The relationship between microbial activity and the supergene modification of ore systems has been a major subject of debate. Here, we present isotopic evidence of microbial-driven secondary copper mineralization in the active cementation zone of the Las Cruces deposit, a volcanogenic massive sulfide deposit located in Iberian Pyrite Belt, Spain. Copper isotopic data show that the lower isotopic ratios (δ65Cu ≈ −9.2 ± 0.11 ‰, the lowest value measured worldwide in a supergene environment) are found in the upper part of the cementation zone, the same zone where the maximum copper grades are found and where there is direct evidence of extremophilic microbial activity. There is a tendency towards higher values downwards through the cementation zone (−9.2 ± 0.11 ‰ to + 1.67 ± 0.11 ‰ δ65Cu) and upwards into the former Cu-depleted gossan that originally capped the cementation zone (−7.79 ± 0.11 ‰ to −1.32 ± 0.11 ‰ δ65Cu). As microbes preferentially sequester the lighter isotope when incorporating intracellular Cu, this distribution indicates that microbes played a major role in the formation of the high-grade zones. Water arrives to the deposit enriched in isotopically heavy copper, likely because it has leached other ore bodies upstream. δ65Cu values of water currently flowing into the system are remarkably more positive than those in the ore, indicating that microbial activity is a major cause of copper isotope fractionation. At least half of the copper transported by the incoming waters remains within the ore body. Our best interpretation is that the large and high-grade cementation zone at Las Cruces is of biogenic origin, and that the primary mineralization acted as a trap for copper transported by groundwater, leading to the formation of an exotic mineralization distal to sub-eroded massive sulfides located upstream.

中文翻译：

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生物介导的表生铜矿化增强：来自 Cu 同位素地球化学的证据


微生物活动与矿石系统的表生改造之间的关系一直是争论的主要话题。在这里，我们展示了位于西班牙伊比利亚黄铁矿带的拉斯克鲁塞斯矿床（Las Cruces 矿床）的活跃胶结带中微生物驱动的次生铜矿化的同位素证据。铜同位素数据显示，较低的同位素比值（δ65Cu ≈ -9.2 ± 0.11 ‰，这是全世界在表生环境中测得的最低值）位于胶结带的上部，该区域发现铜品位最高，并且有极端微生物活性的直接证据。通过胶结带（-9.2 ± 0.11 ‰ 至 + 1.67 ± 0.11 ‰ δ65Cu）并向上进入最初覆盖胶结带的前贫铜铁铝（-7.79 ± 0.11 ‰ 至 -1.32 ± 0.11 ‰ δ65Cu）。由于微生物在掺入细胞内 Cu 时优先螯合较轻的同位素，因此这种分布表明微生物在高品位区的形成中起主要作用。水到达矿床时富含同位素重铜，可能是因为它已经浸出了上游的其他矿体。目前流入系统的水的 δ65Cu 值明显高于矿石中的 δ65Cu 值，这表明微生物活性是铜同位素分馏的主要原因。进水输送的铜中至少有一半留在矿体内。 我们最好的解释是，Las Cruces 的大型高品位胶结带是生物成因，原生矿化作用是地下水输送的铜的陷阱，导致在上游的次侵蚀块状硫化物的远端形成外来矿化。