Pb同位素对江西大湖塘矿集区部分矿床成岩成矿物质来源的指示

大湖塘矿床为近年来赣西北发现的超大型钨铜多金属矿床,其钨资源量达到了超大型规模,与南岭地区典型的钨矿床相比,大湖塘矿床缺乏应有的钨锡、钨钼元素组合,而以钨铜元素组合为特征,铜资源量达到了大型规模。钨、铜为2种地球化学性质迥异的元素,其在同一空间的出现意味着可能存在不同来源端员的混合。笔者测定了大岭上、大岭上东南部大雾塘矿区的一矿带以及平苗与成矿有关的岩体的全岩及矿石铅同位素,利用铀-铅同位素体系特征将本次测定的全岩铅同位素数据中铅发生丢失的样品进行剔除,然后分别将同位素比值投入不同的铅构造模式图解中,发现大湖塘全岩及长石铅数据主要分布于上地壳与地幔之间,可能还有下地壳物质混入。为了得到更为准确的组分来源信息,使用了铅同位素全方位对比法,对比了包括矿石铅、区内出露岩浆岩、区内及邻区相关地层、推测可能出现的岩石端员组分及本次测定的大湖塘矿区成矿岩体的全岩及长石铅同位素值。结果表明,大湖塘成矿岩体来源于新元古代双桥山群深熔作用,成矿物质主要为岩浆来源,其中铜主要来自新元古代变基性岩,钨主要来自元古代地层;其构造动力学背景可能受九瑞地区地壳加厚、拆沉远端系统的影响。

Indication of lead isotopes to source of rock-forming and ore-forming materials of some deposits in Dahutang ore concentration area, Jiangxi Province

The Dahutang deposit is a super-large tungsten-polymetallic mineral deposit discovered in the northwestern Jiangxi province in recent years. Different to typical tungsten deposit in Nanling region which was characterized by tungsten-tin or tungsten-molybdenum assemblage, Dahutang deposit owns super large scale of tungsten reserve and large size of copper contents. Copper and tungsten, however, are two different elements with distinct geochemistry properties. Their appearance in same space may means mixing of several end-member from different sources. In this paper, lead isotopes of bulk granitic rocks related with metallogenesis in Dahutang deposit have been analyzed. After being checking the analyzed data by observing the characteristic of U-Pb system and removing the data suffered lead loss, all the remaining data were plotted into the diagrams of ²⁰⁷Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb versus ²⁰⁶Pb/²⁰⁴Pb. The result showed that our data distribute between the curve of upper crustal and mantle, probably indicating existence of some material from lower crustal. To get more accurate component information, we used the fully Pb-isotope comparison method to contrast the lead isotopes of Yanshanian Dahutang ore-related granitic rocks with those of ore minerals, reginal magmatic rocks and sedimentary rocks from this area and adjacent region. Comparing Results showed that the ore-forming granite was produced by the anatexis of Neoproterozoic stratum and the metallogenic materials of Dahutang deposit were mainly originated from the magma. Copper were mainly derived from Neoproterozoic meta-basite, tungsten were from Neoproterozoic stratum. Granitic rocks related with the mineralization of Dahutang W-Cu deposit are mainly derived from Neoproterozoic stratum.