Geological Characters, Metallogenic Regularity And Model Of The Gold (Copper) Ore Fields In Jinchang, Heilongjiang Province

Jinchang gold(copper)deposit in Dongning County, Heilongjiang Province, is one of the classic gigantic ore fields under exploration. The author carried out an in-depth study in the characteristic and evolution of igneous rocks, geological features, ore-fluid geochemistry, metallogenesis and prospecting orientation aspects, and achieved the following main outcomes:(1) The sequence of magmatic activity of the ore field has went through Late Indosinian and Mid-Yanshanian, in which Late Indosinian is consist of a volcanic activity stage and three intrusive activity stages, and Mid-Yanshanian includes two stages. The magma mainly came from primitive mantle, and there is contamination of crustal materials in the evolution. The mineralization occurs in intrusive rocks of Late Indosinian, but the Au (Cu) mineralization is related closely to the granite porphyry of Lower Cretaceous in space-time and metallogenesis, indicating the granite porphyry is metallogenetic parent rock.(2) Mineralization of gold bodies in the Jinchang gold deposit was divided into three types: cryptoexplosion breccia type, vein type and veinlet-disseminated type. The gold mineralization is comprised of 5 stages from early to late, and quartz-pyrite stage and multimetal sulfide type-quartz stage are the main stage of mineralization. The wall rock alteration consists of 4 zoning, from deep to shallow, potassic zone, sericitization zone, propylitization zone and argillization zone. The deposit was formed about 110 Ma.(3) The fluid inclusion type in the quartz of ore body is complicated, ranging from melt inclusion and melt-fluid inclusion to fluid inclusion, and halite-bearing inclusions are well developed. Studies have shown that vapor-rich fluid inclusions and halite-bearing inclusions coexisted in mineralization fluid indicating boiling characterization. Chalcopyrite is common as daughter minerals, which indicate that the mineralization fluid has a high metal content of copper. The homogenization temperature of fluid inclusions in hydrothermal stage is 160-600℃, while the temperature of the main stage of mineralization is 300-450℃, the salinity is 1.40～73.96% NaCleqv, which indicate that the ore fluid is belong to typical porphyry gold (copper) deposit fluid. The metallogenic materials are mainly from magma, and the fluid boiling is major reason for metal precipitation. The metallogenetic depth is from 2 to 3 km. (4) The ore field has zonation regularity in space. From west to east, the mineral assemblage is corresponding from medium-high temperature to medium-low temperature mineral assemblage, element assemblage is from Mo and Cu to Au and Ag, and the mineralization depth is from deep to shallow. The main ore body has the characteristic of axial element zoning sequence, which, from top to bottom, is Hg-Cu-Bi-Au-Ag-Ni-Co-As-Mo-Sb-Pb-Zn. We can see that the element zoning sequence is inverse zoning which indicates that there might be a blind ore body in deep part. The Ag, Cu, As, Sb, Bi and Hg element assemblage is related closely to the Au mineralization.(5) Three ore body types in the ore field belong to the same porphyry metallogenic system. Combining the characteristic and evolution of igneous rocks, geological features, wall alteration, ore-fluid geochemistry, metallogenic element assemblages and mineral deposits zoning characteristics, the author proved that the deposit belong to porphyry gold (copper) deposit type, and initially established metallogenic model of gold (copper) ore field in Jinchang, and pointed out a great ore-prospecting potential in deep.