K-FELDSPAR RAPAKIVI TEXTURE AND ITS IMPLICATIONS, XIFANPING PORPHYRY COPPER DEPOSIT, SICHUAN

The Xifanping porphyry copper deposit is located in the southwestern Sichuan Province. The host rock is quartz monzonite. There are a lot of K feldspar rapakivi texture in this deposit. The characters of this texture are: (1) The width of the K feldspar rim is an inverse measure of the size of plagioclase porphyritic crystal; (2) The composition of orthoclase in K feldspar varies from 35.88% to 63.28%; (3) Some of the K feldspar replaces plagioclase porphyritic crystal from the edge of the core of the deposit. All these demonstrate that this kind of texture is developed by interaction between ore forming fluids secreted from magma and plagioclase phanerocryst. And the authors find many mafic minerals, such as hornblende and biotite, react with the fluids too during the interaction. The analyses of igneous and hydrothermal biotite suggest that a large amount of copper are leached from these minerals and added into the fluids. So this process promote the mineralization opportunity of porphyry system.