Compositional zoning of fluid inclusions in the Archaean Junction gold deposit, Western Australia: a process of fluid � wall-rock interaction?

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dc.contributor.authorPolito, P A
dc.contributor.authorBone, Yvonne
dc.contributor.authorClarke, Jonathan
dc.contributor.authorMernagh, Terrence
dc.date.accessioned2015-12-10T23:15:27Z
dc.date.issued2001
dc.date.updated2015-12-10T09:45:46Z
dc.description.abstractThe Junction gold deposit, in Western Australia, is an orogenic gold deposit hosted by a differentiated, iron-rich, tholeiitic dolerite still. Petrographic, microthermometric and laser Raman microprobe analyses of fluid inclusions from the Junction deposit indicate that three different vein systems formed at three distinct periods of geological time, and host four fluid-inclusion populations with a wide range of compositions in the H2O-CO2-CH4-NaCl± CaCl2 system. Pre-shearing, pre-gold, molybdenite-bearing quartz veins host fluid inclusions that are characterised by relatively consistent phase ratios comprising H2O-CO2-CH4 ± halite. Microthermometry suggests that these veins precipitated when a highly saline, >340°C fluid mixed with a less saline ≥ 150°C fluid. The syn-gold mineralisation event is hosted within the Junction shear zone and is associated with extensive quartz-calcite ± albite ± chlorite ± pyrrhotite veining. Fluid-inclusion analyses indicate that gold deposition occurred during the unmixing of a 400°C, moderately saline, H2O-CO2 ± CH4 fluid at pressures between 70 MPa and 440 MPa. Post-gold quartz-calcite-biotite-pyrrhotite veins occupy normal fault sets that slightly offset the Junction shear zone. Fluid inclusions in these veins are predominantly vapour rich, with CO2>>CH4. Homogenisation temperatures indicate that the post-gold quartz veins precipitated from a 310 ± 30° fluid. Finally, late secondary fluid inclusions show that a <200°C, highly saline, H2O-CaCl2-NaCl-bearing fluid percolated along microfractures late in the deposite's history, but did not form any notable vein type. Roman spectroscopy supports the microthermometric data and reveals that CH4-bearing fluid inclusions occur in syn-gold quartz grains found almost exclusively at the vein margin, whereas CO2-bearing fluid inclusions occur in quartz grains that are found toward the centre of the veins. The zonation of CO2:CH4 ratios, with respect to the location of fluid inclusions within the syn-gold quartz veins, suggest that the CH4 did not travel as part of the auriferous fluid. Fluid unmixing and post-entrapment alteration of the syn-gold fluid inclusions are known to have occured, but cannot adequately account for the relatively ordered zonation of CO2:CH4 ratios. Instead, the late introduction of a CH4-rich fluid into the Junction shear zone appears more likely. Alternatively, the process of CO2 reduction to CH4 is a viable and plausible explanation that fits the available data. The CH4-bearing fluid inclusions occur almost exclusively at the margin of the syn-gold quartz veins within the zone of high-grade gold mineralisation because this is where all the criteria needed to reduce CO2 to CH4 were satisfied in the Junction deposit.
dc.identifier.issn0812-0099
dc.identifier.urihttp://hdl.handle.net/1885/64669
dc.publisherBlackwell Publishing Ltd
dc.sourceAustralian Journal of Earth Sciences
dc.subjectKeywords: Archean; carbon dioxide; fluid inclusion; geochemistry; gold; mineralization; quartz vein; Australia Carbon dioxide; Fluid inclusions; Geochemistry; Gold; Kambalda; Methane; Western Australia; Yilgarn craton
dc.titleCompositional zoning of fluid inclusions in the Archaean Junction gold deposit, Western Australia: a process of fluid � wall-rock interaction?
dc.typeJournal article
local.bibliographicCitation.lastpage855
local.bibliographicCitation.startpage833
local.contributor.affiliationPolito, P A, University of Adelaide
local.contributor.affiliationBone, Yvonne, University of Adelaide
local.contributor.affiliationClarke, Jonathan, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationMernagh, Terrence, Australian Geological Survey Organisation
local.contributor.authoremailrepository.admin@anu.edu.au
local.contributor.authoruidClarke, Jonathan, u9901428
local.description.embargo2037-12-31
local.description.notesImported from ARIES
local.description.refereedYes
local.identifier.absfor040307 - Ore Deposit Petrology
local.identifier.ariespublicationMigratedxPub978
local.identifier.citationvolume48
local.identifier.doi10.1046/j.1440-0952.2001.00903.x
local.identifier.scopusID2-s2.0-0035693982
local.identifier.uidSubmittedByMigrated
local.type.statusPublished Version

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