The Relationship between Mineralization and the K-Silicate Zone in the Pulang Porphyry Deposit,Northwest Yunnan
The Pulang superlarge copper-gold deposit in Yunnan Province is located in the Zhongdian Island Arc in the southern part of the Yidun Island Arc in the Sanjiang Tethys tectonic domain in southwest China. The mineral assemblage of the K-silicate zone is mainly biotite+quartz+epidote+chlorite,which is obviously different from the typical K-feldspar+biotite+quartz assemblage. Propylitization significantly reworked the K-silicate zone of the Pulang deposit. XRD results show that the average contents of K-feldspar,plagioclase,quartz and biotite in the mineralized monzonite porphyry are 26.2％,26.7％,～16.1％ and～14.4％,respectively. Based on systematic field and indoor observations,the feldspar in the mineralized monzonite porphyry of the deposit is classified in this study into three types according to its formation mechanism,namely primary feldspar (including primary plagioclase:Pl1 and primary K-feldspar:Kfs1),secondary feldspar (Pl2 and Kfs2) and hydrothermal feldspar (Pl3 and Kfs3). Pl1 has high contents of aluminum (Al2O3=22.61％～27.27％) and calcium (CaO=3.68％～9.29％) and low contents of silicon (SiO2=56.09％～63.89％) and sodium (Na2O=6.31％～9.27％). Pl3 has high silicon (SiO2=67.07％～68.97％) and sodium (Na2O=11.02％～11.99％) contents. There is a mixing characteristic in the contents of SiO2,Al2O3,CaO and Na2O in Pl2. The contents of SiO2,K2O,Na2O and Al2O3 in Kfs1 and Kfs3 are 62.75％～64.69％,15.42％～16.89％,0.20％～1.03％ and 17.93％～19.19％,respectively. Compared to primary K-feldspar,the potassium content in secondary K-feldspar is decreased,indicating that potassium in the fluid may be relatively depleted. This may be the main reason for the weak development of K-feldspar in the K-silicate zone of the Pulang deposit. Propylitic alteration overlying the K-silicate zone,in particular the development of chalcopyrite±epidote±chlorite veins,has significantly improved the copper grade of the deposit and increased the copper reserves.
alteration zonationmineral geochemistrygenesis of depositK-silicate zoneporphyry typePulang depositnorthwest Yunnan
万方数据
维普
