Abstract:

The Pulang porphyry copper deposit occurs in the southern segment of the Indosinian YidunZhongdian islandarc belt and is a largesized copper deposit discovered in China in recent years. This deposit has a typical alteration zonation of porphyry copper deposit, varying from potash and silicic alteration in the inner through phyllic alteration in the middle to propylitic alteration in the outer. This paper presents new petrographic observations, homogeneous temperature measurements and laser Raman microprobe analyses of fluid inclusions in quartz grains from the three alteration zones of the deposit. It is shown that the average homogeneous temperature of oreforming fluid decreases from 274.4 ℃ through 236.4 ℃ to 203.0 ℃ with outward variation of alteration zone and indicates an evident temperature decreasing trend, which may be resulted from partial participation of meteoric water in mineralization. The laser Raman microprobe analyzing data are consistent with existence of oreforming fluid with high sulfur and chlorine during mineralization in the deposit, and support occurrence of intensive mineralization caused by this high temperature oreforming fluid with high sulfur and chlorine in the potash and silicic and phyllic alteration zones.

Key words: porphyry copper deposit, alteration zonation, ore-forming fluid, Pulang in Yunnan Province