内蒙古阿拉善地区朱拉扎嘎金矿的成矿时代

Metallogenic epoch of Zhulazaga gold deposit in Alxa area,Inner Mongolia Autonomous Region

内蒙古阿拉善地区朱拉扎嘎金矿是新近发现的特大型层控改造型金矿床,该矿床以产于中元古界地层中和具有巨大的找矿潜力而引人注目。容矿岩石主要为钙质粉砂岩、粉砂质板岩。采用颗粒锆石U-Pb法和40Ar/39Ar法对成矿期花岗斑岩、成矿后期闪长玢岩和含金石英-硫化物矿体进行了年龄测定,获得成矿期花岗斑岩的锆石U-Pb年龄为(304±5)Ma,成矿后闪长玢岩为(259±6)Ma,朱拉扎嘎金矿体中石英的40Ar/39Ar年龄为(282.3±0.9)Ma。这一结果揭示,朱拉扎嘎金矿是华力西晚期形成的,这与前人采用Rb-Sr法测得矿石的等时线年龄(275±6)Ma是一致的。结合阿拉善地区的呼伦西白金矿和欧布拉格铜金矿都是华力西晚期形成的,表明华力西晚期是中国西部最重要的金(铜)矿化期。

Zhulazaga gold deposit is a supper la rge stratabound-reconstructive gold ore deposit that has been found in recent years in Alxa area,Inner Mo ngolia Autonomous Region.The gold d eposit occurs in Mesoproterozoic strata and is of great ore potential.The host rocks are mainly calcareous siltstone and silty slate.Single zircon U-Pb and quartz 40 Ar / 39 Ar methods are applied to determination of U-Pb ages of metallogenic periods granite-porphyry and postmetallogenic periods diorite-porphyrite,and 40 Ar / 39 Ar age of Au-bearing quartz-sulfide ore body.The results show formation ages of(304±5)Ma of the zircon from the granite-porphyry and(259±6)Ma from the diorite-porphyrite.The quartz fro m the Au-bearing quartz-sulfide ore body shows a plateau age of(282.3±0.9)Ma.The Rb-Sr age of Au-bearing sulfi de ore measured before was(275±6)Ma.The close coincidence indicates that Zhulazaga gold deposit was form ed in late Variscan.The gold deposit,together with the other late Varisc an gold deposit,such as Hulunxibai gold dep osit and Oubulage copper-gold deposit in Alxa area,imply that Variscan i s the major Au(Cu)ore-forming epoch in West China.