青海驼路沟钴(金)矿床形成的构造环境及钴富集成矿机制

驼路沟矿床是近年在青海东昆仑造山带内发现的首例独立大型钴(金)矿床。文章在详细解剖该矿床地质特征的基础上,通过主元素和微量元素地球化学、流体包裹体及氢、氧同位素等研究,重点探讨其形成的地质构造环境及钴的富集成矿机制。该矿床整合产于浅变质火山-沉积岩系中,发育高度富钠的热水沉积岩和典型的热水沉积矿石组构。沉积岩的主元素和特征微量元素地球化学研究表明,该矿床形成于活动大陆边缘的局限裂陷海盆环境。喷气岩和诸类型矿石的稀土元素分布模式与地层围岩相似,均以显著富集轻稀土元素、具明显负铕异常为特征,表明是由在赋矿岩系中深循环的大气降水喷出后在距喷口位置较远处沉积而成。钴成矿流体为NaCl-H2O体系,伴生金矿化流体为NaCl-CO2-H2O-N2体系。钴主要分布在硫化物(如黄铁矿)相中,而钴的进一步富集、钴矿物的出现及增多,与变质程度紧密正相关。驼路沟矿床与世界其他典型层控Co-Cu-Au矿床具有十分相似的特征和钴成矿作用方式,均为同生喷流热水沉积成因。

Tectonic setting and metallogenic mechanism of Tuolugou cobalt (gold) deposit, Qinghai Province

The Tuolugou cobalt (gold) deposit, located in the central part of the eastern Kunlun orogenic belt, is the newest large-size independent cobalt (gold) deposit discovered in Qinghai Province, northwestern China. Mine-ralization was largely confined to an EW-striking volcano-sedimentary sequence consisting of four lithologic units which underwent extensively greenschist facies metamorphism and deformation. Na-rich exhalite (quartz albitite ) and typical syngenetic textures of ores are well developed. Major and trace element geochemical data show that this deposit was formed in a restricted aulacogen against the setting of an active continental margin. The exhalite and different types of ores have similar chondrite-normalized REE patterns to wall rocks and are characterized by LREE enrichment and negative Eu anomalies. It is inferred that the exhalite and ores were formed mainly by exhalation of deeply circulating meteoric waters rather far away from the vent. The positive relationship between cobalt and pyrite indicates that cobalt occurred mostly in sulfides. The further enrichment of cobalt and the appearance and increase of cobalt minerals were positively correlated to the increasing extent of metamorphism in the region. These data and the similarity of this deposit to other stratabound Cu-Co and Co-Cu-Au deposits in the world suggest that cobalt in the Tuolugou deposit was most likely formed by the syngenetic exhalative process.