Study On The Mineralization Of Zhaishang Super Large Gold Deposit In Min County, Gansu

This paper depends on the general investigation items of No.5Gold Geological Party of ChinesePeople’s Armed Police Force such as <Reconnaissance Survey of Zhaishang Gold Deposit, Min countyGanSu province>,<Study on Genesis of Zhaishang Gold deposit>,<Study on Mode of Occurrence ofGold in Zhaishang Gold Deposit, Min county, Gansu province>.On the basis of previous researches, this study intends to focus on the research of distribution andmigration of gold element, as well as the occurrence regularity of gold minerals in Zhaishang gold deposit.Furtherly, it studies on the spatio-temporal distribution of gold veins and the forming mechanism of golddeposits. All these studies will provide theory guiding for ore-exploring.This project was carried out according to some theories about metallogenic system, geochemical anomalies,similar analogy and the ideal model of superimposed structure halos.To complete this project, we adopteddifferent methods according to different aspects. Firstly, We collected a great deal of research data andachievments of geology and geochemistry about Zhaishang deposit. Depending on these data, wesystematically analyzed the spatial distribution of gold element and ploted some correlated maps. Secondly,we devote enormous work on the occurrence of gold in various gold ores and minerals by opticalmicroscope, electron probe, X-driffraction etc.Then we summarized and classified the categories of metalmineral in Zhaishang deposit. Thirdly, we detailedly analyzed the spatio-temporal relationship betweenthe gold veins and major geological factors as strata system, tectonic and structural setting, plutons anddykes etc. This analysis afforded the possibilities of summarizing the mineralization and metallogenesis.Fourthly, we systematically carried out some test and analysis such as the major and trace elements, stableisotope and fluid inclusions. Based on these analysis results, we tentatively discussed the metallogenesisand ore-forming process.Based on synthesizing all these research work in Zhaishang gold deposit, We can make severalconclusions beneath.1． The geological background is favourable to the enrichment of gold.Zhai-shang deposit lies in the west of Shanyang-Lixian fault belt and is controlled by secondaryfaults. The strata around Zhaishang deposit is Devonian-Permian system and dominant ore-bearinghost rock is “carbon-silicon” slate, which can absorb gold element. The formation of gold mineralizationis closely associated with strong magmatic activities and mid-acidic dike rock.2． The formation of Zhaishang deposit had undergo three periods and four stages.Thirty gold veins and Twenty-six ore bodies have been distinguished and the total amount of gold resources of333and334reached13,3000kg in Zhaishang deposit. Its ore-forming process has undergoedsedimentary period, tectonic-hydrothermalism superimposed ore-forming period and supergenesis period.The tectonic-hydrothermalism superimposed ore-forming period is mainly studied and it can be dividedinto four stages. Furtherly, the main stage of polymetal sulphide-gold-quartz is divided intodouble-sulphide and sulphide substage, sulphosalt substage and telluride substage.3.GEOCHEMICAL ANOMALIES indicates that the mineralization of gold displays characteristiczonation.The1:200,000and1:50,000map of stream-sediment geochemical anomaly distinctly reveal that theseanomalies generally distribute in shape of cluster, band and group. The1:10000soil geochemical anomaliesspread on north-west which is accordant with the regional fault structure. Rock primary halo indicates thatthe contents of Au, Ag, As, Sb in cataclastic and carbonaceous slates are far high than that in feldsparsquartz sandstone and calc-slate. The trace element research indicate that the distribution of ore-formingelements are not uniformity and concentrate in certain position along the gold veins.4. The Pb-bearing sulphosalt and telluride was identified and the character of gold minerals wasstudied for the first time.In virtue of microscope and electron probe, we studied the metallic minerals and divided them intofive types of sulfide, double sulfide, sulfsalt, telluride and oxygen-containing mineral. In these minerals,pyrite displays obvious mineralogic character and different content of gold. Pyrite grains in wall rock arealways small and present with strawberry-shaped, berry ball-shaped, ball-shaped and cube-shaped etc.However, the pyrite grains in gold ore are relatively coarse and present with cube-shaped,pyritohedron-shaped, allotriomorphic-granular texture, veinlet and net-veined texture. Among thesevarious pyrites, the strawberry-shaped and the cube-shaped pyrite contain little gold and the other typescontain more gold. The sulfosalt in Zhaishang deposit was studied for the first time and divided intoCu-bearing sulfosalt and Pb-bearing sulfosalt. The latter which include jamesonite, arsonboulangerite andmeneghinite was firstly identified in Zhaishang deposit and, more important, they are importantgold-bearing mineral and can preferably indicate presence of the high grade ore body.we regard that sulfosalt mineral is closely associated with the gold ore of Zhaishang, it is one of thegold bearing mineral and it also indicate the high grade ore block.Similarly, telluride was identified for the first time. They are Te-Au-Ag mineral, Te-Ag-Au mineral,Te-Hg mineral.Based on the mineralogic research, We maked the conclusion that the gold ore of Zhaishang deposit formed in low temperature and low pressure environment. Its formation include several stages: enrichmentin sediment, the formation of crystal gold in sulfide section, accompanying with sulfosalt minerals, theformation of gold-bearing telluride, the native gold in sulphate mineral.5Zhaishang gold deposit is closely controlled by stratum, structure, magmatic rock.Zhaishang gold deposit lies in the basin of Min-Li county, the formation of gold ore was controlled byDevonian-Permian system. The inverse S-shaped anticline and north-west fault–shear zone provide spacefor conveying and precipitation of gold-bearing minerals. Because of the active structure and magamatichydrothermalism, the ore-forming fluid can fully react with wall rock，and furtherly migrate and precipitategold-bearing minerals.6. Nonuniform enrichment of gold exists widely in the gold ore belt, gold veins and gold body.Two large gold ore belts, namely, the south and the north gold ore belts, exist in Zhaishang districtand each belt has same character that gold always is enriched in certain places. For example, the north goldore belt can be divided into four mineralization-enrichment parts, they are Wanzulu ore block, the backMagou ore block, Laganliang ore block and the eastern Nana ranch ore block. Samely, this character canalso be observed along the strike of every gold veins.7. The formation of Zhaishang gold deposit is related to migration-differentiation-precipitation process ofore-forming fluid which is formed by mingling of meteoric water and magmatic hydrothermal..During later Indo-Chinese epoch, magmatism extensively existed in the Min-Li area. The mingling ofupward diffusing magmatic hydrothermal and downward infiltrating meteoric water produced abundantore-forming fluid. Then, in regional compressive stress conditon, the ore-forming fluid invaded, penetratedand diffused along the north-west fault. In this process, delamination-infiltration anddelamination-diffusion were the main migration ways of ore-forming fluid. When the physical andchemical condition changed, precipitation, crystallization and accumulation of gold-bearing mineralsultimately occurred in appropriate place.