conformity with U.S. Geological Survey publication standards. Product names used .... Comparison of Assay Results by HBr, CN, and FA Methods. B-l. Table B-l.
HAMDAH GOLD PROSPECT, KINGDOM OF SAUDI ARABIA RESULTS OF GEOLOGICAL AND GEOCHEMICAL EXPLORATION FOR GOLD IN BEDROCK AND OVERBURDEN By
ARTHUR A. BOOKSTROM, EYAD H. JANNADI, PAUL S. BOSCH, BRUCE M. WALKER, RALPH P. CHRISTIAN, RICHARD B. GARTEN, MOHAMMED B. EL KOMI, AND MAJID BEN TALIB
TECHNICAL REPORT USGS-TR-92-6 (IR 857)
MINISTRY OF PETROLEUM AND MINERAL RESOURCES DIRECTORATE GENERAL OF MINERAL RESOURCES JIDDAH, KINGDOM OF SAUDI ARABIA 1413 AH 1992 AD
An Interagency Report prepared by the U.S. Geological Survey, Saudi Arabian Mission for the Ministry of Petroleum and Mineral Resources Kingdom of Saudi Arabia The work on which this report was performed in accordance with a cooperative agreement between the U.S. Geological Survey and the Ministry of Petroleum and Mineral Resources. This report is a product of DGMR work programs during the years 1410 to 1412 and is listed as Subproject 4.2.4.2.01. The information contained in this report is a product of Ministry work; if the information herein is used in any form, either quoted or paraphrased, this report should be properly cited using the full serial number, the authors' names, and the year of publication. The correct citation for this report is: Bookstrom, AJL, Jannadi, E.H., Bosch, P S., Walker, B.M., Christian, R.P., Garten, R.B., El Komi, M.B., and Ben Talib, Majid, 1992, Hamdah gold prospect, Kingdom of Saudi Arabia: Results of geological and geochemical exploration for gold in bedrock and overburden: Saudi Arabian Directorate General of Mineral Resources Technical Report USGS-TR-92-6, 72 p., 7 pits., 3 appendices [Appendix C bound separately].
This report was technically reviewed by P.R. Johnson and EJB. Garten. The report has been edited and reviewed for conformity with U.S. Geological Survey publication standards. Product names used in this report are for descriptive purposes and in no way imply endorsement by the Geological Survey. The area of study covered by this report is shown on the index map below.
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Index map of the Arabian Peninsula showing area of study for this report REPORT DISTRIBUTION: Distribution of this report is limited. Ten copies have been transmitted to the Office of the Deputy Minister, Directorate General of Mineral Resources
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Computer-generated model of the Hamdah gold prospect area-by Ralph p. Christian
HAMDAH GOLD PROSPECT This report is part of a series of five reports on the exploration, metallurgical testing, and preliminary economic analysis of the Hamdah gold prospect. These reports cover the period beginning January 1, 1990 and ending May 31, 1992. The reports in this series are: (1) Albert, T.E., and Garten, R.B., 1992, Hamdah Gold Prospect, Kingdom of Saudi Arabia: Results of laboratory test work on the metallurgical response of ore to heap-leach processing: Saudi Arabian Directorate General of Mineral Resources Technical Report USGS-TR-92-5, 26 p., 2 appendices. (2) Cassiday, M.W., and Carten, R.B., 1992, Hamdah gold prospect, Kingdom of Saudi Arabia: Results of the pilot heap-leach test: Saudi Arabian Directorate General of Mineral Resources Technical Report USGS-TR92-7, 26 p., 7 appendices. (3) Bookstrom, A.A., Jannadi, E.H., Bosch, P S., Walker, B.M., Christian, R.P., Carten, R.B.,E1 Komi, M.B., and Ben Talib, Majid, 1992, Hamdah gold prospect, Kingdom of Saudi Arabia: Results of geological and geochemical exploration for gold in bedrock and overburden: Saudi Arabian Directorate General of Mineral Resources Technical Report USGS-TR-92-6, 72 p., 7 pits., 3 appendices [Appendix C bound separately]. (4) Christian, R.P., Bookstrom, A.A., Aruscavage, P.J., and Marasigan, M.S., 1992, Hamdah gold prospect, Kingdom of Saudi Arabia: Models for estimation of gold resources and reserves: Saudi Arabian Directorate General of Mineral Resources Technical Report USGS-TR-92-8, 27 p., 5 appendices [bound separately]. (5) Christian, R.P. and Bookstrom, A.A., 1992, Hamdah gold prospect, Kingdom of Saudi Arabia: Summary of estimation of gold resources and reserves in overburden and bedrock, with a section on An initial economic model for gold recovery from overburden and bedrock, by JJ. Cape, and K.A. Saib: Saudi Arabian Directorate General of Mineral Resources Technical Report USGS-TR-92-4, 13 p.
CONTENTS ABSTRACT
1
INTRODUCTION Location, Topography, and Climate Ancient Gold Mines Previous Work Purpose Work Programs of 1989 to 1992 Methods.. Bedrock geologic mapping methods Overburden geologic mapping methods Grid surveying methods Geochemical sampling methods Analytical methods Density determination methods Computational methods
3 3 3 6 6 6 8 8 8 9 9 9 10 11
REGIONAL GEOLOGIC SETTING Nabitah Fault, Suture, and Orogeny Hamdah Serpentinite Greenstone Belts Jabal Ishmas-Wadi Tathlith Gold Belt Hamdah-Jabal Riah gold district Hamdah mineral belt LITHOLOGIES OF THE HAMDAH MINERAL BELT Serpentinite Skara-altered Serpentinite Listwaenite and carbonate-altered rocks Talcstone and talc-altered rocks Cataclastic Rocks Phyllonite (undivided) Altered phyllonite Chlorite phyllonite Chlorite-biotite phyllonite Layered Rocks Hornblende schist Carbonaceous schist Biotite schist Dolomite marble Chlorite schist Quartz-biotite schist Igneous Intrusive Rocks Mafic aphanite Biotite diorite Aplite (and pegmatite) Diorite, monzogranite, and granite Summary of Lithologic Relations
11 11 14 15 15 .....16 16 18 18 18 18 21 21 21 21 21 21 21 21 22 22 22 22 22 24 24 24 24 25 25
HAMDAH STRUCTURAL GEOLOGY
27
Imbricate Thrust Faults Intersecting Fold Sets Fold interference patterns Fold shapes Relative ages of fold sets Tectonic models for cross folding Minor Faults and Fractures Summary of Deformational History
27 30 30 30 30 35 35 35
HAMD AH SURFICIAL GEOLOGY Colluvium Alluvium Silt and Paleosol Ancient Mine Wastes Ancient lode-mine waste Ancient placer-mine waste Post-Mine Alluvium EolianSand GOLD IN BEDROCK Ancient Lode-mine Workings Bedrock Geochemicai Anomaly Patterns Guides to Ore Drilling Results Bedrock Gold Resource Estimates Northeast lodes Northwest lodes Southwest lodes Southeast lodes Hypogene Minerals Hydrothermal minerals in serpentinite Hydrothermal minerals in aplite Hydrothermal minerals in phyllonite and schist Supergene Minerals Ore Genesis Magmatic sources of gold Hydrothermal gold transport and deposition Supergene Enrichment
36 36 36 36 36 38 38 38
.
38 ...38 38 44 44 44 45 46 47 47 47 47 50 52 52 53 56 56 57
GOLD IN OVERBURDEN Character of Gold-bearing Overburden Ancient lode-mine dumps Placers and ancient placer-mine dumps Gold-Resource Estimates for Overburden
58 58 58 58 60
GOLD RESOURCES AND RESERVES Reporting Terminology for Resources and Reserves Hamdah Gold Resources and Reserves Overburden-hosted gold resources and reserves Bedrock-hosted gold resources and reserves
65 65 65 65 65
CONCLUSIONS
67
RECOMMENDATIONS v/ ACKNOLEDGMENTS
68
t
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DATASTORAGE Data File Mineral Occurrence Documentation System.
.69 .69 .69
REFERENCES CITED.....
.70
PLATES [Plates in pocket] 1. 2. 3. 4. 5. 6. 7. 8. 9.
Bedrock geologic map of the Hamdah prospect. Surficial geologic map of the Hamdah prospect, Surface gold geochemical grid map of the Hamdah. prospect. Bedrock geochemical patterns for gold, arsenic, copper, and silver. Topographic map, showing locations of drill holes, trenches, and lines of section. Bedrock drill sections. Contour map of bedrock gold. Contour map of overburden gold. Overburden trench sections.
FIGURES 1. Map showing location of the Hamdah gold prospect and other features 2. Oblique aerial photograph of the Hamdah project area 3. Map showing areas of previous work 4. Geologic map of the composite Arabian Shield 5. Geologic map of the Hamdah-Tathlith-Tarib region 6. Geologic map of the Hamdah mineral belt 7. Lithologic logs of representative Hamdah core holes 8. Total alkali-silica diagram for classification of volcanic rocks 9. Schematic correlation diagram illustrating the lithologic relationships of the Hamdah region 10. Photographs showing features of the Hamdah thrust set.. 11. Stereonet showing plunges of lineations 12. Rose diagram showing azimuths of fold axes 13. Geologic map of the Hamdah window 14. Geologic map showing small-scale domes and basins 15. Photographs showing folded features of the Hamdah area 16. Schematic cross section of the Hamdah prospect 17. Photographs showing ancient mine workings in bedrock. 18. Scatter plot of gold versus tons of bedrock ore 19. Photographs and SEM images of mineralized aplite 20. Photographs of visible gold in drill core 21. Photograph of an outcrop of gold ore in the oxide zone 22. Photographs of lode-mine mullock and panned gold grains 23. Photographs showing ancient placer workings and wastes 24. Scatter plot of grams of gold versus tons of overburden ore
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4 5 7 12 13 17 19 23 26 28 31 31 32 33 34 37 39 45 51 55 57 59 62 64
Hi
TABLES 1. Summary of Hamdah geochemical sampling programs
10
2. Whole-rock chemical analyses of Hamdah rock type samples 3. Total bedrock gold-resource estimates 4. Bedrock gold-resource estimates by quadrant
20 45 46
5. Hypogene minerals of the Hamdah prospect
48
6. Supergene minerals of the Hamdah prospect
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7. Overall total overburden gold resource estimates 8. Overburden gold resource estimates by quadrant
60 61
9. Summary of estimates of gold resources and reserves
66
APPENDICES APPENDIX A Summaries of Chemical Analytical Methods Gold determination by the HBr method Gold determination by the CN method Gold determination by the FA method Major-element analysis
A-l
APPENDIX B Comparison of Assay Results by HBr, CN, and FA Methods Table B-l. Check assay results (HBr, CN, and FA methods) APPENDIX C (Bound separately) Summary drill-core logs, showing Ethologies and assays
IV
B-l B-2
C 1-C 145
HAMDAH GOLD PROSPECT, KINGDOM OF SAUDI ARABIA RESULTS OF GEOLOGICAL AND GEOCHEMICAL EXPLORATION FOR GOLD IN BEDROCK AND OVERBURDEN By ARTHUR A. BOOKSTROM, EYAD H. JANNADI, PAUL S. BOSCH, BRUCE M. WALKER, RALPH P. CHRISTIAN, RICHARD B. GARTEN MOHAMMED B. EL KOMI, AND MAJID BEN TALIB
ABSTRACT The 1.5 km2 Hamdah gold prospect, formerly known as the Hajr mine (MODS locality 0619, lat 18°54f48(l, long 43°40f30M), is the site of the largest group of ancient gold-mine workings in the southern half of the Neoproterozoic Arabian Shield. At this prospect, the Hamdah serpentinite (serpentinized meta-harzburgite) has been thrust over hornblende schist (meta-basalt). Ancient mines and unmined gold lodes are localized at the margins of foliated aplite sills that were emplaced along the Hamdah thrust. Phyllonite of the thrust fault grades downward to hornblende schist. Down-section, hornblende schist is interlayered with biotite schist and carbonaceous schist (both metasedimentary), and underlain by quartz-biotite schist (porphyritic meta-rhyolite). Fine-grained ore minerals (magnetite, pyrrhotite, and pyrite; minor arsenopyrite, and loellingite; sparse gold, and traces of electrum, chalcopyrite, sphalerite, and galena) are sparsely disseminated in quartz-carbonate veinlets and(or) in altered rocks along the margins of aplite sills. About 60 percent of the ore in bedrock is localized in phyllonite (altered to clinochlore ± ferroan dolomite ± talc ± relict prograde tremolite ± supergene limonite); about 25 percent is hosted in serpentinite (altered to ferroan dolomite ± talc); about 10 percent occurs in aplite (with hydrothermal quartz ± K-feldspar ± sericite ± calcite); and about 5 percent is hosted in other rock types, such as altered hornblende schist (with clinochlore, chlorite, and pargasitic hornblende) and diorite (chloritized and argillized). Visible gold is rare, but occurs locally in altered phyllonite and serpentinite, along with arsenopyrite, quartz, clinochlore, ferroan dolomite, talc, and limonite. Gold micrograins occur within some loellingite-arsenopyrite grains in quartz-sericite veinlets, in aplite. The Hamdah thrust (along with the rocks above and below it) is folded into northeast- and northwest-trending fold sets. Intersecting fold sets form box-like doubly-plunging anticlines and synclines. Intersecting anticlines form the Hamdah dome. Serpentinite and altered aplite and phyllonite of the ore zone are eroded from the top of the Hamdah dome, exposing hornblende schist in its eroded core. The mineralized Hamdah thrust bounds the dome. It is overlain by serpentinite and is preserved beneath serpentinite around the dome, and in synclinal basins located northeast and southwest of the dome. The northeast syncline hosts the northeast orebody, which is shaped like a flat-bottomed scoop, open to the southeast because of erosion. At an 8 g/t cutoff, the northeast ore zone contains a probable reserve of 1.12 tons of gold in 59,300 tons of ore, averaging 18.8 g/t. Most of the bedrockhosted ore of the southwest orebody has been extracted, as indicated by ancient mine workings, extensive minewaste dumps, and rubble-filled cavities encountered in trenches and drill holes. Gold eroded from the top of the Hamdah dome was deposited in alluvial fans around it. The largest of these is the south alluvial fan, where extensive ancient placer-mine workings and dumps have been trenched and sampled. Ancient mine dumps, derived from lode- and placer-mine workings, contain residual, very fine-grained gold that was not recoverable by ancient methods. Assays of over 4,600 overburden samples indicate a proven reserve of 2.63 tons of gold in 911,500 tons of ore, averaging 2.89 g/t (at a 0.75 g/t cutoff). This ore consists of unconsolidated mine wastes and alluvium, located at or near the surface, and containing very fine-grained free gold. The gold in this ore is amenable to surface-strip mining (without blasting), and to recovery by heap leaching.
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