红山含黄玉花岗岩的形成时代及其成矿能力分析

Formation time of Hongshan topaz-bearing granite and its metallogenic potential prognosis

对闽西南红山含黄玉花岗岩进行了LAM-ICPMS锆石U-Pb定年以及地球化学对比研究。地球化学分析显示红山花岗岩具有富F和高演化的地球化学特征,富含稀有和有色金属成矿元素,如Sn含量为(15·3~54·0)×10-6,W含量(3·04~14·9)×10-6,Nb含量为(22·5~36·7)×10-6,Ta含量为(3·37~7·31)×10-6,U、Th含量分别(6~30)×10-6和(12·1~36·4)×10-6。与含矿花岗岩的对比研究表明红山花岗岩很可能存在与之有成因联系的Sn、U矿床。地球化学填图显示了元素在空间上的分带变化,指出与红山花岗岩有关的成矿作用最可能发生在岩体的东南端,即116°8′E^116°10′E和25°29′N^25°32′N的区域。锆石U-Pb定年结果表明红山花岗岩形成于印支期(~226Ma),因此,其在形成时代、地质产状和成矿作用上不同于华南大多数形成于燕山晚期的含黄玉花岗质岩石。南岭基底变质岩富含W、Sn、Nb、Ta等成矿元素,它们是华南(特别是南岭地区)含矿花岗岩中成矿元素富集的最主要物质来源。

In order to determine the formation age of the Hongshan topaz-bearing granite and make metallogenic potential prognosis, the authors carried out LAM-ICPMS zircon U-Pb dating and detailed geochemical comparison. Geochemical analyses of fifteen samples show that the Hongshan granite is characterized by high F contents and highly evolved geochemical features. It contains abundant metallogenic elements, such as Sn （15.3-54.0）× 10^-6, W （3.04-14.9） ×10^-6, Nb （22.5-36.7） × 10^-6, Ta （3.37-7.31）× 10^-6, U （6-30） ×10^-6 and Th （12.1-36.4 × 10^-6）. Geochemical comparison with other ore-bearing granites in the world indicates that related mineralization, especially Sn and U mineralization, may exists in the Hongshan granite intrusive. Geochemical mapping shows that some geochemical parameters, such as Sn, W, REE, Zr, Th, and Rb, exhibit a rough spatial zonation, with the most evolved samples located in the southeastern part of the pluton, suggesting that the most probable target area of rare-metal deposits may be in the southeastern area, i.e., between 116°8＇E-116° 10＇E and 25°29＇N- 25°32＇ N. LAM-ICPMS zircon U-Pb dating results indicate that the Hongshan granite was formed at-226 Ma. Therefore, it is different from most topaz-bearing granitoids in South China in the formation age, mode of occurrence, and mineralization. The Nanling Range basement metamorphic rocks contain abundant W, Sn, Nb and Ta, and hence serve as the most important ore-forming element source of the Hongshan granite.