摘要
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。
The Mikengshan pluton, which intruded into the rhyolitic tufflava an d pyroclastic rocks of Upper Jurassic Jilongzhang Formation, is a typical exampl e of granite masses that closely related to tin mineralization in Nanling Region . It occurs as a central intrusion and lithologically consists mainly of moyite. This paper presents comprehensive geochemical study results of this pluton, aim ing to further determine its genetic type and elucidate its genesis. Whole-rock Rb-Sr isochron dating for this pluton yields an age of (124.5±0.9) Ma. Geoche mically, the Mikengshan granites are weakly peraluminous, have high silica and a lkalis contents, and high K2O/Na2O, Rb/Sr and Rb/Ba ratios. The rocks also have enriched Ga and HFSE (e.g., Nb and Zr) concentrations, high Ga/Al ratios (= 4.16 ～6.77), and display quite obviously negative europium anomalies. Based on an in tegrated analysis of the geological, geochemical characteristics and tectonic se tting, it is demonstrated that the Mikengshan pluton should be an aluminous A-t ype granite mass rather than a typical S-type one. The granites have higher 錘 d(t) values (=-3.56～-5.13) and lower two-stage Nd model ages (=1 207～1 326 Ma), indicating that mantle components should be involved in the rock-forming p rocess, and thus they can be ascribed to granites that originated from mixing of crustal and mantle materials. Binary mixing simulation illustrates that the rat ios of the mantle components involved in the granite formation process range fro m 53.1%to 60.0%. The more mantle material involvement undoubtedly indicates th at mantle-derived components have great contribution to the ore genesis. This n ew understanding has important significances in further revealing the genetic me chanism of rare polymetallic deposits in Nanling Region.
出处
《地球化学》
CAS
CSCD
北大核心
2005年第1期20-32,共13页
Geochimica
基金
国家自然科学基金(40132010)
国家创新研究群体科学基金(40221301)~~
关键词
含锡花岗岩
铝质A型花岗岩
地球化学
江西省
tin-bearing granite
aluminous A-type granite
geochemistry
Jian gxi Province
