Ore-forming Fluids, Ore Geochemical Characteristics And Genesis Of The Longmenshan Cu Deposit Of Yueshan Area, Anhui Province

Longmenshan copper deposit is located in Yueshan rock mass which belongs to the middle of broken fold belt in northern margin of Yangtze block and contact zone between rock body and surrounding rock. This deposit is one of the most important deposits in the middle and lower Yangtze River copper metallogenic belt. Based on the analysis of the characteristics of geological background, geological of ore deposit, geochemical of deposit, metallogenic geologic condition and ore-forming fluids, then do the researches on the ore-controlling factors, rock-forming mechanism, the genesis of deposit and etc. The main achievements are made as follows:1. Though the researching the characteristics of geological background, and the geological characteristics of deposit, and then divides the mineralization of Longmenshan copper deposit into skarn stage and sulfide stage two periods by the relation of mineral paragenetic association. And skarn stage can be divided into three phase, namely: early skarn phase, terminal skarn phase, oxide phase; sulfide stage can be divided into three phase, namely:quartz sulfidic phase, sulfidic stage and carbonate phase.2. According to petrochemical characteristics of magmatic rocks, trace elements, REE geochemiscal characteristics and diagnostic fluid inclusions characteristics of Yueshan rock mass, we draw the conclusion that the Yueshan rock body has the character of rich kalium and natrium, as well as the character of rich calcium is obvious. Yueshan rock mass is belong to intermediate-felsic and calc-alkaline rock mass. Its light-heavy rare earth elements' Fractionation is obvious; it is strongly enriched in light rare earth elements. Ce,Eu anomaly is not obvious. The relationship between content ofδEu and SiO2 is negative correlation, and the relationship between content ofδEu and CaO is positive correlation.3. Yueshan rock body is the ore-forming rock body of Longmenshan copper deposit. On the basis of the analysis on the magma sources,tectonic environment and rock-forming process, combined with achievements of ore-forming mechanism, we draw the conclusion that Yueshan rock body roots in the deep-seated alkaline basaltic magma. The rock—forming process has undertaken two diferent degrees of assimilation and contamination. The rock-forming model belongs to the typical AFC mechanism.4. Though the researching of the REE geochemiscal characteristics and diagnostic fluid inclusions characteristics of rock mass, alter-rocks, ore and surrounding rock, we draw the conclusion that distribution patterns trend of ore and fresh rock mass of this area is the same. It shows that ore and fresh rock mass of this area have the same magma sources and magmatic evolution approach. The content distribution law of Cu, Fe, Mn, Zn, Pb in the rock mass, alter-rocks, ore and surrounding rock shows that the inner contact zone Close to the rock is more benefited for ore-forming, as well as the contamination of the crust has certain influence on ore-forming.5. By systemic researching the diagnostic fluid inclusions of the Longmenshan copper ore, we find that homogenization temperature is between 191.3～441.3℃, it can be divided into high and intermediate Temperature, the salinity can be also divided into two groups-high and medium-low. The density range in 0.61-1.004g/cm3, belongs to the medium-low-density fluid. The gas phase is mainly composed of H2O and CO2, with minor organic gas; the main anions in the liquid composition are Cl-, NO3- and SO42-, and the cations are Ca2+, Na+ and K+. The ore-forming solutions belong to the H2O-Na+(Ca2+, K+)-Cl-(SO42-,F-)-CO2 type.6. By analysing the ore deposit geologic characteristic, geochemical characteristic, diagnostic fluid inclusions characteristic, ore-controlling factors and rock-forming mechanism, we draw the conclusion that Longmenshan copper deposit is a contact metasomatic copper deposit which relates with silicon-rich and alkaline-rich intermediate-acid diorite.