Quaternary Volcanic-Related Acid Hydrothermal Alteration in the Ugusu Silica Stone Deposit, Western Izu Peninsula, Central Japan: Geology and Alteration

Acid alteration areas accompanying Quaternary volcanoes are widespread in the western Izu Peninsula, central Japan. The Ugusu alteration area is the largest among them and is mined for “silica stone” at the silica body in the core of the alteration area. Silica zone defined by previous studies is subdivided into highly leached brecciated silica zone and residual silica zone, which extend along a NNW‐SSE–NNE‐SSW direction of fractures/faults. Fe‐rich, alunite, advanced argillic alteration, and intermediate argillic alteration zones occur toward the outside surrounding the two silica zones. The ascent of acid hydrothermal fluid would be responsible for the silica zones and surrounding alteration zones at an earlier stage, while the hydrothermal brecciation and silica veins were caused by a limited supply of silica‐saturated fluids at later stages. Based on the available mineral stability relations and fluid inclusion thermometries, the formation temperatures are estimated to be: >300°C for the residual silica zone; >290°C for the diaspore association in the advanced argillic alteration zone; and <260°C for the kaolinite association in the intermediate argillic alteration zone. The later stage quartz druses have been formed at 200–260°C. The Ugusu–Fukata acid hydrothermal systems were active at 1.5–1.2 Ma, which were temporally related to the Tanaba Andesite volcanism. Hydrothermal system at the Seikoshi gold–silver deposit survived until 0.7 Ma after the volcanism. In the western half of the Izu Peninsula, subduction of the Philippine Sea plate underneath the Suruga Trough caused nearly N–S‐trending maximum horizontal compressive stress (σ_Hmax) and the resultant formation of similarly trending alteration areas and Au‐Ag vein‐type deposits in the Ugusu‐Toi‐Seikoshi area. From a practical viewpoint, at the Ugusu silica stone deposit, the fracture‐controlled vertical morphology of the silica body provides an important guide for exploration. Because the alteration zones occur both in the lower and upper sides of the silica bodies, it is important to make sure to which side the alteration zones correspond.     

Gold-bearing Quartz Veins and Hydrothermal Alteration of the Paleozoic Epithermal System in the Francis Creek Area, North Queensland, Australia

Abstract. The Francis Creek area located at the Sybil graben in North Queensland, Australia, has some features of epithermal gold mineralization such as gold-bearing quartz vein and silica body hosted in rhyodacitic rocks of the Late Carboniferous Hells Gate Formation. In order to understand the nature of the paleo-hydrothermal activity in this area and to aid exploration for an economic gold deposit in this area, we carried out hydrothermal alteration mapping surrounding the veins and silica body, over an area of about 7 times 5 km².
We defined two alteration zones and inferred the center of hydrothermal activity. Fluid inclusion shows the boiling feature, and the microthermometry analysis resulted in the trapping temperature of 240°C and low salinity. This temperature is consistent with the formation temperature of clay mineral in the host rocks. On the basis of whole-rock composition, the silica body was identified as silicified rocks. Precious metal minerals such as electrum and acanthite coexist with sulfide minerals. Iodagylite was identified as a product of weathering. The sulfide minerals imply that the low-sulfidation epithermal gold mineralization occurred in the Francis Creek area.     

Geochemical assessment of a siliceous limestone sample for cement making

A low grade siliceous limestone sample from the Jayantipuram mine of Andhra Pradesh, India, has been investigated for its suitability for cement making. Petrological as well as X-ray diffraction pattern studies indicated that the limestone sample was crystalline and dominantly composed of calcite and quartz. They are simple in mineralogy, and yet they have variable silica and lime contents. Geochemical analysis results of twenty five hand picked samples indicated that the limestone from the Jayantipuram mine shows a wide range of variations in LOI (29.94% to 40.64%), SiO2 (6.14% to 27.18%), CaO (37.93% to 50.78%), Al2O3 (0.49% to 2.27%) and Fe2O3 (0.28% to 2.4%). MgO, K2O, Na2O, TiO2 and MnO2 are present in traces. CaO with LOI shows a strong positive correlation where as CaO with SiO2 shows a strong negative correlation because of mineralogical factors. The chemical composition of the limestone reflects its mineralogical composition. The distribution of various elements in the acid-soluble fraction has been studied by the factor analysis method in order to interpret in terms of their mineralogy, sedimentary environment and diagenesis. Mineralogy, recrystallization and other diagenetic changes are the main factors affecting the distribution of the elements and their mutual relationships in the limestone. The aim of this paper is also to analyze how significantly the two parameters, silica modulus and lime saturation factor, influence this low grade siliceous limestone sample from the Jayantipuram mine of Andhra Pradesh, India, for the cement making process from the geochemical data.     

The distribution and concentration of particulate biogenic silica in surface waters of Prydz Bay, Antarctica, during the austral summer of 2011

The concentrations and distributions of particulate biogenic silica （PBSi） in the upper surface waters of Prydz Bay, Antarctica, were investigated during the 27th Chinese National Antarctic Research Expedition cruises of January 2011. We aimed to characterize the correlations between PBSi and plankton, nutrients and particulate organic carbon. The results showed that the concentrations of biogenic silica ranged from 0.76--19.72 ktmol-dm3 and the average concentration of biogenic silica was 6.06 mol.dm3. The distribution of surface PBSi had significant regional characteristics： The concentrations were higher south of 67S than to the north. The distribution of PBSi, chlorophyll a and particulate organic carbon showed similar patterns, and PBSi distribution had a negative correlation with that of silicate. In the vertical direction, the mole ratio of PBSi and POC （Si/Co） decreased with increasing depth. This trend indicated a higher rate of PBSi dissolution, or a lower rate of organic matter reminer- alization rate, in the upper 200 m.     

Quartz types in the Upper Pennsylvanian organic-rich Cline Shale (Wolfcamp D), Midland Basin,Texas: Implications for silica diagenesis,porosity evolution and rock mechanical properties

The origin and form of quartz in mudrocks has significant implications for interpretation of depositional environments, diagenetic pathways, mechanisms of porosity reduction and rock mechanical-property evolution. Quartz types in the Upper Pennsylvanian Cline Shale, Midland Basin, Texas, were examined using a combination of field-emission scanning electron microscopy-based energy-dispersive spectroscopy elemental mapping (to determine mineralogy) and scanning electron microscopy-based cathodoluminescence imaging (to determine quartz types) with the goal of elucidating a high-resolution imaging protocol at the micrometre scale for shale petrology. Also, the unconfined compressive rock strength of shale samples with contrasting proportions of different quartz types was measured using Equotip Bambino analyses. The results suggest that extrabasinal detrital quartz, which accounts for an average of 26 vol.% of the rock in all analyzed samples, is the dominant form of quartz in the Cline Shale. The intergranular clay-size microquartz, which accounts for an average of 10 vol.% of the rock in all analyzed samples, is the dominant form of authigenic quartz. Dissolved radiolarians and sponge spicules are likely sources of silica for clay-size microquartz and other authigenic quartz showing pale-mauve to dark greyish cathodoluminescence colour. Some authigenic quartz in the form of intragranular pore filling and mollusc skeletal replacement displays bright-reddish cathodoluminescence colour, which may be associated with silica released at a different time in the rock's diagenetic history, such as during smectite illitization. Porosity reduction in the Cline Shale predominantly resulted from compaction because of extremely low intergranular volume and the general lack of early cementation. Quartz form significantly impacts rock mechanical properties in the Cline Shale: widely distributed intergranular clay-size microquartz cement is a major factor controlling rock strength. This correlation also applies to other mudrock successions of various geological ages, tectonic histories and lithologies.     

非水溶性钾矿制取碳酸钾研究:副产13X型分子筛

非水溶性钾矿通常以钾长石为主要矿物相。对其进行粉碎、摇床重选、湿法磁选和化学酸浸除铁等预处理,可制得纯度达75%~95%的钾长石粉体。以碳酸钠为助剂,在760~860 ℃的中温下钾长石发生固相分解反应,生成偏硅酸钠、偏铝酸钾(钠)前体化合物,用于水热合成13X 沸石分子筛。滤液为富含[SiO2(OH)2]2-、Na+、K+的碱性溶液,通入CO2 进行酸化反应,生成SiO3·nH2O胶体沉淀,经250 ℃下煅烧即制成白炭黑。剩余滤液为NaHCO3 KHCO3 H2O三元水盐体系,再经浓缩、分离、纯化、结晶,制取碳酸钠和碳酸钾。由此,原矿中SiO2、Al2O3、K2O 3 种主要组分均可制成高值产品,可达到钾长石资源利用率接近100%、“三废”近于零排放的高效节能、清洁生产的“绿色过程”要求。本项技术实现规模化工业生产,将有利于缓解我国水溶性钾盐资源极缺的矛盾,平衡钾盐市场,提高国民经济可持续发展中钾盐资源的保证程度。     

二氧化硅水溶物种与热力学性质

系统综述了热液流体中溶解ＳｉＯ２存在形式的研究成果，指出溶解ＳｉＯ２在天然条件下主要呈真溶液迁移，其形式为Ｈ４ＳｉＯ４或Ｓｉ（ＯＨ）４·２Ｈ２Ｏ及其它水合数的单硅酸和多硅酸；在适宜的条件下，Ｈ３ＳｉＯ－４、ＮａＨ３ＳｉＯ０４、Ｓｉ（ＯＨ）４ＳＯ２－４、（Ｋ，Ｎａ）Ｓｉ（ＯＨ）０５或硅的有机配合物将成为主要的溶解物种。最后，给出了有关上述水溶物种的热力学平衡常数     

Silica dust and non-occupational silicosis——A global perspective

Health risk from various particulates of dust has been of public health concern for many years and scientific observations on dust have been going on for the last 200 years. Diseases resulting from exposure to dust are generally known as pneumoconiosis and have been primarily associated with occupational exposure to silica dust. Silica, which induces silicosis, has been recognized as far back as the Hippocratic times. The aim of the research is to try to assess the nature and scale of health risks from environmental exposure to silica on a global scale, with particular emphasis on non-occupational silicosis （pneumoconiosis）. Thorough literature reviews included studies and literature from non-occupational and occupational silicosis studies along with papers from Geology and Medicine. Non-published studies and local knowledge from Ladakh were used in pertinent of the review. The commonest form of silica （SiO2） is quartz. Other particulates in the atmosphere and finer particles 〈10 when inhaled with oxygen endanger human health; silica is the most threatening for non-occupational silicosis because of its high fibrogenicity. Aerosol minerals can often travel from continent to continent creating a health risk not just in the area of dust source, but also to secluded humans. When emitted into the air environmental exposure to （silica） quartz can occur as component of particulates emissions produced by natural-industrial-agricultural activities. Human exposure to environmental （silica） quartz can be summarized into direct and indirect pathways. Health risk from exposure to silica （quartz） has been widely studied in occupational settings; however there is a scarcity of studies on environmental/non-occupational exposure. Review of epidemiological studies on environment/non-occupational silicosis showed that all the studies lack a good control group and represent a small sample size. Many of these studies are case reports with retrospective histopathology, focusing only on the prevalence and lacking robust exposure measurement. Non-occupational/environmental silicosis is a global public health concem and the areas of dust source could be modified with climate changes. Literature is very scarce in relation to health risks from environmental dust （silica/quartz）, nevertheless the review of occupational studies links silica exposure to numerous diseases in humans.     

纤蛇纹石/酸浸二氧化硅负载TiO_2复合材料的结构性能及其降解罗丹明B的实验研究

以天然纳米矿物纤蛇纹石和酸浸二氧化硅为载体,钛酸四丁酯为钛源,在室温条件下采用溶胶-凝胶法,制备了负载TiO_2的复合光催化材料。采用气体吸附、扫描电子显微镜(SEM)、X射线衍射(XRD)等方法对载体和不同温度煅烧得到的样品进行微观形貌和结构分析,并在紫外光照射下,以10 mg/L罗丹明B为目标污染物评价不同样品的光催化活性。结果表明,750℃煅烧的酸浸二氧化硅负载TiO_2复合材料的光催化性能最好,光照40 min对罗丹明B的去除率达到91.57%,载体良好的吸附能力能够促进污染物的降解。     

ICP—AES法测定硅石样品中多种杂质元素

用电感耦合等离子体原子发射光谱法(ICP-AES)对地质样品硅石中多种杂质元素进行测定。方法确定了各元素的检出限,回收率在92%至105%之间,RSD小于1.93%,实验表明,该方法简便快速,具有很低的检出限和良好的精密度、准确度。