| Xiaoxinancha gold-copper deposit, located in the east of Northeast China, is one of the most improtrant gold-copper deposits in circum-Pafic zone. The geotectonic position of this area belongs to the joint of North China Craton, Xingkai-Jiamusi Block, and west Pacific tectonic territories. Early Paleozoic Qinglongcun group and Wudaogou group is the oldest strata in this area. Hercynian granites are widely disrtributed as batholith. Mesozoic granites occurs only mostly in stocks and veins. At the same time, Mesozoic volcanic eruption is very intensive in this area. Gold, copper deposits and mineral occurrences distribute widely in this area.Hercynian diorite-granodiorite diorite stock is the host rock and ore body of this deposit while the contemporaneous Yanshan magma activities have a close relationship with ore forming. Accompanying these magma activities, a swarm of microdiorite (diorite-porphyrite) diorite dikes emerge in the host rock and in the vicinity of lode ore body. From open pit mining and underground investigation, these dikes formed earlier than the mineralization or adhere to the mineralization stages.Cenozoic NE Xiangfanghe fault divided the whole ore-body into Beishan (North Mountain) and Nanshan (South Mountain) mining area. The Beishan mining area is open pit and Nanshan mining area is underground. The Beishan ore body is firmly controlled by four major NS-NNW faults, between these major faults, subtle faults developed. In these faults crushed zone, discontinuous quartz veins and disseminated sulphide that distribute between these quartz veins consists of the main Beishan open pit area.Sulphide lode and breccias quartz-sulphide constitute the Nanshan mining area. Research shows that the major metallic, minor metallic and gangue minerals are chalcopyrite, pyrite, pyrrhhotie; arsenopyrit, molybdenite, sphalerite, galena, tetrahedrite, bornite, digenite, magnetite, bismuth, stibnite, gold; quartz, chlorite, sericite, and carbonate respectively. According to the texture and structure, mineralization stages are divided into: pyrite-quartz, milk quartz-pyrite, pyrrhotite-chalcopyrite, pyrite-quartz, and quartz-calcite stages.The quartz veins contain abundant fluid inclusions. Study has shown that the vapor-liquid phase is the main type; poly-phase inclusions that contain daughter minerals such as chalcopyrite, magnetite, halite, sylvine, and anhydrite. The average size of these inclusions are from 10 to 35μm, in negative crystal,regular spheroid and xenomorphic. The homogeneous temperature range from 260 to 450℃and the Beishan mining has a higher homogeneous temperature than the Nanshan. Ore-forming fluid are basically of the H2O-NaCl system, with the vapor-liquid systems have a mid-low salinity (1.9-20.2%) and halite bearing inclusions high salinity (27.9-60.6%). Daughter minerals in fluid inclusions were studied by using Laser Raman technique. The sharp peak of Raman spectra of daughter minerals at 291 cm-1 is assigned to the typical vibration of chalcopyrite. According to the Raman spectra and the crystal structure of the mineral under microscopy, we can conclude that this daughter mineral in the fluid inclusions is chalcopyrite. Meanwhile, the daughter minerals locate in the fluid inclusions and they possess the high homogenization temperature with their ambient liquid. All these characteristics indicate that the daughter minerals were crystallized from the mineral bearing fluid, that is, sufficient mineral elements dissolved into the brine as their origins.The sulfur, carbon, hydro and lead isotope indicates that source of ore -forming fluid has the character of mantle fluid. At the same time, metallic minerals fluid inclusion noble gas isotopes were tested. The result show that the 3He/4He, 20Ne/22Ne and 40Ar/36Ar vary between 4.45~0.08Ra,10.2~8.8, and 306~430 respectively, and these isotope date also show that the Nanshan minerals have a high ratio than Beishan. Analyzing from the view of fluid genesis, evolvement, and mineralization characters, these data indicate that the original fluids are generated from the partial melt of ocean plate, which is participated by mantle-plume mantle/asthenosphere. This event was accordant to the time when the Izanagi plate subducted to the Paleo-Asia continent (123-102Ma) and its geological environment belongs to the continental margin. The high temperature, boiling fluids-vapor format the Beishan disseminated sulphide minerals by means of alternation and crystal, the formation of later pyrite-quartz sulphide veins belong to the backfill of the ore-forming fluid. The breccia sulphide veins in the Nanshan are formed by the backfill of the fluid, while the sulphide veins are formed by the deposit-crystal process.The whole ore-forming process can be summated as follows:1. The subduction of the Izanagi plate, degassing and dehydration and partial melt of the plate forms the melt.2. The diffusion of melt and fluid leads to the formation of magma and ore-forming fluid.3. Ore-forming fluid have a complex evolvement process and experience boiling-second boiling process and finally format this disseminated–lode gold-copper deposit.
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