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Clay Minerals in Saprolite Overlying Hydrothermally Altered and Unaltered Rocks, Vera Epithermal Gold Deposit, Australia

Published online by Cambridge University Press:  01 January 2024

David M. K. Murphy  and
Robert J. Gilkes
David M. K. Murphy*
Affiliation:
School of Earth and Environment (M087), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009
Robert J. Gilkes
Affiliation:
School of Earth and Environment (M087), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009
*
* E-mail address of corresponding author: davidmkmurphy@gmail.com
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Abstract

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Differentiating clay minerals that formed in a supergene environment during deep chemical weathering from those that formed during hydrothermal alteration at higher temperatures associated with a mineralizing event is important in the exploration for epithermal Au deposits. The purpose of this study was to further elucidate this topic by comparing morphological and chemical properties of clay minerals in saprolite overlying epithermally altered bedrock at the Vera Au deposit, Queensland, Australia, with those of clay minerals in saprolite overlying bedrock adjacent to the epithermal alteration zone. X-ray diffraction (XRD) and analytical transmission electron microscopy (ATEM) investigations identified kaolinite, illite, and interstratified illite-smectite, together with quartz, Fe and Ti oxide minerals, and the sulfate minerals jarosite, gypsum, alunite, and natroalunite. Kaolinite crystals within the weathered argillic alteration zone proximal to the epithermal quartz vein are generally larger (up to 3 μm in diameter) and better formed (subhedral to euhedral) than crystals in saprolite distal to the hydrothermal alteration zone, in which smaller (mostly <1 μm), subhedral to anhedral crystals dominate. Energy-dispersive spectrometry (EDS) analysis of single crystals indicated that kaolinite within the alteration zone has an Al/Si ratio indistinguishable from reference kaolinite and has small Fe concentrations, whereas distal saprolitic kaolinite has smaller Al/Si and greater Fe/Si ratios, consistent with the formation of low-Fe kaolinite during hydrothermal alteration and higher-Fe kaolinite during weathering. Illite and interstratified illitesmectite (I-S) were distinguished from kaolinite by their morphology and greater K/Si and smaller Al/Si ratios. The Illite and I-S morphology ranged from thin irregular masses through lath-like crystals in hydrothermal samples to larger, irregularly shaped crystals. The Ca/Si and K/Si ratios of single crystals in Ca-saturated clay minerals were consistent with the I-S interstratification parameters determined from XRD patterns.

Keywords

Analytical Electron MicroscopyClay MineralsEpithermal Gold DepositKaoliniteWeatheringX-ray Diffraction
Type
Article
Information
Clays and Clay Minerals , Volume 58 , Issue 6 , December 2010 , pp. 783 - 791
Copyright
Copyright © Clay Minerals Society 2010

References

Butt, C.R.M., and Garland, G.D., 1989 Geomorphology and climate history-keys to understanding geochemical dispersion in deeply weathered terrains, exemplified by gold Proceedings of Exploration’ 87. Third Decennial International Conference on Geophysical and Geochemical Exploration for Minerals and Groundwater Canada Special Volume 3, Ontario Geological Survey 323–334.Google Scholar
Cliff, G., and Lorimer, G.W., 1975 The quantitative analysis of thin specimens Journal of Microscopy 103 203–207 10.1111/j.1365-2818.1975.tb03895.x.CrossRefGoogle Scholar
Dill, H.G., Bosse, H.-R., Henning, K.-H., Fricke, A., and Ahrend, H., 1997 Mineralogical and chemical variations in hypogene and supergene kaolin deposits in a mobile fold belt-the Central Andes of northwestern Peru Mineralium Deposita 32 149–163 10.1007/s001260050081.CrossRefGoogle Scholar
Gualtieri, A.F., Moen, A., and Nicholson, D.G., 2000 XANES study of the local environment of iron in natural kaolinites European Journal of Mineralogy 12 17–23 10.1127/ejm/12/1/0017.CrossRefGoogle Scholar
Hart, R.D., Gilkes, R.J., Siradz, S., and Singh, B., 2002 The nature of soil kaolins from Indonesia and Western Australia Clays and Clay Minerals 50 198–207 10.1346/000986002760832793.CrossRefGoogle Scholar
Hart, R.D., Wiriyakitnateekul, W., and Gilkes, R.J., 2003 Properties of clay minerals from Thailand Clay Minerals 38 71–94 10.1180/0009855033810080.CrossRefGoogle Scholar
Herbillon, A.J., Mestagh, M.M., Vielvoye, L., and Derouane, E., 1976 Iron in kaolinite with special reference to kaolinite from tropical soils Clay Minerals 11 201–220 10.1180/claymin.1976.011.3.03.CrossRefGoogle Scholar
Inoue, A., and Utada, M., 1983 Further investigations of a conversion series of dioctahedral micas/smectites in the Shinzan hydrothermal alteration area, northeastern Japan Clays and Clay Minerals 35 111–120 10.1346/CCMN.1987.0350203.CrossRefGoogle Scholar
Jepson, W.B., and Rowse, J.B., 1975 The composition of kaolinite-an electron microscope microprobe study Clays and Clay Minerals 23 310–317 10.1346/CCMN.1975.0230407.CrossRefGoogle Scholar
Klug, H.P., and Alexander, L.E., 1974 X-ray diffraction Procedures for Polycrystalline and Amorphous Materials New York, London John Wiley and Sons Inc..Google Scholar
Lorimer, G.W., Cliff, G., and Wenk, H.E., 1976 Analytical electron microscopy of minerals Electron Microscopy in Mineralogy Berlin Springer 506–519 10.1007/978-3-642-66196-9_38.CrossRefGoogle Scholar
Ma, C., and Eggleton, R.A., 1998 Surface layer types of kaolinite: a high-resolution transmission electron microscope study Clays and Clay Minerals 47 181–191.Google Scholar
Ma, C., Fitzgerald, J.D., Eggleton, R.A., and Llewellen, D.J., 1998 Analytical electron microscopy in clays and other phyllosilicates: loss of elements from a 90-nm stationary beam of 300-keV electrons Clays and Clay Minerals 46 301–316 10.1346/CCMN.1998.0460309.CrossRefGoogle Scholar
Mas, A., Patrier, P., Beaufort, D., and Genter, A., 2003 Clay- mineral signatures of fossil and active hydrothermal circulations in the geothermal system of the Lamentin Plain, Martinique Journal of Volcanology and Geothermal Research 124 195–218 10.1016/S0377-0273(03)00044-1.CrossRefGoogle Scholar
Mehra, O.P., and Jackson, M.L., 1958 Iron oxide removal from soils and clays by a dithionite-citrate system buffered with sodium bicarbonate Clays and Clay Minerals 7 317–327 10.1346/CCMN.1958.0070122.CrossRefGoogle Scholar
Moore, D.M., and Reynolds, R.C., 1997 X-ray Diffraction and the Identification and Analysis of Clay Minerals 2nd edition New York Oxford University Press.Google Scholar
Mustard, R., Baker, T., Brown, V., and Bolt, S., 2003 Alteration, paragenesis and vein textures, Vera Nancy, Australia. Economic Geology Research Unit, James Cook University, Australia, contribution 61 99–107.Google Scholar
Murphy, D.M.K., 2009 Regolith Expression of Hydrothermal Alteration: A study of the Groundrush and Vera Nancy Gold Deposits of Northern Australia. PhD thesis, The University of Western Australia .Google Scholar
Richards, D.R., Elliot, G.J., Jones, B.H., Berkman, D.A., and Mackenzie, D.H., 1998 Vera North and Nancy gold deposits, Pajingo Geology of Australian and Papua New Guinean Mineral Deposits Melbourne The Australasian Institute ofMining and Metallurgy 685–690.Google Scholar
Rimmer, S.M., and Eberl, D.D., 1982 Origin of an underclay as revealed by vertical variations in mineralogy and chemistry Clays and Clay Minerals 30 422–430 10.1346/CCMN.1982.0300604.CrossRefGoogle Scholar
Robertson, I.D.M., and Eggleton, R.A., 1991 Weathering of granitic muscovite to kaolinite and halloysite and of plagioclase-derived kaolinite to halloysite Clays and Clay Minerals 39 113–126 10.1346/CCMN.1991.0390201.CrossRefGoogle Scholar
Simpson, M.P., Mauk, J.L., and Simmons, S.F., 2001 Hydrothermal alteration and hydrologic evolution of the Golden Cross epithermal Au-Ag deposit, New Zealand Economic Geology 96 773–796.Google Scholar
Srodon, J., Eberl, D.D., and Bailey, S.W., 1984 Illite Micas Washington D.C. Reviews in Mineralogy, 13, Mineralogical Society of America 495–544 10.1515/9781501508820-016.CrossRefGoogle Scholar
St Pierre, T.G., Singh, B., Webb, J., and Gilkes, R.J., 1992 Mossbauer spectra of soil kaolins from south-western Australia Clays and Clay Minerals 40 341–346 10.1346/CCMN.1992.0400315.CrossRefGoogle Scholar
Stanley, C.R., Baker, T., Mustard, R., Brown, V., Radford, N., and Butler, I., 2003 Lithogeochemistry and hydrothermal alteration at the Pajingo low-sulfidation epithermal gold vein, Drummond Basin, Queensland 21st International Geochemical Exploration Symposium, Program with Abstracts Dublin Association of Exploration Geochemists 55.Google Scholar
Tillick, D.A., Peacor, D.R., and Mauk, J.L., 2001 Genesis of dioctahedral phyllosilicates during hydrothermal alteration of volcanic rocks: 1. The Golden Cross epithermal ore deposit, New Zealand Clays and Clay Minerals 49 126–140 10.1346/CCMN.2001.0490203.CrossRefGoogle Scholar
Varajao, A.F.D.C., Gilkes, R.J., and Hart, R.D., 2001 The relationship between kaolinite crystal properties and the origin of materials for a Brazilian kaolin deposit Clays and Clay Minerals 49 44–59 10.1346/CCMN.2001.0490104.CrossRefGoogle Scholar
Watanabe, T., 1981 Identification of illite/montmorillonite interstratifications by X-ray powder diffraction Journal of the Mineralogical Society of Japan, Special Issue 15 32–41 10.2465/gkk1952.15.Special_32 (in Japanese).CrossRefGoogle Scholar
Weaver, C.E., Wampler, J.M., and Pecuil, T.E., 1967 Mossbauer analysis of iron in clay minerals Science 156 504–508 10.1126/science.156.3774.504.CrossRefGoogle ScholarPubMed