豫西南赤土店铅锌矿床地质、流体包裹体和S、Pb同位素地球化学特征

Geology,fluid inclusions and S,Pb isotopic geochemistry of the Chitudian Pb-Zn deposit in Luanchuan,Henan Province

豫西南栾川地区近年铅锌矿勘查取得显著进展,显示出良好的资源前景。赤土店铅锌矿床是新发现的铅锌矿之一,从控矿要素和矿体产状看,有两种矿化类型,即北西西向断裂构造控制的脉状铅锌矿,和石宝沟岩体外围矽卡岩带中的铅锌矿,并以前者为主。在空间上围绕斑岩体往外,构成近斑岩体发育矽卡岩型钼矿化,远斑岩体接触带的围岩矽卡岩中发育矽卡岩型多金属矿床,在斑岩体外围的断裂带中发育脉型铅锌银矿床的空间分布或分带规律。流体包裹体研究显示,成矿阶段温度较高(290～340℃),流体含大量CO2,并发生过流体不混溶分离。S同位素组成(0.20‰～8.30‰,平均3.93‰)显示,硫有深部岩浆(区内斑岩硫集中在2‰～4‰)和地层(分别集中在-13‰～-8‰和6‰～11‰两个区间)两种来源。被矿相学研究证实共生的方铅矿-闪锌矿矿物对计算出平衡温度为388.29℃,亦显示高温特征。Pb同位素组成(206Pb/204Pb=17.005～l7.953,207Pb/204Pb=15.414～15.587,208Pb/204Pb=37.948～39.03)反映,脉状铅锌矿成矿物质可能主要来自斑岩,部分来自地层。综合分析认为,赤土店矿床为与燕山期斑岩有关的铅锌矿,其脉状矿体为岩浆热液充填-交代成因类型。

Numerous Pb-Zn ore veins were recently found in Luanchuan area,southwestern Henan Province.These veins host enormously huge resources of Pb and Zn.The Chitudian ore deposit is one of these newly-discovered Pb-Zn deposits.Its Pb-Zn ore veins are controlled mainly by WNW-trending fractures.Apart from Pb-Zn ore veins,skarn with Pb-Zn mineralization was also discovered recently in the ore deposit,but the economic value is lower than that of the ore veins.Considering that weak Mo mineralization occurs in skarn close to the intrusion in the ore deposit,the authors put forward a mineralization zoning： Mo mineralization in skarn occurs close to the intrusion,Pb-Zn polymetallic mineralization in skarn occurs away from the intrusion,and Pb-Zn mineralization in veins is controlled by fractures much more distant but is around the periphery of the intrusion.Petrography,microthermometry and laser Raman spectrometry of primary fluid inclusions show abundant content of CO2 in the ore-forming fluid,immiscible separation of CO2 and H2O,and homogenization temperatures in a range of 290℃-340℃ during lead-zinc mineralization.δ34S of sulfides from the Chitudian lead-zinc ore deposit vary between-0.32‰ and 8.30‰（averagely 4.01‰）,and show a bimodal distribution with one peak consistent with the peaks of porphyry Mo-W deposits（2‰ to 4‰） and the other peak shifting the heavy δ34S values to the values close to S content of strata（12.43‰ to 18.63‰）,which may indicate that the S of lead-zinc ore veins have two main sources： a magmatic source and a stratatigraphic source.In addition,a pair of paragenetic sphalerite and galena from an ore vein gives a high sulfur isotope equilibrium temperature of 388.29℃.The Pb isotopic compositions of the Chitudian lead-zinc ore deposit are scattered in a relatively small range（206Pb/204Pb=17.005-l7.953,207Pb/204Pb=15.414-15.587,208Pb/204Pb=37.948-39.036）,which accords mainly with the zone defined by Yanshannian porphyry,suggesting that the metals might have been mainly derived from Yanshannian porphyry intrusions,and partialy from the strata.In conclusion,it is reasonable to hold that the Chitudian Pb-Zn deposit is genetically related to Yanshannian porphyry and the Pb-Zn ore veins are of magmatic hydrothermal filling-metasomatic genesis.