The Late Jurassic extensional event in the central part of the South China Block – evidence from the Laoshan’ao shear zone and Xiangdong Tungsten deposit (Hunan,SE China)

ABSTRACT

The Late Mesozoic tectonics strongly reworked the tectonic framework of East Asia. In the South China Block (SCB), the major Late Mesozoic phenomena are featured by numerous magmatic activities, (half-) graben basins opening, and abundant ore deposits formation. The intrinsic relationships of these phenomena with the tectonic regime are still hotly debated, partly due to the lack of structural data. To advance the understanding of these issues, we conducted a detailed structural analysis including field and microscopic observations as well as an Anisotropy of Magnetic Susceptibility (AMS) investigation in the Laoshan’ao shear zone (LSA), which is the northern branch of the major Chaling–Chenzhou–Linwu Fault (CCLF) in the SCB. The new data enable us to reach the following conclusions: the evolution of the LSA can be divided into three deformation phases. D₁ is a NW–SE-stretching event featured by the SE-dipping normal fault with a top-to-the-SE shear sense, coeval with the emplacement of the 154 Ma Batuan syn-tectonic pluton that leads to the development of the Xiangdong tungsten deposit and the opening of the Cretaceous Chaling basin; D₂ is a NE–SW-striking dextral strike–slip event that dislocated the ore veins formed during the D₁ event; D₃ is a NW-directed thrusting event that cross-cut the previous gneissic foliation. D₁ is the major event of the LSA shear zone, interpreted as the reactivation of the CCLF in response to the Late Mesozoic tectonics in the SCB, and indicates a NW-SE extensional regime since the Late Jurassic in the study area. This study also provides an example for an ore-forming process controlled by both the hydrothermal fluid coming from a syn-tectonic granite and the accommodation of tension gashes opened by the regional extensional event.     

矽卡岩型钨矿床成矿相关岩体识别——以江西景德镇朱溪超大型矽卡岩型钨矿床为例

钨矿往往与酸性或中酸性侵入岩相关,对于复式岩体通常仅与某一特定期次岩浆相关,如何确定成矿相关岩体是找矿勘查的一道难题。朱溪矽卡岩型钨矿床位于江南古陆钨矿带,是一个世界级钨矿床。该矿床的形成主要与黑云母二长花岗岩和细粒花岗岩密切相关,此次研究发现黑云母二长花岗岩中的黑云母发生蚀变、分解过程中形成了大量含W金红石(w(WO_3)为0.01%~0.96%)。这类含W次生金红石同样出现在华南地区多个钨矿床的成矿相关岩体中,并且其WO_3含量显著高于与岩浆作用相关的锡矿床和斑岩型铜(金)矿床中的次生金红石的WO_3含量。此外,朱溪矿床中岩浆演化晚期形成的细粒花岗岩中结晶了一些自形板状的原生金红石,这些金红石同样显著富集W元素(w(WO_3)为0.06%~1.12%)。金红石中的Ti容易被W所替代,导致(岩浆)热液体系所经历的W元素富集过程会被结晶的金红石所记录。因此,通过花岗质岩体中黑云母发生蚀变或分解后形成的次生金红石,或岩浆演化晚阶段形成的细晶岩脉中的原生金红石的W元素含量,可以判断岩浆结晶演化过程中是否经历过W元素的富集及相应的富集程度,从而判断花岗质岩体是否具备形成钨矿床的潜力。     

综合物化探方法在粒七湾钨钼矿勘查中的应用实践

化探异常通常直接显示浅部地层元素富集程度,激发极化法对地下岩层含矿位置进行定位,两者有机结合,可对找矿起到事半功倍的作用。本文针对粒七湾钨钼矿与黄铁矿紧密相伴、钨钼矿越富伴随黄铁矿越多的特点,通过激电异常圈定地下金属硫化矿物富集范围,结合化探钨钼异常,其找矿效果良好。应用实践表明,地表有化探钨钼异常而对应地下无激电异常,地下无钨钼矿存在,只有两者异常都存在,地下深部才有可能成矿。这可为本地区寻找同类型矿床提供借签。     

钨矿床地球化学研究进展：以黑钨矿U-Pb、Sm-Nd、Lu-Hf 同位素年代学与微量元素为例

黑钨矿是钨矿床中最主要的矿石矿物之一,对其直接开展定年研究能更有效厘定钨成矿时间。黑钨矿通常含有一定量的U且部分样品具有较高的Sm/Nd比,因而U-Pb及Sm-Nd定年方法广泛地被应用到黑钨矿矿床的定年研究中。但是受黑钨矿U-Pb及Sm-Nd定年方法以及黑钨矿样品自身的制约,U-Pb及Sm-Nd定年成功率较低或结果不理想。文章针对黑钨矿在钨矿床U-Pb年代学和Sm-Nd年代学的发展历程进行了系统的梳理与分析,探讨了黑钨矿U-Pb年代学与Sm-Nd年代学的挑战与机遇。同时结合已发表的黑钨矿Lu、Hf数据,针对黑钨矿Lu-Hf年代学的应用前景进行了评估与展望。已有数据表明,黑钨矿中Lu/Hf比值变化范围较大,有潜力作为Lu-Hf同位素定年的良好对象。文章探讨了黑钨矿用于限定钨矿床成矿时代研究中存在的问题及应对方案,旨在促进未来黑钨矿在钨矿床成矿年代学的发展。     

安徽宁墩地区金钨地球化学异常找矿远景

宁墩地区金、钨地球化学异常以Au、As、W、Bi元素组合为主,异常套合较好、分带明显,异常强度高、规模大,受北东向断裂控制。通过水系沉积物加密采样和土壤、岩石剖面测量及路线地质调查,该区存在次生晕异常和原生晕异常,查证方法技术有效。位于褶皱和断裂构造发育部位的异常,有Au、W等高背景花岗闪长斑岩脉的侵入,物质来源和热源充足,成矿地质条件优越。路线地质调查发现金矿化体四处,但与该区异常强度和规模不相称,尤其是在破碎带矿化蚀变岩石中,Au、W、Mo成矿元素与As、Sb、Bi伴生元素含量均较高,该区显示出较好的Au、W、Mo找矿前景。     

中蒙边境沙麦-玉古兹尔地区钨和钨(钼)矿床地质特征, 形成时代和成因机理

首次对横跨中蒙边境线的沙麦-玉古兹尔钨和钨(钼)矿化集中区代表性钨和钨(钼)矿床进行了系统研究。含矿花岗岩体锆石SHRIMP铀-铅同位素年龄为225.9±2.1 Ma, 钨(钼)矿石辉钼矿铼-锇同位素年龄为224±6.2 Ma, 二者具有明显的成因联系。无论是沙麦钨矿床, 还是玉古兹尔钨(钼)矿床, 其主要成矿期石英流体包裹体数据十分相似, 属中-高温度和中-低盐度NaCl-CO2±H2O流体。考虑到含矿花岗岩的?Nd(t)值均为正值, 同时结合其它地质证据, 可以推测, 钨和钨(钼)矿床是岩浆流体与大气降水相混合的产物。印支期中酸性岩浆活动不仅为成矿体系“注入”大量成矿物质, 而且为热液的对流循环提供了动力和热力来源。研究结果表明, 沙麦-玉古兹尔地区钨和钨(钼)矿床成矿作用与印支期构造-岩浆活动有关, 属与深成侵入岩有关的中-高温热液脉型金属矿床。     

Rock—Forming and Ore—Forming Temperatures of Lianhuashan Tungsten Deposit,Guangdong Province

The Lianhuashan tungsten deposit occurs in the volcanic terrain in the coastal area of Southeast China,where rhyolite,quartz porphyry and granite consitute a complee magmatic series.The orebodies are located in the endo-and exo-contacts between the quartz porphyry and the metasandstone of the Xiaoping coal measues.Hongenization temperatures of melt inclusions in zircon and quartz are 1100℃and 1050℃ for rhyolite,1000℃ and 860℃for quartz porphyry,and 950-1000℃and 820℃ for granite,respectively,demonstrating that the rockforming temperatures dropped successively from the eruptive to the intrusive rocks and that the homogenization temperatures of melt inclusions in zircon are 50-180℃higher than those in quartz.Homogenization temperatures of gas-liquid inclusions in quartz are 230-520℃（mostly 230-270℃）for quartz porphyry,200-450℃（mostly 200-360℃）for ore-bearing quartz veins,150-210℃for granite 170-200℃ for the vein quartz in it.Quartz from the quartz porphyry and from the ore-earing quartz veins show similar characteristics in inclusion type and homogenization temperature,indicating that intergranular solutions must have been formed upon cooling of magma and that ore-forming solutions for the tungstem mineralization were evolved mainly from ore-bearing intergranular solutions in the quartz porphyry.     

广西珊瑚钨锡矿田断裂的构造化学环境及其含矿性评价

在研究区内不同方向断裂力学性质和地球化学特征的基础上，根据元素的应力性质和构造化学环境的内在关系，建立了断裂的构造化学环境判别指标，并以此对断裂的含矿性作出了评价。研究结果表明：ＳＮ向和ＮＮＥ向断裂属开放氧化和较开放偏氧化的构造化学环境，有利于钨矿床和钨锡矿床的形成；ＥＷ向和ＮＷ向断裂属较封闭还原的构造化学环境，不具备钨锡成矿的条件。     

漂塘钨矿木梓园矿区地质找矿成效

20世纪60年代,地质勘查部门曾运用“等距离控矿构造”理论找到了木梓园半隐伏钨-钼矿床.目前,随着矿山生产中段的不断延深,井下各种地质体现象的不断揭露,矿山地质工作者运用“侧列式”成矿地质规律在该矿体340中段以下又找到了南组内接触带矿体,获得较好的地质探矿效果.对这一找矿成效进行了综述.研究认为,其构造控矿的等距性和斜列对称性规律可以用来指导其他脉钨矿床深边部的地质找矿.