Characterstics And Genesis Of Anqing Copper-Iron Deposit, Anhui Province

The Anqing area is an important segment of the Middle-lower Yangtze River Cu-Fe mineralization belt. In the area occur a great number of the Fe-Cu-Au skarn deposits, of which the Anqing Cu-Fe deposit is one of the largest deposits. Due to its large scale, high grade and remarkable geologic feature, the Anqing Cu-Fe deposit is a representative skarn-type one in this area. A comprehensive study has been carried out on the orefield and ore deposit geology, petrography and petrology, especially mineralogy and geochemistry of the Anqing skarn and associated deposit, with a focus on the analysis of their origin based on the study.The following are major achievements obtained in this thesis.1. The petrographic observations indicate that skarns in the Anqing Cu-Fe deposit are ones consisting mainly of diopside or garnet with phases of andradite and cafemic garnet, and minerals of ores mainly include magnetite, chalcopyrite, pyrrhotite and pyrite.2. The petrological studies and major oxide analyses show that diorites of the Yueshan pluton closely associated skarn-type Cu-Fe mineralization belong to high K calc-alkaline series.3. The analyses of trace and rare earth elements display that skarns in the Anqing Cu-Fe deposit are depleted in high field strength elements such as Nb, Ta and Zr, but enriched in magmatophile elements such as Th, La and Ce, and appear different in trace element feature from carbonate wallrocks, but similar to the diorites. Both of skarns and diorites are enriched LREE, but the skarns are relatively depleted in Sr.4. The mineralogical studies support an origin of pyrite phases in the diorites of the Anqing Cu-Fe deposit by magmatic crystallization, but an origin of those in the skarns by replacement, which is consistent with the similarity in REE characteristics between pyrite in the skarns and one in the carbonate wallrocks. Magnetite phases in the diorites, skarns and ores are rich in LREE. However, the diorites are depleted in Ce, evidently different from the skarns and ores. Garnet phases in the skarns are rich in LREE, with an Eu positive anormaly.