新疆铁木尔特铅锌铜矿床锆石U-Pb和黑云母^(40)Ar/^(39)Ar年代学及其矿床成因意义

Zircon LA-ICP-MS U-Pb and biotite ^(40)Ar/^(39)Ar geochronology of the Tiemuert Pb-Zn-Cu deposit, Xinjiang: Implications for ore genesis

新疆铁木尔特铅锌铜矿床位于阿尔泰造山带南缘克兰盆地内,矿体呈脉状产于康布铁堡组火山岩地层中。为准确厘定其成岩成矿时代,作者分别对矿区赋矿火山岩和含矿石英脉中的云母进行了年龄测定,获得2件火山岩样品的锆石LA-ICP-MSU-Pb年龄分别为396±5Ma和405±5Ma,2件黑云母样品的40Ar/39Ar坪年龄分别为240±2Ma和235±2Ma,相应的39Ar/36Ar-40Ar/36Ar等时线年龄分别为238±3Ma和233±3Ma,与坪年龄在误差范围内一致。据此,认为矿区内康布铁堡组火山岩形成于396～405Ma,成矿作用发生于235～240Ma;成岩年龄早于成矿年龄约165Ma。因此,铁木尔特铅锌铜矿为典型的后生矿床,而不可能是同生VMS型矿床。考虑到成矿年龄稍晚于区域大规模变质作用(约250Ma),推测成矿作用与阿尔泰造山带碰撞造山作用有关。结合矿床地质特征和流体包裹体特征,认为铁木尔特铅锌铜矿为典型的陆陆碰撞体制下形成的造山型矿床。

The genesis of the polymetallic deposits in the Altay orogen in Xinjiang has been one of the disputed issues due to the lack of accurate dating data. The Tiemurt Pb-Zn-Cu deposit, which is controlled by the NW-directions faults, occurs as veins in the Devonian volcanic-sedimentary basin of Altay orogenic belt. To constrain the diagenetic and metallogenic ages, a set of integrated zircon U-Pb and biotite ^40Ar/^39Ar geochronological analysis were carried out. The zircons from two volcanic samples from the hosting rocks yield weighted mean 206Pb/238U ages of 396±5Ma and 405±5Ma, respectively, interpreted as the formation age of the Kangbutiebao volcanic rocks. Two biotite samples from the polymetallic sulfide-quartz lodes yield ^40Ar/^39Ar isotopic plateau ages of 240±2Ma and 235±2Ma, respectively, representing the orogenic mineralization age. By summarizing and synthesizing the available isotopic ages and geochemistry data, this paper recognizes a significant collision event and its related mineralization occurred in the Early Triassic epoch in the Altay Orogen. In combination with the characteristics of ore geology and fluid inclusion geochemistry, the Tiemurt Pb-Zn-Cu deposit is concluded as an epigenetic orogenic Pb-Zn-Cu deposit instead of a VMS deposit.