摘要
花岗岩及其造岩矿物以及副矿物中锡含量及其赋存形式的研究表明,个旧花岗岩中的锡主要赋存于黑云母等造岩矿物中。对个旧马松岩体的分析还表明,除造岩矿物外,尚有一部分锡赋存于榍石等副矿物中。黑云母和矽卡岩中锡主要呈类质同象置换形式存在,因而很容易受后期交代作用的影响而释放出来,参与成矿。基于此,可以得出本区锡矿的成矿模式:来自花岗岩浆的演化热液,通过交代蚀变作用摄取了花岗岩中主要赋存于造岩矿物中的锡,在运移过程中又使早期矽卡岩矿物如钙铁榴石等发生分解,汲取部分锡,最终在外接触带以及地层中有利的地质构造环境下,沉淀出有价值的工业矿体。
It can be seen from this study that tin in Gejiu granites is mainly concentrated in rock-formingminerals, especially in biotite, in which tin occurs chiefly as isomorphic replacement of Fe^(3+), Ti^(4+) bythe substitution: Sn^(4+)→Fe^(3+)+Li^+ and Sn^(4+)→Ti^(4+). Large quantity of tin may be brought into ore-forming solution when biotite decomposes (e. g. muscovitization of biotite). As for the Mashong gran-ite, tin may partly exist in accessory minerals such as sphene by the substitution: Sn^(4+)→Ti^(4+). Tin inthis form cannot be easily remobilized for sphene is comparatively stable. Some early skarn mineralssuch as andradite have high tin contents (mostly higher than 450ppm). Mossbauer spectroscopy studyshows that tin in andradite occurs as isomorphic substitution: Sn^(4+)+Fe^(2+)→2Fe^(3+). By contrast, laterskarn minerals, which are the products of replacement of earlier ones, have low tin contents (from 14to 75ppm, much lower than the early skarn minerals). This indicates that the tin in early skarn min-erals can be remobilized into the ore-forming solution when they are replaced by the late hydroxylskarn minerals. Based on these materials, a metallogenetic model of Gejiu tin field can be set up asfollows: tin-bearing ore-forming solution derived from granite magama leaches quantity of tin frombiotite and other rock-forming minerals by replacement of hydrothermal alteration. This tin-enrichedsolution can collect more tin when it replaces the early tin-bearing skarn minerals in contact zone, thusconcentrating tin in the solution. During the mineralization period, cassiterites can be deposited fromthe solution in the outer contact zone and certain favorable localities of the stratigraphic sequences.
出处
《地质找矿论丛》
CAS
CSCD
1991年第2期11-17,共7页
Contributions to Geology and Mineral Resources Research
