作　　者： ; ; ; ;

机构地区： 中国地质大学地球科学学院地质过程与矿产资源国家重点实验室

出　　处： 《地球科学（中国地质大学学报）》 2012年第1期77-92,共16页

摘　　要： 铜绿山Fe-Cu(Au)矿床是长江中下游铁铜成矿带最重要的矽卡岩型矿床之一,矿床的形成与铜绿山石英闪长岩岩株有关.矿区东南部发育有花岗伟晶岩,其形成时间介于石英闪长岩和矽卡岩之间.花岗伟晶岩主要由钾长石、斜长石和石英组成;由石英和钾长石组成的文象结构非常发育.激光阶段加热40Ar/39Ar定年表明,花岗伟晶岩的侵位时间为136.5±0.7Ma(2σ),与石英闪长岩的侵位时代和铜绿山矿床的成矿时代完全一致.铜绿山石英闪长岩与花岗伟晶岩的钾长石具有非常相似的主量元素,平均组成分别为Or81Ab18和Or78Ab21.根据岩相学观察和地球化学分析认为,花岗伟晶岩中的文象结构是在快速冷却体系条件下、钾长石晶体生长边界层的SiO2和Al2O3浓度因生长不平衡发生周期性变化而导致石英和钾长石交替生长形成的.铜绿山石英闪长岩和花岗伟晶岩中钾长石的大离子亲石元素(LILE)含量均较高,但与前者相比,花岗伟晶岩中钾长石的Rb、Pb含量明显增加,Ba、Sr含量显著降低,Li、Cs含量略微降低.大离子亲石元素图解(Rb-Ba、La-Ba、K/Ba-Ba、Rb/Sr-Ba)指示花岗伟晶岩是铜绿山石英闪长岩岩浆晚期高度结晶分异演化的结果.但花岗伟晶岩钾长石中Pb、Li、Ga等元素的变化却与岩浆结晶分异演化趋势相悖,表明流体作用在花岗伟晶岩的形成过程中扮演了重要角色.花岗伟晶岩中的石英发育大量熔融包裹体和高盐度流体包裹体,后者的均一温度为260～435℃,进一步证实花岗伟晶岩是从流体-熔体共存体系中结晶的. Tonglüshan Fe-Cu（Au） deposit is one of the largest skarn deposits in middle-lower Yangtze River metallogenic belt,which is associated with the Early Cretaceous Yangxin quartz diorite stock.Granitic pegmatites are well developed in the southeast mining area,emplaced in the Yangxin quartz diorite pluton and cut by garnet-diopside skarn.The cross-cutting relationships thus indicate that the granitic pegmatites are temporarily intermediate between the quartz diorite and skarn.Granitic pegmatites consist mainly of K-feldspar,plagioclase,and quartz,with conspicuous graphic textures marked by intergrowths of K-feldspar and quartz.K-feldspar with graphic textures from one granitic pegmatite dike has been successfully dated by the 40Ar/39Ar laser microprobe incremental heating technique,yielding a well-defined plateau age of 136.0±1.0 Ma（2σ）,which is interpreted to be the emplacement age of the granitic pegmatite dike.The age constraints indicate that the pegmatites formed coevally with the quartz diorite stock in the mine and related skarn Cu-Au mineralization.In situ laser ablation inductively coupled plasma mass spectrometry（LA-ICPMS） provides a wealth of information on the major and trace elements of K-feldspar from granitic pegmatites and quartz diorite.The average bulk compositions of K-feldspar from the pegmatite and quartz diorite are represented by Or81Ab18 and Or78Ab21,respectively.K-feldspar minerals with graphic textures have higher Si and lower Al than those without graphic texture.Textural and geochemical data indicate that graphic textures in the pegmatites resulted from alternating growth of K-feldspar and quartz due to dynamic alteration of the relative concentration of SiO2 and Al2O3 in areas proximal to the outer zone of growing K-feldspar crystals.Both K-feldspars from quartz diorite and granitic pegmatite are enriched in large-ion lithophile elements（LILE）,but the pegmatite contains more abundant Rb and Pb and lesser amounts of Ba,Sr,Li,and Cs.In the Rb-Ba,La-Ba,K/Ba-Ba,and Rb/Sr-Ba

关 键 词： 花岗伟晶岩 文象结构 定年 铜绿山 微量元素 包裹体 结晶分异 矿床学

领　　域： [天文地球] [天文地球]