CHARACTERISTICS OF ALTERATION AND GENESIS OF THE JINCHANGYU GOLD DEPOSIT

Characteristics of the alteration and zonation of gold deposits play an important role in acquiring the composition and feature of ore-forming fluid,the contribution of wall rocks and the origin of gold deposits.According to the mineral association,composition and their variations in Jinchangyu gold-deposit,four alteration zones can be recognized away from gold-bearing quartz zones,i.e.,weakly altered zone,chloritized zone,sericitized zone and silicifized zone.The mass balance analysis for the altered rocks of the Jinchangyu gold deposit shows that Al₂O₃ has obvious immobility.The chemical composition of the altered rocks is normalized with the content of Al₂O₃ in the weakest altered rock,and the standardized corresponding composition differences between the weakest altered rock and other altered rocks indicate the composition variations during the interaction between wall rocks and the ore-forming fluids.The calculating results suggest that the contents of SiO₂,FeO,CaO,MgO,Sr,Ba,Sc,Zn,Ga,Ta,Au,Ag,Y and Pb in gold-bearing quartz veins are much higher than those in the altered rocks,and SiO 2,Sr and Ba in the altered rocks have an obvious increase relatively to their original rocks in contrary to FeO,CaO,MgO,Sc,V,Y,Pb,P and Cu.The composition of the altered rocks from the weakly altered rocks to gold-bearing quartz veins in the Jinchangyu gold deposit varies irregularly.The composition variation in the altered rocks is not related to the increase of the corresponding composition in the gold bearing vein,and it has minor effects on the composition of ore forming fluid.Despite the existence of some genetic relation,the gold bearing quartz veins and altered wall rocks would form in different conditions.During alteration,wall rocks might release too limited ore-forming elements in quantity to form a large scale gold deposit.Hence,the ore-forming material of the Jinchangyu gold deposit should be mainly derived from deep-source ore-forming fluid.