Mesozoic magmatism and copper polymetallic mineralization processes in the Shanghang-Datian region,Fujian Province,Southeast China

摘要

Various isotopic ages were reported for four granite plutons in the area studied, i. e. , the Tangquan pluton (185-158 Ma); the Zijinshan pluton (157-145 Ma); the Caixi pluton (133 Ma);and the Sifang pluton (108-105 Ma). The Tangquan and Zijinshan plutons belong to Early-Middle Jurassic and Late Jurassic of Early-Mesozoic respectively, and the Caixi and Sifang plutons belong to EarlyCretaceous of Late Mesozoic. Both the Tangquan and Sifang plutons, which are the metaluminous granites with A/CNK ＜ 1.0, are considered to possess the geochemical characteristics of adakite rich in Sr, Ba and poor in HREE, Y, Yb, and are regarded as the most potential host rocks of copper ores. The Zijinshan pluton is regarded as a peraluminous granite with A/CNK ＞ 1.1, and possesses the geochemical features of crust-derived muddy materials resultant from partial melting with enrichments in K, Rb, Th, Y, HREE and depletions in Sr, Ba, and Ti. The Caixi pluton is a weakly peraluminous granite with A/CNK = 1.0-1.1, and its geochemical characteristics are intermediate between the Zijinshan pluton and the Sifang pluton. The Tangquan pluton with higher Na2O contents, which resulted from partial melting of Proterozoic thick lower-crust derived basic rocks in response to underplating of mantle-derived basic magma, is one of the major host rocks of the metallogenic series of copper, iron and polymetallic deposits. The Sifang pluton with higher K2O contents, which was mixed between middle-lower crust-derived granite magma by partial melting and mantle-derived high-K basic magma, giving rise to the increment of K2O in the melt, and extracted large amounts of copper and other metals, as well as sulphur, is one of the major host rocks of the metallogenic series of porphyry copper, gold and polymetallic deposits. Petrological records have shown that there has occurred lithosphere extension since the Early-Middle Jurassic ( 180 Ma) in the region, and the formation of Zijinshan peraluminous granite is ascribed to the extension mechanism. With the time passing by, the lithosphere extension-thinning and underplating tend to intensify gradually. The contribution of the mantle to granite formation also increased gradually.