云开地区庞西垌-金山银金矿田元素迁移特征及成矿地质过程  

Mass transfer during alteration and ore-forming geological process of the Pangxidong-Jinshan Ag-Au ore-field in the Yunkai area

作　　者：黄玺 郑义 虞鹏鹏[1,2,3] 曾长育 HUANG Xi;ZHENG Yi;YU Peng-peng;ZENG Chang-yu(School of Earth Sciences and Engineering,Sun Yat-sen University,Guangzhou 510275,China;Guangdong Provincial Key Laboratory of Geodynamics and Geohazards,Guangzhou 510275,China;Guangdong Provincial Key Laboratory of Geological Processes and Mineral Resource Survey,Guangzhou 510275,China;Guangxi Geological Survey Institute,Nanning 530023,China)

机构地区：[1]中山大学地球科学与工程学院,广东广州510275 [2]广东省地球动力作用与地质灾害重点实验室,广东广州510275 [3]广东省地质过程与矿产资源探查重点实验室,广东广州510275 [4]广西壮族自治区地质调查院,广西南宁530023

出　　处：《地球化学》2021年第4期365-380,共16页Geochimica

基　　金：国家自然科学基金(41872193,41902205);广东省自然科学基金杰出青年基金(2018B030306021);广州市“珠江科技新星”(201710010027);中山大学中央高校基本科研业务费专项资金(2021qntd23)。

摘　　要：粤西‒桂东交界的庞西垌‒金山矿田位于扬子和华夏地块构造结合的钦-杭成矿带内。矿田主要包括庞西垌、金山、中苏、竹根坡、高村等银金矿床,已探明银储量超过1400 t,平均品位195 g/t,金储量超过10 t,是我国重要的银金成矿基地。该矿田中,庞西垌‒金山断裂带是主要的控矿和含矿构造;矿体与该断裂韧脆性特征密切相关。本文对庞西垌断裂带与围岩的接触带做了详细的野外地质剖面测量,发现断裂中心部位为糜棱岩往北西及南东是对称的碎裂岩、花岗片麻质压碎岩(或压碎状花岗片麻岩),接触带两侧为未经蚀变和变形的花岗片麻岩和花岗岩。蚀变带岩石成分迁移结果表明,庞西垌矿区Th、Al、U、Hf、Na和Nb相对迁出、Fe相对迁入,其余元素如Ca、Mg、Y、Ba和K在压碎岩中相对迁入,碎裂岩中相对迁出;金山矿区Si、Ca、Fe、Mg、Y、Nb、Ta和Mn均相对未蚀变岩迁出,Th、Al和Rb则相对迁入,U、Hf、Na和Ba的迁入迁出状态取决于何种蚀变岩性。前人研究表明,庞西垌矿床主成矿期包裹体具有富CO2特点,表现为中低温、低盐度特点,与典型造山型金矿一致。庞西垌和金山矿床矿体产出位置与花岗片麻岩关系密切,矿体稀土元素特征与花岗片麻岩相近,硫化物的硫同位素组成与围岩花岗片麻岩类似,表明矿质可能来源于断裂带接触的花岗片麻岩。结合庞西垌‒金山矿田矿床地质、地球化学特征,本文认为矿体就位与断裂带燕山期韧脆性剪切带形成的破裂面密切相关,高孔隙度的压碎岩、碎裂岩为流体的迁移和沉淀提供了极佳的路径。The western Guangdong–eastern Guangxi Pangxidong–Jinshan ore field is located in the Qin-Hang Metallogenic Belt between the Yangtze and Cathaysia Blocks.The deposits in the ore field include the Pangxidong,Jinshan,Zhongsu,Zhugenpo,and Gaocun Ag-Au deposits with proven Ag reserves of more than 1400 t(average grade of 195 g/t)and Au reserves of more than 10 t.The main controlled and ore-bearing structure is the Pangxidong-Jinshan Fault.The deposits are closely related to the ductile-brittle Pangxidong Fault.In this study,a field profile of the ductile-brittle zone was measured,indicating that the fault contact zone consists of mylonite,cataclastic rocks,and crushed granitoids with unaltered and undeformed granitic gneiss and granite.The results of analyzing the mass transfer during alteration showed that Th,Zr,Al,U,Hf,Na,and Nb were removed,and Fe was enriched in Pangxidong mining area.The remaining Ca,Mg,Y,Ba,and K partitioned to cataclastic rock but not to the cataclasite.For the Jinshan mining area,Si,Ca,Fe,Mg,Y,Nb,Ta,and Mn were removed,and Th,Al,and Rb were enriched.The behavior of Zr,U,Hf,and Na depends on the alteration and lithology types.Previous research has shown that the main mineralization inclusion period of the Pangxidong deposit was characterized by CO2-enrichment with moderate-low homogeneous temperatures and low salinity,consistent with the characteristics of orogenic-type Au deposits.The ore body occurs near the granite-gneiss,and the REE characteristics of the ore body are similar to those of the granite-gneiss.The S isotopic composition in the Pangxidong and Jinshan ore fields is similar to that of granitic gneiss.This indicates that the ore-forming materials were likely derived from the granitic gneiss.Combined with the ore deposit geology and geochemistry,we believe that the emplacement of the ore bodies is closely related to the fractures formed by the ductile–brittle shear zones.Moreover,the high permeability of the cataclastic rocks provided a favorable pathway for ore materials.

关 键 词：造山型金矿 钦-杭成矿带 庞西垌‒金山矿田 韧脆性剪切带 蚀变岩成分迁移 

分 类 号：P595[天文地球—地球化学]