Gregory, DD and Large, RR and Halpin, JA and Lounejeva, E and Wu, S and Bull, SW and Sack, PJ and Lyons, T and Chappaz, A, Accumulation of trace elements into black shale - how to identify a viable source rock for orogenic and Carlin-style gold deposits, Proceedings of the PACRIM 2015 Congress, 18-21 March 2015, Hong Kong, China, pp. 59-64. ISBN 978-1-925100-25-9 (2015) [Refereed Conference Paper]
Copyright 2015 The Australasian Institute of Mining and Metallurgy
Official URL: http://www.ausimm.com.au/
Newly published models suggest that some orogenic and Carlin-style gold deposits formed by the remobilisation of trace elements during interaction with hydrothermal or metamorphic fluids from early sedimentary pyrite that was enriched in Au, As and Te. The released trace elements are transported by the fluids to favourable trap sites where they are deposited. Therefore, early enrichment of Au, As and Te in source rocks (particularly in pyritic black shale) can be crucial to the formation of orogenic and Carlin-style gold deposits.
The most important cause of the enrichment of gold and other trace elements in the sedimentary basins has been examined in this study to determine which basins are the most prospective for the development of orogenic gold deposits. An important influence for Au and other associated trace element accumulation in sedimentary pyrite is the temporal variation of trace element content in the oceans, as revealed by a database of over 1400 analyses of pyrite from black shale through geologic time. It is inferred that sediments coeval with those where sedimentary pyrite is enriched in Au and associated trace elements are more likely to be source rocks of orogenic and Carlin-style gold deposits.
Factor analysis of the trace element content of pyrite through geologic time was conducted to investigate the multivariate relationships amongst trace elements and how these chemical factors explain the uptake of trace elements. One important factor includes Te, Au, Pb and Bi content. The incorporation of these large cations into pyrite is enhanced by As3+ substituting for Fe in pyrite lattice. The As3+ ion occurs in relatively oxidised environments and, thus, it is expected that shales deposited in non-euxinic waters are better source rocks for orogenic gold deposits.
The examination of both the time in which the sediments were deposited and the redox conditions of the basin, and the ocean more broadly, can be used as a guide to approximate the extent of a basin's fertility. To illustrate the use of this exploration tool, examples from the unmineralised Jet Rock Formation (UK) and the mineralised Castlemaine Group (Bendigo, Australia) are presented in this paper.
|Item Type:||Refereed Conference Paper|
|Keywords:||pyrite, palaeo-oceanography, seawater proxy|
|Research Division:||Earth Sciences|
|Research Field:||Exploration Geochemistry|
|Objective Division:||Expanding Knowledge|
|Objective Group:||Expanding Knowledge|
|Objective Field:||Expanding Knowledge in the Earth Sciences|
|UTAS Author:||Gregory, DD (Dr Daniel Gregory)|
|UTAS Author:||Large, RR (Professor Ross Large)|
|UTAS Author:||Halpin, JA (Dr Jacqueline Halpin)|
|UTAS Author:||Lounejeva, E (Ms Elena Lounejeva Baturina)|
|UTAS Author:||Wu, S (Dr Wai Wu)|
|UTAS Author:||Bull, SW (Dr Stuart Bull)|
|Funding Support:||Australian Research Council (DP150102578)|
|Deposited By:||Centre for Ore Deposit Research - CODES CoE|
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