广西栗木锡铌钽矿田成矿物质来源的惰性气体同位素示踪

Noble gas isotopic tracing of ore-forming fluids in Limu tin-niobium-tantalum deposit

文章利用黄铁矿流体包裹体惰性气体同位素,探讨了广西栗木锡铌钽矿田成矿流体的来源。黄铁矿流体包裹体的3He/4He比值为0.14～0.97Ra,远远低于地幔流体的比值,接近饱和大气水的比值,并与地壳流体的比值处在相同的数量级上;40Ar/36Ar比值为555.98～855.11,平均705.55,显然偏离大气氩的同位素组成;40Ar*/4He比值为0.08～0.27,平均值为0.153,接近地壳值;20Ne/22Ne=9.671～9.748和21Ne/22Ne=0.0306～0.0330,具有饱和大气水的Ne同位素比值特征。结果表明,广西栗木锡铌钽矿田老虎头、牛栏岭和金竹源3个矿床的成矿流体是大气水和地壳流体的混合流体;水溪庙矿床的成矿流体也主要是大气水和地壳流体的混合流体,但可能有少量地幔流体的加入。

In this paper, ore-forming fluids and ore genesis are discussed based on the analyses of noble gases isotopes of fluid inclusions trapped in pyrite. 3He/4He ratios of fluids in the Limu tin-niobium-tantalum deposit are 0.14~0.97 Ra （under 1.0 Ra）.These values are smaller than values of mantle fluids and are close to the values of atmosphere saturated water and crust fluids.40Ar/36Ar ratios of fluids are 555.98~855.11 with an average of 705.55, far away from Ar isotopic composition of atmosphere.40Ar＊/4He ratios of fluids are 0.08~0.27 with an average of 0.153, close to the values of the crust and lower than the values of crust fluids.20Ne/22Ne ratios are 9.671~9.748, 21Ne/22Ne ratios are 0.0306~0.0330, having the characteristics of the atmosphere saturated water. He-Ar isotope composition shows that ore-bearing fluids in the Laohutou, Niulanling and Jinzhuyuan deposits were mainly mixed with the atmosphere saturated water and the crust fluids.The data obtained suggest that the ore-bearing fluids were mainly derived from the atmosphere saturated water and the crust fluids, with some mantle fluids probably involved in the ore-forming process of the Shuiximiao deposit.