Study On The Typomorphic Features Of Sphalerite In Ores From Zha Xikang Pb-Zn Polymetallic Deposit,Tibet,China

Located in the western part of Longzi county,the Zhaxikang lead-zinc polymetallic deposit isthe largest Pb-Zn polymetallic deposit in the Tethyan Himalaya Sb-Au polymetallic metallogenic belt.The Zhaxikang Deposit is greatly controversial in metallogenesis and genetic type, whichcontains underground thermal spring type, the sedimentary exhalative and hydrothermal modification type, the magmatic hydrothermal type, superimposed deformation type, and so on. According to the structural and textural characteristics difference of sphalerie, and combining field geological investigation and optical microscopy identification mineral assemblage of sphalerite, we research typomorphic of each stage of sphalerite by usingX-ray powder diffraction(XRD)?electron probe microanalysis(EPMA) and Inductively Coupled Plasma Mass Spectrometry(ICP-MS). Sphalerite in Zhaxikang can be divided into three stages: The stage I sphalerite had dark color and coarse-grainwhose unit cell parameters range from 5.4140 ? to 5.4298 ?, with an average of 5.4253 ?. The content of Fe and In is rich,while poor in Cd and Ga.The mineral crystal had obviously deformation and fracture. The mineral assemblages are sphalerite-galena-pyrite±chalcopyritequartz-Fe-Mn carbonate.The stage II sphalerite had a relatively smaller particles, and was dark brown in color. The content of Fe and In is lower, Cd and Ga varies greatly. Its paragenetic minerals are sphalerite- jamesonite- Fe-Mn carbonate, pyrite- galena ± quartz±arsenopyrite. This stage can be subdivided into three generations:The ?-1 generation as the core, containing a small amount of jamesonite inclusions. The II-2 generation as the inner ring, containing a large amount of jamesonite inclusions which were directionally aligned had complete crystal shape. The II-3 generation as the outer ring, completely free of jamesonite inclusions.The stage ? sphalerite had a relatively smallest particles, and was light brown in color and coarse-grainwhose unit cell parameters range from 5.4174 ? to 5.4205 ?, with an average of 5.4229 ?. The content of Ga and Cd is rich,while poor in Fe and In. The mineral assemblages are Quartz- arsenopyrite-pyrite±stibnite±galena.From the stage?, ? to the stage ?, the grain size of sphalerite crystal became smaller and the color becomes shallower gradually.the crystal cell parameters on the structure became smaller.the content of Fe and In decreased, while the content of Cd and Ga increased, respectively. These characteristics indicates that the typomorphic of sphalerite is closely related to the ore-forming temperature and pressure, etc.Through Zn/Cd and Ga/In ratios, and logGa/Ge- T phase diagram of sphalerite from each stage, we consider that the formation temperature of sphalerite ranges between 225 and 255 ?, which belongs to the medium temperature environment. In the logIn- logGa discriminant diagrams, the ore-forming hydrothermal fluid of sphalerite from the stage ?is related to magmatism, while the stage ? and stage ? are related to the magma mixed with the meteoric waters.