Akita University Institutional Repository System (秋田大学学術情報リポジトリ)
Not a member yet
6110 research outputs found
Sort by
Geology, mineralogy, geochemistry, and genesis of the Vangtat gold belt, Southeastern Laos
Get PDF秋田大学博士（資源学）The Indochina Terrane is a major tectonic unit of mainland Southeast Asia, is bound to the north by the South China Terrane and to the west by the Sibumasu Terrane, with the Truong Son fold belt, and the Loei and Sukhothai fold belts marking broad collision zones with the two continental terranes. Broadly coincident with these tectonic collisions, several internal domains were amalgamated to the Indochina Terrane during the Indosinian orogeny. Magmatism, metamorphism, deformation, and hydrothermal alteration along the domain boundaries surrounding and within the Indochina Terrane resulted in the formation of a variety of precious- and base-metal deposits, notably porphyry-related skarn, epithermal, sediment-hosted, and orogenic gold deposits. The collision orogenesis between the eastern extension of Indochina Terrane with the Kontum Massif resulted in the formation of the Poko suture zone and associated structures, including the Vangtat shear zone, which the subject of this research as the host of a recently discovered orogenic gold belt. A newly discovered orogenic gold belt consists of the Thongkai-Ok, Vangtat, and Gieng Dat deposits, occurs within the Vangtat shear zone and is called as the Vangtat orogenic gold belt. This research aims to (1) clarify the nature and genesis of primary gold mineralization in the Vangtat gold belt, and (2) constrain the age of gold mineralization and to better understand the relationship between Southeast Asia tectonics and mineralization. Base on the study of host geology, geochronology, ore and gangue mineralogy, hydrothermal alteration, fluid inclusion, and sulfur isotope. The Vangtat gold belt is hosted in the early- to mid-Palaeozoic regional metamorphic belt, located in the western part of the Poko suture zone, western margin of the Kontum Massif. The Vangtat gold deposit is one of several actively mined deposits and represented the main economic orebody of the Vangtat gold belt. Two main rock units are found in the deposit scale: the lower unit is made up of metagabbro and the upper unit is composed of metasedimentary lithologies, including pelitic schist, slate, metasandstone and quartzite. The lithological units around the Vangtat deposit, as well as other hard-rock (primary) gold deposits in the district, are covered by a thick (~ up to 50 m) blanket of weathering and supergene oxidation, which led to local gold remobilization and concentration of secondary gold in surficial detrital sediments. This alluvial gold is recovered by artisanal miners through the district and marks the first recorded gold mining in the region. Pelitic schist is the main mineralized host rock of the Vangtat deposit, which is made up of foliated muscovite-chlorite with finely interlayer quartz and plagioclase. Pelitic also contained a minor amount ( 3g/t Au on average; reaching values >100 g/t Au in selected hand specimens and drill core intercepts) occurs only in the quartz-sulfide-graphite-carbonate-white mica-chlorite veins. Lower-grade gold mineralization (avg. < 3g/t Au) occurs in a graphite-carbonate-quartz-sulfide hydrothermal alteration zone that forms an envelope around the veins and grades into a sub-economic to barren altered pelitic schist. Gold is closely associated with sulfide, identically gold concentration decreases together with sulfide content from the quartz-sulfide vein at the center towards the marginally altered host rocks. Pyrite is the main host for gold mineralization in the Vangtat deposit. Most of the auriferous pyrite is homogeneous in texture (i.e. rare of zoning texture is observed), coarse-grained up to ~1 cm, consistent in composition, and less of other elements in solid solution. Other sulfides, such as chalcopyrite, arsenopyrite, sphalerite, galena, bismuthinite, and pyrrhotite occur as minor and trace amounts incorporated with pyrite, most likely occur as inclusion in pyrite. These typical characteristics of auriferous pyrite possibly suggest that pyrite has formed during the hydrothermal processes, which allows the crystallization of pyrite slowly growth and most of the trace elements are partitioned into the separated phases rather than incorporated in solid solution in pyrite. The co-existing and textural relationship of pyrite and arsenopyrite in the mineralized vein suggest an equilibrium condition among them, which applies to estimate the trapping temperature of ore formation in the Vangtat deposit. The range of As content in arsenopyrite plotted in the pyrite-arsenopyrite phase of the Fe-As-S system diagram estimated the temperature range of 335 to 385 ºC. Gold mainly occurs as particle grains inclusions in sulfide, predominantly pyrite, appearing to have been incorporated during the crystallization of sulfides. Free-gold is rarely observed in the mineralization zone. Gold to silver ratio ranges from 5:1 to 25:1, with an average of 10:1. Fluid inclusions trapped in quartz crystals from mineralized veins represented the nature of hydrothermal fluid responsible for gold mineralization in the Vangtat deposit, Vangtat gold belt, indicating that ore-forming fluid has the homogenization temperature range of 190 to 325 ºC (240 to 250 ºC is observed for the majority of fluid inclusions) and salinity range of 0.7 to 10.0 wt% NaCl equivalent (4 to 6 wt% NaCl equivalent is observed for the majority of fluid inclusions). The gas compositions are CO2, CH4, N2, and H2S. The composition of the ore-forming fluid is considered to have been generated via metamorphic dehydration and devolatilization. The presence of these gas compositions in the ore-forming fluid may indicate the reaction of fluid-wall rocks played an important role in gold precipitation. Depth of ore formation is translated using the pressure range of the ore formation, which was estimated by the correlation temperature between (1) homogenization temperature (240 to 250 °C) deduced for microthermometric data, and (2) trapping temperature (336-384 °C) obtained from arsenopyrite geothermometry. Providing the pressure range of 330 to 400 Mpa and translated to the depth range of 10 to 12 km (based on a typical lithostatic pressure gradient of 100 MPa=3 km). Gold is carried as the sulfide complex along with the ore fluid. The precipitation of gold is related to both (1) The destabilization of sulfide complex by sulfidation reaction, which involves the interaction of Fe-bearing mineral (e.g. chlorite) in the host rock and S-bearing fluid, and (2) Changing the physical-chemical of the ore-forming fluid, which relates to the reductive reaction with the carbonaceous material or graphite dominant in the host rock and alteration envelope that facilitated gold extraction. The sulfur isotope composition of auriferous pyrite at the Vangtat deposit ranges from +1.3 and +10.7 ‰, a narrow range is confined from +4 to +6 ‰ for the most population data and corresponding to the high-grade gold assay. These sulfur isotope compositions are not related to the sedimentary sulfur through the geological time, together with a narrow range of sulfur isotope composition may indicate the single source of sulfur. Hence, the input of sulfur sourced from the metasedimentary host rocks can not explain in the sulfur isotope data. However, these sulfur isotope compositions are compatible with the sulfur isotope composition range of the most igneous rocks, and it could potentially be the source of sulfur and ore components. The presence of hydrothermal white mica-bearing auriferous vein from the Thongkai-Ok deposit was subjected for K-Ar dating in order to constrain the age of gold mineralization in the Vangtat gold belt. The results provided a wide range of ages from 348 to 206 Ma. Within the interpretation of excess argon derived from contaminated quartz as an impurity of samples defined the youngest age (206 Ma) of a quartz-free fraction was the closest age of gold mineralization in the Vangtat gold belt. A 206 Ma age of gold mineralization in the Vangtat gold belt, southeast Laos is consistent with regional geological and geochronological data and indicates a post-collisional, post-peak metamorphism hydrothermal gold event that is potentially younger than much of the orogenic gold mineralization in nearby Vietnam. In conclusion, the nature and genesis of gold mineralization in the newly discovered Vangtat gold belt have many similarities to the orogenic gold deposits globally
Consistency between Chromosomal Status Analysis of Biopsied Human Blastocyst Trophectoderm Cells and Whole Blastocyst Cells
Get PDF秋田大学博士（医学
Efficacy of acotiamide on postprandial distress syndrome and epigastric pain syndrome depending on the estimated gastric acid secretion level
Get PDF秋田大学博士（医学
Post-contrast acute kidney injury after catheter angiography and evaluation of risk factors
Get PDF秋田大学博士（医学
Lithology, alteration and mineralization of the Fishtie Cu-Co deposit, Zambian Copperbelt
Get PDF秋田大学博士（資源学）Fishtie is a copper-rich deposit situated southeast of the Zambian Copperbelt (ZCB), about 30 km north of Mkushi town, close to the international boundary between Zambia and the Democratic Republic of Congo. The deposit was discovered in 2004 by First Quantum Minerals (FQM) Limited through systematic application of soil geochemistry, magnetic survey and drilling. This drilling intersected 300 meters wide by over a kilometre long east-west striking copper orebody similar to the ZCB deposits, but hosted at a higher stratigraphic position in the Katanga Supergroup. The reserves are estimated at 55 Mt of copper at an average grade of 1.04%, occurring as oxide, sulfide and mixed oxide-sulfide ores. Cobalt-rich orebodies are present within the copper orebody, but the two metals show different vertical enrichment and depletion trends.
This study was conducted to investigate the following geological characteristics of the Fishtie deposit: (1) the source of the metals, especially copper and cobalt; (2) the source of sulfur; (3) the physical and chemical characteristics of the lithology that are responsible for copper and cobalt mineralization; (4) the timing of mineralization; and (5) the factors controlling the spatial distribution of copper and cobalt metals.
Petrographic results of samples from the Grand Conglomérat Formation sitting on the basement rocks shows chalcopyrite preferentially disseminated in chlorite-rich clasts. These clasts weathered from basement mafic rocks and are considered to be the source of copper and cobalt. Copper and cobalt were leached from detrital mafic minerals during hydrothermal alteration and metamorphism, resulting in decomposition of clasts to chlorite and chalcopyrite. Mineral chemistry of alteration minerals suggest that copper and cobalt were liberated as ions during the alteration of chlorite to biotite. The metal ions were transported to the site of deposition through post-folding faults which provided conduits for the oxidizing mineralizing fluids. Copper and cobalt precipitated as chalcocite, bornite, chalcopyrite, cobaltite and carrollite at the boundary of dolostone and reduced beds of alternating siltstone and sandstone. High-grade copper mineralization of chalcopyrite and bornite formed in folded beds of alternating siltstone and sandstone which acted as traps for mineralizing fluids and hydrocarbons. Copper and cobalt mineralization is zoned from deeper level sulfide mineralization to a shallow supergene mineralization of chalcocite, malachite, heteroginite and cobaltoan dolomite
Application of frequency ratio model and GIS on susceptibility mapping of ground subsidence influenced by earthquake
Get PDF秋田大学博士（工学）Land subsidence is one of typical secondary disaster related to earthquake and occurs annually, worldwide. Accordingly, large economic losses and deaths in densely industrialized and highly populated urban areas as a result of these hazards. As a major earthquake occurred in Iburi subprefecture, Japan on September 2018, Sapporo has also damaged by ground subsidence. The purpose of this study is assessing the vulnerability of earthquake-induced land subsidence in Sapporo, Japan and produce susceptibility map. For this aim, bivariate statistical analysis method (frequency ratio model) and geographic information system (GIS) technique were applicated. For the susceptibility modelling, past ground subsidence location map was prepared. And seven ground subsidence causative factors were considered for the subsidence probability analysis include: geology, slope angle, land use, ground water level, distance from railroad and subway line, intensity of earthquake (MMI) and rainfall. Weightage for each conditioning factors were identified using frequency ratio model to assess subsidence susceptibility index and mapped using GIS. Area under curve (AUC) was applied to verify the performance of predicted model using prepared past ground subsidence location map. The prediction accuracies were (1) 85.17% for Higashi ward, (2) 95.44% for Kiyota ward and (3) 83.22 for Sapporo, respectively.
This result showed sufficient possibility for reliable susceptibility mapping of ground subsidence using GIS and frequency ratio model. EGSSM can be used as a helpful material on ground subsidence risk influenced by earthquake to reduce the scale of damages and manage in advance, effectively. The result of this study can be used as a helpful material for the disaster risk mitigation and efficient management in urban area. Keywords: Ground subsidence, Earthquake, Ground subsidence susceptibility, Frequency ratio model, GIS
RADIATION THERAPY FOR STAGE IIIB UTERINE CERVICAL CANCER IN OUR INSTITUTION： TREATMENT OUTCOMES AND PROGNOSTIC FACTORS.
Get PDF秋田大学博士（医学
