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1.
John K. Zachariah V. Rajamani Gilbert N. Hanson 《Contributions to Mineralogy and Petrology》1997,129(1):87-104
The N–S trending, 2–4 km wide Ramagiri schist belt is made up of three blocks dominated by metavolcanic rocks, separated
and surrounded by granitic rocks of distinct characteristics. The metavolcanic rocks are tholeiitic in composition and are
very similar in their major element composition as well as in their abundances of some trace elements. However, the rare earth
elements (REE) require distinct sources. The rocks of the amphibolite facies eastern block have LREE depleted REE patterns
([Ce/Yb] = 0.7–0.9), requiring derivation from depleted mantle-like sources. The greenschist facies metatholeiitic rocks of
the central block have LREE enriched REE patterns ([Ce/Yb] = 3–6), reflecting the nature of their source(s). The Nd isotopic
data require that the LREE enriched nature could not have been attained significantly prior to its melting. The fine-grained,
upper greenschist facies metatholeiites of the western block have flat to slightly LREE depleted patterns ([Ce/Yb] = 0.8–0.95).
Minor fractional crystallization of rock forming minerals may relate a few samples to each other among samples from each of
the three blocks. Different extents of partial melting of distinct mantle sources have played a dominant role in the generation
of the parent magmas to the central versus eastern and western block metatholeiites.
The geochemical data suggest that the mantle sources were non-lherzolitic, and that these sources may have seen previous episodes
of melt addition and extraction prior to melting that gave rise to the parent melts to the rocks ∼2750 Ma ago. The REE data
indicate that while the sources of the eastern and western block rocks were similar to depleted mantle (ɛNd(
i
) about +2), the source of the central block rocks (ɛNd(
i
) about +3.5) were enriched in large ion lithophile element (LILE)-rich fluids/melts probably derived from subducting oceanic
crust. This and other trace element signatures point to magma extraction in tectonic settings similar to modern island arcs.
Subsequent to magma emplacement and crystallization, all the three suites of rocks were affected by interaction with low-temperature,
crustal derived fluids (ɛNd 2750Ma of about −8 to −12), probably during the accretion of the three blocks of the belt in the present form. The inferred source
characteristics, tectonic setting of magma generation and the crustal fluid processes seem to suggest that Phanerozoic-style
tectonic processes may have been important in the generation of Archean crust in the Dharwar craton.
Received: 31 July 1995 / Accepted: 12 May 1997 相似文献
2.
Tidal freshwater marshes exist at the interface between watersheds and estuaries, and thus may serve as critical buffers
protecting estuaries from anthropogenic metal pollution. Bi-weekly samples of newly deposited marsh sediments were collected
and analyzed for Cu, Zn, and Fe concentrations over 21 months from July 1995 to March 1997 in five distinct habitats at the
head of Bush River, Maryland. Bi-weekly anthropogenic metal enrichments ranged from 0.9–4.7. Anthropogenic excess metal loadings
averaged over 1996 ranged from 6–306 and 25–1302 μg cm−2 year−1 between sites for Cu and Zn, respectively. Based on Fe-normalized trace metal signatures, Susquehanna River sediment does
not significantly contribute to upper Bush River. Organic matter was found to dilute total metal concentrations, whereas past
studies suggested organics enhance labile metal content. Analysis of metal input pathways shows that marsh metals are primarily
imported from nearby subtidal accumulations of historic watershed material by tidal flushing.
Received: 29 April 1999 / Accepted: 7 December 1999 相似文献
3.
Development of groundwater modeling for the Azraq Basin, Jordan 总被引:2,自引:1,他引:1
The three-dimensional groundwater flow model MODFLOW was applied to simulate water level change in the complex multi-aquifer
systems (the Upper and Middle Aquifers) of the Azraq basin. The model was calibrated by matching observed and simulated drawdown
for steady and transient states over the period 1970–1992. Drawdown data for the period 1993–1997 were used to test the model's
ability to predict the response of the aquifers. The model performed well in representing the water level contours of the
Upper and Middle Aquifers for steady state calibration. Agreement between the observed and simulated drawdowns was obtained
for transient state calibration. To predict the aquifer system responses for the period of 1997–2025, four different pumping
schemes (scenarios) have been investigated. The first scenario (present pumping rate) reveals that there will be approximately
a 25 m drop in the water level at the well-field area in 2025. However, the worst scenario (pumping rate at 1.5 times the
present rate) reveals an approximate 39 m drop in the water level at the well-field area in 2025. The safe yield for the Upper
Aquifer System was found to be about 25 million cubic meters (MCM) yearly.
Received: 24 June 1999 · Accepted: 30 November 1999 相似文献
4.
Water quality of two streams near Yellowstone Park, Wyoming, following the 1988 Clover-Mist wildfire
In 1988, wildfire burned over 50% of the Jones Creek watershed near Yellowstone Park, Wyoming. Crow Creek, an adjacent watershed,
was unburned. Water quality data collected from 1989–1993 may show the fire's effect on weathering and nutrient transport.
Jones Creek had 25–75% larger concentrations of dissolved solids than Crow Creek during the sampling period. Both streams
revealed molar ratios consistent with the stoichiometry of andesine and pyroxene hydrolysis in the trachyandesites that underlie
the basins. During 1989, nitrate transported from the unburned Crow Creek basin peaked at 2 mmol ha–1 s–1. This was twice as much as Jones Creek, possibly indicating a source from ash fallout. By 1992 these rates diminished to
0.1 mmol ha–1 s–1 in Crow Creek and increased to 1.8 mmol ha–1 s–1 in Jones Creek, suggesting later nitrate mobilization in the burned watershed. Phosphorus transported from Jones Creek basin
averaged 0.011 mmol ha–1 s–1 during summer 1989, but fell to 0.004 mg ha–1 s–1 in subsequent years.
Received: 28 May 1997 · Accepted: 18 November 1997 相似文献
5.
Hydrogeologic data of 455 water wells comprising geologic logs, water qualities, and aquifer test results are analyzed to
determine hydrogeological characteristics, water quality, and sustainable yield of the groundwater resources of Cheju volcanic
island. The groundwater of the island occurs in unconsolidated pyroclastic deposits and clinkers interbedded in highly jointed
basaltic and andesitic rocks as high-level, basal, and parabasal groundwater under unconfined conditions. The total storage
of groundwater is estimated at about 44 billion m3. The average transmissivity and specific yield of the aquifer are at about 0.34 m2 s–1(29300 m2 day–1) and 0.12, respectively. The average annual precipitation is about 3.39 billion m3, of which 1.49 billion m3– equivalent to 44.0% of the total annual precipitation – is recharged into aquifers, with 0.638 billion m3 year–1 of runoff and 1.26 billion m3 year–1 of evapotranspiration. Based on a groundwater budget analysis, the sustainable yield is estimated at about 0.62 billion m3 year–1, equivalent to 41.6% of annual recharge. A low-permeability marine sedimentary formation (Sehwari formation), composed of
loosely cemented sandy silt, was recently found to be situated at 120±68 m below mean sea level. If the said marine sediment
is distributed as a basal formation of the freshwater zone of the island, most of its groundwater will be of parabasal type.
So the marine sediment is one of the most important hydrogeological boundaries and groundwater occurrences in the area.
Received: 16 January 1997 / Accepted: 16 June 1997 相似文献
6.
Assessment of natural attenuation of aromatic hydrocarbons in groundwater near a former manufactured-gas plant, South Carolina, USA 总被引:1,自引:0,他引:1
J. E. Landmeyer F. H. Chapelle M. D. Petkewich P. M. Bradley 《Environmental Geology》1998,34(4):279-292
Shallow, anaerobic groundwater near a former manufactured-gas plant (MGP) in Charleston, South Carolina, USA, contains mono-
and polycyclic aromatic hydrocarbons (MAHs and PAHs, respectively). Between 1994 and 1997, a combination of field, laboratory,
and numerical-flow and transport-model investigations were made to assess natural attenuation processes affecting MAH and
PAH distributions. This assessment included determination of adsorption coefficients (K
ad
) and first-order biodegradation rate constants (K
bio
) using aquifer material from the MGP site and adjacent properties. Naphthalene adsorption (K
ad
=1.35×10–7 m3/mg) to aquifer sediments was higher than toluene adsorption (K
ad
=9.34×10–10 m3/mg), suggesting preferential toluene transport relative to naphthalene. However, toluene and benzene distributions measured
in January 1994 were smaller than the naphthalene distribution. This scenario can be explained, in part, by the differences
between biodegradation rates of the compounds. Aerobic first-order rate constants of 14C-toluene, 14C-benzene, and 14C-naphthalene degradation were similar (–0.84, –0.03, and 0.88 day–1, respectively), but anaerobic rate constants were higher for toluene and benzene (–0.002 and –0.00014 day–1, respectively) than for naphthalene (–0.000046 day–1). Both areal and cross-sectional numerical simulations were used to test the hypothesis suggested by these rate differences
that MAH compounds will be contained relative to PAHs. Predictive simulations indicated that the distributions of toluene
and benzene reach steady-state conditions before groundwater flow lines discharge to an adjacent surface-water body, but do
discharge low concentrations of naphthalene. Numerical predictions were "audited" by measuring concentrations of naphthalene,
toluene, and benzene at the site in early 1997. Measured naphthalene and toluene concentrations were substantially reduced
and the areal extent of contamination smaller than was both observed in January 1994 and predicted for 1997. Measured 1997
benzene concentrations and distribution were shown to be relatively unchanged from those measured in 1994, and similar to
predictions for 1997.
Received: 26 June 1997 · Accepted: 25 August 1997 相似文献
7.
Petrology and geochemistry of metamorphosed komatiites and basalts from the Sula Mountains greenstone belt, Sierra Leone 总被引:4,自引:0,他引:4
Hugh Rollinson 《Contributions to Mineralogy and Petrology》1999,134(1):86-101
The Sula Mountains greenstone belt is the largest of the late-Archaean greenstone belts in the West African Craton. It comprises
a thick (5 km) lower volcanic formation and a thinner (2 km) upper metasedimentary formation. Komatiites and basalts dominate
the volcanic formation and komatiites form almost half of the succession. All the volcanic rocks are metamorphosed to amphibolite
grade and have been significantly chemically altered. Two stages of alteration are recognised and are tentatively ascribed
to hydrothermal alteration and later regional amphibolite facies metamorphism. Ratios of immobile trace elements and REE patterns
preserve, for the most part, original igneous signatures and these are used to identify five magma types. These are: low-Ti
komatiites – depleted in light REE; low-Ti komatiites – with flat REE patterns; high-Ti komatiitic basalts – with flat REE;
low-Ti basalts – depleted in light REE; high-Ti basalts – with flat REE patterns. Much of the variation between the magma
types can be explained in terms of different melt fractions of the mantle source, although there were two separate mantle
sources one light REE depleted, the other not. The interleaving of the basalts and komatiites produced by this melting indicates
that the two mantle sources were melted simultaneously. The simplest model with which to explain these complex melting processes
is during melting within a rising mantle plume in which there were two different mantle compositions. The very high proportion
of komatiites in the Sula Mountains relative to other greenstone belts suggests either extensive deep melting and/or the absence
of a thick pre-existing crust which would have acted as a “filter” to komatiite eruption.
Received: 10 February 1998 / Accepted: 28 July 1998 相似文献
8.
M. V. Portnyagin L. V. Danyushevsky V. S. Kamenetsky 《Contributions to Mineralogy and Petrology》1997,128(2-3):287-301
We present a detailed mineralogical, petrological and melt inclusion study of unusually fresh, primitive olivine + clinopyroxene
phyric Lower Pillow Lavas (LPL) found near Analiondas village in the northeastern part of the Troodos ophiolite (Cyprus).
Olivine phenocrysts in these primitive LPL show a wide compositional range (Fo82–92) and have higher CaO contents than those from the Upper Pillow Lavas (UPL). Cr-spinel inclusions in olivine are significantly
less Cr-rich (Cr/Cr + Al = 28–67 mol%) compared to those from the UPL (Cr# = 70–80). These features reflect differences in
melt compositions between primitive LPL and the UPL, namely higher CaO and Al2O3 and lower FeO* compared to the UPL at a given MgO. LPL parental melts (in equilibrium with Fo92) had ∼10.5 wt% MgO and crystallization temperatures ∼1210 °C, which are significantly lower than those previously published
for the UPL (14–15 wt% MgO and ∼1300 °C for Fo92). The fractionation path of LPL parental melts is also different from that of the UPL. It is characterized initially by olivine + clinopyroxene
cotectic crystallization joined by plagioclase at ∼9 wt% MgO, whereas UPL parental melts experienced a substantial interval
of olivine-only crystallization. Primitive LPL melts were formed from a mantle source which was more fertile than that of
tholeiites from well-developed intra-oceanic arcs, but broadly similar in its fertility to that of Mid-Ocean Ridge Basalt
(MORB) and Back Arc Basin Basalts (BABB). The higher degrees of melting during formation of the LPL primary melts compared
to average MORB were caused by the presence of subduction-related components (H2O). Our new data on the LPL coupled with existing data for the UPL support the existing idea that the LPL and UPL primary
melts originated from distinct mantle sources, which cannot be related by progressive source depletion. Temperature differences
between these sources (∼150 °C), their position in the mantle (∼10 kbar for the colder LPL source vs 15–18 kbar for the UPL
source), and temporal succession of Troodos volcanism, all cannot be reconciled in the framework of existing models of mantle
wedge processes, thermal structure and evolution, if a single mantle source is invoked. Possible tectonic settings for the
origin of the Troodos ophiolite (forearc regions of intra-oceanic island arc, propagation of backarc spreading into arc lithosphere)
are discussed.
Received: 20 May 1996 / Accepted: 25 March 1997 相似文献
9.
Marjorie Wilson Aryeh E. Shimron Jeffrey M. Rosenbaum Jeremy Preston 《Contributions to Mineralogy and Petrology》2000,139(1):54-67
Early Cretaceous (146–115 Ma) magmatism in the region of Mt. Hermon, Northern Israel, is part of an extensive Mesozoic igneous
province within the Levant associated with the evolution of the Neotethyan passive margin of Gondwana. The initial stages
of activity were characterised by the emplacement of tholeiitic dykes (146–140 Ma) which were uplifted and eroded prior to
the eruption of a sequence of alkali basalts, basanites and more differentiated alkaline lavas and pyroclastics from 127 to
120 Ma. The latest stages of activity (120–115 Ma) were highly explosive, resulting in the emplacement of diatreme breccias.
Trace element and Sr-Nd-Pb isotope data for the most primitive Early Cretaceous mafic igneous rocks sampled suggest that they
were derived by mixing of melts derived by variable degrees of partial melting of both garnet- and spinel-peridotite-facies
mantle sources. Though isotopically heterogeneous, the source of the magmas has many similarities to that of HIMU oceanic
island basalts. Earlier Liassic (200 Ma) transitional basalts and Neogene–Quaternary (15–0 Ma) alkali basalts erupted within
northern Israel also have HIMU affinities. The petrogenesis of the Early Cretaceous and Cenozoic basalts is explained by partial
melting of a lithospheric mantle protolith metasomatically enriched during the Liassic volcanic phase, which may be plume-related.
Received: 23 July 1998 / Accepted: 6 December 1999 相似文献
10.
Geochemistry, genesis, and health implications of fluoriferous groundwaters in the upper regions of Ghana 总被引:9,自引:2,他引:9
The most appropriate and widely used source of drinking water for the populations of the upper regions of Ghana is groundwater.
In general, groundwater quality is acceptable except for some parts of the Bolgatanga and Bongo Districts, where there are
occurrences of elevated levels of natural groundwater fluoride. Concentrations of groundwater fluoride in excess of the World
Health Organization (WHO) maximum guideline value (1.5 mg/l) in the Bongo area have been known since 1978. However, the effect
of fluoride on people ingesting the water did not receive public and medical attention until October 1993, when health personnel
were asked to investigate the cause of stained teeth in school children. The investigation established that 62% of the total
population of school children in the Bongo area had dental fluorosis. Against this background, a study was initiated to understand
the geochemistry, genesis, and distribution of fluoride in relation to the geology of the area. Groundwater fluoride in the
upper regions ranges from 0.11 to 4.60 ppm, with the highest concentrations associated with the fluorine-enriched Bongo coarse-grained
hornblende granite and syenite suite. The source of groundwater fluoride within the Bongo granitoids is dissolution of the
mineral fluorite and dissolution of and anion exchange with micaceous minerals and their clay products. Applying the WHO recommended
guideline values for fluoride in drinking water reveals that 49% of wells in the area deliver water below the optimum level
of 0.5 mg/l F–; these populations are thus prone to dental caries. Twenty-eight percent of the wells fall within the optimum interval for
good dental health (0.5–1.5 mg/l F–). Twenty-three percent of the wells have concentrations above the recommended maximum guideline limit of 1.5 mg/l F–; this population is susceptible to dental and possibly skeletal fluorosis. Climatic conditions of the area suggest that the
individual water consumption is in the order of 3 to 4 l which is higher than the WHO estimate of 2 l/adult/day. In addition,
dietary intake for the upper region population is probably higher than WHO baseline values (0.2–0.5 mg/day). This implies
that a much higher population is susceptible to developing dental and skeletal fluorosis than originally suspected. Geochemical
symbol plot maps help geochemists understand factors controlling the distribution and uptake of fluoride in the upper regions,
but they are of minimal value to health officials responsible for planning epidemiological studies and dental health education
programs in the region. By casting fluoride data into contoured 'geochemical health-risk maps' using intake interval guidelines
more closely aligned to regional climatic and dietary conditions, health officals can better judge the impacts (regional and
population based) of fluoride on segments of the population, such as various sex and age groups.
Received: 11 March 1997 · Accepted: 17 June 1997 相似文献
11.
Maya G. Kopylova John J. Gurney Leon R. M. Daniels 《Contributions to Mineralogy and Petrology》1997,129(4):366-384
More than 99% of mineral inclusions in diamonds from the River Ranch pipe in the Late Archean Limpopo Mobile Belt (Zimbabwe),
are phases of harzburgitic paragenesis, namely olivine (Fo92–93), orthopyroxene (Mg# = 93), G10 garnets and chromites. The diamond inclusion (DI) chemistry demonstrates a limited overlap
with River Ranch kimberlite macrocrysts: the DI garnets are more Ca-undersaturated, and DI spinel and garnet are more Mg-rich.
Most River Ranch diamond inclusions were equilibrated at T = 1080–1320 °C, P = 47–61 kbar, and f
O2 between IW and WM buffers. The P/T profile beneath the Limpopo Mobile Belt (LMB) is consistent with a paleo-heat flow of 41–42 mW/m2, similar to calculations for Roberts Victor, but hotter than for the Finsch, Kimberley, Koffiefontein and Premier Mines.
This is ascribed to the younger tectonothermal age of the LMB and its proximity to Late Archean oceans. Like diamond inclusions
from all other kimberlites studied, the River Ranch DI have a lithospheric affinity and therefore indicate that an ancient,
chemically depleted, thick (at least 200 km) mantle root existed beneath the Limpopo Mobile Belt 530–540 Ma ago. The mantle
root might have developed beneath the continental Central Zone of the LMB as early as the Archean, and could be alien to the
overthrust allochthonous sheet of the Limpopo Belt. Oxygen fugacity estimates for diamond inclusions at River Ranch are similar
to other diamondiferous harzburgites beneath the Kaapvaal craton, indicating that the Kaapvaal mantle as a whole was well
buffered and homogeneous with respect to f
O2 at the time of peridotitic diamond crystallization.
Received: 11 January 1995 / Accepted: 10 June 1997 相似文献
12.
Structurally controlled fluid flow during contact metamorphism in the Ritter Range pendant, California, USA 总被引:1,自引:0,他引:1
John M. Ferry Sorena S. Sorensen Douglas Rumble III. 《Contributions to Mineralogy and Petrology》1998,130(3-4):358-378
The mineralogy and O-isotope geochemistry of siliceous limestones from the Ritter Range pendant constrain the geometry and
amount of fluid flow during contact metamorphism associated with emplacement of a pluton of the Sierra Nevada Batholith. Wollastonite
(Wo) replaces calcite (Cal) + quartz (Qtz) on a layer-by-layer basis in homoclinal beds that strike NW and dip almost vertically.
At the peak of metamorphism (P≈ 1500 bars, T≈ 600 °C) fluid in equilibrium with Cal, Qtz, and Wo has composition XCO2=0.28, requiring that the Wo-forming reaction was driven by infiltration of reactive H2O-rich fluid. The spatial distribution of Wo and Cal + Qtz records that peak metamorphic fluid flow was layer-parallel, upward.
Bounds on the prograde time-integrated fluid flux associated with formation of Wo are set by: (1) the overlap in O-isotope
composition between Wo-bearing and Wo-free rocks (>245 mol fluid/cm2 rock); (2) the amount of fluid that would drive the Wo-reaction front upward to the present level of exposure from a point
at depth where Cal, Qtz, and Wo would be in equilibrium with pure CO2 (<1615 mol/cm2). Back-reaction of Wo to Cal + Qtz records an additional time-integrated retrograde fluid flux of ≈ 200–1000 mol/cm2. The direction and amount of flow inferred from mineralogical and isotopic data agree with the results of the hydrologic
model for metamorphic fluid flow in the area of Hanson et al. (1993). Fingers of Wo-bearing rock that extend farthest from
the fluid source along contacts between limestone and more siliceous rocks point to strong control of flow geometry at the
0.1–100 m scale exerted by premetamorphic structures. Studies that neglect structural control at this scale may fail to predict
correctly fundamental aspects of contact metamorphic fluid flow.
Received: 27 January 1997 / Accepted: 2 October 1997 相似文献
13.
Trace element abundances of high-MgO glasses from Kilauea, Mauna Loa and Haleakala volcanoes, Hawaii
T. P. Wagner D. A. Clague E. H. Hauri T. L. Grove 《Contributions to Mineralogy and Petrology》1998,131(1):13-21
We performed an ion-microprobe study of eleven high-MgO (6.7–14.8 wt%) tholeiite glasses from the Hawaiian volcanoes Kilauea,
Mauna Loa and Haleakala. We determined the rare earth (RE), high field strength, and other selected trace element abundances
of these glasses, and used the data to establish their relationship to typical Hawaiian shield tholeiite and to infer characteristics
of their source. The glasses have trace element abundance characteristics generally similar to those of typical shield tholeiites,
e.g. L(light)REE/H(heavy)REEC1 < 1. The Kilauea and Mauna Loa glasses, however, display trace and major element characteristics that cross geochemical discriminants
observed between Kilauea and Mauna Loa shield lavas. The glasses contain a blend of these discriminating chemical characteristics,
and are not exactly like the typical shield lavas from either volcano. The production of these hybrid magmas likely requires
a complexly zoned source, rather than two unique sources. When corrected for olivine fractionation, the glass data show correlations
between CaO concentration and incompatible trace element abundances, indicating that CaO may behave incompatibly during melting
of the tholeiite source. Furthermore, the tholeiite source must contain residual garnet and clinopyroxene to account for the
variation in trace element abundances of the Kilauea glasses. Inversion modeling indicates that the Kilauea source is flat
relative to C1 chondrites, and has a higher bulk distribution coefficient for the HREE than the LREE.
Received: 4 February 1997 / Accepted: 27 August 1997 相似文献
14.
The environmental conditions prevailing in the Chicam-Toctina drainage system (approx. 138 km2 in Córdoba, Argentina) are considered representative of a number of catchments in Argentina's Sierras Pampeanas Range. Two
groups of ions reflect the sources of dissolved species in the catchment: a) a group (Cl–, SO2–
4, and Na+) which recognizes natural and anthropogenic sources, and which exhibits significant correlations with N–
3 and NO–
2, and b) another group of components (Ca2+, Mg2+, and HCO–
3) which is clearly controlled by carbonate rocks and their waste rock products. In the headwaters, stockpiled marble quarry
mining wastes provide a more open system to CO2 gaseous exchange than the outcropping rocks, thus promoting the increase of carbonate dissolution (up to 4.88 g km–2 s–1 during the rainy season). This specific yield was 20% higher than the amount estimated for an area with fewer extended mining
activities. The dissolved load delivered by the upper reaches is subjected in the lower drainage area to various processes,
mainly controlled by the presence of the city of Alta Gracia (approx. 40,000 inhabitants). In the dry season, due to nutrient
inputs supplied by the city, photosynthetic activity plays a major role controlling stream pH. Hence, the high values of calcite
saturation indexes and the increase of CaCO3 concentration in bed sediments can be explained by calcite precipitation. Such a process could be accompanied by the coprecipitation
on calcium carbonate of low solubility heavy metal carbonates.
Received : 17 January 1997 · Accepted : 31 March 1997 相似文献
15.
L. Melluso S. F. Sethna M. D’Antonio P. Javeri L. Bennio 《Mineralogy and Petrology》2002,74(2-4):323-342
Summary Major element, trace element, Sr- and Nd-isotopes and mineral chemical data are reported for alkaline rocks (lamprophyres,
tephrites, melanephelinites, nephelinites and nepheline syenites) cross-cutting the Deccan Trap lava flows south (Murud-Janjira
area) and north of Mumbai (Bassein). These rocks range from sodic to potassic and have a large span in MgO (12–2 wt%). The
lamprophyres have high content of incompatible elements (e.g., TiO2 > 3.8 wt%, Nb > 130 ppm, Zr > 380 ppm, Ba > 1200 ppm), and relatively high initial (at 65 Ma) 143Nd/144Nd (0.5128) and low 87Sr/86Sr (0.7038–0.7042). They are likely to be small-degree melts (2–3%) of volatile- and incompatible element-enriched mantle
sources, similar to other alkaline rocks in the northern Deccan, though slightly more potassium-rich. The nepheline-rich rocks
have highly porphyritic textures (up to 57% phenocrysts of diopside ± olivine), and anomalously low contents of incompatible
elements (e.g., TiO2 < 1.3 wt%, Nb < 24 ppm, Zr < 100 ppm) indicating that they could not represent liquid compositions. Moreover, their very
low initial 143Nd/144Nd ratios (0.5116–0.5120), at 87Sr/86Sr = 0.7045–0.7049, are unusual in the rocks related to the Deccan Traps and identify a new end-member in this province, that
could be identified as “Lewisian-type” lower crust and/or enriched mantle. The melting episode that generated these alkaline
rocks likely occurred close to the base of the ca. 100 km-thick Indian lithosphere, very shortly after the main eruption of
the Deccan tholeiites.
Received January 14, 2000; revised version accepted September 28, 2001 相似文献
16.
Foresighted and determined local authorities, purposeful exploration (i.e. by seismic reflection) and extensive testing led
to the discovery of a substantial groundwater resource near the community of Seon (Switzerland) at a depth of 268–305 m. Production
tests revealed a hydraulic conductivity of ∼5.10–5 m/s, transmissivity of ∼5.10–4 m2/s and a storage coefficient of ∼2% in the aquifer. Pumping up to 1500 l/min is sustainable; the water quality complies chemically
and bacteriologically with drinking-water requirements. The residence time of several 103 years, determined by isotope techniques, guarantees protection from surface contamination. The elevated temperature of 19.5 °C
of the produced water enables combined use for drinking water and space heating. The environmental benefits are substantial:
the emission reduction amounts up to 780 tons/year CO2 and 1 ton/year SO2.
Received: 21 September 1998 · Accepted: 10 February 1999 相似文献
17.
W. D. Maier S.-J. Barnes G. Chinyepi J. M. BartonJr B. Eglington I. Setshedi 《Mineralium Deposita》2008,43(1):37-60
We studied a number of magmatic Ni–Cu–(PGE) sulfide deposits in two distinct belts in eastern Botswana. The Tati belt contains
several relatively small deposits (up to 4.5 Mt of ore at 2.05% Ni and 0.85% Cu) at Phoenix, Selkirk and Tekwane. The deposits
are hosted by ca 2.7 Ga, low- to medium-grade metamorphosed gabbroic–troctolitic intrusions situated within or at the periphery
of a greenstone belt. The deposits of the Selebi-Phikwe belt are larger in size (up to 31 Mt of ore grade). They are hosted
by high-grade metamorphosed gabbronorites, pyroxenites and peridotites believed to be older than ca 2.0 Ga that intruded gneisses
of the Central Zone of the Limpopo metamorphic belt. The composition of the sulfide mineralisation in the two belts shows
systematic variation. Most of the mineralisation in the Tati belt contains 2–9% Ni and 0.05–4% Cu (Cu/Cu + Ni = 0.4–0.7),
whereas most of the mineralisation in the Selebi-Phikwe belt contains 1–3% Ni and 0.1–4% Cu (Cu/Cu + Ni = 0.4–0.9). The Cu–Ni
tenors of the ores in both belts are consistent with crystallization from a basaltic magma. The Tati ores contain mostly >3 ppm
Pt + Pd (Pt/Pd 0.1–1), with Pd/Ir = 100–1,000, indicative of a differentiated basaltic magma that remained S-undersaturated
before emplacement. Most of the Selebi-Phikwe ores have <0.5 ppm Pt + Pd (Pt/Pd < 0.1–1), with Pd/Ir = 10–500. This suggests
a relatively less differentiated magma that reached S saturation before emplacement. The Tati rocks show flat mantle-normalised
incompatible trace element patterns (average Th/YbN = 1.57), except for strong enrichments in large ion lithophile elements (Cs, Rb, Ba, U, K). Such patterns are characteristic
of relatively uncontaminated oceanic arc magmas and suggest that the Tati intrusions were emplaced in a destructive plate
margin setting. Most of the Selebi-Phikwe rocks (notably Dikoloti) have more fractionated trace element signatures (average
Th/YbN = 4.22), possibly indicating digestion of upper crustal material during magma emplacement. However, as there are also samples
that have oceanic arc-like signatures, an alternative possibility is that the composition of most Selebi-Phikwe rocks reflects
tectonic mingling of the intrusive rocks with the country rocks. The implication is that orogenic belts may have a higher
prospectivity for magmatic Ni–Cu ores than presently recognised. The trigger mechanism for sulfide saturation and segregation
in all intrusions remains unclear. Whereas the host rocks to the intrusions appear to be relatively sulfur poor, addition
of crustal S to the magmas is suggested by low Se/S ratios in some of the ores (notably at Selebi-Phikwe). External S sources
may thus remain unidentified due to poor exposure and/or S mobility in response to metamorphism. 相似文献
18.
Environmental impact of mining waste disposal on a tropical lowland river system: a case study on the Ok Tedi Mine, Papua New Guinea 总被引:3,自引:0,他引:3
The 1000 km long Ok Tedi/Fly River system receives about 66 Mt/year of mining waste from the Ok Tedi copper-gold porphyry
mine. Mine input has increased the suspended sediment load of the Middle Fly River about 5–10 times over the natural background.
A significant yet unknown amount of copper-rich material deposits unevenly in the extensive tropical lowland floodplain. Recent
alluvial sediments of the Fly River floodplain have copper contents of 620 mg/kg (±1σ: 430–900), whereas the regional background
is 40 mg/kg (±σ: 25–60). This pattern is mirrored and enhanced by the gold dispersal pattern with a 7 ppb Au background versus
a 140–275 ppb population in mine-derived material. Very high deposition rates (around 4 cm/y) of mine-derived sediment were
determined in locations close to the creeks and channels which link the Fly River with the outer floodplain. A thin layer
of 1–5 cm of copper-rich material (400–900 mg/kg Cu) was usually found on the bottom of drowned (tributary) valley lakes.
Average dissolved copper content in waters of the inner floodplain is around 9 μg/l (±1σ: 5–14) as compared to unpolluted
water from the outer floodplain with < 2 μg/l Cu. The present Fly River water, about 600 km downstream of the mine site, has
concentrations of 17 ± 3 μg/l dissolved Cu.
Received: 30 June 1996 / Accepted: 9 January 1997 相似文献
19.
Alteration zoning and primary geochemical dispersion at the Bronzewing lode-gold deposit, Western Australia 总被引:1,自引:0,他引:1
The Late Archaean Bronzewing lode-gold deposit is in the Yandal greenstone belt, Western Australia. It is located in a 500-m-wide,
N–S trending, structural corridor consisting of an anastomosing set of brittle–ductile shear zones and is chiefly hosted by
tholeiitic basalts, which are metamorphosed at mid- to upper-greenschist facies. Syn-peak metamorphic alteration surround
all ore bodies, and alteration extends laterally for ≤80 m from individual mineralised structures. Individual alteration haloes
partially overlap and form a >1.5-km-long and ≤300-m-wide domain. The alteration sequence, studied here at 140 m below the
present undisturbed surface, comprises distal calcite–chlorite–albite–quartz, intermediate calcite–dolomite–chlorite–muscovite–albite–quartz
and proximal ankerite–dolomite–muscovite–albite–quartz–pyrite zones. Mass transfer calculations indicate that chemical changes
during alteration include enrichment of Ag, Au, Ba, Bi, CO2, K, Rb, S, Sb, Te and W, and depletion of Na, Sr and Y. The elements Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, P, Ti, V, Zn and Zr
are immobile. The degree of chemical change increases with proximity to gold ore zones. In addition, abundant quartz veins
indicate substantial silica mobility during the hydrothermal event, although there is no large relative silica loss or gain
in the host rock. The broadest anomaly surrounding the Bronzewing gold deposit is defined by tellurium (>10 ppb) which, if
it is a hydrothermal anomaly, extends beyond the 400 × 600 m study area. Anomalous values for CO2, K, Rb and Sb also define wider zones than does anomalous gold (>4 ppb), although even the lithogeochemical gold anomaly
extends across strike for as much as 80 m away from ore and >600 m along the N–S strike of the shear zone corridor. Also carbonation
and sericitisation indices outline large exploration targets at the Bronzewing deposit. Sericitisation indices define anomalies
that extend for tens of metres beyond visible potassic alteration, whereas the anomalies defined by the carbonation indices
do not extend beyond visible carbonation. None of the individual alteration indices or pathfinder elements are able to define
consistent gradients towards ore. However, the respective dimensions of individual geochemical anomalies can be used as an
extensive, although stepwise, vector towards ore. This sequence is, from species with broadest dispersion first, as follows:
Te > CO2/Ca ≥ Sb, 3K/Al, Rb/Ti ≥ Au, W > Y/Ti (depletion) > Ag ≥ Bronzewing ore.
Received: 25 October 1999 / Accepted: 11 May 2000 相似文献
20.
Water from the Kombat mine was delivered to the Omatako dam via the 263-km-long Grootfontein-Omatako canal during test runs
in 1997. It is intended to supply water from Kombat and other underground mines in the Otavi Mountain Land to the capital
Windhoek. The Cu-Pb-Zn orebodies are hosted by carbonate rocks and the mine waters are supersaturated with respect to calcite
and CO2. Along the length of the canal, the CO2 partial pressure drops from 10−2.1 atm at the inlet of the Kombat mine to 10−3.5 atm at the end of the canal. This is accompanied by a drop in Ca concentration from about 60 to about 20 mg/l. The heavy
metal concentrations (Cd, Cu, Mn, Pb and Zn) drop along the course of the canal to values far below the national drinking-water
standard. Scavenging by calcium carbonate precipitation is the major depletion mechanism.
Received: 21 June 1999 · Accepted: 29 August 1999 相似文献