Mineralogy and Sr-Nd-Pb isotopic compositions of quartz diorite in Tonglushan deposit,Hubei Province
ZHAO HaiJie1,MAO JingWen1,XIANG JunFeng1,ZHOU ZhengHua1,WEI KeTao2 and KE YuFu21. MLR Key Laboratory of Metallogeny and Mineral Assessment,Institute of Mineral Resources,Chinese Academy of Geological Sciences,Beijing100037,China2. Geological Team of Southeast Hubei Province,Daye 435100,China
Tonglushan skarn Cu-Fe (Au) deposit is located in the westernmost Daye district of MYLRB. A geochemical and Sr-Nd-Pb isotopic studies were carried out for the Tonglushan quartz diorite,which is closely related to the deposit. The compositions of plagioclases show they are oligoclase (An=21~31). Amphiboles belong to magnesihornblend,have characteristics of low Ti (0.2) and high Mg/(Mg+Fe) (0.5). MF values of biotites vary from 0.58 to 0.66,suggesting biotites are Mg-riched. The rocks are characterized by SiO2 and alkaline compositions between 58.86% and 67.71%,and from 5.67% to 9.63%,respectively,enrichment in light rare earth elements (LREE) and large ion lithophile elements (LILE),but relative depletion in Nb、Ta、Ti elements. They have initial Nd (εNd(t)=-7.65 ~-3.44),Sr ((87Sr/86Sr)i=0.7055~0.7069) and Pb ((206Pb/204Pb)i=17.66~18.00,(207Pb/204Pb)i=15.49~15.56,(208Pb/204Pb)i=37.73~38.19). Comparative analysis demonstrates that Tonglushan and Yangxin intrusions originated from homologous magma. The magma was from the enrich mantle of about 40km deep and at about 889℃ temperature. Amphiboles and biotite thermometers estimate magma crystallized at 650~800℃ and 500~630℃ temperatures,under 1.49kbar pressure,corresponds to the emplacement depth of about 4.9km. Magma has a high oxygen fugacity (fo2) condition,in favor of Cu,Fe and Au ore-forming elements into melt,may be related to plate subduction.