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岩矿显微组构对水银洞金矿成因的指示 总被引：1，自引：0，他引：1
黔西南水银洞金矿为产于上二叠统龙潭组中的超大型、高品位金矿床,矿床由多个金矿体组成.工业金矿体顺层产于龙潭组含煤地层所夹的玄武质、硅质、生物碎屑碳酸盐岩中.对水银洞金矿赋矿地层岩石以及矿石显微组构进行了研究,矿石中主要载金矿物为细粒黄铁矿,具再生边、粒内孔隙、铸模孔隙结构及镶边生物矿化构造、铸模式生物矿化构造,是一典型的具沉积一成岩组构.金矿化与硅化有密切的成因联系,金与SiO2来源于峨嵋山玄武岩的喷溢活动,主要金矿体更多显示与峨嵋山玄武岩准同生特征.矿床为沉积一成岩弱改造成囚金矿床. 相似文献
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Abstract. Vein type tungsten mineralization at Degana is genetically and spatially associated with the Degana Granite. The deposit is characterized by pervasive wall rock alteration around the mineralized quartz veins. Laterally three different alteration zones, greisen, silicification and potassic zones, are marked based on the field features, mineral assemblages and geo-chemical characteristics. In the present paper, systematic mineralogical and chemical variation in these alteration zones is reported. Thick mono-mineralic (zinnwaldite) selvages around the veins characterize the deposit. Plagioclase and alkali feldspar are low in the greisen zones while K-feldspar shows more increase than plagioclase in the potassic zone. Quartz is uniformly high in all the alteration zones, but it shows an anomalous value in the silicification zone. Al2 O3 concentration shows initial depletion in greisen zone with gradual increase away from the contact. MgO and FeO are higher in greisen zone than silicification and potassic zones. The potassic zone is characterized by the depletion of Na2 O and higher value of K2 O.
The common presence of topaz and fluorite as both primary and secondary minerals and fluorine-bearing micas suggest fluorine partitioning in substantial amount between granitic melt and coexisting aqueous fluid phase and higher HF activity during the evolution of hydrothermal fluid. The mutual relationship of the fluorine minerals (topaz and fluorite) in the different alteration zones suggests an increase in the Ca2+ activity and decrease of H+ activity during the fluid evolution from greisenization towards alkali-metasomatised granite and the fluid is assumed to change from low to high activity ratio of Ca2+ /H+. 相似文献
The common presence of topaz and fluorite as both primary and secondary minerals and fluorine-bearing micas suggest fluorine partitioning in substantial amount between granitic melt and coexisting aqueous fluid phase and higher HF activity during the evolution of hydrothermal fluid. The mutual relationship of the fluorine minerals (topaz and fluorite) in the different alteration zones suggests an increase in the Ca
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研究区虎睛石矿床在地质特征、矿物组合、化学成分及琢雕效果等方面与国外虎睛石矿床是完全不同的，属于一种特殊的罕见类型。在分析虎睛石地质特征、开发利用现状的基础上，认为该区的虎睛石资源丰富，琢雕效果好，在国内外市场上具有一定的竞争力和良好的开发利用前景。 相似文献
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福建省区域地质调查队三分队在元坑幅及埔上幅１：５万区调中分别发现了将乐常口大型萤石矿和顺昌南舟萤石矿。两个矿床均位于常口－南舟北东向断裂带中，受其次级张性断裂直接控制，矿床成因类似。 相似文献
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鲕粒作为碳酸盐岩中非常重要的指相颗粒,其研究主要集中在成因上面,而成岩作用研究较少。北京西山地区下苇甸剖面寒武系张夏组发育大套鲕粒灰岩,通过对该剖面野外实测、薄片观察、XRD测试等手段,结合有机碳、热解等地化参数,对鲕粒的硅化机制及其硅质来源做了系统的研究。结果表明,鲕粒溶蚀再沉淀或者新生变形作用造成鲕粒边缘有机质富集,有机质演化释放的有机酸是硅质沉淀的主要因素,硅质来源主要为陆源输入和黏土矿物的转化。由于有机质主要富集在鲕粒边缘,形成有机质膜,从而造成硅质的沉淀主要沿鲕粒边缘发生,形成鲕粒边缘特有的硅化套,这种结果也从侧面反映了微生物在原始鲕粒形成中发挥了重要作用。 相似文献
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锡矿山锑矿床为严格受构造控制的热液型矿床,成矿成晕具有多期多阶段叠加的特点;F75断裂破碎带中元素的含量及叠加晕特征表明,该断裂不仅是导矿构造,而且在局部有利部位成为储矿构造;文章以飞水岩矿段为例,总结了矿体的元素组合及其相关关系,确定了不同成矿阶段矿体的特征元素;单一次成矿形成的原生晕轴向分带序列是As,Hg,F,Li,Ba→Sb→Ag,Cu,Pb,Zn→Mo,Bi,Mn,Co→Ni,Ti,V,W,Sn,Sr;在识别不同成矿阶段的矿体(晕)在空间上的叠加结构基础上,建立了矿床构造叠加晕模式,确定了盲矿预测标志,对矿床深部进行盲矿预测,提出了盲矿的找矿靶位;初步验证工作表明,构造叠加晕方法对锡矿山锑矿飞水岩矿段深部盲矿体的预测效果较好。 相似文献
7.
The chemistry and mineralogy of much of the Late Eocene Blanche Point Formation of South Australia show that biogenic and volcanogenic products were the only significant contributor to the sedimentary record. Intermittent volcanic activity followed by dissolution of the resultant silicic ash and small scale migration of silicon with reprecipitation as the oxide, provides the simplest and most likely explanation for the repetitive nature of the silicification. Seemingly, this was controlled by local silica concentrations which in turn were apparently controlled by the biota. Changes in circulation patterns and/or water depth may have initiated the environmental variations recorded in the formation. 相似文献
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Groundwater silcretes have been recognized recently as major terrestrial silicon sinks and yet their origins are poorly understood. This paper aims to further the understanding of the micro‐fabric, geochemistry and formation of groundwater silcretes, through detailed analyses of silcrete boulders from the South Downs, Sussex, UK. In‐depth petrological investigations of silcrete blocks identified three varieties of silcrete across the study area (saccharoid, hard and pebbly conglomeratic or silcrete breccia), similar to those elsewhere in England. Silcrete fabrics were universally simple and preserved host material structures. Optically continuous quartz overgrowths were the dominant cement and developed on framework grains in the absence of silt‐ and clay‐sized particles. Finer‐grained silica cements occurred in isolated patches and as vein‐ or cap‐like geopetal features. These caps and veins formed through the silicification of illuviated clay‐rich material that entered the host sediment prior to, or in the early stages of, overgrowth formation. Titanium contents were related to the amount of fine‐grained silica and appear to reflect variations in host material chemistry. Subsequent to silicification, the silcretes were altered by at least two phases of ferruginization, characterized by the ingress of iron minerals and partial fabric dissolution or replacement. The study reveals strong similarities in the micromorphology and geochemistry of groundwater silcretes in the study area and those developed in sandy host sediments in neighbouring parts of northwest Europe. Variations that do occur could be explained by differences in the host sediment, geological setting or tectonic history of the respective basins (or sub‐basins), suggesting that there may be a common mechanism for silcrete formation across north‐west Europe. Silcrete development appears to be related to the release of silica accompanying acid leaching of the host material or adjacent strata. In the South Downs, this probably resulted from oxidation of pyrite in the argillaceous and lignitic sediments overlying the host sands. It is envisaged that palaeoenvironmental conditions were of limited importance for silcrete development and that there was no specific ‘era’ of formation, with phased development accompanying landscape evolution through the Neogene into the Pleistocene. 相似文献
10.
Silicification of sulphate evaporites and their carbonate replacements in Eocene marine sediments, Tunisia: two diagenetic trends 总被引：1，自引：0，他引：1
Samples of chert nodules, diagenetic carbonates and evaporites (gypsum/anhydrite) collected from the gypsiferous limestones of the Kef Eddour Member (Ypressian‐Priabonian) near Metlaoui and Sehib (Tunisia) show selective silicification with great variety in the silicified by‐products. Based on δ13C values, which support an organic origin for the carbon, carbonates replaced evaporites microbially through bacterial sulphate reduction. Observations and results suggest two scenarios for chert formation that are related to the rate and timing of diagenetic carbonate replacement of the evaporites (anhydrite/gypsum). In the absence of early diagenetic carbonate phases, silica with δ18O values from +25 to +28·6‰ [standard mean ocean water (SMOW)] replaced the outer parts of anhydrite nodules at pH < 9. In contrast, pore‐fluid pH values > 9 in the innermost parts of the anhydrite nodules prevented silica precipitation. The record of this chemical barrier is preserved in the microquartz rims and geode features that formed in the inner parts of the nodules after dissolution of the anhydrite nucleus. The microbial diagenetic replacement of evaporites (bacterial sulphate reduction) by carbonates (calcite, aragonite and dolomite) favoured silica replacement of carbonates rather than evaporites. Silica, with δ18O signature of +21 to +26‰ (SMOW), replaced carbonates on a volume‐for‐volume basis, yielding a more siliceous groundmass, and accounting for 90–95% of the nodules. The relatively higher δ18O values of quartz replacing anhydrite can be explained by a diagenetic fluid in equilibrium with mixed (meteoric/marine) to marine water. The lower δ18O values of the quartz that replaced the diagenetic carbonates are ascribed to flushing by meteoric water in a later diagenetic stage. The silica supply for chert formation could be derived from the reworked bio‐siliceous deposits (diatomites) to the west of the basin [vestiges of an opal‐CT precursor undetectable by X‐ray diffraction (XRD) were revealed by δ29Si magic‐angle‐spinning nuclear magnetic resonance investigations], diagenesis of the extraformational and overlying clay‐rich beds (the host limestones are clay‐poor as shown by XRD measurements), and minor volcanogenic and hydrothermal contributions during early diagenetic stages. 相似文献