钦杭成矿带南段粤西大金山地区的区域地球化学特征与成矿规律探讨

摘要

The Dajinshan area of Guangdong province,located in the Dajinshan rotating tectonic belt,is the important metallogenic prospect area for S,Ag,Pb,W,Sn and Au.This area contains many mines and mineralization types and wide distribution of metallogenic belt.The 1 ∶ 50000 stream sediment survey presents a ring-shaped composite anomaly which is 35 km long and 2～5 km wide and covers an area of about 220 km2.The elements found in this area are W,Sn,Bi,Mo,Pb,Zn,Ag,Au and etc.,being characteristic of complex element combination,large scale and high anomaly.The main mines surrounding around the Dajinshan tectonic belt contain the Dajinshan W-Sn ore field,the Dajingping pyrite ore field,the Gaocheng Ag-Pb-Zn ore field,the Jiuquling Sn ore field and the Shimentou Pb-Zn ore field.This paper,based on the geochemical anomaly and characteristics of typical deposits,yielded the following understanding.(1) With the dome as the center of the Dajingshan area,the ore-forming elements from the inside to the outside forms regular horizontal zoning:W,Sn,Bi→Sn→Sn,Pb,Zn,Ag→Ag,Pb,Zn(Au) →Au;(2) the vertical zoning of W-Sn and Pb-Zn deposits is clear;(3)W-Sn-Pb-Zn-Ag deposits formed in late Yanshanian.On the basis of the recognition above,the paper established the metallogenic model of the Dajinshan area.The shallow metamorphic rock series formed by Sinian submarine volcano plume(gas) activity provided the source material for the deposits;in early Yanshanian movement,the Dajinshan rotating tectonic belt was formed by sinistral rotation of two regional-scale northeast-trending faults;the late Yanshanian magmatic activity resulted in the expansion of the Dajinshan rotational tectonic belt and drove the deep-sourced hydrothermal fluids carrying part of ore-forming materials such W to dissolve the Sn,Pb,Zn and Ag elements of the Daganshan Formation,and finally these elements precipitated in the various fractures in the tectonic system.%粤西大金山地区位于大金山旋转构造带中,是粤西S、Ag、Pb、W、Sn、Au重要的成矿远景区,该地区矿产地多,矿化类型多,成矿带分布广.其1:5万水系沉积物综合异常为一个环长35 km、宽2～5 km,面积约220 km2的环带状异常,主要由W、Sn、Bi、Mo、Pb、Zn、Ag、Au等元素组成,具有元素组合复杂,规模大,强度高的特点;环绕着大金山旋转构造带分布有大金山大型钨锡矿、大降坪特大型硫铁矿、高枨大型银铅锌矿、九曲岭中型锡矿、石门头中型铅锌矿等矿床.本文基于化探综合异常,解析各典型矿床特征认为:①大金山地区以“穹隆”为中心,成矿元素自内向外依次形成有规律的水平分带:W、Sn、Bi→Sn→Sn、Pb、Zn、Ag→Ag、Pb、Zn(Au)→Au;②钨锡矿床和铅锌矿床具有清晰的垂直分带规律;③钨锡铅锌银矿床均形成于燕山晚期.在此基础上,建立了大金山地区成矿模式:震旦纪海底火山喷流(气)活动形成的浅变质岩系,为锡铅锌银矿床的形成提供了物质来源;燕山运动早期,在两个区域性北东向断裂带的左旋扭动下,形成大金山旋转构造带;燕山晚期岩浆活动使大金山旋转构造带扩容,且携带部分成矿物质(如钨等)的深源热液溶解了大绀山组地层中的锡、铅、锌、银、金等元素,在各裂隙系统中成矿.