| The Sanshi’erzhan gold deposit is located in the northeast of Erguna rising parton the edge of upper Heilong-jiang basin of fault subsidence. By studying thegeological conditions in this area, metallogenic geological conditions of this area issuperiority and has a good prospecting potential.The strata exposed in this mining area is mainly the Feldspathic lithic sandstone,lithic sandstone with fine sand,silt mudstone and coal line in Ershi’erzhanformation,Mid Jurassic. As the cover of Mesozoic clastic,there are only a fewintrusive rocks exposed. In the main of xingkai-Sarah Doyle and Yanshaniangranitoids,mainly rock types is adamellite and quartz diorite,with minor alkalifeldspar granite,syenite granite；fault is the most important structure in this area whichdivided into three directions-NNW,NNE and nearly SN direction,NNE-trending faultstructure is an important mine guide structure,near the fracture with schistose,phyllite,NNW-trending faults is an important host structure.The formation of ore veins is closely associated with felsite, diorite dykes andother shallow intrusive bodies,which produced on both sides of the Schistosity belt,The ore bearing rock is sandstone in er’shierzhan formation. Morphology of ore bodytakes vein in the main, by the control of northwest trending structure.Currently we found nine mineralized alteration zone, nine ore bodies in thestudy area. The main ore minerals in ore body are pyrite and arsenopyrite, with minorchalcopyrite, chalcocite, galena, sphalerite, limonite and magnetite content isminimal. Gangue minerals are mainly quartz, feldspar and a small amount ofcarbonate minerals. The main framework of the ore is mid-fine sand-like structure；structure is massive structure, disseminated structure. The surrounding rock alteration is mainly mid-low temperature alteration, such as silicification, pyrite, and sericitecarbonation.The rare-earth element models of the mining rock and minerals show theenrichment of light elements and the loss of heavy elements rightist type, overall thefractionation of light and heavy rare earth elements is obvious,HREE fractionation isweak； Abnomal of Eu was negative to almost no unusual characteristics,it isrelatively enrich Rb, K, Ba and chemically active incompatible elements U, Th, Pband other large LILE (LILEs), loss of high field strength elements Nb, P, Ti, etc.According to the analysis of the evolution of mining tectonic environment weknow that the formation environment of granite in the study area was formed in islandarc subduction-related tectonic environment；diorite formed in active continentalmargin area； sandstones formed in a continental island arc environment.Bysummarizing predecessors achievements, combined with the work done in this areaspeculated that the formation of the gold deposits undergone three majormineralization from the time evolution, early Jurassic sedimentary mineralization–mid-late Jurassic tectonic squeeze pressure mineralization-later late Jurassicmagmatic hydrothermal mineralization.As early as the early Jurassic,NNE-trendingfault extended and formed the upper Heilong-jiang basin,As the deposits subsidenceand compaction, since the center of the basin has more sediments than the edge, thecenter of the basin endure more pressure, thus fluid moves to the edge of the basin, inthis process, the fluid can dissolved substances which is benefit to mineralization outfrom the formation and became into ore-forming fluids, then the ore-forming fluidsstarted to transport, sedimentation, gold elements enrichment for the first time.In thelate Middle Jurassic-Early Late Jurassic, ancient Pacific plate oblique subduction inthe lower part of the Siberian plate, forming a overthrust structure and a lot of thrustfaults. Resulting in partial melting of oceanic crust and continental crust lithosphericstacking,shortening,thickening strongly,gold elements in Jurassic sandstonesmigration and enriched again,also provide a favorable space for mineralization.Laterin the Jurassic,environment started decompression and the Temperature increases,lithosphere produced massive fluid,supercritical fluid interaction with the mantle, mantle sulphides are oxidized and brought to the superficial of the earth’ ssurface,deep fluid mixing with shallow meteoric, provide a heat-activated for thegold mineralization and gold elements migrationed again, at last mineralizationed in afavorable enviroment.Based on the summarizing of metallogenic geological conditions, mineralizationenrichment regular, prospecting targets,combination with the main ore zone and itsperipheral Au soil anomaly proposed further prospecting direction. |
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