ABSTRACT: Phyllosilicate associations in hydrothermally altered fluorite ore bodies are: Li-chlorite + pyrophyllite _+ interstratified minerals _+ muscovite + ...
Clay Minerals (1993) 28, 275-283
LITHIUM-BEARING HYDROTHERMAL ALTERATION P H Y L L O S I L I C A T E S R E L A T E D TO P O R T A L E T F L U O R I T E ORE ( P Y R E N E E S , H U E S C A , S P A I N ) J. M . G O N Z , / ~ L E Z L O P E Z , I. S U B I A S P I ~ R E Z , C. F E R N A N D E Z - N I E T O AND I. F A N L O G O N Z A L E Z
Cristalografia y Mineralogia, Dpto. Ciencias de la Tierra Universidad de Zaragoza, 50009 Zaragoza, Spain (Received 6 June 1991; revised 14 September 1992)
ABSTRACT: Phyllosilicate associations in hydrothermally altered fluorite ore bodies are: Li-chlorite + pyrophyllite _+ interstratified minerals _+ muscovite + kaolinite. Chlorites, the main alteration minerals, are dioctahedral, d060= 1.489-1-490/~,, of Ia polytype. The structural formulae indicate substitution of AI for Si from 0.61-0.78 atoms. The total octahedral occupancy ranges from 4.52-4-71 atoms, with 0.49-0-69 Li atoms per half cell unit. This composition indicates that the chlorites are intermediate members of the donbassite-cookeite series proposed by Sudo (1978). The mineralogical associations and textural relations suggest that after intensive silicification which produced alkali alteration under acid conditions, pyrophyllite was produced at the expense of muscovite and then Li-bearing donbassite formed from the pyrophyllite. The Li needed for the formation of the chlorites could be genetically related to granitic batholiths which occur close to the fluorite ores.
A l t h o u g h the most c o m m o n chlorite species are trioctahedral, there are o t h e r A l - b e a r i n g species that are di-trioctahedral and di-dioctahedral. The former have recently been r e p o r t e d occurring in different geological settings such as sedimentary, pegmatitic, h y d r o t h e r m a l and m e t a m o r p h i c environments. The A I P E A N o m e n c l a t u r e C o m m i t t e e (Bailey, 1980) distinguished three main Al-species: cookeite, sudoite and donbassite. The first two are di-trioctahedral and their ideal compositions in the trioctahedral layer are A12Li and Mg2A1, respectively; donbassite is mainly Al-bearing and, thus, it is didioctahedral although it can have a considerable content of Li. The aim of this work is to characterize the Li-bearing A1 chlorites which are the main constituent of the h y d r o t h e r m a l alteration phyllosilicate associations related to the Portalet fluorite deposits.
GEOLOGICAL
SETTING
In the Spanish zone of Portalet two exploitation mines, Batallero and Formigal, are situated in the u p p e r catchment area of the T e n a valley, very close to the French border. This area is constituted by Palaeozoic materials cut by both the granodiorite batholite of Panticosa and the andesitic massifs, lava flows and sills of Midi d'Ossau and A n a y e t . Fluorite ores are enclosed by Visean materials c o m p o s e d of dark grey limestones intercalated with some marly-shales and occur as three different morphologies: (1) filling of cavities in silicified limestones; (2) filling of east-west veins spatially related to silicification processes, and (3) 9 1993 The Mineralogical Society
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J. M. Gonzdlez L6pez et al.
disseminated fluorite and small stockwork vein structures, related to silicification. All these morphologies are associated with silica and fluorite replacement of limestones. This process produced laminated facies that can be compared with the fluorite facies of Quinn Canyon Range (Nevada, USA) described by Sainsbury & Kleimhampl (1969). The hydrothermal alteration of these ores has resulted in phyllosilicates which occur in the fluorite host rock, forming white, slightly green or yellow concentrations, as small pockets and irregular lenses, 5-30 cm thick and up to 1 m in length. In the external zone of these concentrations, phyllosilicates occur cementing quartz grains of the silicified host rocks which often contain disseminated fluorite. METHODS Selected altered samples were studied by X-ray diffraction (XRD), optical microscopy and chemical analysis by ICP and electron microprobe. In XRD, powders and oriented samples were examined using a Philips PW 1729 diffractometer (Cu-Ko~ radiation) equipped with a Philips PW 1710 microprocessor and a graphite monochromator. Oriented samples were examined after the following treatments: (a) air-drying at room temperature, (b) ethyleneglycol solvation, and (c) heating at 550~ for 2 h. In addition, randomly oriented powders were prepared for polytype studies and determination of d060 values of the phyllosilicates. The intensities of chlorite basal reflections were calculated using peak areas in XRD diagrams of oriented samples obtained at a scanning speed of 1/4~ 20/rain and paper speed of 4 cm/min. The chemical analysis of the main mineral phases (chlorites and pyrophyllites) were performed by electron microprobe (CAMEBAX, SX 50) using conditions recommended by Velde (1984) to prevent the loss of alkalis and the breakdown of clay minerals. The Li content of chlorites was determined by ICP in X-ray Assay Laboratories (Ontario, Canada). RESULTS AND DISCUSSION Table 1 shows the mineralogical associations of the selected samples determined by XRD, on the basis of the relative intensities of the diagnostic reflections for the different mineral phases. The phyllosilicate associations present in the alterations are: chlorite + pyrophyllite _+ mixed-layered minerals + muscovite + kaolinite. The last two, generally, are present in minor amounts. The XRD pattern (Fig. 1) of chlorite shows a rational sequence of 001 reflections with narrow peaks, suggesting good crystallinity, and a strong 003 reflection, characteristic of dioctahedral chlorites (Bailey & Lister, 1989). The relative intensities of the basal reflections as well as d001 and d060 values are shown in Table 2. These data confirmed the dioctahedral character of the chlorites. The relative intensities of peaks near 2.32 ~ , 2.37 and 2.50 A are 100, 13 + 4, and 72 _+ 11, respectively. These values are similar to those of the Ia polytype given by Bailey & Lister (op. cit.). Upon heating at 550~ 001 reflections are intensified and all other reflections disappear, whereas d0ol decreases slightly, probably because of dehydroxylation of "gibbsitic sheets". Chlorite chemical analyses performed by electron microprobe are shown in Table 3 with the LiO2 contents as analysed by ICP. Structural formulae calculated from the average values of these results indicate that the chlorites have A1 for Si substitution from 0.61 to 0.78
Li-bearing hydrothermal phytlosilicates atoms per 4 tetrahedral 4.71
atoms,
character
with
Li
positions. contents
and Li content,
(Rozinova
& Dubik,
The total octahedral
from
0-49
halfway between
1983; Gomes,
members
Intermediate
et al.,
(Loskutov,
from
the
occupancy.
Itaya,
Japan
a higher
Pyrenees
half
(Henmi samples
substitution
show
The relationship
the
&
ranges between
unit-cell.
those in the literature
Yakamoto,
(Bailey
and
of these Li-donbassites
and,
Novaya
sheet.
(Merceron
Zelmya,
USSR
they are richer in Of them
consequently,
op. i.e.,
by Sudo (1978). France
are similar to the first two, though
Li content
0-204).27
& Lister,
donbassites,
series proposed in Echasieres,
1965)
4.52 and
dioctahedral
for donbassites,
0-77-1-44
o f Si f o r A 1 i n t h e t e t r a h e d r a l
highest
Their
can be classified as Li-bearing
of this series have been reported
1959). The Portalet
A1 and show
occupancy
per
of the possible donbassite-cookeite
members
1989),
0.69
1967) and cookeites,
cit.), clearly indicate that these Al-chlorites intermediate
to
277
all, those
a high
to other dioctahedral
octahedral
c h l o r i t e s is s h o w n
in F i g . 2. TABLE 1. Mineralogical composition.
Bulk sample Sample
Q
Phyllosilicates
F
C
G
Ph
Ch
---
---
X XXX
XX XXX
XX .
XX X
XXX XXX
.
.
.
.
XXX
.
B 1-1 B 1-2
XXX XX
XX X
B 1-3 B 1-4
XXX XXX
XX XXX
-
-
--
--
BI-5
XXX
-
XXX
-
XX X
XX XXX
---
B2-8 B3-9 B3-10 B3-11 B3-12 F6-13
XXX XXX XXX XXX XXX XXX
XX XXX X X X X
---XXX XXX
F6-14 F6-15 F7-16
XXX XXX XXX
X X
XXX XX XX
F7-17
XXX
F7-18
XXX
B2-6 B2-7
F8-19 Fg-20 F9-21 F9-22 F9-23 F10-24 F10-25 F10-26
F10-27 F10-28 Fl1-29 F12-30 F12-31
-X --
XX XXX XX XXX X X XX X
X XXX X XXX XX
X
M
P
XXX X
XXX XXX
.
X
--
X X XXX XXX X X
XX XXX XXX XX X
X XX . -. -
----
XX XX XX
X X
X
XX
--
XX
--
--
X X X
--
X
-XXX X
. X . . XXX
XXX X XX X --
X -----
------
X XXX XX XXX XX XXX
X XXX X X XX XXX
--
--
--
XXX
XXX
------
------
------
XXX XX XXX XX XXX
XXX X XXX X X
X -X -X X --
X -X XX
--
--
---
-
-
. . X
X --
XXX
--
--
-
XX
-.
--
--
XXX
-
XXX XXX XX
--
.
--
XX
X
.
--
--
--
.
.
-.
.
.
K
.
.
.
X X
.
.
X X -
-.
1
-----
X
--
X
-
X
--
XX X X XX X X
-X X ---
--
X
--
---XX
X X X X X
----
Q = quartz; F = fluorspar; C = calcite; G = gypsum; Ph = phyllosilicates; Ch = chlorite; M = muscovite; P = pyrophyllite; I = interstratified; K = kaolinite; X X X = very abundant; X X = abundant; X = present.
J. M. Gonzdlez L6pez et al.
278
P y r o p h y l l i t e is t h e o t h e r p h a s e p r e s e n t as an essential c o m p o n e n t in s o m e of t h e samples studied (Fig. 3). T h e i r p o l y t y p e is 2M, b e c a u s e the intensities of the p e a k s at 9 . 2 / ~ and 3-06 A are b o t h v e r y high and the c o r r e s p o n d i n g p e a k at 4 . 4 2 / ~ is m a r k e d l y l o w e r ( E v a n s & G u g g e n h e i m , 1988). T h e do60 v a l u e s r a n g e b e t w e e n 1.489 and 1.498 •, with m e a n and m o d a l values of 1 . 4 9 3 / ~ . T h e analyses of p y r o p h y l l i t e ( T a b l e 3) show a small a m o u n t of Ca + N a + K, in a c c o r d
B1-2
5
10
15
20
25
30
33
~
FIG. 1. X-ray powder diffraction trace of an oriented sample (B1-2) showing 001 reflections of Li-donbassite. Cu-Ko: radiation.
TABLE2. Crystallochemical parameters of chlorites (XRD). Sample
I(001)
I(002)
I(003)
I(004)
I(005)
d(O01)
d(060)
B1-2 B1-3 B2-6 B3-9 B3-11 F6-14 F8-19 F9-21 F9-23 F10-24 F10-25 F10-26 F10-27 F10-28 F12-30
60 86 80 97 107 75 77 51 63 61 66 70 66 66 56
31 31 38 38 34 69 42 31 37 39 33 46 25 34 27
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
45 51 40 47 47 35 64 80 54 63 60 73 68 73 76
20 19 21 26 22 33 30 44 30 30 57 66 59 67 62
14.088 14.088 14.071 14-092 14.095 14.097 14.065 14.093 14.064 14.080 14.068 14-033 14-046 14-040 14-064
1.490 1-489 1.489 1.489 1.490 1-489 1.489 1.490 1.489 1-490 1.489 1.489 1.490 1.489 1.489
72 15
37 10
100
58 14
39 18
14-072 0.021
1.489 0.0004
i~ SD
)(: mean. SD: standard deviation.
Li-bearing hydrothermal phyllosilicates
279
with Evans & G u g g e n h e i m (1988). T h e tetrahedral substitution of Si for A1 and the total octahedral occupancy agree with N e w m a n & Brown (1987). The other phases present in noticeable amounts are interstratified minerals and micas (Fig. 3). T h e r a n d o m p o w d e r patterns of micas show the presence of 114 and 114 reflections, suggesting 2Mr polytype ( M o o r e & Reynolds, 1989). The d006 is 1.499 A. With respect to interstratified minerals, two types have been detected. Th e most conspicuous is that which shows, in oriented powder patterns (Fig. 4), a superstructure reflection with d0ol ranging b e tw e e n about 22 and 24 A ; when ethylene glycol solvated, this peak shifts to - 2 6 - 2 7 / ~ ; on K-saturation it shifts to - 2 2 .~, and collapses on heating at 550~ This b eh av io u r suggests that it is an interstratified illite-smectite, without excluding the possibility that it could be pyrophyllite-smectite because of the d001 spacings shown in some samples. Interstratified pyrophyllite-smectite has been recognized previously by K o d a m a (1958). T h e 001 reflections indicate periodic stacking sequences. The application of a rationality test by means of the coefficient of variation (CV), Bailey (1982), produces values oscillating b e t w e e n 0-31 and 0.65, all of them
