右江盆地构造演化与卡林型金矿成矿作用

Tectonic evolution and mineralization of Carlin-type gold deposits in Youjiang basin

右江盆地(又称南盘江盆地)经历了古生代—早中生代原型盆地-叠合盆地的复杂构造演化,最终表现为残留盆地。根据大地构造背景、沉积系列组合和岩浆岩发育情况,加里东运动之后右江盆地演化过程分为6个阶段:陆内伸展盆地(早期裂谷)演化阶段(D^(2)_(1)-D^(1)_(2))、大洋伸展盆地(裂陷洋盆)演化阶段(D_(2)-T_(1))、洋盆消亡及前陆挠曲盆地演化阶段(T^(2)_(1)-T^(1)_(3))、褶皱造山及碰撞后伸展阶段(T^(1)_(3)-J_(1))、NW向陆内挤压造山阶段(J_(2)-K^(2)_(1))和局部伸展阶段(K^(3)_(1)-E)。盆地内产出中国重要的卡林型金矿,矿体多赋存于冲断-褶皱带中。这些金矿具有多期成矿特征,大规模成矿主要开始于挤压背景,并持续至造山后伸展阶段,其中集中成矿期有2个。第1期形成于挤压碰撞相关的前陆挠曲盆地演化阶段-碰撞后伸展阶段(235~193 Ma,盆地中南部卡林型金矿),该期成矿受扬子板块和印支板块碰撞造山与古太平洋板块向欧亚板块的俯冲叠加诱发的岩浆熔融作用及其相关热液活动或变质热液控制。第2期为NW向陆内挤压造山-局部伸展阶段(148~103 Ma,整个右江盆地卡林型金矿),该期成矿主要受NW向挤压造山对先存构造叠加改造过程中的岩浆-热液活动影响。早三叠世前伸展背景下岩浆-热液活动对金具有初次富集作用,早白垩世晚期后岩浆-热液活动对金成矿具有叠加改造作用。成矿流体具有混合来源特征,盆地中南部卡林型金矿成矿热液以变质热液为主,盆地中部多为混合来源热液,盆地北部则主要为岩浆热液。通过对比分析,认为不同测年方法获得的年龄可在一定程度上代表成矿年龄,建议利用多种方法联合应用限制卡林型金矿的成矿时代。

Youjiang basin(Nanpanjiang basin)experienced a complex tectonic evolution of Paleozoic prototype basin-superimposed basin,and finally,it appears as a residual basin.According to the tectonic setting,sedimentary series and magmatic rocks,the evolution of Youjiang basin after Caledonian movement can be divided into six stages:intracontinental extensional basin(early rift valley)evolution stage(D^(2)_(1)-D^(1)_(2)),oceanic extensional basin(rift ocean basin)evolution stage(D_(2)-T_(1)),ocean basin extinction and foreland flexure basin evolution stage(T^(2)_(1)-T^(1)_(3)),fold orogeny and post collisional extension stage(T^(1)_(3)-J_(1)),NW trending compression orogeny stage(J_(2)-K^(2)_(1)),and local extension stage(K^(3)_(1)-E).There are a large number of Carlin-type gold deposits in the basin,and most ore bodies occur in thrust-fold belts.The Carlin-type gold deposit has multi-stage metallogenic characteristics,large-scale mineralization mainly began in the compressive background and continued to the post orogenic extension stage,and there are two concentrated metallogenic periods.The first stage was formed in the evolution stage of foreland flexure basin related to collision orogeny to post collisional extension(235-193 Ma,Carlin-type gold deposit in the central and southern part of the basin).The mineralization in this stage was controlled by metamorphic hydrothermal fluids or hydrothermal fluids relate to magmatic melting which induced by the superposition of collision orogeny of the Yangtze Block and the Indochina Block and the subduction of the Paleo-Pacific plate to the Eurasian continent.The second stage was formed in the stage of NW trending compression orogeny to local extension(148-103 Ma,Carlin-type gold deposit in the whole Youjiang basin).The mineralization in this stage was mainly affected by the magmatic hydrothermal activities during the superposition and transformation of the pre-existing structures by the NW trending compression orogeny.Magmatic or metamorphic hydrothermal activities under extensional background before the Early Triassic has the effect of initial enrichment,and it has the effect of superimposed and reformation post mineralization after the Early Cretaceous.The ore-forming fluid of Carlin-type gold deposit has the characteristics of mixed sources.It is mainly metamorphic hydrothermal solution in the central and southern part of the basin,and mostly mixed source hydrothermal solution in the central part of the basin.While,the ore-forming fluid is mainly magmatic hydrothermal solution in the northern part of Youjiang basin.Through comparative analysis,it is considered that the ages obtained by different dating methods can represent the metallogenic age to a certain extent.And the combined application of multiple methods should be used to limit the metallogenic age of Carlin-type gold deposits.