Mineralization Of Yangshan Gold Belt: Constraints From Texture And Constitution Of Gold-bearing Minerals

Yangshan gold belt is located in the southern part of Western Qinling orogenic belt and is an independent gold belt with the largest proven gold resources in Western Qinling.The mineralization is distinctive and is an ideal object to explore the gold mineralization through study of ore mineral paragenetic sequence and constitution.In this paper,we carried out petrography and geochemistry study,aiming at the texture and constitution of gold-bearing minerals of Yangshan gold belt and got results and recognition as follows.1.Host rocks of Yangshan gold belt are Devonian Sanhekou strata and the granitoids in this district.The mineralization styles are simple and are mainly fine disseminated(Pyrite-arsenopyrite granite porphyry ores,altered phyllite ores,altered metalimestone ores and altered metasandstone ores)and minor vein-veinlets style(Pyrite-arsenopyrite quartz vein ores and stibnite quartz vein ores).2.Major gold in Yangshan exists in sulfide as the form of invisible gold while minor is in late ore stage stibnite-quartz veins as native gold.The main gold bearing minerals are pyrite and arsenopyrite.In the main ore stage pyrite,there are plenty of dislocations but no nano particle of gold has been found.Combined with the information that in Au-As paragraph,all stages pyrite plot below the line of “solubility limit of Au in arsenian pyrite”,gold in pyrite is inferred to be structurally bound in solid solution.3.Among all stages of pyrite,Cu,Pb,Sb,Co,Ni,Bi and Mo are enriched in sedimentation-metamorphism period framboidal pyrite;there are most Ag and Te in the early ore stage pyrite(Py1);in main ore stage pyrite(Py2),there are most Au(388.33ppm)and As;late ore stage pyrite(Py3)enriches Mn and Zn most.Main ore stage arsenopyrite enriches Cu,Pb,Sb,Bi,Ag and Au(632.09ppm).There are some Au(0.12ppm),Ag,Cu,Zn,Cr and Sb in late ore stage stibnite.Based on characteristic of major elements and trace elements,it can be inferred that the enrichment of Au and As in main ore stage pyrite and arsenopyrite is because that As replaces S and Au+ replaces Fe2+.4.There is some Au(0.32ppm)in sedimentation-metamorphism period framboidal pyrite and it may provide gold and other element during later metamorphism.