广西富贺钟钨锡多金属矿集区稀有气体同位素特征及其地质意义

桂东北富贺钟地区是广西重要的有色金属基地之一, 在姑婆山复式岩体的西南缘产出有新路、水岩坝和珊瑚3个主要钨锡多金属矿田。本文对不同矿田典型矿床分别开展了稀有气体同位素研究, 根据黄铁矿流体包裹体He、Ar、Ne同位素组成, 进一步讨论了区内钨锡成矿流体来源和壳-幔成矿作用过程。结果表明, 黄铁矿流体包裹体3He/4He=0.53~4.53 Ra、40Ar/36Ar=315.58~600.55、38Ar/36Ar=0.18688~0.19102、20Ne/22Ne=9.737~9.848、21Ne/22Ne=0.0291~0.0304, 显示成矿流体为地壳流体、幔源流体和饱和大气水的混合物, 成矿过程中有地幔物质的加入, 地幔He约占8.7%~75.7%。结合区内成岩、成矿的测年资料及岩石成因等综合分析认为, 区内中生代发生了多期次壳-幔相互作用, 且作用强度经历了强→弱→强的演化过程, 分别导致了姑婆山岩体主体岩性(165~160 Ma)和晚期细粒花岗岩(154~151 Ma)的侵位, 以及钨锡多金属成矿作用(136~100 Ma), 成矿与晚期的细粒花岗岩同位但不同时。

Isotopic Characteristics of Noble Gases of the Fuchuan-Hezhou-Zhongshan W-Sn-polymetallic Ore Concentration Area in Northeastern Guangxi and Their Geological Significance

Located at the conjunction of Fuchuan County, Hezhong City and Zhongshan County in northeastern Guangxi, the Fuchuan-Hezhou-Zhongshan W-Sn-polymetallic ore concentration area is one of the important nonferrous metal producing areas in Guangxi. It consists of three W-Sn-polymetallic orefields (Xinlu, Shuiyanba and Sanhu) lying on the southwestern margin of the Guposhan composite granite mass. In order to study the material sources and metallogenic mechanism of W-Sn-polymetallic deposits in the Fuchuan-Hezhou-Zhongshan ore concentration area, the authors analyzed the noble gases isotopic components of fluid inclusions in pyrite from the Baimianshan Sn-Zn deposit, the Shuiyanba W-Sn deposit and the Changyingling W-Sn deposit. The results indicate that 3He/4He ratios are 0.53~4.53 Ra, 40Ar/36Ar ratios are 315.58~600.55, 38Ar/36Ar ratios are 0.18688~0.19102, 20Ne/22Ne ratios are 9.737~9.848, and 21Ne/22Ne ratios are 0.0291~0.0304. The data obtained suggests that the ore-forming fluid was mixed with meteoric water, mantle fluid and crustal fluid, and the proportion of He derived from the mantle was 8.7%~75.7%. A synthetic analysis of the dating results of the Guposhan granites and mineralization as well as the genesis of granites shows that the Fuchuan-Hezhou-Zhongshan ore concentration area experienced poly-phase crust-mantle interaction in Mesozoic, and the crust-mantle interaction underwent the evolution from high intensity through low intensity to high intensity, resulting in the magmatic emplacement of Guposhan granites (165~160 Ma) and late fine-grained granite (154~151 Ma) as well as mineralization of the W-Sn-polymetallic deposit (136~100 Ma) respectively. The metallogenic epoch was later than that of late fine-grained granite, whereas the W-Sn-polymetallic ore bodies occurred in the same place as the late fine-grained granite.