Comparison of mineral chemistry of biotite between Caledonian Yuechengling and western Dupangling granites in northern Guangxi and its implication for petrogenesis and mineralization
The Caledonian Yuechengling and western Dupangling granites,both located in the western Nanling Range of W-Sn-Cu metallogenic belt,but have different mineralizations.The Yuechengling biotite is mainly composed of iron biotite formed at a relatively low crystallization temperature(avg.,531℃)and high pressure(avg.,277 MPa),showing relatively poor features of magnesium(MgO 8.05%,XMg=0.39),but relatively rich in iron(FeOT 22.4%,IFe=0.61)and aluminum(Al2O3 16.8%),whereas the western Dupangling biotite is pri-mary magnesium biotite formed at a higher crystallization temperature(avg.,687℃)and lower pressure(avg.,194 MPa),showing features of a relatively rich magnesium(MgO 11.9%,XMg=0.56),but poor in iron(FeOT 17.0%,IFe=0.45)and aluminum(Al2O3 15.5%).Together with petrography observations and the published whole rock data,it indicates that the Yuechengling granites are S-type granite,probably formed via partial melting of metapelites in the upper continental crust contaminated,and the western Dupangling granites are more like I-S type granite formed via partial melting of crust-mantle mixed source.Further research indicates that the Yuech-engling granites probably show magmatic features in favor of tungsten and a certain copper ore-forming,such as crust-source,lower oxygen fugacity(log fO2=23.6),high fluorin(F 1.10%,IV(F)=1.62,IV(F/Cl)=6.00,log(fH2O/fHF)fluid=4.78),high iron coefficient(XFe=0.58)and high magma fractionation(log(fH2O/fHCl)fluid=5.10,log(fHF/fHCl)fluid=0.10),and the western Dupangling granites probably have characteristics of crust-mantle mixed source,high oxygen fugacity(log fO2=17.3),high chlorine(Cl 0.04%,log(fHF/fHCl)fluid=0.36),moderate iron coefficient(XFe=0.41)and low magmatic fractionation(log(fH2O/fHCl)fluid=4.41,log(fHF/fHCl)fluid=0.36),which are only conducive for iron ore-forming in small scale.Therefore,petrogenesis and magmatic conditions may be the important factors restricting the metallogenetic ability of different types of metals in Yuechengling and western Dupanglingxi granites.
biotitemineral chemistryoxygen fugacitypetrogenesis and mineralizationCaledonian granitenorthern Guangxi
国家科技期刊平台
NSTL
万方数据
