辽东的主要剪切带及其金矿化特征

MAIN SHEAR ZONES IN EASTERN LIAONING PROVINCE AND FEATURES OF SHEAR-HOSTED GOLD MINERALIZATION

辽东地区构造上位于辽中—吉南元古宙活动带西南部,为胶辽克拉通金矿床分布比较集中的地区。金矿化作用发生于古元古宙变质沉积岩和花岗片麻岩的韧性及脆-韧性剪切带之中,剪切活动与成金事件具同时性关系。矿化剪切带分为3大系统,其中近东—西向和北东—南西向两大系统发育于辽河群分布区,其受控于岩石非均匀性,分别借助于早(吕梁)期S1(≈S0)和S2或D3剪切带而形成,剪切活动(构造事件)与成金事件主要发生于印支运动;丹东韧性剪切带及其相关构造为本区最重要的含矿系统,矿床均顺主构造线分布,并规律性地受控于其次级构造,剪切带的形成和成金事件均在燕山运动时期。本区提供了一个特殊的克拉通成矿作用格局:容矿岩石时代老,成金事件时代新。

The gold deposits in eastern Liaoning province, mainly within a succession of deformed Early Proterozoic metasediments and the granitic gneiss, were tectonically located in southwestern part of the Central Liaoning-Southern Jilin Proterozoic mobile belt, and generally hosted in the ductile and brittle-ductile shear zones of various scales. They could be categorized into three systems. The nearly E-W system included mineralized shear zones that were formed parallel to S1 （≈S0 ） and/or early（ D3 ） S1-parallel shears within the Early Proterozoic metasediments along the pre-existing E-W trending regional folds over western part of the region. Veinletdisseminated, brecciated and alterated foliation-parallel orebodies generally characterized the deposits of this system. Gold mineralization and related shearing activities were determined to have taken place during the Indosinian orogeny. The mineralized shear zones attached to the NE-SW system were S2-parallel shears, some of which might be results of reactivation of early shear zones during gold mineralization, and these events were considered to occur in the Indosinian orogeny, or last to the Yanshanian orogeny. The Dandong ductile shear zone together with its accessory structures constituted the largest gold-bearing system over eastern part of the region. The gold deposits of this system, outcropping along the major structure, were hosted in the sub-order shearing structures within the large one. These deposits made up of medium to steeply dipping auriferous quartz veins. The structural relationships and geochronological data suggested both the initiation of the large shear zone and the associated gold mineralization occurring in the Yanshanian movement. With numerous gold deposits, eastern Liaoning area occupied an important stratigical position in the geology of the Jiao-Liao craton, and provided a special case of gold occurrence contrasting with most other cratonic deposits because of relatively young gold-forming （Mesozoic） and host rocks rather old （Early Proterozoic）.