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密坑山岩体是南岭地区与锡成矿密切相关的典型岩体,侵入于上侏罗统鸡笼嶂组流纹质凝灰熔岩及火山碎屑岩中,为一破火山中央岩株侵入体,其主体岩性为钾长花岗岩,Rb-Sr全岩等时线年龄为(124.5±0.7)Ma。地球化学方面,该岩体具有富Si、偏碱性、富K、Al弱过饱和、Rb/Sr及Rb/Ba比值高、Eu负异常显著、富Ga、Ga/Al比值大(4.14～6.77)、富高场强元素(如Nb和Zr)等特点。地质地球化学特征及产出构造背景的综合分析表明,该岩体不是典型的S型花岗岩,而应属铝质A型花岗岩。岩体的εNd(t)值偏高(-3.56～-5.13),二阶段Nd模式年龄偏低(1207～1326Ma),反映成岩过程中有地幔组分的参与,属壳幔混源花岗岩。二元混合模拟计算显示成岩过程中地幔物质的混入比例为53.1%～60.0%,较高含量地幔组分参与成岩过程无疑指示幔源组分对成矿具有重要贡献,这一认识对于进一步揭示南岭地区稀有多金属矿床的成矿机理具有重要意义。
MIKHENGSHAN ROCK is a typical rock mass closely related to tin mineralization in the Nanling area. It intrudes into rhyolite tuff lava and volcaniclastic rocks in the Upper Jurassic cages. It is a volcanic central rock mass The intrusive body is mainly composed of potash-bearing granite. The Rb-Sr whole-rock isochron age is (124.5 ± 0.7) Ma. In terms of geochemistry, the rock mass is rich in Si, Alkaline, weak in K and Al, with high Rb / Sr and Rb / Ba ratios, significant negative Eu anomalies, large Ga and Ga / Al ratios (4.14 ~ 6.77 ), High field strength elements (such as Nb and Zr) and other characteristics. The comprehensive analysis of the geo-geochemical characteristics and tectonic setting shows that the rock mass is not a typical S-type granite but rather an A-type granite. The εNd (t) value of the rock mass is high (-3.56 ~ -5.13), and the age of the second-stage Nd mode is low (1207 ~ 1326Ma), reflecting the involvement of the mantle component during diagenesis and belonging to crust-mantle mixed source granites. Binary mixed simulation shows that the mixing ratio of mantle materials during the diagenesis is 53.1% ~ 60.0%. The involvement of higher mantle components in the diagenesis undoubtedly indicates that the mantle component has an important contribution to the mineralization. This understanding is further revealed The mineralization mechanism of rare polymetallic deposits in Ling area is of great significance.