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1.
行洛坑钨矿位于武夷山成矿带中部,是该带目前规模最大的钨矿床。钨矿体主要产于强烈蚀变的似斑状黑云母花岗岩岩株顶部,发育细脉浸染状、网脉状及大脉状多种矿化类型,黑钨矿与白钨矿含量近1∶1。关于矿床的流体演化过程与成矿机制目前仍不清楚,成因存在较大争议。本文在详细成矿阶段划分的基础上,对不同阶段产出的不同世代白钨矿开展了系统的原位LA-ICP-MS微量元素和Sr同位素、以及流体包裹体和H-O同位素的研究工作。行洛坑钨矿由早至晚可以划分为3个成矿阶段:细脉浸染状白钨矿-辉钼矿阶段(阶段Ⅰ)、钾长石-白钨矿-黑钨矿-绿柱石阶段(阶段Ⅱ)及硫化物-黑钨矿-白钨矿-碳酸盐阶段(阶段Ⅲ)。流体包裹体研究显示成矿流体为中高温、低盐度的Na Cl-H_2O-CO_2体系。H-O与Sr同位素表明成矿流体主要为岩浆流体,仅成矿晚期阶段有少量的大气降水加入。阶段I白钨矿相对富REE、Mo、Na和Nb,贫Sr;而随着流体演化,白钨矿REE、Mo、Na、Nb含量逐渐降低,Sr含量显著升高。阶段I白钨矿呈自形-半自形粒状,CL图像显示细密的、均匀的震荡环带,稀土元素主要与Na和Nb结合进入白钨矿晶格;阶段Ⅱ、阶段Ⅲ白钨矿呈半自形-他形,不发育或仅发育宽缓的、不规则震荡环带,稀土元素与Ca(Ca的离子空位)结合置换白钨矿中的Ca。结合蚀变与矿化特征,认为阶段I白钨矿形成于低水岩比环境,由初始岩浆流体沿微小裂隙渗透交代而形成;而阶段Ⅱ、Ⅲ白钨矿形成于高水岩比环境,CO_2的不混溶作用伴随强烈的水岩反应导致了钨的富集沉淀。结合矿床地质特征,认为行洛坑钨矿属于广义的斑岩型钨矿,细脉浸染状矿化构成了钨成矿的基础,而网脉状、大脉状矿化的叠加是钨进一步富集的关键。  相似文献   
2.
吴凯  袁洪林  吕楠  张丽鹏 《岩石学报》2020,36(1):141-153
蛇纹石是大洋岩石圈和俯冲带内水和流体活动性元素最重要的载体之一。研究蛇纹石化和蛇纹岩变质脱水过程中流体活动性元素的行为是认识俯冲带元素地球化学循环的关键。蛇纹岩是指主要由蛇纹石类矿物构成的岩石,包括利蛇纹石、纤蛇纹石和叶蛇纹石。蛇纹石化过程中会造成流体活动性元素(B、Li、As、Sb、Pb、Cs、U、Sr和Ba等)的显著富集,并且由于原岩性质、流体成分和氧逸度等条件的不同,大洋岩石圈蛇纹岩和弧前蛇纹岩的特征也略有不同。例如,弧前蛇纹岩具有相对高的As、Sb、B和相对低的U,这反映了俯冲沉积物来源流体的贡献。在俯冲带蛇纹岩的变质脱水过程中,利蛇纹石向叶蛇纹石的转变伴随着矿物内超过50%F和Cl的释放,以及一些流体活动性元素(如B和Li)的迁出;此外,蛇纹石分解形成的变质橄榄石中的流体包裹体指示,蛇纹石脱水分解所产生的流体具有高于原始地幔几个数量级的Cl、Cs、Pb、As、Sb、Ba、Rb、B、Sr、Li和U含量。由于利蛇纹石中的Fe~(3+)含量较叶蛇纹石高,这种矿物相转变过程中也伴随着俯冲通道内的一系列氧化还原过程,从而影响流体性质和新形成的叶蛇纹石的成分。蛇纹岩与岛弧岩浆在流体活动性元素富集规律上的相似性说明蛇纹岩在俯冲带元素循环中扮演着重要的角色。此外,蛇纹石矿物相转变过程中F、Cl、B等元素的释放,可能对于斑岩型金矿、蛇绿岩中的金矿和某些蛇纹岩作为赋矿围岩的硼矿的形成起到重要的作用。  相似文献   
3.
《China Geology》2020,3(2):269-282
Seabed fluid escape is active in the Makran subduction zone, Arabian Sea. Based on the new high-resolution 2D seismic data, acoustic blanking zones and seafloor mounds are identified. Acoustic blanking zones include three kinds of geometries: Bell-shaped, vertically columnar and tilted zones. The bell-shaped blanking zone is characterized by weak and discontinuous reflections in the interior and up-bending reflections on the top, interpreted as gas chimneys. Vertically columnar blanking zone is interpreted as side-imaged gas chimneys associated with focused fluid flow and topped by a seafloor anomaly expressed as a localized reflection discontinuity, which may together serve as a vent structure. Tilted acoustic blanking zone could be induced by accretionary thrust activity and rapid sedimentation surrounding slope. Seafloor mounds occur at the sites of bell-shaped acoustic blanking zone and may be associated with the material intrusion. Bottom simulating refectors (BSRs) are widely distributed and exhibit a series of characteristics including diminished amplitude, low continuity as well as local shoaling overlapping with these acoustic blanking zones. The large amount of gases dissociated from the gas hydrates migrated upwards and then arrived at the near-seafloor sediments, followed by the formation of the gas hydrates and hence the seafloor mound.  相似文献   
4.
《China Geology》2020,3(2):247-261
The Lower Cretaceous Yingcheng Formation in the southern Songliao Basin is the typical tight oil sandstone in China. In order to better predict the petrophysical properties of the tight sandstone reservoirs in the Lower Cretaceous Yingcheng Formation, Songliao Basin, Northeast China, the diagenesis and porosity evolution was investigated using a suite of petrographic and geochemical techniques including thin section analysis, scanning electron microscopy, mercury intrusion and fluid inclusion analysis, on a set of selected tight sandstone samples. Combined with the histories of burial evolution, organic matter thermal evolution and hydrocarbon charge, the matching relationship between reservoir porosity evolution and hydrocarbon accumulation history is analyzed. The result showed that the tight sandstone reservoirs characterized of being controlled by deposition, predominated by compaction, improved by dissolution and enhanced by cementation. The hydrocarbon accumulation period was investigated using a suite of hydrocarbon generation and expulsion history, microfluorescence determination and temperature measurement technology. According to the homogenization temperature of the inclusions and the history of burial evolution, Yingcheng Formation has mainly two phases hydrocarbon accumulation. The first phase of oil and gas is charged before the reservoir is tightened, the oil and gas generated by Shahezi source rocks enter the sand body of Yingcheng Formation, influenced by the carrying capability of sand conducting layer, oil and gas is mainly conducted by the better properties and higher connectivity sand body and enriched in the east, which belongs to the type of densification after hydrocarbon accumulation. The second phase of oil and gas charge after densification, which belongs to the type of densification before the hydrocarbon accumulation.  相似文献   
5.
Neoproterozoic metaturbidites in the Lower Ugab Domain, Namibia, contain a complex network of four sets of quartz-calcite veins, overprinted by km-scale folds associated with four regional foliations. The veins formed by fluid overpressure predating the main deformation. Deformation structures developed at the junction of two mobile belts during the assembly of Gondwana, the NS Kaoko Belt, and the EW trending Damara Belt. Km-scale NS trending folds were initiated during EW constriction in the Kaoko Belt, while their further development and all subsequent events are related to constriction in the EW-Damara Belt, with coeval sinistral strike slip in the Kaoko Belt. Deformation of the veins, and development of four orthogonal foliations are due to gradual changes in the bulk tectonic framework rather than separate orogenic events. The veins are deformed in a complex manner allowing a full 3D reconstruction of regional sequence of events. The local complex tectonics could be reconstructed because of the perfect local exposure and the multitude of veins: it illustrates the potential complexity of tectonic events and structural evolution in apparently simple slate belts.  相似文献   
6.
藏南沙拉岗锑矿流体包裹体红外显微测温研究   总被引:4,自引:0,他引:4  
沙拉岗锑矿是藏南金锑成矿带内最具有代表性的锑矿床。为了更直接地了解该矿床的流体物理化学特征,本文利用红外显微镜对辉锑矿及紧密共生石英中的流体包裹体进行了显微测温研究。红外显微测温分析结果表明,辉锑矿中包裹体均一温度在134.9~221.9℃,峰值在160~190℃之间,盐度在1.7%~7.3%NaCleqv,峰值在5.0%~6.0%NaCleqv之间,密度在0.879~0.958g/cm3之间,平均值为0.934g/cm3;共生石英中包裹体均一温度在142.5~205.6℃,峰值在160~190℃之间,盐度在2.3%~7.0%NaCleqv,峰值在4.0%~6.0%NaCleqv之间,密度在0.910~0.947g/cm3之间,平均值为0.929g/cm3。通过对比研究认为沙拉岗辉锑矿及共生石英形成于同一物理化学条件,捕获同一成矿流体。结合石英中单个流体包裹体激光拉曼成分分析认为成矿流体为含微量CO2、N2、CH4气体的低温、低盐度和低密度的NaCl-H2O热液体系。成矿流体的沸腾作用是辉锑矿大量沉淀主要原因。  相似文献   
7.
扎格拉金矿位于班公湖-怒江结合带东段及冈底斯-念青唐古拉板片北缘的腾冲-班戈岩浆弧带上;受被动陆缘深海复理石建造、 脆-韧性剪切带和深成岩浆活动控制。流体包裹体类型以单相和A型两相盐水溶液包裹体为主;次为B型两相盐水溶液包裹体、 富CO2两相包裹体和含CO2三相包裹体;成矿流体属中低温和中低盐度H2O-NaCl-CO2体系。氢、 氧同位素和相对富含K+、 Na+、Ca2+、 Mg2+、Cl-、SO2-4 的包裹体液相成分;显示成矿流体主要来自长期封存于沉积岩的深循环热(卤)水中;矿床成因类型为浅成中低温地下热(卤)水溶滤型金矿床。其成矿特征和流体性质与穆龙套型金矿床具有诸多相似性;研究该区域对西藏“沙丁板岩系”分布区金铜多金属找矿具有重要意义。  相似文献   
8.
广西苍梧社垌矿床是大瑶山隆起南侧新发现的一个大型斑岩-矽卡岩-石英脉型钨钼多金属矿床。本文重点对其中的石英脉型矿床进行了研究,依据脉体穿插关系及矿物共生组合将成矿过程划分为I石英-黄铁矿阶段、II石英-白钨矿-辉钼矿阶段、III石英-多金属硫化物阶段以及IV石英-方解石-萤石阶段,其中II和III阶段为主成矿阶段。从早到晚,均一温度逐渐下降(第一阶段550℃→370℃,第二阶段370℃→330℃,第三阶段330℃→210℃,第四阶段190℃→150℃),流体密度逐渐上升(0.61g/cm3→0.72g/cm3→0.82g/cm3→0.94g/cm3),盐度先升后降(第一阶段5.86%~8.55%NaCleqv,第二阶段4.49%~43%NaCleqv,第三阶段0.53%~46.37%NaCleqv,第四阶段0%~12.85%NaCleqv)。激光拉曼成分分析显示,社垌石英脉型矿床的成矿流体属于H2O-NaCl体系,但是该体系的流体成分在成矿前后发生了较大的变化,反映第I阶段以氧化环境为主,(II、III、)IV阶段则为还原环境。氢氧同位素研究显示成矿流体来自于岩浆水,后期大气降水的加入导致矿质发生沉淀。此外金属硫化物的δ34S组成(-3.8‰~+1.7‰)平均为-0.46‰,接近于零值,也表明为岩浆来源。引起矿质沉淀的主要原因是流体混合导致的温度下降等环境条件的改变。总体而言,社垌石英脉型钨钼多金属矿床的成矿流体主要来自岩浆热液,为中高温、中低盐度、低密度的NaCl-H2O流体体系,钨钼等多金属成矿与区内加里东期岩浆作用密切相关。  相似文献   
9.
Moreira Gomes is a recently discovered deposit (21.7 t Au) of the Cuiú-Cuiú goldfield, Tapajós Gold Province, Amazonian Craton. The mineralized zone is about 1200 m long, 30–50 m wide, and at least 400 m in depth. The zone is controlled by a subvertical, east–west-trending structure that is related to a left lateral strike-slip fault system. The host rocks are predominantly tonalites of the Creporizão Intrusive Suite (1997 ± 2 Ma) of uncertain tectonic setting (magmatic arc or post-collision). Hydrothermal alteration and mineralization are predominantly of the fissure-filling type and locally pervasive. Sericitization, chloritization, sulfidation, silicification, carbonatization and epidotization are the observed alteration types. Pyrite is the predominant sulfide mineral and bears inclusions of chalcopyrite, galena, sphalerite and minor hessite and bismuthinite. Gold occurs predominantly as inclusions in pyrite and subordinately in the free-milling state in quartz veins. Ag, Pb and Bi have been detected by semi-quantitative EDS analysis.Three types of fluid inclusions, hosted in quartz veins and veinlets, have been identified. (1) one- and two-phase CO2 inclusions; (2) two- and three-phase H2O–CO2-salt inclusions, and (3) two-phase H2O-salt inclusions. The CO2-bearing types are interpreted as the product of phase separation of an immiscible fluid. This fluid presents low to moderate density, low to moderate salinity (1.6–11.8 wt.% NaCl equivalent) and was trapped at 280° to 350 °C. The chemical system of the aqueous inclusions may contain CaCl2 and/or MgCl2, salinity varies from zero to 10.1 wt.% NaCl equivalent. Only locally salinities up to 25% have been recorded. This fluid was trapped between 120° and 220 °C and is interpreted as resulting from mixing of a hotter and more saline aqueous fluid (in part derived from phase separation of the H2O–CO2 fluid) with a cooler and dilute aqueous fluid.The δ34S values of pyrite (−0.3‰ to 3.9‰) are probably related to magmatic sulfur. The isotopic composition of inclusion fluids and of the fluid in equilibrium with hydrothermal minerals (quartz, chlorite, and calcite) show δ18O and δD values that range from +0.5 to +9.8‰, and from −49 to −8‰, respectively. Mineral pairs show equilibrium isotopic temperatures that are compatible with the fluid inclusion homogenization temperatures and with textural relationships of the hydrothermal minerals.Isotopic results combined with mineralogical and fluid inclusion data are interpreted to reflect a magmatic-hydrothermal system that evolved in at least three stages. (1) Exsolution of a CO2-bearing magmatic fluid between 400 °C and 320–350 °C and up to 2.1 kbar (6 km in depth) followed by phase separation and main precipitation of the hydrothermal assemblage composed of chlorite–sericite–pyrite–quartz-gold. (2) Cooling and continuous exsolution of CO2 produced a CO2-depleted and slightly more saline aqueous fluid that was trapped mainly at 250°–280 °C. The predominant hydrothermal assemblage of stage 1 continued to form, but epidote is the main phase at this stage. (3) Mixing of the stage 2 aqueous fluid with a cooler and dilute aqueous fluid of meteoric origin, which was responsible for the main carbonatization phase. The mineralizing fluid was neutral to slightly alkaline and relatively reduced. H2S (and/or HS-) might have been the main sulfur species in the fluid and Au(HS)2- was probably the gold transporting complex. Gold deposition occurred as a consequence of a combination of mechanisms, such as phase separation, mixing and fluid-rock interaction.The Moreira Gomes is a granite-hosted gold deposit that is interpreted to be a product of a magmatic-hydrothermal gold system. The age of ore formation (∼1.86 Ga) is consistent with the final stages of evolution of the widespread high-K, calc-alkaline Parauari Intrusive Suite, although the transitional to predominantly alkaline Maloquinha Intrusive Suite cannot be ruled out. Notwithstanding, the deposit does not show the classic features of (oxidized or reduced) intrusion-related gold deposits of Phanerozoic magmatic arcs.  相似文献   
10.
Normal faults on Malta were studied to analyse fault propagation and evolution in different carbonate facies. Deformation of carbonate facies is controlled by strength, particle size and pore structure. Different deformation styles influence the damage characteristics surrounding faults, and therefore the fault zone architecture. The carbonates were divided into grain- and micrite-dominated carbonate lithofacies. Stronger grain-dominated carbonates show localised deformation, whereas weaker micrite-dominated carbonates show distributed deformation. The weaker micrite-dominated carbonates overlie stronger grain-dominated carbonates, creating a mechanical stratigraphy. A different architecture of damage, the ‘Fracture Splay Zone’ (FSZ), is produced within micrite-dominated carbonates due to this mechanical stratigraphy. Strain accumulates at the point of juxtaposition between the stronger grain-dominated carbonates in the footwall block and the weaker micrite-dominated carbonates in the hanging wall block. New slip surfaces nucleate and grow from these points, developing an asymmetric fault damage zone segment. The development of more slip surfaces within a single fault zone forms a zone of intense deformation, bound between two slip surfaces within the micrite-dominated carbonate lithofacies (i.e., the FSZ). Rather than localisation onto a single slip surface, allowing formation of a continuous fault core, the deformation will be dispersed along several slip surfaces. The dispersed deformation can create a highly permeable zone, rather than a baffle/seal, in the micrite-dominated carbonate lithofacies. The formation of a Fracture Splay Zone will therefore affect the sealing potential of the fault zone. The FSZ, by contrast, is not observed in the majority of the grain-dominated carbonates.  相似文献   
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