青海德尔尼铜(锌钴)矿床硫化物Cu同位素组成及矿床成因探讨

The copper isotopic composition of sulfide ores and deposit genesis of the Dur'ngoi Cu(Zn-Co) deposit in Qinghai Province,China

青海德尔尼铜(锌钴)矿床产出在北西或北西西向超镁铁质岩带中,对其矿床成因长期以来一直存在争议。文中对德尔尼矿床主矿体不同类型硫化物矿石的Cu同位素组成进行了分析,通过与现代海底正在形成的赋存在超镁铁质岩(蛇纹石化橄榄岩)中的块状硫化物矿床进行类比,从构造背景和矿床地质角度探讨了矿床成因,得出以下主要认识:(1)阿尼玛卿构造带可能存在大型拆离断层,超镁铁质岩体和硫化物矿体的产出均与北西向发育的长期活动拆离断层有关;(2)德尔尼矿床属古代海相火山成因块状硫化物矿床,为赋存在超镁铁质岩体中的一个特殊类型(或称为"德尔尼型");(3)硫化物原生矿石Cu同位素组成均为负值,呈富轻Cu同位素特征,表明矿床经历了广泛的后期热液叠加过程。德尔尼矿床控矿构造、岩体特征和后期叠加成矿过程的深入研究不仅对矿床成因认识和找矿具有重要意义,而且为现代海底慢速-超慢速扩张洋中脊超镁铁质岩热液系统成矿研究提供了参考。

Dur＇ngoi massive sulfide Cu（ZwCo） deposit mainly occurs in the ultramafic rock belt with northwest or northewest-west extension direction. The origin of ore deposit has been debated for more than three decades, yet the relationships between tectonics, paleo-fluid circulation, ultramafie rocks and ore deposition are poorly understood. We present new data of the copper isotopic composition of sulfide ores with the different structure types from the Dur＇ngoi deposit. Comparing the massive sulfide deposit hosted in uhramafie hydrothermal systems at the mid-ocean ridge, we discussed the genesis of ore deposit from the tectonic setting and deposit geology. There are some conclusions given as follows： （1） it is supposed that the relationship between uhramafic rocks and ore deposition is related to the large detachment fault occurred in the Animaqing tectonic belt; （2） Dur＇ngoi deposit is a special deposit type（＂Dur＇ngoi type＂） wrapped by ultramafic rock belt, which can be attributed to the ultramafic type of volcanic genetic massive sulfide deposit; （3） the copper isotopic composition of sulfide ores are consistent with negative value, which indicate that the Dur＇ngoi deposit may have undergone widely hydrothermal recycling during the late stage of ore-forming. The further research on tectonic events controlling ore-forming and superimposed metallogenic processes is necessary to better understand the origin and prospecting of ore deposits, furthermore, which is also important for hydrothermal metallogenic processes of modern seafloor sulfide deposit at the slow or ultra-slow spreading ridge.