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1.
Most skarn deposits are closely related to granitoids that intruded into carbonate rocks. The Cihai (>100 Mt at 45% Fe) is a deposit with mineral assemblages and hydrothermal features similar to many other typical skarn deposits of the world. However, the iron orebodies of Cihai are mainly hosted within the diabase and not in contact with carbonate rocks. In addition, some magnetite grains exhibit unusual relatively high TiO2 content. These features are not consistent with the typical skarn iron deposit. Different hydrothermal and/or magmatic processes are being actively investigated for its origin. Because of a lack of systematic studies of geology, mineral compositions, fluid inclusions, and isotopes, the genetic type, ore genesis, and hydrothermal evolution of this deposit are still poorly understood and remain controversial.The skarn mineral assemblages are the alteration products of diabase. Three main paragenetic stages of skarn formation and ore deposition have been recognized based on petrographic observations, which show a prograde skarn stage (garnet-clinopyroxene-disseminated magnetite), a retrograde skarn stage (main iron ore stage, massive magnetite-amphibole-epidote ± ilvaite), and a quartz-sulfide stage (quartz-calcite-pyrite-pyrrhotite-cobaltite).Overall, the compositions of garnet, clinpyroxene, and amphibole are consistent with those of typical skarn Fe deposits worldwide. In the disseminated ores, some magnetite grains exhibit relatively high TiO2 content (>1 wt.%), which may be inherited from the diabase protoliths. Some distinct chemical zoning in magnetite grains were observed in this study, wherein cores are enriched in Ti, and magnetite rims show a pronounced depletion in Ti. The textural and compositional data of magnetite confirm that the Cihai Fe deposit is of hydrothermal origin, rather than associated with iron rich melts as previously suggested.Fluid inclusions study reveal that, the prograde skarn (garnet and pyroxene) formed from high temperature (520–600 °C), moderate- to high-salinity (8.1–23.1 wt.% NaCl equiv, and >46 wt.% NaCl equiv) fluids. Massive iron ore and retrograde skarn assemblages (amphibole-epidote ± ilvaite) formed under hydrostatic condition after the fracturing of early skarn. Fluids in this stage had lower temperature (220°–456 °C) and salinity (8.4–16.3 wt.% NaCl equiv). Fluid inclusions in quartz-sulfide stage quartz and calcite also record similar conditions, with temperature range from 128° to 367 °C and salinity range from 0.2 to 22.9 wt.% NaCl equiv. Oxygen and hydrogen isotopic data of garnet and quartz suggest that mixing and dilution of early magmatic fluids with external fluids (e.g., meteoric waters) caused a decrease in fluid temperature and salinity in the later stages of the skarn formation and massive iron precipitation. The δ18O values of magnetite from iron ores vary between 4.1 and 8.5‰, which are similar to values reported in other skarn Fe deposits. Such values are distinct from those of other iron ore deposits such as Kiruna-type and magmatic Fe-Ti-V deposits worldwide. Taken together, these geologic, geochemical, and isotopic data confirm that Cihai is a diabase-hosted skarn deposit related to the granitoids at depth. 相似文献
2.
The Zhibula Cu skarn deposit contains 0.32 Mt. Cu metal with an average grade of 1.64% and is located in the Gangdese porphyry copper belt in southern Tibet. The deposit is a typical metasomatic skarn that is related to the interaction of magmatic–hydrothermal fluids and calcareous host rock. Stratiform skarn orebodies occur at the contact between tuff and marble in the Lower Jurassic Yeba Formation. Alteration zones generally grade from a fresh tuff to a garnet-bearing tuff, a garnet pyroxene skarn, and finally to a wollastonite marble. Minor endoskarn alteration zonations are also observed in the causative intrusion, which grade from a fresh granodiorite to a weakly chlorite-altered granodiorite, a green diopside-bearing granodiorite, and to a dark red-brown garnet-bearing granodiorite. Prograde minerals, which were identified by electron probe microanalysis include andradite–grossularite of various colors (e.g., red, green, and yellow) and green diopside. Retrograde metamorphic minerals overprint the prograde skarn, and are mainly composed of epidote, quartz, and chlorite. The ore minerals consist of chalcopyrite and bornite, followed by magnetite, molybdenite, pyrite, pyrrhotite, galena, and sphalerite. Three types of fluid inclusions are recognized in the Zhibula deposit, including liquid-rich two-phase inclusions (type L), vapor-rich two-phase inclusions (type V), and daughter mineral-bearing three-phase inclusions (type S). As the skarn formation evolved from prograde (stage I) to early retrograde (stage II) and later retrograde (stage III), the ore-forming fluids correspondingly evolved from high temperature (405–667 °C), high salinity (up to 44.0 wt.% NaCl equiv.), and high pressure (500–600 bar) to low-moderate temperature (194–420 °C), moderate-high salinity (10.1–18.3 and 30.0–44.2 wt.% NaCl equiv.), and low-moderate pressure (250–350 bar). Isotopic data of δ34S (− 0.1‰ to − 6.8‰, estimated δ34Sfluids = − 0.7‰), δDH2O (− 91‰ to − 159‰), and δ18OH2O (1.5‰ to 9.2‰) suggest that the ore-forming fluid and material came from magmatic–hydrothermal fluids that were associated with Miocene Zhibula intrusions. Fluid immiscibility likely occurred at the stage I and stage II during the formation of the skarn and mineralization. Fluid boiling occurred during the stage III, which is the most important Cu deposition mechanism for the Zhibula deposit. 相似文献
3.
The Hetaoping zinc–lead deposit is located in the northern Baoshan block, Sanjiang region, SW China. The ore deposit comprises massive orebodies in the lower part and lenticular and vein-like orebodies in the upper part, both of which are hosted in the marbleized Upper Cambrian limestone and slate of the Hetaoping Formation. Three mineralization stages of Hetaoping skarn system have been recognized based on petrographic observation, which are pre-ore stage (pyroxene–garnet–actinolite–epidote–magnetite), syn-ore stage (sulfides–quartz–calcite–fluorite), and post-ore stage (calcite–quartz–chlorite). Andradite and hedenbergite are dominant in pre-ore garnet and pyroxene, respectively. Ore minerals consist of mainly pyrite, sphalerite, chalcopyrite, bornite and galena. Three types of fluid inclusions have been identified in Hetaoping, including primary two-phase (A type), primary three-phase (B type) and secondary two-phase (C type) inclusions. Based on fluid inclusion microthermometric study, the fluids forming the Hetaoping skarn minerals and sulfides evolved from high-moderate temperature (255–498 °C) and low-moderate salinity (5.0–18.0 wt.% NaCl equiv) in pre-ore stage, through moderate-low temperature (152–325 °C) and low salinity (0.4–14.2 wt.% NaCl equiv) in syn-ore stage, to low temperature (109–205 °C) and low salinity (0.9–10.0 wt.% NaCl equiv) in post-ore stage. The sulfide δ34S values range from 3.7 to 7.1‰ (mean = 5.2‰, n = 29), indicative of a dominantly magmatic sulfur origin. Silicate and carbonate oxygen isotopes give calculated δ18OH2O ranges of 3.9–11.1‰ in prograde stage, − 0.9 to 4.6‰ in early retrograde stage, and − 1.3 to 2.9‰ in late retrograde stage (syn-ore stage), The oxygen isotope data reveal that the prograde fluid in Hetaoping could be primarily magmatic, which has been mixed significantly with meteoric water in the late retrograde stage. Such a fluid mixing process is considered to be a key factor controlling ore precipitation. 相似文献
4.
The Baishan porphyry Mo deposit formed in the Middle Triassic in Eastern Tianshan, Xinjiang, northwestern China. Mo mineralization is associated with the Baishan monzogranite and granite porphyry stocks, mainly presenting as various types of hydrothermal veinlets in alerted wall rocks, with potassic, phyllic, propylitic, and fluorite alteration. The ore-forming process can be divided into four stages: stage I K-feldspar–quartz–pyrite veinlets, stage II quartz–molybdenite ± pyrite veinlets, stage III quartz–polymetallic sulfide veinlets and stage IV barren quartz–calcite veins. Four types of fluid inclusions (FIs) can be distinguished in the Baishan deposit, namely, liquid-rich two-phase (L-type), vapor-rich two-phase (V-type), solid-bearing multi-phase (S-type) and mono-phase vapor (M-type) inclusions, but only the stage I quartz contains all types of FIs. The stages II and III quartz have three types of FIs, with exception of M-type. In stage IV quartz minerals, only the L-type inclusions can be observed. The FIs in quartz of stages I, II, III and IV are mainly homogenized at temperatures of 271–468 °C, 239–349 °C, 201–331 °C and 134–201 °C, with salinities of 2.2–11.6 wt.% NaCl equiv., 1.1–10.2 wt.% NaCl equiv., 0.5–8.9 wt.% NaCl equiv. and 0.2–5.7 wt.% NaCl equiv., respectively. The ore-forming fluids of the Baishan deposit are characterized by high temperature, moderate salinity and relatively reduced condition, belonging to a H2O–NaCl ± CH4 ± CO2 system. Hydrogen and oxygen isotopic compositions of quartz indicate that the ore-forming fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials came predominantly from a deep-seated magma source from the lower continental crust. The Mo mineralization in the Baishan deposit is estimated to have occurred at a depth of no less than 4.7 km, and the decrease in temperature and remarkable transition of the redox condition (from alkalinity to acidity) of ore-forming fluids were critical for the formation of the Baishan Mo deposit. 相似文献
5.
The Phu Lon skarn Cu–Au deposit is located in the northern Loei Fold Belt (LFB), Thailand. It is hosted by Devonian volcano-sedimentary sequences intercalated with limestone and marble units, intruded by diorite and quartz monzonite porphyries. Phu Lon is a calcic skarn with both endoskarn and exoskarn facies. In both skarn facies, andradite and diopside comprise the main prograde skarn minerals, whereas epidote, chlorite, tremolite, actinolite and calcite are the principal retrograde skarn minerals.Four types of fluid inclusions in garnet were distinguished: (1) liquid-rich inclusions; (2) daughter mineral-bearing inclusions; (3) salt-saturated inclusions; and (4) vapor-rich inclusions. Epidote contains only one type of fluid inclusion: liquid-rich inclusions. Fluid inclusions associated with garnet (prograde skarn stage) display high homogenization temperatures and moderate salinities (421.6–468.5 °C; 17.4–23.1 wt% NaCl equiv.). By contrast, fluid inclusions associated with epidote (retrograde skarn stage) record lower homogenization temperatures and salinities (350.9–399.8 °C; 0.5–8 wt% NaCl equiv.). These data suggest a possible mixing of saline magmatic fluids with external, dilute fluid sources (e.g., meteoric fluids), as the system cooled. Some fluid inclusions in garnet contain hematite daughters, suggesting an oxidizing magmatic environment. Sulfur isotope determinations on sulfide minerals from both the prograde and retrograde stages show a uniform and narrow range of δ34S values (?2.6 to ?1.1 ‰ δ34S), suggesting that the ore-forming fluid contained sulfur of orthomagmatic origin. Overall, the Phu Lon deposit is interpreted as an oxidized Cu–Au skarn based on the mineralogy and fluid inclusion characteristics. 相似文献
6.
The Fuxing porphyry Cu deposit is a recently discovered deposit in Eastern Tianshan, Xinjiang, northwestern China. The Cu mineralization is associated with the Fuxing plagiogranite porphyry and monzogranite, mainly presenting as various types of hydrothermal veins or veinlets in alerted wall rocks, with potassic, chlorite, phyllic, and propylitic alteration developed. The ore-forming process can be divided into four stages: stage I barren quartz veins, stage II quartz–chalcopyrite–pyrite veins, stage III quartz–polymetallic sulfide veins and stage IV quartz–calcite veins. Four types of fluid inclusions (FIs) can be distinguished in the Fuxing deposit, including hypersline (H-type), vapor-rich two-phase (V-type), liquid-rich two-phase (L-type), and trace amounts of pure vapor inclusions (P-type), but only the stage I quartz contains all types of FIs. The stages II and III quartz have two types of FIs, with exception of H- and P-types. In stage IV quartz minerals, only the L-type inclusions can be observed. The FIs in quartz of stages I, II, III and IV are mainly homogenized at temperatures of 357–518 °C, 255–393 °C, 234–322 °C and 145–240 °C, with salinities of 1.9–11.6 wt.% NaCl equiv., 1.6–9.6 wt.% NaCl equiv., 1.4–7.7 wt.% NaCl equiv. and 0.9–3.7 wt.% NaCl equiv., respectively. The ore-forming fluids of the Fuxing deposit are characterized by high temperature, moderate salinity and relatively oxidized condition. Carbon, hydrogen and oxygen isotopic compositions of quartz indicate that the ore-forming fluids were gradually evolved from magmatic to meteoric in origin. Sulfur and lead isotopes suggest that the ore-forming materials were derived from a deep-seated magma source. The Cu mineralization in the Fuxing deposit occurred at a depth of ~ 1 km, and the changes of oxygen fugacity, decompression boiling, and local mixing with meteoric water were most likely critical for the formation of the Fuxing Cu deposit. 相似文献
7.
Kafang is one of the main ore deposits in the world-class Gejiu polymetallic tin district, SW China. There are three main mineralization types in the Kafang deposit, i.e., skarn Cu–Sn ores, stratiform Cu ores hosted by basalt and stratiform Cu–Sn ores hosted by carbonate. The skarn mainly consists of garnet and pyroxene, and retrograde altered rocks. These retrograde altered rocks are superimposed on the skarn and are composed of actinolite, chlorite, epidote and phlogopite. Major ore minerals are chalcopyrite, pyrrhotite, cassiterite, pyrite and scheelite. Sulfur and Pb isotopic components hint that the sources of different types of mineralization are distinctive, and indicate that the skarn ore mainly originated from granitic magma, whereas the basalt-hosted Cu ores mainly derived from basalt. Microthermometry results of fluid inclusions display a gradual change during the ore-forming process. The homogenization temperature of different types of inclusions continuously decreases from early to late mineralization stages. The salinities and freezing temperatures exhibit similar evolutionary tendencies with the T homogenization, while the densities of the different types keep constant, the majority being less than 1. Oxygen and hydrogen isotopic values (δ18O and δD) of the hydrothermal fluids fall within ranges of 3.1 to 7.7‰ with an average of 6.15‰, calculated at the corresponding homogenization temperature, and − 73 and − 98‰ with an average of − 86.5‰, respectively. Microthermometry data and H–O isotopes indicate that the ore-forming fluid of the Kafang deposit is mainly derived from magma in the early stage and a mixture of meteoric and magmatic water in late stage. Molybdenite Re–Os age of the skarn type mineralization is 83.4 ± 2.1 Ma, and the stratiform ores hosted by basalt is 84.2 ± 7.3 Ma, which are consistent with the LA-ICP-MS zircon age of the Xinshan granite intrusion (83.1 ± 0.4 Ma). The evidence listed above reflects the fact that different ore styles in the Kafang deposit belong to the same mineralization system. 相似文献
8.
The Kozbudaklar scheelite skarn deposit in the Tavşanlı Zone, located approximately 22 km southeast of Bursa, is hosted by the Triassic calcic İnönü Marble and Eocene Topuk Pluton. At least four stages have been recognized through skarn evolution. Scheelite skarn distributed close to the Topuk Pluton occurred during the early (stage 1) and late (stage 2) prograde substages. The early prograde endo and exoskarn are composed of hedenbergite (Hd96Joh4)–plagioclase (An55–64) and hedenbergite (Hd61–94Joh4–7), accompanied by calcic garnet (Grs38–94Sps1–5Alm0) and scheelite (Pow1–6). The second stage represents a relatively oxidized mineralogy dominated by diopside (Hd16–48Joh0–9), subcalcic garnet (Grs24–92Sps0–11Alm0–31) and scheelite (Pow7–32). The stage 3 and 4 mineral assemblages are characterized by few hydrous minerals in the retrograde stage and intense fracturing.Fluid inclusions from skarn rocks are indicative of multiple fluid events: (1) low-moderate salinity (5–16 wt.%NaCl equiv.) inclusions homogenized dominantly by a high-temperature (308 °C to > 600 °C) liquid phase in stage 1. Fluid inclusions in an early garnet homogenized over a similar temperature range (440 °C and 459 °C) into both liquid and vapor phases. Eutectic temperatures ranging from − 61.7 °C to − 35.0 °C that indicate the presence of H2O–NaCl–(± MgCl2 ± CaCl2)–CO2 solutions; (2) coexisting daughter mineral-bearing high salinity (29.5 ≥ 70 wt.%NaCl equiv.) and vapor-rich moderate salinity (11.5–16.7 wt.%NaCl equiv.) inclusions that homogenized in the liquid phase by the disappearance of the vapor phase at a similar temperature range (308 °C to > 600 °C) in stage 2. Eutectic temperatures range from − 67.9°C to − 51.8°C that shows the presence of H2O–NaCl–CO2–(± CH4/N2) solutions; (3) low-moderate salinity (12.5–7.6 wt.%NaCl equiv.) and temperature (320 °C to 215 °C) inclusions homogenized by the liquid phase in stage 3. Eutectic temperatures range from − 59.5 °C to − 44.2 °C indicating the presence of H2O–NaCl–(± MgCl2 ± CaCl2)–CO2 solutions; (4) inclusions of low salinity (9.9–0.9 wt.%NaCl equiv.) and homogenization temperature (183 °C to 101 °C) in stage 4.These data show that the Kozbudaklar skarn deposit was formed in a magmatic–hydrothermal system. In this model, carbonaceous fluids may have been exsolved from the plutonic rock during its emplacement and crystallization. Fluid inclusion data indicate that fluid boiling and immiscibility occurred at temperatures between 440 °C and 459 °C and pressures ranging from 50 MPa to 60 MPa based on hydrostatic considerations. Early scheelite was precipitated with relatively reduced mineral compositions. As a result of depressurization, Mo-rich scheelite with oxidized minerals formed via high salinity and vapor-rich inclusions. The second scheelite mineralization occurred in a normal hydrothermal system by an infiltration mechanism at pressures between approximately 40 and 1.5 MPa. At shallow depths (< 1.5 MPa) with increasing permeability, sulfide and oxide minerals were deposited in the retrograde stage, greatly assisted by meteoric water. Finally, as a result of the diminishing of ore-forming fluids, post-depositional barren quartz and calcite veins were formed. 相似文献
9.
The Luojiahe Cu deposit in the Zhongtiaoshan region is located in the southern margin of the North China Craton. The orebodies are hosted in the mafic volcanic-sedimentary sequences of the metamorphosed (greenschist-facies) Neoarchean Songjiashan Group. The Luojiahe Cu mineralization can be divided into the primary volcanogenic massive sulfide (VMS) mineralization stage (Stage I, banded or stockwork ores) and the subsequent metamorphic remobilization stage (Stage II, coarse-vein ores).Three types of quartz selected for fluid inclusion (FI) studies were collected from the Stage I banded (Q1) and stockwork (Q2) ores and Stage II coarse-vein (Q3) ores. Four types of FIs were identified: (1) liquid-rich FIs (L-type), (2) pure vapor and vapor-rich FIs (V-type), (3) daughter mineral-bearing FIs (S-type), and (4) CH4-H2O FIs (C-type). Systematical microthermometric and H-O isotopic studies show that the Stage I ore-forming fluids consist predominantly of high salinity evolved seawater (125–220 °C; 23.9–27.9 wt.% NaCl equiv.) and some magmatic-hydrothermal fluids (249–339 °C; 34.5–42.2 wt.% NaCl equiv.). The two fluid end-members are represented by the L-type FIs in Q1 and the S- and V-type FIs in Q2. The temperature- and salinity variation trends of the L-type FIs in Q1 indicate a mixing process between the hot evolved seawater and cold seawater at Stage I. Furthermore, the V- and S-type FI coexistence in Q2 and their microthermometric data suggest that fluid unmixing has occurred in original magmatic fluids at Stage I. In contrast, the Stage II ore-forming fluids consist of CH4-rich metamorphic fluids (192–350 °C; 10.6–43.2 wt.% NaCl equiv.). Carbon isotopic analysis of the Stage II calcite (− 4.58 to − 10.83‰) and graphite (− 32.01 to − 39.16‰) in the ore-hosting chlorite schist indicates that the metamorphic ore-forming fluids had exchanged carbon isotope with graphite. The generation of CH4 may have resulted from the interaction between H2O (released by metamorphic devolatilization) and graphite. The continuous consumption of H2O in the hydrothermal fluid system may have increased the fluid salinity and triggered fluid unmixing in the CH4-NaCl-H2O system. In addition, the VMS metallogenic environment is generally favorable for microbial communities. It is considered that the graphite at Luojiahe may have been derived from sedimentary organic matter formed in seafloor hydrothermal vent systems, as also supported by carbon isotopic data.We propose that at Stage I, the main mineralization may have been resulted from 1) fluid mixing of hot evolved seawater and cold seawater in the near-surface environment; and 2) fluid unmixing caused by the percolation of magmatic fluids into syn-volcanic faults, forming the stockwork ores. At Stage II, the interaction between H2O and graphite may have resulted in the reduction of ore-forming fluids and Cu precipitation, and fluid unmixing in the CH4-NaCl-H2O system may have further promoted the Cu mineralization. 相似文献
10.
In this review, we describe the geological characteristics and metallogenic–tectonic origin of Fe deposits in the Altay orogenic belt within the Xinjiang region of northwestern China. The Fe deposits are found mainly within three regions (ordered from northwest to southeast): the Ashele, Kelan, and Maizi basins. The principal host rocks for the Fe deposits of the Altay orogenic belt are the Early Devonian Kangbutiebao Formation, the Middle to Late Devonian Altay Formation, with minor occurrences of Lower Carboniferous and Early Paleozoic metamorphosed volcano-sedimentary rocks. The principal mineral-forming element groups of the deposits are Fe, Fe–Cu, Fe–Mn, Fe–P, Fe–Pb–Zn, Fe–Au, and Fe–V–Ti. The Fe deposits are associated with distinct formations, such as volcanic rocks, skarn deposits, pegmatites, granite-related hydrothermal vein mineralization, and mafic pluton-related V–Ti-magnetite deposits. The Fe deposits are most commonly associated with volcanic rocks in the upper Kangbutiebao Formation, in the volcano-sedimentary Kelan Basin, and in skarn deposits at several localities, including the lower Kangbutiebao Formation in the volcano-sedimentary Maizi Basin, and the Altay Formation at Jiaerbasidao–Kekebulake region. Homogenization temperatures of fluid inclusions in the prograde, retrograde and sulfide stages of the skarn type deposit are mainly medium- to high-temperature (cluster between 200 and 500 °C), medium-temperature (cluster between 200 and 340 °C) and low- to medium temperature (cluster between 160 and 300 °C), respectively. Ore fluids in the sedimentation period in the volcano-sedimentary type deposit are characterized by low- to medium temperature (with a peak around 190 °C), low to moderate salinity (3.23 to 22.71 wt.% NaCl equiv). Ore fluids in the pegmatite type deposit are characterized by low- to medium temperature (with a peak at 240 °C), low salinity (with a peak around 9 wt.% NaCl equiv). An analysis of the isotopic data for Fe deposits from the Altay orogenic belt indicates that the sulfur was derived from several sources, including volcanic rocks and granite, as well as bacterial reduction of sulfate from seawater. The present results indicate that different deposit types were derived from various sources. The REE geochemistry of rocks and ores from the Fe deposits in the Altay orogenic belt suggests that the ore-forming materials were derived from mafic volcanic rocks. Based on isotopic age data, the timing of the mineralization can be divided into four broad intervals: Early Devonian (410–384 Ma), Middle Devonian (377 Ma), Early Permian (287–274 Ma), and Early Triassic (c. 244 Ma). The ore-forming processes of the Fe deposits are closely related to volcanic activity and the emplacement of intermediate and felsic intrusions. We conclude that Fe deposits within the Altay orogenic belt developed in a range of tectonic settings, including continental arc, post-collisional extensional settings, and intracontinental settings. 相似文献
11.
The Cangyuan Pb-Zn-Ag polymetallic deposit is located in the Baoshan Block, southern Sanjiang Orogen. The orebodies are hosted in low-grade metamorphic rocks and skarn in contact with Cenozoic granitic rocks. Studies on fluid inclusions (FIs) of the deposit indicate that the ore-forming fluids are CO2-bearing, NaCl-H2O. The initial fluids evolved from high temperatures (462–498 °C) and high salinities (54.5–58.4 wt% NaCl equiv) during the skarn stage into mesothermal (260–397 °C) and low salinities (1.2–9.5 wt% NaCl equiv) during the sulfide stage. The oxygen and hydrogen isotopic compositions (δ18OH2O: 2.7–8.8‰; δD: −82 to −120‰) suggest that the ore-forming fluids are mixture of magmatic fluids and meteoric water. Sulfur isotopic compositions of the sulfides yield δ34S values of −2.3 to 3.2‰; lead isotopic compositions of ore sulfides are similar to those of granitic rocks, indicating that the sulfur and ore-metals are derived from the granitic magma. We propose that the Cangyuan Pb-Zn-Ag deposit formed from magmatic hydrothermal fluids. These Cenozoic deposits situated in the west of Lanping-Changdu Basin share many similarities with the Cangyuan in isotopic compositions, including the Laochang, Lanuoma and Jinman deposits. This reveals that the Cenozoic granites could have contributed to Pb-Zn-Cu mineralization in the Sanjiang region despite the abundance of Cenozoic Pb-Zn deposits in the region, such as the Jingding Pb-Zn deposit, that is thought to be of basin brine origin. 相似文献
12.
The Mangabeira deposit is the only known Brazilian tin mineralization with indium. It is hosted in the Paleo- to Mesoproterozoic Mangabeira within-plate granitic massif, which has geochemical characteristics of NYF fertile granites. The granitic massif is hosted in Archean to Paleoproterozoic metasedimentary rocks (Ticunzal formation), Paleoproterozoic peraluminous granites (Aurumina suite) and a granite–gneiss complex. The mineralized area comprises evolved Li-siderophyllite granite, topaz–albite granite, Li–F-rich mica greisens and a quartz–topaz rock, similar to topazite. Two types of greisens are recognized in the mineralized area: zinnwaldite greisen and Li-rich muscovite greisen, formed by metasomatism of topaz–albite granite and Li-siderophyllite granite, respectively. Cassiterite occurs in the quartz–topaz rock and in the greisens. Indium minerals, such as roquesite (CuInS2), yanomamite (InAsO4·2H2O) and dzhalindite (In(OH3)), and In-rich cassiterite, sphalerite, stannite group minerals and scorodite are more abundant in the quartz–topaz rock, and are also recognized in albitized biotite granite and in Li-rich muscovite greisen. The host rocks and mineralized zones were subsequently overprinted by the Brasiliano orogenic event.Primary widespread two-phase aqueous and rare coeval aqueous-carbonic fluid inclusions are preserved in quartz from the topaz–albite granite, in quartz and topaz from the quartz–topaz rock and in cassiterite from the Li-rich muscovite greisen. Eutectic temperatures are − 25 °C to − 23 °C, allowing modeling of the aqueous fluids in the system H2O–NaCl(–KCl). Rare three-phase H2O–NaCl fluid inclusions (45–50 wt.% NaCl equiv.) are restricted to the topaz–albite granite. Salinities and homogenization temperatures of the aqueous and aqueous-carbonic fluid inclusions decrease from the topaz–albite granite (15–20 wt.% NaCl equiv.; 400 °C–450 °C), to the quartz–topaz rock (10–15 wt.% NaCl equiv.; 250 °C–350 °C) and to the greisen (0–5 wt.% NaCl equiv.; 200 °C–250 °C). Secondary fluid inclusions have the same range of salinities as the primary fluid inclusions, and homogenize between 150 and 210 °C.The estimated equilibrium temperatures based on δ18O of quartz–mica pairs are 610–680 °C for the topaz–albite granite and 285–370 °C for the Li-rich muscovite greisens. These data are coherent with measured fluid inclusion homogenization temperatures. Temperatures estimated using arsenopyrite geothermometry yield crystallization temperatures of 490–530 °C for the quartz–topaz rock and 415–505 °C for the zinnwaldite greisens. The fluids in equilibrium with the topaz–albite granite have calculated δ18O and δD values of 5.6–7.5‰ and − 67 to − 58‰, respectively. Estimated δ18O and δD values are mainly 4.8–7.9‰ and − 60 to − 30‰, respectively, for the fluids in equilibrium with the quartz–topaz rock and zinnwaldite greisen; and 3.4–3.9‰ and − 25 to − 17‰, respectively, for the Li-rich muscovite greisen fluid. δ34S data on arsenopyrite from the quartz–topaz rock vary from − 1.74 to − 0.74‰, consistent with a magmatic origin for the sulfur. The integration of fluid inclusion with oxygen isotopic data allows for estimation of the minimum crystallization pressure at ca. 770 bar for the host topaz–albite granite, which is consistent with its evolved signature.Based on petrological, fluid inclusion and isotope data it is proposed that the greisens and related Mangabeira Sn–In mineralization had a similar hydrothermal genesis, which involved exsolution of F-rich, Sn–In-bearing magmatic fluids from the topaz–albite granite, early formation of the quartz–topaz rock and zinnwaldite greisen, progressive cooling and Li-rich muscovite greisen formation due to interaction with meteoric water. The quartz–topaz rock is considered to have formed in the magmatic-hydrothermal transition. The mineralizing saline and CO2-bearing fluids are interpreted to be of magmatic origin, based on the isotopic data and paragenesis, which has been documented as characteristic of the tin mineralization genetically related to Proterozoic within-plate granitic magmatism in the Goias Tin Province, Central Brazil. 相似文献
13.
The Laoshankou Fe–Cu–Au deposit is located at the northern margin of Junggar Terrane, Xinjiang, China. This deposit is hosted in Middle Devonian andesitic volcanic breccias, basalts, and conglomerate-bearing basaltic volcanic breccias of the Beitashan Formation. Veined and lenticular Fe–Cu–Au orebodies are spatially and temporally related to diorite porphyries in the ore district. Wall–rock alteration is dominated by skarn (epidote, chlorite, garnet, diopside, actinolite, and tremolite), with K–feldspar, carbonate, albite, sericite, and minor quartz. On the basis of field evidence and petrographic observations, three stages of mineralization can be distinguished: (1) a prograde skarn stage; (2) a retrograde stage associated with the development of Fe mineralization; and (3) a quartz–sulfide–carbonate stage associated with Cu–Au mineralization. Electron microprobe analysis shows that garnets and pyroxenes are andradite and diopside-dominated, respectively. Fluid inclusions in garnet yield homogenization temperatures (Th) of 205–588 °C, and salinities of 8.95–17.96 wt.% NaCl equiv. In comparison, fluid inclusions in epidote and calcite yield Th of 212–498 and 150–380 °C, and salinities of 7.02–27.04 and 13.4–18.47 wt.% NaCl equiv., respectively. Garnets yield values of 6.4‰ to 8.9‰ δ18Ofluid, whereas calcites yield values of − 2.4‰ and 4.2‰ δ18Ofluid, and − 0.9‰ to 2.4‰ δ13CPDB, indicating that the ore-forming fluids were dominantly magmatic fluids in the early stage and meteoric water in the late stage. The δ34S values of sulfides range from − 2.6‰ to 5.4‰, indicating that the sulfur in the deposit was probably derived from deep-seated magmas. The diorite porphyry yields LA–MC–ICP–MS zircon U–Pb age of 379.7 ± 3.0 Ma, whereas molybdenites give Re–Os weighted mean age of 383.2 ± 4.5 Ma (MSWD = 0.06). These ages suggest that the mineralization-related diorite porphyry was emplaced during the Late Devonian, coincident with the timing of mineralization within the Laoshankou Fe–Cu–Au deposit. The geological and geochemical evidence presented here suggest that the Laoshankou Fe–Cu–Au deposit is a skarn deposit. 相似文献
14.
A calcic skarn deposit occurs along the contact zone between Oligo-Miocene Çatalda? Granitoid and Mesozoic limestones in Susurluk, northwestern Turkey. The skarn zone with little or no retrograde stage is represented by fluid inclusions with high homogenization temperatures (up to >600 °C) and a wide range of salinity (12 to >70 wt.% NaCl). Pluton-derived fluids facilitated occurrence of continuous prograde reactions in the country rocks (particularly in the proximal zone) and oxygen isotopic depletion in calc-silicate and calcite minerals. δ18O of anhydrous minerals within proximal and distal zones indicate that skarn-forming fluids had a magmatic origin. The δ18O values are 5.93–9.08‰ (mean 6.8‰) for garnet, 4.08–9.94‰ (mean 6.4‰) for pyroxene, 4.89–7.92‰ (mean 6.4‰) for wollastonite and 6.65–8.28‰ (mean 7.5‰) for vesuvianite. Temperatures estimated by isotopic compositions of mineral pairs are significantly lower than those measured from the fluid inclusions, indicating that isotopic equilibrium is not preserved between the skarn minerals. δ18O and δ13C values are systematically depleted from marbles to skarn carbonates. Calc-silicate forming reactions and permeability increase triggered by volatilization and consequent strong infiltration of H2O-rich siliceous fluids into the system promoted fluid–rock interaction causing isotopic resetting and isotopic depletion of silicates (e.g. pyroxene and wollastonite) and skarn calcites. 相似文献
15.
The Bianjiadayuan Pb–Zn–Ag deposit in the Southern Great Xing'an Range consists of quartz-sulfide vein-type and breccia-type mineralization related to granite. Vein orebodies are localized in NW-trending extensional faults. Hydrothermal alteration is well developed and includes silicification, potassic alteration, chloritization and sericitization. Three stages of mineralization are recognized based on field evidence and petrographic observation and are marked by assemblages of quartz–arsenopyrite–pyrite (stage I), quartz–pyrrhotite–chalcopyrite–sphalerite (stage II) and quartz–galena–silver minerals (stage III). The granite, with a zircon age of 143.2 ± 1.5 Ma (n = 14, MSWD = 0.93), is subalkaline, peraluminous and is classified as A2-type granite originating in a post-orogenic extensional setting during the opening of suture zone between the North China Craton and the Siberia Craton from the Late Jurassic to the Early Cretaceous. The δ34SCDT values of sulfides, ranging from 3.19 to 10.65‰, are not consistent with the majority of magmatic hydrothermal deposits in the SGXR, possibly implying accessory source in addition to magmatic source. Microthermometric measurements show that ore minerals were deposited at intermediate temperatures (347.8–136.4 °C) with moderate salinities (2.9–14.4 wt.% NaCl). Ore-forming fluids were derived largely from magmatic hydrothermal processes, with the addition of meteoric water in late stage. Successive precipitation of Pb, Zn and Ag occurred with changes of physicochemical conditions. Overall considering mineralization features, ore-forming fluids and materials and tectonic setting and comparing with adjacent deposits, the Bianjiadayuan deposit is a mesothermal magmatic hydrothermal vein-type Pb–Zn–Ag deposit controlled by fractures and related to A2-type granite in response to the tectonic/magmatic/hydrothermal activity in late Jurassic. Besides, the explosive breccias in the west area require more attention in future exploration. 相似文献
16.
This paper contributes to the understanding of the genesis of epigenetic, hypogene BIF-hosted iron deposits situated in the eastern part of Ukrainian Shield. It presents new data from the Krivoy Rog iron mining district (Skelevatske–Magnetitove deposit, Frunze underground mine and Balka Severnaya Krasnaya outcrop) and focuses on the investigation of ore genesis through application of fluid inclusion petrography, microthermometry, Raman spectroscopy and baro-acoustic decrepitation of fluid inclusions. The study investigates inclusions preserved in quartz and magnetite associated with the low-grade iron ores (31–37% Fe) and iron-rich quartzites (38–45% Fe) of the Saksaganskaya Suite, as well as magnetite from the locally named high-grade iron ores (52–56% Fe). These high-grade ores resulted from alteration of iron quartzites in the Saksaganskiy thrust footwall (Saksaganskiy tectonic block) and were a precursor to supergene martite, high-grade ores (60–70% Fe). Based on the new data two stages of iron ore formation (metamorphic and metasomatic) are proposed.The metamorphic stage, resulting in formation of quartz veins within the low-grade iron ore and iron-rich quartzites, involved fluids of four different compositions: CO2-rich, H2O, H2O–CO2(± N2–CH4)–NaCl(± NaHCO3) and H2O–CO2(± N2–CH4)–NaCl. The salinities of these fluids were relatively low (up to 7 mass% NaCl equiv.) as these fluids were derived from dehydration and decarbonation of the BIF rocks, however the origin of the nahcolite (NaHCO3) remains unresolved. The minimum P–T conditions for the formation of these veins, inferred from microthermometry are Tmin = 219–246 °C and Pmin = 130–158 MPa. The baro-acoustic decrepitation analyses of magnetite bands indicated that the low-grade iron ore from the Skelevatske–Magnetitove deposit was metamorphosed at T = ~ 530 °C.The metasomatic stage post-dated and partially overlapped the metamorphic stage and led to the upgrade of iron quartzites to the high-grade iron ores. The genesis of these ores, which are located in the Saksaganskiy tectonic block (Saksaganskiy ore field), and the factors controlling iron ore-forming processes are highly controversial. According to the study of quartz-hosted fluid inclusions from the thrust zone the metasomatic stage involved at least three different episodes of the fluid flow, simultaneous with thrusting and deformation. During the 1st episode three types of fluids were introduced: CO2–CH4–N2(± C), CO2(± N2–CH4) and low salinity H2O–N2–CH4–NaCl (6.38–7.1 mass% NaCl equiv.). The 2nd episode included expulsion of the aqueous fluids H2O–N2–CH4–NaCl(± CO2, ± C) of moderate salinities (15.22–16.76 mass% NaCl equiv.), whereas the 3rd event involved high salinity fluids H2O–NaCl(± C) (20–35 mass% NaCl equiv.). The fluids most probably interacted with country rocks (e.g. schists) supplying them with CH4 and N2. The high salinity fluids were most likely either magmatic–hydrothermal fluids derived from the Saksaganskiy igneous body or heated basinal brines, and they may have caused pervasive leaching of Fe from metavolcanic and/or the BIF rocks. The baro-acoustic decrepitation analyses of magnetite comprising the high-grade iron ore showed formation T = ~ 430–500 °C. The fluid inclusion data suggest that the upgrade to high-grade Fe ores might be a result of the Krivoy Rog BIF alteration by multiple flows of structurally controlled, metamorphic and magmatic–hydrothermal fluids or heated basinal brines. 相似文献
17.
The Yinjiagou Mo–Cu–pyrite deposit of Henan Province is located in the Huaxiong block on the southern margin of the North China craton. It differs from other Mo deposits in the East Qingling area because of its large pyrite resource and complex associated elements. The deposit’s mineralization process can be divided into skarn, sulfide, and supergene episodes with five stages, marking formation of magnetite in the skarn episode, quartz–molybdenite, quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite, and calcite–galena–sphalerite in the sulfide episode, and chalcedony–limonite in the supergene episode. Re–Os and 40Ar–39Ar dating indicates that both the skarn-type and porphyry-type orebodies of the Yinjiagou deposit formed approximately 143 Ma ago during the Early Cretaceous. Four types of fluid inclusions (FIs) have been distinguished in quartz phenocryst, various quartz veins, and calcite vein. Based on petrographic observations and microthermometric criteria the FIs include liquid-rich, gas-rich, H2O–CO2, and daughter mineral-bearing inclusions. The homogenization temperature of FIs in quartz phenocrysts of K-feldspar granite porphyry ranges from 341 °C to >550 °C, and the salinity is 0.4–44.0 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite veins is 382–416 °C, and the salinity is 3.6–40.8 wt% NaCl eqv. The homogenization temperature of FIs in quartz–calcite–pyrite–chalcopyrite–bornite–sphalerite ranges from 318 °C to 436 °C, and the salinity is 5.6–42.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–molybdenite stockworks is in a range of 321–411 °C, and the salinity is 6.3–16.4 wt% NaCl eqv. The homogenization temperature of FIs in quartz–sericite–pyrite is in a range of 326–419 °C, and the salinity is 4.7–49.4 wt% NaCl eqv. The ore-forming fluids of the Yinjiagou deposit are mainly high-temperature, high-salinity fluids, generally with affinities to an H2O–NaCl–KCl ± CO2 system. The δ18OH2O values of ore-forming hydrothermal fluids are 4.0–8.6‰, and the δDV-SMOW values are between −64‰ and −52‰, indicating that the ore-forming fluids were primarily magmatic. The δ34SV-CDT values of sulfides range between −0.2‰ and 6.3‰ with a mean of 1.6‰, sharing similar features with deeply sourced sulfur, implying that the sulfur mainly came from the lower crust composed of poorly differentiated igneous materials, but part of the heavy sulfur came from the Guandaokou Group dolostone. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of sulfides are in the range of 17.331–18.043, 15.444–15.575, and 37.783–38.236, respectively, which is generally consistent with the Pb isotopic signature of the Yinjiagou intrusion, suggesting that the Pb chiefly originated from the felsic–intermediate intrusive rocks in the mine area, with a small amount of lead from strata. The Yinjiagou deposit is a porphyry–skarn deposit formed during the Mesozoic transition of a tectonic regime that is EW-trending to NNE-trending, and the multiepisode boiling of ore-forming fluids was the primary mechanism for mineral deposition. 相似文献
18.
Crnac is an intermediate sulfidation Pb–Zn–Ag epithermal deposit located within the Vardar suture zone of the Central Balkan Peninsula. The epithermal Pb–Zn–Ag mineralization consists of (i) a series of steeply-dipping veins hosted within the Jurassic amphibolites, and (ii) overlying hydrothermal-explosive breccia with angular (level IV) or rounded fragments of listwanite (surface) cemented by epithermal mineralization. The mineralization is related to the Oligocene quartz latite dykes that crosscut the Crnac antiform. Quartz latite rocks predominantly display a shoshonitic character. The obtained 40Ar/39Ar age of fresh quartz latite is 28.9 ± 0.3 Ma. Fine-grained sericite from altered quartz latite is dated at 28.6 ± 0.5 Ma. Early, alteration related fluid inclusions within quartz latite show coexistence of high-density brine and a low-density vapor-saturated phase that homogenized at 280–405 °C. Phase separation occurs at a paleodepth of 0.6 to 0.9 km.Epithermal mineralization developed in three stages: (i) early pyrite–arsenopyrite–pyrrhotite–quartz–kaolinite; (ii) main sphalerite–galena–tetrahedrite–chalcopyrite and (iii) late carbonate–pyrite–arsenopyrite assemblage. The onset of mineral deposition within epithermal veins was initiated by boiling of Na–Cl ± K ± Ca ± Mg fluid at a paleodepth of 0.6 to 0.9 km. Coexisting vapor and liquid-rich inclusions display salinities and trapping temperatures of 4 wt.% NaCl equiv., 280–370 °C and 2–27 wt.% NaCl equiv., 230–375 °C, respectively. Boiling continued throughout the deposition of the sphalerite-galena-tetrahedrite-chalcopyrite assemblage. Late stage carbonate was deposited from diluted, non-boiling, low-temperature Na–Ca–Mg–Cl ± CO2 fluid (0.2 to 4.8 wt.% NaCl equiv., 115–280 °C).About 100–150 m higher in the system, precipitation of listwanite breccia cement began as a result of boiling Na–Cl ± Ca ± Mg ± K fluid of medium salinities (2.6 to 12.1 wt.% NaCl equiv.) at temperatures of 245–370 °C. Boiling and dilution of fluids continue throughout the precipitation of the main sphalerite-galena-tetrahedrite and late, mainly carbonate assemblage. Surface listwanite breccia contain quartz phenocrysts deposited from a homogeneous fluid with a medium salinity (8–10 wt.% NaCl equiv.) and high temperatures (Th = 295–315 °C), whereas the early and main stage of a surface listwanite breccia cement precipitated from a boiling fluid of decreasing salinity and temperature. Aqueous ± CO2, high salinity (16 to 18 wt.% NaCl equiv.), low temperature (120 °C), homogeneously trapped fluid that precipitated late stage carbonates, is most likely a remnant of boiled off fluid. The epithermal assemblage of the surface listwanites precipitated at a paleodepth of 0.4 to 0.6 km.The δ13C values of the late stage ankerite range from − 4.2 to 4.1‰, whereas δ18O range from 9.6 to 17.5‰. The calculated δ18O of fluid that precipitated carbonates within epithermal veins, and listwanite breccia cement range from 6.3 to 11.3‰, indicating a contribution of magmatic water.Deposition of all mineralization types was initiated by neutralization of primary acidic magmatic fluid by water-rock reactions that caused widespread propylitization and sericitization. Extensive and long-lasting boiling combined with dilution by meteoric water increased the pH towards the final stage of hydrothermal activity. 相似文献
19.
The Baiyanghe Be–U–Mo deposit is located in the Late Paleozoic Xuemisitan–Kulankazi island arc of the northwestern margin of the Junggar plate, Northwest China. It is the largest Be deposit (2.2 M tons of ore with grades ranging from 0.2% to 1.4%) in Asia. Orebodies in the deposit occur as fractures along contact zones between the Yangzhuang granite porphyry intrusion and Devonian pyroclastic country rocks and within the porphyry itself. Muscovite–fluorite veins are closely associated with the Be–U–Mo mineralization. A new Ar–Ar dating of the muscovite in this study yields a plateau age of 303.0 ± 1.6 Ma, which constrains the timing of the Be–U–Mo mineralization of the deposit. Three stages of fluorite of different colors have been identified at the deposit, with the earliest dark-purple fluorite more closely associated with the mineralization. Microthermometry of fluid inclusions obtained from the three stages of fluorite suggests that the fluorites were precipitated as veins from low temperature (120–150 °C) hydrothermal fluids with salinity ranging from 4.7 to 19.7 wt.% NaCl eqv. Based on the trace elemental concentrations and REE patterns of the fluorite, the style of veining, and the low salinity and low temperature characters of the fluid inclusions, it is suggested that Be and U were most likely transported as fluoride complexes and Mo as hydroxyl complexes. Pb isotopic compositions of the ores and country rocks, as well as O and H isotopic characters of the ore-related muscovite, indicate mixing between magmatic and meteoric waters; both contributed to formation of the ore-forming fluids. Metallic Be, U, and Mo were most likely leached out from the granite porphyry by the fluids. The fluid mixing led to the reduction of U, Mo, and Be and their precipitation at the deposit. 相似文献
20.
The Zhaxikang Pb-Zn-Sb deposit is one of the most important deposits in the Southern Tibet metallogenic belt. Based on field geology, petrography, melt- and fluid inclusions and C-H-O isotopes, we describe and discuss the mineralization, alteration, and their possible link with magmatic fluids. Our results show that the Zhaxikang deposit shares many geological and geochemical similarities with typical intermediate-sulfidation (IS) epithermal deposits. The Pb-Zn-Sb mineralization is closely related to Fe-Mn carbonate- and silicic alterations, which formed the outer rim around the greisen in the Cuonadong Dome. Orebodies occur mainly as structurally-controlled veins and breccia dikes, with major minerals include sphalerite, galena, pyrite, arsenopyrite, and Fe-Mn carbonates. Main stage ore-forming fluids were of medium temperature (214–292 °C), low salinity (2.6–5.3 wt.% NaCl eqv.) and CO2-bearing.Melt/fluid inclusions in beryl and quartz from the pegmatite indicate that the primary magmatic fluids were derived from the melt-fluid immiscibility. The magmatic fluids were of low salinity (0.2–7.9 wt.% NaCl eqv.), high temperature (298–457 °C) and CO2-rich, and contained minor CH4, N2, C2H6, C3H8 and C6H6. The presence of Mn-Fe carbonates and daughter gahnite minerals in the beryl-hosted inclusions indicates high Mn, Fe and Zn contents in the parental magma and related magmatic fluids. This implies a genetic link between magmatic fluids and the Pb-Zn-Sb mineralization, as also supported by Ar-Ar dating and H-O-C isotopic evidence. We suggest that the Zhaxikang is best classified as an IS epithermal deposit, and the ore-forming fluids are likely to be magma-derived. Boiling of the magmatic fluids led to high-salinity fluids and metal enrichment. High regional geothermal gradient caused by the thermal doming event may have facilitated long distance transportation of magmatic fluids, and led to the formation of a wide alteration zone and distal Pb-Zn-Sb mineralization. The temperature drop and meteoric water involvement may have precipitated the Pb-Zn-Sn minerals in the distal fault systems. 相似文献