The Porphyry Cu-(Mo-Au) Deposit at Altar (Argentina): Tracing Gold Distribution by Vein Mapping and LA-ICP-MS Mineral Analysis
The Porphyry Cu-(Mo-Au) Deposit at Altar (Argentina): Tracing Gold Distribution by Vein Mapping and LA-ICP-MS Mineral Analysis
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DOI：
10.2113/econgeo.109.5.1341
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发表时间：
2014-08
期刊：
影响因子：
5.8
通讯作者：
C. Zwahlen;Stefania Cioldi;T. Wagner;R. Rey;C. Heinrich
中科院分区：
文献类型：
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作者：
C. Zwahlen;Stefania Cioldi;T. Wagner;R. Rey;C. Heinrich
阿尔塔尔斑岩铜（钼金）存款产于中新世至上新世早期铜矿带的高安第斯山脉的阿根廷西部，靠近智利边境。中新世晚期的一组斑岩侵入了更广泛的中新世早期流纹岩到安山质火山岩和次火山岩的杂岩。中央斑岩的钾质蚀变部分被长石破坏性蚀变叠加，最后被泥质至高级泥质蚀变叠加。早期网脉先后被石英黄铁矿脉、电气石脉、硫砷铜矿脉切割。根据对这四种矿脉类型的化验结果和丰度图的相关性分析，我们估计，约11%至26%的铜在祭坛矿体与硫砷铜矿脉，而其余的是与早期网脉和钾蚀变。与安第斯弧后地区典型的铜-Au斑岩相比，金的浓度较低，但高于智利中新世的巨型矿床，阿尔塔中央斑岩矿体的平均Au/Cu重量比为0.14 × 10 −4。在网脉和钾化蚀变域中，金主要与黄铜矿共生。结合岩相学观察和激光烧蚀电感耦合等离子体质谱显微分析的小规模分析表明，在网状脉中的金的一个显着的分数是封闭在黄铁矿作为亚微观颗粒附着在包裹体的Bi-Te-Pb-Ag-富集Cu-Fe硫化物相。自然金的显微颗粒也沿着黄铁矿和黄铜矿之间的晶界出现，很少以较大颗粒出现在硫砷铜矿脉中。
The Altar porphyry Cu-(Mo-Au) deposit occurs in the Miocene to early Pliocene copper belt of the high Andes of western Argentina, close to the Chilean border. A cluster of late Miocene porphyries intruded a more extensive complex of early Miocene rhyolitic to andesitic volcanic and subvolcanic rocks. Potassic alteration in the Central Porphyry was partially overprinted by feldspar-destructive alteration and finally by argillic to advanced argillic alteration. Early stockwork veins have been cut successively by quartz-pyrite veins, tourmaline veins, and enargite veins. Based on correlation analysis of assay results and mapped abundances of these four vein types, we estimate that approximately 11 to 26% of the copper in the Altar orebody is associated with enargite veins, whereas the remainder is associated with the early stockwork veining and potassic alteration. Gold concentration is low compared with typical Cu-Au porphyries of the Andean back-arc region, but higher than in the giant Miocene deposits of Chile, at an average Au/Cu ratio of 0.14 × 10 −4 by weight across the Central Porphyry orebody at Altar. Gold is dominantly associated with chalcopyrite in the domain of stockwork veining and potassic alteration. Small-scale assays in combination with petrographic observations and laser ablation-inductively coupled plasma-mass spectrometry microanalyses show that a significant fraction of the gold in the stockwork veins is enclosed in pyrite as submicroscopic particles attached to inclusions of a Bi-Te-Pb-Ag–enriched Cu-Fe sulfide phase. Microscopic grains of native gold also occur along grain boundaries between pyrite and chalcopyrite, and rarely as larger particles in enargite veins.