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1.
H. Albert Gilg Maria Boni Giuseppina Balassone Cameron R. Allen David Banks Farid Moore 《Mineralium Deposita》2006,41(1):1-16
The Angouran Zn-(Pb–Ag) deposit, Zanjan Province, NW Iran, is located within the central Sanandaj-Sirjan Zone of the Zagros orogenic belt. The deposit has proven and estimated resources of 4.7 Mt of sulfide ore at 27.7% Zn, 2.4% Pb, and 110 g/t Ag, and 14.6 Mt of oxidized carbonate ores at 22% Zn and 4.6% Pb. It is hosted by a metamorphic core complex that is unconformably overlain by a Neogene volcanic and evaporite-bearing marine to continental sedimentary sequence. The sulfide orebody, precursor to the significant nonsulfide ores, is located at the crest of an open anticline at the contact between Neoproterozoic to Cambrian footwall micaschists and hanging wall marbles. 40Ar–39Ar data on muscovite from mineralized and unaltered footwall micaschists suggest a rapid Mid-Miocene exhumation of the metamorphic basement (∼20 Ma) and yield an upper age constraint for mineralization. The fine-grained sulfide ore is massive, replacive, often brecciated, clearly postmetamorphic and dominated by Fe-poor sphalerite, with minor galena, pyrite, anhydrite, quartz, muscovite, dolomite, and rare calcite. Sphalerite contains Na–Ca–Cl brine inclusions (23–25 mass% total dissolved solids) with homogenization temperatures of 180–70°C. Fluid inclusion chemistry (Na–K–Li–Ca–Mg–Cl–Br), ore geochemistry, S, and Pb isotope data suggest that the Angouran sulfide ore formed by the interaction of modified, strongly evaporated Miocene seawater and the lithotypes of an exhumed metamorphic core complex. Minor contributions of metals from Miocene igneous rocks cannot be excluded. Mineralization occurred in a collisional intra-arc setting with high heat flow, probably during the transition from an extensional to a compressional regime. The Angouran deposit may represent a new type of low-temperature carbonate-hosted Zn–Pb ore that is distinct from Mississippi Valley type and sedimentary-exhalative deposits.Editorial handling: B. Lehmann 相似文献
2.
The Otavi Mountain Land is a base metal sulphide ore province in northern Namibia where deposits are hosted by platform carbonates
of the Otavi Group in a foreland fold-and-thrust belt on the northern edge of the Pan-African Damara Belt. Deposits have been
classified as the Berg Aukas- or Tsumeb-types, based on differences in ore association, stratigraphic position and geochemistry
of ores and gangue carbonates. Mineralisation at these deposits is accompanied by carbonate alteration in the form of dolomite
and calcite veins, carbonate recrystallisation, calcitisation and carbonate silicification. Based on cathodoluminescence imaging,
trace and rare earth element (REE), O and C isotope, and fluid inclusion data, a series of carbonate generations, constituting
wall rock alteration around the Tsumeb and Kombat (Tsumeb-type) and Berg Aukas (Berg Aukas-type) deposits, was established.
Similar data obtained on the recently discovered Khusib Springs deposit indicate a strong affinity to Tsumeb-type deposits.
Tsumeb-type deposits are distinguished from Berg Aukas-type deposits by having trace element and REE concentrations that are
significantly higher in the alteration products compared to the carbonate host rocks. Only around Tsumeb-type deposits a relative
enrichment in light REE is noted for the hydrothermal carbonate generations that are cogenetic with the main stage of mineralisation.
Microthermometric results from fluid inclusions in carbonate alteration phases and associated quartz indicate relatively high
salinity (17–23 wt% NaCl equivalent) for the main mineralising and subsequent sulphide remobilisation stages at the deposits
investigated. Estimated mineralisation temperatures are significantly higher for Tsumeb-type deposits (370–405 °C) with early
sulphide remobilisation in Tsumeb at 275 °C, whereas they are lower at Berg Aukas (up to 255 °C). Fluid inclusion leachate
analysis suggests that most of the observed salinity can be ascribed to dissolved, predominantly Ca- and Mg-carbonates and
chlorides with subordinate NaCl. Na-Cl-Br leachate systematics indicate a derivation of the fluid salinity from the interaction
with evaporitic rocks en route. Tsumeb-type mineralisation is interpreted to be derived from fluids expelled during Pan-African
orogeny in the more intensely deformed internal zones of the Damara Belt further south. When the high salinity fluids reached
the carbonate platform after having scavenged high concentrations of base metals, base metal sulphide precipitation occurred
in zones of high porosity, provided by karst features in the carbonate sequence. Results obtained for the Berg Aukas-type
deposits emphasise their derivation from basinal brines, similar to Mississippi Valley-type deposits, and confirm that mineralisation
of the Berg Aukas- and Tsumeb-types are both spatially and temporally distinct.
Received: 5 May 1999 / Accepted: 10 November 1999 相似文献
3.
The Rammelsberg polymetallic massive sulphide deposit was the basis of mining activity for nearly 1000 y before finally closing
in 1988. The deposit is hosted by Middle Devonian pelitic sediments in the Rhenohercynian terrane of the Variscan Orogen.
The deposit consists of two main orebodies that have been intensely deformed. Deformation obscures the original depositional
relationships, but the regional setting as well as the geochemistry and mineralogy of the mineralisation display many characteristics
of the SHMS (sediment-hosted massive sulphide) class of ore deposits. Rammelsberg is briefly compared to the other massive
sulphide deposits in the European Variscan, including Meggen and those deposits in the Iberian Pyrite Belt.
Received: 28 September 1998 / Accepted: 5 January 1999 相似文献
4.
Re-Os isotopes were used to constrain the source of the ore-forming elements of the Tharsis and Rio Tinto mines of the Iberian
Pyrite Belt, and the timing of mineralization. The pyrite from both mines has simila]r Os and Re concentrations, ranging between
0.05–0.7 and 0.6–66 ppb, respectively. 187Re/188Os ratios range from about 14 to 5161. Pyrite-rich ore samples from the massive ore of Tharsis and two samples of stockwork
ore from Rio Tinto yield an isochron with an age of 346 ± 26 Ma, and an initial 187Os/188Os ratio of about 0.69. Five samples from Tharsis yield an age of 353 ± 44 Ma with an initial 187Os/188Os ratio of about 0.37. A sample of massive sulfide ore from Tharsis and one from Rio Tinto lie well above both isochrons
and could represent Re mobilization after mineralization. The pyrite Re-Os ages agree with the paleontological age of 350 Ma
of the black shales in which the ores are disseminated. Our data do not permit us to determine whether the Re-Os isochron
yields the original age of ore deposition or the age of the Hercynian metamorphism that affected the ores. However, the reasonable
Re-Os age reported here indicates that the complex history of the ores that occurred after the severe metamorphic event that
affected the Iberian Pyrite Belt massive sulfide deposits did not fundamentally disturb the Re-Os geochronologic system. The
highly radiogenic initial Os isotopic ratio agrees with previous Pb isotopic studies. If the initial ratio is recording the
initial and not the metamorphic conditions, then the data indicate that the source of the metals was largely crustal. The
continental margin sediments that underlie the deposits (phyllite-quartzite group) or the volcanic rocks (volcanogenic-sedimentary
complex) in which the ores occur are plausible sources for the ore-forming metals and should constrain the models for the
genesis of these deposits.
Received: 15 March 1999 / Accepted: 26 July 1999 相似文献
5.
We have analyzed the chemical composition and boron isotope composition of tourmaline from tourmalinites, granite and a quartz-tourmaline
vein from the Deri ore zone and from a pegmatitic band in the Rampura-Agucha ore body. These two Proterozoic massive sulfide
deposits occur in the Aravalli-Delhi orogenic belt, Rajasthan, northwest India. Tourmaline from stratiform tourmalinites closely
associated with the massive sulfides in the Deri deposit have preserved their original chemical compositions despite regional
and thermal metamorphism in the area. These tourmalines have low Fe/(Fe + Mg) ratios (0.19–0.30; mean 0.26) that suggest formation
close to the sediment-sea water interface. The δ11B values (−15.5 and −16.4‰) are compatible with boron derived from leaching of argillaceous sediments and/or felsic volcanics
underlying the original massive sulfide deposit during its formation. Boron isotope compositions measured in tourmaline from
a post-ore granite and quartz-tourmaline vein in the Deri deposit indicate that boron in these tourmalines was derived from
the tourmalinites produced during ore formation. The boron isotope systematics of a coarse brown tourmaline crystal from a
pegmatitic band on the hanging wall contact of the Rampura-Agucha deposit indicate that 45 ± 25% of the boron within the original
tourmaline was lost during upper amphibolite facies regional metamorphism.
Received: 3 April 1996 / Accepted: 11 April 1996 相似文献
6.
7.
A. V. Obushkov S. F. Struzhkov M. V. Natalenko O. B. Ryzhov S. G. Kryazhev Yu. I. Radchenko 《Geology of Ore Deposits》2010,52(6):459-478
The Engteri is a new hidden Au-Ag deposit in the Russian segment of the Pacific ore belt. The discovery of this deposit merits
special attention, because it involves repeated attempts to reappraise a lowprospective ore occurrence, which were crowned
with success as a result of fulfillment of large-scale drilling project. The average Au grade is 18.6 gpt. The deposit is
classified as the gold geochemical type of Au-Ag deposits. The major ore mineral is pyrite, which amounts to no less than
95% of the total ore minerals. The native phases comprise electrum and to a lesser extent native gold of low fineness (730).
The homogenization temperature of fluid inclusions is 125–255°C with a distinct maximum at 145–150°C. Despite blind localization
of some orebodies, the Engteri deposits bears evidence for a deep erosion level: (1) small vertical range of economic mineralization
(50–100 m); (2) predominant occurrence of massive sugarlike quartz with a low sulfide content; (3) prevalence of massive and
brecciated textures above rhythmically banded textures; and (4) lack of low-temperature propylites. The southern part of the
ore field distinguished by occurrence of rhythmically banded, framework-tabular, and brecciated texture has the best prospect
for revealing new orebodies. The Engteri deposit allowed us to outline the following prospecting guides and methods of prospecting
for hidden Au-Ag deposits: (1) these deposits are regularly arranged in ore clusters between heavy concentrate anomalies of
cinnabar and gold-silver or silver-base-metal occurrences (method of missed link); (2) findings of fragments of ore mineral
assemblages with sporadically high Au and Ag contents in barren calcite-quartz veins (method of indicators); (3) linear zones
of ankeritization in the fields of low- and mediumtemperature propylites (mapping of metasomatic rocks); and (4) pyrite-quartz
veinlets with rhythmically banded pockets (mineralogical mapping of halos of stringer-disseminated mineralization). 相似文献
8.
Epithermal mineralization and ore controls of the Shasta Au-Ag deposit, Toodoggone District, British Columbia, Canada 总被引：1，自引：0，他引：1
The Shasta gold-silver deposit, British Columbia, Canada, is an adularia-sericite-type epithermal deposit in which deposition
of precious metals coincided with the transition of quartz- to calcite-dominant gangue. Mineralization is associated with
stockwork-breccia zones in potassically altered dacitic lapilli tuffs and flows, and consists of pyrite, sphalerite, chalcopyrite,
galena, acanthite, electrum and native silver. Pre- and post-ore veins consist solely of quartz and calcite, respectively.
Fluid inclusion microthermometry indicates that ore minerals were deposited between 280 ° and 225 °C, from a relatively dilute
hydrothermal fluid (˜1.5 wt.% NaCl equivalent). Abundant vapor-rich inclusions in ore-stage calcite are consistent with boiling.
Oxygen and hydrogen isotopic data (δ18Ofluid = −1.5 to −4.1‰; δDfluid = −148 to −171‰) suggest that the fluid had a meteoric origin, but was 18O-enriched by interaction with volcanic wallrocks. Initial (˜280 °C) fluid pH and log f O2 conditions are estimated at 5.3 to 6.0, and −32.5 to −33 bar, respectively; during ore deposition, the fluid became more
alkaline and oxidizing. Ore deposition at Shasta is attributed to localization of meteoric hydrothermal fluids by extensional
faults; mineralization was controlled by boiling in response to hydraulic brecciation. Calcite and base metal sulfides precipitated
due to the increase in pH that accompanied boiling, and the associated decrease in H2S concentration led to precipitation of gold and silver.
Received: 23 February 1995 / Accepted: 16 April 1996 相似文献
9.
Vein-type tin mineralization in the Dadoushan deposit, Laochang ore field, Gejiu district, SW China, is predominantly hosted in Triassic carbonate rocks (Gejiu Formation) over cupolas of the unexposed Laochang equigranular granite intrusion. The most common vein mineral is tourmaline, accompanied by skarn minerals (garnet, diopside, epidote, phlogopite) and beryl. The main ore mineral is cassiterite, accompanied by minor chalcopyrite, pyrrhotite, and pyrite, as well as scheelite. The tin ore grade varies with depth, with the highest grades (~1.2 % Sn) prevalent in the lower part of the vein zone. Muscovite 40Ar–39Ar dating yielded a plateau age of 82.7 ± 0.7 Ma which defines the age of the vein-type mineralization. Measured sulfur isotope compositions (δ 34S = −4.1 to 3.9 ‰) of the sulfides (arsenopyrite, chalcopyrite, pyrite, and pyrrhotite) indicate that the sulfur in veins is mainly derived from a magmatic source. The sulfur isotope values of the ores are consistent with those from the underlying granite (Laochang equigranular granite, −3.7 to 0.1 ‰) but are different from the carbonate wall rocks of the Gejiu Formation (7.1 to 11.1 ‰). The calculated and measured oxygen and hydrogen isotope compositions of the ore-forming fluids (δ 18OH2O = −2.4 to 5.5 ‰, δD = −86 to −77 ‰) suggest an initially magmatic fluid which gradually evolved towards meteoric water during tin mineralization. 相似文献
10.
Rb-Sr study of Au-Ag Shkol'noe deposit (Kurama Mountains, north Tadjikistan): age of mineralization and time scale of hydrothermal processes 总被引：2，自引：0，他引：2
The epithermal Au-Ag Shkol'noe deposit is located in the Kandjol ore field, Kurama Mountains. This region is a part of the
east-west trending Late Hercynian Bel'tau-Kurama volcanic belt, an Andean-style collisional margin. The deposit comprises
a number of quartz-carbonate veins hosted by the syn-subductional Middle Carboniferous Karamazar granodiorites. The Au-Ag
mineralization is considered to be the result of the earliest hydrothermal event in the region. The Rb-Sr isochron age 296.3 ± 1.3 Ma
and an initial 87Sr/86Sr0=0.7071 ± 2 ratio were obtained for an adularia-sericite-quartz-calcite sample from Au-Ag mineralization. The 87Sr/86Sr ratio range from 0.70645 ± 10 to 0.70741 ± 10 was obtained for the calcites from the earlier and later mineral assemblages.
The Rb-Sr age is interpreted as a real geological age of the Au-Ag mineralization. It corresponds to the initial stage of
the Late Carboniferous – Early Permian collision following the main syn-subduction stage of Bel'tau-Kurama volcanic belt evolution.
The comparison of the Rb-Sr age with previously obtained 40Ar-39Ar and K-Ar data for adularia from the Au-Ag mineralization implies that gangue minerals of the Shkol'noe deposit bears the
fingerprint of at least three events in its history. They are (1) Au-Ag mineralization at 296.3 ± 1.3 Ma; and (2) two subsequent
thermal pulses at 277 ± 4 and 263–267 ± 8 Ma. The minimum time scale for the hydrothermal activity within the Shkol'noe deposit
is thus approximately 30 million years. A general uniformity of the strontium source during the hydrothermal processes within
the Au-Ag Shkol'noe deposit (87Sr/86Sr0=0.70645 ± 10 to 0.70741 ± 10) is suggested as well as within the Bel'tau-Kurama belt (87Sr/86Sr0=0.7051–0.707). The slight shift into a higher strontium isotope composition of the hydrothermal minerals of the Shkol'noe
deposit in comparison with other deposits and rocks of the Bel'tau-Kurama belt may be ascribed to the contribution of relatively
radiogenic strontium from the Karamazar-type granitoids. The mobilization of low radiogenic strontium during propylitic alteration
of diabase dikes emplaced after the Au-Ag mineralization could be responsible for comparatively low 87Sr/86Sr ratios in some of the latest post-dike carbonates.
Received: 4 August 1998 / Accepted: 25 August 1998 相似文献
11.
The Niujiaotang Cd-rich zinc deposit,Duyun, Guizhou province,southwest China: ore genesis and mechanisms of cadmium concentration 总被引：3，自引：0，他引：3
The Niujiaotang zinc deposit in southeastern Guizhou, China, is a Mississippi Valley-type Zn deposit within Early Cambrian carbonate rocks. Sphalerite is enriched in cadmium (average 1.4 wt.% Cd), which occurs mostly as isomorphous impurities in the sphalerite lattice. Discrete cadmium minerals (greenockite and otavite) are rare and are found almost exclusively in the oxidation zone of the deposit, probably formed as secondary minerals during weathering–leaching processes. Geochemical data show that the sulfides are enriched in heavy sulfur, with δ34S ranging from +10.0‰ to +32.8‰ (mean +22.5‰). The consistent Pb isotopic compositions in different sulfide minerals are similar to that of Cambrian strata. The ore lead probably came from U- and Th-rich upper crustal rocks, such as the Lower Cambrian Wuxun Formation. The ore fluid is of low-temperature (101°C to 142°C) type, with a Na–Ca–Mg–Cl-dominant composition, and is interpreted as oil-field brine. The data indicate that the metals were mainly derived from the Early Cambrian strata (Qingxudong and Wuxun Formations), whereas sulfur is sourced from sulfate in Cambrian strata or oil-field brines of the Majiang petroleum paleoreservoir. The genetic model for the deposit invokes an Early Cambrian shallow-sea environment on the Yangtze Platform. Zinc and Cd in seawater were concentrated in abundant algae via unknown biological mechanisms, resulting in large amounts of Zn- and Cd-rich algal ooliths. During the Ordovician, concurrent with destruction of the Majiang petroleum paleoreservoir, oil-field brines migrated from the center of the basin to the margin leaching metals from the Cambrian strata. In the Niujiaotang area, preexisting Zn and Cd, particularly in the Qingxudong and Wuxun Formation, were further mobilized by hot brines rising along the Zaolou fault system, forming stratiform and generally conformable Zn–Cd orebodies in reactive carbonate lithologies. 相似文献
12.
Chemical composition of tourmaline from the Yunlong tin deposit, Yunnan, China: implications for ore genesis and mineral exploration 总被引：1，自引：0，他引：1
Summary ?The Yunlong tin deposit is located in the northern part of the Lancangjiang metamorphic zone of the Sanjiang Tethys orogen
series in western Yunan province of China. It consists of vein-type cassiterite ores, which are mainly hosted in migmatites
of Caledonian age. Abundant tourmaline is associated with the ores, quartz–tourmaline veins and barren migmatized gneiss and
migmatites. A detailed electron microprobe study has been carried out to document the chemical compositions of tourmaline
from this deposit. The results exhibit a systematic compositional change that might be used as tracer for ore genesis and
in prospecting for tin mineralization. Tourmalines from the ore bodies are dravite with Fe/(Fe + Mg) ratios of 0.09 ∼ 0.31
and Ca/(Ca + Na) ratios of 0.03 ∼ 0.40. These tourmalines are also rich in chromium (up to 0.74 wt% Cr2O3) and tin (up to 0.42 wt% Sn). In contrast, tourmalines from the barren migmatites are mostly schorl with Fe/(Fe + Mg) ratios
of 0.38 ∼ 0.94 and Ca/(Ca + Na) ratios of 0.00 ∼ 0.14. Tourmalines from quartz–tourmaline veins that occur between ore bodies
and the migmatites show intermediate compositions, i.e., Fe/(Fe + Mg) = 0.09 ∼ 0.59, Ca/(Ca + Na) = 0.01 ∼ 0.22.
It is suggested that the Mg-rich nature of the tourmaline can be used as an exploration tool in this region to target tin
mineralization, because the tourmalines show increasing Mg contents and are more dravitic when approaching the ore bodies.
It is likely that the formation of the Yunlong tin deposit was related to migmatitic-hydrothermal processes. The high Mg and
Cr contents in tourmalines from the ore bodies were probably derived from the local meta-sedimentary and meta-volcanic rocks
of the Precambian Chongshan Group rather than from the granites in the region.
Received December 28, 2000; revised version accepted January 25, 2002 相似文献
13.
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
14.
Stephanos P. Kilias Jon Naden Ioannis Cheliotis Thomas J. Shepherd Heleni Constandinidou John Crossing Ioannis Simos 《Mineralium Deposita》2001,36(1):32-44
The Profitis Ilias gold deposit, located on the western part of Milos Island, Greece, is the first epithermal gold deposit
discovered in the Pliocene–Pleistocene Aegean volcanic arc. Estimated ore reserves are 5 million tonnes grading 4.4 g/tonne
Au and 43 g/tonne Ag. The deposit is closely associated with a horst and graben structure, and occurs in a series of steep
interconnected crustiform-banded quartz veins up to 3 m wide, extending to depths of at least 300 m. The mineralisation occurs
in three stages and is hosted by 3.5–2.5 Ma old silicified and sericitised rhyolitic lapilli-tuffs and ignimbrites. It consists
of pyrite, galena, chalcopyrite, electrum and native gold. Additionally, adularia occurs with quartz mainly in veins. Homogenisation
temperatures of primary liquid-rich inclusions vary from 145 to 399 °C for the ore stage, and 112 to 263 °C for the post-ore
stage. Salinities range between 0.1 and 11.4 wt% NaCl equiv. and 0.93 to 8.5 wt% NaCl equiv. for the ore stage and the post-ore
stage, respectively. Rare vapour-rich inclusions in ore stage quartz homogenise between 368 and 399 °C and estimates of eutectic
melting (−25 to −38 °C) indicate the presence of Ca and Mg in the ore fluids. Sample elevation versus fluid inclusion Th–salinity relationships show (1) a high-salinity trend, where moderate-temperature (300–250 °C) and moderate-salinity brines
(∼3 wt% NaCl equiv.) trend to high-salinity (up to 15 wt% NaCl equiv.) fluids with lower (∼25–50 °C) homogenisation temperatures,
and (2) a high-Th trend where moderate-salinity and moderate-temperature brines (200–250 °C; 3 wt% NaCl equiv.) develop into low-salinity (<1 wt%
NaCl equiv.), high-temperature (>350 °C) fluids. These trends are best explained by extreme boiling and vapourisation phenomena
between 200 and 250 °C. The 430–450 m asl (metres above sea level) level marks the transition between a lower liquid-dominated
segment of the system where only the steep high-salinity trend is seen, and an upper vapour-dominated segment where the high-Th trend or a combination of both are seen. There is a close spatial association between mineable gold grades and the upper
segment of the system. Depth-to-boiling curves suggest that the paleo-surface was ∼200 m above the present summit of Profitis
Ilias. Comparison of the mineralisation and fluid geochemistry at Profitis Ilias with that of the nearby modern geothermal
system indicates that the processes of metal mineralisation have probably been continuous since the Late Pliocene.
Received: 24 February 2000 / Accepted: 15 July 2000 相似文献
15.
Factors controlling copper solubility and chalcopyrite deposition in the Sungun porphyry copper deposit, Iran 总被引：14，自引：0，他引：14
The Sungun porphyry copper deposit is hosted in a Diorite/granodioritic to quartz-monzonitic stock that intruded Eocene volcanosedimentary
and Cretaceous carbonate rocks. Copper mineralization is associated mainly with potassic alteration and to a lesser extent
with sericitic alteration. Based on previously published fluid inclusion and isotopic data by Hezarkhani and Williams-Jones
most of the copper is interpreted to have deposited during the waning stages of orthomagmatic hydrothermal activity at temperatures
of 400 to 300 °C. These data also indicate that the hydrothermal system involved meteoric waters, and boiled extensively.
In this work, thermodynamic data are used to delineate the stability fields of alteration and ore assemblages as a function
of fS2, fO2 and pH. The solubility of chalcopyrite was evaluated in this range of conditions using recently published experimental data.
During early potassic alteration (>450 °C), Copper solubility is calculated to have been >50 000 ppm, whereas the copper content
of the initial fluid responsible for ore deposition is estimated, from fluid inclusion data, to have been 1200–3800 ppm. This
indicates that initially the fluid was highly undersaturated with respect to chalcopyrite, which agrees with the observation
that veins formed at T > 400 °C contain molybdenite but rarely chalcopyrite. Copper solubility drops rapidly with decreasing temperature, and at
400 °C is approximately 1000 ppm, within the range estimated from fluid inclusion data, whereas at 350 °C it is only 25 ppm.
These calculations are consistent with observations that the bulk of the chalcopyrite deposited at Sungun is hosted by veins
formed at temperatures of 360 ± 60 °C. Other factors that, in principle, may reduce chalcopyrite solubility are increases
in pH, and decreases in fO2 and aCl−. Our analysis shows, however, that most of the change in pH occurred at high temperature when chalcopyrite was grossly undersaturated
in the fluid, and that the direction of change in fO2 increased chalcopyrite solubility. We propose that the Sungun deposit formed mainly in response to the sharp temperature
decrease that accompanied boiling, and partly as a result of the additional heat loss and decrease in aCl−, which occurred as a result of mixing of acidic Cu-bearing magmatic waters with cooler meteoric waters of lower salinity.
Received: 8 July 1998 / Accepted: 8 April 1999 相似文献
16.
Pongkor (west Java, Indonesia): a Pliocene supergene-enriched epithermal Au-Ag-(Mn) deposit 总被引：2，自引：0，他引：2
J. P. Milési E. Marcoux T. Sitorus M. Simandjuntak J. Leroy L. Bailly 《Mineralium Deposita》1999,34(2):131-149
The Pongkor gold-silver epithermal deposit with reserves of at least 98 tonnes of gold and 1026 tonnes of silver, average
grades 16.4 g/t Au and 171.2 g/t Ag is one of the most recent and largest gold and silver discoveries in Indonesia, proven
within a short period (1988–1991). 40Ar/39Ar dating on adularia samples give an age of 2.05 ± 0.05 Ma. The deposit is of the low-sulfidation epithermal type and consists
of four main mineralized quartz veins located close to the internal rim of a volcano-tectonic depression (caldera). This resulted
from an explosive ignimbritic eruption that produced pyroclastic flows and accretionary lapilli with rare intercalations of
epiclastic rocks. This volcanic unit unconformably overlies Miocene subaqueous volcanic andesitic rocks with interbedded epiclastic
rocks. The mineralized bodies are thick (average 4.2 m), steeply dipping, quartz-carbonate-adularia veins with a very low
sulfide content (<0.5 wt.%). Their genesis is related to an extensional episode within a tectonic corridor showing NW-SE and
NNE-SSW conjugate strike-slip faults, the major vein being located on the inner rim of the caldera. The vein fill reveals
four successive stages of deposition marked by a specific facies: (1) carbonate-quartz breccia with dominant quartz and calcite
and minor kutnahorite, rhodochrosite, and rhodonite (CQ facies), (2) a network of banded quartz and former carbonate transformed
into manganese oxides through supergene alteration (MOQ facies), (3) banded opaline milky quartz (BOQ facies), and (4) grey,
locally banded, sulfide-rich quartz breccia cutting all the other types (GSQ facies). Adularia was deposited at the same time
as the quartz. The mineralogy and internal structures of the veins (crustiform banding, vugs, collapse breccia) clearly indicate
a dilational context, which is common in low-sulfidation epithermal systems. Gold and silver grades, as well as sulfide mineral
abundances, increase steadily through stages 1 to 4, locally reaching 1 kg/t in the GSQ facies. The sulfides are dominated
by pyrite, accompanied by common acanthite-aguilarite, polybasite-pearceite and electrum in which the gold content ranges
from 48 to 74 wt.%. Sphalerite, galena, chalcopyrite and hessite are fairly rare, although present within the CQ facies. The
fluid inclusions of the four facies show homogenization temperatures ranging from 150 to 382 °C, indicating boiling of a hydrothermal
fluid with an initial temperature of around 205 °C; no marked difference is seen in the GSQ facies, which has the highest
gold content. Salinities are low, generally below 1 wt.% eq. NaCl. Lead isotope compositions of the associated volcanic rocks
and the mineralization are very similar, 206Pb/204Pb between 18.706 and 18.814␣and between 18.744 and 18.801 respectively, demonstrating a genetic link between the Pliocene
volcanism and the auriferous hydrothermal activity. The isotopic signature suggests that the source of the mineralization
and associated volcanic rocks is an underlying ancient continental crust that melted and remobilized during the Pliocene volcanic
and hydrothermal events. These conclusions seem applicable to the entire Bayah Dome. The existence of both a tectonic corridor
and a caldera favoured channelling of the hydrothermal fluids and the deposition of primary ore in the veins. Late intense
weathering of the ore deposit, to depths of 250 m below the surface, has given rise to manganese oxide layers, limonite zones,
and silver micronuggets within the veins, as well as to gold enrichment.
Received: 25 June 1997 / Accepted: 10 March 1998 相似文献
17.
The Kalyadi polymetallic copper deposit occurs within the Middle Archaean (≥3.0 Ga), medium-grade Kalyadi schist belt which
consists predominantly of ultramafic-mafic schists interbedded with chemogenic chert, detrital high Al-Mg schists and siliceous
schists. This sedimentary exhalative type (SEDEX type) ore-body is the only copper deposit hosted in cherts in the western
Dharwar craton. The Kalyadi supracrustal rocks are intruded by tonalite-trondhjemitic gneisses (ca. 3.0 Ga) and granite (ca.
2.6 Ga). The Kalyadi copper deposit is polygenetic in nature. The primary ores represented by disseminations of pyrite ± linneite
and chalcopyrite ± magnetite essentially along the bedding lamination of the metachert are referred to as the metamorphosed
chert-sulphide rhythmites of a primary stratiform type. The ore is of low-grade and records imprints of at least two events
of deformation. Pyrite is characterised by high-Co values (262–4524 ppm) and high–Co/Ni ratios (3.0–19.7). Rare earth element
patterns of the primary ores and the host metacherts are identical, characterised by La enrichment, absence of Eu anomalies
and flat to depleted HREE patterns with δ
34 S = −0.8‰. The secondary (remobilised) ores are structurally controlled occurring as veins and stringers discordant to the
bedding lamination or schistosity. The constituent ores are chalcopyrite-pyrite-pyrrhotite with minor pentlandite. These sulphides
with low-Co/Ni ratios (0.87–1.80), have either a strong positive or negative Eu anomaly and show slight HREE enrichment. The
δ
34 S value ranges from +2.64 to −4.29‰. It is interpreted that the primary stratiform ores and the cherts were derived from
volcanogenic hydrothermal fluids as syngenetic/chemical deposits in a deep sea environment. The secondary epigenetic mineralisation
is related to subsequent migmatisation, deformational events and granitic activity.
Received: 8 September 1995 / Accepted: 18 November 1996 相似文献
18.
Geological and geochemical constraints on the genesis of the Xiangquan Tl-only deposit,eastern China
The Xiangquan Tl deposit, located in the northern part of the Middle–Lower Yangtze Valley metallogenic belt, eastern China, is the only known Tl-only deposit. It is hosted in micritic limestone, marl and mudstone of the Lower Ordovician Lunshan Formation. The orebodies are controlled by the Xiao–Xiaolongwang–Dalongwang anticline and two reverse faults, and are generally stratabound and lenticular. Tl is only ore metal contained in disseminated, massive, brecciated and banded ores. The ore is composed of Tl-bearing pyrite, and gangue minerals quartz, fluorite, barite and carbonate. Alteration minerals include fluorite, barite, fine grained quartz and carbonate. Tl occurs isomorphously replacing iron in the lattice of pyrite, and less commonly as tiny independent Tl-bearing minerals which may be lafossaite (TlAsS2) or lorandite (TlCl) appearing as 0.1–1 μm-sized cubic crystals. Xiangquan is a submarine sedimentary deposit and demonstrates that Tl, as a normally dispersed element, can form not only part of poly-metallic deposits but also as independent Tl deposits. 相似文献
19.
G. Xu 《Mineralium Deposita》1997,32(1):58-69
The Zn-Pb-Ag deposit contained in the metasediments of middle Proterozoic age at Dugald River forms one of a number of significant
zones of sulphide mineralization within the Eastern Fold Belt of the Mount Isa Inlier. It is characterized by its high Zn
+ Pb grade, high Zn/(Zn+Pb) ratio and strong structural controls with the present resource standing at 38 million tons averaging
13% Zn, 2.1% Pb and 42 g/t Ag. Microstructural timing relationships and a variety of microscopic ore textures indicate that
the deposit resulted from replacement and partial infill of carbonaceous and pyritic host rocks by hydrothermal ore-forming
fluids during the D4 deformation event. This genesis is contrary to earlier syngenetic-based interpretations, but accords with the discordant
nature and structural controls on emplacement of the mineralization. Key timing criteria include (1) truncation of S2 and/or S3 by the late ore minerals, (2) replacement textures in undeformed mineral paragenesis, (3) slightly preferred dimensional
orientation and undulating extinction of quartz and muscovite that are intergrown but which crystallized earlier than sulphide
minerals in veins. The presence of these microstructural relationships throughout the deposit and the complete absence of
any syngenetic stratiform precursor to zinc-lead-silver mineralization indicates that the zinc, lead and silver at Dugald
River were epigenetically introduced rather than just having undergone syngenetic deposition during sedimentation and remobilization
during deformation. The regional distribution of the mineralization in a specific stratigraphic zone is most likely due to
the partitioning of deformation between different rock types. This caused the weaker lithology to accommodate significantly
higher strain than adjacent more competent units, resulting in fracturing and localization of the syntectonic mineralization.
Received: 8 September 1995 / Accepted: 12 April 1996 相似文献
20.
Gossan Hill is an Archean (∼3.0 Ga) Cu–Zn–magnetite-rich volcanic-hosted massive sulfide (VHMS) deposit in the Yilgarn Craton
of Western Australia. Massive sulfide and magnetite occur within a layered succession of tuffaceous, felsic volcaniclastic
rocks of the Golden Grove Formation. The Gossan Hill deposit consists of two stratigraphically separate ore zones that are
stratabound and interconnected by sulfide veins. Thickly developed massive sulfide and stockwork zones in the north of the
deposit are interpreted to represent a feeder zone. The deposit is broadly zoned from a Cu–Fe-rich lower ore zone, upwards
through Cu–Zn to Zn–Ag–Au–Pb enrichment in the upper ore zone. New sulfur isotope studies at the Gossan Hill deposit indicate
that the variation is wider than previously reported, with sulfide δ34S values varying between −1.6 and 7.8‰ with an average of 2.1 ± 1.4‰ (1σ error). Sulfur isotope values have a broad systematic
stratigraphic increase of approximately 1.2‰ from the base to the top of the deposit. This variation in sulfur isotope values
is significant in view of typical narrow ranges for Archean VHMS deposits. Copper-rich sulfides in the lower ore zone have
a narrower range (δ34S values of −1.6 to 3.4‰, average ∼1.6 ± 0.9‰) than sulfides in the upper ore zone. The lower ore zone is interpreted to have
formed from a relatively uniform reduced sulfur source dominated by leached igneous rock sulfur and minor magmatic sulfur.
Towards the upper Zn-rich ore zone, an overall increase in δ34S values is accompanied by a wider range of δ34S values, with the greatest variation occurring in massive pyrite at the southern margin of the upper ore zone (−1.0 to 7.8‰).
The higher average δ34S values (2.8 ± 2.1‰) and their wider range are explained by mixing of hydrothermal fluids containing leached igneous rock
sulfur with Archean seawater (δ34S values of 2 to 3‰) near the paleoseafloor. The widest range of δ34S values at the southern margin of the deposit occurs away from the feeder zone and is attributed to greater seawater mixing
away from the central upflow zone.
Received: 10 June 1999 / Accepted: 28 December 1999 相似文献