Abstract A diverse array of microorganisms, found within the uppermost lithosphere, can mediate the dissolution and precipitation of minerals and therefore contribute to the formation of laterites. The Salobo iron-oxide copper gold (IOCG) mine in Brazil is an ideal environment to examine the specific interaction between iron-oxidising bacteria and ferrous iron-bearing minerals during formation of a ~60 m thick laterite weathering profile. We identified bacteria using DNA extracted from samples in active weathering zones. Many of the identified species are capable of oxidising the ferrous iron and/or reduced sulphur that occurred in minerals associated with the unweathered rocks of the deposit. Fe-bearing phyllosilicates have been variably altered to clays along cleavage planes by bacterial iron oxidation. Accelerated weathering of fresh rocks in laboratory-scale leaching column experiments was conducted using an endemic Acidithiobacillus ferrooxidans ssp. previously cultured from the Salobo mine. There were strong similarities between field samples from the Salobo laterite zone, and experimental leachate chemistry, associated precipitates, and fossilised bacteria remnants, particularly with respect to ferric (oxyhydr)oxide formation. Groundwaters in the Salobo laterite zone have circumneutral pH, whereas some iron-oxidising bacteria thrive in, and locally create, more acidic conditions (~pH 3). The leaching experiments showed that bacterially-facilitated silicate weathering, and bornite (Cu5FeS4) oxidation, can consume acid generated by bacterial oxidation reactions, creating an effective equilibrium with ferric (oxyhydr)oxide precipitation. However, the current acid neutralisation capacity of the ferricrete horizon at the top of the laterite zone was minimal. While bacterial activity promoted mineral oxidation and decomposition within the thick laterite at the Salobo mine, related iron mobility is restricted to the micrometre scale by essentially instantaneous precipitation of ferric (oxyhydr)oxide that eventually transforms via inorganic dehydration to goethite and hematite. Similar processes to those described in this study have likely occurred during the formation of many other iron-rich laterites.

中文翻译：

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细菌诱导的富铁矿石中铁硅酸盐氧化对红土形成的贡献，巴西萨洛博 IOCG 矿

摘要 在岩石圈最上层发现的各种微生物可以调节矿物的溶解和沉淀，因此有助于红土的形成。巴西的 Salobo 氧化铁铜金 (IOCG) 矿是检查在形成约 60 m 厚的红土风化剖面过程中铁氧化细菌与含铁矿物之间特定相互作用的理想环境。我们使用从活跃风化区样本中提取的 DNA 来鉴定细菌。许多已识别的物种能够氧化亚铁和/或还原的硫，这些存在于与矿床未风化岩石相关的矿物中。含铁的页硅酸盐已通过细菌铁氧化沿解理面不同程度地转变为粘土。在实验室规模的浸出柱实验中，新鲜岩石的加速风化是使用地方性氧化亚铁硫杆菌 ssp 进行的。以前从萨洛博矿养殖。萨洛博红土带的现场样品与实验性渗滤液化学、相关沉淀物和化石细菌残余物之间存在很强的相似性，特别是在三氧化二铁的形成方面。萨洛博红土带的地下水具有环绕中性的 pH 值，而一些铁氧化细菌在酸性更强的条件（~pH 3）中茁壮成长，并在当地产生。浸出实验表明，细菌促进的硅酸盐风化和斑铜矿 (Cu5FeS4) 氧化可以消耗细菌氧化反应产生的酸，从而与氧化铁（羟基）沉淀形成有效平衡。然而，目前红土带顶部铁质混凝土层的酸中和能力很小。虽然细菌活动促进了 Salobo 矿厚红土中矿物的氧化和分解，但由于氧化铁（羟基）的瞬时沉淀，最终通过无机脱水转化为针铁矿和赤铁矿，因此相关的铁迁移率被限制在微米级。在许多其他富含铁的红土的形成过程中，可能发生了与本研究中描述的过程类似的过程。相关的铁迁移率被限制在微米级，主要是氧化铁（羟基）的瞬时沉淀，最终通过无机脱水转化为针铁矿和赤铁矿。在许多其他富含铁的红土的形成过程中，可能发生了与本研究中描述的过程类似的过程。相关的铁迁移率被限制在微米级，主要是氧化铁（羟基）的瞬时沉淀，最终通过无机脱水转化为针铁矿和赤铁矿。在许多其他富含铁的红土的形成过程中，可能发生了与本研究中描述的过程类似的过程。