广西新路锡矿田某些成矿特征的探讨

DISCUSSION ON SOME CHARACTERISTICS OF MINERALIZATION IN XINLU TIN OREFIELD, GUANGXI

本文通过野外调查、矿床地质特征和岩矿测试资料研究,探讨了新路锡矿田的成矿物质来源,主要成矿地层岩石特征和锡石的铌钽含量特征。据硫、氧、铅同位素组成特征及其它地质事实为论据,认为新路锡矿田成矿物质锡主要源自花岗岩,而铅、锌源自地层,成矿热液主要为岩浆热液。对地层岩石特征研究表明,有利成矿层位主要是信都组上段顶部至东岗组下、中段与融县组,其岩石组合是由碎屑岩—碳酸盐岩过渡地段,或碳酸盐岩,它不仅有利于充填交代成矿,而且对矿床伴生铅、锌起到矿源层作用。据矿床中锡石单矿物的铌、钽含量、Ta/Nb比值与其它矿床的对比结果认为:①六合坳矿床形成于弱酸性—碱性介质环境,成矿温度较高:②白面山矿床形成于相对偏酸性介质环境中,成矿温度稍低,这个结论与其它方法得出的结果一致。

through survey in the field and research on geological characteristics and test data of rocks and minerals of tin deposits, the authors discuss the resources of ore -forming materials, the petrological characteristics of major ore - forming strata and the contents of niobium and tantalum of cassiterite in Xinlu tin oret'ield. According to the characteristics of the isotopic composition of S, O, Pb and other geological evidences, the authors consider that: in the Xinlu tin orefield, the major tin is derived from granite, lead and zinc from strata and the ore-forming hydrothermal solution mainly from magmatic water. The studies on petrological characteristics of strata reveals that favourably mineralized layers are mainly distributed from the top of upper member of Xindu Formation to the lower and middle member of Donggangling Formation, namely, in the transitional section between clastic rocks and carbonate rocks or carbonate rocks, which are favourable to cavity filling and metasomatism and are the source beds for the accompanying lead and zinc. Compared with those of other deposits, the content1 of niobium and tantalum and the value of Ta Nb of cassiterite show that Liuhe'ao tin deposit was formed in light acid - alkahc environment with higher temperature; whereas Baimianshang tin deposit was produced in relatively acid environment with a little lower temperature than the former's. This conclusion shows no difference with that reached by other geological methods.