Chemical fingerprint of iron oxides related to iron enrichment of banded iron formation from the Cauê Formation - Esperança Deposit, Quadrilátero Ferrífero, Brazil: a laser ablation ICP-MS study

Chemical signatures of iron oxides from dolomitic itabirite and high-grade iron ore from the Esperança deposit, located in the Quadrilátero Ferrífero, indicate that polycyclic processes involving changing of chemical and redox conditions are responsible for the iron enrichment on Cauê Formation from Minas Supergroup. Variations of Mn, Mg and Sr content in different generations of iron oxides from dolomitic itabirite, high-grade iron ore and syn-mineralization quartz-carbonate-hematite veins denote the close relationship between high-grade iron ore formation and carbonate alteration. This indicates that dolomitic itabirite is the main precursor of the iron ore in that deposit. Long-lasting percolation of hydrothermal fluids and shifts in the redox conditions have contributed to changes in the Y/Ho ratio, light/heavy rare earth elements ratio and Ce anomaly with successive iron oxide generations (martite-granular hematite), as well as lower abundance of trace elements including rare earth elements in the younger specularite generations.

位于铁四角地区（Quadrilátero Ferrífero）的埃斯佩兰萨矿床（Esperança deposit）中，白云质铁英岩（dolomitic itabirite）与富铁矿石内铁氧化物的化学特征表明，涉及化学与氧化还原条件变化的多旋回过程，是米纳斯超群（Minas Supergroup）考伊组（Cauê Formation）铁富集作用的成因。白云质铁英岩、富铁矿石及成矿期石英-碳酸盐-赤铁矿脉（syn-mineralization quartz-carbonate-hematite veins）中不同世代铁氧化物的锰（Mn）、镁（Mg）与锶（Sr）含量变化，揭示了富铁矿石形成与碳酸盐蚀变之间的密切联系。这表明白云质铁英岩是该矿床铁矿石的主要母源岩。热液流体（hydrothermal fluids）的长期渗滤作用与氧化还原条件的变迁，导致了不同世代铁氧化物（假象赤铁矿（martite）-粒状赤铁矿（granular hematite））的钇/钬（Y/Ho）比值、轻/重稀土元素比值与铈（Ce）异常发生演化，同时年轻世代镜铁矿（specularite）中包括稀土元素在内的微量元素丰度显著降低。