湖南龙山锑金矿床白云母~(40)Ar-~(39)Ar年代学及其意义初探

龙山锑金矿是湘中Sb-Au矿集区内规模最大的脉状锑金矿床,但其精确的成矿时代尚未厘定。本次工作发现该矿床第Ⅰ成矿阶段的石英硫化物脉中发育少量的热液白云母。通过40Ar-39Ar年代学测定,确定了白云母的~(40)Ar-~(39)Ar同位素坪年龄为162. 5±1. 8Ma,相应的等时线年龄为161. 1±1. 2Ma(MSWD=1. 0),反等时线年龄为161. 1±1. 2Ma(MSWD=1. 0)。根据矿物共生组合特征,认为白云母的~(40)Ar-~(39)Ar坪年龄能代表龙山锑金矿床的成矿年龄。结合湘中地区其他锑(金)矿床的年代学研究成果,本文认为,该地区在155~162Ma之间有一次热液成矿事件,与南岭地区165~150Ma与花岗岩有关的钨锡多金属矿床的成矿时代相一致。湘中地区已有的S同位素地球化学和地球物理学资料表明,该地区锑金矿床的形成可能与岩浆作用有关,类似于南岭地区晚侏罗世钨锡多金属矿床的构造背景。

Preliminary study on muscovite 40Ar-39Ar geochronology and its significance of the Longshan Sb-Au deposit in Hunan Province

The Longshan Sb-Au deposit is the largest lode-type Sb-Au deposit in the central Hunan Province Sb-Au ore-concentration area, while the precise geochronology has not been confirmed. This work found an amount of hydrothermal muscovite occurred in quartz sulfide veins in the first stage of mineralization. By the ⁴⁰Ar-³⁹Ar chronology study, we confirm that the muscovite yielded a ⁴⁰Ar-³⁹Ar plateau age of 162.5±1.8Ma, with an isochron age of 161.1±1.2Ma (MSWD=1.03) and an inverse isochron age of 161.1±1.2Ma (MSWD=1.01). Based on the characteristics of mineral assemblages, we infer that the ⁴⁰Ar-³⁹Ar system in muscovite remain to be closed with ore deposition, and constrain the formation of the Longshan Sb-Au deposit. In combination with geochronology research of other antimony (gold) deposits in the central Hunan Province, this paper argues that there was a relatively large hydrothermal mineralization event between the 155~162Ma in this area. And the result is coincident with a large number of tungsten tin polymetallic deposits related to granite formed in 165~150Ma in Nanling region. Integrated study of available S isotopic geochemistry and geophysical evidences, we conclude that the formation of Sb-Au deposits in central Hunan Province was related to the magmatism, similar to the tectonic background of the Late Jurassic tungsten tin polymetallic deposits in Nanling region.