中国云南金顶铅锌矿碎屑灌入体和水力压裂构造的观察及流体动力学分析  

Observations of clastic injection and hydraulic fracturing structures in the Jinding Zn-Pb deposit,Yunnan,China and hydrodynamic analysis

作　　者：池国祥[1] 薛春纪[2] 卿海若[1] 薛伟[2] 张江伟[2] 孙远强[2] 

机构地区：[1]加拿大里贾纳大学地质系,萨斯喀彻里贾纳S4S 0A2 [2]地质过程与矿产资源国家重点实验室,中国地质大学(北京)地球科学与资源学院,北京100083

出　　处：《地学前缘》2011年第5期29-42,共14页Earth Science Frontiers

基　　金：加拿大自然科学基金项目(NSERC-Discovery);中国国家自然科学基金项目(41072069,40772061,40930423);国家重点基础研究发展计划“973”项目(2009CB421005);长江学者和创新团队计划项目(IRT0755);高等学校学科创新引智计划项目(B07011)

摘　　要：金顶铅锌矿曾被认为是形成于相对被动地受构造与沉积相控制的盆地流体,类似于许多其他沉积岩容矿的金属矿床。然而,一些近期研究显示在金顶矿区露天采场存在砂岩灌入体、侵位角砾岩和水力压裂构造,说明矿床可能形成于超压流体的爆发性释放。文中报道在地下坑道(跑马坪和峰子山)中新观察到的与超压流体有关的构造,这些构造显示比露天采场有更清楚的交切关系。所观察到的构造包括:(1)灌入固结岩石缝隙的砂岩(±岩石碎块)岩墙;(2)侵入松散或半固结沉积物中的砂岩(±岩石碎块)体;(3)裂散的半固结砂岩体;(4)固结岩石受水力压裂作用然后被热液矿物胶结而形成的角砾岩和岩脉。砂岩灌入体和水力压裂构造中矿石矿物(闪锌矿)胶结物的发育表明,这些构造的形成时代与矿化时代相同。多向水力压裂和角砾岩的发育表明矿化过程中应力差很小,这与矿化前强烈的水平挤压构造应力场不同。根据砂岩岩墙中碎屑大小计算出来的流体流速可能高达11m/s。碎屑灌入体和水力压裂构造可能形成于超高压流体的爆发性释放,这可能和深部岩浆侵入或地震活动有关。这些活动周期性地打开了深部的高压流体库。由于碎屑灌入体和水力压裂构造与成矿流体的来源紧密联系在一起,它们与成矿作用密切相关,可以用作成矿指示。The Jinding Zn-Pb deposit has been generally considered to have formed from circulating basinal fluids in a relatively passive way,with fluid flow being controlled by structures and sedimentary facies,similar to many other sediments-hosted base metal deposits.However,several recent studies revealed the presence of sand injection structures,intrusive breccias,and hydraulic fractures in the open pit of the Jinding deposit and suggested that the deposit was formed from explosive release of overpressured fluids.This study reports new observations of fluid overpressure related structures from underground workings（Paomaping and Fengzishan）,which show clearer crosscutting relationships than in the open pit.The observed structures include：（1） sand（± rock fragment） dikes injecting into fractures in solidified rocks;（2） sand（± rock fragment） bodies intruding into unconsolidated or semi-consolidated sediments;（3） disintegrated semi-consolidated sand bodies;and（4） veins and breccias formed from hydraulic fracturing of solidified rocks followed by cementation of hydrothermal minerals.The development of ore minerals（sphalerite） in the cement of the various clastic injection and hydraulic fractures indicate that these structures were formed at the same time as mineralization.The development of hydraulic fractures and breccias with random orientation indicates small differential stress during mineralization,which is different from the stress field with strong horizontal shortening prior to mineralization.Fluid flow velocity may have been up to more than 11 m/second based on calculations from the size of the fragments in the clastic dikes.The clastic injection and hydraulic fracturing structures are interpreted to have formed from explosive release of overpressured fluids,which may have been related to either magmatic intrusions at depth or seismic activities which episodically tapped an overpressured fluid reservoir.Because the clastic injection and hydraulic structures are genetically linked

关 键 词：流体动力学 碎屑灌入体 砂岩岩墙 液压角砾岩 水力压裂 金顶 流体超压 

分 类 号：P618.42[天文地球—矿床学] P618.43[天文地球—地质学]