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1.
Chilean manto-type (CMT) Cu(–Ag) hydrothermal deposits share a characteristic association of volcano-sedimentary Jurassic to Lower Cretaceous host rocks, style of mineralization, ore and associated mineralogy and geochemistry, with ore grades typically > 1%Cu, that make this family of deposits significant and interesting, both academically and economically. Although often stratabound, geological evidence supports an epigenetic origin for these deposits. We present a detailed stable isotope study of La Serena and Melipilla–Naltahua Lower Cretaceous deposits, central Chile, which reveals extremely negative δ34S values, to − 50‰, which are among the lowest values found in any ore deposit. In addition, the range of δ34S values from sulfides in the two areas is very wide: − 38.3 to − 6.9‰ in La Serena, and − 50.4 to − 0.6‰ in Melipilla–Naltahua. These new data significantly extended the reported range of δ34S data for CMT deposits. Co-existing sulfates range from 7.9 to 14.3‰, and are exclusive to La Serena deposit. The wide sulfide isotopic range occurs at deposit and hand specimen scale, and suggests a polygenic sulfur source for these deposits, where bacteriogenic sulfide dominates. While sulfur isotope data for the bulk of Jurassic CMT deposits, northern Chile, suggests a predominant magmatic source in their origin (mean = − 2.7 ± 1.9‰, 1σ), contributions of a magmatic component is only likely to be involved at Melipilla–Naltahua deposit.The δ13C values obtained for calcites associated with the mineralization range from − 20.1 to 0.2‰ also suggesting polygenic carbon sources, with the likely strong involvement of degradation of organic matter and leaching of limestone.Two different genetic models, with involvement of hydrocarbon, are proposed for both areas. For Melipilla–Naltahua, a two-step model can be developed as follows: 1) Framboidal pyrite growth, with very low δ34S, formed by bacterial sulfate reduction in an open system, and with diagenetic degradation of oil-related brines, leaving pyrobitumen. 2) Cu-bearing stage, replacing of framboidal pyrite, inheriting depleted sulfur as low as − 50.4‰, together with sulfides directly precipitated from a hydrothermal fluid with δ34S close to 0‰. For La Serena, a single step model fits best, without framboidal pyrite generation. Cu-bearing sulfides were precipitated mainly in veins where Cu plus base metal-bearing hydrothermal fluids mixed with H2S generated by bacterial sulfate reduction in the host rocks. Isotopic evidence clearly illustrates that bacterial activity, perhaps enhanced by hydrothermal activity, was fed by hydrocarbon brines and sulfate remobilized from continental evaporites. It is possible that variable ecological conditions led to different extents of isotopic fractionation, adding to the typical sulfur isotopic heterogeneity of such bacterial systems. For both areas, the Cu-bearing stage occurred during the peak to waning stages of the very low-grade metamorphism that affected the Lower Cretaceous sequence.  相似文献   

2.
The Palinuro volcanic complex and the Panarea hydrothermal field, both located in the Tyrrhenian Sea (Italy), are associated with island arc magmatism and characterized by polymetallic sulfide mineralization. Dissolved sulfide concentrations, pH, and Eh measured in porewaters at both sites reveal a variable hydrothermal influence on porewater chemistry.Multiple sulfur isotopic measurements for disseminated sulfides (CRS: chromium reducible sulfur) extracted from sediments at Palinuro yielded a broad range in δ34S range between ?29.8 and + 10.2‰ and Δ33S values between + 0.015 and + 0.134‰. In contrast, sediments at Panarea exhibit a much smaller range in δ34SCRS with less negative values between ?11.3 and ?1.8‰. The sulfur isotope signatures are interpreted to reflect a mixture between hydrothermal and biogenic sulfide, with a more substantial biogenic contribution at Panarea.Multiple sulfur isotope measurements were performed on sulfides and elemental sulfur from drill core material from the Palinuro massive sulfide complex. δ34S and Δ33S values for pyrite between ?32.8 and ?1.1‰ and between ?0.012 to + 0.042‰, respectively, as well as for elemental sulfur with δ34S and Δ33S values between ?26.7 and ?2.1‰ and between + 0.035 and + 0.109‰, respectively, point to a microbial origin for much of the sulfide and elemental sulfur studied. Moreover, data suggest a coupling of bacterial sulfate reduction, sulfide oxidation and sulfur disproportionation. In addition, δ34S values for barite between + 25.0 and + 63.6‰ are also in agreement with high microbial turnover of sulfate at Palinuro.Although a magmatic SO2 contribution towards the formation of the Palinuro massive sulfide complex is very likely, the activity of different sulfur utilizing microorganisms played a fundamental role during its formation. Thus, porewater and multiple sulfur isotope data reveal differences in the hydrothermal activity at Palinuro and Panarea drill sites and underline the importance of microbial communities for the origin of massive sulfide mineralizations in the hydrothermal subsurface.  相似文献   

3.
The Huangshaping Pb–Zn–W–Mo polymetallic deposit, located in southern Hunan Province, China, is one of the largest deposits in the region and is unique for its metals combination of Pb–Zn–W–Mo and the occurrence of significant reserves of all these metals. The deposit contains disseminated scheelite and molybdenite within a skarn zone located between Jurassic granitoids and Carboniferous sedimentary carbonate, and sulfide ores located within distal carbonate-hosted stratiform orebodies. The metals and fluids that formed the W–Mo mineralization were derived from granitoids, as indicated by their close spatial and temporal relationships. However, the source of the Pb–Zn mineralization in this deposit remains controversial.Here, we present new sulfur, lead, and strontium isotope data of sulfide minerals (pyrrhotite, sphalerite, galena, and pyrite) from the Pb–Zn mineralization within the deposit, and these data are compared with those of granitoids and sedimentary carbonate in the Huangshaping deposit, thereby providing insights into the genesis of the Pb–Zn mineralization. These data indicate that the sulfide ores from deep levels in the Huangshaping deposit have lower and more consistent δ34S values (− 96 m level: + 4.4‰ to + 6.6‰, n = 13) than sulfides within the shallow part of the deposit (20 m level: + 8.3‰ to + 16.3‰, n = 19). The δ34S values of deep sulfides are compositionally similar to those of magmatic sulfur within southern Hunan Province, whereas the shallower sulfides most likely contain reduced sulfur derived from evaporite sediments. The sulfide ores in the Huangshaping deposit have initial 87Sr/86Sr ratios (0.707662–0.709846) that lie between the values of granitoids (0.709654–0.718271) and sedimentary carbonate (0.707484–0.708034) in the Huangshaping deposit, but the ratios decreased with time, indicating that the ore-forming fluids were a combination of magmatic and formation-derived fluids, with the influence of the latter increasing over time. The lead isotopic compositions of sulfide ores do not correlate with sulfide type and define a linear trend in a 207Pb/204Pb vs. 206Pb/204Pb diagram that is distinct from the composition of the disseminated pyrite within sedimentary carbonates and granitoids in the Huangshaping deposit, but is similar to the lead isotopic composition of sulfides within coeval skarn Pb–Zn deposits in southern Hunan Province. In addition, the sulfide ores have old signatures with relative high 207Pb/206Pb ratios, suggesting that the underlying Paleoproterozoic basement within southern Hunan Province may be the source of metals within the Huangshaping deposit.The isotope geochemistry of sulfide ores in the Huangshaping deposit shows a remarkable mixed source of sulfur and ore-forming fluids, and the metals were derived from the basement. These features are not found in representative skarn-type Pb–Zn mineralization located elsewhere. The ore-forming elements (S, Pb, and Zn) from the granitoids made an insignificant contribution to sulfide precipitation in this deposit. However, the emplacement of granitoids did provide large amounts of heat and fluids to the hydrothermal system in this area and extracted metals from the basement rocks, indicating that the Jurassic magmatism associated with the Huangshaping deposit was crucial to the Pb–Zn mineralization.  相似文献   

4.
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   

5.
The Snowdon caldera of North Wales is host to base metal sulfide-bearing veins and stockworks, mineralized breccias, disseminated sulfides, and localized zones of semi-massive to massive sulfide, with subordinate magnetite-rich veins. The late Ordovician host volcanic sequence accumulated in a shallow marine, back-arc environment in the Welsh Basin, which forms part of the Avalon Zone of the British and Irish Caledonides. New field evidence, sulfur isotopes, and U-Pb dating indicate that the Snowdon mineralization is genetically and temporally related to Late Ordovician magmatism and caldera formation. It is interpreted to represent volcanogenic pipe-style sulfide mineralization, resulting from focused hydrothermal fluids moving along caldera-related faults and simultaneous dispersal of fluids through the volcaniclastic pile. Sulfur isotope data suggest that, whilst a limited contribution of magmatic S cannot be ruled out, thermochemical reduction of contemporaneous Ordovician seawater sulfate was the dominant mechanism for sulfide production in the Snowdon system, resulting in a mean value of about 12‰ in both the host volcanic strata and the mineralized veins. Despite the tectonic setting being prospective for VMS deposits, strata-bound sulfide accumulations are absent in the caldera. This is attributed to the shallow water depths, which promoted boiling and the formation of sub-seafloor vein-type mineralization. Furthermore, the tectonic instability of the caldera and the high energy, shallow marine environment would have limited preservation of any seafloor deposits. The new U-Pb dates for the base (454.26 ± 0.35 Ma) and top (454.42 ± 0.45 Ma) of the host volcanic rocks, indicate that the Snowdon magmatic activity was short lived, which is likely to have limited the duration and areal extent of the ore-forming system. The absence of massive sulfide mineralization is consistent with the general paucity of economic VMS deposits in the Avalon Zone. Despite the highly prospective geological setting this study further illustrates the importance of volcanic facies mapping and associated paleo-environmental interpretations in VMS exploration.  相似文献   

6.
The Yukeng–Banling deposit is a typical fault-controlled hydrothermal Cu–Au deposit in the Shanmen Volcanic Basin (SVB), SE China. Ore bodies commonly occur as lodes, lenses and disconnected pods dipping SW with vertical zonation of ore minerals. Ore-related hydrothermal alteration is well developed on both sides of the veins, dominated by silicification, sericitization, chloritization and argillation with a banded alteration zonation. The mineralization can be divided into three stages (stages I, II and III). Native gold is present as veinlets in fractures of fine-grained pyrite from stage II.Zircon U–Pb and Rb–Sr isochron ages indicate that the Cu–Au mineralization is coeval with the Caomen alkaline granite and Xiaokeng quartz-diorite, both emplaced at ca. 102 Ma. Microthermometric measurements of fluid inclusions in quartz and sphalerite from stage II veins indicate that the Yukeng–Banling deposit is an epithermal deposit. Six ore-related quartz grains have δDH2O values of − 69 to − 43‰, and δ18OH2O values calculated using total homogenization temperatures that range from − 2.0 to 0.7‰. All samples plot in an area between the magmatic field and the meteoric line, suggesting that the ore-forming fluids are derived from a mixed source of magmatic and meteoric waters. δ34S values for eight pyrite separates range from − 2.1 to + 4.1‰ with an average of + 1.7‰, and δ34S values for galena and sphalerite are 2.3‰ and 2.2‰, similar to magmatic sulfur. Four alkaline granite samples have Pb isotopic ratios (206Pb/204Pb)t = 18.175–18.411, (207Pb/204Pb)t = 15.652–15.672 and (208Pb/204Pb)t = 38.343–38.800. Three quartz-diorite samples have ratios (206Pb/204Pb)t, (207Pb/204Pb)t and (208Pb/204Pb)t of 18.277–18.451, 15.654–15.693 and 38.673–38.846, respectively. These age-calculated lead isotopic data for alkaline granite are similar to those for the analyzed sulfides. Co/Ni ratios for stage II pyrites range from 1.42 to 5.10, indicating that the Yukeng–Banling deposit records the past involvement of magmatic hydrothermal fluids. The isotope data, together with geological, mineralogical and geochronological evidence, favor a primary magmatic source for sulfur and metals in the ore fluids. Mixing of the Cu- and Au-rich fluids with meteoric water led to precipitation of the Cu–Au veins along NW-trending faults.The Yukeng–Banling deposit, the contemporaneous Caomen alkaline granite and Xiaokeng quartz-diorite in the SVB formed under an extensional setting, due to high-angle subduction of the paleo-Pacific plate. The extensional setting facilitated the formation of Cu- and Au-rich magmas which was derived from enriched mantle and lower crust.  相似文献   

7.
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   

8.
The Hadamengou-Liubagou Au-Mo deposit is the largest gold deposit in Inner Mongolia of North China. It is hosted by amphibolite to granulite facies metamorphic rocks of the Archean Wulashan Group. To the west and north of the deposit, there occur three alkaline intrusions, including the Devonian-Carboniferous Dahuabei granitoid batholith, the Triassic Shadegai granite and the Xishadegai porphyritic granite with molybdenum mineralization. Over one hundred subparallel, sheet-like ore veins are confined to the nearly EW-trending faults in the deposit. They typically dip 40° to 80° to the south, with strike lengths from hundreds to thousands of meters. Wall rock alterations include potassic, phyllic, and propylitic alteration. Four distinct mineralization stages were identified at the deposit, including K-feldspar-quartz-molybdenite stage (I), quartz-pyrite-epidote/chlorite stage (II), quartz-polymetallic sulfide-gold stage (III), and carbonate-sulfate-quartz stage (IV). Gold precipitated mainly during stage III, while Mo mineralization occurred predominantly in stage I. The δDH2O and δ18OH2O values of the ore-forming fluids range from −125‰ to −62‰ and from 1.4‰ to 7.5‰, respectively, indicating that the fluids were dominated by magmatic water with a minor contribution of meteoric water. The δ13CPDB and δ18OSMOW values of hydrothermal carbonate minerals vary from −10.3‰ to −3.2‰ and from 3.7‰ to 15.3‰, respectively, suggesting a magmatic carbon origin. The δ34SCDT values of sulfides from the ores vary from −21.7‰ to 5.4‰ and are typically negative (mostly −20‰ to 0‰). The wide variation of the δ34SCDT values, the relatively uniform δ13C values of carbonates (typically −5.5‰ to −3.2‰), as well as the common association of barite with sulfides suggest that the minerals were precipitated under relatively high fo2 conditions, probably in a magmatic fluid with δ34SƩS ≈ 0‰. The Re-Os isotopic dating on molybdenite from Hadamengou yielded a weighted average age of 381.6 ± 4.3 Ma, indicating that the Mo mineralization occurred in Late Devonian. Collectively, previous 40Ar-39Ar and Re-Os isotopic dates roughly outlined two ranges of mineralizing events of 382–323 Ma and 240–218 Ma that correspond to the Variscan and the Indosinian epochs, respectively. The Variscan event is approximately consistent with the Mo mineralization at Hadamengou-Liubagou and the emplacement of the Dahuabei Batholith, whereas the Indosinian event roughly corresponds to the possible peak Au mineralization of the Hadamengou-Liubagou deposit, as well as the magmatic activity and associated Mo mineralization at Xishadegai and Shadegai. Geologic, petrographic and isotopic evidence presented in this study suggest that both gold and molybdenum mineralization at Hadamengou-Liubagou is of magmatic hydrothermal origin. The molybdenum mineralization is suggested to be associated with the magmatic activity during the southward subduction of the Paleo-Asian Ocean beneath the North China Craton (NCC) in Late Devonian. The gold mineralization is most probably related to the magma-derived hydrothermal fluids during the post-collisional extension in Triassic, after the final suturing between the Siberian and NCC in Late Permian.  相似文献   

9.
Copper and iron skarn deposits are economically important types of skarn deposits throughout the world, especially in China, but the differences between Cu and Fe skarn deposits are poorly constrained. The Edong ore district in southeastern Hubei Province, Middle–Lower Yangtze River metallogenic belt, China, contains numerous Fe and Cu–Fe skarn deposits. In this contribution, variations in skarn mineralogy, mineralization-related intrusions and sulfur isotope values between these Cu–Fe and Fe skarn deposits are discussed.The garnets and pyroxenes of the Cu–Fe and Fe skarn deposits in the Edong ore district share similar compositions, i.e., dominantly andradite (Ad29–100Gr0–68) and diopside (Di54–100Hd0–38), respectively. This feature indicates that the mineral compositions of skarn silicate mineral assemblages were not the critical controlling factors for variations between the Cu–Fe and Fe skarn deposits. Intrusions associated with skarn Fe deposits in the Edong ore district differ from those Cu–Fe skarn deposits in petrology, geochemistry and Sr–Nd isotope. Intrusions associated with Fe deposits have large variations in their (La/Yb)N ratios (3.84–24.6) and Eu anomalies (δEu = 0.32–1.65), and have relatively low Sr/Y ratios (4.2–44.0) and high Yb contents (1.20–11.8 ppm), as well as radiogenic Sr–Nd isotopes (εNd(t) = − 12.5 to − 9.2) and (87Sr/86Sr)i = 0.7067 to 0.7086. In contrast, intrusions associated with Cu–Fe deposits are characterized by relatively high Sr/Y (35.0–81.3) and (La/Yb)N (15.0–31.6) ratios, low Yb contents (1.00–1.62 ppm) without obvious Eu anomalies (δEu = 0.67–0.97), as well as (87Sr/86Sr)i = 0.7055 to 0.7068 and εNd(t) = − 7.9 to − 3.4. Geochemical evidence indicates a greater contribution from the crust in intrusions associated with Fe skarn deposits than in intrusions associated with Cu–Fe skarn deposits. In the Edong ore district, the sulfides and sulfates in the Cu–Fe skarn deposits have sulfur isotope signatures that differ from those of Fe skarn deposits. The Cu–Fe skarn deposits have a narrow range of δ34S values from − 6.2‰ to + 8.7‰ in sulfides, and + 13.2‰ to + 15.2‰ in anhydrite, while the Fe skarn deposits have a wide range of δ34S values from + 10.3‰ to + 20.0‰ in pyrite and + 18.9‰ to + 30.8‰ in anhydrite. Sulfur isotope data for anhydrite and sedimentary country rocks suggest that the formation of skarns in the Edong district involved the interaction between magmatic fluids and variable amounts of evaporites in host rocks.  相似文献   

10.
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   

11.
The Wulaga gold deposit, located in Heilongjiang province, NE China, is a subvolcanic rock-hosted, low-sulfidation epithermal gold deposit, and has an Au reserve of about 84 tons. The gold mineralization occurs in a crypto-explosive breccia, and is spatially and temporally associated with an Early Cretaceous granodioritic porphyry. Three individual stages of mineralization have been identified in the Wulaga gold deposit: an early white quartz-euhedral vein stage, a fine-grained pyrite–marcasite–stibnite–chalcedony stage, and a late calcite–pyrite stage. The sulfur isotopic values of sulfide minerals vary in a wide range from − 4 to 4.9‰, but are concentrated in the range of − 3 to 0‰, implying that sulfur in the hydrothermal fluids was derived from magmatic volatiles. Lead isotopic results of the granodioritic porphyry (206Pb/204Pb = 18.341–18.395, 207Pb/204Pb = 15.507–15.523, 208Pb/204Pb = 38.174–38.251) and sulfide minerals (206Pb/204Pb = 18.172–18.378, 207Pb/204Pb = 15.536–15.600, 208Pb/204Pb = 38.172–38.339) are comparatively consistent and clustered together between the orogenic and upper mantle lines, indicating the lead in the ores is closely related to the parent magma of the granodioritic porphyry. The REE patterns of fluid inclusions trapped in sulfides are similar to those of the granodioritic porphyry, which confirms the magmatic origin of the REE in the hydrothermal fluids. The characteristics of S and Pb isotopes and REE suggest that the ore-forming materials of the Wulaga gold deposit are partly magmatic in origin, and related to a high-level hydrous granodioritic magma.  相似文献   

12.
The mineralization area (Altınpınar, Torul–Gümüşhane) is situated in the Southern Zone of the Eastern Pontides Orogenic Belt (EPOB), which is one of the important metallogenic provinces in the Alpine–Himalayan belt and is intruded by the late Carboniferous granitic rocks (Gümüşhane Granitoid), an early to middle Jurassic volcano-sedimentary unit consisting mainly of basaltic–andesitic volcanic and pyroclastic rocks (Şenköy Formation) and Eocene basaltic–andesitic volcanic rocks (Alibaba Formation). The studied Pb–Zn ± Au mineralizations are related to silica veins ranging from a few millimeters to a maximum of 40 cm in thickness and are localized within fracture zones developed along the contact between the Gümüşhane Granitoid and Şenköy Formation. Silicic, sulfidic, hematitic, argillic, intense chloritic and carbonate alteration are the most common types from the fault lines toward the outer zones. Cavity filling and banded structures are widely observed. The mineral paragenesis comprises galena, sphalerite, pyrite, chalcopyrite, tennantite and quartz. Mineral chemistry studies indicate that ion exchange occurs between Zn and Fe in sphalerites, and the Zn/Cd ratio of sphalerites varies between 50.65 and 144.64. The homogenization temperatures measured from fluid inclusions vary between 170 °C and 380 °C, especially between 250 °C and 300 °C, and the wt.% NaCl eqv. salinity of ore-forming fluids is between 2.4 and 7.3 (4.7 on average), supporting an epithermal system in their origin. The values of sulfur isotopes, which are obtained from pyrite and galena minerals, range between − 8.3‰ and − 2.3‰, indicating that sulfur, which enables mineral formation, originates from magmatic genesis. The average formation temperature of the ore is 317 °C as determined with a sulfur isotope geothermometer. The values of oxygen and hydrogen isotopes vary between 8.5‰ and 10.2‰ and − 91‰ and −73‰, respectively. With regard to the compositions of oxygen and hydrogen isotopes, fluids comprising the mineralization are formed by the mixture of magmatic water and meteoric water. This situation is supported by the fact that the increase in the homogenization temperature indicates dilution with surface water but depends on the increase in the salinity of fluid inclusions. Considering all the data, it is clear that the studied mineralization is an epithermal vein-type mineralization that is related to granitic magmas.  相似文献   

13.
The Aerhada Pb-Zn-Ag deposit is located in the western segment of the Great Hinggan Range Ag-Pb-Zn-Cu-Mo-Au-Fe metallogenic belt in NE China. Orebodies occur mainly as vein type and are hosted by sandstone and siliceous slate. Three stages of primary mineralization, including an early arsenopyrite-pyrite-quartz, a middle polymetallic and silver sulfides-quartz and a late sphalerite-pyrite-calcite-fluorite are recognized. Four types of fluid inclusions have been identified in the ore-bearing quartz and fluorite veins, i.e., liquid-rich, gas-rich, three-phase CO2 aqueous inclusions, and pure gas or liquid aqueous inclusions. Microthermometric studies on fluid inclusions reveal that homogenization temperatures from early to late stages range from 253° to 430 °C, 195° to 394 °C and 133° to 207 °C, respectively. Fluid salinities range from 2.9 to 14.0 wt.% NaCl equiv. The vapor composition of the ore fluid is dominated by H2O, CO2 and CH4, with minor proportions of N2. The fluid δ18OH2O and δDH2O values vary from +1.6 to +9.3‰ and −122 to −56‰, respectively, and reflect a magmatic fluid and a meteoric fluid dominant hydrothermal system for the early and late stages of mineralization, respectively. The calculated δ34SH2S values of hydrothermal fluids in equilibrium with sulfides range from +5.2 to +7.1‰, suggesting a mixed source for sulfur, i.e., the local magmatic and sedimentary rocks. The Pb isotope compositions of sulfides are similar to those of the local magmatic and sedimentary rocks, implying that lead and possibly silver relate to these sources. The noble gas isotope compositions of fluid inclusions hosted in ore minerals suggest that the ore-forming fluids were dominantly derived from a deep mantle source. Fluid mixing and dilution are inferred as the dominant mechanisms for ore deposition. The Aerhada Pb-Zn-Ag deposit can be classified as a medium to low temperature hydrothermal vein type deposit.  相似文献   

14.
The Koru and Tesbihdere mining districts in Biga Peninsula, Northwestern Turkey, consist of twelve deposits covering approximately 12 km2. The epithermal Au-Ag enriched base metal veins and associated low-grade breccia and stockwork at Koru and Tesbihdere are hosted by Oligocene subaerial and calc-alkaline volcanic rocks including basaltic andesite lavas, dacitic lava-tuffs, rhyolitic lava-domes and tuffs. NW- to N-trending strike-slip faults and E- and NE-trending faults constitute the most important ore-controlling structures in the Koru and Tesbihdere districts respectively. In the Koru mining district, galena is the dominant ore mineral in barite-quartz veins containing sphalerite, chalcopyrite, pyrite, bornite, enargite and tennantite. According to base metal content, the Tesbihdere mining district can be subdivided into sphalerite-galena dominated Tesbihdere mineralization and chalcopyrite-pyrite dominated Bakır and Kuyu Zones mineralization. Gold is present in small quantities with maximum 3.14 g/t Au values either as free grains in quartz or as micro inclusions in pyrite and galena. The most widespread silver minerals are polybasite, pearceite, argentite and native silver which commonly occur as replacements of galena, sphalerite and pyrite, and other sulfides, or as fillings of microfractures in sulfides and quartz.Microthermometric measurements of primary liquid-rich fluid inclusions in sphalerite, barite and quartz in Koru indicate that the veins were formed at temperatures between 407 and 146 °C from fluids with salinities between 0.7 and 12.5 wt.% equiv. NaCl. Barite from the Tahtalıkuyu, Kuyutaşı and 5th Viraj mineralization show the highest homogenization temperatures. Fluid inclusion data for ore-stage quartz and sphalerite from the Tesbihdere mining district, indicate that these minerals were deposited at temperatures between 387 and 232 °C from more diluted fluids with moderate salinities between 0.2 and 10.6 wt.% NaCl equiv. Tahtalıkuyu and 5th Viraj mineralization show only boiling trends while Kuyutaşı, Tesbihdere, Bakır and Kuyu Zones mineralization show both boiling and isothermal mixing trends. The O and H isotope compositions of ore fluids from the Tahtalıkuyu (δ18O = − 1.40 to 0.25‰; δD = − 72.49 to − 52.68‰) and Kuyutaşı (δ18O = − 2.29 to 3.59‰; δD = − 90.70 to − 70.93‰) mineralization indicate that there was a major contribution from a magmatic component to ore genesis. Based on 9 quartz samples associated with orebodies at the Tesbihdere mining district, the relatively higher δ18O and lower δD isotope compositions from hydrothermal fluids could be attributed to a relatively dilute fluid derived by the mixing with meteoric water. The Pb isotope compositions also reveal that most of the lead in both mining districts is derived from the Oligocene-Miocene magmatic rocks, possibly with smaller contributions from the Eocene magmatic rocks.  相似文献   

15.
East Qinling is the largest porphyry molybdenum province in the world; these Mo deposits have been well documented. In West Qinling, however, few Mo deposits have been discovered although granitic rocks are widespread. Recently, the Wenquan porphyry Mo deposit has been discovered in Gansu province, which provides an insight into Mo mineralization in West Qinling. In this paper we report Pb isotope compositions for K-feldspar and sulfides, S isotope ratios for sulfides, the results obtained from petrochemical study and from in situ LA-ICP-MS zircon U-Pb dating and Hf isotopes. The granitoids are enriched in LILE and LREE, with REE and trace element patterns similar to continental crust, suggesting a crustal origin. The Mg# (40.05 to 56.34) and Cr and Ni contents are high, indicating a source of refractory mafic lower crust. The εHf(t) values of zircon grains from porphyritic monzogranite range from ? 2.9 to 0.6, and from granitic porphyry vary from ? 3.3 to 1.9. The zircons have TDM2 of 1014 to 1196 Ma for the porphyritic monzogranite and 954 to 1224 Ma for the granitic porphyry, implying that these granitoids were likely derived from partial melting of a Late Mesoproterozoic juvenile lower crust. The Pb isotope compositions of the granitoids are similar to granites in South China, showing that the magma was sourced from the middle–lower crust in the southern Qinling tectonic unit. The Pb isotopic contrast between the Mo-bearing granitoids and ores shows that the Pb in the ore-forming solution was derived from fractionation of a Triassic magmatic system. δ34S values of sulfides are between 5.02 and 5.66‰, similar to those associated with magmatic-hydrothermal systems. LA-ICP-MS zircon U-Pb dating yields crystallization ages of 216.2 ± 1.7 and 217.2 ± 2.0 Ma for the granitoids, consistent with a previously reported molybdenite Re-Os isochron age of 214.4 ± 7.1 Ma. This suggests that the Mo mineralization is related to the late Triassic magmatism in the West Qinling orogenic belt. In view of these geochemical results and known regional geology, we propose that both granitoid emplacement and Mo mineralization in the Wenquan deposit resulted from the Triassic collision between the South Qinling and the South China Block, along the Mianlue suture. Since Triassic granitoid plutons commonly occur along the Qinling orogenic belt, the Triassic Wenquan Mo-bearing granitoids highlight the importance of the Triassic tectono-magmatic belt for Mo exploration. In order to apply this metallogenic model to the whole Qinling orogen, further study is needed to compare the Wenquan deposit with other deposits.  相似文献   

16.
Copper–gold–bismuth–tellurium mineralization in the Stanos area, Chalkidiki Peninsula, Greece, occurs in the Proterozoic- to Silurian-aged Serbomacedonian Massif, which tectonically borders the Mesozoic Circum-Rhodope metamorphic belt to the west and crystalline rocks of the Rhodope Massif to the east. This area contains the Paliomylos, Chalkoma, and Karambogia prospects, which are spatially related to regional NW–SE trending shear zones and hosted by marble, amphibolite gneiss, metagabbro, and various muscovite–biotite–chlorite–actinolite–feldspar–quartz schists of the Silurian Vertiskos Unit. Metallic minerals occur as disseminated to massive aggregates along foliation planes and in boudinaged quartz veins. Iron-bearing sulfides (pyrite, arsenopyrite, and pyrrhotite) formed prior to a copper-bearing stage that contains chalcopyrite along with galena, sphalerite, molybdenite, and various minerals in the system Bi–Cu–Pb–Au–Ag–Te. Fluid inclusion homogenization temperatures of primary aqueous liquid–vapor inclusions in stage I quartz veins range from 170.1 °C to 349.6 °C (peak at ~ 230 °C), with salinities of 4.5 to 13.1 wt.% NaCl equiv. Calculated isochores intersect P–T conditions associated with the upper greenschist facies caused by local overpressures during late-stage tectonic movement along the shear zone in the Eocene, which produced stretching and unroofing of rocks in the region. Values of δ34S for sulfides in the Stanos shear zone range from 2.42 to 10.19‰ and suggest a magmatic sulfur source with a partially reduced seawater contribution. For fluids in equilibrium with quartz, δ18O at 480 °C varies from 5.76 to 9.21‰ but does not allow for a distinction between a metamorphic and a magmatic fluid.A 187Re–187Os isochron of 19.2 ± 2.1 Ma for pyrite in the Paliomylos prospect overlaps ages obtained previously from intrusive rocks spatially-related to the Skouries porphyry Cu–Au, the Asimotrypes Au, and the intrusion-related Palea Kavala Bi–Te–Pb–Sb ± Au deposits in northern Greece, as well as alteration minerals in the carbonate-replacement Madem Lakkos Pb–Zn deposit. Ore-forming components of deposits in the Stanos area were likely derived from magmatic rocks at shallow depth that intruded an extensional shear environment at ~ 19 Ma.  相似文献   

17.
The Yinshan Cu–Au–Pb–Zn–Ag deposit is located in Dexing, South China. Ore bodies are primarily hosted in low-grade phyllite of the Neoproterozoic Shuangqiaoshan Group along EW- and NNW-striking fault zones. Pb–Zn–Ag mineralization is dictated by Jurassic rhyolitic quartz porphyries (ca. 172 Ma), whereas Cu–Au mineralization is associated with Jurassic dacite porphyries (ca. 170 Ma). The main ore minerals are pyrite, chalcopyrite, galena, sphalerite, tetrahedrite–tennatite, gold, silver, and silver sulphosalt, and the principal gangue minerals are quartz, sericite, calcite, and chlorite. Two-phase liquid-rich (type I), two-phase vapor-rich (type II), and halite-bearing (type III) fluid inclusions can be observed in the hydrothermal quartz-sulfides veins. Type I inclusions are widespread and have homogenization temperatures of 187–303 °C and salinities of 4.2–9.5 wt.% NaCl equivalent in the Pb–Zn–Ag mineralization, and homogenization temperatures of 196–362 °C and salinities of 3.5–9.9 wt.% NaCl equivalent in the Cu–Au mineralization. The pervasive occurrence of type I fluid inclusions with low-moderate temperatures and salinities implies that the mineralizing fluids formed in epithermal environments. The type II and coexisting type III inclusions, from deeper levels below the Cu–Au ore bodies, share similar homogenization temperatures of 317–448 °C and contrasting salinities of 0.2–4.2 and 30.9–36.8 wt.% NaCl equivalent, respectively, which indicates that boiling processes occurred. The sulfur isotopic compositions of sulfides (δ34S = −1.7‰ to +3.2‰) suggest a homogeneous magmatic sulfur source. The lead isotopes of sulfides (206Pb/204Pb = 18.01–18.07; 207Pb/204Pb = 15.55–15.57; and 208Pb/204Pb = 38.03–38.12) are consistent with those of volcanic–subvolcanic rocks (206Pb/204Pb = 18.03–18.10; 207Pb/204Pb = 15.56–15.57; and 208Pb/204Pb = 38.02–38.21), indicating a magmatic origin for lead in the ore. The oxygen and hydrogen isotope compositions (δ18O = +7.8‰ to +10.5‰, δD = −66‰ to −42‰) of inclusion water in quartz imply that ore-forming fluids were mainly derived from magmatic sources. The local boiling process beneath the epithermal Cu–Au ore-forming system indicates the possibility that porphyry-style ore bodies may exist at even deeper zones.  相似文献   

18.
The regional geologic setting of the Adycha-Taryn metallogenic zone, one of the areas most productive for noble-metal mineralization in northeastern Russia, is discussed. The intricate metallogenic history of the zone and the prolonged geodynamic activity of its ore-hosting structures are documented. Different types of mineralization, such as hydrothermal-metamorphogenic, gold-bismuth, gold-quartz, gold-antimony, and silver-antimony, are described. New data on the isotopic compositions of oxygen in quartz, sulfur in sulfides, and oxygen and carbon in carbonates from different mineralization types are presented. The early metamorphogenic quartz beyond the ore zones has δ18O = + 20.1 ± 2.0‰. At the gold-bismuth deposits, the δ18O values of quartz are within the narrow range of + 12.5 ± 0.4‰. Quartz from the gold-quartz mineralization shows much wider variation in δ18O values, from + 14.2 to + 19.5‰. A similar range (δ18O = + 16.1 to + 19.2‰) is observed for the gold-antimony mineralization. Cryptograined quartz from the silver-antimony mineralization is enriched in light oxygen isotopes (δ18O = -3.2 to + 4.7‰). The following δ34S values (‰) have been established in sulfides of mineralization of different types: gold-bismuth -3.7 to -2.2 (Apy) and -6.7 to -6.8 (Py); gold-quartz -2.1 to + 2.4 (Apy), -6.6 to + 5.4 (Py), and -6.1 to + 4.2 (St); gold-antimony -2.0 to + 1.6 (Apy), -3.5 to + 2.1 (Py), and -5.3 to + 0.2 (St); and silver-antimony -2.0 to -1.9 (Apy), -2.2 ± 0.1 (Py), and -5.7 to -5.6 (St). The δ13C and δ18O values are contrasting in the studied types of mineralization, varying respectively from -6.9 to -5.9‰ and from + 2.1 to + 5.7‰ (gold-bismuth), from -9.1 to -6.1‰ and from + 12.4 to 18.7‰ (gold-quartz), from -12.1 to -9.5‰ and from + 15.0 to + 16.3‰ (gold-antimony), from -11.6 to -11.1‰ and from + 1.5 to + 4.7‰ (silver-antimony). Metamorphogenic calcites are rich in both heavy C (-1.1 to -1.7‰) and heavy O (+ 20.3 to + 20.5‰) isotopes. Microthermometric study and crush-leach analysis of fluid inclusions have revealed differences in the composition of ore-forming fluids and formation conditions for different types of mineralization. The isotopic compositions of O, C, and S of mineral-forming fluids suggest a significant input of magmatic fluids to the formation of gold-bismuth and gold-antimony deposits, the contribution of metamorphic fluids increases at gold-quartz deposits, and meteoric water is involved in the formation of silver-antimony deposits.  相似文献   

19.
Although Zn–Pb deposits are one of the most important Cd reservoirs in the earth, few studies have focused on the Cd isotopic fractionation in Zn–Pb hydrothermal systems. This study investigates the causes and consequences of cadmium and sulfur isotope fractionation in a large hydrothermal system at the Tianbaoshan Zn–Pb–Cd deposit from the Sichuan–Yunnan–Guizhou (SYG) metallogenic province, SW China. Moderate variations in Cd and S isotope compositions have been measured in sphalerite cover a distance of about 78 m. Sphalerite has δ114/110Cd values ranging from 0.01 to 0.57‰, and sulfides (sphalerite, galena and chalcopyrite) have δ34SCDT values ranging from 0.2 to 5.0‰. Although δ34SCDT and δ114/110Cd values in sphalerites have no regular spatial variations, the δ34SCDT values in galena and calculated ore-forming fluid temperatures decreased from 2.1 to 0.2‰ and from about 290 to 130 °C, respectively, from the bottom to the top of the deposit. Heavy Cd isotopes are enriched in early precipitated sphalerite in contrast to previous studies. We suggest that Cd isotopic compositions in ore-forming fluids are heterogeneous, which result in heavy Cd isotope enrichment in early precipitated sphalerite. In comparison with other Zn–Pb deposits in the SYG area, the Tianbaoshan deposit has moderate Cd contents and small isotope fractionation, suggesting differences in origin to other Zn–Pb deposits in the SYG province.In the Tianbaoshan deposit, the calculated δ34S∑S-fluids value is 4.2‰, which is not only higher than the mantle-derived magmatic sulfur (0 ± 3‰), but also quite lower than those of Ediacaran marine sulfates (about 30 to 35‰). Thus, we suggest that reduced sulfur of ore-forming fluids in the deposit was mainly derived from the leaching of the basement, which contains large amount of volcanic or intrusive rocks. Based upon a combination of Cd and S isotopic systems, the Tianbaoshan deposit has different geochemical characteristics from typical Zn–Pb deposits (e.g., the Huize deposit) in SYG area, indicating the unique origin of this deposit.  相似文献   

20.
The Lanping basin is a significant Pb–Zn–Cu–Ag mineralization belt in the Sanjiang Tethyan metallogenic province. A series of sediment-hosted Himalayan Cu–Ag–Pb–Zn polymetallic deposits have been discovered in the western part of the basin, controlled by a thrust–nappe system. In the thrust–nappe system, the Cu orebodies mainly occur in the western and relatively deep part of the mineralization system (the root zone), whereas the Pb–Zn–Ag (± Cu) orebodies occur in the eastern and relatively shallow part of the system (the front zone), both as vein-type mineralization.In this paper we present new data, combined with existing data on fluid inclusions, isotopes and geologic characteristics of representative deposits, to provide the first study that contrasts mineralizing fluids in the Cu–Ag (Mo) and Pb–Zn–Ag (Cu) polymetallic deposits.Fluid inclusion and isotope studies show that the Cu–Ag (Mo) mineralization in the root zone formed predominantly from deep crustal fluids, with the participation of basinal brines. The deep crustal fluids are marked by high CO2 content, relatively high temperatures (280 to 340 °C) and low salinities (1 to 4 wt.% NaCl equivalent), whereas the basinal brine shows relatively low temperatures (160 °C to 220 °C) and high salinities (12 to 22 wt.% NaCl equivalent), containing almost no CO2. In comparison, hydrothermal activity associated with the Pb–Zn–Ag (± Cu) deposits in the front zone is characterized by basinal brine, with relatively low temperatures (130 °C to 180 °C), high salinities (9 to 24 wt.% NaCl equivalent), and low CO2 concentrations. Although evolved meteoric waters have predominantly been proposed as the source for deep crustal fluids, magmatic and metamorphic components cannot be completely excluded. The basinal brine was predominantly derived from meteoric water.The δ34S values of sulfides from the Cu–Ag (Mo) deposits and Pb–Zn–Ag (± Cu) deposits range from − 17.9 to 16.3‰ and from 2.5 to 11.2‰, respectively. These ranges may relate to variations in physicochemical conditions or compositional variation of the sources. Lead isotope compositions indicate that the ore-forming metals were predominantly derived from sedimentary rocks of the Lanping basin.  相似文献   

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