摘要
科洛金矿床位于黑龙江省嫩江—黑河构造混杂岩带中,为一正在勘查的中型金矿床。前人研究认为该矿床为一中温、富水、低盐度的韧性剪切带型金矿床。但随着勘查工作的持续开展,新发现了大量含多金属硫化物的石英脉型矿石。为进一步明确该矿床成因,对科洛金矿床内韧性变形和浸染状-团块状两种不同产状黄铁矿进行了系统的成分标型及稳定同位素特征研究。结果表明:韧性变形黄铁矿较浸染-团块状黄铁矿的S/Fe值低,Au、Ag、Co含量高,As含量低,总体显示韧性变形黄铁矿相对贫硫;黄铁矿微量元素显示两类黄铁矿REE具有相似的地球化学特征,整体呈轻稀土富集、重稀土亏损的"右倾"式稀土配分模式。稀土元素总量为17.00×10^-6~66.95×10^-6,韧性变形黄铁矿含量明显偏低,LREE/HREE值为5.25~12.50,相对较稳定。Y/Ho值与地幔和地壳重合范围较多,Zr/Hf值、Nb/Ta值变化范围较大,显示成矿环境不稳定;黄铁矿^3He含量为2.405×10^-13~10.811×10^-13,^4He含量为3.35×10^-7~4.99×10^-7,^3He-^4He图和R/Ra-40Ar/36Ar图显示成矿流体有以地幔为主的壳幔混源特征,成矿过程应有大气降水的参与;黄铁矿δ^34S变化范围小,集中在+2.3‰^+7.6‰(韧性变形黄铁矿δ^34S平均值偏低),稍正向偏离陨石硫特征;黄铁矿的^206Pb/^204Pb=18.157~18.211;^207Pb/^204Pb=15.542~15.594;^208Pb/^204Pb=38.032~38.218(韧性变形黄铁矿的^206Pb/^204Pb、^207Pb/^204Pb、^208Pb/^204Pb平均值偏低),均显示与造山作用关系密切。利用黄铁矿化学成分特征元素Co/Ni值及Co-Ni成因判别图解认为科洛金矿有热液成因矿床特征;利用w(Fe+S)-w(As)图解和Co-Ni-As含量图解显示石英脉型矿石反映浅成低温热液型金矿特征。综合区域变质变形事件、典型矿床特征及矿区内已取得的年龄、流体包裹体等相关数据认为,科洛金矿床应存在两期矿化:三叠纪形成的韧性剪切带型金矿床和白垩纪形成的浅成低温热液型金矿床。建议在今后的矿产勘查中注意寻找真正的韧性剪切带型金矿。
The mid-sized Keluo gold deposit is located in the Heihe-Nenjiang tectonic melange belt,Heilongjiang Province,China.The ore bodies in the deposit occur as both ductile deformed and disseminated-massive types.The deposit has been significantly mined but the genesis of the deposit is elusive.Here we report typomorphic characteristics and He-Ar,S,Pb isotopes of pyrite,intending to establish the ore genesis mechanisms of the Keluo gold deposit.Pyrite from ductile deformed ore body showed lower S/Fe ratios(mean 1.99)and As content(mean 382×10^-6),and higher Au(mean 383×10^-6),Ag(152×10^-6)and Co(1249×10^-6)contents than pyrite from disseminated-massive ores(mean S/Fe,As,Au,Ag,and Co values of 2.01,503×10^-6,234×10^-6,96×10^-6,845×10^-6,respectively).Trace elements of the two types of pyrite showed similar REE features,i.e.enriched LREE,depleted HREE,and inclined REE patterns.The total REE content of pyrite ranged from 17.00×10^-6to 66.95×10^-6with deformed pyrite showing lower REE concentrations,and LREE/HREE ratios ranged from 5.25 to 12.50.The large variations in Y/Ho,Zr/Hf and Nb/Ta ratios indicate an unstable ore-forming environment.Moreover,the^3He and^4He values of pyrite were(2.405-10.811)×10^-13and(3.35-4.99)×10^-7,respectively.The^3He vs.^4He and R/Ra vs.40Ar/36Ar discrimination diagrams indicated a dominated mantle source with minor contribution from continental crust,further implying that the meteoric water played a vital role during gold mineralization.Theδ^34S values of pyrite ranged from+2.3‰to+7.6‰showing lowerδ^34S values for deformed pyrite than disseminated-massive pyrite,with mean values of+2.65‰and+5.07‰,respectively.The Pb isotopic study of pyrite showed that the ratios^206Pb/^204Pb,^207Pb/^204Pb and^208Pb/^204Pb ranged in 18.157-18.211,15.542-15.594and 38.032-38.218,respectively,and all these values indicate great affinity with ore genesis.Pb isotopic compositions further show that deformed pyrite has relatively low mean values of^206Pb/^204Pb(18.171),^207Pb/^204Pb(15.542),and^208Pb/^204Pb(38.054),as compared with those of disseminated-massive pyrite(18.200,15.581and 38.172,respectively).The Co/Ni ratios and Co vs.Ni discrimination diagram indicate that the Keluo deposit belongs to the hydrothermal type,whereas the w(Fe+S)vs.w(As)and Co-Ni-As diagrams indicate that the main mineralization stage exhibits epithermal characteristic.Combined with previous regional deformation events,deposit features,geochronological and fluid inclusion studies,we conclude that there are two stages of mineralization in the Keluo deposit,including the Triassic orogenic and the later Cretaceous epithermal type.Based on this study,we propose that more attention should be paid to orogenic Au during ore prospecting in the Heihe-Nenjiang tectonic melange belt.
作者
李成禄
李胜荣
袁茂文
杜兵盈
李文龙
Masroor ALAM
刘东园
刘浩
LI Chenglu;LI Shengrong;YUAN Maowen;DU Bingying;LI Wenlong;Masroor ALAM;LIU Dongyuan;LIU Hao(Heilongjiang Institute of Natural Resources,Harbin 150036,China;China University of Geosciences(Beijing),Beijing 100083,China;Heilongjiang Institute of Geological Sciences,Harbin 150080,China;Department of Earth Sciences,Karakoram International University Gilgit,15100,Pakistan)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2020年第5期99-115,共17页
Earth Science Frontiers
基金
黑龙江省国土资源科研项目(黑国土科研201603)
黑龙江地质勘查公益项目(GY-2018003)
国家自然科学基金项目(41872038)。
