摘要
铜陵矿集区是长江中下游成矿带七大矿集区之一 ,构造上经历了晚古生代的陆缘裂陷、中三叠世的陆_陆碰撞和侏罗纪—白垩纪的陆内构造_岩浆活动。晚石炭世的海底喷流沉积形成了广泛分布的块状硫化物 ,除部分构成块状硫化物矿床外 ,还为燕山期中酸性岩浆活动形成的矽卡岩型矿床提供了部分硫和金属物质。为了查明海西期喷流沉积流体系统及其时空展布特征 ,在铜陵矿集区内开展了以流体活动记录为对象的蚀变_流体填图工作。结果显示 ,海西期喷流沉积流体系统不仅形成以块状硫化物为主体的喷流沉积记录 ,而且在下伏岩系中遗留了区域规模的流体蚀变记录。以块状硫化物为主体的喷流沉积记录构成 3个喷流沉积旋回 ,在垂向上和横向上均具有成分和结构的分带性。流体蚀变记录在上部构成顺层蚀变带 ,在中部构成沿断裂和裂隙充填的石英_硫化物脉体群 ,在下部则构成半整合蚀变带 ,表明喷流沉积流体系统由下渗的海水在下部半整合蚀变带形成储集区 ,经高地热异常的加热后 ,沿中部脉体群向上迁移 ,在进入顺层蚀变带后沿砂岩层向两侧扩散 ,最后经同生断裂和裂隙向海底喷出。块状硫化物与蚀变岩、喷流沉积旋回及硫化物硫同位素的空间展布特征 ,显示区内存在 3个受基底断裂控制的NWW向延伸的流体活动域 ,包含
Tongling area, one of the 7 ore concentration areas in the Middle_Lower Yangtze metallogenic belt of eastern China, has tectonically undergone a geological history from Late Paleozoic continental rifting through Middle Triassic continent_continent collision to Jurassic_Cretaceous intra_continental tectono_magmatic activation. The Carboniferous sedimentary_exhalative processes in the area produced widespread massive sulfides 303～321 Ma in age, which, in addition to forming some Cu_bearing massive pyrite deposits, mainly provided considerable sulfur and metals for skarn Cu mineralization associated with the Yanshanian felsic intrusions. To understand the Carboniferous submarine hydrothermal system, the authors chose about 1000 km 2 in Tongling district for geological fluid mapping. The thick footwall sequences associated with the massive sulfide formation were widely altered. This hydrothermal alteration is considered to reflect the large_scale hydrothermal fluid flow associated with Late Paleozoic crustal rifting and subsidence. There occurred three hydrothermal alteration types, i.e., deep_level semiconformable silicification (S 1), fracture_controlled quartz_sulfide alteration (S 2_3 ), and upper_level concordant quartz_sericite_chlorite alteration (D 3), thus forming distinct zones in the mapped area. Comparisons with modern geothermal systems suggest that the semiconformable silicification zone has recorded a sub_seafloor aquifer with the most productive hydrothermal fluid flow. The fracture_controlled quartz_sulfide alteration formed transgressive zones, which likely indicate the upflow path of high_flux fluids from the hydrothermal aquifer. The lateral zonation of the concordant alteration zones and its relationship with overlying massive sulfide lenses suggest the lateral flow and diffusive discharging of hydrothermal fluids in the permeable sandstone sequence. 3 large_ and 14 medium_small sized massive sulfide deposits as well as 23 massive sulfide ore spots were mapped in detail so as to reveal regional stratabound characteristics. The associated exhalite and chemical sedimentary rocks include (1) anhydrite_barite, (2) jasper_chert, (3) Mg_rich mudstone_pyrite shale, (4) barite lenses, (5) siderite_Fe_bearing dolomite, and (6) Mn_rich shale_mudstone, which usually comprise three sulfide_exhalite cyclic units in this district. The spatial distribution of these alteration zones and associated massive sulfides and exhalites, together with regional variation in δ 34 S of hydrothermal pyrite, suggests three NWW_extending fluid flow domains comprising several fluid domains, controlled by the basement faults and syndepositional faults. Each fluid domain appears to consist at least of two upflow zones, with estimated range of about 5～8 km in the mapped area.
出处
《矿床地质》
CAS
CSCD
北大核心
2004年第3期281-297,共17页
Mineral Deposits
基金
国土资源部专项研究计划"大型矿集区深部精细结构与含矿信息"(编号 :2 0 0 10 10 3 )
国家自然科学基金重点项目 (批准号 :40 2 3 40 5 1)联合资助
关键词
地质学
喷流沉积流体系统
块状硫化物
区域蚀变铜陵
长江中下游成矿带
geology, exhalative_sedimentary fluid system, massive sulfides, regional alteration, Tongling, Middle_Lower Yangtze metallogenic belt
