上黑龙江盆地虎拉林金矿床硫、铅同位素特征及其成因探讨

虎拉林矿床位于中亚造山带东段额尔古纳地块之上,处于上黑龙江盆地西侧,东与砂宝斯、老沟等金矿床相邻。矿床载金矿物主要为薄膜状、粒状及脉状黄铁矿,成矿与早白垩世花岗斑岩、石英斑岩及隐爆角砾岩有密切联系。在对矿床详尽的野外工作基础上,通过对金属硫化物硫、铅同位素分析研究,探讨成矿物质来源,揭示矿床成矿规律。研究结果表明,上黑龙江盆地虎拉林矿床矿石及围岩中黄铁矿δ34SV-CDT分布于0.7‰~2.2‰,平均为1.18‰,集中于1.0‰左右,呈塔式分布,显示主要为岩浆硫特征;铅同位素206Pb/204Pb、207Pb/204Pb、208Pb/204Pb值分别为18.468~18.511、15.578~15.625、38.215~38.370,分布范围较小,且具有造山带铅特征。铅同位素μ值为9.41~9.50,均小于9.58;ω值为35.04~35.93,均值35.49,小于正常铅ω值;Th/U为3.60~3.66,显示出具有壳幔混源特征;在铅同位素构造环境判别图中,显示出具有下地壳部分熔融的特征;Δγ-Δβ图解显示矿床铅来源于上地壳与地幔混合带俯冲岩浆作用成因的铅同位素源区。综合矿床类型、矿体产出特征、矿体及围岩硫、铅同位素特征认为,虎拉林金矿区成矿物质主要来源于下地壳物质熔融形成的深部岩浆,同时存在上地幔与上地壳部分熔融物质的参与,成矿过程与早白垩世岩浆活动关系密切,形成于蒙古—鄂霍茨克洋闭合后伸展环境背景下。

A Study of Sulfur and Lead Isotope Characteristics and Genesis of the Hulalin Gold Deposit in Upper Heilongjiang Basin

The Hulalin deposit is located on the Erguna block in the east part of the central Asian orogenic belt,lies on the west side of the upper Heilongjiang basin and is adjacent to the Shaobaosi and Laogou gold deposits in the east.The gold-bearing minerals are mainly in thin-film,granular and veined pyrite forms.Mineralization is closely related to Early Cretaceous granitic porphyry,quartz porphyry and cryptoexplosive breccia.Based on detailed field work of the deposit,the authors investigated the source of metallogenic materials and the ore-forming regularity through the analysis and study of sulfur and lead isotopes of metallic sulfide.The results show that theδ34SV-CDT values of pyrite from the Hulalin ore deposit and surrounding rocks in the upper Heilongjiang basin vary from 0.7‰to 2.2‰,1.18‰on average,and are concentrated around 1.0‰,exhibiting a tower distribution,showing that it is mainly magma sulfur.The 206Pb/204Pb,207Pb/204Pb and 208Pb/204Pb values of lead isotopes vary respectively from 18.468 to 18.511,from 15.578 to 15.625,and from 38.215 to 38.370.The distribution range is narrow and exhibits orogenic belt lead characteristics.Theμvalues of lead isotope vary from 9.41 to 9.50,all less than 9.58;theωvalues vary from 35.04 to 35.93,with an average value of 35.49,lower than that of normal lead values;Th/U ratios are in the range of 3.60~3.66.The above features show the mixed crust and mantle source characteristics.The map of lead isotopic tectonic environment shows the characteristics of partial melting of the lower crust.Δγ-Δβdiagram shows that the ore lead from the mantle and the crust mixed with subduction magmatism formed lead isotope source area.A combinational study of deposit type,orebody characteristics,orebody and wall rock sulfur and lead isotope characteristics shows that the metallogenic materials of the Hulalin gold mining area were mainly derived from the deep crustal substance formed by molten lava,with the participation of the partial melting of the upper mantle and the crust material,that the ore-forming process was closely related to the early Cretaceous magmatic activity,and that they were formed in the background of the stretching of Mongolia–Okhotsk after its closure.