Comparison of fluid inclusion data and mineralization processes for Australian orogenic gold and intrusion-related gold systems

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• 出版年：2007
• 作者：Terry P.Memagh；E.N.Bastrakov；Khin Zaw；A.S.Wygralak；L.A.I.Wyborn
• 单位1：Geoscience Australia,GPO Box 378,Canberra，ACT,2601,Australia
• 语种：英文
• 作者关键词：Fluid inclusions；Isotopes；Orogenic gold deposits；Intrusion-related gold deposits
• 起始页：21
• 总页数：12
• 刊名：岩石学报
• 是否内版：否
• 刊频：月刊
• 创刊时间：1985
• 主办单位：中国矿物岩石地球化学学会；中国科学院地质与地球物理研究所
• 电子信箱：Ihzd@ public.tpt.tj.cn
• 卷：23
• 期：1
• 期刊索取号：P350.66357

摘要

We have examined the fluid inclusion data and fluid chemistry of Australian orogenic and intrusion-related gold depositsto determine if similar mineralization processes apply to both styles of deposits. The fluid inclusion data from the Yilgam craton, thewestem subprovince of the Lachlan orogen, the Tanami, Tennant Creek and Pine Creek regions, and the Telfer gold mine show thatmineralization involved fluids with broadly similar major chemical components (i.e.H₂O+NaCl+CO₂±CH₄±N₂).Thesedeposits formed over a wide range of temperature-pressure conditions (＜200to＞500℃,＜100～400MPa). Low salinity,CO₂-bearing inclusions and low salinity aqueous inclusions occur in both systems but the main difference between these two types ofdeposits is that most intrusion-related gold deposits also contain at least one population of high-salinity aqueous brine. Oxygen andhydrogen isotope data for both styles of deposit usually cannot distinguish between a magmatic or metamorphic source for the ore-bearingfluids. However, sulfur and lead isotope data for the intrusion-related gold deposits generally indicate either a magmatic source ormixing between magmatic and sedimentary sources of fluid. The metamorphic geothermal gradients associated with intrusion-related golddeposits are characterized by low pressure, high temperature metamorphism and high crustal geothermal gradients of＞30/km. Whereamphibole breakdown occurs m a granite source region, the spatially related deposits are more commonly associated with Cu-Audeposits rather than Au-only deposits that are associated with lower temperature granites. The dominant processes thought to cause goldprecipitation in both types of deposits are fluid-rock interaction (e.g.desulfidation) or phase separation. Consideration of the physicaland chemical properties of the H₂O-NaCl-CO₂ system on the nature of gold precipitation mechanisms at different crustal levels infersdifferent roles of chemical (fluid-rock interaction) versus theological (phase separation and/or fluid mixing) host-rock controls on golddeposition. This also implies that at the site of deposition, similar precipitation mechanisms operate at similar crustal levels for bothorogenic and intrusion-related gold deposits.