The Genesis of the Xiaohongshilazi Pb-Zn(Ag)deposit:Evidence from S-Pb isotopes and elemental characteristics
The Xiaohongshilazi Pb-Zn(Ag)deposit is a representative medium-sized deposit within the Jizhong-Yanbian copper-nickel polymetallic metallogenic belt,previous views for deposit types mainly include Volcanogenic Massive Sulfide(VMS)-type,medium-low temperature hydrothermal vein type,and exhalative deposits overprinted by hydrothermal fluid,which seriously restricts the understanding of mineralization and prospecting within orefield and the in region.In this paper,in-situ elemental and S-Pb isotopic analyses were conducted for metal sulfide and whole-rock S isotope analysis for ore-bearing wall-rocks.The Fe-Zn contents(4.48％～10.33％,53.67％～62.12％)of sphalerite is consistent with those of medium-temperature hydrothermal deposits(3％～10％,50％～60％,mineralization temperature about 200℃),the Zn/Cd ratios(53.68～76.75)also indicate medium-low temperature mineralization(high temperature:Zn/Cd＞500;low temperature:Zn/Cd＜250),and the corresponding temperature for Ga/Ge ratios of sphalerite in lg(Ga/Ge)-T diagram is about 100～180℃,the aforementioned temperature ranges are basically consistent with the homogenization temperature of fluid inclusion reported in previous literatures(90～250℃).The Zn/Cd ratios(53.68～76.75)and Cd contents(7577 × 10-6～11266 × 10-6)of sphalerite are in agreement with the characteristics of Mississippi Vally-Type(MVT)deposit;the Fe/S ratio of pyrite(0.76～1.29,the average value is 0.89)is close to the theoretical value for typical MVT deposits(0.88).The δ34SV-CDT values of metal sulfide range from-9.6‰ to-0.5‰,and are generally negative;and the δ34SV-CDT values of the ore-bearing wall-rocks are from-8.5‰ to 4.2‰,there is a large overlap(mainly concentrated in-9.0‰ to-2.0‰),which indicates that the wall-rocks provide reduced sulfur,and the ancient basement may provide some light sulfurs.Pb isotope ratios of metal sulfide are 206Pb/204Pb=18.30～18.39,207Pb/204Pb=15.61～15.63,208Pb/204Pb=38.38～38.44,which imply that lead is mix sourced,the ore-forming materials probably originated from the upper crust and orogenic belts.The model age calculation shows that the metamorphic rocks in the Upper Archean Wulashan Group may be the initial source lead.To sum up,the geochemical characteristics of the Xiaohongshilazi Pb-Zn(Ag)deposit are basically consistent with the MVT-type deposit,yet there are little differences in geological characteristics,thus it is speculated as an MVT-like deposit.
The Xiaohongshilazi depositS-Pb isotopesElemental analysisOre genesisMVT-like deposit
万方数据
维普
