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Geology of Winu-Ngapakarra, Great Sandy Desert of Western Australia, a Recently Discovered Intrusion-Related Cu-Au Deposit
Economic Geology ( IF 5.8 ) Pub Date : 2023-08-01 , DOI: 10.5382/econgeo.5005
Hilke Dalstra 1 , Adam Black 2 , Inna Mudrovska 2
Affiliation  

The Winu-Ngapakarra Cu-Au deposit (Winu) was discovered in late 2017. Winu is hosted in metamorphosed massive sandstones, siltstones, and lesser mafic rocks that are possible distal and deep-water correlatives of the Malu Formation of the Yeneena basin, also host to the large Telfer Au-Cu deposit. Structure at Winu is dominated by an inclined dome formed through interference between NNW- and WNW-trending folds. Copper-gold mineralization occurs in en echelon left-stepping lodes with strike lengths between 350 and 750 m and vertical depths exceeding 750 m, northerly trends, and moderate easterly dips. These higher-grade lodes are surrounded by an extensive halo of low-grade mineralization. Two gold-rich lodes in the southeast part of the Winu deposit strike roughly easterly, toward a gold-rich satellite deposit (Ngapakarra) approximately 2 km east of Winu.Mineralization at Winu is hosted by numerous thin, brittle veins and breccias. At least four distinct vein sets associated with Cu-Au mineralization are recognized: V1—early, weakly mineralized K-feldspar-white mica stockworks; V2—transitional magmatic-hydrothermal K-feldspar–rich veins; V3—quartz-sulfide–rich veins, breccias, and fractures and quartz-bismuth-gold veins with similar timing; and V4—poorly mineralized quartz veins. Barren carbonate-, chlorite-, white mica-, and pyrite-rich fractures (V5), breccias, and faults as well as thin dolerite dikes cut mineralization at Winu. Re-Os dating of molybdenite intergrown with chalcopyrite yielded ages of 658 to 655 Ma for the mineralized veins at Winu, and Ar-Ar dating of biotite yielded 619 Ma for an unmineralized post-ore quartz-biotite vein. A well-developed supergene chalcocite blanket overlies the primary mineralization.Element associations and vein and alteration textures and mineralogy classify Winu as an intrusion-related Cu-Au deposit of Neoproterozoic age. Although it shares features with the reduced porphyry copper-gold group, other features, such as the dominance of pyrite over pyrrhotite and the presence of trace amounts of sulfate minerals in the mineralization, are more in accordance with oxidized, intrusion-related systems. Mineralization at Winu was most likely triggered by rapidly changing stress fields during the Paterson orogeny and cooling of multiple fluid pulses above an intruding granite pluton that progressively decreased in temperature over time.Winu is unique in this region in that it preserves evidence for an early, reduced intrusion-related gold system overprinted by a more oxidized intrusion-related copper system.

中文翻译:

西澳大利亚大沙漠 Winu-Ngapakarra 的地质,最近发现的与侵入有关的铜金矿床

Winu-Ngapakarra 铜金矿床 (Winu) 于 2017 年底发现。Winu 赋存于变质块状砂岩、粉砂岩和较小的镁铁质岩石中,这些岩石可能与 Yeneena 盆地 Malu 组的远端和深水相关物有关。特尔弗 (Telfer) 大型金铜矿床所在地。维努的结构主要是由 NNW 和 WNW 走向的褶皱之间的干扰形成的倾斜圆顶。铜金矿化赋存于左阶梯状矿脉中,走向长度在350~750 m之间,垂直深度超过750 m,走向偏北,缓东倾。这些较高品位的矿脉被广泛的低品位矿化环所包围。维努矿床东南部的两个富金矿脉大致向东走向,朝向位于威努以东约 2 公里处的富含金矿的卫星矿床 (Ngapakarra)。威努的矿化由许多薄而脆的矿脉和角砾岩组成。至少发现了四种与铜-金矿化相关的不同矿脉组: V1——早期弱矿化的钾长石-白云母网;V2—过渡型岩浆热液富钾长石矿脉;V3—富含石英硫化物的矿脉、角砾岩和裂缝以及时间相似的石英-铋-金矿脉;V4—矿化不良的石英脉。富含碳酸盐、绿泥石、白云母和黄铁矿的贫瘠裂缝 (V5)、角砾岩和断层以及薄辉绿岩岩脉切割了威努的矿化区。对与黄铜矿共生的辉钼矿进行铼锇测年,得出威努矿化脉的年龄为 658 至 655 Ma,黑云母 Ar-Ar 测年结果显示,未矿化的后矿石英黑云母脉的年龄为 619 Ma。发育良好的表生辉铜矿覆盖层覆盖在原生矿化之上。元素组合、脉、蚀变结构和矿物学将Winu 归类为新元古代与侵入相关的铜-金矿床。尽管它与还原斑岩铜金矿群具有相同的特征,但其他特征,例如黄铁矿相对于磁黄铁矿的优势以及矿化中存在微量硫酸盐矿物,更符合氧化的侵入相关系统。维努的矿化很可能是由帕特森造山运动期间快速变化的应力场以及侵入花岗岩体上方的多个流体脉冲的冷却引发的,随着时间的推移,温度逐渐降低。
更新日期:2023-08-01
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