陕西凤县八卦庙超大型金矿床成矿地质特征及成矿作用  

Geology and Metallogenesis of the Baguamiao Giant Gold Deposit in Fengxian, Shaanxi Province

作　　者：冯建忠[1] 汪东波[2] 王学明[3] 邵世才[1] 马治国 张选固 

机构地区：[1]北京矿产地质研究所,北京100012 [2]中国地质科学院地质研究所,北京100037 [3]中国地质调查局发展研究中心,北京100083 [4]陕西八卦庙金矿,陕西凤县721700 [5]陕西省地质勘查局717地质队,陕西宝鸡721000

出　　处：《地质学报》2003年第3期387-398,共12页Acta Geologica Sinica

基　　金：国家重点基础研究项目(编号G1999043213);国家科技攻关项目(编号96-914-01-04)

摘　　要：本文通过Ar-Ar同位素计时、稳定同位素示踪、石英位错观察、差异应力计算和热水沉积岩研究等,探讨了八卦庙超大型金矿床的成矿作用和成矿机制。NW向无根揉皱石英脉含Au 0.5×10^(-6)～4×10^(-6),矿化元素组合为Au+Cu+Pb+Zn,Ar-Ar坪年龄232.58±1.59Ma;NE向石英脉含An大于4×10^(-6),可达37.2×10^(-6),Au为主,Ar-Ar年龄为131.91±0.98Ma。研究表明:①泥盆纪热水沉积岩为金矿床的形成提供了矿源,成矿热液水以岩浆水为主,从矿质富集到成矿至少经历了印支期挤压推覆、韧性剪切→印支晚期—燕山期岩浆热液作用;②印支晚期和燕山早期(即韧性构造变形向脆性变形的转换期)是本区金矿成矿的高峰期;③多期成矿作用叠加、多次脉动式构造活动的“应力泵”作用是该超大型金矿床成矿的主因。The Baguamiao gold deposit, Fengxian County, is a giant one in Qinling orogene. NW-trending quartz veins and NE-trending quartz veins are widely present. The former with an Ar-Ar age of 232. 58 ±1. 59 Ma is the result of plastic rheology in ductile shearing, and the latter with an Ar-Ar age of 131. 91 ± 0. 98 Ma symbolizes the filling and metasomatism of magmatic hydrothermal solution. Based on geochronology and geologic settings, it is suggested that the gold deposit should have witnessed syn-orogenic event (Indosinian) and post-orogenic event (Yanshannian). In addition, analysis of the Au background value and sedimentation environment indicates that Au was enriched in Devonian exhalation to form source bed along the syn-sedimentary faults. Stable isotopes reveals that the ore-forming fluid is mainly derived from magmatic hydrothermal process. Based on regional geological settings, combined with quartz dislocation analysis, it is proposed that the spatial overlapping of NW-trending quartz veins and NE quartz veins represents the superimposition of brittle shear deformation on ductile shear deformation. At the end of the first structuring and hydrothermal solution event and the beginning of the second structuring and hydrothermal solution event, the altered rocks are most highly mineralized. Rich ores were formed on the structural transition period. The calculation of stress and Au contents proves that each pulse structural event forms a stress period. Au mineralization of NW-trending quartz veins intends to increase toward the end of ductile shearing in Indosinian synorogeny and Au mineralization of NE-trending quartz veins intends to decrease toward the end of brittle shearing in Yanshanian post-orogeny. The overprinting of multi-epoch mineralization events and multi-epoch pulse structural pump on the same location is responsible for the formation of the Baguamiao giant gold deposit.

关 键 词：八封庙金矿 热水沉积 脆-韧性剪切 位错 成矿年代 秦岭 陕西 成矿作用 地质特征 

分 类 号：P618.51[天文地球—矿床学]