湘西北五伦铅锌矿床闪锌矿Rb-Sr定年及其地质意义

五伦铅锌矿床位于扬子陆块东南缘之江南（雪峰）造山带北西侧，是湘西北铅锌矿带内新近发现的热液脉型矿床.铅锌矿床产于万民岗背斜轴部，矿体沿NE向比铁溪-陈家河断裂旁侧派生的NW向断裂呈陡倾脉状产出，直接容矿围岩为奥陶系下统桐梓组和红花园组.对该矿床主成矿期的闪锌矿进行Rb-Sr等时线法定年，获得成矿年龄为238.9±4.5 Ma（MSWD=1.8），（87Sr/86Sr）_i值为0.710 86±0.000 16，指示其主成矿期为中三叠世晚期.结合已有的成矿年代学资料，通过地球动力学背景探讨，结果表明湘西北地区至少存在两期铅锌成矿作用，分别对应于加里东期构造运动后伸展作用和印支早期华南陆块汇聚碰撞形成的局部伸展作用.五伦铅锌矿床的成矿物质应主要来源于含矿层之下成矿元素高含量的南华纪-寒武纪早期地层中的碎屑岩系，其较高的（87Sr/86Sr）_i值指示成矿过程中陆壳影响较为明显. 

Rb-Sr Dating of Sphalerites from Wulun Lead-Zinc Deposit in Northwestern Hunan and Its Geological Significance

The Wulun lead-zinc deposit lies to the northwest of Jiangnan (Xuefeng) orogenic belt on the southeastern margin of Yangtze block, as a newly discovered hydrothermal vein type of lead-zinc deposit in the lead-zinc ore belt along the Wanmingang anticline in northwestern Hunan. The ore bodies outcrop in the Lower Ordovician Tongzi and Honghuayuan formations as steep-dipping veins controlled by NW trending faults which derived by NE trending Bitiexi-Chenjiahe fault. Rb-Sr dating of sphalerite yielded an isochron age of 238.9±4.5 Ma (MSWD=1.8) with initial 87Sr/86Sr value of 0.710 86±0.000 16 for the deposit, which shows that the end of Middle Triassic is the main mineralization period for the Wulun lead-zinc deposit. Integrated with the existing metallogenic geochronology data, and the discussing of the geodynamical setting, it is indicated that there are at least twice lead-zinc mineralization in northwestern Hunan, which was respectively related to the post-orogenic extension of late Caledonian tectonism and the local stretching derived from collision of South China block in the early Indosinian. The metallogenic materials of Wulun lead-zinc deposit shall be mainly derived from the clastic rocks with high ore-forming elements in the Nanhua-Early Cambrian stratas underlying the ore-bearing layers. The relatively high initial Sr isotope ratio indicates that the influence of continental crust was obvious in the metallogenic process.