黔东铅锌矿的成矿规律及成矿模式

A Genetic Model for Mineralization of the Zinc-Lead Belts in Eastern Guizhou

黔东铅锌矿产于加里东期的黔东走滑盆地西缘，赋存于加里东晚期盆地关闭时形成的舒缓的前陆褶皱带中，容矿地层主要为清虚洞组中上部，矿床多产于碳酸盐超层序的深水生物建隆－藻丘或席状藻复合体中，控矿构造主要是盆地关闭时形成的ＮＥ向断层和隆起。矿床以整合型矿化为主，具多层性，矿物共生组合为黄铁矿－闪锌矿－（方铅矿）－方解石－（白云石）－（重晶石），矿化可分二期或三期，每期的淀积顺序基本都是黄铁矿－闪锌矿－方解石（白云石），而方铅矿、重晶石则形成于最后－期矿化的后期。矿石铅为典型的上地壳铅，与把榔组（乌训组）细碎屑岩岩铅演化到加里东晚期时的铅同位素组成非常相近，矿石流与容矿地层的硫酸盐硫有关。矿床形成温度为１８０～２００℃，形成深度约４ｋｍ，成矿压力约０．５ｋＰｔ，金属硫化物淀积在Ｅｈ值较低，ｐＨ值由低变高的物化条件下。矿床成因机理是：成矿的盆源热液是赋存在把榔组（乌训组）富Ｚｎ、Ｐｂ、Ｆｅ细碎屑岩中的建造水，在深埋过程中，特别是在地幔异常热事件中，因热流值增高而温度升高，盐度增大，ｐＨ值降低，极大地增加了Ｐｂ、Ｚｎ、Ｆｅ的溶解度而形成的。它们由于孔隙流体的压力差，顺传输层或传输构造运移至容矿层的各类矿储中，因与富ＳＯ－?

Eastern guizhou zinc-lead ore belt lie at the neighbourood ofwestern margin of a Caledonian strike-slip basin, which has developed into agentle-dipping foreland folding zone due to shrinking and enclosing of the basin atthe end of Caledonian time. The deposits are hosted by the mid to upperQingxudong Formation of the Lower Cambrian, by predominantly algae moundsor/and sheet-like alga .complexes in a carbonate supersequence. The Zn-Pbmineralization is mainly controlled by northeast-trending faults formed prior to thebasin enclosing.Most of the orbodies occur conformtly along numerous horizons of beddedcarbonate rocks within the Qingxudong Formation. The mineralogical associationsare pyrite, sphalerite. galena, calcite, dolomite, and barite. The mineralization canbe identified as two or three stages during each of which they deposited generally.in the sequence of pyrite, sphalerite, and calcite (possibly also dolomite) exceptfor the depostion of galena and barite at the end of the last stage.The lead isotopic data in the ores plot on Doe and Zartman's (1979) the uppercrust curve, and is extremely close to the rock chips of the fine elastics of theBalahg (Wuxun) Formation in lead isotopic compositions evolving till the lateCaledonian. Origin of the sulfur in the ores is probably related to sulfate sulfuroccuring in the host rocks. The mineralization took place at 100°to 200℃ and 0. 5kpa (approximately 4 km deep ) and the metal sulfides deposited underpysicochemical envrionment of low Eh values and of the shift from low to high pHvalues.So, the studies support the mineralization mechanism of the zinc-lad depositsas the following. The ore-forming hydrothermal fluids were derived from theBalang Formation-trapped formational water of connate water which had the initialenrichment in the ore components of Zn,Pb and Fe as indicated by the lead isotopicdata, this water became heated with increase in the burial depth, particularly bymantle thermal anomalies, during the sedimentary basin evolution, and the hightemperature, in conjunction of the salinity of solution with low PH, caused the I'larger solubilities of Zn, Ph and Fe to form a hydrothermal fluid system with highconcentration of ore components. These hydrothermal solutions high rich in orecomponents were driven into the various ore reservoirs in the host rocks throughpermeable horizons and approperiate structural channels by differenciate of porefluid pressures. The ore materials dissolved in the hydrothermal solutions of theore reservoirs were finally deposited owing to decreasing temperatures, changingPH values, and increasing concentration of reducing sulfur when the ore--formingsolutions mixed with the permeating-down meteoritic water rich in SO: andinteracted with the host rocks.In the author's opinion, it is reasonable that the zinc-lead deposits studied areclassified as the type of basin-derived hydrothermal deposits.