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1.
Fluid inclusion studies were made on the basis of the geological data on the strata-bound ore de-posits of China including those of Pb,Zn,Au,Ag,Sb,U,Hg,W,quartz-crystal and sparry-calcite.An attempt was made to approach the model of formation for each type of ore depos-its by considering the material sources,the migration of fluids and the conditions of mineralization.It is found that ore-forming fluids (especially H2O)originate as heated underground water reacts with the wallrocks and dissolves Na^ ,Ca^2 ,K^ ,Cl^ ,HCl^- and Mg^2 .The ore fluids are mainly of NaCl-Ca-HCO3-H2O system with salinities ranging from 4to 14wt.%.NaCl equivalent and densities ranging from 0.9 to 1.0g/cm^3.It may be concluded that the deposits were formed at temperatures ranging from 150 to 250℃ under pressures from 300 to 1000 bars.Ore deposition may have been controlled by temperature and pressure or by the mixing among different fluids. 相似文献
2.
Thermodynamic study of the association and separation of copper and gold in the Shizishan ore field, Tongling, Anhui Province, China 总被引:1,自引:0,他引:1
Xiao-chun Xu Zan-zan Zhang Qi-neng Liu Jing-wei Lou Qiao-qin Xie Ping-li Chu Ray L. Frost 《Ore Geology Reviews》2011,43(1):347-358
The Shizishan ore field is the largest gold–copper ore field in the Tongling ore district of Anhui Province, China. Copper and gold deposits in the district are present as one-commodity deposits or as deposits with both commodities. Copper and gold mineralization are either cogenetic or are temporally and spatially distinct. We present the results of systematic geochemical analysis of fluid inclusions from typical Au–Cu deposits in the Shizishan ore field; these data are used to determine the solubility of Cu and Au in the ore-forming fluids and to ascertain the mechanisms and factors that controlled variations in the association and separation of copper and gold mineralization. Our results indicate that copper in the ore-forming fluids was transported as CuCl2− and CuCl0 complexes and that the solubility of copper was controlled by variations in Cl− concentration. In addition, the precipitation of copper was controlled by changes in temperature, pH, fO2, and fO2. In comparison, gold in the ore-forming fluids was transported as Au(HS)2− and Au2S(HS)22− complexes, and the solubility of gold was controlled by variations in total sulfur concentration; the precipitation of gold was controlled by temperature, pH, fO2, and fO2. These differences between the two elements meant that copper and gold in the ore-forming fluids responded in different ways to changes in physicochemical conditions. Copper precipitated under relatively acidic conditions at high temperatures, while gold precipitated under weakly alkaline conditions at relatively low temperatures; this dissociation resulted in the temporal and spatial separation and zonation of copper and gold mineralization in the Shizishan ore field. 相似文献
3.
The formation of large accumulations of Au and Sn and independent metallogenic provinces, zones, and clusters is based on
both the heterogeneous structure of the Earth’s crust and the upper mantle, which results in the diversity of the sources
of magmas and ore-forming elements, and the differences in the geochemical properties of these elements. During the transport
of Au and Sn by fluid-magma columns, the mobility of the metals is affected and polarized by their different affinity to the
silicate-forming clusters of melt, oxygen, and other strong oxidizers. This influence promoted the divergence of the migration
paths of these elements to ore concentration levels. By the moment of the release of the ore-forming fluids, the metallogenic
characteristics of the melts with contrasting redox potentials were usually already established, which is supported by the
preferential association of the tin and gold mineralization with ilmenite-and magnetiteseries granitoids, respectively. Combined
concentrations of the metals could potentially be produced by fluid-magma systems with transitional degrees of the melt oxidation.
However, even in such cases, the simultaneous concentration of tin and gold was hampered by the opposing redox reactions of
the formation of the most common minerals of these metals: the main tin migration species — Sn2+— had to be oxidized with the formation of cassiterite, whereas the mobile gold species — Au+ or Au3+ — had to be reduced with the formation of native gold. Perhaps, this is why the combined concentrations of tin and gold are
characterized by the dominance of one of the metals with a tendency for their accumulation in mineral complexes of different
stages. The redox state of the melts controlling the migration activity of the metals depended on the duration of the movement
of the fluid-magma columns toward the levels of ore concentrations. This parameter is a function of the depths of their generation
and their movement velocity, which were controlled by the geodynamic conditions. 相似文献
4.
The Song Hien Rift basin is considered as one of the important regions for gold deposits in North East Vietnam. Host rocks of a number gold deposits in the Song Hien Rift basin are mainly in Lower Triassic sedimentary formations. However, there is the Hat Han gold deposit hosted in fined-grained mafic magmatic rocks with similar characteristics as gold deposit hosted in the Triassic sediments. Sulphur isotopic compositions of sulphide are similar to those in carbonaceous shale, suggesting that the sulphur was ‘borrowed’ from sedimentary rocks in filling the rift basin. Gold-bearing sulphides (pyrite and arsenopyrite) are the main form of Au presence in the ore. Gold in pyrite is present as Au+ 1, and a minor amount of as nanoparticles of native Au (Au0); whereas in arsenopyrite, gold is chemically bound as the octahedral complex AuAs2. Analysis of geology, as well as geochemical and isotopic studies show that the genesis of the Hat Han gold deposit is not related to the Cao Bang mafic magmatism; instead the latter only serves as (ore) host rock. The geochemical results presented above suggest that the gabbro host rock only supplies iron needed for sulphide formation. With regard to ore genesis, the Hat Han gold deposit in the Song Hien rift basin was generated in the similar way as sediment-hosted gold deposit. There are many similar typomorphic features between the Hat Han deposit and Carlin-like deposits in the Nanpanjang sedimentary basin in China. 相似文献
5.
The Tuwaishan, Baoban, Erjia, Bumo and other gold deposits in western Hainan occur in Precambrian metamorphic clastic rocks
and are structurally controlled by the Gezhen shear zone. Fluid inclusion studies have been carried out of the gold deposits
mentioned above. The homogenization temperatures of the whole fluid inclusion population range from 140°C to 370°C, indicating
that gold was precipitated mainly at 240–250°C. The salinities are within the range of 2.0–9.2 wt% NaCl equiv. and the pressure
of formation of the deposits was estimated at about 270×105−500×105Pa, corresponding to a depth of about 1.1–2.0 km under lithostatic confinement. Chemical studies show that the ore fluid is
of the Na+(K+)-Ca2+-Cl−(F−) type. Theδ
18O andδD values of the fluid vary from −2.7‰- +4.4‰ and −50‰–−87‰ Evidence developed from fluid inclusions and geological setting
indicates that the ore fluid was a mixture of magmatic and meteoric-hydrothermal waters. Changes in chemical composition andδ
18O andδD of fluid inclusions from one ore field to another seem to be related with regional tectonism, metamorphism and magmatism. 相似文献
6.
J. P. Richards C. J. Bray D. M. DeR. Channer E. T. C. Spooner 《Mineralium Deposita》1997,32(2):119-132
The Porgera gold deposit in Papua New Guinea is a world-class example of an alkalic-type epithermal gold system (stage II),
which overprints a precursor stage of magmatic-hydrothermal gold mineralization (stage I). Gas and ion chromatographic analyses
of fluid inclusions contained in vein minerals from both mineralization stages have been carried out in order to constrain
the compositions of the fluids involved in, and the processes attending, ore deposition. These data indicate the presence
of three end-member liquids, the most dilute of which was present throughout the mineralization history and is interpreted
to represent evolved groundwater of meteoric origin. Its composition is estimated to have been approximately 500 mM Na+, 10 mM K+, 5 mM Li+, 250 mM Cl−, 0.15 mM Br−, and 0.01 mM I−, plus significant concentrations of dissolved gases. More saline liquids were also present during the two main stages of
ore formation, and although their compositions differ, both are interpreted to have been derived at least in part from magmatic
fluids, and to have been the media by which gold was introduced into the system. Stage I minerals contain fluid inclusions
which decrease in salinity towards this dilute end-member composition through the vein paragenesis, reflecting progressive
dilution at depth of the magmatic fluid source by groundwaters. Ore deposition is thought to have been caused largely by simple
cooling and/or wallrock reactions, although limited in situ fluid mixing may also have occurred. The most saline fluids, present
in early quartz and pyrite, contain at least 810 mM Na+, 530 mM Ca2+, 130 mM K+, 12 mM Li+, 87 mM SO4
2−, 960 mM Cl−, 1.1 mM Br−, and 0.05 mM I−, plus significant but variable concentrations of dissolved gases. Fluid inclusions from stage II hydraulic breccia veins
reveal the presence of two distinct liquids with contrasting salinities, which were present at different times during vein
formation. A higher salinity liquid appears to have predominated during mineralization, whereas lower salinity groundwaters
filled the structures during intervening periods. The ore-forming fluid may have been forcibly injected into the veins from
depth during fracturing and depressurization events, displacing the resident groundwaters in the process. The original composition
of this fluid is estimated to have been at least 1770 mM Na+, 59 mM K+, 180 mM Li+, 210 mM SO4
2−, 680 mM Cl−, 1.4 mM Br−, and 0.09 mM I−, plus 1.5 mol% CO2, 0.19 mol% CH4, and 0.04 mol% N2. Gas chromatographic analyses of fluid inclusions from stage II samples show a decrease in total gas content between early
unmineralized veins and post-mineralization vuggy quartz (suitable samples could not be obtained from the ore stage itself).
Post-mineralization samples plot along an experimental gas-saturation curve in the CO2-CH4-H2O-NaCl system, obtained at conditions similar to those attending stage II ore deposition at Porgera (200–300 bar, ˜165 °C).
These results are interpreted to indicate a period of depressurization-induced phase separation during hydraulic fracturing,
which resulted in rich ore deposition. Volatile gases such as CH4 and N2, in addition to CO2 in solution, are shown to have a significant negative effect on total gas solubility. This effect may be of critical importance
in lowering the temperature and increasing the depth (pressure) at which phase separation can occur in epithermal systems.
Received: 28 November 1995 / Accepted: 17 July 1996 相似文献
7.
Gold deposits of Uzbekistan are localized in the Kyzylkum, Nurata, and Kurama ore districts of the Kyzylkum-Kurama metallogenic
belt. They comprise a consecutive series of deposit types corresponding to the series of geochemical associations: (Au-W)—(Au-As)—(Au-Te)—(Au-Ag)—(Au-Sb)—(Au-Hg),
which are arranged as a system of zones in orebodies, deposits, ore fields, and ore districts. The distribution of chemical
elements characterized by average global concentrations in the crust within the ppm-ppb (10−6-10−9 t) range was studied in ores of gold deposits using an ICP MS Elan DRC II device. Mineral nanoassemblages with a grain size
of 10−6 to 10−9 m were examined with a Jeol YXA 8800R Superprobe. The Au-W, Au-As, and Au-Te associations with Bi tellurides and maldonite
in ore dominate at hypo- and meso-abyssal gold deposits of the Kyzylkum district (Muruntau, Myutenbay). The contribution of
the Au-Sb association with Pb, Ag, and Fe sulfoantimonites and aurostibite increases at the Daughyztau, Kokpatas, and Amantaitau
gold deposits. The Au-As, Au-Te, and Au-Sb associations with Bi tellurides, maldonite, sulfoantimonites, and aurostibite dominate
at the mesoabyssal gold deposits of the Nurata district (Charmitan, Guzhumsay). The Au-Te and Au-Ag associations with Au,
Ag, Pb, Sb, Bi, and Hg tellurides and Bi selenides dominate at the hypabyssal gold deposits of the Kurama district (Kochbulak,
Kayragach). The gold-silver deposits of the Kyzylkum district (Kosmanachi, Vysokovol’tnoe) and the Kurama district (Kyzylalmasay,
Arabulak) are close in composition. They are characterized by development of intermetallides, sulfides, sulfosalts, and selenides
of Au-Ag and occasionally Au-Sb associations. Fineness of gold decreases from early to late geochemical associations, whereas
the size of gold grains increases in the same direction from nanogold to visible gold. The studies at the micro- and nanolevel
make it possible to establish the attributes of specific gold mineralization, to substantiate prospecting guides, and to estimate
the erosion level and resource potential of hidden ore objects. The greater and more diverse a set of micro- and nanominerals,
the larger a gold deposit is. 相似文献
8.
T. Oberthür T. G. Blenkinsop U. F. Hein M. Höppner A. Höhndorf T. W. Weiser 《Mineralium Deposita》2000,35(2-3):138-156
In the Mazowe area some 40 km NW of Harare in Zimbabwe, gold mineralization is hosted in a variety of lithologies of the
Archean Harare-Bindura-Shamva greenstone belt, in structures related to the late Archean regional D2/3 event. Conspicuous
mineralzogical differences exist between the mines; the mainly granodiorite-hosted workings at Mazowe mine are on pyrite-rich
reefs, mines of the Bernheim group have metabasalt host rocks and are characterized by arsenopyrite-rich ores, and Stori's
Golden Shaft and Alice mine, both in metabasalts, work sulfide-poor quartz veins. In contrast to the mineralogical diversity,
near-identical fluid inventories were found at the different mines. Both H2O-CO2-CH4 fluids of low salinity, and highly saline fluids are present and are regarded to indicate fluid mixing during the formation
of the deposits. Notably, these fluid compositions in the Mazowe gold field markedly contrast to ore fluids “typical” of Archean
mesothermal gold deposits on other cratons. Stable isotope compositions of quartz from the various deposits (δ18O=10.8 to 13.2‰ SMOW), calcite (δ18O=9.5 to 11.9‰ SMOW and δ13C=−3.2 to −8.0‰ PDB), inclusion water (δD=−28 to −40‰ SMOW) and sulfides (δ34S=1.3 to 3.2‰ CDT) are uniform within the range typical for Archean lode gold deposits worldwide. The fluid and stable isotope
compositions support the statement that the mineralization in the Mazowe gold field formed from relatively reduced fluids
with a “metamorphic” signature during a single event of gold mineralization. Microthermometric data further indicate that
the deposits formed in the PT range of 1.65–2.3 kbar and 250–380 °C. Ages obtained by using the Sm/Nd and Rb/Sr isotope systems on scheelites are 2604 ± 84 Ma
for the mineralization at Stori's Golden Shaft mine, and 2.40 ± 0.20 Ga for Mazowe mine. The Archean age at Stori's is regarded
as close to the true age of gold mineralization in the area, whereas the Proterozoic age at Mazowe mine probably reflects
later resetting.
Received: 30 September 1998 / Accepted: 17 August 1999 相似文献
9.
Geology and geochemistry of telluride-bearing Au deposits in the Pingyi area, Western Shandong, China 总被引:2,自引:0,他引:2
Summary Telluride-bearing gold deposits of the Pingyi area, western Shandong, China, are located on the southeastern margin of the
North China Craton. There are two main types of deposits: (i) mineralized cryptoexplosive breccia, e.g., Guilaizhuang; and
(ii) stratified, finely-disseminated mineralization hosted in carbonate rocks, e.g., Lifanggou and Mofanggou deposits. In
Guilaizhuang, the cryptoexplosive breccia is formed within rocks of the Tongshi complex and Ordovician dolomite. The mineralization
is controlled by an E–W-trending listric fault. Stratified orebodies of the Lifanggou and Mofanggou deposits are placed along
a NE-trending, secondary detachment zone. They are hosted within dolomitic limestone, micrite and dolomite of the Early-Middle
Cambrian Changqing Group. The mineralization in the ore districts is considered to be related to the Early Jurassic Tongshi
magmatic complex that formed in a continental arc setting on the margin of the North China Craton. The host rocks are porphyritic
and consist predominantly of medium- to fine-grained diorite and pyroxene (hornblende)-bearing monzonite. SHRIMP U–Pb zircon
dating of diorites give a 206Pb/238U weighted mean age of 175.7 ± 3.8 Ma. This is interpreted as representing the crystallization age of the Tongshi magmatic
complex. Considering the contact relationships between the magmatic and host sedimentary rocks, as well as the genetic link
with the deposits, we conclude that this age is relevant also for the formation of mineralization in the Pingyi area. We hence
consider that the deposits formed in the Jurassic. The principal gold minerals are native gold, electrum and calaverite. Wall-rock
alteration comprises pyritization, fluoritization, silicification, carbonatization and chloritization. Fluid inclusion studies
indicate that all the analyzed inclusions are of two-phase vapor–liquid NaCl–H2O type. Homogenization temperatures of the fluid inclusions vary from 103 °C to 250 °C, and the ice melting temperatures range
from −2.5 °C to −13.5 °C, corresponding to a salinity range of 4.65 to 17.26 wt.% NaCl equiv. The δ34S values of pyrite associated with gold mineralization exhibit a narrow range of −0.71 to + 2.99‰, implying that the sulfur
was probably derived from the mantle and/or dioritic magma. The δ13CPDB values of the fluid inclusions in calcite range from −7.3 to 0.0‰. The δ18OSMOW values of vein quartz and calcite range from 11.5 to 21.5‰, corresponding to δ18Ofluid values of −1.1 to 10.9‰; δD values of the fluid inclusions vary between −70 and −48‰. The isotope data for all three deposits
suggest mixing of ore-forming fluids derived from the mantle and/or magma with different types of fluids at shallow levels.
Pressure release and boiling of the fluids, as well as fluid-rock interaction (Lifanggou and Mofanggou) and mixing of magmatically-derived
fluids with meteoritic waters (Guilaizhuang) played an important role in the ore-forming processes. 相似文献
10.
THEJINLONGSHANGOLDOREBELTINZHEN’ANCOUN TY,SOUTHERNSHAANXIPROVINCE,ISLOCATEDINTHEWEST ERNQINLINGGOLDPROVINCE(NO.16INFIG.1;CHEN YANJINGETAL.,2004).ITWASDISCOVEREDINTHEDEVO NIANSTRATAINTHELATE1980S).ITSGEOLOGICALSETTING ANDMETALLOGENICEVOLUTIONARESIMILARTOT… 相似文献
11.
M. Gebre-Mariam D. I. Groves N. J. McNaughton E. J. Mikucki J. R. Vearncombe 《Mineralium Deposita》1993,28(6):375-387
The Racetrack Au−Ag deposit, in the Archaean Yilgarn Block, Western Australia, is hosted by a porphyritic basalt in a low
greenschist facies setting and is associated with a brittle strike-slip fault system. Three distinct and successive stages
of hydrothermal activity and late quartz-carbonate veining resulted in multiple veining and/or brecciation: Stages I and II
are Au-bearing, whereas Stage III and late veins are barren. The ore shows features of both classic epithermal and mesothermal
deposits. Alteration assemblages, typified by sericitization, carbonization, silicification and chloritization, are similar
to those of mesothermal gold deposits, wheras the quartz vein-textures including comb, rosette, plumose and banded, ore mineralogyof
arsenopyrite, pyrite, chalcopyrite, sphalerite, galena, freibergite, tetrahedrite, tennantite, fahlore, electrum and gold,
and metal associations (Cu, As, Ag, Sn, Sb, W, Au and Pb) are more characteristics of epithermal deposits. Fluid inclusions
related to Stage II are two phase and aqueous with 1–8 (average 4) wt. % NaCl equiv. and CO2 content of <0.85 molal. Pressure-corrected homogenisation temperatures range from 190°C to 260°C. Mineral assemblages indicate
that ore fluid pH ranged between 4.2 and 5.3, fO
2 between 10−38.8 and 10−39.6 bars, and mΣs between 10−3.2 and 10−3.6. Calculated chemical and stable isotope compositions require a component of surface water in the ore fluid depositing the
mineralisation, but evidence for deep crustal Pb indicates that deeply sourced fluids were also involved. The deposit is interpreted
to have formed in a shallow environment via mixing of deeply sourced fluids, from at least as deep as the base of the greenstone
belt, with surface waters. It therefore represents the upper crustal end-member of the crustal depth spectrum of Archaean
lode-gold mineralisation. 相似文献
12.
The Janggun iron deposits, Republic of␣Korea, occur as lens-shaped magnesian skarn, magnetite and base-metal sulfide orebodies
developed in the Cambrian Janggun Limestone Formation. Mineralization stage of the deposits can be divided into two separate
events. The skarn stage (107 Ma) consists of magnetite, pyrrhotite, base-metal sulfides, carbonates and magnesian skarn minerals.
The hydrothermal stage (70 Ma) consists of base-metal sulfides, native bismuth, bismuthinite, tetrahedrite, boulangerite,
bournonite and stannite. Mineral assemblages, chemical compositions and thermodynamic considerations indicate that formation
temperatures, −log fs2 and −log fo2 values of ore fluids from the skarn stage were 433 to 345 °C, 8.1 to 9.7 bar and 29.4 to 31.6 bar, and the hydrothermal stage
was 245 to 315 °C, 10.4 to 13.2 bar and 33.6 to 35.4 bar, respectively. Thermochemical considerations indicate that the XCO2 during magnesian skarnization ranged from 0.06 to 0.09, and the activity of H+ presumably decreased when the fluids equilibrated with host dolomitic limestone which resulted in a pH change from about
6.1 to 7.8, and decreases in fo2 and fs2. The δ34S values of ore sulfides have a wide range from 3.2 to 11.6 ‰ (CDT). Calculated 34SH2
S values of ore fluids are 2.9 to 5.4 ‰ (skarn stage) and 8.7 to 13.5 ‰ (hydrothermal stage). These are interpreted to represent
an initial deep-seated, igneous source of sulfur which gave way to influence of oxidized sedimentary sulfur to hydrothermal
stage. The δ13C values of carbonates in ores range from −4.6 to −2.5 ‰ (PDB). It is likely that carbon in the ore fluids was a mixture of
deep-seated magmatic carbon and dissolved carbon of dolomitic limestone. The δ18OH2
O and δD values (SMOW) of water in the ore fluids were 14.7 to 1.8 and −85 to −73 ‰ during the skarn stage and 11.1 to −0.2
and −87 to −80 ‰ in the hydrothermal stage.
Received: 5 March 1997 / Accepted: 28 August 1997 相似文献
13.
Gold ore-forming fluids of the Tanami region, Northern Australia 总被引:1,自引:0,他引:1
Fluid inclusion studies have been carried out on major gold deposits and prospects in the Tanami region to determine the compositions
of the associated fluids and the processes responsible for gold mineralization. Pre-ore, milky quartz veins contain only two-phase
aqueous inclusions with salinities ≤19 wt% NaCl eq. and homogenization temperatures that range from 110 to 410°C. In contrast,
the ore-bearing veins typically contain low to moderate salinity (<14 wt% NaCl eq.), H2O + CO2 ± CH4 ± N2-bearing fluids. The CO2-bearing inclusions coexist with two-phase aqueous inclusions that exhibit a wider range of salinities (≤21 wt% NaCl eq.).
Post-ore quartz and carbonate veins contain mainly two-phase aqueous inclusions, with a last generation of aqueous inclusions
being very CaCl2-rich. Salinities range from 7 to 33 wt% NaCl eq. and homogenization temperatures vary from 62 to 312°C. Gold deposits in
the Tanami region are hosted by carbonaceous or iron-rich sedimentary rocks and/or mafic rocks. They formed over a range of
depths at temperatures from 200 to 430°C. The Groundrush deposit formed at the greatest temperatures and depths (260–430°C
and ≤11 km), whereas deposits in the Tanami goldfield formed at the lowest temperatures (≥200°C) and at the shallowest depths
(1.5–5.6 km). There is also evidence in the Tanami goldfield for late-stage isothermal mixing with higher salinity (≤21 wt%
NaCl eq.) fluids at temperatures between 100 and 200°C. Other deposits (e.g., The Granites, Callie, and Coyote) formed at
intermediate depths and at temperatures ranging from 240 to 360°C. All ore fluids contained CO2 ± N2 ± CH4, with the more deeply formed deposits being enriched in CH4 and higher level deposits being enriched in CO2. Fluids from deposits hosted mainly by sedimentary rocks generally contained appreciable quantities of N2. The one exception is the Tanami goldfield, where the quartz veins were dominated by aqueous inclusions with rare CO2-bearing inclusions. Calculated δ
18O values for the ore fluids range from 3.8 to 8.5‰ and the corresponding δD values range from −89 to −37‰. Measured δ
13C values from CO2 extracted from fluid inclusions ranged from −5.1 to −8.4‰. These data indicate a magmatic or mixed magmatic/metamorphic source
for the ore fluids in the Tanami region. Interpretation of the fluid inclusion, alteration, and structural data suggests that
mineralization may have occurred via a number of processes. Gold occurs in veins associated with brittle fracturing and other
dilational structures, but in the larger deposits, there is also an association with iron-rich rocks or carbonaceous sediments,
suggesting that both structural and chemical controls are important. The major mineralization process appears to be boiling/effervescence
of a gas-rich fluid, which leads to partitioning of H2S into the vapor phase resulting in gold precipitation. However, some deposits also show evidence of desulfidation by fluid–rock
interaction and/or reduction of the ore-fluid by fluid mixing. These latter processes are generally more prevalent in the
higher crustal-level deposits. 相似文献
14.
Two kinds of mylonite series rocks, felsic and mafic, have been recognized in the NW-striking shear zone of the Jiapigou gold
belt. During ductile deformation, a large amount of fluid interacted intensively with the mylonite series rocks: plagioclases
were sericitized and theAn values declined rapidly, finally all of them were transformed to albites; dark minerals were gradually replaced by chlorites
(mostly ripidolite). Meanwhile, large-scale and extensive carbonation also took place, and the carbonatization minerals varied
from calcite to dolomite and ankerite with the development of deformation. The δ13C values of the carbonates are −3.0‰ – −5.6‰ suggesting a deep source of carbon. The ductile deformation is nearly an iso-volume
one (f
v≈1). With the enhancement of shear deformation, SiO2 in the two mylonite series rocks was depleted, while volatile components suchs as CO2 and H2O, and some ore-forming elements such as Au and S were obviously enriched. But it is noted that the enrichment of Au in both
the mylonite series rocks did not reach the paygrade of gold. The released SiO2 from water-rock interactions occurred in the form of colloids and absorbed gold in the fluid. When brittle structures were
formed locally in the ductile shear zone, the ore-forming fluids migrated to the structures along microfractures, and preciptated
auriferous quartz because of reduction of pressure and temperature. Fluid inclusion study shows that the temperature and pressure
of the ore-forming fluids are 245–292°C and 95.4–131.7 MPa respectively; the salinity is 12.88–16.33wt% NaCl; the fluid-phase
is rich in Ca2+, K+, Na+, Mg2+, F− and Cl−, while the gaseous phases are rich in CO2 and CH4. The δD and δ18O, values of the ore-forming fluid are −84.48‰ – −91.73‰ and −0.247‰ – +2.715‰ respectively, suggesting that the fluid is
composed predominantly of meteoric water.
This project is financially supported by the National Natural Science Foundation of China (No. 9488010). 相似文献
15.
Wenchao Su Hongtao Zhang Ruizhong Hu Xi Ge Bin Xia Yanyan Chen Chen Zhu 《Mineralium Deposita》2012,47(6):653-662
Arsenian pyrite in the Shuiyindong Carlin-type gold deposit in Guizhou, China, is the major host for gold with 300 to 4,000 ppm Au and 0.65 to 14.1 wt.% As. Electron miroprobe data show a negative correlation of As and S in arsenian pyrite, which is consistent with the substitution of As for S in the pyrite structure. The relatively homogeneous distribution of gold in arsenian pyrite and a positive correlation of As and Au, with Au/As ratios below the solubility limit of gold in arsenian pyrite, suggest that invisible gold is likely present as Au1+ in a structurally bound Au complex in arsenian pyrite. Geochemical modeling using the laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis of fluid inclusions for the major ore forming stage shows that the dominant Au species were Au(HS)2− (77%) and AuHS(aq)0 (23%). Gold-hydroxyl and Gold-chloride complexes were negligible. The ore fluid was undersaturated with respect to native Au, with a saturation index of −3.8. The predominant As species was H3AsO30 (aq). Pyrite in the Shuiyindong deposit shows chemical zonation with rims richer in As and Au than cores, reflecting the chemical evolution of the ore-bearing fluids. The early ore fluids had relatively high activities of As and Au, to deposit unzoned and zoned arsenian pyrite that host most gold in the deposit. The ore fluids then became depleted in Au and As and formed As-poor pyrite overgrowth rims on gold-bearing arsenian pyrite. Arsenopyrite overgrowth aggregates on arsenian pyrite indicate a late fluid with relatively high activity of As. The lack of evidence of boiling and the low iron content of fluid inclusions in quartz, suggest that iron in arsenian pyrite was most likely derived from dissolution of ferroan minerals in the host rocks, with sulfidation of the dissolved iron by H2S-rich ore fluids being the most important mechanism of gold deposition in the Shuiyindong Carlin-type deposit. 相似文献
16.
Fluid origin and structural enhancement during mineralization of the Jinshan orogenic gold deposit, South China 总被引:3,自引:0,他引:3
The Jinshan orogenic gold deposit is a world-class deposit hosted by a ductile shear zone caused by a transpressional terrane
collision during Neoproterozoic time. Ore bodies at the deposit include laminated quartz veins and disseminated pyrite-bearing
mylonite. Most quartz veins in the shear zone, with and without gold mineralization, were boudinaged during progressive shear
deformation with three generations of boudinage structures produced at different stages of progressive deformation. Observations
of ore-controlling structures at various scales indicate syn-deformational mineralization. Fluid inclusions from pyrite intergrown
with auriferous quartz have 3He/4He ratios of 0.15–0.24 Ra and 40Ar/36Ar ratios 575–3,060. δ18Ofluid values calculated from quartz are 5.5–8.4‰, and δD values of fluid inclusions contained in quartz range between −61‰ and
−75‰. The δ13C values of ankerite range from −5.0‰ to −4.2‰, and ankerite δ18O values from 4.4‰ to 8.0‰. The noble gas and stable isotope data suggest a predominant crustal source of ore fluids with
less than 5% mantle component. Data also show that in situ fluids were generated locally by pervasive pressure solution, and
that widespread dissolution seams acted as pathways of fluid flow, migration, and precipitation. The in situ fluids and fluids
derived from deeper levels of the crust were focused by deformation and deformation structures at various scales through solution-dissolution
creep, crack-seal slip, and cyclic fault-valve mechanisms during progressively localized deformation and gold mineralization. 相似文献
17.
Study on the Physical and Chemical Conditions of Ore Formation of Hetai Ductile Shear Zone—Hosted Gold Deposit and Discovery of Melt Inclusions 总被引:1,自引:0,他引:1
The Hetai ductile shear zone-hosted gold deposit occurs in the deep-seated fault mylonite zone of the Sinian-Silurian metamorphic rock series. In this study there have been discovered melt inclusions, fluid-melt inclusions and organic inclusions in ore-bearing quartz veins of the ore deposit and mylonite for the first time. The homogenization temperatures of the various types of inclusions are 160℃, 180 - 350℃, 530℃ and 870℃ for organic inclusions, liquid inclusions, two-phase immiscible liquid inclusions and melt inclusions, respectively. Ore fluid is categorized as the neutral to basic K+ -Ca2+ -Mg2+ -Na+ - SO2- 4-HCO3-Cl- system. The contents of trace gases follow a descending order of H2O>CO2>CH4>(or < ) H2>CO>C2H2>C2I-I6>O2>N2.The concentrations of K , Ca2 + ,SO2-4,HCO3-,Cl- H2O and C2H2 in fluid inclusions are related to the contents of gold and the Au/Ag ratios in ores from different levels of the gold deposit. This is significant for deep ore prospecting in the region. Daughter minerals in melt inclusions were analyzed using SEM. Quartz, orthoclase, wollastonite and other silicate minerals were identified. They were formed in different mineral assemblages.This analysis further proves the existence of melt inclusions in ore veins. Sedimentary metamorphic rocks could form silicate melts during metamorphic anatexis and dynamic metamorphism, which possess melt-solution characteristics. Ore formation is related to the multi-stage forming process of silicate melt and fluid. 相似文献
18.
Calculations based on the available thermodynamic data of AuCl
2
−
and Au (HS)
2
−
indicate that AuCl
2
−
is responsible for the transport and enrichment of gold during the stage of pre-concentration in the source bed while Au
(HS)
2
−
is the main gold species involved in the formation of gold deposits in response to hydrothermal reworking. Acid chloride
solutions witha
Cl
− > 10° and sulfur-rich solutions with aΣs in excess of 10−2 are held as important criteria for gold enrichment in the source bed and for the formation of gold deposits by subsequent
hydrothermal event, respectively. 相似文献
19.
Derivation of gold by oxidative metamorphism of a deep ductile shear zone: Part 1. Conceptual model 总被引:3,自引:0,他引:3
Quartz-carbonate gold deposits were emplaced in shear zones at or above the brittle-ductile transition. Some of the largest deposits are known to have formed along major, long-lived, transcurrent shears. Shears of this type widened downwards in the ductile regime, as a result of decreasing rock viscosity with depth; some were as wide as 40 km at depths of granulite facies metamorphism. Ductile shears are permeable and, since the permeability is along microfractures, fluid flow was pervasive, providing the opportunity for extensive chemical reaction. Reaction rates were enhanced by shear heating and by deformation-induced stress gradients in minerals, and reductions in grain size. Fluid flow tended to be upwards, because of pressure drop into the brittle portion of the shear. Given the wedge-shaped profile of ductile shears, fluids that had passed through a large volume of lower crust would have been focused at the brittle-ductile transition. Thus, if processes existed to selectively remove elements during fluid movement through the lower crust, these elements would also have been focused at this transition.One of the most constant features of quartz-carbonate lodes is carbonate alteration, which may extend kilometers out from major deposits. The 13C signature of this is consistent with a mantle source for the CO2. Upward-moving CO2 vapour of probable mantle origin has been implicated in the dehydration of amphibolite facies rocks to granulites and the concomitant depletion of large ion lithophile elements (LILE). The best documented cases of modification of the lower crust by CO2 are from major shear zones. CO2 streaming at depth could only have occurred under conditions more oxidizing than that required for graphite stability. These conditions favour solubility of gold by (a) oxidizing Au0 to Au+; (b) by dissolving sulphide from the rocks to complex with Au+. Recent work has shown that some major Archean gold deposits were derived from relatively oxidized fluids.A conceptual model is outlined for the genesis of at least some quartz-carbonate gold deposits. CO2 permeating deep ductile shear zones dehydrated amphibolite facies rocks. A relatively oxidized CO2-H2O fluid was produced, which dissolved sulphide and gold from large volumes of lower crust. Gold was carried upwards in the narrowing shear, to be focused and precipitated at or above the brittle-ductile transition. 相似文献
20.
1IntroductionTheHongshijinggolddepositislocatedinthenorthofLuobupouLakeofRuoqiang ,about 30 0kmsouthwestofHamiCity ,Xinjiang .ItwasdiscoveredbytheSixthGeologicalTeamofXinjiangduringgeo chemicalexploration .TheHongshijinggolddeposit,whichoccursinthegold bearingformationcomposedofMiddleandLateCarboniferousvolcanicandpyroclasticrocks ,isabrittle ductileshearzonetypegolddepositcontrolledbyariftbelt.TheHongshijinggolddepositislocatedinthesouthwestoftheHongshi jing -Maotoushanmineralizationb… 相似文献