皖南池州桂林郑钼矿床成矿岩体的年代学和地球化学特征及其地质意义

摘要

桂林郑钼矿床位于江南隆起带与下扬子坳陷带之间的过渡带内,是皖南地区首次发现的大型钼矿床.本次工作对桂林郑钼矿床与成矿有关的花岗斑岩体进行了地质特征和岩相学观察、锆石LA-ICP-MS U-Pb定年和全岩地球化学分析.研究结果显示,桂林郑花岗斑岩的成岩年龄为127.6±1.5Ma,为早白垩世,对应于江南过渡带三阶段(149～ 137Ma、134～119Ma、116～110Ma)成岩成矿作用的第二阶段.桂林郑花岗斑岩富集K、Th、U等大离子亲石元素,具有低Sr高Yb特点,亏损Nb、Ta、Zr、Hf高场强元素,为高钾钙碱性-碱性的Al型花岗岩,岩浆源于中下地壳,上升过程中经历了显著的分离结晶作用.通过成岩年代与地球化学特征对比显示,桂林郑花岗斑岩体形成于陆内伸展环境,是该钼矿床的成矿岩体.%The Guilinzheng molybdenum deposits located in the transition zone between Lower Yangtze depression and Jiangnan uplift,which is the first large-type molybdenum deposit explored in the southern Anhui Province.Based on the detailed geological and petrographic observation,this work focus on the granite porphyry beneath Mo deposit,the zircon LA-ICP-MS U-Pb dating results of the granite porphyry show that their weighted 206Pb/238U age is 127.6 ± 1.5Ma,which indicate that the intrusion intruded in the Early Cretaceous.This age,compared with previous research,suggests that Yanshanian magmatic activity in the transition zone could be divided into three stages (149 ～ 137Ma,134 ～ 119Ma and 116 ～ 110Ma).The whole-rock geochemical analysis results show that the granite porphyry is metaluminous high-K calc-alkaline granites and enriched in Si,K,LILE and HFSE elements (Nb,Ta,Zr,Hf).The granite porphyry with low Sr high Yb contents is identified as is a typical A-type granites intrusion.The granite porphyry magma has experienced significant fractional crystallization during its emplacement.Petrology,geochronology and geochemistry characteristics indicate that the granite porphyry beneath Guilinzheng Mo deposit was formed in a continental extension background,which is genetically related with the formation of the Guilinzheng Mo deposit.