| This paper chose the Nichitai gold deposit which located in the east section of Eastern Kunlun mountains,and the Pianyanzi gold deposit that located in the Dadu River Valley,which are both orogenic gold deposits as the research object.Based on detailed study to the geological characteristics and occurrence state of Au between the two deposits,with analysis of the two deposits,the paper summarizes the geological characteristics and occurrence state of Au of the two deposits.Nachitai gold deposit locates in the middle of east part of Eastern Kunlun,and its tectonic position is between Middle-Kunlun fault belt and South-Kunlun fault belt,that is compound collage belt in south of Eastern Kunlun.The exposed strata in the mining area is mainly Wanbaogou Group in middle-late Proterozoic.The lithology is mainly dolomite,limestone and epimetamorphic detrital rock.The mineral composition of the deposit is relatively simple.The metalic minerals are mainly arsenopyrite and pyrite,and arsenopyrite is primary ore mineral,while other secondly ore minerals are magnetite and limonite.The nonmetalic minerals are mainly quartz,calcite,dolomite,illite,etc.The main ore structure are idiomorphic-hypidiomorphic tecture,allotriomorphic granular texture,etching texture and crumpled texture.The main ore structure are massive structure,sparse disseminated structure,and stripped structure.According to the degree of oxidation,the ore types in the area can be divided into primary ore and oxidized ore.The main type of primary ore is disseminated ore,which gold bearing pyrite and arsenopyrite are both fine grained disseminated distribution.Oxidized ore is mainly tanned altered cataclastic type,with little gold.The country rock alteration of the mining area are mainly:arsenopyritization,pyritization,carbonatization silification,ferritization and sericitization.Nachitai gold deposit is a middle-low temperature hydrothermal orogenic type deposits.Pianyanzi mining area is located in the Kang Dian earth axis north rim,and in Huashan syncline east yard of Kangding great fault north west outcropping strata inthe mining area have DengyingFormation of upper Sinian series,Hanfengya Group in Devonian and The Upper Triassic-lower jurassic,additionally in deposits in the east south which have Lengzhuguan group of Kangding formation of pre-Sinian system.The main orebody mainly produces in the Dengying formation whose lithology is mainly rich algal dolomite.Ore mineral compositions are complex.Metalic minerals are mainly have pyrite,tetrahedrite,galena,geocronite,bournonite and other sulfides,sulfosalts,and malachite,covellite,braunite,anglesite and other secondary oxide.Main nonmetallic minerals are sellaite,quartz,bruiachite,calcite and so on.The sellaite is the uppermost ore mineral,secondly are pyrite tetrahedrite and geocronite et al.Ore texture mainly have automorphic-hypautomorphic crystal structure,xenomorphic granular texture,etching texture,porphyritic-like texture,prikilitic texture,skeletal texture,explanation graphic texture.Structure of oers have clumpy structure,dense disseminated structure,scattered disseminated structure,mottled structure and multihole honeycombed structure.Mining of ore grade is mainly influenced by the ore type of restriction.The main ore types are type of sellaite,polymetallic sulphide(sulfosalt)-sellaite-type of quarte ore,Pyrite-quartz type and other type of surrounding rock of mineralization.The oxidized ore mainly have the type of hydrosiderite,and high alloy content.Wall-rock alteration mainly have silication,pyritization,sericitization,carbonation and so on,The silicification and pyritization have close relationship with gold mineralization.The type of Pianyanzi deposit is Orogenic-type brittle-ductile shear zone gold deposits.By observing the study suggests,the ore-forming process can be divided into two sessions:Hydrothermal mineralization stage and Supergene oxidation Period.The Hydrothermal mineralization stage also can be further divided into four stages of mineralization:(?)pyrite-quarte phase.(?)gold-sellaite,Fluorite Phase(?)gold – sulphide-sulfosalt minerals-quarte phase,(?)Pyrite – dolomite-quarte phase.Through the means of microscope microscopic observation,phase analysis,scanning electron microscopy,electron probe test analysis research show the occurrence state of the Nachitai deposit is mainly independent minerals.Gold minerals are dominantly native gold,quite high fineness.the mineral in deposit are generally small and the particle size belong to microscopic gold which distributed with a star-shaped.The particle morphology of gold is more complicated,poor euhedral crystal degree and occured primarily in a vermicular,dendritic and harbor shaped.According to the existence place,the existing way and the relationship withgold-bearing mineral,the distribution state of gold are divided in two kinds: inclusion gold and fissure gold.The main distribution of gold is inclusion gold which hosting in as-bearing pyrite and arsenopyrite.Gold-bearing mineral are dominantly arsenopyrite and subordinately as-bearing pyrite.The Au in Pianyanzi gold deposit hosts in gold-bearing minerals in the form of independent mineral mainly.Besides,Au-Ag solid solution and gold compound are also the occurrence states in Pianyanzi gold deposit.In the area,gold mineral includes native gold,,chromium-containing native gold and calaverite.the quality of gold is very good.The types of gold mineral are natural gold and electrum.The particle granularity of gold mineral in ore is large span,and it has been found from several ?m to 0.3mm.So its granularity should belongs to minding and micro-gold.The particle morphology of gold mineral is complicated and various which is(oval)round granular,dendritic,veins and other irregular.According to the observation and research,the Disseminated state of gold in the ore in this area can be divided into including gold,fissure gold and crystal fractured gold.As a typical sellaite type gold deposit,the most important gold-bearing minerals in ore is sellaite in Pianyanzi gold deposit,followed by pyrite,tetrahedrite,geocronite and other polymetallic sulfide,sulfosalt minerals,in addition to quartz and oxidation products of limonite.There are two stages of mineralization associated with gold in Nachitai deposit,while it occurs as four stages of superimposed mineralization in Pianyanzi deposit. |
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