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1.
《地学前缘(英文版)》2022,13(2):101347
The subeconomic Mount Novit Zn-Pb-Ag deposit is located approximately 20 km south of Mount Isa, Queensland. In contrast to the nearby Mount Isa, Hilton and George Fisher Zn-Pb-Ag deposits, mineralisation at Mount Novit is situated to the west of the regional-scale Mount Isa Fault and is hosted in the Moondarra Siltstone as opposed to the Urquhart Shale. Lower-grade (<4 wt.% Zn + Pb) Zn-Pb-Ag mineralisation primarily replaces pre-existing carbonate alteration and veining and consists of pyrrhotite, pyrite and sphalerite with lesser galena. Higher-grade (>10 wt.% Zn + Pb) mineralisation occurs as a matrix supported breccia dominated by sphalerite and pyrrhotite with galena, pyrite, and magnetite. In-situ U–Pb geochronology was completed on apatite and two textural varieties of monazite. Fine-grained (<50 µm) subhedral to anhedral monazite is located within highly foliated biotite alteration directly adjacent Zn-Pb-Ag mineralisation and yields a mean weighted 207Pb/206Pb age of 1527 ± 18 Ma (MSWD = 1.06). This age is consistent with the formation of highly foliated biotite alteration during D3 deformation of the Isan Orogeny. Apatite from the same fabric yields a lower intercept age of 1443 ± 29 Ma (MSWD = 1.30). Consistent with previous studies, this age is interpreted to represent the age of a major thrusting event along the Mount Isa Fault that resulted in the cooling of the Mount Novit area below ~375 °C. Coarse-grained monazite is coeval with Zn-Pb-Ag mineralisation and yields a mean weighted 207Pb/206Pb age of 1457 ± 11 Ma (MSWD = 0.28). Sphalerite from Mount Novit has low concentrations (<1 ppm) of Ge and Ga and a relatively high concentration of In (5 to >10 ppm), possibly reflecting the leaching of the metals from an underlying basement unit. The GGIMFis geothermometer (Frenzel et al., 2016) produced a mean formation temperature of 345 ± 52 °C. The timing and temperature of Zn-Pb-Ag mineralisation is consistent with the age and cooling temperature of apatite presented in this study. Based on these correlations, we suggest that Zn-Pb-Ag mineralisation at Mount Novit was emplaced during an episode of major thrusting along the Mount Isa Fault, with the precipitation of Zn-Pb-Ag mineralisation driven by the cooling of the Mount Novit area below ~375 °C. A key implication of this study is a new model for synorogenic Zn-Pb-Ag mineralisation to the south of Mount Isa, which contrasts with the widely accepted regional-scale syngenetic metallogenic model. 相似文献
2.
Melissa J. Gregory Bruce F. Schaefer Reid R. Keays Andy R. Wilde 《Mineralium Deposita》2008,43(5):553-573
The syn-tectonic breccia-hosted Mount Isa Cu deposit in northwest Queensland is the largest sediment-hosted Cu deposit in
Australia. Whole-rock samples of chalcopyrite-rich Cu ore form an isochron with a Re–Os age of 1,372 ± 41 Ma. This age is
more than 100 Ma younger than the previously accepted age of Cu ore formation, an Ar–Ar mineral age for biotite separated
from the host rocks within the alteration envelope to the Cu orebody. This discrepancy cannot be unequivocally resolved due
to a lack of other absolute geochronological constraints for Cu mineralisation or the deformation event associated with Cu
emplacement. The 1,372 ± 41 Ma date may reflect (a) the time of Cu deposition, (b) the time of a hydrothermal event that reset
the Re–Os signature of the Cu ore or (c) mixing of the Re–Os isotope systematics between the host rocks and Cu-bearing fluids.
However, a range of published Ar–Ar and Rb–Sr dates for potassic alteration associated with Cu mineralisation also records
an event between 1,350 and 1,400 Ma and these are consistent with the 1,372 Ma Re–Os age. The 1.8 Ga Eastern Creek Volcanics
are a series of tholeiitic basalts with a primary magmatic Cu enrichment which occur adjacent to the Mount Isa Cu deposit.
The whole-rock Os isotopic signature of the Eastern Creek Volcanics ranges from mantle-like values for the upper Pickwick
Member, to more radiogenic/crustal values for the lower Cromwell Member. The Re–Os isotope signature of the Cu ores overlaps
with those calculated for the two volcanic members at 1,372 Ma; hence, the Os isotope data are supportive of the concept that
the Os in the Cu ores was sourced from the Eastern Creek Volcanics. By inference, it is therefore postulated that the Eastern
Creek Volcanics are the source of Cu in the Mount Isa deposit, as both Os and Cu are readily transported by oxidised hydrothermal
fluids, such as those that are thought to have formed the Cu orebody. The Pickwick Member yields a Re–Os isochron age of 1,833 ± 51 Ma,
which is within error of previously reported age constraints. The initial 187Os/188Os isotopic ratio of 0.114 ± 0.067 (γOs = −0.7) is slightly subchondritic, and together with other trace element geochemical
constraints, is consistent with a subcontinental lithospheric mantle source. The Pickwick Member records a minimum age of
ca. 1.95 Ga for melt depletion in the subcontinental lithospheric mantle beneath the Mount Isa Inlier prior to the extraction
of the magmas which formed the Eastern Creek Volcanics. This corresponds with the end of subduction-related magmatism along
the eastern margin of the Northern Australian Craton, which included the Mount Isa Inlier. 相似文献
3.
Mineralogy and geochemistry of the sodium metasomatism-related uranium occurrence of Aricheng South, Guyana 总被引:2,自引:0,他引:2
Paul Alexandre 《Mineralium Deposita》2010,45(4):351-367
The Aricheng South uranium occurrence is associated with Na metasomatism that affected the granitoids of the Kurupung Batholith
in western Guyana. The mineral paragenesis indicates that late-magmatic albitization was followed by chlorite alteration of
biotite. A minor amount of uraninite occurs in fractures in the newly formed albite crystals, often in company of calcite.
The main mineralization stage occurred later than albitization and chloritization and is represented by brannerite disseminated
in a groundmass of fine-grained hydrothermal zircon. Whole rock geochemistry supports the temporal dissociation of albitization
from the main ore stage. Brannerite, zircon, and uraninite are often partially altered to secondary brannerite, zircon, and
coffinite, respectively. Stable oxygen (chlorite, calcite) and hydrogen (chlorite) isotope compositions suggest that a highly
evolved meteoric fluid, or at least one corresponding to a very high rock/fluid ratio (δ18O of approx. 3.4% to 4‰ and δD of approx. −80‰) may have caused the pre-ore alteration assemblage. The fluids in equilibrium
with main ore stage zircon have δ18O of approx. 6.8‰ and appear to be of magmatic origin. The Aricheng occurrence geochemically, mineralogically, thermally,
and paragenetically resembles the Valhalla U deposit in northern Australia despite differences between the deposits’ host
lithologies, whereas the Lagoa Real and Espinharas U deposits in Brazil have host rock lithology that resembles that of Aricheng. 相似文献
4.
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
5.
Re-evaluation of the petrogenesis of the Proterozoic Jabiluka unconformity-related uranium deposit, Northern Territory, Australia 总被引:1,自引:0,他引:1
Paul A. Polito T. Kurt Kyser David Thomas Jim Marlatt Garth Drever 《Mineralium Deposita》2005,40(3):257-288
The world class Jabiluka unconformity-related uranium deposit in the Alligator Rivers Uranium Field, Australia, contains >163,000 tons
of contained U3O8. Mineralization is hosted by shallow-to-steeply dipping basement rocks comprising graphitic units of chlorite–biotite–muscovite
schist. These rocks are overlain by flat-lying coarse-grained sandstones belonging to the Kombolgie Subgroup. The deposit
was discovered in 1971, but has never been mined. The construction of an 1,150 m decline into the upper eastern sector of
the Jabiluka II deposit combined with closely spaced underground drilling in 1998 and 1999 allowed mapping and sampling from
underground for the first time. Structural mapping, drill core logging and petrographic studies on polished thin sections
established a detailed paragenesis that provided the framework for subsequent electron microprobe and X-ray diffraction, fluid
inclusion, and O–H, U–Pb and 40Ar/39Ar isotope analysis. Uranium mineralization is structurally controlled within semi-brittle shears that are sub-conformable
to the basement stratigraphy, and breccias that are developed within the hinge zone of fault-related folds adjacent to the
shears. Uraninite is intimately associated with chlorite, sericite, hematite ± quartz. Electron microprobe and X-ray diffraction
analysis of syn-ore illite and chlorite indicates a mineralization temperature of 200°C. Pre- and syn-ore minerals extracted
from the Kombolgie Subgroup overlying the deposit and syn-ore alteration minerals in the Cahill Formation have δ18Ofluid and δD
fluid values of 4.0±3.7 and −27±17‰, respectively. These values are indistinguishable from illite separates extracted from diagenetic
aquifers in the Kombolgie Subgroup up to 70 km to the south and east of the deposit and believed to be the source of the uraniferous
fluid. New fluid inclusion microthermometry data reveal that the mineralising brine was saline, but not saturated. U–Pb and
207Pb/206Pb ratios of uraninite by laser-ablation ICP-MS suggest that massive uraninite first precipitated at ca. 1,680 Ma, which is
coincident with the timing of brine migration out from the Kombolgie Subgroup as indicated by 40Ar/39Ar ages of 1,683±11 Ma from sandstone-hosted illite. Unmineralized breccias cemeted by chlorite, quartz and sericite cross-cut
the mineralized breccias and are in turn cut by straight-sided, high-angle veins of drusy quartz, sulphide and dolomite. U–Pb
and 207Pb/206Pb ratios combined with fluid inclusion and stable isotope data indicate that these post-ore minerals formed when mixing between
two fluids occurred sometime between ca. 1,450 and 550 Ma. Distinct 207Pb/206Pb age populations occur at ca. 1,302±37, 1,191±27 and 802±57 Ma, which respectively correlate with the intrusion of the Maningkorrirr/Mudginberri
phonolitic dykes and the Derim Derim Dolerite between 1,370 and 1,316 Ma, the amalgamation of Australia and Laurentia during
the Grenville Orogen at ca. 1,140 Ma, and the break-up of Rodinia between 1,000 and 750 Ma. 相似文献
6.
Stable isotope geochemistry and diagenetic mineralization associated with the Tono sandstone-type uranium deposit in Japan 总被引:5,自引:0,他引:5
The Tono sandstone-type uranium mine area, middle Honsyu, Japan is composed of Miocene lacustrine sedimentary rocks in the
lower part (18–22 Ma) and marine facies in the upper part (15–16 Ma). Calcite and pyrite occur as dominant diagenetic alteration
products in these Neogene sedimentary rocks. The characteristics of calcite and pyrite differ significantly between lacustrine
and marine facies. Abundant pyrite, calcite, organic matter, and small amounts of marcasite or pyrrhotite occur in the lacustrine
facies, whereas small amounts of calcite and framboidal pyrite, organic matter and no marcasite or pyrrhotite are found within
the marine units. The δ13C values of calcite in the lacustrine deposits are low (−19 to −6‰ PDB) but those in marine formation are high (−11 to +3‰).
This implies that the contribution of marine carbonate is larger in upper marine sedimentary rocks, and carbon in calcite
in the lower lacustrine formation was derived both from oxidation of organic matter and from dissolved marine inorganic carbon.
The δ34S values of framboidal pyrite in the upper marine formation are low (−14 to −8‰ CDT), indicating a small extent of bacterial
seawater sulfate reduction, whereas those of euhedral-subhedral pyrite in the lower lignite-bearing arkose sandstone are high
(+10 to +43‰), implying a large extent of closed-system bacterial seawater sulfate reduction. The δ34S and δ13C data which deviate from a negative correlation line toward higher δ13C values suggest methanogenic CO2 production. During diagenesis of the lacustrine unit, large amounts of euhedral-subhedral pyrite were formed, facilitated
by extensive bacterial reduction of seawater sulfate with concomitant oxidation of organic matter, and by hydrolysis reactions
of organic matter, producing CH4 and CO2. Uranium minerals (coffinite and uraninite) were also formed at this stage by the reduction of U6+ to U4+. The conditions of diagenetic alteration within the lacustrine deposits and uranium mineralization is characterized by low
Eh in which nearly equal concentrations of CH4 and HCO3
− existed and reduced sulfur species (H2S, HS−) are predominant among aqueous sulfur species, whereas diagenetic alteration of the marine formations was characterized by
a predominance of SO4
2− among dissolved sulfur species. Modern groundwater in the lacustrine formation has a low Eh value (−335 mV). Estimated and
measured low Eh values of modern and ancient interstitial waters in lacustrine environments indicate that a reducing environment
in which U4+ is stable has been maintained since precipitation of uranium minerals.
Received: 9 February 1996 / Accepted: 11 April 1997 相似文献
7.
The source of metasomatic fluids in iron-oxide–copper–gold districts is contentious with models for magmatic and other fluid sources having been proposed. For this study, δ
18O and δ
13C ratios were measured from carbonate mineral separates in the Proterozoic eastern Mt Isa Block of Northwest Queensland, Australia. Isotopic analyses are supported by petrography, mineral chemistry and cathodoluminescence imagery. Marine meta-carbonate rocks (ca. 20.5‰ δ
18O and 0.5‰ δ
13C calcite) and graphitic meta-sedimentary rocks (ca. 14‰ δ
18O and −18‰ δ
13C calcite) are the main supracrustal reservoirs of carbon and oxygen in the district. The isotopic ratios for calcite from the cores of Na–(Ca) alteration systems strongly cluster around 11‰ δ
18O and −7‰ δ
13C, with shifts towards higher δ
18O values and higher and lower δ
13C values, reflecting interaction with different hostrocks. Na–(Ca)-rich assemblages are out of isotopic equilibrium with their metamorphic hostrocks, and isotopic values are consistent with fluids derived from or equilibrated with igneous rocks. However, igneous rocks in the eastern Mt Isa Block contain negligible carbon and are incapable of buffering the δ
13C signatures of CO2-rich metasomatic fluids associated with Na–(Ca) alteration. In contrast, plutons in the eastern Mt Isa Block have been documented as having exsolved saline CO2-rich fluids and represent the most probable fluid source for Na–(Ca) alteration. Intrusion-proximal, skarn-like Cu–Au orebodies that lack significant K and Fe enrichment (e.g. Mt Elliott) display isotopic ratios that cluster around values of 11‰ δ
18O and −7‰ δ
13C (calcite), indicating an isotopically similar fluid source as for Na–(Ca) alteration and that significant fluid–wallrock interaction was not required in the genesis of these deposits. In contrast, K- and Fe-rich, intrusion-distal deposits (e.g. Ernest Henry) record significant shifts in δ
18O and δ
13C towards values characteristic of the broader hostrocks to the deposits, reflecting fluid–wallrock equilibration before mineralisation. Low temperature, low salinity, low δ
18O (<10‰ calcite) and CO2-poor fluids are documented in retrograde metasomatic assemblages, but these fluids are paragenetically late and have not contributed significantly to the mass budgets of Cu–Au mineralisation. 相似文献
8.
Jan-Marten Huizenga Jens Gutzmer David Banks Lynnette Greyling 《Mineralium Deposita》2006,40(6-7):686-706
The Pering deposit is the prime example of Zn–Pb mineralisation hosted by stromatolitic dolostones of the Neoarchean to Paleoproterozoic Transvaal Supergroup. The hydrothermal deposit centers on subvertical breccia pipes that crosscut stromatolitic dolostones of the Reivilo Formation, the lowermost portion of the Campbellrand Subgroup. Four distinct stages of hydrothermal mineralisation are recognised. Early pyritic rock matrix brecciation is followed by collomorphous sphalerite mineralisation with replacive character, which, in turn, is succeeded by coarse grained open-space-infill of sphalerite, galena, sparry dolomite, and quartz. Together, the latter two stages account for ore-grade Zn–Pb mineralisation. The fourth and final paragenetic stage is characterised by open-space-infill by coarse sparry calcite. The present study documents the results of a detailed geochemical study of the Pering deposit, including fluid inclusion microthermometry, fluid chemistry and stable isotope geochemistry of sulphides (δ34S) and carbonate gangue (δ13C and δ18O). Microthermometric fluid inclusion studies carried out on a series of coarsely grained crystalline quartz and sphalerite samples of the latter, open-space-infill stage of the main mineralisation event reveal the presence of three major fluid types: (1) a halite–saturated aqueous fluid H2O–NaCl–CaCl2 (>33 wt% NaCl equivalent) brine, (2) low-salinity meteoric fluid (<7 wt% NaCl) and (3) a carbonic CH4–CO2–HS− fluid that may be derived from organic material present within the host dolostone. Mixing of these fluids have given rise to variable mixtures (H2O–CaCl2–NaCl ±(CH4–CO2–HS−), 2 to 25 wt% NaCl+CaCl2). Heterogeneous trapping of the aqueous and carbonic fluids occurred under conditions of immiscibility. Fluid temperature and pressure conditions during mineralisation are determined to be 200–210°C and 1.1–1.4 kbar, corresponding to a depth of mineralisation of 4.1–5.2 km. Chemical analyses of the brine inclusions show them to be dominated by Na and Cl with lesser amounts of Ca, K and SO4. Fluid ratios of Cl/Br indicate that they originated as halite saturated seawater brines that mixed with lower salinity fluids. Analyses of individual brine inclusions document high concentrations of Zn and Pb (∼1,500 and ∼200 ppm respectively) and identify the brine as responsible for the introduction of base metals. Stable isotope data were acquired for host rock and hydrothermal carbonates (dolomite, calcite) and sulphides (pyrite, sphalerite, galena and chalcopyrite). The ore-forming sulphides show a trend to 34S enrichment from pyrite nodules in the pyritic rock matrix breccia (δ34S = −9.9 to +3.7‰) to paragenetically late chalcopyrite of the main mineralisation event (δ34S = +30.0‰). The observed trend is attributed to Rayleigh fractionation during the complete reduction of sulphate in a restricted reservoir by thermochemical sulphate reduction, and incremental precipitation of the generated sulphide. The initial sulphate reservoir is expected to have had an isotopic signature around 0‰, and may well represent magmatic sulphur, oxidised and leached by the metal-bearing brine. The δ18O values of successive generations of dolomite, from host dolostone to paragenetically late saddle dolomite follow a consistent trend that yields convincing evidence for extensive water rock interaction at variable fluid–rock ratios. Values of δ13C remain virtually unchanged and similar to the host dolostone, thus suggesting insignificant influx of CO2 during the early and main stages of mineralisation. On the other hand, δ13C and δ18O of post-ore calcite define two distinct clusters that may be attributed to changes in the relative abundance in CH4 and CO2 during waning stages of hydrothermal fluid flow. 相似文献
9.
Deep seismic reflection profiling confirms that the Paleo- to Mesoproterozoic Mount Isa mineral province comprises three vertically stacked and partially inverted sedimentary basins preserving a record of intracontinental rifting followed by passive margin formation. Passive margin conditions were established no later than 1655 Ma before being interrupted by plate convergence, crustal shortening and basin-wide inversion at 1640 Ma in both the 1730–1640 Ma Calvert and 1790–1740 Ma Leichhardt superbasins. Crustal extension and thinning resumed after 1640 Ma with formation of the 1635–1575 Ma Isa Superbasin and continued up to ca. 1615 Ma when extensional faulting ceased and a further episode of basin inversion commenced. The 1575 Ma Century Pb–Zn ore-body is hosted by syn-inversion sediments deposited during the initial stages of the Isan Orogeny with basin inversion accommodated on east- or northeast-dipping reactivated intrabasinal extensional faults and footwall shortcut thrusts. These structures extend to considerable depths and served as fluid conduits during basin inversion, tapping thick syn-rift sequences of immature siliciclastic sediments floored by bimodal volcanic sequences from which the bulk of metals and mineralising fluids are thought to have been sourced. Basin inversion and fluid expulsion at this stage were entirely submarine consistent with a syn-sedimentary to early diagenetic origin for Pb–Zn mineralisation at, or close to, the seafloor. Farther east, a change from platform carbonates to deeper water continental slope deposits (Kuridala and Soldiers Cap groups) marks the position of the original shelf break along which the north–south-striking Selwyn-Mount Dore structural corridor developed. This corridor served as a locus for strain partitioning, fluid flow and iron oxide–copper–gold mineralisation during and subsequent to the onset of basin inversion and peak metamorphism in the Isan Orogeny at 1585 Ma. An episode of post-orogenic strike-slip faulting and hydrothermal alteration associated with the subvertical Cloncurry Fault Zone overprints west- to southwest-dipping shear zones that extend beneath the Cannington Pb–Zn deposit and are antithetic to inverted extensional faults farther west in the same sub-basin. Successive episodes of basin inversion and mineralisation were driven by changes in the external stress field and related plate tectonic environment as evidenced by a corresponding match to bends in the polar wander path for northern Australia. An analogous passive margin setting has been described for Pb–Zn mineralisation in the Paleozoic Selwyn Basin of western Canada. 相似文献
10.
The Sanbaqi uranium deposit in Hunan Province, south China, is the largest of a group of paleokarst-hosted uranium deposits
in Lower Carboniferous limestone. Mineralization is localized in cavities and fault-breccias formed by dissolution of carbonates.
Four episodes of karst formation are recognized: late Triassic-early Jurassic, late Jurassic-early Cretaceous, Cretaceous-Tertiary
and Recent. Field relations indicate that the main uranium mineralization is related to the second karst episode. This is
supported by isotopic ages of two pitchblende samples at 129 Ma and 134 Ma, as indicated by their nearly concordant data points
on concordia plot. These ages are in the time range of the early Yanshanian tectonic movements that affected southern China,
and the faulting related to the movements likely triggered the mineralization process at the Sanbaqi deposit. Associated minerals
include pyrite, millerite, ullmannite, niccolite, molybdenite, chalcopyrite, sphalerite, galena, calcite and dolomite. Fluid
inclusion studies on calcite reveal that temperature of ore deposition was from 181° to 150 °C. The δ18O and δD values of the ore fluids range from 1.5 to 7.9 per mil and from −30.4 and −54.8 per mil, respectively. The mineralogical,
fluid inclusion and isotopic data indicate that the minerlization took place in episodic pulses of hydrothermal fluids that
were introduced along a set of ring faults. Mobilization and redeposition of earlier formed ore minerals in an open system
added to the complexity of the paragenetic sequence. Younger episodes of mineralization occurred during the later karst events
as suggested by the geological and additional pitchblende U-Pb isotopic data, during the Cretaceous-Tertiary late Yanshanian
tectonic movements and recently. Finally, a comparison of the Sanbaqi uranium deposit with the uranium deposits hosted by
solution collapse breccia pipes of the Colorado Plateau, USA, shows that they have many similarities.
Received: 9 July 1996 / Accepted: 17 January 1997 相似文献
11.
Luke Ootes Steve Goff Valerie A. Jackson Sarah A. Gleeson Robert A. Creaser Iain M. Samson Norman Evensen Louise Corriveau A. Hamid Mumin 《Mineralium Deposita》2010,45(6):549-566
The timing of Cu–Mo–U mineralisation at the Nori/RA prospect in the Paleoproterozoic Great Bear magmatic zone has been investigated
using Re–Os molybdenite and 40Ar–39Ar biotite geochronology. The Re–Os molybdenite ages presented are the first robust sulphide mineralisation ages derived from
the Great Bear magmatic zone. Cu–Mo–U mineralisation is hosted in early to syn-deformational hydrothermal veins consisting
of quartz and K-feldspar or more commonly tourmaline-biotite-quartz-K-feldspar, with associated wall-rock alteration assemblages
being predominantly biotite. Sulphide and oxide minerals consist of chalcopyrite, molybdenite and uraninite with lesser pyrite
and magnetite. Elevated light rare earth elements and tungsten concentrations associated with the Cu–Mo–U mineralisation have
also been reported at the prospect by previous workers. Molybdenite and uraninite occur intimately in dravitic tourmaline
growth zones and at grain margins, attesting to their syngenetic nature (with respect to hydrothermal veining). Two molybdenite
separates yield Re–Os model ages of 1,874.4 ± 8.7 (2σ) and 1,872.4 ± 8.8 Ma (2σ) with a weighted average model age of 1,873.4 ± 6.1 Ma (2σ). Laser step heating of biotite from the marginal alteration of the wall-rock adjacent to the veins yields a 40Ar–39Ar maximum cooling age of 1,875 ± 8 Ma (MSWD = 3.8; 2σ), indistinguishable from the Re–Os molybdenite model age and a previously dated ‘syn-tectonic’ aplitic dyke in the region.
Dravitic tourmaline hosts abundant primary liquid–vapour–solid-bearing fluid inclusions. Analytical results indicate liquid–vapour
homogenisation at >260°C constraining the minimum temperature of mineralisation. The solids, which are possibly trapped, did
not homogenise with the liquid–vapour by 400°C. Salinities in the inclusions are variable. Raman spectra identify that at
least some of the solids are calcite and anhydrite. Raman spectra also confirm the vapour phases contain some CO2; whereas clathrates or CH4 was not observed or detected. Quartz grains only host secondary fluid inclusions, which fluoresce under ultraviolet light,
indicating trapped hydrocarbons. We speculate that these resulted from Phanerozoic fluid circulation through the Proterozoic
basement. The collective interpretation of the age, hydrothermal character and associated metals, high temperature and variable
salinity suggests that the Nori/RA Cu–Mo–U mineralisation can be linked with the earliest stages of plutonism in the Great
Bear magmatic zone. From a regional perspective, the mineralisation may pre-date the extensive multi-element mineralisation
now recognised as part of the iron oxide copper–gold (IOCG) spectrum of deposits. As IOCG provinces generally contain a variety
of mineralisation styles, we interpret this as the earliest phase of the extensive mineralising system. 相似文献
12.
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
13.
Isotope geochemistry of ore fluids for the Dongsheng sandstone-type uranium deposit, China 总被引:2,自引:1,他引:2
The Dongsheng sandstone-type uranium deposit is one of the large-sized sandstone-type uranium deposits discovered in the northern part of the Ordos Basin of China in recent years. Geochemical characteristics of the Dongsheng uranium deposit are significantly different from those of the typical interlayered oxidized sandstone-type uranium ore deposits in the region of Middle Asia. Fluid inclusion studies of the uranium deposit showed that the uranium ore-forming temperatures are within the range of 150–160℃. Their 3He/4He ratios are within the range of 0.02–1.00 R/Ra, about 5–40 times those of the crust. Their 40Ar/36Ar ratios vary from 584 to 1243, much higher than the values of atmospheric argon. The δ18OH2O and δD values of fluid inclusions from the uranium deposit are -3.0‰– -8.75‰ and -55.8‰– -71.3‰, respectively, reflecting the characteristics of mixed fluid of meteoric water and magmatic water. The δ18OH2O and δD values of kaolinite layer at the bottom of the uranium ore deposit are 6.1‰ and -77‰, respectively, showing the characteristics of magmatic water. The δ13CV-PDB and δ18OH2O values of calcite veins in uranium ores are -8.0‰ and 5.76‰, respectively, showing the characteristics of mantle source. Geochemical characteristics of fluid inclusions indicated that the ore-formation fluid for the Dongsheng uranium deposit was a mixed fluid of meteoric water and deep-source fluid from the crust. It was proposed that the Jurassic-Cretaceous U-rich metamorphic rocks and granites widespread in the northern uplift area of the Ordos Basin had been weathered and denudated and the ore-forming elements, mainly uranium, were transported by meteoric waters to the Dongsheng region, where uranium ores were formed. Tectonothermal events and magmatic activities in the Ordos Basin during the Mesozoic made fluids in the deep interior and oil/gas at shallow levels upwarp along the fault zone and activated fractures, filling into U-bearing clastic sandstones, thus providing necessary energy for the formation of uranium ores. 相似文献
14.
Ian Cartwright Ian S. Buick Roland Maas 《Contributions to Mineralogy and Petrology》1997,128(4):335-351
The Jervois region of the Arunta Inlier, central Australia, contains para- and orthogneisses that underwent low-pressure
amphibolite facies metamorphism (P = 200–300 MPa, T = 520–600 °C). Marble layers cut by metre-wide quartz + garnet ± epidote veins comprise calcite, quartz, epidote, clinopyroxene,
grandite garnet, and locally wollastonite. The marbles also contain locally discordant decimetre-thick garnet and epidote
skarn layers. The mineral assemblages imply that the rocks were infiltrated by water-rich fluids (XCO2 = 0.1–0.3) at ∼600 °C. The fluids were probably derived from the quartz-garnet vein systems that represent conduits for fluids
exsolved from crystallizing pegmatites emplaced close to the metamorphic peak. At one locality, the marble has calcite (Cc)
δ18O values of 9–18‰ and garnet (Gnt) δ18O values of 10–14‰. The δ18O(Gnt) values are only poorly correlated with δ18O(Cc), and the δ18O values of some garnet cores are higher than the rims. The isotopic disequilibrium indicates that garnet grew before the
δ18O values of the rock were reset. The marbles contain ≤15% garnet and, for water-rich fluids, garnet-forming reactions are
predicted to propagate faster than O-isotopes are reset. The Sm-Nd and Pb-Pb ages of garnets imply that fluid flow occurred
at 1750–1720 Ma. There are no significant age differences between garnet cores and rims, suggesting that fluid flow was relatively
rapid. Texturally late epidote has δ18O values of 1.5–6.2‰ implying δ18O(H2O) values of 2–7‰. Waters with such low-δ18O values are probably at least partly meteoric in origin, and the epidote may be recording the late influx of meteoric water
into a cooling hydrothermal system.
Received: 29 April 1996 / Accepted: 12 March 1997 相似文献
15.
Summary Re–Os molybdenite ages from the exocontact of the Hnilec granite-greisen body provide temporal constraints for tin, tungsten
and molybdenite mineralisation in the Gemeric Superunit, Slovakia. Two molybdenite separates were taken from a representative
sample of the Sn–W–Mo mineralisation at Hnilec and their Re–Os ages of 262.2 ± 0.9 and 263.8 ± 0.8 Ma (2-sigma) are in excellent
agreement. The obtained Re–Os molybdenite ages are similar to recent but less precise electron microprobe monazite (276 ±
13 Ma) and U–Pb single zircon (250 ± 18 Ma) ages from the Hnilec granite intrusion, supporting a granite-related greisen origin
for the Sn–W–Mo mineralisation. Our precise Re–Os molybdenite ages resolve the long time controversy over the timing of high-temperature
mineralisation in the Gemeric Superunit. These Permian ages eliminate suggestions of an Alpine age. The sulphur isotope composition
of the studied molybdenite is δ34S(CDT) = 1.71 ± 0.2‰ and is consistent with a magmatic sulphur source. Field observations indicate the lack of a broad contact aureole
in the vicinity of the Hnilec granite body. Shallow level granite emplacement in schistose host rocks was accompanied by alteration
and formation of tin-tungsten greisen in the upper part of the granite and exocontact molybdenite mineralisation, both commonly
lacking in other granite bodies within the Gemeric Superunit. 相似文献
16.
Diopside-rich, skarn-hosted, copper–gold ore derived primarily from carbonaceous metapelites at Mount Elliott forms a distinctive
member of the spectrum of Cu–Au–(Fe oxide) deposit styles in the Cloncurry district of the Paleoproterozoic to Mesoproterozoic
Mount Isa Block. The mine sequence is a package of carbonaceous metapelites and metagreywackes containing amphibolites derived
from tholeiitic basic rocks. A 40Ar–39Ar age spectrum with an extensive plateau-like segment at 1,510 ± 3 Ma from an actinolite associated with sulfides is taken
to represent the age of mineralization and is identical within error to the ages of most of the nearby batholithic granitoids.
The mine sequence is locally intruded by 1- to 10-m-thick late- to post-tectonic trachyandesite dykes, which were emplaced
during the hydrothermal activity that created the orebodies and have affinities with the regional high potassium “Eureka”
supersuite granitoids. Stable isotope data are consistent with dominantly magmatic fluids during mineralization and the regionally
distinctive skarn (Ca–Mg) and Cu–Au–Ni–Co–Te–Se (low Pb–Zn–Ag–Sb) chalcophile element associations may reflect a primitive
magmatic fluid source and/or leaching of these elements from country rocks. Mount Elliott is an unusual skarn deposit characterized
by pronounced early albitization (K–Fe–Mg depletion) of the host rocks succeeded by predominantly open-space deposition of
sodic diopside ± actinolite ± scapolite ± andradite ± magnetite ± sulfides ± apatite ± allanite ± tourmaline ± calcite. The
Ca–Fe–Mg(–Na)-rich (manganese-poor) chemistry was imposed from the fluid phase in the absence of carbonate-rich protoliths.
Immobile trace element (Ti, Zr, Nb) geochemistry shows that Mount Elliott skarns formed in both metasedimentary and mafic
metavolcanic host rocks, but the former are the main hosts of ore in upper and lower ore zones that represent most of the
resource. Banded skarns derived from a distinct calc-silicate/marble package at the nearby SWAN prospect have higher Nb/TiO2 and Zr/TiO2 ratios than the Mount Elliott metasediment-derived skarns, consistent with different provenance of the detrital components
in the two sequences. Medium- to coarse-grained massive skarn and skarn breccia in the Mount Elliott lower ore zone formed
in pelites and the trachyandesite dykes are the only intrusive rocks that could be genetically related to the mineralization
in the immediate vicinity of the orebodies.
Received: 1 September 1999 / Accepted: 28 September 2000 相似文献
17.
Lead isotope ratios of galena from the carbonate-hosted massive sulphide deposits of Kabwe (Pb-Zn) and Tsumeb (Pb-Zn-Cu)
in Zambia and Namibia, respectively, have been measured and found to be homogeneous and characteristic of upper crustal source
rocks. Kabwe galena has average isotope ratios of 206/204Pb = 17.997 ± 0.007, 207/204Pb = 15.713 ± 0.010 and 208/204Pb = 38.410 ± 0.033. Tsumeb galena has slightly higher 206/204Pb (18.112 ± 0.035) and slightly lower 207/204Pb (15.674 ± 0.016) and 208/204Pb (38.276 ± 0.073) ratios than Kabwe galena. The isotopic differences are attributed to local differences in the age and
composition of the respective source rocks for Kabwe and Tsumeb. The homogeneity of the ore lead in the two epigenetic deposits
suggests lead sources of uniform isotopic composition or, alternatively, thorough mixing of lead derived from sources with
relatively similar isotopic compositions. Both deposits have relatively high 238U/204Pb ratios of 10.31 and 10.09 for Kabwe and Tsumeb galenas, respectively. These isotope ratios are considered to be typical
of the upper continental crust in the Damaran-Lufilian orogenic belt, as also indicated by basement rocks and Cu-Co sulphides
in stratiform Katangan metasediments which have a mean μ-value of 10.25 ± 0.12 in the Copperbelt region of Zambia and the
Democratic Republic of Congo (formerly Zaire). The 232Th/204Pb isotope ratios of 43.08 and 40.42 for Kabwe and Tsumeb suggest Th-enriched source regions with 232Th/235U (κ-values) of 4.18 and 4.01, respectively. Model isotopic ages determined for the Kabwe (680 Ma) and Tsumeb (530 Ma) deposits
indicate that the timing of the mineralisation was probably related to phases of orogenic activity associated with the Pan-African
Lufilian and Damaran orogenies, respectively. Galena from the carbonate-hosted Kipushi Cu-Pb-Zn massive sulphide deposit in
the Congo also has homogeneous lead isotope ratios, but its isotopic composition is comparable to that of the average global
lead evolution curve for conformable massive sulphide deposits. The μ (9.84) and κ (3.69) values indicate a significant mantle
component, and the isotopic age of the Kipushi deposit (456 Ma) suggests that the emplacement of the mineralisation was related
to a post-tectonic phase of igneous activity in the Lufilian belt. The isotope ratios (206/204Pb, 207/204Pb, 208/204Pb) of the three deposits are markedly different from the heterogeneous lead ratios of the Katangan Cu-Co stratiform mineralisation
of the Copperbelt as well as those of the volcanogenic Nampundwe massive pyrite deposit in the Zambezi belt which typically
define radiogenic linear trends on lead-lead plots. The host-rock dolomite of the Kabwe deposit also has homogeneous lead
isotope ratios identical to the ore galena. This observation indicates contamination of the Kabwe Dolomite Formation with
ore lead during mineralisation.
Received: 8 September 1997 / Accepted: 21 August 1998 相似文献
18.
C. O'Reilly G. R. T. Jenkin M. Feely D. H. M. Alderton A. E. Fallick 《Contributions to Mineralogy and Petrology》1997,129(2-3):120-142
Fluid inclusions in granite quartz and three generations of veins indicate that three fluids have affected the Caledonian
Galway Granite. These fluids were examined by petrography, microthermometry, chlorite thermometry, fluid chemistry and stable
isotope studies. The earliest fluid was a H2O-CO2-NaCl fluid of moderate salinity (4–10 wt% NaCl eq.) that deposited late-magmatic molybdenite mineralised quartz veins (V1) and formed the earliest secondary inclusions in granite quartz. This fluid is more abundant in the west of the batholith,
corresponding to a decrease in emplacement depth. Within veins, and to the east, this fluid was trapped homogeneously, but
in granite quartz in the west it unmixed at 305–390 °C and 0.7–1.8 kbar. Homogeneous quartz δ18O across the batholith (9.5 ± 0.4‰n = 12) suggests V1 precipitation at high temperatures (perhaps 600 °C) and pressures (1–3 kbar) from magmatic fluids. Microthermometric data
for V1 indicate lower temperatures, suggesting inclusion volumes re-equilibrated during cooling. The second fluid was a H2O-NaCl-KCl, low-moderate salinity (0–10 wt% NaCl eq.), moderate temperature (270–340 °C), high δD (−18 ± 2‰), low δ18O (0.5–2.0‰) fluid of meteoric origin. This fluid penetrated the batholith via quartz veins (V2) which infill faults active during post-consolidation uplift of the batholith. It forms the most common inclusion type in
granite quartz throughout the batholith and is responsible for widespread retrograde alteration involving chloritization of
biotite and hornblende, sericitization and saussuritization of plagioclase, and reddening of K-feldspar. The salinity was
generated by fluid-rock interactions within the granite. Within granite quartz this fluid was trapped at 0.5–2.3 kbar, having
become overpressured. This fluid probably infiltrated the Granite in a meteoric-convection system during cooling after intrusion,
but a later age cannot be ruled out. The final fluid to enter the Granite and its host rocks was a H2O-NaCl-CaCl2-KCl fluid with variable salinity (8–28 wt% NaCl eq.), temperature (125–205 °C), δD (−17 to −45‰), δ18O (−3 to + 1.2‰), δ13CCO2 (−19 to 0‰) and δ34Ssulphate (13–23‰) that deposited veins containing quartz, fluorite, calcite, barite, galena, chalcopyrite sphalerite and pyrite (V3). Correlations of salinity, temperature, δD and δ18O are interpreted as the result of mixing of two fluid end-members, one a high-δD (−17 to −8‰), moderate-δ18O (1.2–2.5‰), high-δ13CCO2 (> −4‰), low-δ34Ssulphate (13‰), high-temperature (205–230 °C), moderate-salinity (8–12 wt% NaCl eq.) fluid, the other a low-δD (−61 to −45‰), low-δ18O (−5.4 to −3‰), low-δ13C (<−10‰), high-δ34Ssulphate (20–23‰) low-temperature (80–125 °C), high-salinity (21–28 wt% NaCl eq.) fluid. Geochronological evidence suggests V3 veins are late Triassic; the high-δD end-member is interpreted as a contemporaneous surface fluid, probably mixed meteoric
water and evaporated seawater and/or dissolved evaporites, whereas the low-δD end-member is interpreted as a basinal brine
derived from the adjacent Carboniferous sequence. This study demonstrates that the Galway Granite was a locus for repeated
fluid events for a variety of reasons; from expulsion of magmatic fluids during the final stages of crystallisation, through
a meteoric convection system, probably driven by waning magmatic heat, to much later mineralisation, concentrated in its vicinity
due to thermal, tectonic and compositional properties of granite batholiths which encourage mineralisation long after magmatic
heat has abated.
Received: 3 April 1996 / Accepted: 5 May 1997 相似文献
19.
The Lengenbach Pb-Zn-As-Tl-Ba mineralisation is located in Triassic dolostones of the Penninic zone in the Swiss Alps where
Alpine metamorphism reached upper greenschist to lower amphibolite grade. Geochemical data are used to constrain the origin
of this unique occurrence. Two metamorphic redox environments are present: the As(III)-rich zone is controlled by barite-pyrite
while the reduced zone contains graphite or pyrrhotite-pyrite and formally zerovalent As. The As(III)-rich zone is characterised
by a mineral assemblage consistent with fO2 in the stability field of barite+pyrite. An As-(Pb, Tl)-rich sulphide melt coexisted with a hydrothermal fluid at >kk300 °C
in this zone. Mineralised dolostones are anomalous in As, Pb, Ag, Tl, Hg, Zn, Ba, Cd, Fe, Cu, Mo, U, V, B, Ga, Cr and possibly
Sn and Au (in order of decreasing enrichment). As, Pb and Zn are present in the 0.1 to 1% range, Tl and Ag reach several hundred
ppm. Uraninite is concentrated in silicate-rich bands and yields a late Alpine U-Pb age of 18.5±0.5 Ma. Pb- and S isotopic
variations are interpreted by metamorphic overprinting and re-equilibration within an isochemically metamorphosed mineralisation.
Hydrothermal sulphides are more strongly affected by uranogenic Pb than massive Pb-As-sulphides representing a former sulphide
melt. The least overprinted mineralisation is characterised by 206Pb/204Pb U003U=18.44−18.56, 207Pb/204Pb=15.60−15.75, 208Pb/204Pb =38.44−38.84 and δ34S (sulphide)=−25±2‰. S isotopic variations are largely a result of sulphide-sulphate re-equilibration yielding temperatures
of 450± 30 °C. 87Sr/86Sr ratios of mineralised samples are lower than or equal to host dolostones, precluding major infiltration of basement-derived
fluids during Alpine metamorphism. The Sr source (87Sr/86Sr close to 0.708) probably was seawater with a radiogenic, detrital mineral component. The genesis of the unique Lengenbach
mineralisation is interpreted as the result of isochemical metamorphic overprinting of a carbonate hosted stratiform sulphide
mineralisation. Well-crystallised sulphide minerals in fissures and druses formed during retrograde cooling of a sulphide
melt in equilibrium with a hydrothermal fluid. The primary mineralisation was probably formed at or close below the sea floor
and fed by sulphide-poor hydrothermal fluids. Sulphide was largely derived from seawater by open system bacterial sulphate
reduction. U, V and Mo may be seawater-derived.
Received: 1 February 1995/Accepted: 10 January 1996 相似文献
20.
The Chelopech deposit is one of the largest European gold deposits and is located 60 km east of Sofia, within the northern
part of the Panagyurishte mineral district. It lies within the Banat–Srednegorie metallogenic belt, which extends from Romania
through Serbia to Bulgaria. The magmatic rocks define a typical calc-alkaline suite. The magmatic rocks surrounding the Chelopech
deposit have been affected by propylitic, quartz–sericite, and advanced argillic alteration, but the igneous textures have
been preserved. Alteration processes have resulted in leaching of Na2O, CaO, P2O5, and Sr and enrichment in K2O and Rb. Trace element variation diagrams are typical of subduction-related volcanism, with negative anomalies in high field
strength elements (HFSE) and light element, lithophile elements. HFSE and rare earth elements were relatively immobile during
the hydrothermal alteration related to ore formation. Based on immobile element classification diagrams, the magmatic rocks
are andesitic to dacitic in compositions. Single zircon grains, from three different magmatic rocks spanning the time of the
Chelopech magmatism, were dated by high-precision U–Pb geochronology. Zircons of an altered andesitic body, which has been
thrust over the deposit, yield a concordant 206Pb/238U age of 92.21 ± 0.21 Ma. This age is interpreted as the crystallization age and the maximum age for magmatism at Chelopech.
Zircon analyses of a dacitic dome-like body, which crops out to the north of the Chelopech deposit, give a mean 206Pb/238U age of 91.95 ± 0.28 Ma. Zircons of the andesitic hypabyssal body hosting the high-sulfidation mineralization and overprinted
by hydrothermal alteration give a concordant 206Pb/238U age of 91.45 ± 0.15 Ma. This age is interpreted as the intrusion age of the andesite and as the maximum age of the Chelopech
epithermal high-sulfidation deposit. 176Hf/177Hf isotope ratios of zircons from the Chelopech magmatic rocks, together with published data on the Chelopech area and the
about 92-Ma-old Elatsite porphyry–Cu deposit, suggest two different magma sources in the Chelopech–Elatsite magmatic area.
Magmatic rocks associated with the Elatsite porphyry–Cu deposit and the dacitic dome-like body north of Chelopech are characterized
by zircons with ɛHfT90 values of ∼5, which suggest an important input of mantle-derived magma. Some zircons display lower ɛHfT90 values, as low as −6, and correlate with increasing 206Pb/238U ages up to about 350 Ma, suggesting assimilation of basement rocks during magmatism. In contrast, zircon grains in andesitic
rocks from Chelopech are characterized by homogeneous 176Hf/177Hf isotope ratios with ɛHfT90 values of ∼1 and suggest a homogeneous mixed crust–mantle magma source. We conclude that the Elatsite porphyry–Cu and the
Chelopech high-sulfidation epithermal deposits were formed within a very short time span and could be partly contemporaneous.
However, they are related to two distinct upper crustal magmatic reservoirs, and they cannot be considered as a genetically
paired porphyry–Cu and high-sulfidation epithermal related to a single magmatic–hydrothermal system centered on the same intrusion. 相似文献