华南S型火山杂岩与成矿

S-TYPE VOLCANIC COMPLEXES IN SOUTH CHINA AND METALLOGENESIS

笔者发现华南存在Ｓ型火山杂岩．根据其中富铝矿物特征，Ｓ型火山杂岩可分成三种组合：合石榴子石（±红柱石）组合，含黄玉组合和含堇青石－斜方辉石组合。这些Ｓ型火山杂岩的特征是：高硅。过铝质，相对富钾，中等碱质，富集不相容元素，高的Ｆ／Ｃｌ和Ｒｂ／Ｓｒ值，弱的铈和强的铕负异常，海鸥型稀土配分模式，低的εＮｄ值，高的２０７Ｐｂ／２０４Ｐｂ值，较高的（８７Ｓｒ／８６Ｓｒ）ｉ和δ１８Ｏ值以及较古老的Ｎｄ模式年龄．这些特征表明，华南Ｓ型火山杂岩可能是由无古代变质沉积岩部分熔融形成的．Ｓ型火山杂岩与锡：钠等矿化有密切的成因联系．

S-type volcanic complexes in South China have been found by the authors..According to the assembleages and characteristics of their Al-rich minerals, they can be divided into three assemblages. (1) Garnet (± andalusite)-bearing assemblage: it occurs inJ3-K1volcanic rocks of Dongxiang-Xiangshan area, Jiangxi Province, and graniticporphyries and clastoporphyritic lavas of Tashan-Xiling area, Guangdong Province. Thegarnets are near-liquidus phases, euhadral to subhadral, sometimes including someTi-bearing magnetite and needle apatite microcrystals. In composition, the almanditeend-member is prominent(44.8-75.3mol%), spessartine (0.5-30.8mol%),grossular(5.0-40.3)mol%) and pyrope (0.8-22.4mol%) subordinate. Prismatic andalusiteusually occurs as the near-solidus phases, frequently containing some felsic mineral inclusion. (2) Topaz-bearing assemblage: it occurs in the tin-bearing topazites, subvolcanicrhyolitic prophjries, granitic prophyries, and granites in Jiangxi and GuangdongProvinces. As a characteristic Al-rich mineral, the 'our-topaz of magmatic genesis, asshown by determination of X ray diffraction and probe analyses, has relatively short b axis(8.781-8.797A) and high F/ OH ratio of 1.70-1.75/ 0.30-0.25. (3) Cordierite-orthoyroxene -bearing assemblage: it occurs in Jiangzhou volcanic rocks and Taimasubvolcanic clastoporphyritic lavas of Triassic age in Guangxi Province (discussed in another paper).Geochemically, as a whole the S-type volcanic complexes have higher silica(SiO2 > 67%), peralumina (A / NKC > 1 .0), relatively rich potassium, middle alalinity, especially rich plagioclase-incompatible elements (Rb, Zr, W, Sn, Nb, Ta), depletedplagioclase-compatible elements (Sr, Ba, Eu) and markedly higher Rb / Sr and F / Cl tios . Moreover, they have weaker Ce and particularly intensive Eu negative anomalies, theREE distribution patterns are similar to sea-gull shape. In isotopic compositions, they havelower εNd(-6.2--9.5) and older Nd model ages (1.4-2.0Ga) and higher 207Pb/ 204Pb(15.588-15.808), (87Sr / 86Sr),(0.7084-0.7151 ) and δ18O(8.5-12.0‰ ). These characteristicsindicate that S-type volcanic complexes in South China were formed by partial melting ofProterozoic metasedimentary rocks. They have close genetic relationship with tin--and uranium-mineralizations in South China.