萨瓦亚尔顿金矿床的同位素组成特征及其成因意义

ISOTOPIC COMPOSITION AND GENETIC INDICATION OF SAWAYA′ERDUN GOLD DEPOSIT, XINJIANG

新疆西南天山的萨瓦亚尔顿金矿床 ,赋存于中 -上石炭统浊积岩系地层中。矿化受构造破碎带控制 ,以含矿的石英细 (网 )脉和含矿的石英 -碳酸盐细 (网 )脉形式产出。矿体呈似层状和透镜状 ,矿石的矿物组成和矿石类型复杂 ,矿石中金与黄铁矿、毒砂、黄铜矿等硫化物密切共生 ,金矿物以银金矿为主。成矿具多阶段性。据发现的生物化石和铷 -锶同位素 ,控矿地层时代为中—上石炭统。铅和硫同位素组成表明 ,成矿物质主要来自于深部较老的地层和岩石 ;硅同位素组成显示 ,硅质由地层和岩石提供 ;氢氧同位素特征显示 ,成矿作用乃通过大气降水补给的地下水渗入深部 ,经加热循环并溶滤围岩中的矿质 ,随后迁移到减压空间和有利岩性层中而成矿。钾 -氩法测定表明 ,成矿作用发生于燕山中—晚期。萨瓦亚尔顿金矿床的众多特征与乌兹别克斯坦穆龙套金矿床的特征极具可比性 。

The Sawaya'erdun gold deposit located in the west of Xinjiang is one of the most important gold deposits found in China in the recent years. The deposit occurs in the turbidite sequence of the Middle Upper Carboniferous, and the mimeralization is restricted to the fracture zones developed in the sequence. With layered or lensoid morphology, the orebodies extend in the NE SW trend, being consistent with the extension of the fracture zones. The ore is composed of gold bearing quartz and quartz siderite stringer stockwork with disseminated metal sulfides. Gold in the ore is characterized by microtexture and low fineness and associated with pyrite, arsenopyrite, and chalcopyrite. The lead compositions obtained from the ore are as follows: 206 Pb/ 204 Pb=18.654~18.382; 207 Pb/ 204 Pb=15.470~15.659; 208 Pb/ 204 Pb=38.752~38.062. The δ 34 S values of the metal sulfides analyzed range between 2.61‰ and -1.02‰. The δD values from quartz and siderite vary from -42.5‰ to -72.2‰, the δ 18 O, from 2.94‰ to -11.57‰, and the δ 13 C CO 2 , from -2.35‰ to -10.50‰ . The mineralization dates between 167±18 Ma and 98±9 Ma, using K Ar method. Based on the characteristics of the isotopic composition, it is suggested that the Sawaya'erdund deposit was developed during the late Yanshan movement and the host and underlying strata supplied the source for the mineralization. It could formulate a model of circulating meteoric water becoming a heated hydrothermal at depth, dissolving gold and other metals from the country rocks through which it traversed , and carrying these up to the pressure reduced environment the fracture zones, where they were precipitated because of boiling derived from the reduced pressure. The features of the Sawaya'erdun gold deposit are similar to those of the famous Muruntar gold deposit located in Uzbekistan, and it is the most typical Muruntar type gold deposit discovered so far in China.