东天山天宇铜镍硫化物矿床磁黄铁矿Re-Os同位素物质来源示踪

Re-Os isotopic analysis of pyrrhotite from Tianyu Cu-Ni sulfide deposit in Eastern Tianshan Mountains,Xinjiang: Constraints on sources of ore-forming materials

天宇岩浆铜镍硫化物矿床的矿体由浸染状矿体和块状矿体组成。采用同位素稀释Triton-plus测定了浸染状矿石和块状矿石的磁黄铁矿Re-Os同位素比值。结果表明:浸染状矿石w(Re)为11.82×10^(-9)~45.28×10^(-9),w(Os)为0.944×10^(-9)~8.528×10^(-9),187Os/188Os初始比值为0.885~2.332,γOs为607~1763;块状矿石w(Re)为49.38×10^(-9)~315.10×10^(-9),w(Os)为0.191×10^(-9)~42.420×10^(-9),187Os/188Os初始比值为0.654~3.322,γOs为423~2555。Re、Os含量、同位素组成和特征值表明,该矿床物质为壳-幔混合来源,块状矿石可能比浸染状矿石经历了更强的地壳物质混染。浸染状矿体发育透闪石化、蛇纹石化、绿泥石化蚀变,表明存在岩浆期后热液活动,但块状矿体热液蚀变不明显,块状矿石的Re-Os同位素特征可能是与地壳岩石直接作用的结果。地壳混染作用发生在深部岩浆房,同时也发生在岩浆侵位及再次迁移过程中,这些过程造成块状矿体与浸染状矿体不同的同位素特征。

The Tianyu Cu-Ni sulfide deposit is composed of spatially adjacent disseminated orebody and massive orebody,with the former formed earlier than the latter.In this study,the authors used isotopic dilution Triton-plus to determine the Re-Os isotopic ratios of pyrrhotite from the disseminated ore and the massive ore.In the disseminated ore,the Re content is from 11.82 × 10（-9）to 45.28 × 10（-9）,the Os content is from 0.944 × 10（-9）to 8.528 × 10（-9）,the initial187 Os/188 Os ratio is from 0.885 to 2.332,and γOsis from 607 to 1763.In massive ore,the Re content is from 49.38 × 10（-9）to 315.10 × 10（-9）,the Os content is from 0.191 × 10（-9）to 42.420 × 10（-9）,the initial187 Os/188 Os ratio is from 0.654 to 3.322,and γOsis from 423 to 2555.Element content,isotopic composition and characteristic values of Re and Os indicate that the ore-forming material in the Tianyu ore deposit was a mixed source of the crust and the mantle,and the massive ore experienced a higher degree of crustal contamination than the disseminated ore.Alteration of tremolite,serpentine and chlorite is developed in the disseminated ore,which indicates post-magmatic hydrothermal activity.In contrast,the massive ore does not show obvious magmatic hydrothermal alteration.Re-Os isotopic characteristics of the massive ore might have resulted from direct interaction with crustal rocks.As a result,crustal contamination was developed both in the deep magma chamber and at the present position of the orebody.