Electron microprobe analysis and REE geochemical characteristics of minerals from the Meishan iron deposit in Nanjing-Wuhu area, Eastern China

Abstract: The Meishan iron deposit is located in the northern Ningwu Basin of the Middle-Lower Yangtze River metallogenic belt, and occurs at the contact zone between the gabbro-diorite porphyry and the pyroxene andesite of the Late Cretaceous Dawangshan Formation. The garnets of the Meishan iron deposit are similar to those of skarn deposits in end member, classified as andradite-grossular series. Magnetite and hematite display the characteristics of both Kiruna-type and porphyry copper deposits. Hematite and siderite were formed by hydrothermal fluids, and the hematite has at least two types. Gabbro-diorite porphyry (host rocks), magnetite and apatite share similar chondrite-normalized REE distribution patterns, indicating the same source. Nevertheless, the gabbro-diorite porphyry fails to show Eu anomalies and possibly resulted from magmatic fractional crystallization with high oxygen fugacity. Negative Eu anomalies of magnetites and apatites might have resulted from the enrichment of Eu2+ in the albites during the process of albitization. Iron was extracted from Fe2+-rich silicate minerals and migrated into the ore-forming fluid due to albitization of the gabbro-diorite porphyry.