Chemical and isotopic compositions of rocks, ores, and hydrothermal minerals from the Rainbow and Logachev-2 hydrothermal fields

The aim of this paper is to analyze and compare mineralogy and geochemistry of copper-zinc sulfide ores from the Logachev-2 and Rainbow hydrothermal fields of the Mid-Atlantic Ridge (MAR) confined to serpentinite protrusions. It was found that Zn(Fe) and Cu, Fe(Zn) sulfides had been deposited in black smokers pipes almost simultaneously from intermittently flowing, nonequilibrium H2S-low solutions of different temperatures. Pb isotope composition confirmed that the deep oceanic crust had been a source of lead. The ores from the Rainbow field are 20-fold higher in Co than ores restricted to basalts and show a high ratio of Co/Ni=46. The ores from the Rainbow field are enriched in 34S isotope (aver. d34S=10 per mil) because of constant flow of cold sea water into the subsurface zone of the hydrothermal system. Ores from the Logachev-2 field are 8 times higher in gold compared to other MAR regions. Sulfide ores from the Rainbow and Logachev-2 fields have no analogues among MAR ore occurrences in terms of enrichment in valuable components (Zn, Cd, Co, and Au).本研究旨在分析并对比大西洋中脊（Mid-Atlantic Ridge，MAR）Logachev-2与Rainbow热液田内赋存于蛇纹岩隆起区的铜锌硫化物矿石的矿物学与地球化学特征。研究发现，Zn(Fe)与Cu、Fe(Zn)型硫化物几乎同时沉积于黑烟囱管道中，其物质来源为间歇性涌出的不同温度、低H₂S浓度的非平衡热液溶液。铅同位素组成证实，深部大洋地壳为铅的物质来源。Rainbow热液田的矿石中钴（Co）含量是仅赋存于玄武岩中的矿石的20倍，且Co/Ni比值高达46。Rainbow热液田的矿石富集34S同位素（平均δ³⁴S=10‰），成因在于冷海水持续注入热液系统的地下带。Logachev-2热液田的矿石中金（Au）含量为大西洋中脊其他区域的8倍。就有价组分（锌、镉、钴、金）的富集程度而言，Rainbow与Logachev-2热液田的硫化物矿石在大西洋中脊的已知矿化点中尚无同类可比者。