华南与花岗岩有关的一种新类型的锡成矿作用:矿物化学、元素和同位素地球化学证据  

New type of tin mineralization related to granite in South China:evidence from mineral chemistry,element and isotope geochemistry.

作　　者：蒋少涌[1] 赵葵东[1] 姜耀辉[1] 凌洪飞[1] 倪培[1] 

机构地区：[1]南京大学地球科学系成矿作用国家重点实验室,南京210093

出　　处：《岩石学报》2006年第10期2509-2516,共8页Acta Petrologica Sinica

基　　金：基金委优秀创新群体基金项目(40221301);教育部科学研究重大项目(306007)的资助

摘　　要：华南是我国最重要的锡成矿省,产有大量的与花岗岩有关的大型-超大型锡多金属矿床。近年来,在湘南新探明一个超大型锡矿床—芙蓉锡矿床,其中,最重要的锡矿化产在骑田岭花岗岩体西南部的破碎蚀变带内,与绿泥石化密切相关。骑田岭花岗岩富含角闪石,具有较高的氧逸度,显示出准铝的地球化学特征,在花岗岩形成过程中发生过壳-慢岩浆混合作用。这些特点都表明骑田岭花岗宕并不同于一般的 S 型含锡花岗岩,而显示出 A 型花岗岩的地球化学特征。同位素定年分析表明,芙蓉锡矿床主成矿阶段的形成时代要晚于骑田岭花岗岩侵位年龄近20Ma。氢、氧同位素分析表明,发生过水-岩反应的大气降水在成矿流体中占有很重要的地位。硫同位素分析表明花岗岩和地层都提供了成矿所需的硫。因此,用花岗岩浆结晶分异过程中分离出富锡的岩浆流体来形成锡矿的传统模式并不适合于解释芙蓉锡矿的形成。我们认为芙蓉锡矿的形成主要与骑田岭花岗岩的绿泥石化蚀变有关,循环的大气降水与花岗岩发生水-岩反应,富锡的铁镁矿物在蚀变成绿泥石的同时释放出 Sn 和 Ti 等金属到流体中,当物理化学条件改变时,沉淀形成锡矿体。这是一种比较独特的锡矿化模式,丰富了华南与花岗岩有关的锡矿化类型。South China is the most important Sn metallogenic province and there are many large and super-large granite-related tin deposits. Recently a giant tin deposit, the Furong, has been found in the southern Hunan province. Tin mineralized bodies mainly occur in the fault zones and alteration zones of the Qitianling granites, which genetically related to chlorite alteration. The Qitianling granites contain hornblende and have high oxygen fugacity, and are metaluminous. Elemental and isotopic geochemistry suggests that the granites were produced by the mixing of the mantle-derived mafic magma and the crust-derived felsic magma. Therefore, the Qitianling granites are distinctly different from common S-type tin granites and are more similar to A-type granites. Isotope dating results indicate that the age of main stage tin mineralization is 20Ma later than the emplacement of the Qitianling granites. H-O isotope data indicate a dominant influence of meteoric water associated with chlorite alteration. The sulfur isotope data suggest both the granite and the sedimentary strata provided the sulfur for mineralization. Fractional crystallization of the magma and tin deposition directly from exsolved magmatic-hydrothermal fluids may not be the major mechanism for the tin mineralization in the Furong deposit. Instead, we suggested that tin mineralization may be related with the post-emplacement chloritization of the Qitianling granites. Sn-rich mafic minerals （amphibole, biotite, titanite） released tin and other metals （e. g. Ti ） into the hydrothermal fluids when these minerals were altered to chlorites. Then cassiterite and rutile precipitated together with chlorite when the physical and chemical condition of the Sn and Ti-rich fluids changed. It is a very special model for granite-related tin mineralization. This study provides a new insight into granite-related Sn metallogenesis in South China.

关 键 词：芙蓉锡矿床 骑田岭花岗岩 绿泥石化 华南地区 

分 类 号：P597[天文地球—地球化学] P588.121[天文地球—地质学]