least some of the sulfur was derived from a magmatic reservoir(s). These signatures are very similar to deposits in the Cobar district (e.g. CSA, New Cobar, Peak and Perseverance) which also have similar values (see Seccombe & Brill 1989; Seccombe 1990; Jiang & Seccombe 2000; Seccombe et al. in prep.).
Photograph 8. Gossanous (ex-sulfide) filled fractures within altered sedimentary rocks of the Girilambone Group in the Blind Calf–Dunbars lode area (494830E 6393280N, Zone 55) (Photographer P.M. Downes).
Photograph 9. A mineralised zone in drillhole PCN094 (445678E, 6490134N, Zone 55) from the Pipeline Ridge deposit – Baledmund Formation. The photograph shows a laminated quartz–pyrite filled fracture within a silica–white mica-altered felsic rock. Width of core is 6 cm. (Photographer P.M. Downes).
By contrast, the S-isotope signatures for Group 4 deposits are very different from Group 1, 2 and some Group 3 deposits and suggest that little or no magmatic sulfur was included in these deposits. In addition, the data distribution for Gundaroo, Mallee Bull and Manuka support the interpretation that multiple sulfur reservoirs (reduced seawater sulfate and sulfur from unfractionated seawater/basinal fluids) contributed to ore deposition. The lack of a magmatic signature and presence of unfractionated seawater at Mallee Bull was unexpected given that it is copper–gold-rich — suggesting that fluid mixing with cooler basinal fluids was an important mechanism for ore precipitation.
Quarterly Notes
23
Lead isotopes Preliminary interpretation of the new lead isotope data, combined with data from earlier studies (CSIRO lead-isotope database; David 2005, 2008; Mernagh 2008, Huston et al. 2016), had highlighted the following interpretations. • The lead-isotope data for feldspars from the Derrida and Mount Allen granites and Nombiginni Volcanics are crustal and have late Silurian lead model ages. The lead model ages are slightly older although within error of the U–Pb data for zircons dated by the SHRIMP technique (see Table 2). These data imply that deposits sourcing lead from the volcanic- and granite-material forming the fill to the Cobar Basin and related units should have a crustal signature and late Silurian or more evolved (younger) lead model ages. • Mallee Bull has a crustal lead-isotope signature with a lead model age of ~442 Ma — significantly older than other deposits included in the present study. The data imply that the majority of lead in the deposit was sourced from a crustal reservoir that was less evolved (older) than that for the Cobar Basin with the data being consistent with the interpretation that the lead was sourced from a Benambran-age lead reservoir — such as the deformed Ordovician basement that is interpreted to underlie the basin. • Hera has a crustal lead-isotope signature with a lead model age of ~420 Ma. The data are consistent with the majority of lead being sourced from the host late Silurian sequence (Cobar Basin and/or Mouramba Shelf) with little or no lead being sourced from older (basement) reservoirs. • Nymagee has a crustal lead-isotope signature with data from this study having late Silurian lead model ages (range 428–420 Ma; average 424 Ma) — consistent with the interpretation that lead included in the deposit was sourced from the host late Silurian quartzo-feldspathic sequence (i.e. Cobar Basin and/or Mouramba Shelf). However, some data from previous studies are less evolved — suggesting that lead was also sourced from an older reservoir. These data are consistent with this lead being sourced from basement-derived material incorporated into the late Silurian sequence and/ or that some lead was also sourced from nearby Ordovician basement units. • The lead isotope data for deposits included in the present study from the Canbelego–Mineral Hill Volcanic Belt have lead model ages that support the interpretation that multiple crustal reservoirs contributed lead to these systems. For Yellow Mountain and Blind Calf there is a range of data with lead model ages indicating that lead
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was sourced from both less-evolved (i.e. older and probably basement-derived) and younger (late Silurian) reservoirs. By contrast the data for Pipeline Ridge lies in a tight group, has a crustal signature and an average lead model age of ~433 Ma — significantly older than the host unit (Baledmund Formation — 419.3 ± 2.8 Ma, Table 2). These data probably reflect a mixed signature, with lead being sourced from both older (Ordovician basement) and younger (host volcanic package) reservoirs. • The lead-isotope data for Condobolin (now interpreted to be a zoned magmatic system rather than epithermal — see Downes & Burton 2000 vs Fitzherbert et al. in press) imply that the majority of lead was dominantly sourced from a late Ordovician–earliest Silurian crustal reservoir (possibly younger than the host Girilambone Group) and from a more evolved reservoir (possibly of Early Devonian age). In addition, some of the data trend along a crustal–mantle mixing curve of Carr et al. (1995) implying that mantle-derived lead was included in the system. The data are unlike those for other systems included in the present study, with features more similar to those for deposits in the eastern Lachlan Orogen — rather than for deposits in the central Lachlan Orogen where crustal values are dominant (Huston et al. 2016). • Gundaroo and Manuka (Wonawinta) are associated with the Winduck Shelf. For Gundaroo (Ridge zone) the lead-isotope data plot in a tight group and suggest that lead was sourced from a late Silurian crustal reservoir. By contrast, the data for Manuka (from present and earlier studies) show that crustderived lead was sourced from reservoirs with lead model ages ranging from mid-Silurian (~429 Ma) to late Early Devonian (~400 Ma) in age. These data for Manuka do not form a distinct cluster but suggest that the lead-isotope reservoirs contributing lead (Cobar Basin and/or Winduck Shelf) continued to evolve until just before the Middle Devonian Tabberabberan Orogeny and that the mineralising event at Manuka was unable to homogenise lead from multiple sources. • Limited lead-isotope data are available from this study for the BMW and Mount Allen (Au) zones associated with units of the Mount Hope Trough. BMW has a crustal signature with the limited data suggesting that lead was sourced from the host volcanic sequence and a slightly less-evolved (older) reservoir. The data for Mount Allen is similar but more evolved and indicates an Early Devonian (~414 Ma) lead reservoir — suggesting that the skarn-like mineralisation at Mount Allen is associated with an Early Devonian intrusion possibly related to the Boolahbone Granite.
• Limited lead-isotope data are also available for Sandy Creek and South Shuttleton which are hosted by the Cobar Basin. The data for Sandy Creek plot in a tight group, with a crustal signature, and suggest that the lead was sourced from a midSilurian reservoir or, more likely, that it represents a mixed basement/basin signature. By contrast, data for South Shuttleton are very different. The single analysis for South Shuttleton from the present study is crustal and has an Early Devonian (~415 Ma) lead model age. Data from earlier studies at South Shuttleton are similarly crustal but have a wide spread of lead model ages — ranging from earliest Devonian to Middle Devonian (~390 Ma). This implies that the lead reservoir (interpreted to be the Cobar Basin) continued to evolve until the mineralising event (i.e. post peak deformation associated with the Tabberabberan Orogeny). The lead-isotope data for the present study overlap with the data from earlier studies. The combined results imply that several of the deposits included in the present study sourced lead from reservoirs less evolved (older) than the late Silurian volcanic and basinal sequences which host the majority of mineralisation. Deposits such as Mallee Bull, Sandy Creek, Pipeline Ridge, Blind Calf and Yellow Mountain have sourced lead and potentially other metals from units forming basement to the Cobar Superbasin. In addition, the range of data for South Shuttleton and Manuka also imply that the lead-isotope signatures for reservoirs hosted by the Winduck Shelf and western Cobar Basin continued to evolve. However, the relatively tight datasets for deposits such as Hera and Nymagee on the eastern side of the Cobar Basin imply that the lead reservoirs hosted by these late Silurian sequences lost their uranium and thorium early in their depositional history.
Other studies Other studies undertaken as part of the Nymagee project included: preparation of a solid geology map for the Nymagee 1:250 000 map sheet area; a detailed structural evaluation of the former May Day gold mine; geochemical sampling of the Break O’Day Amphibolite; and reassessment and updating of the mineral occurrences dataset for the area. The results from these studies are summarised below.
Basement interpretation A solid geology (basement) interpretation of the Nymagee 1:250 000 map sheet area was prepared as part of the Nymagee project (Burton 2016). This interpretation utilised existing 1:100 000 scale outcrop geological mapping from 1980s and early 1990s (Scheibner 1985; MacRae & Pogson 1985; MacRae 1988,
1989; Trigg 1988; and Pogson 1991b) and extended units under cover utilising the regional gravity and aeromagnetic datasets together with data from exploration company drill- and water bore-logs. The results of this study are summarised below: • The Tarran Volcanics (not shown — example at 32.491°S, 146.452°E) and associated intrusions as well as dolerite dykes (not shown — example at 32.443°S, 146.624°E), which are spatially associated with the Erimeran Granite, are more extensive than previously mapped. Also, as previously recognised, there is a strong structural control to their distribution with a zone of north-northeasterly trending dolerite dykes (Bogolo Zone — not shown) interpreted as acting as tensile zone bounded by the Rookery and Nyora faults. • Apparent within the geophysical datasets are interpreted granite plutons that intrude the Girilambone Group at depth in the northeastern part of the study area (not shown — can be observed in geophysical datasets at: 32.35°S, 146.77°E; 32.12°S, 146.66°E; 32.03°S, 146.73°E). In addition there are a number of small intrusions, at depth, adjacent to the Erimeran and Thule granites as well as possible granite, at depth, to the east of Mount Hope. • The Gilgunnia Granite (Figure 2) is more extensive than is apparent in outcrop. In addition, that body appears to have acted as a rigid body during deformation and may have been, in part, responsible for the northeast-trending highstrain zone that developed in the Gilgunnia area, southeast of the granite. This zone is host to the structurally controlled high-sulfide (epigenetic) gold–base metal mineralisation at May Day mine (see below). • The Scotts Craig Fault (Figure 2) is more extensive than previously mapped, extending across the entire north–south length of the Nymagee 1:250 000 map sheet area to intersect the Rookery Fault in the vicinity of the Queen Bee mine. This fault may have been active during deposition of the Cobar Supergroup.
May Day Geological and structural mapping were undertaken in the open cut at the former May Day gold mine (Figure 2) to better understand the geological setting and deformation history of the western side of the Cobar Basin (Burton 2012). At May Day, the host sequence includes variably altered crystal-vitric tuffs and tuffaceous siltstones of the Mount Halfway Volcanics and interbedded sandstones, siltstones and claystones of the overlying upper Amphitheatre Group. The contact between the two is gradational.
Quarterly Notes
25
Amphitheatre Group
North
Sandstone, siltstone and claystone
Steeply plunging mineralised shoots develop within shear zone with associated alteration of host sequence North
Axial planar cleavage
East
Volcaniclastic units Mount Halfway Volcanics
Steep northeast-plunging asymmetric folding
East Mount Halfway Volcanics
Deposition - late Silurian to Early Devonian
Shear fabric axial planar to folds
Stage 1 Event Initial deformation and emplacement of mineralisation (?Cobar Basin inversion and/or deformation)
North
Fault A initial faulting East North Fault B subsequent faulting East
Stage 2(a) Event Further deformation (?Carboniferous Kanimblan Orogeny)
Figure 11. Interpreted geological/structural history of the May Day mine area (modified from Burton 2012).
The sequence has been deformed. The initial deformation (Stage 1) resulted in the development of steeply northeast-plunging upright folds, an associated northeast-trending axial planar cleavage and shearing. Alteration associated with the sheared volcaniclastic sequence includes a talc–carbonate (calcite>siderite), phengite, Mg-chlorite assemblage with possible amphibole and phlogopite (see Downes et al. submitted). Later deformation (Stage 2) resulted in the development of oblique-thrust faulting that displaced the sequence and earlier structures, adding to the complexity of the area. This model is shown in Figure 11. The mineralisation at May Day is generally associated with talc–carbonate–phengite–chlorite schist (this study) and includes zones, up to 30 m wide, of disseminated pyrite with minor galena, sphalerite, pyrrhotite and trace chalcopyrite with more intense sulfidic zones, up to 0.5 m wide, that form steeply plunging tabular bodies commonly associated with quartz veining and silicification (Clifford McElroy & Associates Pty Ltd 1973a, b, c; Hawley 1982). Some
26
August 2016
Amphitheatre Group
Fault A
Stage 2(b) continued deformation (?Kanimblan Orogeny) 2016_05_030
earlier workers (e.g. Clifford McElroy & Associates Pty Ltd 1973a; Suppel 1984) regarded the deposit as having a volcanogenic origin — interpreting the talc– chlorite schist as alteration developed within footwall ‘volcanics’ although others (e.g. Hawley 1982) also suggested that the mineralisation may be epigenetic. Burton (2012) proposed that May Day is a deformationrelated “Cobar-type” gold–base metal deposit that formed synchronous with Stage 1 during transpressive deformation — i.e. a structurally controlled (orogenic) high-sulfide base metal–gold system similar to that for the Cobar mineral field.
Geochemistry The Break O’Day Amphibolite (not shown in Figure 2 — located at 32.404°S, 146.607°E) consists of a series of disconnected, remanently magnetised, variably calcsilicate-altered metabasalt pods, hosted by Girilambone Group sedimentary rocks and contact metamorphosed by the Erimeran Granite — which implies a probable Ordovician age (Pogson 1991a; Burton 2014a). Pogson (1991a) suggested that these
basalts are tholeiites, whilst Burton (2014a), based on new whole rock geochemical data, proposed that the basalts formed as intraplate oceanic islands (seamounts) during the Ordovician. They are similar to basalts in the Sussex–Byrock 1:100 000 map sheet area further north (outside the study area) (see Burton et al. 2012). In the Melrose area there is a strong northwesttrending magnetic high to the east of the Erimeran Granite which corresponds to metasediments and mafic volcanic rocks of the Girilambone Group (MacRae & Pogson 1985). A sample of metabasalt from this area has geochemistry consistent with N-type mid-ocean ridge basalts (MORB) with an enriched or plume component (Burton 2014a). The data also match those for metabasalts associated with the Tritton and Tottenham copper deposits (Burton 2011, 2014b) which are also hosted by Girilambone Group sequences. Isaacs (2000) noted that interpretation of whole rock geochemistry for Early Devonian dolerite dykes associated with the Erimeran Granite is complex, with both MORB and continental-plate basalt signatures being present. Further geochemical sampling by Burton (2016) suggests that these dolerite dykes have a within-plate tholeiitic character, as does the Parkvale Gabbro (not shown — located at 32.322°S, 146.686°E), which is probably of the same age — based upon observations from this study and Pogson (1991a).
Mineral occurrences As part of the present study, the department’s Metallic, Industrial and Exploration (MetIndEx) database was updated from that compiled by Suppel and Gilligan (1993). This study was largely office-based but also included inspection of core and field visits to major sites of economic interest.
Discussion Igneous units and age dating New SHRIMP U–Pb dating of volcanic units and granites have clarified previous issues particularly related to the age of the Mineral Hill Belt, Nymagee Igneous Complex (NIC), and the age of the Mount Halfway and related volcanic units relative to the Ural Volcanics to the south. This helped to establish a general age progression of S-, I- and A-type magmatism in the region relative to that elsewhere within the Lachlan Orogen. The age of the NIC, which has multiple structural fabrics, has been the subject of debate. Brown (1975) suggested that the NIC was Middle Ordovician based on the presence of deformation-related fabrics and that it had intruded the Girilambone Group. Pogson
and Hilyard (1981) obtained a Rb–Sr isotopic age of 457 ± 112 Ma for the foliated phases of the NIC. However, the large error for this result was due to the small range in Rb/Sr values in the subsamples used to construct the isochron. More recently, Isaacs (2000) and this study were unable to resolve the magmatic crystallisation age of the NIC using U–Pb SHRIMP dating of zircons due to lack of magmatic overgrowths on abundant inherited zircons, although Isaacs (2000) obtained a single analysis for zircon of 425 ± 28 Ma. Further U–Pb SHRIMP dating using monazite (TRI39) gave a well constrained date of 428.1 ± 4.3 Ma (this study) which is interpreted to be the timing of magma crystallisation. This result can be verified using data from Pogson and Hilyard (1981) by using the monazite age to calculate the initial Sr ratio from the measured present day 87Sr/86Sr values. Initial ratios calculated from the data of Pogson and Hilyard (1981) using the monazite crystallisation age are generally in the range 0.7095 to 0.7125 — typical of Lachlan Orogen S-type values (McCulloch & Chappell 1982). Ages significantly younger or older than 428 Ma will have the effect of driving the calculated initial ratio to unrealistically higher or lower values. For example, if the foliated phase of the NIC crystallised at 440 Ma, the initial Sr ratios so calculated would be in the range 0.7065 to 0.7097, more typical of isotopically primitive I-type granites and rocks of direct mantle derivation. The results of this study confirm that the Ural Volcanics and Mount Hope Group volcanic rocks are not contemporaneous, nor co-magmatic (cf. Bull et al. 2008). Magmatic ages for the Ural Volcanics using SHRIMP are of the order of 412.2 ± 2.6 Ma — significantly younger than those of the Mount Hope Group that are bracketed by the Regina Volcanics and Mount Halfway Volcanics at 418.7 ± 3.1 Ma and 422.8 ± 2.6 Ma respectively (Table 2). In addition, the Mount Hope Group volcanic rocks and related granites are S-type (this study) while the Ural Volcanics are A-type (Blevin 2004; Meakin et al. 2005). New SHRIMP U–Pb zircon ages for volcanic rocks from the Canbelego–Mineral Hill Volcanic Belt (Mineral Hill Volcanics, Baledmund Formation) obtained as part of this study are somewhat younger than previous ages reported by Spandler (1998) for Mineral Hill, but are very similar and within error of the dates for the contemporaneous Florida Volcanics (421.7 ± 2.7 Ma) and Queen Bee Porphyry (417.6 ± 3.0 Ma) by Black (2005). Bodorkos et al. (2013) also obtained a magmatic crystallisation age of 418.3 ± 3.0 Ma for a flow-foliated rhyolite, informally named the ‘Peak rhyolite’ from the Peak gold mine near Cobar — younger than a previous U–Pb SHRIMP zircon date of 423.2 ± 3.5 Ma by Black (2007). To this temporal grouping may also be added: the buried Fountaindale
Quarterly Notes
27
Granodiorite, which was dated by LA-ICP-MS U–Pb zircon dating to 420 ± 2 Ma (relative to reference zircon FC-1, Norman 2004); and the Wilmatha Granite located immediately to the east of Mineral Hill, dated at 421.1 ± 3.4 Ma (SHRIMP U–Pb zircon dating, Spandler 1998). Thus the Canbelego–Mineral Hill Volcanic Belt is interpreted as an extensive and distinct I-type package of volcanic and related intrusive rocks relative to the S-type Mount Hope Group and younger A-type Ural Volcanics. The volcanic rocks of the Mount Hope Group are also spatially and temporally associated with S-type granite plutonism represented by the Gilgunnia and Mount Allen granites. The close genetic and spatial relationship between the Gilgunnia Granite and the Mount Hope Volcanics has been previously recognised by Scheibner (1987). S-type magmatism in the Nymagee region extended from > 428 Ma to around 419 Ma while I-type magmatism ranged from 421 Ma to 414 Ma. A-type magmatism is represented by the Boolahbone Granite (415.8 ± 3.1 Ma), Tarran Volcanics (415 ± 3.9 Ma) and Ural Volcanics (Shepherds Hill quarry, 412.2 ± 2.6 Ma). The S-type magmatism also show two age ranges: a group of older S-type granites (e.g. Urambie, Erimeran) that are older than 424 Ma and merge back in age with the more ‘typical’ Lachlan Orogen S-type granite ages of around 430 Ma to the south in the Cargelligo 1:250 000 map sheet area, and a relatively tight age grouping of S-type volcanic rocks and related granites (Gilgunnia and Mount Allen granites and the Mount Halfway, Nombiginni and Regina volcanics and related units) around 419 to 423 Ma. These younger S-types overlap with the I-types around 422 to 419 Ma and between the I-types and A-types with the Boolahbone Granite being contemporaneous with I-type plutonism and volcanism. The older S-type granite group is not accompanied by a complementary S-type volcanic package within the study area. A general younging in granite ages from S- through I- to A-types, coupled with overall general younging to the east, has been used as evidence for tectonic roll-back models coupled with a general easterly retreat of subduction (Collins & Richards 2008; Kemp et al. 2009). However, a growing number of granite SHRIMP ages in the Bourke, Nymagee and Ardlethan region by Bodorkos et al. (2013) indicate that age distribution patterns for granites in the Lachlan are more complicated and do not necessarily support a simple eastwards younging in granite magmatic crystallisation ages on an orogenic scale.
Timing of deformation Multiple deformation-related events are evident within the Nymagee project area, with potential deformation events including the Benambran, Cobar,
28
August 2016
Tabberabberan and Kanimblan orogenies. The timing of regional deformation of the Girilambone Group has been attributed to the Benambran Orogeny (MacRae 1987b; Pogson 1991a) — based on regional relationships between that unit and intrusions/ overlying sequences of the Cobar Supergroup. This is supported by 40Ar/39Ar dating of muscovite from the Girilambone Group in the Tottenham area (to the east of the study area) which yielded dates of 435.2 ± 2.6 Ma and 440.2 ± 2.6 Ma (Fergusson et al. 2005). In addition, the lead-isotope data for Mallee Bull and for Mineral Hill (Downes & Poulson in prep.) indicate that there was a loss of U and Th about that time — supporting the interpretation that deformation occurred in latest Ordovician to earliest Silurian times. The timing of deformation for the late Silurian to Early Devonian Cobar Basin, Mount Hope Trough and Winduck Shelf has been the subject of ongoing debate. Glen et al. (1992) reported a range of wholerock K–Ar (402 ± 8 Ma, 402 ± 8 Ma and 405 ± 8 Ma) and 40Ar/39Ar (378.8 ± 2.4 Ma, 387.1 ± 3.0 Ma, 395.6 ± 4.0 Ma, 396.2 ± 1.4 Ma, 397.3 ± 1 Ma and 403.8 ± 0.9 Ma) ages for units in the Cobar area (Cobar Basin) and proposed that cleavage development occurred between 395 and 400 Ma (late Early Devonian) (i.e. the Cobar deformation — see Scheibner & Basden 1998). In addition: Glen et al. (1992) noted that the age constraint for the lower part of the Mulga Downs Group was late Early Devonian (from Powell et al. 1987 — who proposed that the Mulga Downs Group ranged in age from late Early to Late Devonian and possibly as young as the Early Carboniferous); suggested that the boundary between the Mulga Downs Group and underlying Winduck Group was paraconformable; and proposed that deformation in the western Cobar Basin was largely Carboniferous in age. However the interpretation of the K–Ar and 40Ar/39Ar data by Glen et al. (1992) was based on two major assumptions: that detrital micas identified in the samples had undergone sufficient heating during the deformation event to reset the K–Ar and 40Ar/39Ar dating systems and that the Mulga Downs Group was no older than late Early Devonian. Closure temperature for white micas is dependent on several factors, including grainsize, rock-type, cooling rate and structural state (i.e. muscovite — two-layered monoclinic vs phengite — three-layered trigonal; see Snee 2002). As a result, a wide range of closure temperatures have been reported, with Harrison et al. (2009) suggesting that closure-temperature for muscovite can be up to 425°C (range 370°C to 420°C — their figure 13) whilst for phengite the closure temperature is unknown. However, Snee (2002) noted that, based on work by Till and Snee (1995), the closure temperature for phengite could be as high as 525°C.
The metamorphic grade for the Cobar Basin has yet to be mapped, but in the Nymagee study area the grade for the southern Cobar Basin, Mouramba Shelf and Kopyje Shelf are uniformly sub- to lowest greenschist facies (see Downes et al. submitted). In addition, those authors recorded that phengitic white micas (i.e. phengite) are commonly present within Cobar Basin sedimentary rocks. Further north, Brill (1988a, b) suggested that metamorphic grades at Endeavor (Elura) and near Cobar were prehnite–pumpellyite to lowest greenschist facies — again reflecting a low temperature for regional metamorphism. Thus metamorphic grades suggested for the Cobar area are too low to reset the argon thermochronology of the detrital micas recorded in the samples analysed by Glen et al. (1992) — even assuming that the white micas were muscovite rather than phengite (as is commonly present). It is suggested that the whole rock data from Glen et al. (1992) represents a combination of argon sourced from deformation/alteration- and detrital-related white micas and do not represent the timing of cleavage development/deformation. Regarding the age of the Mulga Downs Group, Sherwin (2013) reviewed the palaeontological data for the Group and revised the age range of that unit from the ~Pragian–Emsian boundary to no younger than the Eifelian (i.e. 407.6 ± 2.6 Ma to 387.7 ± 0.8 Ma — timescale of Gradstein et al. 2012) — with little or no time gap between deposition of the Winduck (Lochkovian to Pragian) and overlying Mulga Downs groups. The boundary between these two units has been described as conformable through disconformable to locally unconformable by Powell et al. (1987). In addition, field observations made as part of the present study and supported by the interpretation of seismic line 09GA-RS2 (Survey 188; east–west across the central part of the Nymagee 1:250 000 map sheet area; 188 — data available at Geoscience Australia website: http://www.ga.gov. au/metadata-gateway/metadata/record/gcat_69989) indicate that there was no major or apparent disruption to sedimentation between the Winduck and Mulga Downs groups. So, what was the timing of deformation in the Cobar Basin? Perkins et al. (1994) reported 40Ar/39Ar dates for three alteration-related muscovite samples (Stages 4 and 5) from volcanic rocks at the Peak mine of 401 ± 1.0 Ma, 382.6 ± 1.0 Ma and 385.4 ± 1.0 Ma, and suggested that Cu–Au mineralisation formed at 401 ± 1.0 Ma whereas Pb–Zn mineralisation formed at 384 ± 1.4 Ma. Sun et al. (2000) suggested that deformation occurred somewhat later at between 385 Ma and 389.2 Ma — based on their 40Ar/39Ar dating of material from Endeavor and a review of data from Glen et al. (1992). In addition, Huston et al. (2016) reported new high-
precision Pb-isotope data for mineralisation in the Cobar area, and noted that the data reflect mixing of Pb sources (as suggested by Lawrie & Hinman 1998), but several of their data have lead model ages between 390 Ma and 375 Ma (see their figure 9). With the exception of a single 40Ar/39Ar analysis for muscovite from the Peak mine (401 ± 1.0 Ma) which has a poor spectrum and large error bars (Perkins et al. 1994), all data support the interpretation that deformation in the Cobar Basin occurred between 390 Ma and ~380 Ma — coincident with or post-peak Tabberabberan Orogeny which Glen (2005) suggested was Eifelian in age (393.3 ± 1.2 to 387.7 ± 0.8 Ma — timescale of Gradstein et al. 2012). 40Ar/39Ar dating of micas intergrown with sulfides at Hera gave a preliminary date of 382 Ma (Downes & Phillips in prep). Whilst this date has yet to be confirmed, it also supports Middle Devonian timing for deformation and mineralisation associated with the Cobar Basin. Scheibner and Basden (1998) suggested that deformation in the western Cobar Basin was largely Carboniferous in age — based on the interpretation that the Mulga Downs Group was Middle to Late Devonian. However, if there is no stratigraphic break between the Mulga Downs Group and underlying Winduck Group, and both units are Early Devonian, then it is likely that deformation in this area is also Tabberabberan in age. This is supported by the lead isotope data for the Manuka (Wonawinta) area which have lead model ages ranging from mid-Silurian to late Early Devonian (~389 Ma), but no younger — implying that U and Th was removed from the sequences shortly thereafter (thus fossilising the reservoir) (Downes & Poulson in prep). This suggests that the major dewatering event in the area was related to the Tabberabberan Orogeny. An unexpected outcome of the present study was the recognition that the Cocoparra Group, which lies on the adjacent Cargelligo 1:250 000 map sheet area to the south, is very likely a stratigraphic equivalent to the Mulga Downs Group and may overlap in time with the upper Winduck Group. Sherwin (2016) noted that fossils in the Cocoparra Group are few and poorly preserved, but indicate an Early to mid-Devonian age and that part of that unit represents a marine environment. Correlation of the Cocoparra Group with the Mulga Downs Group effectively removes any Late Devonian sedimentary sequences from the area between Wilcannia and Tullamore, in central New South Wales, suggesting that the last major deformation for this area was the Tabberabberan Orogeny and not the Kanimblan Orogeny. Examination of the regional fold patterns for the Nymagee 1:250 000 map sheet area, together with the structural history for the May Day open cut (Burton
Quarterly Notes
29
2012), suggest that minor deformation occurred later than the Tabberabberan Orogeny (as evidenced by a change to the sigma 1 direction) and it is proposed that this deformation was related to the Kanimblan Orogeny. However, the extent of this event has not been quantified as part of this study.
146°09′E 32°02′S
145°35′E 32°02′S
NYMAGEE
LACHLAN DOWNS
Implications for mineralisation
30
August 2016
Thule Granite
Boolahbone Granite
Gilgunnia May Day
Gilgunnia Range EC
MD 2-Siegals
Mount Kennan Volcanics feldspar-phyric dacite EC
Mount Victor EC
Mount Kennan Volcanics quartzphyric dacite EC
Nombiginni EC
Wagga Tank Mount Kennan Volcanics quartz-phyric rhyolite EC MOUNT ALLEN
Coan
Nombinnie-Regina EC
Double Peak Mount Allen EC Mount Allen Mount Allen EC
Granite
KILPARNEY
Mount Hope Mount Solitary
Mount Solar
Matakana 33°02′S 145°34′E
CARGELLIGO
HILLSTON
33°02′S 146°08′E
REFERENCE Outcropping units (continued) Nombiginni Volcanics Regina Volcanics
Gold
Copper
Simplified commodity Base metal
The general age progression of S-, I- and A-type magmatism in the region, as noted above, has important implications for mineralisation. Much of the tin–tungsten mineralisation associated with the Wagga Tin Belt, which extends from south of Wagga Wagga through Ardlethan to Tallebung (within the present study area), is associated with dominantly S-type magmatism. The timing of mineralisation associated with this zone ranges from approximately 430 Ma to ~415 Ma (Bodorkos et al. 2013; P Blevin pers. comm. March 2016). As part of the present study cassiterite from the Tallebung Sn system was dated using the U–Pb LA-ICP-MS technique, which yielded a date of 418 ± 6 Ma. Barry (2016) undertook additional U–Pb LA-ICP-MS of alluvial cassiterite from Tallebung and suggested that two cassiterite populations were present. These include an older group of analyses that averaged 429.2 ± 9.8 Ma (n=4; 95% confidence) and a second younger group that averaged 413.2 ± 8.8 Ma (n=2; 95% confidence). The samples that Barry (2016) analysed were from the Department’s Economic Rock and Minerals Collection and were not collected in-situ from the Tallebung tin field so the actual location of the samples analysed may be suspect and not be from Tallebung. However, assuming that they are from the Tallebung area they indicate that the older S-type granites such as the Thule and parts of the Erimeran are prospective for Sn–W mineralisation, particularly in areas where the upper parts of these granite bodies may be preserved. Local areas of greisenisation in both the Thule and the Erimeran Granites have been observed in the field. In addition the presence of younger S-type granites in the Nymagee area suggests that the progenitor to the Tallebung tin field is at depth. The new dating for volcanic rocks of the Mount Hope Trough and Canbelego–Mineral Hill Volcanic Belt (Kopyje Shelf), supported by the findings of the palaeontological review, have shown that felsic volcanism in these two areas occurred at the same time in the late Silurian to earliest Devonian. The study has significantly simplified the volcanic stratigraphy of the Mount Hope Group. There are six compositionally and texturally distinct coherent rhyolitic/dacitic units identified within the sequence (four of which are shown on Figure 8) and three major volcaniclastic units. In addition, eight volcanic centres were identified
Gilgunnia Granite
Bedooba EC
Occurrence Small
Locality
Medium
Major road, sealed
Large
Major road, unsealed Minor road, unsealed
Coherent volcanic units Type 2 rhyolite
1:100 000 map sheet
Type 3 rhyolite
Unit boundary
Type 4 rhyolite Type 5 rhyolite Eruptive centre (EC) Outcropping units Ambone Volcanics Coando Volcanics Double Peak Volcanics Goona Volcanics Mount Halfway Volcanics Mount Kennan Volcanics
0
10
20 km 2016_05_031
Figure 12. Distribution of mineralised zones and their proximity to interpreted volcanic centres associated with the Mount Hope Group.
(Figure 9). We support the earlier work by Bull et al. (2008) and other workers that this volcanic package formed in a deep water environment. Figure 12 shows the location of mineralisation hosted by or adjacent to the Mount Hope Group. An important outcome of the review of mineralisation associated with the Mount Hope Group carried out as part of the preparation of the Cobar 1:500 000 metallogenic map (Fitzherbert et al. in press) is that magmaticrelated mineralisation is spatially associated with the Boolahbone Granite — the youngest intrusion in the area. Furthermore, the observation by Simpson (2014) that the magmas associated with the Mount Hope Group were anhydrous and relatively hot suggests that these units would drive hydrothermal fluids/alteration of the volcanic pile, but may not have contributed sulfur and/or metals to the system, thus limiting the potential for significant VAMS-type systems to form. This is supported by the S-isotope data for zones such as MD2–Siegals. By contrast, for the Canbelego–Mineral Hill Volcanic Belt two lava-types are present — a rhyolitic facies and a dacitic facies. There is clear evidence that the dacitic lavas formed after the rhyolites (Simpson 2015). In addition, based on the available thin sections the area has not undergone significant regional or contact metamorphism. However, in contrast to the Mount Hope Trough where deep water conditions existed, the Canbelego–Mineral Hill Volcanic Belt formed under shallow marine to subaerial conditions. Associated with this belt is epithermal mineralisation at Mineral Hill and Pipeline Ridge. Based on the available data (including a preliminary 40Ar/39Ar date from Downes & Phillips in prep. for white mica) from Mineral Hill, that deposit formed in the latest Silurian at approximately 420 Ma — coincident with volcanism. As noted above, Simpson (2015) reported that the magmas associated with the Mount Hope Group were anhydrous and of unusually high temperature whilst for the Canbelego– Mineral Hill Volcanic Belt the same features were not observed. In addition for Mineral Hill and Pipeline Ridge there is a clear magmatic component in the available S-isotope data, suggesting that the magmas related to those systems were intimately involved with the mineralising process. A major outcome of the present study is the recognition that the majority of the southern Cobar Superbasin underwent sub-greenschist to lowest greenschist facies metamorphism; that only late diagenetic conditions existed for the Winduck Shelf; and that significantly hotter conditions are preserved within alteration-related assemblages associated with structurally-controlled high-sulfide mineralised zones (such as Hera and Nymagee). In addition, for several of the zones included in the HyLogger™ study there
are systematic changes in chlorite composition from Fe- and/or Fe–Mg-chlorites to more Mg-rich varieties associated with mineralisation. That suggests the oreforming fluids were undersaturated with respect to iron. Furthermore, many of the zones had S-isotope values between 4 and 8 per mil – implying that some sulfur was sourced from a reservoir containing magmatic sulfur. Finally, the lead-isotope data for a number of zones, including Mallee Bull, Sandy Creek, Pipeline Ridge, Blind Calf and Yellow Mountain have lead-isotope values consistent with lead and potentially other metals being sourced from units in the basement to the Cobar Superbasin. The available data support a model whereby hot, moderate salinity fluids were generated within basement to the Cobar Superbasin, leached metals and some sulfur from both basement (likely source of copper and gold) and basinal sequences and deposited metals in pre-existing structurally controlled dilatant sites. Based on the range of S-isotope data and presence of gold as well as base metals in many mineralised zones it is suggested that fluid mixing is an important mechanism to trigger sulfide precipitation. Also, cooling of ore-forming fluids is important (based on the narrow alteration zones associated with most zones and thermal contrast between those zones and the surrounding wall rocks). The nature of the initial ore-forming fluids and timing of events is still open to debate. One possibility is that some of the fluids may be magmatic in origin (based on the presence of observed garnet at Hera and similar high temperature minerals in other zones — J Fitzherbert pers. comm. March 2016) whilst an alternate model may be that the fluids were generated during deformation (supported by lead-isotope data that is younger than the host sequences, absence of intrusions younger than 410 Ma, and preliminary dating for Hera at ~382 Ma).
Conclusions The Nymagee project has provided a focus for new work in a key part of the Central Subprovince of the Lachlan Orogen. The results to date have already made significant changes to the understanding of that area and companies have been enthusiastic in supporting the project. Important outcomes include those summarised here. • There is a general age progression of S-, I- and A-type magmatism in the study area. • Units of the Mount Hope Group, Amphitheatre Group and Kopyje Group are late Silurian to earliest Devonian in age. • The stratigraphy of the Mount Hope Group can be simplified, with six lava types recognised and a number of volcanic centres also recognised. • The majority of the southern Cobar Superbasin
Quarterly Notes
31
underwent sub-greenschist to lowest greenschist facies metamorphism and only late diagenetic conditions existed for the Winduck Shelf. • Deformation in the area is Middle Devonian. • For structurally controlled high-sulfide zones it is proposed that, based on sulfur- and lead-isotope data, hot fluids leached sulfur and base metals from basement to the Cobar Superbasin in addition to basinal sequences (e.g. Hera, Mallee Bull, Nymagee), and that these fluids deposited their metals by fluid mixing with possible cooling of these fluids to trigger sulfide precipitation. • Mineralisation at the May Day mine is associated with transpressive deformation, similar to that observed within the Cobar mineral field, suggesting that similar high-strain zones may also have potential for structurally controlled, epigenetic gold and base metal mineralisation.
Acknowledgements The authors acknowledge the ongoing support given by many individuals and companies. These include but are not limited to: Ian Cooper, Vlad David, Stuart Jeffrey, Trangie Johnston, Chris Johnston, Marty Lenard, Steve Leggett, Ian Mackenzie, Adam McKinnon, Shane Mele, Peter Muccilli, Michael Oates and Kristy Vassallo. In addition, a project like this is dependent on the technical support from the many co-workers including: Michael Bruce (GSNSW), Sol Buckman (University of Wollongong), Emma Chisholm (GA), David Phillips (University of Melbourne), Simon Poulson (University of Nevada) and Mark Schmitz (Boise State University) — we wish to acknowledge their valuable contribution. Martin Scott is thanked for his detailed review of our paper and Kate Holdsworth is thanked for preparing our figures.
References Adamson C.L., Brooks C., Brunker R.L., Bryan J., Conolly J., Kriewaldt M., Lloyd A.C., McClatchie L., Mulholland C.St.J., Raggatt H.G., Rayner E.O., Russell R.T. & Sullivan C.J. 1968. Nymagee 1:250 000 geological series sheet SI55-2. Geological Survey of New South Wales, Sydney. Barry C.M. 2015. U/Pb LA-ICP-MS geochronology of cassiterites from New South Wales and the Northern Territory, Australia. Geological Survey of New South Wales, Report GS2016/0206. Black L.P. 2005. SHRIMP U–Pb zircon ages obtained during 2004/05 for GSNSW. Geological Survey of New South Wales, Report GS2005/745. Black L.P. 2007. SHRIMP U–Pb zircon ages obtained during 2006/07 for NSW Geological Survey projects. Geological Survey of New South Wales, File GS2007/298.
32
August 2016
Blevin P.L. 1999. Igneous and metallogenic assessment of selected units on the Nymagee 1:250 000 and adjacent sheets. Unpublished report to Triako Resources Limited. Geological Survey of New South Wales, Report GS2016/0586. Blevin P.L. 2002. The igneous geology and metallogeny of the Nymagee 1:250,000 sheet and environs, NSW. AMIRA Project P515 report. Blevin P.L. 2003. A Re–Os molybdenite date from Melrose, NSW: comments on age and Re content. In: Mackenzie I., Miller C. & Randell J. Yellow Mountain joint venture, annual report of exploration activities on exploration licences 5721, 5787 for the period ending 3 May 2004. Geological Survey of New South Wales, File GS2004/399. Blevin P.L. 2004. Chemistry of igneous units of the Cargelligo 1:250 000 map sheet area, New South Wales (revised and updated). Geological Survey of New South Wales, File GS2004/451. Blevin P.L & Jones M. 2004. Chemistry, age and metallogeny of the granites and related rocks of the Nymagee region, NSW. In: McQueen K.G. & Scott K.M. eds. Proceedings of the Exploration Field Workshop Cobar Region 2004, pp. 15–19. CRC LEME Publication. Bodorkos S.1, Blevin P.L., Eastlake M.A., Downes P.M., Campbell L.M., Gilmore P.J., Hughes S.K., Parker P.J. & Trigg S.J. 2015. New SHRIMP U–Pb zircon ages from the central and eastern Lachlan Orogen, New South Wales July 2013–June 2014. Geoscience Australia Record 2015.002; Geological Survey of New South Wales, Report GS2015/0002. Bodorkos S., Blevin P.L., Simpson C.J., Gilmore P.J., Glen R.A., Greenfield J.E., Hegarty R. & Quinn C.D. 2013. New SHRIMP U–Pb zircon ages from the Lachlan, Thomson and Delamerian orogens, New South Wales: July 2009–June 2010. Geoscience Australia Record 2013/29, Geological Survey of New South Wales, Report GS2013/0427. Brill B.A. 1988a. Geochemistry and genesis of the CSA Cu–Pb–Zn seposit, Cobar, N.S.W., Australia. PhD thesis, University of Newcastle, (unpubl.). Brill B.A. 1988b. Illite crystallinity b0 and Si content of K-white mica as indicators of metamorphic conditions in low-grade metamorphic conditions in low-grade metamorphic rocks at Cobar, New South Wales, Australian Journal of Earth Sciences 35, 295– 302. Brown R.E. 1975. The Nymagee Igneous Complex and associated rocks. Geological Survey of New South Wales, Report GS1975/368. Bull K.F. 2006. Facies architecture, geochemistry and tectonic significance of the Ural Volcanics and the Mount Hope Volcanics, Central Lachlan Fold Belt, NSW. PhD thesis, University of Tasmania (unpubl.).
Bull K.F., Crawford A.J., McPhie J., Newberry R.J. & Meffre S. 2008. Geochemistry, geochronology and tectonic implications of Late Silurian–Early Devonian volcanic successions, Central Lachlan Orogen, New South Wales. Australian Journal of Earth Sciences 55, 235–264. Burton G.R. 2011. Interpretation of whole rock geochemical data for samples of mafic schists from the Tritton area, central New South Wales. Geological Survey of New South Wales, Report GS2012/0264. Burton G.R. 2012. A geological study of the May Day open cut mine, Gilgunnia area. Geological Survey of New South Wales, Report GS2012/1797. Burton G.R. 2014a. Geological investigation of the Break O’Day Amphibolite, Nymagee area. Geological Survey of New South Wales, Report GS2015/0141. Burton G.R. 2014b. Interpretation of whole rock geochemical data for samples of mafic schists from the Tottenham area, central New South Wales. Geological Survey of New South Wales, Report GS2014/0215. Burton G.R. 2016. Geological and geophysical interpretation of the bedrock units in the Nymagee 1:250 000 map sheet area. Geological Survey of New South Wales, Report GS2015/0142. Burton G. R., Trigg S. J. & Campbell L.M. 2012. Explanatory notes for the Sussex 8135 and Byrock 8136 1:100 000 geological sheets. Geological Survey of New South Wales, Maitland. Bush A. 1980. The formation of volcanic-hosted massivesulfide mineralisation at Mineral Hill. PhD thesis University of Tasmania, Hobart (unpubl.). Carne J.E. 1908. The copper mining industry and the distribution of copper ores in NewSouthWales. Geological Survey of New South Wales. Mineral Resources 6. Carne J.E. 1911. The tin-mining industry and the distribution of tin ores in New South Wales. Geological Survey of New South Wales. Mineral Resources 14. Carne J.E. 1912. The tungsten-mining industry in New South Wales. Geological Survey of New South Wales. Mineral Resources 15. Carr G.R., Dean J.A., Suppel D.W. & Heithersay P.S. 1995. Precise lead isotope fingerprinting of hydrothermal activity associated with Ordovician to Carboniferous metallogenic events in the Lachlan Fold Belt of New South Wales. Economic Geology 90, 1467–1505. Chisholm E.I., Blevin P.L., Downes P.M. & Simpson C.J. 2014. New SHRIMP U–Pb zircon ages from the central Lachlan Orogen and Thomson Orogen, New South Wales: July 2011–June 2012. Geoscience Australia: Canberra Record 2014/32, Geological Survey of New South Wales, Report GS 2013/1837.
Clifford McElroy & Associates Pty Limited 1973a. Application for prospecting aid May Day prospect EL 365 by Millstern Exploration Pty Limited with accompanying geological report. Geological Survey of New South Wales, File GS1974/122. Clifford McElroy & Associates Pty Limited 1973b. Interim report to Mt. Hope Minerals N.L. on exploratory drilling at the May Day area, EL 365, NSW, 4th October 1973. Geological Survey of New South Wales, File GS1974/122. Clifford McElroy & Associates Pty Limited 1973c. Interim report to Mt. Hope Minerals N.L. on exploratory drilling at the May Day area, EL 365, NSW, 23rd November 1973. Geological Survey of New South Wales, File GS1974/122. Collins W.J. 2002. Nature of extensional accretionary orogens. Tectonics 21, 1258–1272. Collins W.J. & Richards S.W. 2008. Geodynamic significance of S-type granites in circum-Pacific orogens. Geology 36(7), 559–562. Colquhoun G.P. & Cameron R.G. 2005. Geological history. In: Colquhoun G.P., Meakin N.S. & Cameron R.G. (compilers) 2005. Cargelligo 1:250 000 Geological Sheet SI/55-6, 3rd edition, Explanatory Notes, pp. 13–17. Geological Survey of New South Wales, Maitland, NSW. Colquhoun G.P., Hendrickx M.A. & Meakin N.S. 2005. Wagga Group. In: Colquhoun G.P., Meakin N.S. & Cameron R.G. (compilers) 2005. Cargelligo 1:250 000 Geological Sheet SI/55-6, 3rd edition, Explanatory Notes, pp. 19–30. Geological Survey of New South Wales, Maitland, NSW. Colquhoun G.P., Meakin N.S. & Cameron R.G. (compilers) 2005. Cargelligo 1:250 000 Geological Sheet SI/55-6, 3rd edition, Explanatory Notes. Geological Survey of New South Wales, Maitland, NSW. David V. 2005. Structural setting of mineral deposits in the Cobar Basin. PhD thesis, University of New England (unpubl.). David V. 2006. Cobar Superbasin System metallogenesis. In: Lewis P.C. 2006 Mineral Exploration Geoscience in New South Wales Extended Abstracts, pp. 39–51. Mines and Wines Conference, Cessnock NSW SMEDG (Sydney Mineral Exploration Discussion Group). David V. 2008. Lead isotopes Wagga Tank EL6695. In: David V. 2008. Exploration licence 6695 Wagga Tank Annual report. Geological Survey of New South Wales File GS2008/0178. David V. 2010. Cobar style deposits — from dwarfs to giants. 13th Quadrennial IAGOD Symposium 2010, 31–32. David V. & Glen D. 2004. The geological framework of the Cobar Basin. In: McQueen K.G. & Scott K.M. eds. Proceedings Exploration Field Workshop Cobar Region 2004, pp. 31–36. CRC LEME Publication.
Quarterly Notes
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Downes P.M. 2009. Sulfur- and lead-isotope signatures of selected middle Silurian to Carboniferous mineral systems of the Lachlan Orogen, eastern New South Wales — implications for metallogenesis. PhD thesis, University of Newcastle (unpubl.). Downes P.M., Blevin P.L., Burton G.R., Clissold M.E. & Simpson C.J. 2013. Keys to understanding the Central Lachlan — the Nymagee mineral systems project. AIG Bulletin 55, 53–59. Downes P.M., Blevin P., Reid W.J., Barnes R.G. & Forster D.B. 2011. Metallogenic map of New South Wales — 1:1 500 000 Map. Geological Survey of New South Wales, Department of Industry and Investment, Maitland, Australia. Downes P.M. & Burton G.R. 2000. Mineralisation. In: Lyons, P., Raymond, O.L., & Duggan, M.B., eds. Forbes 2nd edition 1:250,000 Geological Sheet SI/55-7, (2nd edition), Explanatory Notes, pp. 177–197. AGSO Record 2000/20. Downes P.M. & Phillips D. (in prep). 40Ar/39Ar Geochronology of the mineral systems in the southern Cobar Superbasin: implications for metallogenesis in the central Lachlan Orogen, New South Wales. Downes P.M. & Poulson S. (in prep). Isotope signatures of selected Silurian to Devonian mineral systems in the Nymagee area — Central Lachlan Orogen, New South Wales. Downes P.M, Tilley D.B., Fitzherbert J. & Clissold M.E. submitted. Regional metamorphism and the alteration response of selected Silurian to Devonian mineral systems in the Nymagee area, Central Lachlan Orogen, New South Wales — a HyLogger™ case study. Australian Journal of Earth Sciences. Felton E.A. 1981. Geology of the Canbelego1:100 000 Sheet 8134. New South Wales Geological Survey, Sydney. Felton E.A., Brown R.E. & Fail A.P. 1983. Canbelego1:100 000 Geological Sheet 8134. Geological Survey of New South Wales, Sydney. Fergusson C.L., Fanning C.M., Phillips D. & Ackerman B.R. 2005. Structure, detrital zircon U–Pb ages and 40Ar/39Ar geochronology of the Early Palaeozoic Girilambone Group, central New South Wales: subduction, contraction and extension associated with the Benambran Orogeny. Australian Journal of Earth Sciences 52, 137–159. Fitzherbert J. A., Downes P. M., & Blevin P. L. in press. Cobar 1:500 000 Special Metallogenic Map. Geological Survey of New South Wales, Maitland, Australia. Flint R.B., Ambrose G.J. & Campbell K.S.W. 1980. Fossiliferous Lower Devonian boulders in Cretaceous sediments of the Great Artesian Basin. Transactions of the Royal Society of South Australia 104, 57–65.
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August 2016
Foster D.A., Gray D.R. & Bucher M. 1999. Chronology of deformation within the turbiditedominated, Lachlan orogen: implications for the tectonic evolution of eastern Australia and Gondwana. Tectonics 18, 452–485. Giles A. D. 1993. Preliminary investigation and interpretation of fluid inclusions in core samples WON4 (113.2m) and WON-7 (134m). In: Allan A.D. 1993. Exploration Licence 3255 “Lachlan Downs” first annual report for the period ending 16th January 1993. Geological Survey of New South Wales File GS1993/188. Glen R.A. 1982. Nature of late-Early to Middle Devonian tectonism in the Buckambool area, Cobar, New South Wales. Journal of the Geological Society of Australia 28, 127–138. Glen R.A. 1987. Geology of the Wrightville 1:100 000 Sheet 8034. Geological Survey of New South Wales, Sydney. Glen R.A. 2005. The Tasmanides of eastern Australia. In: Vaughan A.P.M., Leat P.T. & Pankhurst R.J. eds. Terrane processes at the margins of Gondwana, pp. 23–96. Geological Society, London, Special Publications 246, (0305-8719). Glen R.A. 2013. Refining accretionary orogen models for the Tasmanides of eastern Australia. Australian Journal of Earth Sciences 60, 315–370. Glen R.A., Dallmeyer R.D. & Black L.P. 1992. Isotopic dating of basin inversion — the Palaeozoic Cobar Basin, Lachlan Orogen, Australia. Tectonophysics 214, 249–268. Glen R.A., MacRae G.M., Pogson D.J., Scheibner E., Agostini A. & Sherwin L. 1985. Summary of the geology and controls of mineralization in the Cobar region. Geological Survey of New South Wales, Report GS1985/203. Glen R.A., Powell C.McA. & Khaiami R. 1987. Devonian to ?Carboniferous sedimentary rocks. In: Glen R.A. Geology of the Wrightville 1:100,000 Sheet 8034. pp. 149–203. Geological Survey of New South Wales, Sydney. Gradstein F.M., Ogg J.G., Schmitz M.D. & Ogg G.M. 2012. The Geologic Time Scale 2012. 2 Vols. Elsevier. Harrison T.M., Celerier J., Aikman A.B., Hermann J. & Heizeler M.T. 2009. Diffusion of 40Ar in muscovite. Geochemica et Cosmochimica Acta 73, 1039–1051. Hawley D. 1982. M.L. 546, May Day Prospect, Gilgunnia area, Cobar region. Geological Survey of New South Wales, File GS1981/291. Huston D.L., Champion D.C., Mernagh T.P., Downes P.M., Jones P., Carr G., Forster D. & David V. 2016. Metallogenesis and geodynamics of the
Lachlan Orogen: new (and old) insights from spatial and temporal variations in lead isotopes. Ore Geology Reviews 76, 257–267. Isaacs D. 2000. Evolution of the Nymagee region: utilising geochemistry, geochronology and geophysics. BSc (Honours) thesis, Australian National University, Canberra (unpubl.). Jiang Z. & Seccombe P. K. 2000. Source of oreforming components at the Peak mine, Cobar, NSW — evidence from isotope studies. In: McQueen K. G. & Stegman C. L. (eds.). Central West Symposium Cobar 2000: Geology, Landscapes and Mineral Exploration: WA, CSIRO Extended Abstracts, pp. 41–45. Cobar, Commonwealth Scientific and Industrial Research Organisation. Kemp A.I.S., Hawkesworth C.J., Collins W.J., Gray C.M., Blevin P.L. & Edinburgh Ion Microprobe Facility 2009. Isotopic evidence for rapid continental growth in an extensional accretionary orogen: the Tasmanides, eastern Australia. Earth and Planetary Science Letters 284, 455–466. Lawrie K.C. & Hinman M.C. 1998. Cobar-style polymetallic Au–Cu–Ag–Pb–Zn deposits. AGSO Journal of Australian Geology & Geophysics 17, 169–187. MacRae G.P. 1987a. Geology of the Lachlan Downs 1:100,000 Sheet 8033. New South Wales Geological Survey, Sydney. MacRae G.P. 1987b. Geology of the Nymagee 1:100 000 Sheet 8133. New South Wales Geological Survey, Sydney. MacRae G.P. 1988. Nymagee 1:100 000 Geological Sheet 8133. New South Wales Geological Survey, Sydney. MacRae G.P. 1989. Lachlan Downs 1:100 000 Geological Sheet 8033. Geological Survey of New South Wales, Sydney. Macrae, G.P. & Pogson, D.J. 1985. Gindoono 1:100 000 Geological Sheet 8232, provisional edition 1985, Geological Survey of New South Wales, Sydney (unpubl.). McCulloch M.T. & Chappell B.W. 1982, Nd isotopic characteristics of S- and I-type granites. Earth and Planetary Science Letters 58, 51–64. Meakin N.S. 2005. Derrida Phase. In: Colquhoun G.P., Meakin N.S. & Cameron R.G. (compilers) 2005. Cargelligo 1:250 000 Geological Sheet SI/55-6, 3rd edition, Explanatory Notes, pp 49–50. Geological Survey of New South Wales, Maitland, NSW. Meakin N.S., Colquhoun G.P. & Cameron R.G. 2005. Ural Volcanics. In: Colquhoun G.P., Meakin N.S. & Cameron R.G. (compilers) 2005. Cargelligo 1:250 000 Geological Sheet SI/55-6, 3rd edition, Explanatory Notes, pp. 73–81. Geological Survey of New South Wales, Maitland, NSW.
Mernagh T.P. 2008. Question 3: what and where are the fluid reservoirs for a mineral system? In: van der Wielen S. & Korsch R. eds. 3D architecture and predictive mineral analysis of the Central Lachlan Subprovince and Cobar Basin, New South Wales, final report for the pmd*CRC T11 project, pp. 85–116. Geoscience Australia, Canberra. Morrison G., Blevin P.L., Miller C., Hill P. & Mackenzie I. 2004. Age and setting of the Mineral Hill Au–base metal deposits. In: Bierlein F.P & Hough M.A. eds. Tectonics to mineral discovery — deconstructing the Lachlan Orogen, pp. 83–93. Geological Society of Australia Abstracts 74. Norman M. 2004. Zircon age dating of sample TYM063, Fountaindale Granodiorite. Report A04-2004. Research School of Earth Sciences, Australian National University, Canberra (unpubl.). Northcott M.J. 1986. The geology and alteration associated with the Great Central copper mine and Anomaly 3 polymetallic gossan, Mount Hope, centralwestern New South Wales. BSc Honours thesis, University of Adelaide (unpubl.). Paterson R.G. 1974. The geology and economic potential of the Nymagee mine, Cyprus Mines Corporation final report. Geological Survey of New South Wales, File GS1973/431. Percival I.G. 1999. Microfossiliferous cherts from the Forbes 1:250 000 map sheet, New South Wales. Palaeontological report 99/02. Geological Survey of New South Wales, Report GS1999/513. Percival I.G. 2006. Sussex 1:100 000 sheet: Palaeontological determinations. Unpublished Palaeontological Report 2006/01. Geological Survey of New South Wales, File GS2006/845. Percival I.G. 2007. Byrock 1:100 000 sheet: Palaeontological determinations. Unpublished Palaeontological Report 2007/01. Geological Survey of New South Wales, File GS2007/856. Perkins C., Hinman M.C. & Walshe J.L. 1994. Timing of mineralization and deformation, Peak Au mine, Cobar, New South Wales. Australian Journal of Earth Sciences 41, 509–522. Pickett J.W. 1984. Early Devonian conodonts from Beulah Tank, Manuka, via Cobar. Palaeontological Report 1984/9. Geological Survey of New South Wales, File GS1984/240. Pickett J.W. 1986. Early Devonian conodonts from limestones in the Gundaroo Sandstone on Manuka Station. Palaeontological Report 1986/1. Geological Survey of New South Wales, File GS1986/009. Pickett J.W. & McClatchie L. 1991. Age and relations of stratigraphic units in the Murda Syncline area. Geological Survey of New South Wales, Quarterly Notes 85, 9–32.
Quarterly Notes
35
Pogson D.J. 1991a. Geology of the Bobadah 1:100 000 sheet 8233. Geological Survey of New South Wales, Sydney. Pogson D.J. 1991b. Bobadah 1:100 000 Geological Sheet 8233, 1st edition. Geological Survey of New South Wales, Sydney. Pogson D.J. & Hilyard D. 1981. Results of isotopic dating related to Geological Survey of New South Wales investigations, 1974–1978. Geological Survey of New South Wales Records 20(2), 251–273. Powell C.McA., Khaiami R. & Scheibner E. 1987. Middle Devonian–?Early Carboniferous. pp. 107–140. In: Scheibner E. 1987. Geology of the Mount Allen 1:100 000 Geological Sheet 8032. Geological Survey of New South Wales, Sydney. Rayner E.O. 1969. The copper ores of the Cobar region, New South Wales: a report on the geology and mineralogy of the copper deposits of the Cobar region, with special reference to the characteristics of deep-zone, high-temperature, iron-rich copper ores. Geological Survey of New South Wales, Memoir Geology 10. Ritchie A. 1969. Ancient fish of Australia. Australian Natural History, 16, 218–223. Ritchie A. 1973. Wuttagoonaspis gen. nov., an unusual arthrodire from the Devonian of western New South Wales, Australia. Palaeontographica (A) 143, 58–72. Ryan S.J. 1987. The geology and genesis of the polymetallic Wagga Tank prospect, Mount Hope, N.S.W. BSc Honours thesis, University of Adelaide (unpubl.). Scheibner E. 1985. Mount Allen 1:100 000 Geological Sheet 8032. Geological Survey of New South Wales, Sydney. Scheibner E. 1987. Geology of the Mount Allen 1:100 000 Geological Sheet 8032. Geological Survey of New South Wales, Sydney. Scheibner E. & Basden H. 1998. Geology of New South Wales — Synthesis: Volume 2, Geological evolution. Geological Survey of New South Wales, Memoir Geology 13 (2). Seccombe P.K., Jiang Z. & Downes P.M. (in prep.). Sulfur isotope and fluid inclusion geochemistry of metamorphic Cu–Au vein deposits, Cobar, NSW, Australia. Seccombe P.K. 1990. Fluid inclusion and sulphur isotope evidence for syntectonic mineralisation at the Elura mine, southeastern Australia. Mineralium Deposita 25, 304–312. Seccombe P.K. & Brill B.A. 1989. Fluid inclusion and S, 0, H and C isotopic evidence for metamorphic Cu, Zn, Pb and Au ore formation at Cobar, New
36
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South Wales, Australia. 28th International Geological Congress, Washington, Abstracts 3, 66. Sherwin L. 1995. Siluro-Devonian brachiopods from the Amphitheatre and Winduck Groups (Cobar Supergroup), western New South Wales. Association of Australasian Palaeontologists, Memoir 18, 61–96. Sherwin L. 2010. Gondwanan tectonics and European events in the Silurian of Australasia. Bolletino della Società Paleontologica Italiana 49(1), 83–88. Sherwin L. 2013. Revised Nymagee 1:250 000 SiluroDevonian time–space plot. Geological Survey of New South Wales, Report GS2013/1885. Sherwin L. 2016. Implications of a revised age for the Cocoparra Group, central New South Wales. Geological Survey of New South Wales, Report GS2016/0325. Sherwin L. & Meakin N.S. 2010. The Early Devonian trilobite Craspedarges from the Winduck Group, western New South Wales. Proceedings of the Linnean Society of New South Wales 131, 115–122. Simpson C. 2014. Nymagee project: petrographic reassessment of the Mount Halfway Volcanics and other formations in the Mount Hope Group. Geological Survey of New South Wales, Report GS2015/0221. Simpson C. 2015. Petrographic re-assessment of thin sections from the late Silurian Canbelego–Mineral Hill Volcanic Belt. Geological Survey of New South Wales, Report GS2015/1051. Snee L.W. 2002. Argon thermochronology of mineral deposits — a review of analytical methods, formulations, and selected applications. U.S. Geological Survey Bulletin 2194, U.S. Department of the Interior, 39 pp. Spandler M. 1998. The geology of the Mineral Hill field, central NSW: igneous evolution and Cu/Au mineralisation. BSc (Honours) thesis, Australian National University, Canberra (unpubl.). Sun Y., Jiang Z., Seccombe P.K. & Feng Y. 2000. New dating and a review of previous data for the development, inversion and mineralization in the Cobar Basin. In: McQueen K.G. & Stegman C.L. eds. Central West Symposium Cobar 2000. Geology, Landscapes and Mineral Exploration WA CSIRO Extended Abstracts 113–116. Suppel D.W. 1984. A study of mineral deposits in the Cobar Supergroup, Cobar region, New South Wales. MSc thesis University of New South Wales, Sydney (unpubl.). Suppel D.W. & Gilligan L.B. 1993. Metallogenic study and mineral deposit data sheets, Nymagee 1:250 000
metallogenic map SI/55-2. Geological Survey of New South Wales, Sydney. Suppel D.W. & Pogson D.J. 1993. Nymagee 1:250 000 metallogenic map SI/55–2. Geological Survey of New South Wales, Sydney. Till A.B. & Snee L.W. 1995. 40Ar/39Ar evidence that formation of blueschists in continental crust was synchronous with foreland fold and thrust belt deformation, western Brooks Range, Alaska. Journal of Metamorphic Geology, 13, 41–60. Trigg S.J. 1987. Geology of the Kilparney 1:100,000 Sheet 8132. Geological Survey of New South Wales, Sydney. Trigg S.J. 1988. Kilparney 1:100 000 Geological Sheet 8133. Geological Survey of New South Wales, Sydney. Watson E.B. & Harrison T.M. 1983. Zircon saturation revisited: temperature and composition effects in a variety of crustal magma types. Earth and Planetary Science Letters 64, 295–304. Young G.C. 1995. Timescales calibration and development. 4. Devonian. Australian Phanerozoic timescales. Biostratigraphic charts and explanatory notes, second series. AGSO Record 1995/33, 1–47. Young G.C. 2006. Devonian fish remains, biostratigraphy and unconformities, Narromine 1:250 000 map sheet area, central New South Wales (Lachlan Fold Belt). Australian Journal of Earth Sciences 53, 605–615.
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Appendix 1. Location and details of samples dated as part of the present study. Geological unit or zone
Sample number
Baledmund Formation
PCN092 226.75–227.95m
445676
6490177
GA
Blind Calf dyke
PB-12-DBC-01
495075
6393090
RSES - ANU
Boolahbone Granite
TRI-52
390917
6400795
RSES - ANU
PB_11_NYM_04
460155
6363135
RSES - ANU
Erimeran Granite
PB_11_NYM_02
457879
6427979
RSES - ANU
Gilgunnia Granite
TRI-47
404689
6426707
RSES - ANU
Mineral Hill Volcanics (Freytag Dome)
TRI-58
498093
6394801
RSES - ANU
Mount Allen Granite
PB_11_NYM_05
387735
6382290
RSES - ANU
Mount Halfway Volcanics
ZFXDD1 408.9m
393436
6401285
GA
Nombiginni Volcanics
PB_11_NYM_14
397686
6388361
RSES - ANU
Nymagee felsic dykes
PDNY 12.002
441397
6450003
RSES - ANU
Nymagee Igneous Complex
PB_11_NYM_03
433476
6460419
RSES - ANU
Nymagee Igneous Complex
TRI-39
437234
6463435
RSES - ANU
Nymagee Igneous Complex
TRI-39
437234
6463435
RSES - ANU (monazite)
R7 unnamed granite
DD09NV0005 278.80–280.70m
404874
6438153
GA
Regina Volcanics
PB-12-REG-01
393003
6359039
RSES - ANU
Tallebung (mineralisation)
Tallebung cassiterite
460350
6376960
RSES - ANU (cassiterite)
Tarran Volcanics
TRI-37
458563
6421111
RSES - ANU
Thule Granite
CCRC 535 28m
381799
6433401
GA
Thule Granite
CCR 144 366.68–370.00m
387185
6457300
GA
Thule Granite
TRI-54
382863
6405505
RSES - ANU
(formerly Shepherds Hill Volcanics)
PDNY 12.003
429594
6343176
RSES - ANU
Urambie Granite
GRB-MO-04
445520
6382110
GA
Derrida Granite (now Urangie Granite)
MGAE
MGAN
Analysed at
Ural Volcanics
Abbreviations: GA = Geoscience Australia; RSES - ANU = Research School of Earth Sciences, Australian National University.
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August 2016
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Coal
Plain language is used to describe how titles work. The titles, acronyms, exploration and mining methods are explained. We outline the role of government in assessing applications and ensuring companies comply with title conditions.
Minerals Petroleum and Gas Titles | Applications
Search maps by
Company information
stage:
Search by applicants and title holders (companies, organisations, individuals) and find links to company documents such as licences, conditions and Reviews of Environmental Factors (REFs).
Applications, assessments and approvals are clearly defined in stages. Exploration Application Exploration Licence
Process
Assessment Lease Application
An interactive diagram shows the process involved in progressing from applications to approved titles for exploration and production activities. It also shows where community consultation and engagement takes place.
Assessment Lease Mining/Production Application Mining/Production Lease
Responsive design
Map layers
Location search
Works on computers and mobile devices (tablets and phones)
See titles in relation to parks, forests, strategic agricultural land and more
Search the whole state or specific locations in NSW Version 1.0 19.06.15
39 Visit www.commonground.nsw.gov.au on your computer, tablet or phone Quarterly Notes
Future papers: ‘Metamorphism in the Cobar Basin: Current state of understanding and implications for mineralisation’ by J.A. Fitzherbert et al. ‘A 3D model for the Koonenberry Belt from geologically constrained inversion of potential field data’ by Robert J. Musgrave and Stephen Dick
NSW Department of Industry, Division of Resources & Energy 516 High Street, Maitland NSW 2320 PO Box 344 Hunter Region Mail Centre NSW 2310 T: 1300 736 122 T: (02) 49316666
www.resourcesandenergy.nsw.gov.au
