四川会理岔河元古宙锡矿床的地质特征及成因探讨

GEOLOGY AND GENESSIS OF THE PROTEROZOIC TIN DEPOSIT AT CHAHE, HUILI, WESTSICHUAN

岔河锡矿床产于元古宙裂谷环境中,其形成与晋宁期的花岗质岩浆活动有关。矿化及有关的矽卡岩化蚀变为含矿热液对大理岩等围岩交代的产物,皆围绕岩体接触带分布,并呈现良好的分带。含矿热液主要来自花岗岩,它提供了主要的流体和锡。锡的迁移、富集主要经历了岩浆结晶分异及围岩蚀变两个过程,分异作用是锡在热液中逐渐富集的主要原田,而云英岩化等蚀变中“脱载”出来的锡难以造成锡矿化。

Chahe tin deposit is one of the oldest tin deposits in China. Its tectonic stting is considered to be a proterozoic rift bordering the west margin of Yangtze plate-form. The rift sediments named Huili Group comprises a huge sequence of flysch formation, which underwent regional dynamic metamorphism and intrusion of granites. The tin deposit occurrs as replacement products of marbles and meta-basi-tes contacting with the Jinning granites. Three episods can be distinquished among the granites and only the latest one was directly related to tin mineralization.The skarn alteration and related mineralization exhibit distinct zoning, from outer inward the following mineral associatons occurr: (1) pyroxene + wollastonite; (2) idocrase + garnet; (3) casiterite + actinolite + magnetite; upon which the late casiteritesulphides developed. These zones extend in the form of lenses or striti-forms, obviously controlled by the properties-of the country rocks.The granites are believed to be the major source of tin and fluids; the transportation and deposition of tin were to a large extent resulted by the differentiation of magma;the release of tin by gre-senization seems impossible.