Hostname: page-component-586b7cd67f-gb8f7 Total loading time: 0 Render date: 2024-11-26T03:05:43.346Z Has data issue: false hasContentIssue false
  • English
  • Français

Metamorphic fluids and gold

Published online by Cambridge University Press:  05 July 2018

G. Neil Phillips
G. Neil Phillips*
Affiliation:
Key Centre In Economic Geology, Geology Department, James Cook University, Townsville, Qld. 4811, Australia
Get access Rights & Permissions [Opens in a new window]

Abstract

Low-salinity fluids (T > 200°C reduced S, modest CO2) and high geothermal gradients are common to many gold deposits and provinces. In contrast, host rocks, hosting structures, depth of formation (in the crust during deposition), subsequent metamorphic overprint, alteration mineralogy and isotopic signatures can vary dramatically within single deposits or provinces. Gold deposits with co-product base metals are an exception to the above comments, and probably relate to saline fluids.

The low salinity fluids inferred for major gold-only deposits are not easily explained by seawater, basinal brines, meteoric fluid or common magmatic processes. In contrast, metamorphic devolatilisation of mafic/greywacke rocks is one effective way to produce low-salinity metamorphic fluids with characteristics matching the gold fluids. Such an origin also explains the link to geothermal gradients.

The transition from chlorite—albite—carbonate assemblages to amphibole-plagioclase assemblages (commonly greenschist—amphibolite facies boundary) involves considerable loss of metamorphic fluid whose composition is buffered by the mineral assemblage, and is a function of P and T. This low salinity, H2O-CO2 fluid is evolved at T > 400°C commonly carries reduced sulphur, and may contain Au complexed with this sulphur. This auriferous fluid is likely to mix with other fluid types during times of elevated temperature, especially magmatic fluids at depth, and upper crustal fluids at higher levels.

Gold deposits in Archaean greenstone belts exhibit good evidence of low salinity, H2O-CO2 fluids of T > 300°C these include examples from Canada, Australia, Brazil, Zimbabwe, India, and South Africa. Turbidite-hosted (slate-belt) deposits exhibit similar evidence for such fluids but commonly with appreciable CH4; the Victoria and Juneau (Alaska) goldfields are examples. The Witwatersrand goldfields also show evidence of low salinity, H2O-CO2 fluids carrying reduced sulphur and gold, but their distribution and timing are not well established. Epithermal (sensu lato) gold deposits have evidence for low salinity fluids carrying Au and S, but are much more diverse in character than those from the previously mentioned gold provinces: this probably arises from mixing of several fluid types at high crustal levels. Together these four types of gold provinces account for over 80% of the primary gold mined to date.

Keywords

metamorphic fluidsgoldlow-salinity fluids
Type
Research Article
Information
Mineralogical Magazine , Volume 57 , Issue 388 , September 1993 , pp. 365 - 374
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1993

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bickle, M. J., Morant, P., Bettenay, L. F., Boulter, C. A., Blake, T. S., and Groves, D. I. (1985) Archaean tectonics of the Shaw Batholith, Pilbara Block, Western Australia: structural and metamorphic tests of the batholith concept. In Evolution of Archaean Supracrustal Sequences (Ayers, L. A., Thurston, P. C., Card K. D., and Webber, W., eds.)–Geol. Soc. Can., Spec. Pap., 28, 325–41.Google Scholar
Cassidy, K. F. (1988) Petrology and alteration of an Archaean granitoid-hosted gold deposit, Lawlers, Western Australia. In Advances in Understanding Precambrian Gold Deposits, Volume II (Ho, S. E. and Groves, D. I., eds.)— Geol. Dept. and Univ. Ext., Univ. West. Aust. Publ. 12, 165–83.Google Scholar
Clark, M. E., Archibald, N. J., and Hodgson, C. J. (1986) The structural and metamorphic setting of the Victory gold mine, Kambalda, Western Australia. In Gold ‘86 (Macdonald, A. J., ed.). An International Symposium on the Geology of Gold Deposits. Toronto, 243-54.Google Scholar
Cox, S. F., Etheridge, M. A., and Wall, V. J. (1986) The role of fluids in syntectonic mass transport, and the localisation of metamorphic vein-type ore deposits. Ore Geol. Rev., 2, 65–86.Google Scholar
Cox, S. F., Wall, V. J., Etheridge, M. A., and Potter, T. F. (1991) Structural controls and the role of fault dynamics during the formation of vein-hosted gold deposits in the Bendigo-Ballarat zone of the Lachlan Fold Belt. Economic Geology Research Unit, James Cook Univ., Townsville, Contribution 39, 37 pp.Google Scholar
Craw, D. (1988) Shallow-level metamorphic fluids in a high uplift rate metamorphic belt; Alpine Schist, New Zealand. J. Met. Geol. 6, 1–16.Google Scholar
Fyfe, W. S. and Kerrich, R. (1984) Gold: natural concentration processes. In Gold “82 (Foster, R. P., ed.). Rotterdam, Balkema, 99–127.Google Scholar
Fyfe, W. S. and Kerrich, R. Price, N. J., and Thompson, A. B. (1978) Fluids in the Earth's crust. Elsevier, Amsterdam, 383 pp.Google Scholar
Goldfarb, R. J., Newberry, R. J., Pickthorn, W. J., and Gent, C. A. (1991) Oxygen, hydrogen, and sulfur isotope studies in the Juneau gold belt, Southeastern Alaska: constraints on the origin of hydrothermal fluids. Econ. Geol. 86, 66–80.Google Scholar
Golding, S. D., McNaughton, N. J., Barley, M. E., Groves, D. I., Ho, S. E., Rock, N. M. S., and Turner, J. V. (1989) Archean carbon and oxygen reservoirs: their significance for fluid sources and circulation paths for Archean mesothermal gold deposits of the Norseman-Wiluna Belt, Western Australia. In The Geology of Gold Deposits: The Perspective in 1988. (Keays, R. R., Ramsay, W. R. H. and Groves, D. I., eds.). Econ. Geol. Mon. 6, 376–388.Google Scholar
Hinman, M., (1990) Timing of syndeformational base and precious metal mineralisation controlled by deformation partitioning at Peak, Cobar, NSW. Gondwana: Terranes and Resources. Tenth Austra-lian Geological Convention, Geol. Soc. Aust. Abs., 25, 174.Google Scholar
Ho, S. E., Groves, D. I., and Phillips, G. N. (1985) Fluid inclusions as indicators of the nature and source of ore fluids and ore depositional conditions for Archaean gold deposits of the Yilgarn Block, Western Australia. Geol Soc. S. Africa, Trans., 88, 149–58.Google Scholar
Jemielita, R. A., Davis, D. W., and Krogh, R. E. (1990) U-Pb evidence for Abitibi gold mineralization postdating greenstone magmatism and metamor-phism. Nature, 346, 831–4.Google Scholar
Kerrich, R. (1986) Archaean lode gold deposits of Canada. Part I: A synthesis of geochemical data from selected mining camps, with emphasis on patterns of alteration. Econ. Geol. Res. Unit, lnfo. Circ., Univ. Witwatersrand, Johannesburg, 182. 30 pp.Google Scholar
Kerrich, R. and Fryer, B. J. (1981) The separation of rare elements from abundant base metals, in Archean lode gold deposits: Implications of low water/rock source regions. Econ. Geol., 76, 160–6.Google Scholar
Lawrie, K. C. (1990) Structural and microstructural timing criteria used to identify syntectonic base metal deposits: the Elura and Woodcutters deposits as examples. Gondwana: Terranes and Resources, Tenth Australian Geological Convention. Geol. Soc. Aust. Abs. 25, 291.Google Scholar
Lawrie, K. C. (1991) Facies analysis and exploration models for sediment-hosted, syntectonic, gold and base metal deposits. In Facies Models in Exploration and Development of Hydrocarbon and Ore Deposits. (Bouma, A. H. and Carter, R. M., eds.). Utrecht, The Netherlands: VSP. 3-18.Google Scholar
Moyle, A. J., Doyle, B. J., Hoogvliet, H., and Ware, A. R. (1990) Ladolam gold deposit, Lihir Island. In Geology of the Mineral Deposits of Australia and Papua New Guinea. —(Hughes, F. E. ed.). AuslMM, Melbourne, 1793-805.Google Scholar
Myers, R. E., McCarthy, T. S., and Stanistreet, I. G. (1990) A tectono-sedimentary reconstruction of the development and evolution of the Witwatersrand Basin, with particular emphasis on the Central Rand Group. S. Afr. J. Geol., 93, 180–201.Google Scholar
Perring, C. S., Groves, D. I., and Ho, S. E. (1987). Constraints on the source of auriferous fluids for Archaean gold deposits. In Recent Advances in Understanding Precambrian Gold Deposits. (Ho, S. E. and Groves, D. I., eds.)—-Geol. Dept. and Univ. Ext., Univ. West. Aust. Publ. 11, 287–306.Google Scholar
Phillips, G. N. (1986) Geology and alteration in the Golden Mile, Kalgoorlie, Econ. Geol. 81, 779–808.Google Scholar
Phillips, G. N. (1991) Gold deposits of Victoria: A major province within a Palaeozoic sedimentary succession. World Gold 91, Aust. Inst. Min. MetaU., Melbourne 237-45.Google Scholar
Phillips, G. N. and Groves, D. I., (1983). The nature of Archaean gold-bearing fluids as deduced from gold deposits of Western Australia. J. Geol. Soc. Aust., 30, 25–39.Google Scholar
Phillips, G. N. and Groves, D. I., (1984) Fluid access and fluid-wall rock interaction in the genesis of the Archaean gold–quartz vein deposit at Hunt mine, Kambalda, Western Australia. In Gold ‘82. (Foster, R. P., ed.). Balkema, Rotterdam, 389–416.Google Scholar
Phillips, G. N. and Myers, R. E. (1989) The Witwatersrand gold fields: part II. An origin for Witwatersrand gold during metamorphism and associated alteration. Econ. Geol. Monog., 6, 598–608.Google Scholar
Phillips, G. N. and Law, J. D. M. (1992) Metamorphic petrology of the Witwatersrand Supergroup. Univ. Wits. Econ. Geol. Res. Unit lnfo. Circ. 248, 43 pp.Google Scholar
Phillips, G. N. Myers, R. E. and Palmer, J. A. (1987) Problems with the placer model for Witwatersrand gold. Geology, 15, 1027–30.Google Scholar
Phillips, G. N. Klemd, R., and Robertson, N. S. (1988) Summary of some fluid inclusion data from the Witwatersrand Basin and surrounding granitoids. Mem. Geol. Soc. India 11, 59–65.Google Scholar
Phillips, G. N. Myers, R. E., Law, J. D. M., Bailey, A. C., Cadle, A. B., Beneke, S. D. and Giusti, L. (1989) The Witwatersrand gold fields: part I. Postdepositional history, synsedimentary processes, and gold distribution. Econ. Geol. Monog. 6, 585–97.Google Scholar
Powell, R., Will, T. M., and Phillips, G. N. (1991) Metamorphism in Archaean greenstone belts: Calculated fluid compositions and implications for gold mineralization. J. Metam. Geol. 9, 141–50.Google Scholar
Rock, N. M. S. and Groves, D. I. (1988) Do tampro-phyres carry gold as well as diamonds? Nature, 332, 253–5.Google Scholar
Roering, C., Barton, J. M. Jr. and Winter, H. de la R. (1990) The Vredefort structure: A perspective with regard to new tectonic data from adjoining terranes. Tectonophysics, 171, 7–22.Google Scholar
Smith, T. J., Cloke, P. L. and Kesler, S. E. (1984) Geochemistry of fluid inclusions from the Mclntyre— Hollinger gold deposit, Timmins, Ontario, Canada. Econ. Geol., 79, 1265–85.Google Scholar
Wall, V. J. and Ceplecha, J. C. (1976) Deformation and metamorphism in the development of gold—quartz mineralisation in slate belts. Intern. Geol. Cong., Abst., 25, 142–3.Google Scholar
Wyman, D. A. and Kerrich, R. (1988) Lamprophyres: a source of gold. Nature, 332, 209–210.Google Scholar