GEOLOGICAL FEATURES AND CONTROLLING FACTORS OF LEAD-ZINC DEPOSITS IN YESHUIHE,GANSU PROVINCE
Zhang Lianchang (Xi'an College of Geology)
The Yeshuihe lead-zinc deposits are located in the southwest part of the Xicheng orefield in the west Qinling.The host rocks are the third member of the middle Debonian Guangjingbar Formation. They are composed of limestone, phyllite etc., and their ore-bearing structures are mainly the interstratified fracture zone of the limestone, the contract zone of the lim-estonephyllite and the anticlial axis. Concerning the orebodies, their scale is small, but their quantity is great. Their distribution is in group. The ore-body attitude is probably in conformity with the wallrock one, but it is unconformity under a microscope.The mineralogical compositions are simple.The fabrics of the ore are mainly vein, disseminated and brecciated. The wallrock alteration is obvious.There are mainly silification and carbonatization in it. The study of microelements in the mining area layers indicates that there is not any source bed in the mining area. The constituent range of the sulfide deposit isotope is 6.7…18.0‰.The source of the sulphur is thought to be related to the sulfate in the sea water. Lead in the deposit is normal.The author considered that the source of the metals came mainly from subterrane.Based on fluid inclusions and hydrogen-oxygen isotopes, the ore-forming fluid is meta-morphic solusion. Through a synthetical study of regional geology and deposit geology, the author believes that the Yeshuihe deposit belongs to the epigenetic strata-bound deposit in Indo-China epoch. The main controlling fectors of the ore deposit are structure, lithology, stratigraphy and hydrothermal events, among which structure plays a leading role.