滇西保山地块陡崖铁铜多金属矿床石榴子石年代学及其地球化学特征

Geochronology and geochemical characteristics of the Douya iron-copper polymetallic deposit in the Baoshan block,western Yunnan

陡崖夕卡岩型铁铜多金属矿床位于保山—镇康铅锌多金属矿带北段。区内矿体产于寒武系上统核桃坪组和沙河厂组中,岩性主要为大理岩化灰岩和夹泥质灰岩。目前,矿区内尚未揭露中酸性岩体。为厘清该矿床的成矿时代、成矿的物理化学条件和成矿流体的性质,我们对该矿床的石榴子石开展了细致的岩相学工作、地球化学分析以及LA-SF-ICP-MS U-Pb定年测试。结合野外调查与岩相学工作,主量元素特征表明:保山陡崖矿床产出的石榴子石属于钙铝榴石钙铁榴石固溶体系列,且该矿区的石榴子石可划分为两类(GrtⅠ和GrtⅡ)。微量元素特征表明:在陡崖矿床,随着温度、氧逸度的变化,流体体系的pH值经历了早期的中性—晚期的酸性的转变。通过应用石榴子石LA-SF-ICP-MS U-Pb定年方法,获得468~461 Ma的可靠年龄数据,表明滇西保山地块陡崖矿床成矿作用发生于中奥陶世。结合双脉地、清水河花岗岩与之相似的稀土配分曲线以及形成时代,推测该矿床可能与岩石圈地幔的拆沉作用有关,其源区主要为古老大陆地壳部分熔融,并有幔源物质的加入。

The Douya iron-copper polymetallic deposit is a skarn-type deposit located in the northern portion of the Baoshan-Zhenkang lead-zinc polymetallic ore belt.The orebodies are found in the Hetaoping Formation and Shahechang Formation of the Upper Cambrian system,characterized by marbled limestone intercalated with argillaceous limestone.No intermediate-acid rock bodies have been identified within the deposit.To elucidate the age of ore formation,physical and chemical conditions of ore formation,and properties of ore-forming fluids,comprehensive petrographic analysis,geochemical analysis,and LA-SF-ICP-MS U-Pb dating were conducted on garnets from the deposit.The major element characteristics of the garnets from the Douya deposit in the Baoshan block indicate that they belong to the grossular-andradite solid solution series and can be classified into two types:Grt I and Grt II.Variations in temperature and oxygen fugacity within the Douya deposit have influenced the trace element composition,indicating a transition in the pH of the fluid system from early neutrality to late acidity.LA-SF-ICP-MS U-Pb dating of the garnets yielded reliable age data of 468461 Ma,suggesting that mineralization at the Douya deposit occurred during the Middle Ordovician.The similar rare earth distribution curve and formation age of Shuangmaidi and Qingshuihe granites suggest a potential connection between these deposits and the delamination of the lithospheric mantle.It is proposed that the main source of mineralization in the Douya deposit involves the partial melting of ancient continental crust in combination with materials derived from the mantle.