豫西南泥湖矿田钼钨及铅锌银矿床地质特征及其成矿机理探讨

Characteristics and Metallogenic Mechanism of Mo-W and Pb-ZnAg Deposits in Nannihu Ore Field,Western Henan Province

豫西南泥湖钼钨铅锌银矿田位于华北克拉通南缘金堆城—南泥湖钼钨多金属成矿带的东部。在矿田内除了早期探明的斑岩—夕卡岩型钼钨矿床和夕卡岩型多金属硫铁矿床外,最近几年又在其外围发现了热液脉型铅锌银矿床,它们在空间上呈规律性分布。成矿流体及硫、铅同位素研究表明:钼钨及多金属硫铁矿床与铅锌银矿床为同一成矿系统的产物,成矿流体主要来源于岩浆水,晚期有大气水加入,成矿物质和花岗斑岩一起源于下地壳。年代学研究表明:钼钨铅锌银大规模成矿作用发生在140 M a左右,形成于中国东部构造体制大转换晚期的岩石圈伸展环境。其成矿机理为:在华北克拉通南缘由于俯冲的扬子板片可能发生断离,软流圈物质通过板片断离窗上涌,幔源岩浆在壳幔边界附近发生底侵作用,诱发碰撞加厚的下地壳部分熔融形成含矿的花岗质岩浆,沿NNE向断层与EW向的断层交汇处上升并在较高的构造层次上侵位,形成花岗斑岩体以及钼钨矿床、多金属硫铁矿床及铅锌银矿床。

The Nannihu Mo-W-Pb-Zn-Ag ore field in west Henan Province is tectonically located in the east part of Jinduicheng-Nannihu Mo-W polymetallic metallogenic belt of south margin of the North China Craton. There occur porphyry-skarn Mo-W, skam polymetallic pyrite and hydrothermal silver-lead-zinc vein deposits exhibiting zoning outward porphyries. The ore-forming fluids show that these deposits are in the same metallogenic system and the hydrothermal solution is mainly derived from primary magmatic water in the early stage and from the mixture of the primary magmatic water and meteoric water in the late stage. Sulfur and lead isotope components show that the ore substances and related porphyries are derived from the lower crust. The large-scale Mo-W-Pb- Zn-Ag mineralization occurred at about 140 Ma according to the Re-Os isotopic dating. Based on the study of Mesozoic tectonic evolution, we propose that the large-scale mineralization was the consequence of lithospheric extension during the late stage of the tectonic regime changing its main stress from NS-trending to EW-trending. The metallogeny is as follows ： during the subducted Yangtze continental slab broke-off possibly in south margin of the North China Craton in Middle-Late Jurassic, the underplating of the mafic magma near the boundary between the mantle and the crust caused by upwelling of the asthenosphere through slab window, drove partial melting of the thickened lower crust, forming the ore-bearing granitic magma. The ore-bearing granitic magma intruded along intersection of the NNE-trending and EW-trending faults and emplaced at the shallow places, attributing the formation of the granitic porphyries, the Mo-W, polymetallic pyrite and Pb-Zn-Ag mineralization.