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1.
This paper reports the first results of a study of 11 isotope systems (3He/4He, 40Ar/36Ar, 34S/32S, 65Cu/63Cu, 62Ni/60Ni, 87Sr/86Sr, 143Nd/144Nd, 206–208Pb/204Pb, Hf–Nd, U–Pb, and Re–Os) in the rocks and ores of the Cu–Ni–PGE deposits of the Norilsk ore district. Almost all the results were obtained at the Center of Isotopic Research of the Karpinskii All-Russia Research Institute of Geology. The use of a number of independent genetic isotopic signatures and comprehensive isotopic knowledge provided a methodic basis for the interpretation of approximately 5000 isotopic analyses of various elements. The presence of materials from two sources, crust and mantle, was detected in the composition of the rocks and ores. The contribution of the crustal source is especially significant in the paleofluids (gas–liquid microinclusions) of the ore-forming medium. Crustal solutions were probably a transport medium during ore formation. Air argon is dominant in the ores, which indicates a connection between the paleofluids and the atmosphere. This suggests intense groundwater circulation during the crystallization of ore minerals. The age of the rocks and ores of the Norilsk deposits was determined. The stage of orebody formation is restricted to a narrow age interval of 250 ± 10 Ma. An isotopic criterion was proposed for the ore-bearing potential of mafic intrusions in the Norilsk–Taimyr region. It includes several interrelated isotopic ratios of various elements: He, Ar, S, and others.  相似文献   

2.
Komatiites are mantle-derived ultramafic volcanic rocks. Komatiites have been discovered in several States of India, notably in Karnataka. Studies on the distribution of trace-elements in the komatiites of India are very few. This paper proposes a simple, accurate, precise, rapid, and non-destructive wavelength-dispersive x-ray fluorescence (WDXRF) spectrometric technique for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in komatiites, and discusses the accuracy, precision, limits of detection, x-ray spectral-line interferences, inter-element effects, speed, advantages, and limitations of the technique. The accuracy of the technique is excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Zr, Nb, Ba, Pb, and Th and very good (within 4%) for Y. The precision is also excellent (within 3%) for Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th. The limits of detection are: 1 ppm for Sc and V; 2 ppm for Cr, Co, and Ni; 3 ppm for Cu, Zn, Rb, and Sr; 4 ppm for Y and Zr; 6 ppm for Nb; 10 ppm for Ba; 13 ppm for Pb; and 14 ppm for Th. The time taken for determining Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Zr, Nb, Ba, Pb, and Th in a batch of 24 samples of komatiites, for a replication of four analyses per sample, by one operator, using a manual WDXRF spectrometer, is only 60 hours.  相似文献   

3.
《Applied Geochemistry》2001,16(2):137-159
Five hundred and ninety-eight samples of terrestrial moss (Hylocomium splendens and Pleurozium schreberi) collected from a 188,000 km2 area of the central Barents region (NE Norway, N Finland, NW Russia) were analysed by ICP-AES and ICP-MS. Analytical results for Al, B, Ba, Ca, K, La, Mg, Mn, Na, P, Rb, Si, Sr, Th, U and Y concentrations are reported here. Graphical methods of data analysis, such as geochemical maps, cumulative frequency diagrams, boxplots and scatterplots, are used to interpret the origin of the patterns for these elements. None of the elements reported here are emitted in significant amounts from the smelting industry on the Kola Peninsula. Despite the conventional view that moss chemistry reflects atmospheric element input, the nature of the underlying mineral substrate (regolith or bedrock) is found to have a considerable influence on moss composition for several elements. This influence of the chemistry of the mineral substrate can take place in a variety of ways. (1) It can be completely natural, reflecting the ability of higher plants to take up elements from deep soil horizons and shed them with litterfall onto the surface. (2) It can result from naturally increased soil dust input where vegetation is scarce due to harsh climatic conditions for instance. Alternatively, substrate influence can be enhanced by human activity, such as open-cast mining, creation of ‘technogenic deserts’, or handling, transport and storage of ore and ore products, all of which magnify the natural elemental flux from bedrock to ground vegetation. Seaspray is another natural process affecting moss composition in the area (Mg, Na), and this is most visible in the Norwegian part of the study area. Presence or absence of some plant species, e.g., lichens, seems to influence moss chemistry. This is shown by the low concentrations of B or K in moss on the Finnish and Norwegian side of the (fenced) border with Russia, contrasting with high concentrations on the other side (intensive reindeer husbandry west of the border has selectively depleted the lichen population).  相似文献   

4.
最新的流行病学研究表明,空气中较高浓度的悬浮细颗粒可能对人类的健康有不利的影响。根据该项研究显示,由于心脏病、慢性呼吸问题和肺功能指标恶化而导致死亡率的升高与细尘粒子有关。这些研究结果已经促使欧盟于1999年4月出台了限制空气中二氧化硫、二氧化氮、氧化氮、铅和颗粒物含量的法案(1999/30/EC),对各项指标包括对可吸入PM10颗粒的浓度提出了新的限制性指标。PM10颗粒是指可以通过预分级器分离采集的气体动力学直径小于10μm的细颗粒。目前研究的兴趣重点逐步偏向PM2.5这些更细微颗粒物,PM2.5这种颗粒物对健康有明显的不利影响。在欧盟指令2008/50/EC中,对PM10和PM2.5都提  相似文献   

5.
This paper discusses the result of the detailed investigations carried out on the coal characteristics, including coal petrography and its geochemistry of the Pabedana region. A total of 16 samples were collected from four coal seams d2, d4, d5, and d6 of the Pabedana underground mine which is located in the central part of the Central-East Iranian Microcontinent. These samples were reduced to four samples through composite sampling of each seam and were analyzed for their petrographic, mineralogical, and geochemical compositions. Proximate analysis data of the Pabedana coals indicate no major variations in the moisture, ash, volatile matter, and fixed carbon contents in the coals of different seams. Based on sulfur content, the Pabedana coals may be classified as low-sulfur coals. The low-sulfur contents in the Pabedana coal and relatively low proportion of pyritic sulfur suggest a possible fresh water environment during the deposition of the peat of the Pabedana coal. X-ray diffraction and petrographic analyses indicate the presence of pyrite in coal samples. The Pabedana coals have been classified as a high volatile, bituminous coal in accordance with the vitrinite reflectance values (58.75–74.32 %) and other rank parameters (carbon, calorific value, and volatile matter content). The maceral analysis and reflectance study suggest that the coals in all the four seams are of good quality with low maceral matter association. Mineralogical investigations indicate that the inorganic fraction in the Pabedana coal samples is dominated by carbonates; thus, constituting the major inorganic fraction of the coal samples. Illite, kaolinite, muscovite, quartz, feldspar, apatite, and hematite occur as minor or trace phases. The variation in major elements content is relatively narrow between different coal seams. Elements Sc,, Zr, Ga, Ge, La, As, W, Ce, Sb, Nb, Th, Pb, Se, Tl, Bi, Hg, Re, Li, Zn, Mo, and Ba show varying negative correlation with ash yield. These elements possibly have an organic affinity and may be present as primary biological concentrations either with tissues in living condition and/or through sorption and formation of organometallic compounds.  相似文献   

6.
《Chemical Geology》2007,236(1-2):13-26
We examined the coprecipitation behavior of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides under two different fluoride forming conditions: at < 70 °C in an ultrasonic bath (denoted as the ultrasonic method) and at 245 °C using a Teflon bomb (denoted as the bomb method). In the ultrasonic method, small amounts of Ti, Mo and Sn coprecipitation were observed with 100% Ca and 100% Mg fluorides. No coprecipitation of Ti, Mo, Sn and Sb in Ca–Al–Mg fluorides occurred when the sample was decomposed by the bomb method except for 100% Ca fluoride. Based on our coprecipitation observations, we have developed a simultaneous determination method for B, Ti, Zr, Nb, Mo, Sn, Sb, Hf and Ta by Q-pole type ICP-MS (ICP-QMS) and sector field type ICP-MS (ICP-SFMS). 9–50 mg of samples with Zr–Mo–Sn–Sb–Hf spikes were decomposed by HF using the bomb method and the ultrasonic method with B spike. The sample was then evaporated and re-dissolved into 0.5 mol l− 1 HF, followed by the removal of fluorides by centrifuging. B, Zr, Mo, Sn, Sb and Hf were measured by ID method. Nb and Ta were measured by the ID-internal standardization method, based on Nb/Mo and Ta/Mo ratios using ICP-QMS, for which pseudo-FI was developed and applied. When 100% recovery yields of Zr and Hf are expected, Nb/Zr and Ta/Hf ratios may also be used. Ti was determined by the ID-internal standardization method, based on the Ti/Nb ratio from ICP-SFMS. Only 0.053 ml sample solution was required for measurement of all 9 elements. Dilution factors of ≤ 340 were aspirated without matrix effects. To demonstrate the applicability of our method, 4 carbonaceous chondrites (Ivuna, Orgueil, Cold Bokkeveld and Allende) as well as GSJ and USGS silicate reference materials of basalts, andesites and peridotites were analyzed. Our analytical results are consistent with previous studies, and the mean reproducibility of each element is 1.0–4.6% for basalts and andesites, and 6.7–11% for peridotites except for TiO2.  相似文献   

7.
Most sulfide-rich magmatic Ni-Cu-(PGE) deposits form in dynamic magmatic systems by partial melting S-bearing wall rocks with variable degrees of assimilation of miscible silicate and volatile components, and generation of barren to weakly-mineralized immiscible Fe sulfide xenomelts into which Ni-Cu-Co-PGE partition from the magma. Some exceptionally-thick magmatic Cr deposits may form by partial melting oxide-bearing wall rocks with variable degrees of assimilation of the miscible silicate and volatile components, and generation of barren Fe ± Ti oxide xenocrysts into which Cr-Mg-V ± Ti partition from the magma. The products of these processes are variably preserved as skarns, residues, xenoliths, xenocrysts, xenomelts, and xenovolatiles, which play important to critical roles in ore genesis, transport, localization, and/or modification. Incorporation of barren xenoliths/autoliths may induce small amounts of sulfide/chromite to segregate, but incorporation of sulfide xenomelts or oxide xenocrysts with dynamic upgrading of metal tenors (PGE > Cu > Ni > Co and Cr > V > Ti, respectively) is required to make significant ore deposits. Silicate xenomelts are only rarely preserved, but will be variably depleted in chalcophile and ferrous metals. Less dense felsic xenoliths may aid upward sulfide transport by increasing the effective viscosity and decreasing the bulk density of the magma. Denser mafic or metamorphosed xenoliths may also increase the effective viscosity of the magma, but may aid downward sulfide transport by increasing the bulk density of the magma. Sulfide wets olivine, so olivine xenocrysts may act as filter beds to collect advected finely dispersed sulfide droplets, but other silicates and xenoliths may not be wetted by sulfides. Xenovolatiles may retard settling of – or in some cases float – dense sulfide droplets. Reactions of sulfide melts with felsic country rocks may generate Fe-rich skarns that may allow sulfide melts to fractionate to more extreme Cu-Ni-rich compositions. Xenoliths, xenocrysts, xenomelts, and xenovolatiles are more likely to be preserved in cooler basaltic magmas than in hotter komatiitic magmas, and are more likely to be preserved in less dynamic (less turbulent) systems/domain/phases than in more dynamic (more turbulent) systems/domains/phases. Massive to semi-massive Ni-Cu-PGE and Cr mineralization and xenoliths are often localized within footwall embayments, dilations/jogs in dikes, throats of magma conduits, and the horizontal segments of dike-chonolith and dike-sill complexes, which represent fluid dynamic traps for both ascending and descending sulfides/oxides. If skarns, residues, xenoliths, xenocrysts, xenomelts, and/or xenovolatiles are present, they provide important constraints on ore genesis and they are valuable exploration indicators, but they must be included in elemental and isotopic mass balance calculations.  相似文献   

8.
Sulfide minerals in the Boulder batholith occur 1. as disseminated grains, visible in hand specimens; 2. in aplitic-pegmatitic pods and masses; 3. along joint and shear surfaces; 4. in hydrothermal veins; and 5. as minute masses within pyrite and silicate minerals and along intergranular sites. Hydrothermally altered rocks have an average sulfide content of 0.8 weight per cent, compared to an average of 0.01 per cent for unaltered rocks. Unaltered rock of the batholith may contain as much as 0.7 weight per cent sulfide. Sulfide inclusions in pyrite, the most abundant sulfide of the batholith, are common and represent a captured iss-phase which later changed to chalcopyrite plus pyrrhotite or mackinawite. Inclusions are most abundant, and more complex, in pyrites of hydrothermally altered and ore rocks. Electron-probe analyses show that pyrites of the Boulder batholith have very similar compositions to those found for pyrites from other ore deposits around the world.  相似文献   

9.
The Bonin archipelago represents an uplifted fore-arc terrainwhich exposes the products of Eocene supra-subduction zone magmatism.Chichijima, at the centre of the chain, represents the typelocality for the high-Mg andesitic lava termed boninite. Therange of extrusives which constitute the boninite series volcanicsare present on Chichijima, and are disposed in the sequenceboninite-andesite-dacite with increasing height in the volcano-stratigraphy.Progression to evolved compositions within the Chichijima boniniteseries is controlled by crystal fractionation from a boniniteparental magma containing 15% MgO. Olivine and clinoenstatiteare the initial liquidus phases, but extraction of enstatiticorthopyroxene, followed by clinopyroxene and plagioclase, isresponsible for the general evolution from boninite, throughandesite, to dacite. Some andesites within the overlying MikazukiyamaFormation are petrographically distinct from the main boniniteseries in containing magnetite phenocrysts and a high proportionof plagioclase. As such, these andesites have affinities withthe calc-alkaline series. Major and trace element data for 74 boninitic series rocks fromChichijima are presented. Although major element variation isdominantly controlled by high-level crystal fractionation, thelarge variations in incompatiable trace element concentrationsat high MgO compositions cannot be explained by this mechanism.Nd, Pb, and Sr isotopic data indicate the following: (1) a strongoverprint on 87Sr/86Sr by seawater alteration; (2) Pb isotopeslie above the northern hemisphere reference line (NHRL) andare thus similar to the <30-Ma are and basin lavas of theIzu—Bonin system, and (3) Nd(40 Ma) ranges between 2.8and 6.8 within the boninite series volcanics. Differences inrare-earth elements (REE), Zr, Ti, and 143Nd/144Nd at similardegrees of fractionation can be explained by the addition ofa component of fixed composition from the down-going oceaniccrustal slab to a variably depleted source region within theoverlying wedge. Data presented for Sm/Zr and Ti/Zr indicatethat boninite series volcanics are characterized by low valuesfor both of these ratios. In particular, boninites appear tohave uniquely low Sm/Zr ratios. These characteristics may bethe result of slab melting in the presence of residual amphibole;the resultant melt could combine with typical slab dehydrationfluids and infiltrate the overlying mantle wedge. Such a fluid—meltcomponent could mix either with shallow mantle or directly withprimitive melts from depleted mantle. Trace elements, REE, andisotope data thus point to a model for boninite genesis whichrequires tightly constrained pressure—temperature conditionsin the slab combined with melting of a variably depleted sourcein the overlying wedge. Such constraints are rarely met exceptduring the subduction of juvenile oceanic crust beneath a young,hot overriding plate.  相似文献   

10.
The field setting, petrography, mineralogy, and geochemistry of a suite of picrite basalts and related magnesian olivine tholeiites (New Georgia arc picrites) from the New Georgia Volcanics, Kolo caldera in the active ensimatic Solomon Islands arc are presented. These lavas, with an areal extent in the order of 1002 km and almost 1 km thick in places, are located close to the intersection of the Woodlark spreading zone with the Pacific plate margin. They contain abundant olivine (Fo94-75) and diopside (Cr2O3 1.1-0.4%, Al2O3 1–3%), and spinels characterised by a large range in Cr/(Cr+Al) (0.85–0.46) and Mg/(Mg+ Fe++) (0.65–0.1). The spinels are Fe+++ rich, with Fe+++/ (Fe++++Cr+Al) varying from 0.06 to 1.0. A discrete group of spinels with the highest Cr/(Cr+Al) (0.83–0.86) and lowest Fe+++ contents are included in the most Mg-rich olivine (Fo91–94) and both may be xenocrystal in origin.The lavas, which range between 10–28% MgO, define linear trends on oxide (element) — MgO diagrams and these trends are interpreted as olivine (0.9) clinopyroxene (0.1) control lines. For the reconstructed parent magma composition of these arc picrites, ratios involving CaO, Al2O3, TiO2, Zr, V and Sc are very close to chondritic. REE patterns are slightly LREE — enriched ((La/Sm)N 1.3–1.43) and HREE are flat. All lavas show marked enrichments in K, Rb, Sr, Ba, and LREE relative to MORB with similar MgO contents, but the TiO2 content of the proposed parent magma is close to those of postulated primary MORB liquids. It is proposed that the arc parent magma was produced by partial melting of sub-oceanic upper mantle induced by the introduction of LILE — enriched hydrous fluids derived by dehydration and/or partial melting of subducted ocean crust and possibly minor sediments.  相似文献   

11.
The Kuskokwim River at Bethel, Alaska, drains a major mercury-antimony metallogenic province in its upper reaches and tributaries. Bethel (population 4000) is situated on the Kuskokwim floodplain and also draws its water supply from wells located in river-deposited sediment. A boring through overbank and floodplain sediment has provided material to establish a baseline datum for sediment-hosted heavy metals. Mercury (total), arsenic, antimony, and selenium contents were determined; aluminum was also determined and used as normalizing factor. The contents of the heavy metals were relatively constant with depth and do not reflect any potential enrichment from upstream contaminant sources.  相似文献   

12.
Terrestrial geochemistry of Cd,Bi, Tl,Pb, Zn and Rb   总被引：1，自引：0，他引：1  
About 2000 common magmatic, metamorphic and sedimentary rocks and rockforming minerals contained in 465 individual samples have been analyzed for 6 trace metals and potassium with high precision, mainly by combined distillation and AAS methods. Estimates of average abundances in the continental crust are: 98 ppb Cd. 82 ppb Bi. 490 ppb Tl, 14.8 ppm Pb, 77 ppm Zn and 98 ppm Rb (K/Rb: 223). These averages are close to the mean concentrations of the 6 elements in sedimentary and in low to medium grade metamorphic rocks. In relation to the upper mantle the earth's crust has very effectively accumulated Rb, Pb, Tl (and Bi). Cd and Zn are equally distributed between the upper and lower crust. Bi, Tl, Rb, Pb and K are accumulated in the upper relative to the lower continental crust by factors between 3.5 and 1.4. This is mainly due to higher concentrations in granites and lower abundances in granulites relative to gneisses and schists. The five metals form large ions with bulk coefficients less than one for the partition between metamorphic rocks and anatectic granitic melts. The major hosts of Rb, Tl, Pb and Bi in rocks are minerals with 8- to 12-coordinated sites such as mica, K-feldspar, plagioclase etc. (except for some preference of Bi for sphene and apatite). As examples of significant correlations those of Pb with Tl, K, Bi and Rb in mafic rocks and of Bi with K, Rb, Tl and Pb in sedimentary rocks can be reported. In granites and gneisses hydroxyl containing Fe2+-Mg-silicates are major host minerals for Zn and Cd. Except in some carbonate rocks Cd has no preference for Ca minerals.  相似文献   

13.
Doklady Earth Sciences - The Co, Hf, Ce, Cr, Th, and REE characteristics are analyzed for modern sediments collected by a bottom grab during the 67th and 68th cruises of R/V Akademik Mstislav...  相似文献   

14.
The Samchampi-Samteran alkaline igneous complex (SAC) is a near circular, plug-like body approximately 12 km2 area and is emplaced into the Precambrian gneissic terrain of the Karbi Anglong district of Assam. The host rocks, which are exposed in immediate vicinity of the intrusion, comprise granite gneiss, migmatite, granodiorite, amphibolite, pegmatite and quartz veins. The SAC is composed of a wide variety of lithologies identified as syenitic fenite, magnetite ± perovskite ± apatite rock, alkali pyroxenite, ijolite-melteigite, carbonatite, nepheline syenite with leucocratic and mesocratic variants, phonolite, volcanic tuff, phosphatic rock and chert breccia. The magnetite ± perovskite ± apatite rock was generated as a cumulus phase owing to the partitioning of Ti, Fe at a shallow level magma chamber (not evolved DI = O1). The highly alkaline hydrous fluid activity indicated by the presence of strongly alkalic minerals in carbonatites and associated alkaline rocks suggests that the composition of original melt was more alkalic than those now found and represent a silica undersaturated ultramafic rock of carbonated olivine-poor nephelinite which splits with falling temperature into two immiscible fractions—one ultimately crystallises as alkali pyroxenite/ijolite and the other as carbonatite. The spatial distribution of varied lithotypes of SAC and their genetic relationships suggests that the silicate and carbonate melts, produced through liquid immiscibility, during ascent generated into an array of lithotypes and also reaction with the country rocks by alkali emanations produced fenitic aureoles (nephelinisation process). Isotopic studies (δ18O and δ13C) on carbonatites of Samchampi have indicated that the δ13C of the source magma is related to contamination from recycled carbon.  相似文献   

15.
The Kay Tanda epithermal Au deposit in Lobo, Batangas is one of the Au deposits situated in the Batangas Mineral District in southern Luzon, Philippines. This study aims to document the geological, alteration, and mineralization characteristics and to determine the age of the mineralization, the mechanism of ore deposition, and the hydrothermal fluid characteristics of the Kay Tanda deposit. The geology of Kay Tanda consists of (i) the Talahib Volcanic Sequence, a Middle Miocene dacitic to andesitic volcaniclastic sequence that served as the host rock of the mineralization; (ii) the Balibago Diorite Complex, a cogenetic intrusive complex intruding the Talahib Volcanic Sequence; (iii) the Calatagan Formation, a Late Miocene to Early Pliocene volcanosedimentary formation unconformably overlying the Talahib Volcanic Sequence; (iv) the Dacite Porphyry Intrusives, which intruded the older lithological units; and (v) the Balibago Andesite, a Pliocene postmineralization volcaniclastic unit. K‐Ar dating on illite collected from the alteration haloes around quartz veins demonstrated that the age of mineralization is around 5.9 ± 0.2 to 5.5 ± 0.2 Ma (Late Miocene). Two main styles of mineralization are identified in Kay Tanda. The first style is an early‐stage extensive epithermal mineralization characterized by stratabound Au‐Ag‐bearing quartz stockworks hosted at the shallower levels of the Talahib Volcanic Sequence. The second style is a late‐stage base metal (Zn, Pb, and Cu) epithermal mineralization with local bonanza‐grade Au mineralization hosted in veins and hydrothermal breccias that are intersected at deeper levels of the Talahib Volcanic Sequence and at the shallower levels of the Balibago Intrusive Complex. Paragenetic studies on the mineralization in Kay Tanda defined six stages of mineralization; the first two belong to the first mineralization style, while the last four belong to the second mineralization style. Stage 1 is composed of quartz ± pyrophyllite ± dickite/kaolinite ± diaspore alteration, which is cut by quartz veins. Stage 2 is composed of Au‐Ag‐bearing quartz stockworks associated with pervasive illite ± quartz ± smectite ± kaolinite alteration. Stage 3 is composed of carbonate veins with minor base metal sulfides. Stage 4 is composed of quartz ± adularia ± calcite veins and hydrothermal breccias, hosting the main base metal and bonanza‐grade Au mineralization, and is associated with chlorite‐illite‐quartz alteration. Stage 5 is composed of epidote‐carbonate veins associated with epidote‐calcite‐chlorite alteration. Stage 6 is composed of anhydrite‐gypsum veins with minor base metal mineralization. The alteration assemblage of the deposit evolved from an acidic mineral assemblage caused by the condensation of magmatic volatiles from the Balibago Intrusive Complex into the groundwater to a slightly acidic mineral assemblage caused by the interaction of the host rocks and the circulating hydrothermal waters being heated up by the Dacite Porphyry Intrusives to a near‐neutral pH toward the later parts of the mineralization. Fluid inclusion microthermometry indicates that the temperature of the system started to increase during Stage 1 (T = 220–250°C) and remained at high temperatures (T = 250–290°C) toward Stage 6 due to the continuous intrusion of Dacite Porphyry Intrusives at depth. Salinity slightly decreased toward the later stages due to the contribution of more meteoric waters into the hydrothermal system. Boiling is considered the main mechanism of ore deposition based on the occurrence of rhombic adularia, the heterogeneous trapping of fluid inclusions of variable liquid–vapor ratios, the distribution of homogenization temperatures, and the gas ratios obtained from the quantitative fluid inclusion gas analysis of quartz. Ore mineral assemblage and sulfur fugacity determined from the FeS content of sphalerite at temperatures estimated by fluid inclusion microthermometry indicate that the base metal mineralization at Kay Tanda evolved from a high sulfidation to an intermediate sulfidation condition.  相似文献   

16.
The Trinity River (Texas, USA) contains in its watershed 23 different reservoir lakes, the largest one being Lake Livingston situated in the lower Trinity River watershed and two potentially polluting metroplexes, Dallas and Houston. In order to determine fluxes of nutrients and trace metals to Galveston Bay, a survey that included 24 discreet samples collected over a year and at various stages of discharge was carried out during 2000–2001. Geochemical (i.e., sorption by Fe oxyhydroxides), biological (i.e., seasonal uptake by sinking algae in Lake Livingston), and hydrological (i.e., dilution effects by increasing flow rates) controls were found to be mainly responsible for variations in dissolved trace metal concentrations rather than pollution sources. The Trinity River loads of suspended sediments and pollutant trace metals entering Galveston Bay at Anahuac were <20% of those reaching Lake Livingston, and only a few percent of the total upstream trace metal load is entering the Gulf of Mexico. Thus, during the transit through the 23 man-made lakes and an estuary, >96% of the pollutant trace metal load is lost to sediments.  相似文献   

17.
The Jutulsessen area, can provide a vital clue to the supercontinent assembly of Gondwana Land as it is situated within the Circum East Antarctic Mobile Belt just east of the Penksockett rift marking the divide between the central Dronning Maud Land from the Western Dronning Maud Land. This landmass is dominated by migmatitic quartzo-feldspathic rocks intruded by syn to post-tectonic granites. The work highlights the data from western part cDML area with a view to arrive at a more comprehensive model for the cDML and subsequently to the super continent assembly. Granitic and migmatitic gneisses comprising of amphibolitic and biotite rich enclaves. The gneisses show variations from quartzo-felspathic gneiss to amphibolitic gneiss. The area has witnessed complex geological history involving at different deformational episodes with concomitant metamorphism. The pervasive dominant foliation trends NW-SE with shallow to medium dips towards SW. In the Stabben area, a nonfoliated intrusive syenite-gabbro pluton limits the gneissic exposures. Compositionally, the orthogneisses plot in the monzogranitegranodiorite field where as the mafic dykes/enclaves plot in the basalt-andesite-rhyodacite field. The bulk geochemical characteristics suggest significant crustal contamination. Garnet-biotite Fe-Mg exchange thermometry gives peak metamorphic temperature of 483° C for the gneisses and 628° C for the dioritic enclave within gneisses. A peak metamorphic grade of upper amphibolite to granulite facies is deduced from the mineral assemblages. Widespread anatexis has led to extensive occurrence of migmatites in the area. Recent geochronological studies assign an age of 1170 Ma to 970 Ma for the migmatites/gneisses and an emplacement age of 501 Ma for the Stabben gabbro and syenite. The discriminant plots of the Jutulsessen rocks indicate diverse origin ranging from pre-plate collision to post-collision orogenic tectonic setting. The mafic enclaves/dykes show ocean island arc to MORB affinities. Voluminous addition of juvenile crust during the Pan-African orogeny strongly overprints earlier structures.  相似文献   

18.
The lower part of the Cretaceous Sego Sandstone Member of the Mancos Shale in east‐central Utah contains three 10‐ to 20‐m thick layers of tide‐deposited sandstone arranged in a forward‐ and then backward‐stepping stacking pattern. Each layer of tidal sandstone formed during an episode of shoreline regression and transgression, and offshore wave‐influenced marine deposits separating these layers formed after subsequent shoreline transgression and marine ravinement. Detailed facies architecture studies of these deposits suggest sandstone layers formed on broad tide‐influenced river deltas during a time of fluctuating relative sea‐level. Shale‐dominated offshore marine deposits gradually shoal and become more sandstone‐rich upward to the base of a tidal sandstone layer. The tidal sandstones have sharp erosional bases that formed as falling relative sea‐level allowed tides to scour offshore marine deposits. The tidal sandstones were deposited as ebb migrating tidal bars aggraded on delta fronts. Most delta top deposits were stripped during transgression. Where the distal edge of a deltaic sandstone is exposed, a sharp‐based stack of tidal bar deposits successively fines upward recording a landward shift in deposition after maximum lowstand. Where more proximal parts of a deltaic‐sandstone are exposed, a sharp‐based upward‐coarsening succession of late highstand tidal bar deposits is locally cut by fluvial valleys, or tide‐eroded estuaries, formed during relative sea‐level lowstand or early stages of a subsequent transgression. Estuary fills are highly variable, reflecting local depositional processes and variable rates of sediment supply along the coastline. Lateral juxtaposition of regressive deltaic deposits and incised transgressive estuarine fills produced marked facies changes in sandstone layers along strike. Estuarine fills cut into the forward‐stepped deltaic sandstone tend to be more deeply incised and richer in sandstone than those cut into the backward‐stepped deltaic sandstone. Tidal currents strongly influenced deposition during both forced regression and subsequent transgression of shorelines. This contrasts with sandstones in similar basinal settings elsewhere, which have been interpreted as tidally influenced only in transgressive parts of depositional successions.  相似文献   

19.
The Markandeya River Basin stretches geographically from 15o56′ to 16o08′ N latitude and 74o37′ to 74o58′ E longitude, positioned in the midst of Belgaum district, in the northern part of Karnataka. The groundwater quality of 54 pre-monsoon samples in the Markandeya River Basin was evaluated for its suitability for drinking and irrigation purposes by estimating pH, EC, TDS, hardness and alkalinity besides major cations (Na+, K+, Ca2+, Mg2+) and anions (HCO3–, Cl–, SO42–, PO43-, F-, NO3–), boron, SAR, % Na, RSC, RSBC, chlorinity index, SSP, non-carbonate hardness, Potential Salinity, Permeability Index, Kelley’s ratio, Magnesium hazard and Index of Base Exchange. Negative Index of Base Exchange indicates the chloro-alkaline disequilibrium in the study area and the majority of water samples fall in the rock dominance field based on Gibbs’ ratio. Permeability indices of classes I and II suggest suitability of groundwater for irrigation. Based on Cl, SO4, HCO3 concentrations, water samples can be classified as normal chloride (96.3%) and normal sulfate (94.4%) and normal bicarbonate (44.4%) water types.  相似文献   

20.
The distribution of As, Mo, Ni and Se in the aqueous and solid phases of U mine tailings in the Deilmann Tailings Management Facility (DTMF), located at the Key Lake mine in northern Saskatchewan, Canada, was defined using as-discharged tailings samples collected monthly starting in 1996 and core samples collected from the DTMF from 3 locations on 3 occasions between 2004 and 2009. These data indicated that the DTMF can be divided into two geochemical zones; tailings generated from the Deilmann ore body between 1996 and 2000 and tailings from the McArthur River ore body, mined after July 2000. The Deilmann tailings solids are generally characterized by greater elemental concentrations than those in the McArthur River tailings, particularly for As, Co and Ni. These elevated concentrations are attributed to the abundance of Ni–Co–As–S minerals in this ore. The mean aqueous concentrations of As, Mo, Ni, and Se are 3.7, 23.2, 0.14, and 0.02 mg L−1, respectively, in the Deilmann porewaters and 0.20, 4.16, 0.06, and 0.03 mg L−1, respectively, in the McArthur River porewaters. Similarly, the mean As, Mo, Ni, and Se solid phase concentrations are 5.89 × 103, 69.9, 3.20 × 103, and 17.4 μg g−1, respectively, for the Deilmann tailings and 440, 13.6, 551, and 3.03 μg g−1 in the McArthur River tailings. Statistically, pH remained unchanged from the time of discharge while Eh values have remained oxic with no significant change between the two tailings types over 15 a of residence time. Results from sequential extractions, thermodynamic modeling, and results of complimentary research indicated that ferrihydrite solubility is the dominant control on aqueous As concentrations and also plays a role in controlling dissolved Mo, Ni and Se.  相似文献   

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