西藏当雄县拉屋铜铅锌多金属矿床喷流沉积成因

Exhalative Sedimentary Genesis of Lawu Copper-Lead-Zinc Deposit in Dangxiong County of Tibet

拉屋铜铅锌多金属矿床位于纳木错—嘉黎断裂带南侧的上石炭统—下二叠统来姑组中,矿体分布受日音拿背斜控制。矿区内矿化类型以层纹状、层状矿化为主,晚期有脉状矿化叠加。在矿床地质特征研究基础上,通过矿石和容矿围岩的稀土元素、稳定同位素地球化学特征分析,探讨了成矿物质来源及矿床成因。研究显示,矿床容矿围岩稀土元素具有弱Ce负异常(0.89～0.95)和Eu中等亏损(0.56～0.64)的特点。硫化物硫同位素δ34S值变化范围为-2.92‰～-0.42‰,平均值为-1.68‰,为深源硫来源。矿石中石英包裹体氢氧同位素组成显示,矿床成矿热液流体早期以深循环的海水与岩浆水的混合流体为主,中、晚期则有为长时间大气降水的参与,成矿流体来源以大气降水为主。综合研究表明:拉屋铜铅锌多金属矿床属于喷流沉积-叠加改造型矿床,具有喷流沉积型矿床的特征,燕山期则表现为岩浆热液活动叠加改造。

The Lawu copper-lead-zinc deposit in Dangxiong,Tibet,is hosted in the Upper Carboniferous-Lower Permian Laigu Group in the southern part of the Namucuo-Jiali fault belt.The ore bodies are controlled by the Riyinna anticline and faults of different directions.The mineralization in the deposit can be divided into two types,the early layered and laminated and the later veined ores.The derivation of the ore-forming materials and the genesis of the deposit are discussed by studying on the geological characteristics of the deposit,the stable isotope and REE of the ores and their host rocks.It shows that the REE of the host rocks is characterized by weak negative anomalies of Ce/Ce（0.89-0.95）and moderately depleted Eu/Eu（0.56-0.64）.δ34S value of the sulfide is from-2.92‰ to-0.42‰,averaging-1.68‰,indicating that sulfur might come from a deep-source.Hydrogen and oxygen isotope compositions of the fluid inclusions in quartz in the ores indicate that the ore-forming fluid of the deposit was dominantly formed by the mixing of the deeply circulated seawater and the magmatic water at the early period of mineralization.However,the late stage of mineralization was featured by long time of involvement and dominance of meteoric waters.The study shows that the Lawu copper-lead-zinc deposit belongs to a sedimentary exhalative Cu-Pb-Zn deposit superimposed by the Yanshanian magmaic hydrothermal activity.