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1.
RANDIVE K R KORAKOPPA M M MULEY S V VARADE A M KHANDARE H W LANJEWAR S G TIWARI R R ARADHI K K 《Journal of Earth System Science》2015,124(1):213-225
Journal of Earth System Science - Green mica (fuchsite or chromian-muscovite) is reported worldwide in the Archaean metasedimentary rocks, especially quartzites. They are generally associated with... 相似文献
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《Ore Geology Reviews》2010,37(4):333-349
Gold mineralization at Jonnagiri, Dharwar Craton, southern India, is hosted in laminated quartz veins within sheared granodiorite that occur with other rock units, typical of Archean greenstone–granite ensembles. The proximal alteration assemblage comprises of muscovite, plagioclase, and chlorite with minor biotite (and carbonate), which is distinctive of low- to mid-greenschist facies. The laminated quartz veins that constitute the inner alteration zone, contain muscovite, chlorite, albite and calcite. Using various calibrations, chlorite compositions in the inner and proximal zones yielded comparable temperature ranges of 263 to 323 °C and 268 to 324 °C, respectively. Gold occurs in the laminated quartz veins both as free-milling native metal and enclosed within sulfides. Fluid inclusion microthermometry and Raman spectroscopy in quartz veins within the sheared granodiorite in the proximal zone and laminated auriferous quartz veins in inner zone reveal the existence of a metamorphogenic aqueous–gaseous (H2O–CO2–CH4 + salt) fluid that underwent phase separation and gave rise to gaseous (CO2–CH4), low saline (~ 5 wt.% NaCl equiv.) aqueous fluids. Quartz veins within the mylonitized granodiorites and the laminated veins show broad similarity in fluid compositions and P–T regime. Although the estimated P–T range (1.39 to 2.57 kbar at 263 to 323 °C) compare well with the published P–T values of other orogenic gold deposits in general, considerable pressure fluctuation characterize gold mineralization at Jonnagiri. Factors such as fluid phase separation and fluid–rock interaction, along with a decrease in f(O2), were collectively responsible for gold precipitation, from an initial low-saline metamorphogenic fluid. Comparison of the Jonnagiri ore fluid with other lode gold deposits in the Dharwar Craton and major granitoid-hosted gold deposits in Australia and Canada confirms that fluids of low saline aqueous–carbonic composition with metamorphic parentage played the most dominant role in the formation of the Archean lode gold systems. 相似文献
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A series of experiments was conducted on the decomposition of natural and chemically mixed chlorites to examine the stable hydrous phases in the MgO–FeO–Al2O3–SiO2–H2O (MFASH) system under 5–12 GPa and 700–1100 °C. The upper pressure and temperature limits of the stability region of chlorite are consistent with those observed in previous studies. The hydrous aluminum bearing pyroxene (phase HAPY) and Mg-sursassite (Sur) were observed just above the temperature stability region of chlorite (Chl); clinohumite (cHm) was observed coexisting with phase HAPY at 6 GPa and 800 °C and coexisting with the 23-Å phase at 7 GPa and 800 °C, which may suggest the transportation of water through Chl → (HAPY → cHm) → 23-Å phase along a relatively warm slab. The 23-Å phase has a wider stability region in the pure MASH system (up to 12 GPa and 1100 °C) than it does in the MFASH system (7–10 GPa, up to 1000 °C). The stability of the 23-Å phase beyond the chlorite breakdown pressure indicates that it may play an important role in transporting water into the deep Earth and even into the mantle transition zone. 相似文献
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Yan-Jun Li Jun-Hao Wei Hua-Yong Chen Jun Tan Le-Bing Fu Gang Wu 《Mineralium Deposita》2012,47(7):763-780
The Maoduan Pb–Zn–Mo deposit is in hydrothermal veins with a pyrrhotite stage followed by a molybdenite and base metal stage. The Re–Os model ages of five molybdenite samples range from 138.6 ± 2.0 to 140.0 ± 1.9 Ma. Their isochron age is 137.7 ± 2.7 Ma. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the nearby exposed Linggen granite porphyry gave a 206Pb/238U age of 152.2 ± 2.2 Ma and the hidden Maoduan monzogranite yielded a mean of 140.0 ± 1.6 Ma. These results suggest that the intrusion of the Maoduan monzogranite and Pb–Zn–Mo mineralization are contemporaneous. δ 34S values of sulfide minerals range from 3.4‰ to 4.8‰, similar to magmatic sulfur. Four sulfide samples have 206Pb/204Pb = 18.252–18.432, 207Pb/204Pb = 15.609–15.779, and 208Pb/204Pb = 38.640–39.431, similar to the age-corrected data of the Maoduan monzogranite. These isotope data support a genetic relationship between the Pb–Zn–Mo mineralization and the Maoduan monzogranite and probably indicate a common deep source. The Maoduan monzogranite has geochemical features similar to highly fractionated I-type granites, such as high SiO2 (73.7–75.2 wt.%) and alkalis (K2O + Na2O = 7.8–8.9 wt.%) and low FeOt (0.8–1.3 wt.%), MgO (~0.3 wt.%), P2O5 (~0.03 wt.%), and TiO2 (~0.2 wt.%). The granitic rocks are enriched in Rb, Th, and U but depleted in Ba, Sr, Nb, Ta, P, and Ti. REE patterns are characterized by marked negative Eu anomalies (Eu/Eu* = 0.2–0.4). The Maoduan monzogranite, having (87Sr/86Sr) t = 0.7169 to 0.7170 and εNd(t) = −13.8 to −13.7, was probably derived from mixing of partial melts from enriched mantle and the Paleoproterozoic Badu group in an extensional tectonic setting. 相似文献
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Élisa Morichon Thierry Allard Daniel Beaufort David Quirt 《Physics and Chemistry of Minerals》2010,37(3):145-152
Natural radiation-induced defects were identified in specimens of sudoite (Al–Mg di-trioctahedral chlorite) related to unconformity-type
uranium deposits at the base of the Athabasca Group (Saskatchewan, Canada), using electron paramagnetic resonance (EPR) spectroscopy
at X- and Q-band frequencies. X-band spectra indicate the presence of a main native defect, named the As-center, whose EPR signal is dominated by an axially distorted spectrum with apparent principal components as follows: g
// = 2,051 and g
⊥ = 2,005, and a secondary defect with apparent component g = 2,025. The study of oriented specimens shows that the main defect has its g
// component perpendicular to the (ab) plane of sudoite. The As-center corresponds to an electron hole located on oxygen atoms of the structure and is likely associated with Si, according
to the lack of hyperfine structure. The As-center in sudoite has EPR parameters similar to the A-center in kaolinite and dickite, and the Ai-center in illite. The saturation behavior of EPR spectra as a function of power demonstrates that native defects of sudoite
are different from those known in other clays, such as kaolinite, dickite or smectite, but are similar to those of illite.
The isochronal annealing data suggest that the main defect in sudoite is stable to more than 300°C. The corresponding defects
characterized in sudoite may have the potential for tracing past radionuclide migration around unconformity-type uranium deposits. 相似文献
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The Wittichen Co–Ag–Bi–U mining area (Schwarzwald ore district, SW Germany) hosts several unconformity-related vein-type mineralizations
within Variscan leucogranite and Permian to Triassic redbeds. The multistage mineralization formed at the intersection of
two fault systems in the last 250 Ma. A Permo-Triassic ore stage I with minor U–Bi–quartz–fluorite mineralization is followed
by a Jurassic to Cretaceous ore stage II with the main Ag and Co mineralization consisting of several generations of gangue
minerals that host the sub-stages of U–Bi, Bi–Ag, Ni–As–Bi and Co–As–Bi. Important ore minerals are native elements, Co and
Ni arsenides, and pitchblende; sulphides are absent. The Miocene ore stage III comprises barite with the Cu–Bi sulfosalts
emplectite, wittichenite and aikinite, and the sulphides anilite and djurleite besides native Bi, chalcopyrite, sphalerite,
galena and tennantite. The mineral-forming fluid system changed from low salinity (<5 wt.% NaCl) at high temperature (around
300°C) in Permian to highly saline (around 25 wt.% NaCl + CaCl2) at lower temperatures (50–150°C) in Triassic to Cretaceous times. Thermodynamic calculations and comparison with similar
mineralizations worldwide show that the Mesozoic ore-forming fluid was alkaline with redox conditions above the hematite–magnetite
buffer. We suggest that the precipitation mechanism for native elements, pitchblende and arsenides is a decrease in pH during
fluid mixing processes. REE patterns in fluorite and the occurrence of Bi in all stages suggest a granitic source of some
ore-forming elements, whereas, e.g. Ag, Co and Ni probably have been leached from the redbeds. The greater importance of Cu
and isotope data indicates that the Miocene ore stage III is more influenced by fluids from the overlying redbeds and limestones
than the earlier mineralization stages. 相似文献
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The Transfiguration Cu–Pb–Zn–Ag deposit, enclosed within reduced grey sandstone, is associated with continental red beds of
the Lower Silurian Robitaille Formation in the Quebec Appalachians, Canada. The Robitaille Formation rests unconformably on
foliated Cambro-Ordovician rocks. The unconformity is locally cut by barite veins. The basal unit of the Robitaille Formation
comprises green wacke and pebble conglomerate, which locally contain calcite nodules. The latter have microstructures characteristic
of alpha-type calcretes, such as “floating” fabrics, calcite-filled fractures (crystallaria) and circumgranular cracks. Massive,
grey sandstone overlies the basal green wacke and pebble conglomerate unit, which is overlain, in turn, by red, fine-grained
sandstone. Mineralisation occurred underneath the red sandstone unit, chiefly in the grey sandstone unit, as disseminated
and veinlet sulphides. Chalcopyrite, the most abundant Cu sulphide, replaced early pyrite. Calcrete, disseminated carbonate
and vein carbonate have stable isotope ratios varying from −7.5‰ to −1.1‰ δ13C and from 14.7‰ to 21.3‰ δ18O. The negative δ13C values indicate the oxidation of organic matter in a continental environment. Sulphur isotope ratios for pyrite, chalcopyrite
and galena vary from −19‰ to 25‰ δ34S, as measured on mineral concentrates by a conventional SO2 technique. Laser-assisted microanalyses (by fluorination) of S isotopes in pyrite show an analogous range in δ34S values, from −21‰ to 25‰. Negative and positive δ34S values are compatible with bacterial sulphate reduction (BSR) in systems open and closed with respect to sulphate. We interpret
similarly high δ34S values for sulphide concentrates (25.1‰) and for vein barite (26.2‰) to result from rapid and complete thermochemical reduction
of pore-water sulphate. Two early to late diagenetic stages of mineralisation best explain the origin of the Transfiguration
deposit. The first stage was characterised by the ponding of groundwater over the Taconian unconformity, recorded by calcrete
and early pyrite formation via BSR in grey sandstone. Early pyrite contains up to 2 wt.% Pb, which is consistent with Pb fixation
by sulphate-reducing bacteria. The second stage (II) is defined by the replacement of early pyrite by chalcopyrite, as well
as by sulphide precipitation via either BSR or thermochemical sulphate reduction (TSR) in grey sandstone. This event resulted
from the synsedimentary fault-controlled percolation and mixing of (1) an oxidising, sulphate-bearing cupriferous fluid migrating
per descensum from the red-bed sequence and (2) a hydrocarbon-bearing fluid migrating per ascensum from the Cambro-Ordovician basement. Mixing between the two fluids led to sulphate reduction, causing Cu sulphide precipitation.
The positive correlation between Cu and Fe3+/Fe2+ bulk rock values suggests that Fe acted as a redox agent during sulphate reduction. Stage II diagenetic fluid migration is
tentatively attributed to the Late Silurian Salinic extensional event. 相似文献
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Liu Han-Lun Han Yi Wang Ke-Yong Li Wen Li Jian Cai Wen-Yan Fu Li-Juan 《Arabian Journal of Geosciences》2018,11(24):1-13
Arabian Journal of Geosciences - Soil toxic metal pollution is one of the most prominent environmental problems in the rapid industrialization of societies because of the considerable harm caused... 相似文献
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New data on platinum mineralization in ores, metasomatic rocks, concentrates, and tailings and wastes of some gold–polymetallic, Au–Bi, Cu–Mo porphyry, Cu–Ni, and titanomagnetite ore deposits and occurrences of the Upper Amur Region are presented. The contents of platinoids, Au and Ag in multimetal ores of gold-polymetallic, Au–Bi, Cu–Mo porphyry, Cu–Ni, and titanomagnetite ore deposits and ore occurrences are given. In addition, recommendations on the necessity of continuing scientific studies, revision, and resampling works in the search for platinoids in other complex ores of deposits and occurrences of the Upper Amur Region are given. 相似文献
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Irene Cantarero Pierre Lanari Olivier Vidal Gemma Alías Anna Travé Vinyet Baqués 《International Journal of Earth Sciences》2014,103(1):165-188
The neoformation of chlorite and K-white mica in fault rocks from two main faults of the central Catalan Coastal Ranges, the Vallès and the Hospital faults, has allowed us to constrain the P–T conditions during fault evolution using thermodynamic modeling. Crystallization of M1 and M2 muscovite and microcline occured as result of deuteric alteration during the exhumation of the pluton (290 °C > T > 370 °C) in the Permian. After that, three tectonic events have been distinguished. The first tectonic event, attributed to the Mesozoic rifting, is characterized by precipitation of M3 and M4 phengite together with chlorite and calcite C1 at temperatures between 190 and 310 °C. The second tectonic event attributed to the Paleogene compression has only been identified in the Hospital fault with precipitation of low-temperature calcite C2. The shortcut produced during inversion of the Vallès fault was probably the responsible for the lack of neoformed minerals within this fault. Finally, the third tectonic event, which is related to the Neogene extension, is characterized in the Vallès fault by a new generation of chlorite, associated with calcite C4 and laumontite, formed at temperatures between 125 and 190 °C in the absence of K-white mica. Differently, the Hospital fault is characterized by the precipitation of calcite C3 during the syn-rift stage at temperatures around 150 °C and by low-temperature fluids precipitating calcites C5, C6 and PC1 during the post-rift stage. During the two extensional events (Mesozoic and Neogene), faults acted as conduits for hot fluids producing anomalous high geothermal gradients (50 °C/km minimum). 相似文献
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Here we report the occurrence of some uncommon mineral assemblages including pääkönenite, aurostibite, native arsenic, native antimony, and native bismuth found in the Baogutu gold deposit in the western Junggar, Xinjiang, NW China. The mineralization could be generally subdivided into two types: the gold-bearing quartz-vein type mineralization and disseminated mineralization in the wall rocks. The sulfide minerals in gold lodes commonly include pyrite, arsenopyrite, marcasite, and stibnite. However, the L7 lode in No. 4 orebody and the L1 lode in No. 11 orebody of the Baogutu gold deposit are quite different in terms of their mineral assemblages. The L7 lode contains native arsenic–quartz veins in shallow levels and stibnite–quartz veins at depth. Gold-bearing minerals (electrum, native gold, and rarely aurostibite) mainly coexist with pääkönenite, stibnite, native arsenic, and native antimony. The crystallization of As- and Sb-bearing minerals was likely to have consumed H2S from the hydrothermal fluid, which probably triggered the precipitation of native gold. The L1 lode consists of several discontinuous sulfide-dominated lensoid orebodies. The massive sulfide ores that produced most of the gold resource are characterized by an intimate association between native bismuth and native gold mineralization. 相似文献
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David M. Evans Finn M. Barrett Hazel M. Prichard Peter C. Fisher 《Mineralium Deposita》2012,47(1-2):175-196
Significant and widespread enrichment of platinum, palladium, and gold has been found within the Nkenja mafic–ultramafic body located in southern Tanzania in the central part of the Ubendian metamorphic belt. This body is dominated by partly serpentinized chromitiferous dunite, wehrlite and olivine clinopyroxenite, which are tectonically intercalated with amphibolitized metagabbro. The dunites contain both disseminated and seam-type chrome spinel with an Al-rich composition. The seams are thin, impersistent and, together with enclosing dunite, often show deformation at granulite facies conditions. Forsterite contents of olivine in the dunite range from 87 to 92?mol%. Clinopyroxene in wehrlite and clinopyroxenite is diopsidic with significant contents of Al and Na. Clinopyroxene forms irregular bands and crosscutting veins in the dunite, as well as occurring as weakly dispersed isolated grains in the dunite. Elevated levels of Pt, Pd and Au occur in all ultramafic rocks, but not amphibolitized metagabbro, and there is a weak correlation between high abundances of platinum-group element (PGE) and chromitites. PGE values are erratically distributed and are associated with trace to minor amounts of disseminated sulphides (pyrrhotite, pentlandite, heazlewoodite, chalcopyrite and bornite). The abundances of all PGE are consistently anomalous, suggesting a primary igneous control by sulphides in ultramafic rock. However, there has evidently been a strong metamorphic and/or hydrothermal overprint on what was probably an original magmatic concentration of PGE-bearing sulphides. Geological mapping and petrological evidence, as well as the style of PGE sulphide mineralization, are consistent with the Nkenja ultramafic body being part of the crustal section of a dismembered Palaeoproterozoic ophiolite. 相似文献
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The Shuangqing Fe–Pb–Zn–Cu deposit is located in the Xiangride County of Qinghai Province, China, and is a typical example of skarn deposits in the East Kunlun Mountains. Skarnization and mineralization took place along the contact zone between Carboniferous carbonates and the concealed Triassic plagiogranite. LA–ICP–MS U–Pb dating of zircons from the plagiogranite has yielded ages of 227.2 ± 1.0 and 226.54 ± 0.97 Ma, which are interpreted as the emplacement age of the plagiogranite. Molybdenites separated from ore-bearing quartz-veins yielded a Re–Os isochron age of 226.5 ± 5.1 Ma. These age data confirm that both intrusion and related skarn mineralization initiated at ~ 227 Ma. Re contents of molybdenite, zircon εHf(t) and 176Hf/177Hf values fall into the ranges 3.31 to 6.58 μg/g, − 8.6 to − 0.0, and 0.282403 to 0.28263850, respectively. The timing of the Shuangqing Fe–Pb–Zn–Cu mineralization coincided with a major change in the stress field in East Kunlun from transpression to extension, related to the partial melting of thickening crustal materials in a post-collisional tectonic setting. 相似文献
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Jian-Wei Li Xin-Fu Zhao Mei-Fu Zhou Paulo Vasconcelos Chang-Qian Ma Xiao-Dong Deng Zorano Sérgio de Souza Yong-Xin Zhao Gang Wu 《Mineralium Deposita》2008,43(3):315-336
The Tongshankou Cu–Mo deposit, located in the westernmost Daye district of the Late Mesozoic Metallogenic Belt along the Middle-Lower
reaches of the Yangtze River, eastern China, consists mainly of porphyry and skarn ores hosted in the Tongshankou granodiorite
and along the contact with the Lower Triassic marine carbonates, respectively. Sensitive high-resolution ion microprobe zircon
U–Pb dating constrains the crystallization of the granodiorite at 140.6 ± 2.4 Ma (1σ). Six molybdenite samples from the porphyry ores yield Re–Os isochron age of 143.8 ± 2.6 Ma (2σ), while a phlogopite sample from the skarn ores yields an 40Ar/39Ar plateau age of 143.0 ± 0.3 Ma and an isochron age of 143.8 ± 0.8 Ma (2σ), indicating an earliest Cretaceous mineralization event. The Tongshankou granodiorite has geochemical features resembling
slab-derived adakites, such as high Sr (740–1,300 ppm) and enrichment in light rare earth elements (REE), low Sc (<10 ppm),
Y (<13.3 ppm), and depletion in heavy REE (<1.2 ppm Yb), and resultant high Sr/Y (60–92) and La/Yb (26–75) ratios. However,
they differ from typical subduction-related adakites by high K, low MgO and Mg#, and radiogenic Sr–Nd–Hf isotopic compositions,
with (87Sr/86Sr)
t
= 0.7062–0.7067, ɛ
Nd(t) = −4.37 to −4.63, (176Hf/177Hf)
t
= 0.282469–0.282590, and ɛ
Hf(t) = −3.3 to −7.6. The geochemical and isotopic data, coupled with geological analysis, indicate that the Tongshankou granodiorite
was most likely generated by partial melting of enriched lithospheric mantle that was previously metasomitized by slab melts
related to an ancient subduction system. Magmas derived from such a source could have acquired a high oxidation state, as
indicated by the assemblage of quartz–magnetite–titanite–amphibole–Mg-rich biotite in the Tongshankou granodiorite and the
compositions of magmatic biotite that fall in the field between the NiNiO and magnetite–hematite buffers in the Fe3+–Fe2+–Mg diagram. Sulfur would have been present as sulfates in such highly oxidized magmas, so that chalcophile elements Cu and
Mo were retained as incompatible elements in the melt, contributing to subsequent mineralization. A compilation of existing
data reveals that porphyry and porphyry-related Cu–Fe–Au–Mo mineralization from Daye and other districts of the Metallogenic
Belt along the Middle-Lower reaches of the Yangtze River took place coevally in the Early Cretaceous and was related to an
intracontinental extensional environment, distinctly different from the arc-compressive setting of the Cenozoic age that has
been responsible for the emplacement of most porphyry Cu deposits of the Pacific Rim. 相似文献
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Milos Island contains several epithermal deposits (e.g., Profitis Ilias–Chondro Vouno Pb–Zn–Ag–Au–Te–Cu, Triades–Galana–Agathia–Kondaros Pb–Zn–Ag–Bi–W–Mo ± Cu–Au, and Katsimoutis–Kondaros–Vani Pb–Zn–Ag–Mn) of Late Pliocene to Early Pleistocene age. These deposits are hosted in calc-alkaline volcanic rocks emplaced as a result of three successive magma pulses in an emergent volcanic edifice: submarine rhyolitic to rhyodacitic cryptodomes at ca. 2.7. Ma (Profitis Ilias–Chondro Vouno), submarine to subaerial andesite to dacite domes at ca. 2.2 to 1.5 Ma (Triades–Galana–Kondaros–Katsimouti–Vani). Hydrothermal alteration of the volcanic rocks includes advanced argillic- (both hypogene and steam-heated), argillic, phyllic, adularia-sericite and propylitic types. In the northern sector (Triades–Galana–Agathia–Kondaros), initial magma degassing derived from andesitic–dacitic intrusives along NE–SW to E–W trending faults resulted in the development of pre-ore hypogene advanced argillic alteration (dickite, alunite, ± diaspore, pyrophyllite, halite, and pyrite) in a submarine environment. Mineralogical data indicate common features among the Profitis Ilias–Chondro Vouno, Kondaros–Katsimoutis–Vani and Triades–Galana mineralized centers, all of which are characterized by the presence of galena, Fe-poor sphalerite, and chalcopyrite as well as abundant barite, adularia, sericite and, to a lesser extent, calcite, which are typical of intermediate-sulfidation epithermal type deposits. Locally, at Triades–Galana and Kondaros–Agathia, high-sulfidation conditions prevailed as suggested by the presence of coexisting enargite and covellite. The high silver and gold content of the western Milos deposits is derived from Ag-bearing sulfosalts (polybasite, pearceite, pyrargyrite, freibergite) and tellurides. Gold at Profitis Ilias, both as native gold and silver-gold tellurides, is present in base-metal precipitates within multicomponent blebs, which recrystallized to form hessite, petzite, altaite, coloradoite, and native gold. Mineralogical evidence (e.g. microchimney structures, copper sulfides, widespread occurrence of barite, aragonite) suggests that precious metal mineralization in western Milos mineralization formed in a submarine setting.We present information on the surface distribution of Au, Ag, Cu, Pb, Zn, As, Sb, Hg, Mo, Bi, W and Cd at western Milos. Gold is enriched at Profitis Ilias–Chondro Vouno deposits and to a lesser extent at Triades–Galana. Arsenic is absent from the southern sector but shows elevated concentrations together with molybdenum, bismuth and tungsten at the northern sector (Triades–Galana, Vani deposits). The differences in precious and base metal abundances may be related to the depths at which the deposits are exposed, and/or different sources of magma. The metal signatures of the Triades–Galana and Agathia–Kondaros–Katsimouti–Vani (Mo–Bi–W–As–Hg–Ag–Au) occurrences compared to Profitis Ilias (Te–Au–Ag) reflect different sources of magma (dacite–rhyodacite for Profitis Ilias, andesite–dacite for Triades–Galana, and dacite for Kondaros–Katsimoutis). The enrichment of Te, Mo, W, and Bi in the deposits is a strong indication of a direct magmatic contribution of these metals.At western Milos, precious and base-metal vein mineralization was deposited during episodic injection of magmatic volatiles and dilution of the hydrothermal fluids by seawater. The mineralization represents seafloor/sub-seafloor precipitation of sulfides that formed in stockwork zones. Base and precious metal mineralization formed from intermediate- to high-sulfidation state fluids and mostly under boiling conditions as indicated by the widespread occurrence of adularia associated with metallic mineralization. We speculate that the widespread occurrence of boiling and the shallow depth of the precious- and base-metal emplacement prevented the formation of seafloor massive sulfides. 相似文献