江苏南京梅山铁矿床外围多金属矿体地质地球化学特征初探

南京梅山铁矿床是宁芜地区典型的玢岩型铁矿床。本次工作在梅山铁矿床主矿体外围及顶部(即"铁矿近矿指示蚀变带")发现了金、铜、钼多金属矿体,这在长江中下游白垩系火山岩盆地中尚属首次。研究表明,金、铜、钼多金属矿化主要赋存在磁铁矿主矿体上部大王山组辉石安山岩或火山碎屑岩中。主量元素地球化学特征显示,辉石安山岩属于低硅、高钾玄武质安山岩,其与辉长闪长玢岩可能来自同一个火山岩浆;稀土元素地球化学研究表明,多金属矿体的δEu正异常明显,与玢岩铁矿的磁铁矿之间存在互补关系,与辉长闪长玢岩有相似的稀土元素配分形式,推测多金属矿化与辉长闪长玢岩有关。流体包裹体研究表明,与金成矿有关的流体包括高温低盐度和中低温低盐度流体2种类型。

A tentative discussion on geological and geochemical characteristics of polymetallic orebodies in periphery of Meishan iron deposit, Nanjing, Jiangsu Province

The Meishan iron deposit in the Ningwu basin is considered to be a typical porphyrite-type iron deposit. Au, Cu and Mo polymetallic ores were found in the periphery of the main Meishan magnetite orebody. No similar findings have been reported in the middle and lower reaches of the Yangtze River, especially in the Ningwu basin. Based on the corresponding studies, the authors found that polymetallic ores occur in the pyroxene-andesite of the Dawngshan Formation and are located in the periphery of the main Meishan magnetite orebody. Geochemical studies of main elements indicate that the pyroxene-andesite is a kind of low silicon and high potassium basalt-andesite, and the pyroxene-andesite and gabbro-diorite porphyrite might have been derived from the same magma. Contrary to negative Eu anomalies of magnetites in the main Meishan magnetite orebody, the polymetallic ores show positive Eu anomalies and have similar chondrite normalized REE patterns to gabbro-diorite porphyrite, indicating that the polymetallic ores were genetically associated with gabbro-diorite porphyrite. Furthermore, calcite associated with gold mineralization contained high and low temperature and low salinity fluid inclusions.