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331.
332.
Katsumi Marumo Tetsuro Urabe Akiko Goto Yoshinori Takano Miwako Nakaseama 《Resource Geology》2008,58(3):220-248
This report presents mineralogical, geochemical and isotopic data on samples obtained using the Benthic Multi‐coring System (BMS) to drill a submarine hydrothermal deposit developed in a caldera on the summit of the Suiyo Seamount in the Izu–Bonin Island Arc, south of Japan. This deposit is regarded as the first example of Kuroko‐type sulfide mineralization on a volcano at the volcanic front of an island arc. The mineralization and hydrothermal alteration below the 300 × 150‐m area of active venting was investigated to depths of 2–9 m below the sea floor. Drilling beneath the area of active venting recovered a sequence of altered volcanic rocks (dacite lavas, pyroclastic rocks of dacite–rhyolite compositions and pumice) associated with sulfide veining and patches/veins of anhydrite. No massive sulfide was found, however, and the subsea‐floor mineralization to 10 m depth is dominated by anhydrite and clay minerals with some sulfides. Sulfide‐bearing samples contained high Au (up to 42 ppm), Ag (up to 263 ppm), As (up to 1550 ppm), Hg (up to 55 ppm), Sb (up to 772 ppm), and Se (up to 24 ppm). Electron probe microanalyzer indicated that realgar, orpiment, and mimetite were major As‐bearing minerals. The sulfides were also characterized by high Zn (>10%) compared to Cu (<6.3%) and Pb (<0.6%). The δ202Hg/198Hg, δ202Hg/199Hg and δ202Hg/200Hg of the sulfide‐bearing dacite samples and a sulfide chimney decreased with increasing Hg/Zn concentration ratio. The variation of the δ202Hg/198Hg ranged from ?2.8 to +0.5‰ to relative to S‐HG02027. The large range of these δ202Hg/198Hg was greater than might be expected for such a heavy element and may be due to a predominance of kinetic effects. The variation of δ202Hg/198Hg of sulfide‐bearing dacite samples suggested that light Hg isotope in the vapor mixed with oxygenated seawater near sea floor during mineralization. Lead isotope ratios of the sulfide were very similar to those of the dacite lava, suggesting that lead is of magmatic origin. The 87Sr/86Sr ratio (0.70872) of anhydrite was different from that of the dacite lava, and suggests an Sr derivation predominantly from seawater. Hydrothermal alteration of the dacite in the Suiyo hydrothermal field was characterized by Fe‐sulfides, anhydrite, barite, montmorillonite, chlorite/montmorillonite mixed‐layer minerals, mica, and chlorite with little or no feldspar or cristobalite. Hydrothermal clay minerals changed with depth from montmorillonite to chlorite/montmorillonite mixed‐layer minerals to chlorite and mica. Hydrogen isotope ratios of chlorite/montmorillonite and mixed‐layer, mica‐chlorite composites obtained below the active venting sites ranged from ?49 to ?24‰, suggesting seawater as the dominant fluid causing alteration. Oxygen isotope ratios of anhydrite ranged from 9.2 to 10.4‰ and anhydrite formation temperatures were calculated to be 188–207°C. Oxygen isotope ratios ranged from +5.2 to +9.2‰ for montmorillonite, +3.2 to +4.5‰ for chlorite/montmorillonite mixed‐layer minerals, and +2.8 to +3.8‰ in mixtures of chlorite and mica. The formation temperatures of montmorillonite and of the chlorite–mica mixture were 160–250°C and 230–270°C, respectively. The isotope temperatures for clay minerals (220–270°C) and anhydrite (188°C) were significantly lower than the borehole temperature (308.3°C) measured just after the drilling, suggesting that temperature at this site is now higher than when clay minerals and anhydrite were formed. 相似文献
333.
Selahattin Kadir A. Piril Önen-Hall S. Nihal Aydin Cengiz Yakicier Nurten Akarsu Murat Tuncer 《Environmental Geology》2008,54(2):391-409
The Cretaceous-Eocene volcano-sedimentary units of the Zonguldak region of the western Black Sea consist of subalkaline andesite
and tuff, and sandstone dominated by smectite, kaolinite, accessory chlorite, illite, mordenite, and analcime associated with
feldspar, quartz, opal-CT, amphibole, and calcite. Kaolinization, chloritization, sericitization, albitization, Fe–Ti-oxidation,
and the presence of zeolite, epidote, and illite in andesitic rocks and tuffaceous materials developed as a result of the
degradation of a glass shards matrix, enclosed feldspar, and clinopyroxene-type phenocrysts, due to alteration processes.
The association of feldspar and glass with smectite and kaolinite, and the suborientation of feldspar-edged, subparallel kaolinite
plates to fracture axes may exhibit an authigenic smectite or kaolinite. Increased alteration degree upward in which Al, Fe,
and Ti are gained, and Si, Na, K, and Ca are depleted, is due to the alteration following possible diagenesis and hydrothermal
activities. Micromorphologically, fibrous mordenite in the altered units and the presence of needle-type chrysotile in the
residential buildings in which cancer cases lived were detected. In addition, the segregation pattern of cancer susceptibility
in the region strongly suggested an environmental effect and a genetic influence on the increased cancer incidence in the
region. The most likely diagnosis was Li-Fraumeni syndrome, which is one of the hereditary cancer predisposition syndromes;
however, no mutations were observed in the p53 gene, which is the major cause of Li-Fraumeni syndrome. The micromorphology
observed in the altered units in which cancer cases were detected may have a role in the expression of an unidentified gene,
but does not explain alone the occurrence of cancer as a primary cause in the region. 相似文献
334.
Peter Neumayr John Walshe Steffen Hagemann Klaus Petersen Anthony Roache Peter Frikken Leo Horn Scott Halley 《Mineralium Deposita》2008,43(3):363-371
Hydrothermal sulfide–oxide–gold mineral assemblages in gold deposits in the Archaean St. Ives gold camp in Western Australia
indicate extremely variable redox conditions during hydrothermal alteration and gold mineralization in space and time. Reduced
alteration assemblages (pyrrhotite–pyrite) occur in deposits in the southwest of the camp (e.g., Argo, Junction deposits)
and moderately to strongly oxidized assemblages (magnetite–pyrite, hematite–pyrite) occur in deposits in the Central Corridor
in the northeast (e.g., North Orchin, Revenge deposits). Reduced mineral assemblages flank the Central Corridor of oxidized
deposits and, locally, cut across it along E–W trending faults. Oxidized mineral assemblages in the Central Corridor are focused
on gravity lows which are interpreted to reflect abundant felsic porphyritic intrusions at about 1,000 m below present surface.
Hydrothermal magnetite predates and is synchronous with early phases of gold-associated albite–carbonate–pyrite–biotite–chlorite
hydrothermal alteration. Later-stage, gold-associated pyrite is in equilibrium with hematite. The spatial distribution and
temporal sequence of iron sulfides and oxides with gold indicate the presence of at least two spatially restricted but broadly
synchronous hydrothermal fluids with contrasting redox states. Sulfur isotope constraints support the argument that the different
mineral assemblages reflect differences in redox conditions. The δ
34S values for pyrite for the St. Ives gold camp range between −8.4‰ and +5.1‰ with the negative values occurring in oxidized
magnetite-rich domains and slightly negative or positive values occurring in reduced, pyrrhotitic domains. Preliminary spatial
and paragenetic analysis of the distribution of iron sulfides and oxides in the St. Ives camp suggests that gold grades are
highest where the redox state of the hydrothermal alteration assemblages switches from relatively reduced pyrrhotite–pyrite
to relatively oxidized magnetite–pyrite and hematite–pyrite both in space and time. Gold deposition is inferred to have occurred
where fluids of contrasting redox state mixed. 相似文献
335.
Christina Yan Wang Hazel M. Prichard Mei-Fu Zhou Peter C. Fisher 《Mineralium Deposita》2008,43(7):791-803
The Jinbaoshan Pt–Pd deposit in Yunnan, SW China, is hosted in a wehrlite body, which is a member of the Permian (∼260 Ma)
Emeishan Large Igneous Province (ELIP). The deposit is reported to contain one million tonnes of Pt–Pd ore grading 0.21% Ni
and 0.16% Cu with 3.0 g/t (Pd + Pt). Platinum-group minerals (PGM) mostly are ∼10 μm in diameter, and are commonly Te-, Sn-
and As-bearing, including moncheite (PtTe2), atokite (Pd3Sn), kotulskite (PdTe), sperrylite (PtAs2), irarsite (IrAsS), cooperite (PtS), sudburyite (PdSb), and Pt–Fe alloy. Primary rock-forming minerals are olivine and clinopyroxene,
with clinopyroxene forming anhedral poikilitic crystals surrounding olivine. Primary chromite occurs either as euhedral grains
enclosed within olivine or as an interstitial phase to the olivine. However, the intrusion has undergone extensive hydrothermal
alteration. Most olivine grains have been altered to serpentine, and interstitial clinopyroxene is often altered to actinolite/tremolite
and locally biotite. Interstitial chromite grains are either partially or totally replaced by secondary magnetite. Base-metal
sulfides (BMS), such as pentlandite and chalcopyrite, are usually interstitial to the altered olivine. PGM are located with
the BMS and are therefore also interstitial to the serpentinized olivine grains, occurring within altered interstitial clinopyroxene
and chromite, or along the edges of these minerals, which predominantly altered to actinolite/tremolite, serpentine and magnetite.
Hydrothermal fluids were responsible for the release of the platinum-group elements (PGE) from the BMS to precipitate the
PGM at low temperature during pervasive alteration. A sequence of alteration of the PGM has been recognized. Initially moncheite
and atokite have been corroded and recrystallized during the formation of actinolite/tremolite, and then, cooperite and moncheite
were altered to Pt–Fe alloy where they are in contact with serpentine. Sudburyite occurs in veins indicating late Pd mobility.
However, textural evidence shows that the PGM are still in close proximity to the BMS. They occur in PGE-rich layers located
at specific igneous horizons in the intrusion, suggesting that PGE were originally magmatic concentrations that, within a
PGE-rich horizon, crystallized with BMS late in the olivine/clinopyroxene crystallization sequence and have not been significantly
transported during serpentinization and alteration. 相似文献
336.
Utilizing theories of minerageny and prospecting mineralogy, the authors studied the attitude, morphotype and chemical composition of metallic minerals of pyrite, gold, chalcopyrite, galena and sphalerite, non-metallic minerals of quartz, carbonate, dolomite and rutile in the Puziwan gold deposit. The study shows the following results. (1) The mineral assemblage is complex and the species of sulfide are abundant with occurrences of sulfosalt minerals. (2) The composition in the minerals is complex and there rich micro elements, including As, Sb, Bi, Se, Te, Au, Ag, Cu, Pb, Zn, and Cr, Ni, V. The typomorphic characteristics of the association of the elements and their specific value suggest that gold mineralization is associated with shallow magmatic hydrothermal activity, the oreforming fluid is the mixture of abundant rising alkali magmatic water originating from the mantle or the lower crust and the descending acid atmospheric water. (3) Ankerite, Fe-rich sphalerite, granular Ti-rich rutile are widely distributed, which indicate great denudation depths, high mineralization temperature. The deposit is found in the middle and shallow positions of the porphyry series. The deep layers are not favorable for gold mineralization. (4) Copper minerals are rich in the ores and sulfides have high content of copper, suggesting possible porphyry-type Cu (Au) mineralization in deep positions and the surrounding areas. 相似文献
337.
338.
鞍本地区鞍山群变质矿物及变质作用 总被引:6,自引:0,他引:6
鞍本地区鞍山群变质岩出露区可分为鞍山、辽阳、本溪三个小区。所有的变质岩均属角闪岩相,从西向东,变质程度递增。三个小区最先出现的特征变质矿物分别是铁铝榴石、十字石和夕线石。退化变质作用由西向东递减,在东-西鞍山矿区已退变为绿片岩相,在绿泥片岩中普通角闪石仅作为残留矿物出现在绿泥石的核心。鞍山小岭子矿区有紫苏辉石、红柱石和尖晶石组合,它们是燕山期花岗岩围岩中的接触变质矿物。 相似文献
339.
340.
国内外已广泛使用高光谱方法提取和识别岩石和矿物的技术。本文利用这个技术,在地面光谱测试、数据处理和光谱特征分析的基础上,提取和识别出斑岩钼矿区的蚀变矿物,通过分析与钼矿化蚀变的相关性,从12种主要蚀变矿物中优选出5种在矿区具有代表性的蚀变矿物:绢云母、蒙脱石、伊利石化绢云母、高岭石(结晶差)和铁镁绿泥石。结合其空间分布和分带特征,分析了与钼矿化的关系,进而划分出内、中和外三个蚀变带,预测了矿区的找矿方向,并提供了一种新的找矿思路。 相似文献