Carbonate-hosted Pb-Zn Deposits Research Articles

Cd–Pb isotopic characteristics within the Hehuashan carbonate-hosted Pb–Zn deposit, Middle-Lower Yangtze River Metallogenic Belt: Constraints for ore-forming metal sources and implications for exploration

The Hehuashan carbonate-hosted Pb–Zn deposit is a large-scale deposit situated in the Middle-Lower Yangtze-River Metallogenic Belt (MLYRMB) in China. It contains 0.99 million tons of Zn at an average grade of 1.5 % and 0.41 million tons of Pb at an average grade at 1.9 %, accompanied by critical metals of Cd and Ga. The ores are mainly composed of breccia-type and vein-type in the deposit. Though previous chemical compositions of sphalerite showed that Cd is enriched in both two types of mineralization and the sulfide sulfur isotopes research showed that the reduced sulfur is derived from the marine sulfate reduction, the source of ore-forming metals is still unclear. In this research, we studied the non-traditional stable isotope of Cd and the radioactive isotope Pb of the Hehuashan deposit to discuss the ore-forming metal sources and provide genesis constraints to the Hehuashan Pb–Zn deposit. The sphalerite Cd isotopic compositions are relatively concentrated but the Zn/Cd ratios are scattered in the Hehuashan deposit, of which the early-stage sphalerite δ114/110Cd values ranged from 0.21 ‰ to 0.30 ‰ with an outlier of 0.09 ‰, mean of 0.22 ‰ and a wide range of Zn/Cd ratios (78 to 430), and the late-stage sphalerite δ114/110Cd values ranged from 0.09 ‰ to 0.15 ‰ with two outliers of −0.05 ‰ and 0.52 ‰, mean of 0.17 ‰ with also a wide range of Zn/Cd ratios (50 to 286), both stages of Cd isotopic compositions are overlapped with the ranges of diorite and OIB & MORB, implying the Cd is might be derived from the dioritic intrusions of the Hehuashan deposit district, and the varied Zn/Cd ratios imply that the limestone also provided some of ore-forming metals to the both two ore-forming stages. Additionally, the Pb isotopic compositions of galena in the two mineralization stages exhibit a concentrated range (206Pb/204Pb = 18.2806 – 18.4190, 207Pb/204Pb = 15.6262 – 15.6484, and 208Pb/204Pb = 38.5710 – 38.6529) and all the Pb isotopic data points of the Hehuashan deposit are plotted in the right-hand side of the geochron and the overlapped field of marine sediments, Tongling dioritic intrusions, and Lower Triassic limestones in the Tongling area in the diagrams of (207Pb/204Pb)i vs. (206/204Pb)i and in the field (208Pb/204Pb)i vs. (206/204Pb)i, implying that the Pb is mainly derived from the magma of dioritic intrusions and marine sediments. Subsequently, the sulfide Cd–Pb isotopic compositions show that the ore-forming metals in the Hehuashan deposit are mainly originated from the dioritic intrusions and marine sediments. The plots of deposit genesis classification show that the Cd isotopic compositions in the Hehuashan deposit are unsuitable to the plots of δ114/110Cd vs. Zn/Cd ratios, but imply the metals were derived from multi sources. Finally, the Cd-Pb studies of the Hehaushan Pb–Zn deposit show that the earlier Lower Triassic carbonate formations and its contact with dioritic rocks should be ideal exploration targets for Pb–Zn and associated Cd sources in the Tongling mining area.

Fluid Mixing, Organic Matter, and the Origin of Permian Carbonate-Hosted Pb-Zn Deposits in SW China: New Insights from the Fuli Deposit

The Fuli Pb-Zn deposit is situated at the southwestern margin of the Yangtze Block in Yunnan. The deposit, which is hosted in the Permian Yangxin Formation dolomite, is a recent discovery. Our study indicates a significant presence of fluid inclusions in sphalerite from the Fuli Pb-Zn deposit, with fewer inclusions observed in dolomite and calcite. We conducted comprehensive petrographic, microthermometric, and laser Raman analyses on the inclusions within sphalerite and dolomite. Additionally, six samples of dolomite from the mineralization period were selected for H-O isotope analysis. The results of our study reveal the characteristics of ore-forming fluids and explore the mechanisms of ore formation. The study results indicate that the Fuli Pb-Zn deposit is a low- to medium-temperature hydrothermal deposit with fluid inclusions mainly composed of two-phase gas-liquid inclusions. Salinity and homogenization temperature analyses affirmed that there are two types of fluids present, one with low salinity and the other with high salinity. Laser Raman tests demonstrated the presence of CH4, N2, and CO2 in the gas phase of the inclusions. Microthermometric analyses indicated that the sphalerite ore-forming fluids consist of a multicomponent system of Mg2+ and Ca2+ enriched fluids. The features of the ore-forming fluids in the Fuli deposit arise from a blend of high-temperature, low-salinity metamorphic fluids and low-temperature, high-salinity basin brines. The basin brines in question have the potential to emanate from the Youjiang Basin. The formation of the ore is ascribed to the TSR and the mixing of fluids. The combination of these processes provided the requisite materials (SO42−), catalysts (Mg2+), and reducing agents (organic matter, CH4, and H2S) required to initiate the thermochemical sulfate reduction (TSR). As the TSR proceeded, it caused a shift in the pH of the fluids, thus promoting the precipitation of metal sulfides.

Zinc isotopes revealed the role of ore-hosting carbonate rocks in the formation of MVT deposits: A case study of the Huize Pb[sbnd]Zn deposit, SW China

Although carbonate rocks are important for carbonate-hosted PbZn deposits, there is no effective constraint on the role of carbonate rocks during the PbZn mineralization process. This paper uses the giant Huize PbZn deposit (>7 Mt. metals @ 25–35 % Pb + Zn) as a case study and employs zinc isotopes to gain new insights into such issue. The Huize deposit, located in the Sichuan-Yunnan-Guizhou (SYG) PbZn metallogenic province, is the largest carbonate-hosted deposit in the western Yangtze Block, SW China. Zinc isotope compositions of sphalerite, altered carbonate rocks and fresh carbonate rocks from the Huize deposit are of +0.39 ‰ to +0.68 ‰ (mean + 0.52 ‰, n = 20), −0.25 ‰ to +0.34 ‰ (mean + 0.07 ‰, n = 11) and + 0.35 ‰ to +0.71 ‰ (mean + 0.51 ‰, n = 6), respectively. The initial δ66Zn value of hydrothermal fluids calculated by the Rayleigh fractionation simulation is +0.4 ‰. Such zinc isotope signatures are significantly different from those of potential source rocks, such as the basement Proterozoic metamorphic rocks (δ66Zn = +0.10 ‰ to +0.34 ‰, mean + 0.22 ‰), the host Upper Ediacaran to Middle Permian sedimentary rocks (δ66Zn = −0.24 ‰ to +0.35 ‰, mean + 0.1 ‰) and the cover Upper Permian Emeishan basalts (δ66Zn = +0.30 ‰ to +0.44 ‰, mean + 0.35 ‰). Hence, it is likely that the carbonate rocks acted zinc source and provided heavy zinc isotopes for the PbZn mineralization. The ore-forming fluids extracted the heavy zinc isotopes of the ore-hosting carbonate rocks, resulting in the zinc isotopes of the altered carbonate rocks being far lighter than those of the marine carbonate rocks (δ66Zn = +0.24 ‰ to +1.32 ‰). The sulfur isotope compositions (+12.9 ‰ to +15.6 ‰, mean + 14.3 ‰, n = 20) of sphalerite from the Huize deposit also suggested that the source of reduced sulfur is the marine sulfate minerals within the ore-hosting carbonate rocks. Therefore, carbonate rocks play key roles in the formation of carbonate-hosted PbZn deposits: 1) provide ore-forming elements and ore-hosting space through dissolution; 2) cause isotope variation (e.g., zinc isotopes) by isotope exchange; 3) act as a carbonate buffer to adjust physicochemical conditions (e.g., pH) via cyclical carbonate dissolution, CO2 degassing and recrystallization. On the other hand, the zinc isotope mapping shows that the western part of the SYG PbZn metallogenic province has lighter zinc isotopes than those of the eastern part. This suggests that the migration pathway of hydrothermal fluids is likely west to east, which provides a new clue for regional PbZn ore prospecting. The outcomes have important benefits for understanding the genesis of PbZn deposits, the role of carbonate rocks and the application of zinc isotopes.

Fingerprinting Pb-Zn mineralization events in the SW Yangtze Block, South China: A case from Yuanbaoshan deposit

The southwestern Yangtze Block represents one of the world’s largest lead–zinc provinces, comprises more than 400 known carbonate-hosted Pb-Zn deposits and contains over 30 million tons (Mt) of total Pb + Zn reserves. The Pb-Zn deposits in this area have been studied extensively by economic geologists, but the origin and mineralization processes of these deposits are still controversial. The Yuanbaoshan deposit is a typical carbonate-hosted Pb-Zn deposit of medium scale (0.19 Mt P + Zn reserves @ 0.7–26.31 wt%), which is in the northern part of the Pb-Zn mineral belt in the southwest margin of the Yangtze Block. In this study, we have conducted LA-ICP-MS sulfides trace elements, S isotope analyses, together with gangue carbonate C-O stable isotope analyses and pyrite Rb-Sr dating. We present Rb-Sr isotopic data on the pyrite that yields an isochron age of 196.4 ± 2.3 Ma. The mineralization temperature at Yuanbaoshan, as determined by the Ga, Ge, In, Mn and Fe (GGIMF) in sphalerite geothermometer, ranges from 161 to 264 ℃ (Sp1) and 141 to 246 ℃ (Sp2). The δ13CPDB values range from −0.66 to 0.61 ‰, δ18OSMOW values range from 15.6 to 17.3 ‰. In situ S isotopes show that the δ34S values of sulfides range from −1.4 to 17.73 ‰. The field, petrologic, geochemical and isotopic data from our study lead to the following salient findings. (1) The dissolved carbon and oxygen of ore forming-fluids of these Pb-Zn deposits were mainly derived from sedimentary carbonate dissolution. (2) The reduced S in the sulfide of the Yuanbaoshan Pb-Zn deposit is mainly derived from the thermochemical sulfate reduction (TRS) and the reduced S produced by the pyrolysis of S-containing organic matter in the carbonaceous mudstone of the Ebian Group. (3) The large-scale Pb-Zn mineralization in the southwest margin of the Yangtze Block was influenced by the post-collision extension between the Indosinian Block and the South China Block during ca. 200 Ma.

Source and genesis of Chapai carbonate-hosted Zn-Pb deposit, South China: Constraints from in-situ S and Pb isotopes of sulfide and sulfate minerals

Chapai deposit is a special medium-sized carbonate-hosted Zn-Pb deposit (4.27Mt of sulfide ore with 8.15 % Zn, 3.44 % Pb, and 53.39 g/t Ag, as well as 0.82Mt of oxidized ore with 2.8 % Zn and 1.2 % Pb and 27.68 g/t Ag) with upper oxidized ore and lower sulfide ore of South China. Due to the shortage of detailed geological and geochemical constraints, the ore genesis of single stage magmatic hydrothermal mineralization or superposition of multi-stage mineralization remains unclear. Therefore, detailed geological and geochemical analyses of in-situ S isotopic compositions of sulfide and sulfate, trace elements of sphalerite, and ore Pb isotopic compositions were performed to decode the source and genesis of the Chapai deposit. Based on the investigation and microscopic observation, mineralization of the Chapai Zn–Pb deposit has obvious early hydrothermal alternation in the early hydrothermal sulfide stage (S1) and the late hydrothermal sulfide stage (S2) as well as the supergene oxidized mineralization stage (S3). The trace elements Cu, Ag, Ga, Sb, As and Ge are incorporated into S1 and S2 stages of sphalerite mainly through the following substitution mechanisms: Zn2+↔ (Fe2+, Cd2+),2Zn2+↔ (Ag+, Cu+) +(As3+, Ga3+, Sb3+), 3Zn2+↔ Ge4++2(Cu++Ag+), 4Zn2+↔(Cu++Ag+) + Sb3++Ge4++□(vacancy). In situ δ34S values of sulfides and sulfates are within a greater range (–3.0 to + 32.2 ‰), and are significantly higher in S2 compared to S1 stage, implying the mixing of two isotopically different end-members of hydrothermal fluids and wall rocks by sulfate reduction. The S isotope of sphalerite and galena crystallized in the early stage close to 0 ‰ may be controlled by magmatic-hydrothermal fluid source, while the increased S isotope in the late stage may be derived from the increased decomposition of organic matter and organic sulfate reduction (TSR). The Pb isotopic data (206Pb/204Pb = 18.355 ∼ 18.819, 207Pb/204Pb = 15.720 ∼ 15.778, and 208Pb/204Pb = 38.912 ∼ 39.222) indicate that the sources of metallogenic materials in the Chapai deposit are primarily upper crust basement rocks. The geothermometer studies of sphalerite in Chapai deposit show that it was generated from a medium–low temperature (142 ∼ 255 °C) condition. The low Zn/Cd ratios and high concentrations of Cd and Ge in sphalerite are in agreement with those of Mississippi Valley-type (MVT) deposits. Hence, the Chapai deposit was formed in a medium–low temperature magmatic- hydrothermal system and can be categorized as a MVT deposit within Nanling region (NR).

Linking carbonate-hosted Zn[sbnd]Pb deposit to deep mantle activity: Evidence from in situ U[sbnd]Pb geochronology of calcite from the world-class Huayuan Zn[sbnd]Pb ore field in South China

Carbonate-hosted ZnPb deposits are a major source of zinc, lead, and some critical raw metal resources worldwide (e.g., germanium and gallium). However, the timing and geodynamics setting of their mineralization remain enigmatic, leading to ongoing debates about their origins. To shed light on these issues, we utilized LA-ICP-MS in situ UPb dating of ore-related calcites to determine the timing and geodynamic setting of mineralization events in the world-class Huayuan carbonate-hosted ZnPb ore field in South China. The petrographic and cathodoluminescence features, fluid inclusion characteristics, and the Pb isotope data indicate that the tested calcites were formed from the same ore-forming fluids as the intergrown sphalerite and were not overprinted by possible later hydrothermal fluids. Our results show that the calcite UPb ages of 510–495 Ma refute the previously proposed Mississippi Valley-type (MVT) model, which suggested that the younger Caledonian orogeny (460–420 Ma) played a significant role in the genesis of the Huayuan ZnPb ore field. Instead, our findings link the formation of this ore field to crustal extension and high heat flux resulting from mantle upwelling events in northeast Gondwana during the Cambrian. The findings indicate that deep mantle processes can trigger shallow crustal fluid circulation to create a giant carbonate-hosted ZnPb ore field in a long-dormant rift.We present a genetic model proposing that the extensive carbonate platform of the Qingxudong Formation was likely a “brine factory” that supplied the brines to the Proterozoic basement through reactivated syn-rift faults. The high heat flux from upwelling mantle not only heated these brines to high temperatures but also caused early maturation of organic matter in the lower Cambrian Niutitang black shales to generate hydrocarbons. The hydrocarbons migrated into the limestone of the Qingxudong Formation. Meanwhile, the hot brines leached Zn and Pb from the Proterozoic basement rock. These ZnPb bearing brines ascended to the Qingxudong Formation where they mixed with the hydrocarbons. These hydrocarbons acted as reducing agents for ZnPb sulfide precipitation, forming the Huayuan giant ZnPb ore field. Furthermore, UPb dating results of syn-mineralization calcite, together with the relationships between the ores and host rocks, indicate that ZnPb mineralization occurred over timespans during or shortly after host-rock deposition and continuing during lithification for several million years in this ore field. The similar prolonged duration of mineralization may be relatively prevalent in other carbonate-hosted ZnPb deposits/ore fields. We therefore recommend that reliable age dating for all mineralization stages is necessary to establish genetic models for carbonate-hosted ZnPb deposits.

Selenium enrichment in the Dingtoushan carbonate-hosted epigenetic Pb-Zn deposit in the western Yangtze Block, SW China

Selenium (Se) is a typical dispersed element (crust Clarke value only 0.05 × 10-6) and is mainly enriched in black shales (>20 × 10-6). Selenium can also be associated with Pb-Zn and U deposits. In carbonate-hosted epigenetic hydrothermal Pb-Zn deposits, the selenium contents in sulfides are commonly < 50 × 10-6, and the selenium is mainly enriched in galena, whereas the selenium contents in sphalerite are often < 10 × 10-6. There are few studies on Se-rich carbonate-hosted epigenetic hydrothermal Pb-Zn deposits, and the origin of such deposits needs more in-depth exploration. In this study, we selected the Dingtoushan Se-rich Pb-Zn deposit in the western Yangtze Block, SW China, and utilized in-situ trace elements and S-Pb isotopes of Se-rich sphalerite to investigate this issue. There are two textures of sphalerite formed in the Dingtoushan deposit, of which subhedral sphalerite (Sp-I) precipitated during the early stage, whereas euhedral sphalerite (Sp-II) generated during the late stage. The results of trace elements show that the Dingtoushan deposit is significantly enriched in selenium (>22 × 10-6) compared with other carbonate-hosted Pb-Zn deposits (<22 × 10-6, generally < 10 × 10-6) in the Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province. In detail, a positive correlation between Se, Cd, In and Cu contents and sulfur isotopes of sphalerite is identified at the deposit scale, but no relationship is observed at the grain scale. In addition, the late stage Sp-II with δ34S values of −7‰ to −3‰ is rich in selenium and other trace elements, whereas the early stage Sp-I with isotopically light sulfur (δ34S = -29 ‰ to −8‰) is depleted of them. This indicates that in the early stage, insufficient addition of hydrothermal fluid resulted in relatively low temperature, and sulfur formed by bacterial sulfate reduction (BSR) was mainly involved in mineralization. With the addition of a large amount of hydrothermal fluid, thermochemical sulfate reduction (TSR) was induced, which leads to the formation of sphalerite in the late stage with relatively high δ34S values. Furthermore, the Pb isotopes reveal that the ore-forming metals were likely derived from the Cambrian black shales. Hence, we infer that fluid mixing is the main sulfide precipitation mechanism and may cause the positive correlation of selenium concentrations and δ34S values. On the other hand, at the grain scale of sphalerite, the variation of selenium contents shows a negative correlation with temperature, suggesting that temperature may play a critical role in selenium enrichment in sphalerite. This study highlights that selenium enrichment in sphalerite is jointly controlled by fluid mixing and temperature. The degree of fluid mixing dominated the selenium concentration in hydrothermal fluid, but high temperature may not be conducive to selenium incorporation into sphalerite. Our new results indicate that sphalerite in the carbonate-hosted epigenetic hydrothermal deposits is also a major host for selenium and such type deposits may have a great economic potential for selenium resource.

Hydrothermal reduction of sulfates by ferrous carbonate: Implications for the origin of reduced sulfur in carbonate-hosted Pb-Zn deposits associated spatially with basalts

Reduced sulfur derived from thermochemical sulfate reduction (TSR) in Pb-Zn deposits is one of the long-debated issues in economic geology. The formation of - 2 valent sulfur (S2-) in Pb-Zn deposits associated spatially with basalts, may be related to the thermal reduction of SO42- by ferrous ions (Fe2+). In the present study, hydrothermal experiments on the reduction of magnesium sulfate (MgSO4) by ferrous carbonate (FeCO3) were carried out to investigate the thermodynamics feasibility, kinetic characteristics and reaction mechanisms for the inorganic reduction of sulfates. The results show that the reduction of MgSO4 by FeCO3 is thermodynamically stronger than TSR of oil, gaseous hydrocarbons and solid bitumen. Moreover, this reduction reaction occurs at threshold temperatures below 300 °C under hydrothermal conditions, yielding the main products of magnetite (Fe3O4), pyrite (FeS2) and pyrrhotite (Fe7S8). The reaction mechanism for the studied multiphase system at 400 − 525 °C involves at least nine elementary steps. The chemical kinetics for the FeCO3 −MgSO4 − H2O system is in accordance with the phase boundary control reaction model with apparent activation energy of 70 kJ/mol. The formation of S2- in carbonate-hosted Pb-Zn deposits associated spatially with basalts is most likely a two-stage sulfate reduction process involving Fe2+ (90 −140 °C) and organic matters (>140 °C) in series. The new findings from the inorganic reduction of sulfates would contribute to clarification of the genesis of Pb-Zn deposits and help to reconceptualize some of the long-standing controversial issues in this field.

Multi-layer metallogeny of the maoping carbonate-hosted Pb–Zn deposit, SW China: Constraints from C–O–S–Pb isotopes

The Maoping carbonate-hosted Pb–Zn deposit, located in the Sichuan-Yunnan-Guizhou metallogenic belt (SYGMB), comprises numerous ore bodies hosted in Devonian and Carboniferous Systems. Multi-layer Pb–Zn mineralization (two or more systems) at deposit scale is still rare in the SYGMB and poorly understood. Although δ18O values (+9.4 to +12.3‰) of calcite in Devonian System is similar to those (+9.2 to +12.0‰) of calcite in Carboniferous System, δ13C values (−1.7 to −0.2‰) of calcite in Devonian System is significantly higher than those (−5.4 to −2.7‰) of calcite in Carboniferous System. Such C–O isotopic characteristics suggest that the source of C was ore-hosting carbonate rocks, whereas the source of O was basement metamorphic rocks. The simulation of C–O isotopes shows that water-rock interaction was the main mechanism for calcite precipitation. The δ34S values (+18.3 to +22.7‰) of sulfides in Devonian System are higher than those (+7.1 to +17.5‰) of sulfides in Devonian System. This implies that reduced sulfur in Devonian System originated from Devonian marine sulfate, while those in Carboniferous System originated from Carboniferous marine sulfate. Such S isotopic compositions also show that thermochemical sulfate reduction (TSR) was the dominant mechanism for the reduction of marine sulfate. The isotopic ratios (206Pb/204Pb = 18.680–18.744, 207Pb/204Pb = 15.753–15.764, 208Pb/204Pb = 39.282–39.399) of galena in Devonian System and those (206Pb/204Pb = 18.554–18.581, 207Pb/204Pb = 15.722–15.752, 208Pb/204Pb = 39.018–39.109) of galena in Carboniferous System are similar to those of basement metamorphic rocks and cover carbonate rocks. This indicates that ore-forming metals had mixed sources. Considering the above results, the multi-layer metallogeny is the mixing of metal and sulfate-bearing fluids with metal-rich but reduced sulfur-poor fluids at the depositional site where methane or other organic matter reduces sulfate and precipitates sulfides. In the future, A multi-layer exploration strategy for Pb–Zn deposits in the SYGMB should be emphasized.

LA-ICP-MS analyses of trace elements in zoned sphalerite: A study from the Maoping carbonate-hosted Pb-Zn(-Ge) deposit, southwest China

In southwest China, many Pb-Zn deposits are described as low temperature carbonate-hosted deposits or Mississippi Valley-type (MVT) deposits. But trace element distribution and concentration in sphalerite between deposits may significantly vary and could possibly imply alternative deposit-types. An investigation was carried out on sphalerite (Sp-II) in the main ore stage of the Maoping carbonate-hosted Pb-Zn(-Ge) deposit (Southwest China), based on laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Here, Sp-II is divided into the dark red, yellow–brown, and light-yellow zones. Principal component analysis revealed element clusters distributed within distinct zoning types in Sp-II: the dark red zones are enriched in Mn, Fe, and Cd; the yellow–brown zones are enriched in Cu, Ge, Ag, and Sb; the light-yellow zones are enriched in Ga. Trace elements in Sp-II record temperature and sulfur fugacity (fS2) evolution of ore-forming fluid system, which tends to decrease from the dark red to yellow–brown to light-yellow zones. The formation of Sp-II may be an external process resulting from the varieties of temperature and fS2 in the ore-forming fluid, which may be driven by rock buffer. Here, Manganese, Fe, and Cd are preferentially incorporated in the relatively higher temperatures and fS2, whereas Ga is preferentially incorporated in the relatively lower those. Regardless of the zoning type, strong binary correlations between Ge and Cu as well as the high similarity of their concentration distribution in mapping images suggest coupled substitutions as Ge4+ + 2Cu+ ↔ 3Zn2+ and/or Ge2+ + 2Cu+ ↔ 2Zn2+ + vacancy. A trace element comparison of various Pb-Zn deposits in the world, including our new data from Maoping shows a distinctive signature for the Maoping deposit. Homogenization temperatures (217–430 ℃, mean 298 ℃) of the newly discovered ore body (No. VI) support that Maoping is a medium–high temperature carbonate-hosted deposit.

Mixing in Two Types of Fluids Responsible for Some Carbonate-Hosted Pb–Zn Deposits, SW China: Insights from the Maoping Deposit

Carbonate-hosted Pb–Zn deposits are of major economic importance. The Sichuan–Yunnan–Guizhou metallogenetic belt (SYGMB), located on the western margin of the Yangtze Block, comprises over 400 carbonated-hosted Pb–Zn deposits. However, ore-forming fluids recorded in these deposits have led to controversy regarding ore genesis. We investigated a fluid system for the Maoping deposit in the SYGMB, based on fluid inclusions, and H–O–He–Ar isotopic studies. The results showed that ore-forming fluids in the Maoping deposit are characterized by mixing of high-temperature and low-salinity metamorphic fluids and low-temperature and high-salinity basinal brines. The Precambrian basement is considered to produce metamorphic fluids, while the basinal brines are said to originate from the Youjiang Basin. The mineralization at the depositional site appears to reflect the coincidence of the metamorphic fluids, basinal brines, Carboniferous coal seams, and structural-stratigraphic traps. Regional-scale data show large-scale heterogeneity in fluid properties, including basinal brines, metamorphic fluids, and organic fluids. Furthermore, the data suggest a precipitation model for some high-grade Pb–Zn deposits in the SYGMB. These findings will contribute to an understanding of deposit types in the SYGMB.

The Characteristics and Origin of Barite in the Giant Mehdiabad Zn-Pb-Ba Deposit, Iran

Abstract Mehdiabad is the world’s largest Mississippi Valley-type (MVT) Zn-Pb deposit (394 million tonnes [Mt] of metal ore at 4.2% Zn, 1.6% Pb) and contains significant barite resources (&amp;gt;40 Mt). Such large accumulations of barite are not common in carbonate-hosted Zn-Pb deposits. Therefore, the origin of the barite and its association with the Zn-Pb mineralization is of significant interest for further investigation. Field work and petrographic studies indicate that the Zn-Pb-Ba orebodies in the Mehdiabad deposit are hosted by Lower Cretaceous carbonate units of the Taft and Abkuh Formations. Fine- to coarse-grained barite with lesser siderite formed in three stages (S1, S2, and S4), along with a quartz-sulfide stage (S3) with minor quartz, sphalerite, galena, chalcopyrite, and pyrite, and the main Zn-Pb sulfide stage (S5) with massive sphalerite and galena. The barites have δ34S values from 17.7 to 20.6‰, δ18O values from 13.2 to 16.8‰, Δ33SV-CDT values from –0.001 to 0.036‰, and initial 87Sr/86Sr ratios from 0.707327 ± 0.000008 to 0.708593 ± 0.000008 (V-CDT = Vienna-Canyon Diablo Troilite). The siderites have δ13CV-PDB values from –3.8 to –2.7‰, and δ18OV-SMOW values from 18.2 to 20.9‰ (V-PDB = Vienna-Pee Dee Belemnite, V-SMOW = Vienna-standard mean ocean water). These geochemical data, and the barite morphology, point to a diagenetic origin for all stages of barite. We suggest that S1 and S2 barite precipitated from pore fluids at the sulfate-methane transition zone in a methane-diffusion-limited environment with increasing methane content. S4 barite precipitated when the methane- and barium-bearing cold-seep fluid migrated to the shallow carbonate sediments and formed a methane-in-excess setting. For the three stages, the SO42- in barite came from the residual SO42- in pore fluids undergoing sulfate-driven anaerobic oxidation of methane, and the Ba2+ came from dissolved biogenic barite and terrigenous materials in the Taft and Sangestan Formations. Primary fluid inclusions trapped in S3 quartz have salinities of 5.6 to 8.1 wt % NaCl equiv and homogenization temperatures of 143.8° to 166.1°C. The quartz has δ18OV-SMOW values ranging from 9.8 to 22.5‰ and δ30Si values from –1.3 to –0.9‰. These data indicate hydrothermal fluid flow occurred between the diagenetic S2 and S4 events. Secondary fluid inclusions with salinities of 17.70 to 19.13 wt % NaCl equiv and homogenization temperatures of 123.0° to 134.0°C are found in the S3 quartz, too. They might represent the hydrothermal event formed by basinal brines in S5. According to the ore textures and the comparison of the sulfur isotopes between S5 Zn-Pb sulfides and the digenetic barites, the barite provided a host and a sulfur source for the later Zn-Pb mineralization. The relationship between barite and the Zn-Pb mineralization indicates that significant accumulations of sulfates may be a critical exploration target for this kind of giant deposit.

Geology and geochemistry of Zn-Pb(-Ge-Ag) deposits in the Sichuan-Yunnan-Guizhou Triangle area, China: A review and a new type

Mississippi Valley Type (MVT)1 deposits represent the majority of carbonate-hosted Zn–Pb deposits globally. They typically form in an extensional tectonic setting along passive margins. However, studies on carbonate-hosted Zn–Pb deposits in the Sichuan–Yunnan–Guizhou Triangle area (SYGT) reveal differences in terms of the essential features of typical MVT deposits. We discuss the main features of these deposits, controlled by folds and faults, high-grade Zn–Pb ores and symbiotic or associated elements (i.e., abundant Ag and dispersed amounts of Ge, Ga, and Cd) of significant economic value. Based on a comparison of Pb-Zn deposits in SYGT and classical MVT deposits formed in an extensional tectonic setting, as well as a subsequent discussion on deposit classification, we propose that the Huize-style Zn–Pb deposits are a new deposit style, whose basic features can guide future ore exploration. We define the Huize-style deposits based on four factors: i) Hierarchical ore-controlling system of strike-slip fault-fold structures, ii) litho-facies associated with typical alternation and mineralisation, iii) ore-forming geochemical features revealed by typical mineral assemblages, mineralisation alteration zoning, fluid-inclusion, isotope geochemistry and metallogenic acid–alkali geochemical barriers, and iv) different prospecting methods to those typically used for MVT deposits. The Huize-style and typical MVT deposits constitute the carbonate-hosted non-magmatic epigenetic hydrothermal-type (CNHT) Zn–Pb deposits.

In situ geochemical and Rb-Sr dating analysis of sphalerite from the Liangyan Pb–Zn deposit in northwestern Guizhou, China: Implication for timing of ore formation

The Liangyan Zn–Pb deposit, located on the southwestern margin of the Yangtze Platform, is a carbonate–hosted Zn–Pb deposit. The deposit contains over 45.4 thousand tons of ore containing Pb + Zn metals at a grade of 5.95 % Zn and 2.18 % Pb. The in-situ trace element analysis of sphalerite from this deposit was carried out by LA–ICP–MS. The analysis revealed the trace element compositions and the correlation between the Rb/Sr ratio and trace elements with temperature (e.g., Mn, In, Cd and Ga). The correlation between Rb/Sr ratio and Mn, In, Cd, and Ga is 0.99, 0.80, 0.71, and 0.70, respectively. The Rb/Sr ratio correlation is negative with Mn, Ga, and In, but positive with Cd. The reliable ore-forming age of the Liangyan deposit is 214.8 ± 4.3 Ma by the grinding stage dissolution technique of sphalerite residue and leachate.

Mineral textures, mineral chemistry and S isotopes of sulphides from the Tianbaoshan Pb–Zn–Cu deposit in the Sichuan–Yunnan–Guizhou triangle: implications for mineralization process

AbstractThe carbonate-hosted Pb–Zn deposits in the Sichuan–Yunnan–Guizhou (SYG) triangle region are important Indosinian deposits in South China. The Tianbaoshan deposit is a typical large Pb–Zn deposit in the SYG area and occurs as pipe-like type, hosted by Sinian dolostone. It contains ∼26 Mt Zn–Pb ore (7.76–10.09 % Zn, 1.28–1.50 % Pb and 93.6 g t−1 Ag) and &gt;0.1 Mt Cu ore (2.55 % Cu). In this study, the detailed mineral textures, mineral chemical and sulphur isotopic compositions of the various sulphides have been analysed to constrain the abnormal enrichment mechanism and mineralization relationship. Four mineralization stages have been recognized: Stage 1, minor early pyrite (Py1) with relics and infill of intergranular dolomite or quartz grains; Stage 2, Cu mineralization with coarse-grained, elliptical crystal chalcopyrite (Cp1); (3) Stage 3, Zn mineralization with dark fine-grained sphalerite (Sph1) and light coarse-grained sphalerite (Sph2); and (4) Stage 4, as represented by a quartz–calcite assemblage with galena, minor pyrite (Py2) and chalcopyrite (Cp2). The petrography of the sulphide minerals (Py1, Cp1, Sph1 and Sph2) demonstrates a mutual inclusion relationship. The nature of this relationship from core to rim and their similar sulphur isotope values (5.5–8.3 ‰) indicates a single sulphur source, suggesting that the different mineralization types are the result of different stages of a continuous hydrothermal system. Sphalerite geothermometer study suggests that sphalerite in the Tianbaoshan deposit formed in a low-temperature (&lt;200 °C) hydrothermal system. The low concentrations of Mn and In, low In/Ge ratios and high Fe/Cd ratios in the sphalerite are consistent with those of Mississippi Valley-type (MVT) deposits, but different from those of magmatism-related deposits (e.g. epithermal, skarn and VMS deposits). The positive δ34S values for Py1 (5.1–7.9 ‰), Cp1 (5.1–7.2 ‰), Sph1 (4.7–7.4 ‰), Sph2 (3.9–8.7 ‰), Py2 (4.4–9.3 ‰) and Cp2 (5.0–6.8 ‰) indicate a sulphur source from thermochemical reduction of coeval seawater sulphate. Widely developed dissolved textures (caverns and breccias) with massive sulphide infillings and deformed host rock remnants suggest that replacement of host dolostones by ore fluids was volumetrically significant and the ore formed nearly simultaneously with the cavities. The Tianbaoshan deposit is a typical MVT deposit, which resulted from mixing of a H2S-rich fluid and a metal-rich fluid, with thermochemical sulphate reduction occurring before ore precipitation rather than during ore precipitation.

The Origin of Carbonate Components in Carbonate Hosted Pb-Zn Deposit in the Sichuan-Yunnan-Guizhou Pb-Zn Metallogenic Province and Southwest China: Take Lekai Pb-Zn Deposit as an Example

The Lekai lead–zinc (Pb-Zn) deposit is located in the northwest of the Sichuan–Yunnan–Guizhou (SYG) Pb-Zn metallogenic province, southwest China. Even now, the source of the metallogenic fluid of Pb-Zn deposits in the SYG Pb-Zn metallogenic province has not been recognized. Based on traditional lithography, rare earth elements (REEs), and carbon–oxygen (C–O) isotopes, this work uses the magnesium (Mg) isotopes of hydrothermal carbonate to discuss the fluid source of the Lekai Pb-Zn deposit and discusses the fractionation mechaism of Mg isotopes during Pb-Zn mineralization. The REE distribution patterns of hydrothermal calcite/dolomite are similar to that of Devonian sedimentary carbonate rocks, which are all present steep right-dip type, indicating that sedimentary carbonate rocks may be serve as the main source units of ore-forming fluids. The C–O isotopic results of hydrothermal dolomite/calcite and the δ13CPDB–δ18 OSMOW diagram show that dolomite formation is closely related to the dissolution of marine carbonate rocks, and calcite may be affected to some extent by basement fluid. The Mg isotopic composition of dolomite/calcite ranges from −3.853‰ to −1.358‰, which is obviously lighter than that of chondrites, mantle, or seawater and close to that of sedimentary carbonate rock. It shows that the source of the Mg element in metallogenic fluid of Lekai Pb-Zn deposit may be sedimentary carbonate rock rather than mantle, chondrites, or seawater. In addition, the mineral phase controls the Mg isotope fractionation of dolomite/calcite in the Lekai Pb-Zn deposit. Based on the geological, mineralogical, and hydrothermal calcite/dolomite REE, C–O isotope, and Mg isotope values, this work holds that the mineralization of the Lekai Pb-Zn deposit is mainly caused by basin fluids, influenced by the basement fluids; the participation of basement fluids affects the scale and grade of the deposit.

Mapping hydrothermal and supergene alteration zones associated with carbonate-hosted Zn-Pb deposits by using PRISMA satellite imagery supported by field-based hyperspectral data, mineralogical and geochemical analysis

Delineating hydrothermal alteration and supergene caps is fundamental for mineral exploration of sulfide ores. The aim of this study is to apply a multi-scale workflow based on hyperspectral remote and proximal sensing data in order to delineate hydrothermal dolomitization and supergene alteration associated with the Mississippi Valley-Type Zn-Pb(-Ag) deposit of Jabali (Western Yemen). The area was investigated through hyperspectral images derived from the new launched Italian Space Agency’s PRISMA satellite, which has a higher spectral resolution compared to multispectral sensors and covers the mineral-diagnostic wavelength regions (such as the 2100 nm to 2300 nm range) with a Signal to Noise Ratio (SNR) ≥ 100. Spectral mineral maps were produced through the band ratios method using specific feature extraction indices applied to the hyperspectral satellite data. The results were validated by using Visible Near InfraRed (VNIR) to Short Wave InfraRed (SWIR) reflectance spectra, mineralogical (XRPD) and geochemical (ICP-ES/MS) analyses on rock samples collected in the Jabali area. The dolomites footprint was mapped using a PRISMA Level 2C image, by enhancing the spectral differences between limestones and dolomites in the SWIR-2 region (major features centered at 2340 nm and 2320 nm, respectively). Gossans were detected due to the Fe3+ absorption band in the VNIR region at 900 nm. The Zn-Pb mineralized area, extended for approximately 25 km2, was thus identified by recognizing gossan occurrences in dolomites. The study demonstrates that the PRISMA satellite is effective in identifying Zn-Pb mineralized outcrops in sedimentary basins.

Critical metal enrichment in carbonate-hosted Pb-Zn systems: Insight from the chemistry of sphalerite within the Hehuashan Pb-Zn deposit, Middle-Lower Yangtze River Metallogenic Belt, East China

Carbonate-hosted Pb–Zn deposits frequently contain significant amounts of critical metals such as Cd, Ga, Ge, Tl, and In. However, the characteristics of critical metal enrichments and the geochemical controls of the critical metal enrichments present within different types of sphalerite in individual deposits remain poorly constrained. Textural observations and in-situ laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) and associated elemental mapping allows the investigation of the controls on the incorporation of critical metals into sphalerite within the Hehuashan carbonate-hosted Pb–Zn deposit, East China, which contains 639.36 t Cd at an average grade of 0.0020 % and 161.23 t Ga at an average grade of 0.0161 %. Two ore-formation stages (early and late) and five textural types of sphalerite are present in the deposit, namely fine-grained brown sphalerite (FCS), irregular sphalerite (IS), oolitic sphalerite (OS), banded sphalerite (BS), and coarse-grained sphalerite (CCS), all of which are present within breccia-, vein-, and massive ores. The FCS, IS, OS, and BS formed during early stage mineralization whereas the CCS formed during the later stages of mineralization. Large variations of Cd, Ga, Ge, Tl, and In concentrations are present within these sphalerites with an average Cd of 5997 ppm in OS, 14003 ppm in FCS, 962 ppm in IS, 2565 ppm in BS, and 5250 ppm in CCS; Ga of 1047 ppm in OS, 5 ppm in FCS, 3 ppm in IS, 15 ppm in BS, and 33 ppm in CCS; Ge of 166 ppm in OS, 21 ppm in FCS, 530 ppm in IS, 13 ppm in BS, and 4 ppm in CCS. The Cd within this sphalerite is incorporated by direct substitution between Cd2+ and Zn2+ whereas Ga concentrations are correlated to monovalent cation concentrations (Cu and Ag) and Ge concentrations are not correlated to monovalent cation concentrationss, indicative of an unusual vacancy-related substitution of Ge for Zn. Trace and minor element distribution variations and the calculated temperatures of formation of the deposit suggest that the ore-forming fluids associated with the system evolved significantly over the multiple stages of mineralization recorded within the study area. In addition, the deposit records two critical metal enrichment events associated with the early and late stages of mineralization within the Hehuashan Pb–Zn deposit, respectively; an early event associated with enrichments in Cd, Ge, and In, and a late event associated with enrichments in Cd and Ga, indicating that carbonate-hosted Pb–Zn deposits should be considered significant potential sources for critical metals such as Cd, Ga, Ge. However, the concentrations of these critical metals vary within the different types of sphalerite present in in individual Pb–Zn deposits, suggesting that thhe Hehuashan deposit, and other similar deposits within the MLYRMB, may have undergone at least two critical metal enrichments events that should be targeted for future critical metal exploration.

Constraints of C[sbnd]H[sbnd]O[sbnd]S[sbnd]Pb isotopes and fluid inclusions on the origin of the giant Zhugongtang carbonate-hosted Pb–Zn deposit in South China

The Sichuan–Yunnan–Guizhou (SYG) metallogenic province on the western margin of the Yangtze Block has long been a research focus and is an important region of Pb–Zn mineralization in China, but its genesis is poorly constrained. This study examines the Zhugongtang carbonate-hosted Pb–Zn deposit (>3.0 Mt, 0.09–35.04 wt% Pb + Zn), the largest discovery made in the past decade in the southeastern part of the SYG metallogenic province. Fluid inclusions from sphalerite and calcite, CHO–isotopes from calcite, and S–Pb isotopes from sulfide minerals in the Zhugongtang Pb–Zn deposit were analyzed to understand the sources and genesis of the metals and hydrothermal fluids. Fluid inclusions in sphalerite and calcite from the largest ore body indicate that the fluids of the main mineralization stage had low temperatures (105 °C–210 °C) and moderate salinities (0.35–12.89 wt% NaCl equiv.). The sulfides are characterized by narrow ranges of sulfur isotope compositions (δ34Spyrite = +14.27 ‰ to +15.89 ‰, δ34Ssphalerite = +14.31 ‰ to +15.53 ‰, and δ34Sgalena = +10.64 ‰ to +12.97 ‰), indicating that reduced sulfur was derived from sedimentary sulfate in the Devonian to Permian carbonate host rocks by thermochemical sulfate reduction with the addition of organic matter. The δ13CPDB and δ18OSMOW values of calcite range from − 8.6 ‰ to +0.82 ‰ and +15.45 ‰ to +19.41 ‰, respectively, which are similar to values for mantle, marine carbonate rocks, and sedimentary organic matter. The negative correlation between δ13CPDB and δ18OSMOW values indicates that CO2 in the hydrothermal fluids was sourced from marine carbonate rocks and sedimentary organic matter. Calculated δ18OH2O and δDH2O values range from +3.5 ‰ to +7.5 ‰, and −93 ‰ to −52 ‰, respectively, indicating that the ore-forming fluids were dominantly metamorphic, but diluted by meteoric water that had reacted with organic matter. The galena samples yield 206Pb/204Pb values of 18.52 to 18.82, 207Pb/204Pb of 15.68 to 15.93, and 208Pb/204Pb values of 38.97 to 39.96. The μ and ω values of the sulfides range from 9.61 to 10.07 and 38.84 to 43.67, respectively. These data plot on the upper crust Pb evolution curve, generally in the field of Devonian to lower Permian sedimentary rocks, although the value for one sample falls in the field of Proterozoic metamorphic rocks, pointing to a complex origin for the ore-forming materials. Overall, the fluid inclusion and isotope data, together with geological evidence, suggest that the ore-forming fluids of the Pb–Zn deposit were sourced from deep metamorphic water with the features of low temperatures and moderate salinities, and the ore-forming metals were sourced from Devonian to lower Permian sedimentary rocks and partly from basement rocks. The genesis of the Zhugongtang ore is typical of SYG-type deposits.

The mineralization of Daxiao carbonate-hosted Pb-Zn deposit, northeast Yunnan province, SW China: Constraints from Rb-Sr isotopic dating and H[sbnd]O[sbnd]S-Pb isotopes

The Sichuan-Yunnan-Guizhou (SYG) Pb-Zn metallogenic province located in western Yangtze Block contains more than 400 carbonate-hosted Pb-Zn deposits. Uncertain mineralization age and ore-forming material source causing debates on the genesis of these carbonate-hosted Pb-Zn deposits. To address this issue, the Daxiao Pb-Zn deposit was chosen as a case study. The orebodies of Daxiao deposit are hosted in Mesoproterozoic Heishan formation argillaceous dolomite interbedded with slate. Three main mineralization stages have been identified, including syn-sedimentary stage, hydrothermal stage and supergene stage. The ore minerals consist of galena, sphalerite, chalcopyrite, argentite, smithsonite, anglesite and cerussite in the deposit. The early hydrothermal stage sphalerite yielded a Rb-Sr isochron age of 223.5 ± 2.9 Ma, consistent with the spike of Pb-Zn mineralization in SYG metallogenic province. Quartz in hydrothermal stage yields δDSMOW values of −69.6 to −65.8 ‰ and calculated δ18OFluid values of + 3.4 – +5.6 ‰, showing an affinity of metamorphic water. While the quartz in supergene stage yields δDSMOW values of −68.3 to −65.8 ‰ and calculated δ18OFluid values of −4.1 to −1.7 ‰, indicating abundant basinal brine or meteoric water had mixed into ore-forming fluid during its evolution from hydrothermal stage to supergene stage. Sulfur isotopic composition (δ34S = +6.3 – +19.1 ‰) of different stage sulfides reveal that the ore-forming sulfur originated from sulfates within the wall rocks, and mainly reduced by Thermal-chemical reduction (TSR). Moreover, the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of early hydrothermal stage sphalerite are 18.282 – 18.312, 15.603 – 15.681and 38.287 – 38.311, respectively. Those of late hydrothermal stage galena are 18.315 – 18.491, 15.676 – 15.721 and 38.314 – 38.326, respectively. All of them plot in the overlapping area of Emeishan flood basalts, Kunyang and Huili groups and Sinian to Triassic strata, indicating that these wall rocks jointly contributed the ore-forming metals for these Pb-Zn deposits in SYG metallogenic province. Hence, a metallogenic model for Daxiao and other carbonate-hosted Pb-Zn deposit in SYG metallogenic province was proposed: In the thrustfold systems caused by the subduction of Paleo-Pacific and the closure of Jinshajiang-Ailaoshan Paleo-Tethys ocean in Late Triassic to Early Jurassic. The fluids originated from metamorphic water migrated along deep faults and extracted ore-forming materials from wall rocks (including Proterozoic basement rocks, Sinian to Triassic sedimentary wall rocks and Permian Emeishan flood basalts), and then precipitated ores in the secondary thrust faults or interlayered fractures within these thrustfold systems.