共查询到20条相似文献，搜索用时 109 毫秒
1.
2.
丁青蛇绿岩体位于班公湖—怒江缝合带东段,该缝合带与雅鲁藏布江缝合带并列,是寻找我国铬铁矿床的重要地区。该蛇绿岩体呈近南东向展布,总面积近600 km2,主要由地幔橄榄岩、辉石岩、辉长岩、辉绿岩、玄武岩、斜长花岗岩、硅质岩和泥质岩组成。根据空间分布,丁青蛇绿岩分为东、西两个岩体。在前人工作基础上,通过地质填图、实测剖面、探槽和钻孔编录,共发现豆荚状铬铁矿矿点83处,其中东岩体27处,西岩体56处。根据铬铁矿产出和围岩特征,丁青铬铁矿可分为4种产出类型。类型I:矿体呈脉状产出,围岩为条带状或透镜状纯橄榄岩和块状方辉橄榄岩;类型II:矿体呈透镜状、豆荚状或不规则团块状产出,围岩为薄壳状纯橄榄岩和斑杂状或块状方辉橄榄岩;类型III:矿体呈浸染状弥散分布于纯橄榄岩中,围岩为条带状纯橄榄岩和块状或斑杂状方辉橄榄岩;类型IV:矿体呈条带状产出,围岩为条带状或透镜状纯橄榄岩和具定向结构的方辉橄榄岩。根据矿石构造特征,主要分为块状、脉状、浸染状、浸染条带状4种类型。块状和脉状铬铁矿为矿石的主要类型,少量为浸染状和浸染条带状,局部纯橄榄岩中发育极少量瘤状或豆状构造。本研究选择了13处代表性铬铁矿点开展了详细的岩石学、矿相学、矿物学和矿物化学等工作。根据矿石中铬尖晶石的矿物化学特征,可将丁青铬铁矿矿体分为高铬(Cr#=78～86)、中高铬(Cr#=60～74)、中铬(Cr#2=30～51)和低铬(Cr#=9～14)4种类型(Cr#=100×Cr/(Cr+Al))。丁青东岩体赋存有中高铬型和中铬型铬铁矿,缺少高铬型铬铁矿;西岩体赋存有高铬型和中铬型铬铁矿,缺少中高铬型铬铁矿。同时在丁青东、西岩体内均发现存在一种Cr#极低的铬铁矿,暂定为"低铬型铬铁矿"。这些不同类型的铬铁矿体与野外产出有一定的对应关系,也可能后者制约了它们的成因。与罗布莎岩体中的典型高铬型铬铁矿对比,丁青豆荚状铬铁矿在矿物组合和矿物化学成分等方面具有许多相似性,认为存在较大的找矿空间。 相似文献
3.
4.
5.
基性-超基性岩体广泛分布于巴基斯坦北部印度河缝合带和中南部碰撞带,发育有与蛇绿岩有关的铬铁矿床,多数岩体工作程度偏低。铬尖晶石是指示岩石成因和构造环境的有效标志。铬尖晶石矿物化学研究表明其岩体可划分为3类,其中尚拉-明戈拉、德尔盖、瓦齐里斯坦、穆斯林巴赫和贝拉岩体中造矿铬尖晶石的成分显示富Cr、贫Al、低Ti特征,副矿物铬尖晶石的Cr#变化范围指示其构造背景为大洋中脊向俯冲带之上的过渡环境,与我国罗布莎含矿岩体非常相似。通过对比分析典型豆荚状铬铁矿成矿地质特征和成矿规律,认为贝拉、穆斯林巴赫等岩体成矿条件有利,具较大找矿潜力。 相似文献
6.
应用电子探针技术研究北京密云放马峪铬铁矿床成因——来自含铬尖晶石矿物化学的证据 总被引：1，自引：1，他引：0
似层状铬铁矿床长期以来被认为是岩浆分异成因,但近年来有学者提出其中个别产在蛇绿岩中。本文选择北京放马峪似层状铬铁矿床中纯橄岩、辉橄岩和辉石岩中不同类型的含铬尖晶石进行了电子探针分析。研究表明,岩浆早期的纯橄岩和辉橄岩中的铬尖晶石富铬(Cr2O3平均43.32%),而岩浆晚期辉石的结晶消耗了大量Cr3+,由于氧逸度的升高,在辉石岩的单斜辉石中出溶贫铬的铬磁铁矿(Cr2O3平均10.32%)和富铝尖晶石(Cr2O3平均15.77%)。与世界上不同类型铬尖晶石的矿物化学特征进行对比,可以认为放马峪铬铁矿床是产在阿拉斯加型岩体中的早期岩浆矿床,而与蛇绿岩无关。本文对放马峪铬铁矿床成因和成矿专属性的限定,为这类镁铁-超镁铁岩体的铬、铜镍、铂族元素的找矿勘查提供了依据。 相似文献
7.
提要：岗上超镁铁质岩主要由纯橄岩和石榴橄榄岩组成,主要组成矿物橄榄石、铬铁矿、石榴子石、单斜辉石和斜方辉石等。铬铁矿的Cr#[Cr/(Cr+Mg)×100]从51到89变化,铬铁矿矿物表现为4期次演化的特点,反映了从岩浆期向榴辉岩相、角闪岩相和绿片岩相演化特征。随着超镁铁质岩的演化,铬铁矿中Cr#不断增大,而铬铁矿Mg#〔Mg×100/(Mg+Fe2+)〕不断减少,氧逸度不断增加。在绿片岩相－绿片角闪岩相退变质过程中,铬铁矿中Cr、Mg和Al减少,Fe相对增加,产生富Cr尖晶石变质作用样式。晚期剪切变形等次生变化有利于富铬铬铁矿矿物的形成和铬铁矿的富集。同时,绿片岩相变质作用降低了铬铁矿与其他硅酸盐矿物的结合强度,降低了开采强度和成本,使原本不易于开采的铬铁矿体变得可以开采。这些意味着该地区铬铁矿矿体展布要结合区域构造特征和变质作用进行研究、尤其是结合中晚期脆韧性构造进行分析。 相似文献
8.
西藏罗布莎蛇绿岩中不同产出的纯橄岩及成因探讨 总被引：2，自引：2，他引：0
罗布莎蛇绿岩中的纯橄岩有三种产出情况,除了与豆荚状铬铁矿伴生的薄壳状纯橄岩外,还有产在方辉橄榄岩底部被认为是堆晶岩的厚层状纯橄岩和方辉橄榄岩中的透镜状纯橄岩。厚层状纯橄岩约700～1000m厚,以橄榄石富镁(Fo93～95),单斜辉石低铝富镁(Al2O30.47%～0.85%,Mg#95～97),铬尖晶石高铬低镁(Cr#值平均77,Mg#平均51)为特征。该纯橄岩中的浸染状铬铁矿也是高铬低镁型,但Mg#值(平均59)高于厚层状纯橄岩的副矿物铬尖晶石。薄壳状纯橄岩与厚层状纯橄岩成分相近,其橄榄石Fo92～94,单斜辉石Al2O3<1%和Mg#95～97;铬尖晶石的Cr#值平均71,Mg#值平均52。与薄壳状纯橄岩伴生的块状铬铁矿为高镁高铬型,但Mg#值(平均68)相对更高些,Cr#值平均79。透镜状纯橄岩的特征是橄榄石Fo(91～92)和铬尖晶石Cr#(60左右)均低于前两类纯橄岩,但单斜辉石的Al2O3(1.41%～1.71%)则高于前两者。透镜状纯橄岩的矿物成分与方辉橄榄岩重叠,两者为渐变过渡关系。研究对比表明,罗布莎厚层状纯橄岩不同于经典的蛇绿岩的超镁铁质堆晶岩,认为将其成因解释为拉斑玄武质熔体与地幔橄榄岩的反应较为合理。透镜状纯橄岩与方辉橄榄岩存在成生联系,可能是地幔橄榄岩高度部分熔融的产物,或熔体和方辉橄榄岩在原位发生反应的产物;薄壳状纯橄岩成因与厚层状纯橄岩相同,但与其相伴的块状铬铁矿是否由拉斑玄武质熔体与方辉橄榄岩反应形成,值得商榷。 相似文献
9.
10.
11.
Abstract Fluid evolution paths in the COHN system can be calculated for metamorphic rocks if there are relevant data regarding the mineral assemblages present, and regarding the oxidation and nitrodation states throughout the entire P-T loop. The compositions of fluid inclusions observed in granulitic rocks from Rogaland (south-west Norway) are compared with theoretical fluid compositions and molar volumes. The fluid parameters are calculated using a P-T path based on mineral assemblages, which are represented by rocks within the pigeonite-in isograd and by rocks near the orthopyroxene-in isograd surrounding an intrusive anorthosite massif. The oxygen and nitrogen fugacities are assumed to be buffered by the coexisting Fe-Ti oxides and Cr-carlsbergite, respectively. Many features of the natural fluid inclusions, including (1) the occurrence of CO2-N2-rich graphite-absent fluid inclusions near peak M2 metamorphic conditions (927° C and 400 MPa), (2) the non-existence of intermediate ternary CO2-CH4-N2 compositions and (3) the low-molar-volume CO2-rich fluid inclusions (36–42 cm3 mol?1), are reproduced in the calculated fluid system. The observed CO2-CH4-rich inclusions with minor N2 (5 mol%) should also include a large proportion of H2O according to the calculations. The absence of H2O from these natural high-molar-volume CO2-CH4-rich inclusions and the occurrence of natural CH4-N2-rich inclusions are both assumed to result from preferential leakage of H2O. This has been previously experimentally demonstrated for H2O-CO2-rich fluid inclusions, and has also been theoretically predicted. Fluid-deficient conditions may explain the relatively high molar volumes, but cannot be used to explain the occurrence of CH4-N2-rich inclusions and the absence of H2O. 相似文献
12.
Bo Barker Jørgensen Michael E. Böttcher Lev N. Neretin 《Geochimica et cosmochimica acta》2004,68(9):2095-2118
The main terminal processes of organic matter mineralization in anoxic Black Sea sediments underlying the sulfidic water column are sulfate reduction in the upper 2-4 m and methanogenesis below the sulfate zone. The modern marine deposits comprise a ca. 1-m-deep layer of coccolith ooze and underlying sapropel, below which sea water ions penetrate deep down into the limnic Pleistocene deposits from >9000 years BP. Sulfate reduction rates have a subsurface maximum at the SO42−-CH4 transition where H2S reaches maximum concentration. Because of an excess of reactive iron in the deep limnic deposits, most of the methane-derived H2S is drawn downward to a sulfidization front where it reacts with Fe(III) and with Fe2+ diffusing up from below. The H2S-Fe2+ transition is marked by a black band of amorphous iron sulfide above which distinct horizons of greigite and pyrite formation occur. The pore water gradients respond dynamically to environmental changes in the Black Sea with relatively short time constants of ca. 500 yr for SO42− and 10 yr for H2S, whereas the FeS in the black band has taken ca. 3000 yr to accumulate. The dual diffusion interfaces of SO42−-CH4 and H2S-Fe2+ cause the trapping of isotopically heavy iron sulfide with δ34S = +15 to +33‰ at the sulfidization front. A diffusion model for sulfur isotopes shows that the SO42− diffusing downward into the SO42−-CH4 transition has an isotopic composition of +19‰, close to the +23‰ of H2S diffusing upward. These isotopic compositions are, however, very different from the porewater SO42− (+43‰) and H2S (−15‰) at the same depth. The model explains how methane-driven sulfate reduction combined with a deep H2S sink leads to isotopically heavy pyrite in a sediment open to diffusion. These results have general implications for the marine sulfur cycle and for the interpretation of sulfur isotopic data in modern sediments and in sedimentary rocks throughout earth’s history. 相似文献
13.
Structurally hosted lode gold-bearing quartz vein systems in metamorphic terranes possess many characteristics in common, spatially and through time; they constitute a single class of epigenetic precious metal deposit, formed during accretionary tectonics or delamination. The ore and alteration paragenesis encode numerous intensive and extensive variables that constrain the pressure—temperature—time—deformation—fluid (P—T—t—d—f) evolution of the host terrane and hence the origin of the deposits. The majority of lode gold deposits formed proximal to regional translithospheric terrane—boundary structures that acted as vertically extensive hydrothermal plumbing systems; the structures record variably thrust, and transpressional—transtensional displacements. Major mining camps are sited near deflections, strike slip or thrust duplexes, or dilational jogs on the major structures. In detail most deposits are sited in second or third order splays, or fault intersections, that define domains of low mean stress and correspondingly high fluid fluxes. Accordingly, the mineralization and associated alteration is most intense in these flanking domains. The largest lode gold mining camps are in terranes at greenschist facies; they possess greenschist facies hydrothermal alteration assemblages developed in cyclic ductile to brittle deformation that reflects interseismic—coseismic cycles. Interseismic episodes involve the development of ductile S—C shear zone fabrics that lead to strain softening. Pressure solution and dislocation glide microstructures signify low differential stress, slow strain rates of ≤ 10−13 s−1, relatively high confining stress, and suprahydrostatic fluid pressures. Seismic episodes are induced by buildup of fluid pressures to supralithostatic levels that induce hydraulic fracturing with enhanced hydraulic conductivity, accompanied by massive fluid flow that in turn generates mineralized quartz veins. Hydrothermal cementing of ductile fabrics creates ‘hardening’, lowers hydraulic conductivity, and hence promotes fault valve behaviour. Repeated interseismic (fault valve closed), coseismic (valve open) cycles results in banded and/or progressively deformed veins. Alteration during both interseismic and coseismic episodes typically involves the hydrolysis of metamorphic feldspars and Fe, Mg, Ca-silicates to a muscovite/paragonite—chlorite ± albite/K-feldspars assemblage; carbonization of the metamorphic minerals to Ca, Fe, Mg-carbonates; and sulphidation of Fe-silicates and oxides to sulphides. Geochemically this is expressed as additions of K, Rb, Ba, Cs, and the volatiles H2O, CO2, CH4, H2S in envelopes of meter to kilometer scale. K/Rb and K/Ba ratios are close to average crustal values, potentially ruling out late stage magmatic fluids where K/Rb and K/Ba are respectively lower and higher than crustal values. Smaller deposits are present in subgreenschist, and amphibolite to granulite facies terranes. The former are characterized by subgreenschist facies alteration assemblages, vein stockworks, brittle fracturing and cataclastic microstructures, whereas the latter feature amphibolite to granulite facies alteration assemblages, ductile shear zones, ductilely deformed veins, and microstructures indicative of dislocation climb during interseismic episodes. Hence the lode gold deposits constitute a crustal continuum of deposits from subgreenschist to granulite facies, that all formed synkinematically in broad thermal and rheological equilibrium with their host terranes. These characteristics, combined with the low variance of alteration assemblages in the higher temperature deposits, rules out those being metamorphosed counterparts of greenschist facies deposits. Deposits at all grades have a comparable metal inventory with high concentrations of Au and Ag, where Au/Ag averages 5, with enrichments of a suite of rare metals and semi-metals (As, Sb, ± Se, Te, Bi, W, Mo and B), but low enrichments of the base (Cu, Pb, Zn, Cd) and other transition (Cr, Ni, Co, V, PGE, Sc) metals relative to average crust. The hydrothermal ore-forming fluids were dilute, aqueous, carbonic fluids, with salinities generally ≤ 3 wt.% NaCl equivalent, and X(CO2 ± CH4) 10–24 wt.%. They possess low Cl but relatively high S, possibly reflecting the fact that metamorphic fluids are generated in crust with ∼ 200 ppm Cl, but ∼ 1 wt.%S. Primary fluid inclusions are: (1) H2OCO2, (2) CO2-rich with variable CH4 and small amounts of H2O, and (3) 2-phase H2O (liquid-vapor) inclusions. Inclusion types 2 and 3 represent immiscibility of the type 1 original ore fluid. Immiscibility was triggered by fluid pressure drop during the coseismic events and possibly by shock nucleation, leading to highly variably homogenization temperatures in an isothermal system. A thermodynamic evaluation of alteration assemblages constrains the ore fluid pH to 5–6; redox controlled by the HSO4/H2S and CO2/CH4 buffers; and XCO2 that varies. The higher temperature deposits formed under marginally more oxidizing conditions. Stable isotope systematics of the ore and gangue minerals yields temperatures of 200–420°C, consistent with the crustal spectrum of the deposits, very high fluid rock ratios, and disequilibrium of the externally derived ore fluids with wall rocks. The ore fluid δD and δ18O overlap the metamorphic and magmatic ranges, but the total dataset for all deposits is consistent only with dominantly metamorphic fluids. Carbon isotope compositions of carbonates span −11 to +2% and show provinciality: this is consistent with variable proportions of reduced C (low δ13C) and oxidized C (higher δ13C) in the source regions contributing CO2 and CH4 to the ore fluids. In some instances, C appears to have been derived dominantly from proximal to the deposits, as in the Meguma terrane (δ13C ∼ − 22%). Sulphur isotope compositions range from 0 to +9‰, and are consistent with magmatic S, dissolution or desulphidation of magmatic sulphides, or average crustal sulphides. 34S-depleted sulphides occur in ore bodies such as Hemlo where fluid immiscibility led to loss of H2S and consequent fluid oxidation. Gold is probably transported as an Au(HS)−2 complex. Relatively high S but low Cl in the hydrothermal fluid may explain the high Au slow base metal characteristic of the deposits. Gold precipitated in ore bodies due to loss of S from the ore fluid by sulphidation of wall rock, or immiscibility of H2S; and by oxidation or reduction of the fluid, or by chemisorption, or some combination of these processes. Most lode gold deposits have been brittly reactivated during uplift of host terranes, with secondary brines or meteoric water advecting through the structures. These secondary fluids may remobilize gold, generate retrograde stable isotope shifts, reset mineral geochronometers, and leave trails of secondary fluid inclusions. Data on disturbed minerals has led to invalid models for lode gold deposits. The sum of alteration data leads to a model for lode gold deposits involving a clockwise P—T—t evolution and synkinematic and synmetamorphic mineralization of the ‘deep later’ type. During terrane accretion oceanic crust and sediments are subcreted beneath the terrane boundary. Thermal equilibration generates metamorphic fluids that advect up the terrane structure, at lithostatic fluid pressure, into the seismogenic zone where the majority of deposits form. Thus many lode gold deposits are on intrinsic part of the development of subduction—accretion complexes of the high-T, low-P type. 相似文献
14.
The world-class Natalka gold deposit, northeast Russia: REE patterns, fluid inclusions, stable oxygen isotopes, and formation conditions of ore 总被引：1，自引：0，他引：1
N. A. Goryachev O. V. Vikent’eva N. S. Bortnikov V. Yu. Prokof’ev V. A. Alpatov V. V. Golub 《Geology of Ore Deposits》2008,50(5):362-390
REE patterns of hydrothermally altered rocks, fluid inclusions, and stable oxygen isotopes of quartz were studied at the Natalka gold deposit. Metasomatic rocks formed under decompression reveal gradual depletion in LREE and HREE relative to siltstone of the protolith. The HREE patterns of metasomatic rocks formed under decompression are uniform; an insignificant removal of LREE can be noted. The progressive extraction of REE with increasing alteration of rocks could have been due to the effect of magmatogenic or meteoric fluid. Because a Ce anomaly is absent, the participation of oxidized meteoric water was limited. The inverse correlation between the total REE content and the Eu anomaly value in altered rocks indicates a substantial role of magmatogenic fluid. The REE patterns of altered rocks formed under compression show that the role of metamorphic fluid was not great. All metasomatic rocks are enriched in LREE, so that the enrichment of fluid in LREE as well may be suggested. Three fluid compositions were captured as fluid inclusions: (1) H2O-CO2-NaCl-MgCl2 with a salinity of 1.0–4.9 wt % NaCl equiv, (2) CO2-CH4, and (3) H2O-NaCl-MgCl2 with a salinity of 7.0–5.6 wt % NaCl equiv. Compositions (1) and (2) coexisted in the mineral-forming system at 250–350°C and 1.1–2.4 kbar as products of phase separation under conditions of decreasing P and T. The interaction of this fluid with host rocks resulted in the formation of extensive halos of beresitized rocks with sulfide disseminations. The precipitation of arsenopyrite and pyrite led to the substantial depletion of mineral-forming fluid in H2S and destabilization of the Au(HS)2? complex. The fluid with the third composition arose due to the boiling of the H2O-CO2-CH4-NaCl-MgCl2 liquid and was responsible for metasomatic alteration of host rocks. The late mineral assemblages were deposited from this fluid at the initial stage of ore formation. The high methane concentrations in the ore-forming fluid were likely caused by interaction of hydrothermal ore-bearing solutions with carbonaceous host rocks. The δ18O values of quartz from quartz-scheelite-pyrite-arsenopyrite and sulfide-sulfosalt mineral assemblages vary from +11.6 to +14.1‰ and +11.2 to +13.5‰, respectively. The parental fluids of the early and late mineral assemblages probably were derived from a magmatic source and were characterized by $ \delta ^{18} O_{H_2 O} REE patterns of hydrothermally altered rocks, fluid inclusions, and stable oxygen isotopes of quartz were studied at the Natalka
gold deposit. Metasomatic rocks formed under decompression reveal gradual depletion in LREE and HREE relative to siltstone
of the protolith. The HREE patterns of metasomatic rocks formed under decompression are uniform; an insignificant removal
of LREE can be noted. The progressive extraction of REE with increasing alteration of rocks could have been due to the effect
of magmatogenic or meteoric fluid. Because a Ce anomaly is absent, the participation of oxidized meteoric water was limited.
The inverse correlation between the total REE content and the Eu anomaly value in altered rocks indicates a substantial role
of magmatogenic fluid. The REE patterns of altered rocks formed under compression show that the role of metamorphic fluid
was not great. All metasomatic rocks are enriched in LREE, so that the enrichment of fluid in LREE as well may be suggested.
Three fluid compositions were captured as fluid inclusions: (1) H2O-CO2-NaCl-MgCl2 with a salinity of 1.0–4.9 wt % NaCl equiv, (2) CO2-CH4, and (3) H2O-NaCl-MgCl2 with a salinity of 7.0–5.6 wt % NaCl equiv. Compositions (1) and (2) coexisted in the mineral-forming system at 250–350°C
and 1.1–2.4 kbar as products of phase separation under conditions of decreasing P and T. The interaction of this fluid with host rocks resulted in the formation of extensive halos of beresitized rocks with sulfide
disseminations. The precipitation of arsenopyrite and pyrite led to the substantial depletion of mineral-forming fluid in
H2S and destabilization of the Au(HS)2− complex. The fluid with the third composition arose due to the boiling of the H2O-CO2-CH4-NaCl-MgCl2 liquid and was responsible for metasomatic alteration of host rocks. The late mineral assemblages were deposited from this
fluid at the initial stage of ore formation. The high methane concentrations in the ore-forming fluid were likely caused by
interaction of hydrothermal ore-bearing solutions with carbonaceous host rocks. The δ18O values of quartz from quartz-scheelite-pyrite-arsenopyrite and sulfide-sulfosalt mineral assemblages vary from +11.6 to
+14.1‰ and +11.2 to +13.5‰, respectively. The parental fluids of the early and late mineral assemblages probably were derived
from a magmatic source and were characterized by = +6.3 to +8.8‰ at 350°C and +3.6 to +5.9‰ at 280°C, respectively. The narrow interval of oxygen isotopic compositions shows
that this source was homogeneous. The data obtained allow us to suggest that the deposit formation was related to magmatic
activity, including the direct supply of ore components from a magma chamber and mobilization of these components in the processes
of dehydration and decarbonation during contact and regional metamorphism.
Original Russian Text ? N.A. Goryachev, O.V. Vikent’eva, N.S. Bortnikov, V.Yu. Prokof’ev, V.A. Alpatov, V.V. Golub, 2008,
published in Geologiya Rudnykh Mestorozhdenii, 2008, Vol. 50, No. 5, pp. 414–444. 相似文献
15.
Aqueous-carbonaceous and later pure aqueous fluid inclusions in quartz from a ferberite (Fe.95Mn.05 WO4) vein within the low-grade metamorphic aureole of the Borne granite (French Massif Central) have been studied by microthermometry and Raman spectrometry. The bulk V?-X properties of the aqueous-carbonaceous inclusions have been derived using the equation of state of Heyenet al. (1982) for the low-temperature CO2-CH4 system. A P-T path has been proposed for their trapping using the equations of state of Jacobs and Kerrick (1981a) for the H2O-CO2-CH4 system. Two main episodes were reconstructed for the history of the aqueous-carbonaceous fluid. (1) Primary H2O-CO2-CH4 vapourrich inclusions in quartz indicated the early circulation of a low-density fluid (65 mole% H2O-34 mole% CO2-1 mole% CH4 and traces of N2: d = 0.35 gcm?3) at around 550° ± 50°C and 700 ± 100 bar. Fluid cooled approximately isobarically to 450°-400°C and was progressively diluted by H2O with a concomitant increase in density. The fO2 of the H2OCO2-CH4 fluid, estimated from the equilibrium CO2 + 2H2O CH4 + 2O2, first ranged from 10?22 to 10?27 bar, close to the Q-F-M buffer. Within analytical errors, these values were consistent with the presence of graphite in equilibrium with the fluid. (2) A drop in PCO2, and therefore a drop in fO2, was recorded by the secondary liquid-rich inclusions in quartz. The inclusions, formed at and below 400°C, were composed of H2O and CH4 only, and fO2 at that stage was below that fixed by the graphite-fluid equilibrium. This second episode in the fluid-rock system could be explained by the drop of temperature below the blocking temperature of the graphite-fluid equilibrium. According to this interpretation, the blocking of the graphite-fluid equilibrium occurred at T ≥ 370°C and probably at 400°C on account of the pressure correction. Mass spectrometric data show that ferberite contains H2O, CO2 and CH4 in fluid inclusions, which lie in the gap of the V?-X properties of the aqueouscarbonaceous fluid in quartz. Deposition of ferberite probably occurred at around 400°C, the previously inferred blocking temperature, resulting from either the drop in PCO2, the drop fO2 and/or the related pH-increase.It is concluded that the existence of a blocking-temperature for the graphite-fluid chemical equilibrium may be a critical factor for maintaining a stable fluid pressure gradient in geothermal systems occurring under greenschist facies conditions in graphite-bearing rocks. 相似文献
16.
纳米比亚欢乐谷地区白岗岩型铀矿床流体包裹体特征及成矿作用 总被引：4，自引：1，他引：3
文章对纳米比亚欢乐谷地区白岗岩型铀矿床流体包裹体的温度、盐度、密度和成分等进行了系统的分析研究,厘定了成矿流体的类型及基本性质,并对该地区铀成矿的物理化学条件和成矿流体来源进行了初步探讨。研究表明,该地区白岗岩型铀矿床的成矿流体可分为2个期次:主成矿期和叠加改造期。主成矿期的流体为岩浆晚期的残余高温、低盐度热液,其气相成分主要是CO2,含少量H2O、N2和CH4;叠加改造期的流体为中-低温、低盐度热液,其气相成分以CO2和H2O为主,含少量CH4和N2,来源于岩浆期后热液与大气水的混合。 相似文献
17.
Sulfide and platinum mineralization in the Merensky Reef: evidence from hydrous silicates and fluid inclusions 总被引：5，自引：1，他引：5
Christian G. Ballhaus Eugen F. Stumpfl 《Contributions to Mineralogy and Petrology》1986,94(2):193-204
The base metal sulfides of the Merensky Reef are associated with hydrous silicates and intense deuteric hydrous alteration of cumulus and postcumulus silicates. Biotite and phlogopite crystallized in the vicinity of sulfides from a volatile-enriched highly fractionated intercumulus melt. Amphibole, chlorite, and talc are later alteration phases of cumulus pyroxene and intercumulus plagioclase. Biotite is often accompanied by zircon, rutile, and quartz. Accessory quartz hosts a complex suite of H2O-NaCl-(CaCl2)-CO2-CH4 fluid inclusions which have thus far not been described from the Merensky Reef. The earliest fluid inclusion compositions are NaCl-(H2O) with less than 10 vol.% water; CO2 coexisting with a halite daughter crystal and brine; and polyphase inclusions with up to six daughter and accidental phases and high contents of divalent cations. The maximum trapping temperature is around 730° C at 4 to 5 kb pressure. Later inclusion generations are H2O-NaCl, CO2-H2O, and pure CO2 and CH4. The presence of Cl-rich fluids during the intercumulus stage of the crystallizing Merensky Reef is directly related to the mode of sulfide precipitation. Prior to sulfide unmixing in a hydrous magma sulfur is likely to be present as H2S. Sulfur saturation causes reaction of H2S with oxides of the silicate melt to form a sulfide melt plus water. During reaction the magma is enriched in water until a separate fluid unmixes. It carries all compounds with high fluid/melt partition coefficients, as well as metals capable of forming OH- and Cl-complexes. Precious metals are assumed to have fractionated into the Cl-rich fluid as Cl-complexes rather than being dissolved in the sulfide melt. During the cooling evolution of the fluid the precious elements precipitate around the periphery of sulfide melt droplets. The model proposed explains the distribution pattern of platinum-group minerals in the Merensky Reef better than any orthomagmatic mineralization concept offered so far. 相似文献
18.
采用分阶段加热爆裂法测定了不同成因热液矿床脉石英流体包裹体的氩同位素,计算出各温度段内大气氩的相对含量,从而,总结出大气降水热液矿床、再平衡岩浆水热液矿床等成矿流体的氩同位素组成特征及其演化规律。典型的大气降水热液矿床,其成矿流体以具有高大气Ar组分(约95%-100%)为特征;再平衡岩浆水热液矿床成矿流体的Ar同位素组成特征取决于与其有成因关系的初始岩浆水的Ar同位素组成及矿源层和围岩的性质,产于古老变质岩中的,一般以具有低大气Ar组分(约6%-20%)为特征,其它的再平衡岩浆水热液矿床在主成矿温度范围内一般为50%-60%左右。 相似文献
19.
Mingguo Zeng 《中国地球化学学报》2010,29(4):431-437
The 2008-05-12 Wenchuan mud-volcano-earthquake was accompanied with eruption of a huge volume of gas and stone, revealing
that earthquakes generally result from instant reverse phase explosion of supercritical water (SCW) at the supercritical point.
In the deep parts of the crust and mantle there still exists a large amount of supercritical water equivalent in order of
magnitude to that of the Earth’s hydrosphere. Soft fluids which exist in the MOHO at the top of the upper mantle are the so-called
deep supercritical fluids (SCWD). Supercritical water (SCW) has n×103 times strong capability to dissolve gas. Its viscosity is extremely low and its diffusivity is extremely strong. Therefore,
it can naturally migrate toward a region with relatively negative pressure. In the steep break zone of the MOHO at the 57–65
km depth beneath the earthquake belt, due to mutation of overburden pressure, SCWD can automatically separate out CaSiO3 and other inorganic salts, evolving into the SCW (H2O-CO2-CH4O system. In going upwards to the 10–20-km depth of the crust SCW will be accumulated as an earthquake-pregnant reservoir
in the broken terrain. The phase-transition heat of SCW is estimated at 606.62 kJ/kg and the reverse phasing kinetic energy
is 2350.8 kJ/kg. When automatic exhaust at the time of decompression reaches the critical pressure (Pc), the instant explosion
reverse phase will be normal-state air water. It will release a huge volume of energy and high-kinetic-energy gas which has
been expanded by a factor of 1000, leading to the breaking of the country rocks overlying the earthquake-pregnant reservoir,
thus giving rise to a Ms 8.0 earthquake. As a result, there were formed eruptive and air-driven (pneumatic) debris flows whose
volumatric flow rate reaches n×1014 m3/s, and their force greatly exceeds the power of INT explosive of the same equivalent value. 相似文献
20.
During the manufacturing of chromate salts (1972–1992) large quantities of Chromite Ore Processing Residue (COPR) were released
into a decantation pond east of the former chemical plant of Porto-Romano (Durres, Albania), giving rise to yellow colored
pond sediments. These Cr(VI) bearing sediments were deposited upon Quaternary silty-clay lagoonal sediments rich in iron oxides
and organic matter. The pH values in these lagoonal sediments vary around 6.6, while in the pond sediments, it is mainly acidic
(due to the presence of the sulfur stock piles in the area and the release of the H2SO4 from the activity of the former chemical plant), varying between 1.4 and 3.8. Continuous leaching of the COPR waste resulted
in yellow-colored surface water runoff. The prediction of pH changes in the different types of sediments based upon acid/base
neutralizing capacity (ANC/BNC) jointly with the quantitative data on release of heavy metals and especially Cr is considered
an important advantage of the pHstat leaching test if compared to conventional leaching procedures. Thus, factors controlling the leaching of Cr(VI), Cr(III),
Ca, Al, Fe, Mg from the COPR were investigated by means of pHstat batch leaching tests and mineralogical analysis. Moreover, mathematical and geochemical modeling complemented the study.
The COPR in the area contain very high concentrations of chromium 24,409 mg/kg, which mainly occurs as Cr(III) (75–90%) as
well as Cr(VI) (25–10%). The leaching of Cr(VI) occurs in all the range (2–10) of the tested pH values, however, it decreases
under acidic conditions. Beside some reduction of Cr(VI) to Cr(III), the Cr(VI) content of the leachtes remains relatively
high in the acidic environment, while the limning of Cr(VI) pond sediments will increase the release of the latter specie.
The leaching of the Cr(III) occurs strictly under acidic conditions, whereby limning of these sediments will give rise to
the lower solubility of Cr(III). The key mineral phases responsible for the fast release of the Cr(VI) are: the chromate salts
(i.e. sodium chromate and sodium dichromate), while sparingly soluble chromatite (CaCrO4) and hashemite (BaCrO4) release Cr(VI) very slowly. Thus, pH and mineral solubility have been identified as key factors in the retention and the
release of the hexavalent CrO4
2− and Cr2O7
− from the COPR-rich pond sediments. 相似文献