摘要
矿床成矿物质的来源是长期以来研究矿床地质的人们十分关注的问题。随着同位素测试技术的发展和同位素地质应用的日益扩大,硫化物及硫酸盐的硫和碳酸盐的碳、氧同位素组成的研究,是解释有关矿床成因及成矿物质来源的有用工具。本文对一种新的钼矿类型——黄龙铺碳酸岩脉型钼(铅)矿床的硫、碳、氧同位素组成及其特征进行了研究,并据此探讨该矿床成矿物质来源。
The molybdenum(lead)deposits of carbonatite vein-type of Huanglongpu occur in the Yushan fault-upwarping area bordering the Sino-Korean Paraplatform.The orecontrolling structure is a NW-trending deep fracture zone,Whereas the ore bodies are distributed chiefly along the intersection of the NE-NNE and NW-trending faults.The ore bodies are composed mainly of large vein-groups occurring in metaspilite of the Proterozoic Xionger Group.The mineralogical composition of the ore bodies is rather complex.Ore minerals are chiefly pyrite,molybdenite and galena,with a small amount of magnetite,hematite,sphalerite,chalcopyrite,plumbodavidite,betafite,yttroeschynite,bastnasite,orthite,wulfenite,monazite and leucoxene.Gangue minerals are essentially calcite,quartz and barytocelestine.Following the formation of calcite,there occur mineralization and enrichment of molybdenum and lead.The mineralization age of the deposits is 206 m.y.,earlier than that of granite(128 m.y.)and granoporphyry(124 m.y.)found in this district.The sulfur isotope composition of 25 sulfide and 8 sulfate minerals,as well as the carbon and oxygen isotope composition of 8 calcites have been studied.The data obtained show that theδS^(34)values of sulfide and sulfate minerals from the deposits range from-14.7 to+7.9 per mil.All the sulfide minerals have negativeδS^(34)values(ranging from-4 to-14.7‰)and are characterized by light sulfur isotopes.However,sulfate minerals have positiveδS^(34)values(ranging from+4.7 to+7.9‰),and are characterized by being richer in heavy sulfur isotopes.It indicates the allocation of sulfur isotopes in different minerals and variation in the redox conditions during the formation of ores.And carbon and oxygen isotopes in calcites are uniform and stable,with theirδC^(18)values ranging from-6.6 to-7.0 per mil,and theδO^(18)values,from+8.5 to+9.5 per mil.At the same time,pyrrhotite and.graphite are absent in the ores,reflecting a higher oxygen fugacity of the ore-forming environment.By means of detailed study,total sulfur and carbon values of the ore fluid of the deposits have been obtained.TheδS_(∑S)^(34)is+1.0 per mil,and theδC_(∑C)^(18)is—5.0 per mil,respectively,and the initial Sr^(87)/Sr^(86)ratio of calcite is 0.706.On the basis of these data,the authors have come to the conclusion that sulfur and carbon of the deposits were derived from the upper mantle source.The calculatedδO_(H_(2)O)^(18)values of ore-forming fluid at 280—290℃in equilibrium with calcites are+2.8 to+4.12 per mil,which is lower thanδO_(H_(2)O)^(18)values of primary magmatic water.This may be due to the mixture of deepseated fluid with underground water.Therefore,one may suppose that ore-forming metals,such as Mo and Pb,except for part of them,have the same source as sulfur and carbon do,but the possibility of some Mo and Pb being derived from country rocks be ruled out.The variation of fO_(2)and pH during the ore-formation may be a main factor in the precipitation of ores.
作者
黄典豪
王义昌
聂凤军
江秀杰
Huang Dianhao;Wang Yichang;Nie Fengjun;Jiang Xiujie(Institute of Mineral Deposits,Chinese Acade my of Geological Sciences;No.13 Geological Party,Shaanxi)
出处
《地质学报》
1984年第3期252-264,共13页
Acta Geologica Sinica
