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1.
Twenty nine samples of silica sinter, ranging in age from modern to Miocene, record temporal changes in both mineralogy and
texture. When first deposited, sinters consist largely of noncrystalline spheres (<1–8 μm diameter) of opal-A exhibiting varying
degrees of close-packing. Particle densities range from 1.5 to 2.1 g cm−3, total water 4–10 wt%, and porosities 35–60%. Changes over ∼10,000 years following deposition are slight although the spheres
may be invested by an additional film of secondary silica. For the next 10,000 to ∼50,000 years, the silica incrementally
crystallises to become poorly crystalline opal-CT and/or opal-C; spherical particles of thin-bladed crystals (lepispheres)
replace opal-A particles and coalesce in microbotryoidal aggregates (∼10–30 μm diameter). Amygdaloidal fibrous clusters occur
with lepispheres. As silica lattice ordering becomes enhanced, total water content drops to <7 wt%, particle density increases
to ∼2.3 g cm−3, and porosity reduces to <30%. The change from opal-A to opal-C takes place over a briefer periods (∼50 years) in silica
sinters that contain other materials (e.g. calcite, sulfur, alunite, plant remains). Sinters older than ∼50,000 years have
recrystallised to microcrystalline quartz. With the onset of quartz crystallisation at ∼20,000 years, total water is <0.2 wt%,
particle density approximates quartz (2.65 g cm−3), and porosity is <4%. The progressive changes in silica species and texture yield ageing profiles for sinters that may serve
as guides to the paleohydrology of geothermal systems and/or epithermal ore deposits in areas where surface thermal activity
has declined or ceased.
Received: 18 November 1998 / Accepted: 6 July 1999 相似文献
2.
Mineralogy of gold in the Elshitsa massive sulphide deposit, Sredna Gora zone, Bulgaria 总被引:1,自引:0,他引:1
The Elshitsa volcanic hosted massive sulphide deposit occurs in the central part of the Srena Gora metallogenic zone in Bulgaria.
The gold-bearing massive sulphide mineralization is considered to be the product of an island arc volcano-plutonic process
and hydrothermal activity that took place during the Late Cretaceous. In addition to the major gold-hosted opaque minerals
such as pyrite, chalcopyrite, sphalerite and galena there are minor phases of tennantite, goldfieldite, Se-bearing aikinite,
native silver and bornite in the massive sulphide lenses and stringer zones. Most of the sulphide minerals are Se-bearing.
All of the six mineral assemblages that were deposited during the pyrite and copper-pyrite stages of mineralization are gold-bearing.
The gold tenor as a rule is less than 1 g/t. Native gold and electrum occur as blebs or intergranular particles in the sulphide
minerals. Gold in the early massive pyrite is of submicroscopic type (< 0,1 μm) and of colloidal ori-gin. Pyrite deformation
and recrystallization in the temperature range 250°–160 °C has led to Au and Ag migration to cracks and grain boundaries of
the sulphide minerals. As a result of these process the native gold and electrum grain size increases from submicroscopic
(< 0,1 μm) in the early colloform pyrite to microscopic (0,1–100 μm) and macroscopic (> 100 μm) in the late gold-sulphide
assemblages. The electrum fineness in 41 individually studied grains varies between 780 and 992‰ with a mean of 895‰. Native
silver was found in association with bornite. Cu, Te, Sb and Bi are the most common trace-elements in gold and electrum. The
Cu-Zn-Pb association is most important as a Au-Ag-carrier. A model for gold behaviour during sulphide deformation is proposed
involving coarsening of gold grain size from the earlier to the later sulphide mineral assemblages.
Received: 4 December 1995 / Accepted: 23 September 1996 相似文献
3.
Vein-hosted mesothermal stibnite-gold mineralisation at the Hillgrove Au-Sb mine in northeastern New South Wales has a halo
of veinlet and disseminated auriferous arsenopyrite and arsenian pyrite in metasedimentary and granitic host rocks. About
50–55% of the gold produced at Hillgrove occurs invisibly in arsenopyrite and pyrite. Gold losses of ∼20% into tailings are
due to this mineral chemical factor. From PIXE probe analyses, it has been found that arsenopyrite contains 255–1500 ppm Au
and pyrite 24–223 ppm Au, with Au contents of each mineral correlating moderately with As content. Arsenopyrite and pyrite
also contain anomalous values of Cu, Ag and Sb, whereas paragenetically later stibnite contains little invisible gold, but
minor Fe, As, Ag, Cu and Pb. The precipitation of invisible gold in arsenopyrite and pyrite by a possible (Fe, Au)3+= (As-S)3− substitution mechanism may have been facilitated by rapid, non-equilibrium conditions involving pressure decreases and wall
rock reaction (sulphidation, carbonatisation), as a prelude to the main stage of stibnite and gold deposition.
Received: 15 January 1999 / Accepted: 12 October 1999 相似文献
4.
The effect of distribution of iron-oxyhydroxide grain coatings on the transport of bacterial cells in porous media 总被引:3,自引:0,他引:3
E. P. Knapp Janet S. Herman George M. Hornberger Aaron L. Mills 《Environmental Geology》1998,33(4):243-248
Among the demonstrated processes influencing the transport of bacteria through aquifers, the deposition of cells on mineral
surfaces is one of the most important. For example, understanding the transport of introduced bacteria through aquifers is
essential to designing some in situ bioremediation schemes. The impact of the presence and distribution of Fe(III)-oxyhydroxide-coated
sand grains on bacterial transport through porous media was evaluated in column experiments in which bacteria (short rods;
1.2 μm length) were eluted through columns of quartz sand (0.5–0.6 mm in diameter) for several conditions of chemical heterogeneity
of mineral substrate. Fe(III)-oxyhydroxide-coated sand was present as 10% of the mass, and it was arranged in three treatments:
(1) homogeneously distributed, and present as a discrete layer (2) at the top and (3) at the bottom of 14-cm-long sand columns.
A pulse input of 108 cells ml–1 was introduced in an artificial groundwater solution flowing at 14 cm h–1 through the column, and eluted cells were counted. Peak breakthrough occurred at 1.0 pore volume. A large proportion of cells
were retained; 14.7–15.8% of the cells were recovered after three pore volumes of solution had eluted through clean quartz
sand, and only 2.1–4.0% were recovered from the Fe(III)-oxyhydroxide-coated sand mixtures. The three physical arrangements
of the chemical heterogeneity resulted in essentially the same breakthrough of cells, indicating that the spatial distribution
of iron coating does not affect the transport of bacteria. The results of the column transport experiments, which mimic hydrogeological
conditions encountered in field problems, are consistent with our mechanistic understanding of bacterial sorption.
Received: 10 April 1996 · Accepted: 17 February 1997 相似文献
5.
Zhiwen Dong Zhongqin Li Cunde Xiao Feiteng Wang Mingjun Zhang 《Environmental Earth Sciences》2010,60(7):1361-1368
Windblown mineral aerosol dust derived from the crustal surface is an important atmospheric component affecting the earth’s
radiation budget. Deposition of atmospheric dust was measured in the fresh snow on glacier no. 1 at the headwater of the Urumqi
River in eastern Tian Shan, central Asia. An analysis of seasonal variation of concentrations of dust particles in the snow
suggests that the number concentration of dust particle is significantly high from April to June, which may be caused by Asian
dust storms in the spring. The comparison of mass-size distribution of dust particles from April to August shows an obvious
seasonal change trend. The distribution of particles changes from single model (3–21 μm) in the non-dust period before dust
events in April, to bi-model (3–21 and 20–80 μm) during the Asian dust period, and to single model (3–21 μm) after July in
the non-dust period again. The Ca2+ concentration in the fresh snow is also very high from April to June, while NH4
+ and SO4
2−, as water-soluble constituents, have concentration changes that are different from each other. Backward trajectory was also
employed to examine the transport process of air mass in this region. 相似文献
6.
Roberto Oyarzun Paloma Cubas Pablo Higueras Javier Lillo Willians Llanos 《Environmental Geology》2009,58(4):761-777
The Rodalquilar mineral deposits (SE Spain) were formed in Miocene time in relation to caldera volcanic episodes and dome
emplacement phenomena. Two types of ore deposits are recognized: (1) the El Cinto epithermal, Au–As high sulphidation vein
and breccia type; and (2) peripheral low sulphidation epithermal Pb–Zn–Cu–(Au) veins. The first metallurgical plants for gold
extraction were set up in the 1920s and used amalgamation. Cyanide leaching began in the 1930s and the operations lasted until
the mid 1960s. The latter left a huge pile of ~900,000–1,250,000 m3 of abandoned As-rich tailings adjacent to the town of Rodalquilar. A frustrated initiative to reactivate the El Cinto mines
took place in the late 1980s and left a heap leaching pile of ~120,000 m3. Adverse mineralogical and structural conditions favoured metal and metalloid dispersion from the ore bodies into soils and
sediments, whereas mining and metallurgical operations considerably aggravated contamination. We present geochemical data
for soils, tailings and wild plant species. Compared to world and local baselines, both the tailings and soils of Rodalquilar
are highly enriched in As (mean concentrations of 950 and 180 μg g−1, respectively). Regarding plants, only the concentrations of As, Bi and Sb in Asparagus horridus, Launaea arborescens, Salsola genistoides, and Stipa tenacissima are above the local baselines. Bioaccumulation factors in these species are generally lower in the tailings, which may be
related to an exclusion strategy for metal tolerance. The statistical analysis of geochemical data from soils and plants allows
recognition of two well-differentiated clusters of elements (As–Bi–Sb–Se–Sn–Te and Cd–Cu–Hg–Pb–Zn), which ultimately reflect
the strong chemical influence of both El Cinto and peripheral deposits mineral assemblages. 相似文献
7.
M.C. Corriveau H.E. Jamieson M.B. Parsons J.L. Campbell A. Lanzirotti 《Applied Geochemistry》2011,26(9-10):1639-1648
Windblown and vehicle-raised dust from unvegetated mine tailings can be a human health risk. Airborne particles from As-rich abandoned Au mine tailings from Nova Scotia, Canada have been characterized in terms of particle size, As concentration, As oxidation state, mineral species and texture. Samples were collected in seven aerodynamically fractionated size ranges (0.5–16 μm) using a cascade impactor deployed at three tailings fields. All three sites are used for recreational activities and off-road vehicles were racing on the tailings at two mines during sample collection. Total concentrations of As in the <8 μm fraction varied from 65 to 1040 ng/m3 of air as measured by proton-induced X-ray emission (PIXE) analysis. The same samples were analysed by synchrotron-based microfocused X-ray absorption near-edge spectroscopy (μXANES) and X-ray diffraction (μXRD) and found to contain multiple As-bearing mineral species, including Fe–As weathering products. The As species present in the dust were similar to those observed in the near-surface tailings. The action of vehicles on the tailings surface may disaggregate material cemented with Fe arsenate and contribute additional fine-grained As-rich particles to airborne dust. Results from this study can be used to help assess the potential human health risks associated with exposure to airborne particles from mine tailings. 相似文献
8.
Feras Youssef Gunay Erpul Pieter Bogman Wim M. Cornelis Donald Gabriels 《Environmental Geology》2008,55(4):741-750
The trap efficiency of a catcher in wind erosion measurements plays a significant role, and in many cases suspension trap
efficiencies at high wind velocities are still unknown. The sediment trap efficiency generally changes with particles size
and with wind speed. In this study, the efficiency of Vaseline Slide (VS) and Modified Wilson and Cooke (MWAC) catchers were
determined with different sand particle sizes (<50, <75, 50–75, 200–400, and 400–500 μm) at a fixed wind speed (13.3 ms−1) and with different soil textures at different wind velocities (10.3, 12.3, and 14.3 ms−1) in the wind tunnel of the International Center for Eremology (ICE), Ghent University, Belgium. The traps were placed at
different heights (4, 6.5, 13, 20, 120, and 192 cm for VS and 1.5, 3, 5, 8, 11, and 30 cm for MWAC) to catch saltating and
suspended sediments in a 12-m long, 1.2-m wide and 3.2-m high working section of the wind tunnel. In the sand particle experiments,
the efficiency of the VS catcher was 92% for particles smaller than 50 μm and decreased with increasing particles size, falling
to 2.2% for 400–500 μm particle size at 13.4 ms−1. However, the MWAC’s efficiency was 0% for particles smaller than 50 μm and increased with increasing particle size to 69.5%
at 400–500 μm. In the experiments with different soil textures, the efficiency of each catcher significantly changed with
soil and with wind speed. It also considerably varied with the catchers: for instance, for sand (S), the MWAC efficiency was
very high (67.4, 113.4, and 90.5% at 10.3, 12.3, and 14.4 ms−1, respectively) while the efficiency of VS was relatively very low (5.2, 4.4, and 1.9% at 10.3, 12.3, and 14.4 ms−1, respectively). Results indicated that the efficiency depends critically on the particle size, type of catcher, and wind
speed, and these could be helpful to increase the robustness of wind erosion measurements. 相似文献
9.
L. G. Medaris Jr. E. D. Ghent H. F. Wang J. H. Fournelle E. Jelínek 《Mineralogy and Petrology》2006,86(3-4):203-220
Summary In the Kutná Hora Complex, the Běstvina Formation, which is similar to Gf?hl granulite, contains eclogite that has escaped
widespread retrograde recrystallization. The eclogite assemblage, garnet + omphacite + quartz + rutile ± plagioclase, yields
an estimate for peak metamorphic conditions of 18–20 kbar and 835–935 °C, which is comparable to that determined from felsic
granulite, 14–20 kbar and 900–1000 °C. Garnet in eclogite exhibits both prograde and retrograde compositional zoning, from
which constraints on thermal history of the Gf?hl terrane can be derived by diffusion modelling. At 900 °C, a garnet grain
of 800–1000 μm radius would homogenize in 7.5–11.7 million years, but the existence of compositional gradients on a length
scale of 100–200 μm suggests that the duration of peak metamorphism may have been limited to ∼500,000 years. Diffusion modelling
of retrograde zoning in garnet yields a cooling rate of 150–100 °C/m.y. for a radius of 800–1000 μm and initial temperature
of 900 °C. The relatively brief duration of high-pressure/high-temperature metamorphism and rapid cooling and exhumation of
the Gf?hl terrane may be a consequence of lithospheric delamination during Early Carboniferous collision of Bohemia (Teplá-Barrandia)
and Moldanubia (Franke, 2000). 相似文献
10.
Thirty-nine samples of basaltic core were collected from wells 121 and 123, located approximately 1.8 km apart north and
south of the Idaho Chemical Processing Plant at the Idaho National Engineering Laboratory. Samples were collected from depths
ranging from 15 to 221 m below land surface for the purpose of establishing stratigraphic correlations between these two wells.
Elemental analyses indicate that the basalts consist of three principal chemical types. Two of these types are each represented
by a single basalt flow in each well. The third chemical type is represented by many basalt flows and includes a broad range
of chemical compositions that is distinguished from the other two types. Basalt flows within the third type were identified
by hierarchical K-cluster analysis of 14 representative elements: Fe, Ca, K, Na, Sc, Co, La, Ce, Sm, Eu, Yb, Hf, Ta, and Th.
Cluster analyses indicate correlations of basalt flows between wells 121 and 123 at depths of approximately 38–40 m, 125–128 m,
131–137 m, 149–158 m, and 183–198 m. Probable correlations also are indicated for at least seven other depth intervals. Basalt
flows in several depth intervals do not correlate on the basis of chemical compositions, thus reflecting possible flow margins
in the sequence between the wells. Multi-element chemical data provide a useful method for determining stratigraphic correlations
of basalt in the upper 1–2 km of the eastern Snake River Plain.
Received: 16 February 1996 · Accepted: 1 April 1996 相似文献
11.
Heavy meals in urban roadside soils, part 1: effect of particle size fractions on heavy metals partitioning 总被引:8,自引:0,他引:8
Urban roadside soils are important environmental media for assessing heavy metal concentrations in urban environment. However, among other things, heavy metal concentrations are controlled by soil particle grain size fractions. In this study, two roadside sites were chosen within the city of Xuzhou (China) to reflect differences in land use. Bulk soil samples were collected and then divided by particle diameter into five physical size fractions, 500–250, 250–125, 125–74, 74–45, < 45 μm. Concentrations of metals (Ti, Cr, Al, Ga, Pb, Ba, Cd, Co, Cu, Mn, Ni, V, Zn, Mo, As, Sb, Se, Hg, Bi, Ag) were determined for each individual fraction. These metals could be roughly classified into two groups: anthropogenic element (Pb, Ba, Cd, Cu, Zn, Mo, As, Sb, Se, Hg, Bi, Ag) and lithophile element (Ti, Cr, Al, Ga, Co, Mn, Ni, V) in terms of values of enrichment factor. As expected, higher concentrations of anthropogenic heavy metals (Cu, Zn, Mo, As, Hg, Bi, Ag) are observed in the finest particle grain size fraction (i.e. < 45 μm). However, heavy metals Se, Sb and Ba behave independently of selected grain size fractions. From the viewpoint of mass loading, more than 30% of the concentrations for all anthropogenic heavy metals are contributed by the particle grain size fractions of 45–74 μm at site 1 and more than 70% of the concentrations for all heavy metals are contributed by the particle grain size fractions of 45–74 and 74–125 μm at site 2. These results are important for transport of soil-bound heavy metals and pollution control by various remedial options. 相似文献
12.
Stephen J. Covey-Crump 《Contributions to Mineralogy and Petrology》1997,129(2-3):239-254
The normal grain growth behaviour of four different, but all nominally pure, calcite powders (99%+ analytic grade calcite,
99.7% chalk, 99.97% crushed Iceland Spar, 99.95%+ chelometric grade calcite) has been investigated as a function of temperature
(550, 600, 650, 700 °C) and confining pressure (100, 190 MPa) under both “dry” and hydrostatic (P
fluid = P
total) conditions. The initial particle size of both the analytic grade and chelometric grade calcite was about 5 μm, and that
of the chalk was about 3 μm, while the experiments on the Iceland Spar were conducted on powders of three different initial
particle sizes (3.4, 7.5, 38.5 μm). On each material, at each pressure/temperature condition 6 to 15 experiments, equally
spaced in log time from 15 minutes to 50 days, were conducted. Under dry conditions all four materials recrystallized to aggregates
which contained less than 2% porosity and which had a grain size of between 4 and 20 μm (depending on the initial particle
size). Subsequently the aggregates coarsened by normal grain growth, with the kinetics of the growth process being controlled
by the rate at which the grain boundaries could drag the residual pores with them as they migrated. Under nominally identical
conditions both the mechanism and rates of pore drag differed greatly for the different materials, implying that this process
is highly sensitive to trace solute impurity concentrations. This sensitivity renders the task of providing a systematic account
of dry calcite grain growth kinetics highly problematic. Under hydrostatic conditions all the powders followed the same normal
grain growth kinetics in which the growth process was rate-controlled by diffusion through the pore fluid on the grain boundaries.
An activation enthalpy of 162.6 kJ mol−1 and an activation volume of 34.35 cm3 mol−1 was obtained for this process.
Received: 23 May 1996 / Accepted: 8 July 1997 相似文献
13.
Hydrogeologic and hydrochemical framework of the shallow groundwater system in the southern Voltaian Sedimentary Basin, Ghana 总被引:4,自引:0,他引:4
The southern Voltaian Sedimentary Basin underlies an area of about 5000 km2 in east-central Ghana. Groundwater in the basin occurs in fractures in highly consolidated siliciclastic aquifers overlain
by a thin unsaturated zone. Aquifer parameters were evaluated from available aquifer-test data on 28 shallow wells in the
basin. Hydraulic-conductivity values range from 0.04–3.6 m/d and are about two orders of magnitude greater than the hydraulic
conductivity calculated using Darcy's Law and the average groundwater velocity estimated from carbon-14 dating. Linear-regression
analysis of the transmissivity and specific-capacity data allowed the establishment of an empirical relationship between log
transmissivity and log specific capacity for the underlying aquifers.
Groundwater chemistry in the basin is controlled by the weathering of albitic plagioclase feldspar. The weathering rates of
various minerals were estimated using 14C-derived average velocity in the basin. The weathering rate of albite was calculated to be 2.16 μmol L–1 yr–1 with the resulting formation of 3.3 μmol L–1 yr–1 of kaolinite and 0.047 μmol L–1 yr–1 of calcite. The low porosity and permeability of the aquifers in the basin are attributed to the precipitation of secondary
minerals on fracture surfaces and interlayer pore spaces.
Received, September 1997 Revised, July 1998, August 1998 Accepted, August 1998 相似文献
14.
A comparison of geochemical information obtained from two fluvial bed sediment fractions 总被引:3,自引:1,他引:3
Ross. A. Sutherland 《Environmental Geology》2000,39(3-4):330-341
A total of 121 bed sediment samples were collected from a 5.8-km stretch of Manoa Stream, Hawaii. Samples were physically
partitioned into two grain-size fractions, <63 μm and 63–125 μm, acid digested and analyzed by ICP-AES and FAAS. Non-parametric
matched-pair statistical testing and correlation analysis were used to assess differences and strengths of association between
the two fractions for Al, Ba, Cu, Fe, Mn, Ni, Pb, Ti and Zn. Results indicated statistically significant differences between
fractions for all elements except Mn. Concentrations were significantly greater in the <63 μm fraction for Al, Cu, Pb, Ti
and Zn, while Ba, Fe and Ni were higher in the 63–125 μm fraction. Though some elements had statistically significant differences
between fractions (Al, Ba, Fe and Zn) percentage differences were in the range of analytical precision of the instrument and
thus differences were not practically significant. Correlation analysis indicated strong positive associations for all elements
between the two fractions (p<0.0001). Three contamination indices indicated similar degrees of pollution for each size fraction
for four elements having an anthropogenic signal (Ba, Cu, Pb and Zn). The environmental information obtained from the 63–125 μm
fraction was essentially equivalent to that from the <63 μm fraction. In this system it is clear that both bed sediment fractions
indicate anthropogenic enrichment of trace metals, especially Pb, and further supports previous research that has found that
aquatic sediments are critical median for tracing sources of pollution.
Received: 17 August 1998 · Accepted: 30 October 1998 相似文献
15.
In the Hudson River estuary, fine mud and toxic metals are enriched in the upstream turbidity maximum. The mechanisms causing
the enrichment were assessed through the analysis of suspended-sediment concentration (SSC) (bottom and surface), particle
size, and trace metal distributions. Bottom SSCs varied across the study area by a factor of ten, and the turbidity maximum
activity was observed in between kilometers 45 and 80. The particle-size analysis defined two accumulation modes: <4.65 and
>22.1 μm. The ratio of the fine-to-coarse mode increased from 1.75 to 2.75 in the turbidity maximum. The fine mud concentration
(55–60%) in the turbidity maximum was found to have a high correlation (r=0.98;p<0.005) with the concentration of <2-μm particles. A conceptual model was derived in order to understand the possible mechanisms
by which fine mud (and specifically <2-μm particles) is concentrated. The two dominant size modes were analyzed for toxic
metals. The upstream tributaries are major sources of metals compared to point sources at downstream locations. In the turbidity
maximum, Cd, Cu, Zn, and Pb are significantly enriched compared to average shale metal values and ERM toxicity guidelines
by 580, 42, 10, 16 and 12, 7, 2.4, 1.4 times, respectively. Decreasing metal concentrations downstream of the turbidity maximum
imply that Haverstraw Bay acts as temporary storage for fine particles and enriched metals. It is demonstrated in this study
that toxic metals are enriched in Haverstraw Bay due to the mud accumulation. The high levels of toxic metals in the sediments
of the Hudson River estuary are a major concern because human activities (dredging and river traffic) cause resuspension of
sediments and can change the mobility patterns of bioavailable contaminants.
Received: 4 June 1997 · Accepted: 9 September 1997 相似文献
16.
Seepage from a tailings dam is the major source of groundwater pollution in the Selebi-Phikwe area, where mining of sulphidic
nickel–copper–cobalt ore started in 1973 and will continue until 2014. The seepage water has a pH in the range of 1.7–2.8
and is strongly enriched in SO4
2− (5,680 g/L) and heavy metals (6,230 μg/L Ni, 1,860 μg/L Cu and 410 μg/L Co). The fracture aquifer affected by pollution from
the dam exhibits a remarkable capacity of heavy-metal sorption. Most of the Ni, Cu and Co is scavenged at less than 500 m
distance downgradient from the polluting source, whereas SO4
2− is not immobilized significantly. The heavy-metal sorption process is assumed to be due to surface complexation, which is
supported by a relatively high groundwater pH (in the range of 6.2–7.8 at >200 m distance from the tailings dam). The objective
of this study is to demonstrate that the sorption process can be incorporated into a realistic three-dimensional reactive-transport
groundwater model that is implicitly charge-balanced. The simulations are performed with the PHAST1.2 program, which is based
on the HST3D flow and transport code and the hydrochemical PHREEQC2.12 code. 相似文献
17.
Possible types of anion-cation packing of mineral surface were evaluated. Their role was estimated for the decoration of minerals
with gold under vacuum (process simulating crystallization on a surface), mineral growth and intergrowth, adsorption, surface
diffusion, and other surface processes. It was shown that there are two distinct types (I and II) of mineral surfaces differing
in the character of crystallization of gold nanoparticles during decoration. Type I includes surfaces showing predominant
formation of gold nanoparticles (5–15 nm) on growth (dissolution, evaporation) steps, dislocations, and point defects. These
surfaces are represented by packed layers of O−2 anions, alternating anions and cations, and identical atoms. Type II includes surfaces with the statistical distribution
(109–12 cm−2) of gold nanoparticles (5–30 nm). Such patterns are characteristic of surfaces with packing of OH− groups, OH− in combination with O−2, and with the statistical distribution of anions and cations. Type I surfaces show low adsorption capacity and a large extent
of diffusion on them (∼103–4 nm). In contrast, type II surfaces have high adsorption capacity and low (∼50 nm) surface diffusion. Minerals dominated by
type I surfaces grow by the layer and spiral mechanisms, and those dominated by type II surfaces grow by the normal mechanism.
Original Russian Text ? N.D. Samotoin, L.O. Magazina, 2006, published in Geokhimiya, 2006, No. 10, pp. 1068–1084. 相似文献
18.
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
19.
Mobility and retention of trace elements in hardpan-cemented cassiterite tailings, north Queensland, Australia 总被引:1,自引:0,他引:1
This study reports on the mobility and retention of trace elements in cassiterite tailings at the inactive Jumna mill, tropical north Queensland. Since the 1980s, the uncapped tailings have developed laterally discontinuous Fe-rich hardpans, which are located in the higher parts of gently sloping tailings masses and at the top (<50 cm) of the tailings piles. Hardpan-cemented tailings comprise thin layers (typically ∼0.2–2 mm thick) of HFO (hydrous ferric oxides) and sulfate efflorescences cementing tailings grains. In comparison to the tailings, the hardpan-cemented tailings contain significantly higher median As, Ca, Cd, Co, Cu, Fe, In, Mn, Mo, Stotal, Th, U, Y and Zn values. Partial leaching studies of tailings and pond water analyses indicate that wetting and acidification of Fe-cemented tailings removes significant proportions of trace elements into pore and surface waters. Tin shows no mobility due to the presence of weathering-resistant cassiterite (SnO2) and, As and Pb display limited mobility possibly due to their coprecipitation with jarosite-type phases and HFO materials at the top of the tailings profile. By contrast, the trace elements Cd, Ce, Cu, La, Ni, Pb, U and Zn display the greatest mobility, possibly due to their incorporation in soluble sulfate efflorescences and sorption onto mineral and HFO surfaces. Hence, the Fe-rich hardpans do not protect the sulfidic tailings from further oxidation nor do they cause permanent sequestration of trace elements. 相似文献
20.
Heavy rainfalls, between 25 and 100 mm·h–1, were simulated on Pliocene/Quaternary sediments. To reproduce the heterogeneity
of natural environments, 231 small plots of various sizes (between 2.5 and 3.5 m2; mean: about 3 m2) were used. The duration of all simulations was 1 h. We used water that had been collected during natural rainfall. The concentration
of clay particles in the sheet wash depended upon the concentration of dissolved sodium in the wash (for about 42%) and of
the sheet wash quantity (for about 37%). Under natural water conditions colloidal matter, like clay minerals, is charged negatively
and therefore is destabilized by metal cations such as in the case of Na+. Results suggest that relatively higher concentrations of montmorrillonite were related to higher concentrations of sodium
as opposed to illite and kaolinite. Microflakes of up to 25 μ were observed to vary between face-to-edge and face-to-face
modes (competition between protons and other cations). The concentration of dissolved sodium (Na+) in the runoff water depends on water and sodium balances such as atmospheric input, infiltration, evaporation and surface
water runoff. The reduction of vegetation cover increases the amount of salt and amorphous matter in/on the topsoil between
heavy rainfall generations. The best predictor to explain montmorillonite, illite and kaolinite in % of mineral clay-sized
matter in the surface water runoff (sheet wash) is the percentage of each clay mineral in the topsoil. As opposed to illite
and kaolinite, more sheet wash indicate for montmorillonite relatively higher concentrations in the wash. The results of model
simulations were confirmed on different field plots of about 1 ha and small catchments during natural heavy rainfall events.
Models can also be used to understand and to better simulate sheet, rill and gully erosion, micropedimentation; and pedimentation. 相似文献