河南栾川三道沟铅锌银矿床方解石地球化学特征及Sm-Nd年龄研究

Geochemistry and Sm-Nd age of calcites from the Sandaogou Pb-Zn-Ag deposit in Luanchuan, western Henan Province

三道沟铅锌银矿床位于华北陆块南缘栾川多金属矿集区西部。受断裂控制的薄脉状矿体赋存于新元古界栾川群南泥湖组碎屑岩、碳酸盐岩地层中。本文在矿床地质特征和矿物学研究的基础上，对早、中、晚3个成矿阶段的9件热液方解石进行微量元素、稀土元素和Sm-Nd同位素测年研究。结果表明方解石的稀土元素总量（∑REE）为6．42～216μg／g，富集重稀土元素，HREE／LREE比值为1．47～5．94；δEu=0．62—2．71，具弱Ce异常；强烈亏损Nb和Zr，富集Pb。从成矿早阶段到晚阶段，∑REE值、LREE／HREE比值和δEu值逐渐减小。Y／Ho-La／Ho图解和Tb／Ca—Tb／La图解均指示该矿床方解石为热液成因。方解石147Sm／144Nd和143Nd／144Nd同位素比值具有良好的线性关系，等时线年龄为（138．3±2．6）Ma（2σ，MSWD=2．3）。结合矿集区内成岩-成矿年代学资料，认为三道沟矿床与区内最晚阶段的花岗质岩浆活动（136～142Ma）有关，属于栾川Mo-W-Pb-Zn-Ag多金属成矿系统中的热液脉型铅锌银矿床。

The Sandaogou hydrothermal Pb-Zn-Ag deposit is located in the western part of the Luanchuan polymetallic ore district on the southern margin of the North China Block. Vein-shaped ore bodies occur in clastic and carbonate strata of the Nannihu Formation of the Neoproterozoic Luanchuan Group. Based on the study of the geological setting and mineralogy of the deposit, we performed trace element analysis and Sm-Nd isotopic dating on 9 hydrothermal calcites from three ore-forming stages. The results show that the calcites are enriched in heavy rare-earth elements with the total REE contents （∑REE） of 6.42-216 μg/g and a HREE/LREE ratio of 1.47-5.94 （ ∑Eu = 0.62-2.71）. The calcites show a slight Ce anomaly, but are strongly depleted in Nb and Zr and enriched in Pb. EREE, LREE/HREE and δEu decrease gradually from the early stage to the late stage of mineralization. The calcites show that they are of hydrothermal genesis, as indicated on the Y/Ho-La/Ho and Tb/Ca-Tb/La diagrams. The isochron age of calcites is （138.3±2.6） Ma （2σ, MSWD = 2.3）, with a good linear relationship between 1478m/144Nd and 143Nd/laaNd ratios. Combining the results of this study and the geochronologic data of diagenesis-metallogeny in the Luanchuan ore district, we suggest that the formation of the Sandaogou deposit is related to the last stage of granitic magma activity （142-136 Ma） in the Luanchuan district. The Sandaogou deposit is a vein-type hydrothermal Pb-Zn-Ag deposit that belongs to the Luanchuan Mo-W-Pb-Zn-Agpolymetallic ore-forming system.