川滇地区密西西比河谷型铅锌矿床成矿地质背景及成因探讨

THE GEOLOGICAL SETTING, CHARACTERS AND ORIGIN OF MISSISSIPPI VALLEY-TYPE Pb-ZnDEPOSITS IN SICHUAN AND YUNNAN PROVINCES

川滇地区密西西比河谷型铅锌矿床具有明显的层控性和岩控性 ,大多数矿床都赋存于灯影组白云岩中。矿床的形成温度比较低 ,主成矿阶段的温度为 140～ 2 0 0℃ ,而且各矿床的形成温度十分接近。矿床发育大规模的白云石化。本区的地质演化经历了双层基底、连续盖层 ,以及前陆盆地 -造山带耦合几个主要演化阶段。这些阶段分别为矿床的形成提供了物质基础、流动通道以及流体驱动力 ,从而在燕山期 -喜山期由于成矿流体的大规模流动 ,形成了川滇地区大面积分布的密西西比河谷型铅锌矿床。

Along the border of Southeast Sichuan and East Yunnan (Fig.1) there are numerous Mississippi Valley-type Pb-Zn deposits. Some characteristics of the deposits are: (1) the deposits are hosted in Late Proterozoic and Mississippian rocks, especially in dolomite; (2) fluid-inclusion studies of the deposits show that the homogenization temperatures fall predominantly between 140-200℃; (3) around the deposits the Proterozoic limestone has altered to dolomite. Regional dolomitization covers a large area; (4) there are some aquifers in the region. The most important one for the ore fluids is Late Proterozoic sandstone, named the Doushantuo Formation.; It has been suggested that all the deposits were formed by regional migration of ore-forming brines. Hydrologic modeling of regional brine migration is that when the Longmenshan-Jingpingshan orogenic belt, situated west of the area, uplifted in the Yenshanian and Himalayan movements (Jurassic to Eogene), the gravity drove the ore-forming fluids from the orogenic belt to the locus of mineralization and resulted in the formation of the deposits.;