With new advances in rapid-acquisition geochemical and hyperspectral techniques, exploration companies are now able to detect subtle halos surrounding orebodies at minimal expense. The Nimbus Ag-Zn-(Au) deposit is unique in the Archean Yilgarn Craton of Western Australia. Due to its mineralogy, alteration assemblages, geochemical affinity, and tectonic setting, it is interpreted to represent a shallow water (~650 mbsl) and low-temperature (<250 °C) volcanogenic massive sulfide (VMS) deposit with epithermal characteristics (i.e., a hybrid bimodal felsic deposit). We present a detailed paragenetic account of the Nimbus deposit, and establish lithogeochemical and hyperspectral halos to mineralization to aid exploration. Mineralization at Nimbus is characterized by early units of barren massive pyrite that replace glassy dacitic lavas, and underlying zones of polymetallic sulfides that replace autoclastic monomict dacite breccias. The latter are dominated by pyrite-sphalerite-galena, a diverse suite of Ag-Sb ± Pb ± As ± (Cu)-bearing sulfosalts, minor pyrrhotite, arsenopyrite, and rare chalcopyrite. The main sulfosalt suite is characterized by pyrargyrite, and Ag-rich varieties of boulangerite, tetrahedrite, and bournonite. Zones of sulfide mineralization in quartz-sericite(±carbonate)-altered dacite are marked by significant mass gains in Fe, S, Zn, Pb, Sb, Ag, As, Cd, Ni, Cu, Ba, Co, Cr, Tl, Bi, and Au. Basaltic rocks show reduced mass gains in most elements, with zones of intense quartz-chlorite-carbonate±fuchsite alteration restricted to thick sequences of hyaloclastite, and near contacts with dacitic rocks. Broad zones of intense silica-sericite alteration surround mineralization in dacite, and are marked by high Alteration Index and Chlorite-Carbonate-Pyrite Index (CCPI) values, strong Na-Ca depletion, and an absence of feldspar (albite) in thermal infrared (TIR) data. White mica compositions are predominantly muscovitic in weakly altered sections of the dacitic footwall sequence. More paragonitic compositions are associated with zones of increased sericitization and high-grade polymetallic sulfide mineralization. Chlorite in dacitic rocks often occurs adjacent to zones of sulfide mineralization and is restricted to narrow intervals. Carbonate abundance is sporadic in dacite, but is most abundant outside the main zones of Na-Ca depletion. Basaltic rocks are characterized by strongly paragonitic white mica compositions, and abundant chlorite and carbonate. Shifts from Ca carbonates and Fe-rich chlorites to more Mg-rich compositions of both minerals occur in more intensely hydrothermally altered basaltic hyaloclastite, and near contacts with dacitic rocks. Hanging-wall polymict conglomerates are characterized by minor amounts of muscovitic to phengitic white mica (2205–2220 nm), and an absence of chlorite and carbonate alteration.

中文翻译：

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西澳大利亚东部金矿田超地带中雨云的岩石地球化学和高光谱晕变到Ag-Zn-Au矿化

随着快速采集地球化学和高光谱技术的新进展，勘探公司现在能够以最小的成本检测出矿体周围的细微晕圈。Nimbus Ag-Zn-（Au）矿床在西澳大利亚的太古代的Yilgarn Craton中是独特的。由于其矿物学，蚀变组合，地球化学亲和力和构造背景，它被解释为代表浅水（〜650 mbsl）和低温（<250°C）具有超热特征的火山成块大块硫化物（VMS）矿床（即，一种混合​​双峰长英质矿床）。我们介绍了Nimbus矿床的详细共生描述，并建立了岩石化学和高光谱晕圈来矿化，以帮助勘探。Nimbus的矿化特征是，早期的贫瘠块状黄铁矿取代了玻璃状的熔岩，以及多金属硫化物的下层区域，这些区域取代了自碎屑的单镁硅酸盐角砾岩角砾岩。后者由黄铁矿-闪锌矿方铅矿，各种含Ag-Sb±Pb±As±（Cu）的亚硫酸盐，次黄铁矿，毒砂和稀有的黄铜矿组成。主要的亚硫酸盐套件的特征是硫铁锰矿和富银的勃兰格石，四面体和硼锌矿变种。石英-绢云母（±碳酸盐）改变的菱铁矿中硫化物矿化带的特征是，Fe，S，Zn，Pb，Sb，Ag，As，Cd，Ni，Cu，Ba，Co，Cr，Tl， Bi和Au。玄武岩在大多数元素中的质量增加都减少了，强烈的石英-亚氯酸盐-碳酸盐±烟灰石蚀变带被限制在玻碳石的厚层序中，并且接近于镁铁矿岩。硅藻土强烈变化的宽广区域围绕着钠铁矿的矿化作用，其特征是高的蚀变指数和亚氯酸盐-碳酸盐-黄铁矿指数（CCPI）值，强的Na-Ca损耗以及热红外中没有长石（阿尔比特）（ TIR）数据。白云母成分在胶泥底盘序列的弱变化部分中主要是粘液溶质的。更多的副生质成分与增加的绢云母化和高品位的多金属硫化物矿化区有关。胶凝岩中的亚氯酸盐通常发生在硫化物矿化区附近，并被限制在狭窄的区间内。钠铁矿中的碳酸盐丰度是零星的，但在Na-Ca贫化的主要区域以外最为丰富。玄武岩的特征是强烈的白云母白云母成分，以及丰富的亚氯酸盐和碳酸盐。从碳酸钙和富铁的亚氯酸盐向富含镁的两种矿物的转变发生在热液变化更剧烈的玄武质破硅质岩中，并与大晶岩近距离接触。悬挂壁的多聚体砾岩的特征是少量的粘液云母至白云母（2205–2220 nm），并且不存在亚氯酸盐和碳酸盐蚀变。