滇东南南捞铜钨矿床S-Pb同位素特征

Sulfur and Lead Isotopic Geochemistry of Nanlao Cu-W Deposit in Southeastern Yunnan Province,China

南捞是近年来滇东南老君山西北部地区新发现的矽卡岩铜钨矿床,由田房、布忙和高井槽等矿段组成,已探明铜钨资源储量均达到中型。为了查明其矿床成因,开展了矿床地质和S-Pb同位素等研究。结果表明,田房矿段中硫化物以似层状毒砂、脉状黄铜矿和黄铁矿等硫化物为主,其中,黄铜矿δ34SCDT值在4.05‰11.02‰之间,呈塔式分布,暗示矿石S以岩浆或深部热液为主,并可能受地壳混染。不同金属矿物Pb同位素差异显著,具多来源特征。田房、布忙矿段中各矿石单矿物铅同位素组成206Pb/204Pb、207Pb/204Pb和208Pb/204Pb分别为:白钨矿,18.41218.761、15.60015.789、38.50439.094;黄铜矿,18.30118.345、15.65215.696、38.48838.564;黄铁矿,17.87118.972、15.41516.037、38.00839.769;毒砂,17.91718.093、15.52415.650、38.00438.283。对比研究表明,矿石与寒武系片岩和大理岩具有不同的Pb同位素组成,与加里东期南捞片麻岩或燕山期老君山花岗岩有相似分布范围。结合年代学研究成果,本文认为南捞Cu-W矿床的矿石Pb及其成矿金属物质可能起源于加里东期岩浆作用,其成矿作用与加里东期花岗岩作用更为密切,南捞片麻岩与寒武系的内外接触带附近,尤其是高温矿物组合部位可能是矿化的有利部位,该类矿化在该区找矿潜力巨大。

Nanlao Cu-W deposit,one of newly discovered skarn deposits,is located in the north-western of Laojunshan district,and its Cu and W reserves reach the middle scale. To clarify its ore genesis,an investigation with geological feature and sulfur and lead isotope on this deposit is carried out. Sulfur isotopic compositions of sulfides have a relatively uniform δ34 SCDTvalue ranging from 4. 05‰ to 11. 02‰,suggesting a mixture of magmatic and strata sulfur origin. Radioactive lead in different ore minerals is significantly different, which shows a multi-source character. The isotopic composition of lead ranges in206 Pb/204 Pb,207 Pb/204 Pb,and208 Pb/204 Pb are 18. 412-18. 761,15. 600-15. 789,and 38. 504-39. 094 for scheelite,18. 301-18. 345,15. 652-15. 696,and 38. 488-38. 564 for chalcopyrite,17. 871-18. 972,15. 415-16. 037,and 38. 008-39. 769 for pyrite,and 17. 917-18. 093,15. 524-15. 650,and 38. 004-38. 283 for arsenopyrite,respectively. In comparison,they are obviously different from that of the Cambrian,but consistent with that of the Caledonian or Late Yanshanian magmatic rocks,combined withgeochronology research result,hinting to the Pb and ore-forming metals are probably derived from the Caledonian magmatism. It is a mesothermal to hyperthermal deposit related to the Caledonian magmatism,contact belt between Nanlao gneiss and the Cambrian is the favourable setting for ore formation.