Study On The Fluid Inclusions Of The Zhushahong Porphyry Cu Deposit, Dexing, Jiangxi Province

Zhushahong is one of the copper porphyry deposits in the Dexing ore field which is composed of Tongchang, FuJiawu and Zhushahong. Based on logging of the21drills on five exploration lines in the mine area, the order of the formation of mineral veins and the different mineral assemblages (A, B and D veins) are distinguished. And through analysis of H-O isotopes of single minerals including altered minerals and gauge minerals, we track the origin of ore forming fluid during complicated mineralization and alteration process of Zhushahong porphyry Cu deposit. We also establish a detailed revolution and mineralization mechanism.Through field survey and lab research of X-ray powder diffraction analysis, it turns out that the alteration zoning of Zhushahong is similar to other porphyry deposit in arc settings belt. Timely, the alteration changes from potassic and propylitization alterations in early time, to phyllic alteration and argillization alteration in transitional phase.According to the systematic microthermometry and LRM analysis of the14different type veins, the characteristics of ore-forming fluid of alteration and mineralization system of Zhushahong porphyry copper-gold deposit are completely recognized. The characteristics and evolution of ore-forming fluid are as follows:(1) In the early stage, the four A-type veins were formed when the porphyry rock had not been completely solidified, so that the veins are irregluar and unclearly bordered with wall rock or porphyry rock and large-scale of K-feldspar alteration; Fluid inclusions are mainly LVH (the fluid inclusion is composed of liquid, gas bubble and one or moe daugther metal mineral or transparent minerals) and VL (the two phase fluid inclusion is composed of more gas than liquid in volume) types,with homogenization temperature of350～550℃and the salinity of52.9-69.9%NaCl and2.9～16.8%NaCl;(2) In the middle stage, the five B-type veins were largely formed. Most of B-type veins are straight and along with the chalcopyrite, molybdenite, bornite mineralization. Fluid inclusions in this stage are mainly composed of VL and LV (the two phase aqueous fluid inclusion is composed of more liquid than gas in volume) and a few of LVH types, with captured temperature of248～405℃and salinity of38.6～58.0%NaCl and0.9～10.6%NaCl;(3) At the post-minerlization stage, five D-type veins with or without alterated Hydromica halo were fromed when the mineralizaiton system was opened and meteoric water and undergrand water infused into the open fissure with large py-Q-ser alteration. Fluid inclusions in this stage are mainly LV with homogenization temperature of127～326℃and salinity of0.4～5.1%NaCl. In conclusion, the characteristics of ore-forming fluid of Zhushahong changed from high temperatures, high salinities at early stage to low temperatures, low salinities at later stage. According to the result of laser Raman analysis (LRM), there are still CO2-bearing fluid inclusions in most of A, B and D veins. Some daugther metal minerals and transparent minerals contained in the fluid inclusions are still unidentified.The primary copper mineralization of Zhushahong start at late stage of potassic alteration, and main copper mineralization is firstly in transitional phase, and secondly in the quartz-sericite alteration phase. Mo mineralization forms mainly in the quartz-sericite alteration phase.