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Element mobility and spatial zonation associated with the Archean Hamlet orogenic Au deposit, Western Australia: Implications for fluid pathways in shear zones

Citation

Hood, SB and Cracknell, MJ and Gazley, MF and Reading, AM, Element mobility and spatial zonation associated with the Archean Hamlet orogenic Au deposit, Western Australia: Implications for fluid pathways in shear zones, Chemical Geology, 514 pp. 10-26. ISSN 0009-2541 (2019) [Refereed Article]


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Copyright Statement

2019 The Authors. Published by Elsevier B.V. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0) http://creativecommons.org/licenses/by-nc-nd/4.0/

DOI: doi:10.1016/j.chemgeo.2019.03.022

Abstract

Mass balance equations can be used to understand metasomatism. Here we use 2726 multi-element chemical analyses to quantify the effect of metasomatism associated with Au mineralisation at the Hamlet Gold Mine (Hamlet), Yilgarn Craton, Western Australia. Principal components analysis is first used to identify covarying elements and six groups of elements are identified: (1) relatively immobile elements, with Zr and Hf providing an appropriate reference frame for mass balance calculations; (2) elements associated with mafic rocks, such as Ca, Co, Fe, Ge, Mg, Mn, and Zn; (3) elements related to potassic alteration, Ba, Cs, K, Rb, and Tl; (4) elements related to sodic alteration, Be, Na, and Sr; (5) chalcophile elements, including Bi, weakly associated with Au; and (6) Au, Te, and S representing the main Au-mineralising event. A statistically-rigorous approach is then used to quantify element addition and depletion and provides 95% confidence limits for changes in mass. To achieve this, the basaltic host rocks are divided into four subunits based on Cr content. Sample subsets are then created to select altered rocks and least-altered protolith rocks, using discrimination diagrams. Pairings of least altered-altered samples from each basalt subunit are used to construct matrices via bootstrapping. Mass balance results from these matrices indicate similar element mobility associated with Au mineralisation across the four basalt subunits, with up to 24% mass loss. Key potassic and sodic group elements are enriched in the Au mineralised zones at the expense of elements with a mafic-association. Spatial patterns of mass change are linear and repetitive within the steeply-dipping Hamlet Shear Zone, interpreted to represent a mesh-like geometry of metasomatism within the plane of the shear zone. Localised enrichment of K, Na, and Bi are related to Au distribution while Ca depletion zones reflect the movement of reactive fluid along the shear plane.

Item Details

Item Type:Refereed Article
Keywords:mass balance, metasomatism, ore deposit, orogenic gold, shear zone, fluid flow, Archean, St Ives, Hamlet, Au lode
Research Division:Earth Sciences
Research Group:Geochemistry
Research Field:Exploration Geochemistry
Objective Division:Mineral Resources (excl. Energy Resources)
Objective Group:Mineral Exploration
Objective Field:Precious (Noble) Metal Ore Exploration
UTAS Author:Hood, SB (Mr Shawn Hood)
UTAS Author:Cracknell, MJ (Dr Matthew Cracknell)
UTAS Author:Reading, AM (Professor Anya Reading)
ID Code:132179
Year Published:2019
Web of Science® Times Cited:1
Deposited By:CODES ARC
Deposited On:2019-04-26
Last Modified:2019-05-06
Downloads:8 View Download Statistics

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