西藏冈底斯岛弧带甲马铜多金属矿床成矿物质来源及成因研究

甲马铜多金属矿床位于冈底斯岛弧构造带甲马弧内沉积盆地内。它呈层状、似层状展布于该盆地中的多底沟组礁灰岩(J_3d)与林布宗组砂板岩(K_1l)之间的过渡带内,并严格受地层层位的控制。其含矿岩石为热水交代夕卡岩和与矿床有密切成因关系的热水沉积岩(透辉石-斜长石岩)。通过容矿岩石和矿床的同位素、稀土元素、矿物包裹体成分等示踪研究,认为矿床的成矿金属物质来自盆地基底——弧火山岩;成矿流体来自古海底热水循环系统;硫来自地层中的生物硫;水—岩反应(交代)是成矿重要机制。故该矿床系古海底热水交代成因,属与古海底热水循环系统有关的一种独特的热水交代型夕卡岩矿床。

Sources of Ore-forming Materials and the Genesis of the Jiama Copper and Polymetallic Deposit in Gandise Island-arc Belt, Xizang

The Jiama copper and polymetallic deposit, located in an inter-arc sedimentary basin, occurs as stratiform and stratoid bodies in the transitional zone between the carbonate rock (J3d) and sandy slate (K1l). Hydrothermal altered skarn and hydrothermal-sedimentary diopside-feldspar rocks relate to the formation of the deposit are ore-bearing rocks of the Jiama deposit. On the basis of studies on isotopic, REE, components of fluid inclusions in the minerals from the deposit, this article holds that ore-forming metals of the deposit came from arc-volcanics, basement of the Jiama intra-arc basin; ore-forming fluids originated from the old seafloor hydrothermal circulatory system; sulphur of the deposit are characterized by biogenetic sulfur; and water-rock interaction (metasomatism) is an important mechanism of ore-formation in the Jiama deposit. Thus, this paper argues that the deposit belongs to the products of old seafloor hydrothermal metasomatism, and the deposit is a special exhalation one bound up with the old seafloor hydrothermal circulatory system.