Study on the Characteristics and Origin of Ore-forming Fluids of Nancha Gold Deposit in Jilin Province

Located in the Southwestern end of the Laoling uplift belt in Liao-Ji rifting zone, Nancha gold deposit is a medium-sized altered rock type deposit and was discovered in the late 1980s. The mineralization belts(ore bodies) mainly occurred in the contact zone between dolomitic marble of Zhenzhumen formation and schist of Huashan formation in Liaohe group of middle Proterozoic Era. Its hydrothermal mineralization experiences three stages:Ⅰ pyrite-quartz stage; Ⅱ pyrite-chalcopyrite-quartz stage; Ⅲ rarely sulfides-carbonate-quartz stage. The study shows that only aqueous two-phase fluid inclusions were developed in ores of different stages. The homogeneous temperature in stageⅠ is 180~260℃, and the salinity is 4.78%~9.47%Nacl. In stage Ⅲ the temperature and the salinity is 164~188℃ and 2.76%~4.94%Nacl respectively. The results of hydrogen-oxygen isotope analysis shows that the δ18OH₂O-SMOW and δD V-SMOW composition of mineralization in stageⅠ is 3.3~5.3‰ and -90.5~-92.6‰ respectively; and in stage Ⅲ that is -6.5~-8.2‰ and -105.4~-117.7‰, which means that the fluids of stageⅠmainly came from magmatic solutions and in stage Ⅲ mainly from meteoric water. The decreasing of temperature of magma-derived solutions, combined with meteoric water, may be the main mechanisms of gold deposition.