Mississippi Valley-type Deposits Research Articles

U–Pb geochronology of carbonate-hosted Pb–Zn ores reveals plate-tectonic evolution of eastern Asia during the early Paleozoic

The Mississippi Valley–type (MVT) deposits reached their maximum abundance during the final assembly of Pangea. The intense orogenic activity during this assembly in relatively low latitudes created abundant opportunities for the migration of sedimentary brines into the interior carbonate platforms landward of the orogenic belts, leading to the formation of MVT deposits. Thus, dating the MVT deposits can potentially aid in the reconstruction of the plate tectonic evolution during the assembly of Pangea. The Yangtze Craton hosts significant carbonate-hosted Zn–Pb deposits (> 60 Mt Pb + Zn metals), accounting for 30% of China’s Zn–Pb resources. However, determining the timing of zinc and lead mineralization in these reservoirs is challenging. This study employs LA-ICP-MS U–Pb geochronology on calcites to date Zn–Pb deposits hosted in Lower Cambrian limestone in the Huayuan orefield. Three generations of calcite formation were dated: the first recorded the pre-ore deposition of Lower Cambrian limestone at 517 ± 10 Ma, the second marked a hydrothermal event linked to stratiform sphalerite ore formation at 501.4 ± 8.4 Ma, and the third was associated with discordant breccia-hosted Zn–Pb mineralization at 397.5 ± 9.6 Ma. Our results indicate that Paleozoic carbonate-hosted Pb–Zn mineralization in the Yangtze Craton is linked to (1) the final assembly of Gondwana in the late Cambrian-early Ordovician (520–480 Ma); and (2) the intracontinental orogeny response to Jiangnan Uplift (420–400 Ma). This study highlights the temporal relationship between low temperature carbonate-hosted mineralization and orogenic events that are consistent with classic MVT models worldwide. It also contributes geochronological data for the reconstruction of plate-tectonic evolution during Pangea assembly. Furthermore, it demonstrates the potential of in situ U–Pb calcite geochronology to date ore deposits lacking syn-ore minerals suitable for traditional dating methods.

Potential for the Recovery of Selected Metals and Critical Raw Materials from Slags from Polymineral Zn–Pb Ore Metallurgy—Part I

Slags from the Silesia–Cracow Upland (Poland), including ten historical slags (deposited in waste dumps) and four contemporary slags (from current production), were examined to compare their chemical and mineralogical properties as well as to assess their potential for the recovery of selected metals and critical raw materials. The historical slags associated with the smelting of polymetallic ores originating from Mississippi Valley-type (MVT) deposits consisted primarily of gypsum. The contemporary slags, obtained from industrial waste rich in zinc and lead, were predominantly spinels (magnesium-aluminate and ferric) that exhibited higher iron content (up to 46.6 wt% of Fe2O3) compared to the historical slags (up to 26.1 wt% of Fe2O3). The zinc content was similar for both the slag types (3.5 wt% Zn). The average titanium and arsenic contents in the old and contemporary slags were at the same level as well, with 0.21 wt% (Ti) and 0.13 wt% (As), respectively. The contemporary slags contained higher levels of critical raw materials, such as cobalt, nickel, copper, and manganese, compared to the historical slags. Rare earth elements (REEs) were also more abundant in the contemporary slags, with an average content of 212 ppm, while the historical slags averaged 124 ppm. These findings underscore the potential for recovering valuable metals and critical raw materials from such slags, presenting opportunities for resource optimisation and environmental management.

Reaction pathway, mechanism and kinetics of thermochemical sulfate reduction: insights from in situ Raman spectroscopic observations at elevated temperatures and pressures

In Earth’s crust, thermochemical sulfate reduction (TSR) is a common organic–inorganic interaction, which is in close association with the carbon cycle in sedimentary basins and metal sulfide precipitation in Mississippi Valley-type deposits. However, the reaction pathway and mechanism of TSR need further investigation, mainly due to the complex sulfur species involved in this reaction. Here we applied in situ Raman spectroscopy to disclose the stepwise transformation from sulfate to sulfide and the reaction kinetics in the CH4-Na2SO4/MgSO4/H2SO4-H2O systems at elevated temperatures and pressures. Our results indicate that sulfate is transformed to H2S through a series of reduction and disproportionation reactions. Once dissolved H2S reaches a certain concentration, it reacts with sulfate to form intermediate valence sulfur species (S0 and S3−), which quickly oxidize methane to generate CO2 and H2S. The formation of S3− and S0 is responsible for the autocatalytic effect in TSR. The sulfur speciation significantly affects the reaction kinetics, which could be divided into three stages based on the in situ observations. Extrapolated kinetic data show that TSR could proceed fast under the catalysis of H2S, and the half-life of methane is ∼7.10 million years at 200 °C. Subsequent numerical modeling strongly supports that in situ sulfate reduction could provide sufficient reduced sulfur for the formation of giant Mississippi Valley-type deposits, thus serving as an efficient mineralizing mechanism.

Barite Replacement as a Key Factor in the Genesis of Sediment-Hosted Zn-Pb±Ba and Barite-Sulfide Deposits: Ore Fluids and Isotope (S and Sr) Signatures from Sediment-Hosted Zn-Pb±Ba Deposits of Iran

Iran hosts more than 350 Precambrian to Cenozoic sediment-hosted Zn-Pb±Ba and barite-sulfide deposits, including shale-hosted massive sulfide (SHMS, also called SEDEX) and Irish-type and Mississippi Valley-type (MVT) mineralization, and barite is a common mineral in these deposits. In the SHMS deposits, barite is typically found as fine-grained disseminations in thin laminae. In these deposits, the sulfide laminae often occur as diagenetic replacements and as bands containing authigenic and diagenetic barite and pyrite framboids. In the Irish-type Zn-Pb-Ba and stratabound barite-sulfide deposits, barite exhibits various textures, including fine-grained disseminated barite, banded zebra textures, veins, and massive barite lenses. In some of the giant Irish-type deposits, as well as in the stratabound barite-sulfide mineralization, the main stratabound sulfide ore is developed within a barite envelope and is characterized by the replacement of barite and pyrite by chalcopyrite, galena, and sphalerite. In the MVT deposits, the formation of barite is often related to dolomitization, and sulfide mineralization involves the replacement of the dolomitized carbonate rocks, as well as associated barite. Fluid inclusion studies on the Irish-type deposits indicate that the temperatures and salinities of the sulfide-forming fluids are higher compared to those of the barite-forming fluids. Fluid inclusion analyses of coarse-grained barites from Irish and MVT deposits reveal their hydrothermal origin. The δ3⁴S values of sulfide minerals (pyrite, sphalerite, and galena) in Irish-type deposits exhibit a broad range of low values (mostly −28 to +5‰), primarily revealing a process of bacterial sulfate reduction (BSR). However, the textures (replacement, colloform, and banded) and more positive sulfur isotope values (+1 to +36‰) in the SHMS Zn-Pb deposits suggest that bacterial sulfate reduction (BSR) plays a less significant role. We suggest that thermochemical sulfate reduction (TSR) connected to the direct replacement of barite plays a more relevant role in providing sulfur for the sulfide mineralization in the SHMS, barite-sulfide, and MVT deposits. Based on the textual evidence, sulfur isotopic data, and fluid inclusion studies, barite has been identified as a key controller for the subsequent Zn-Pb mineralization by providing a suitable host and significant sulfur contribution in the sediment-hosted Zn-Pb and stratabound barite-sulfide deposits. This implies that diagenetic barite might be a precursor to all types of sediment-hosted Zn-Pb mineralization.

Not so fast: Million-years of metal precipitation in Mississippi Valley type deposits inferred from in-situ petrochronology of hydrothermal carbonates

Mississippi Valley-type (MVT) deposits contain about 20% of global zinc resources and host critical raw materials crucial to the development of green technologies. Despite their economic and strategic importance, there is a lack of consensus on the duration of mineralizing fluid flow events in MVT systems. This study couples in-situ U-Pb dating with Sr-isotope and trace element analysis of syn- and post-ore gangue carbonates to establish: (1) timing and duration, (2) redox evolution, and (3) flow rates of mineralizing fluids in the world-class San Vicente Zn-(Pb) deposit (Peru). New radiometric ages bracket the crystallization of syn-mineralization dolomite, characterized by high Fe and Mn contents and Sr isotopic values overlapping with that of host carbonates, between 103.2 ± 4.1 Ma and 70.6 ± 5.6 Ma. This age interval reveals a direct genetic relationship between flow of mineralizing fluids and late Cretaceous Andean compressional tectonics. Basinal fluid expulsion coeval with known tectonic events continues in the district until Pliocene times, driving episodic crystallization of post-ore hydrothermal carbonates between 61.6 ± 9.3 and 2.7 ± 0.2 Ma. The low Mn and Fe content and high 87Sr/86Sr values characteristic of these post-ore, bedding-parallel and cross-cutting carbonate veins indicate a colder, oxidized environment. Our findings highlight the contribution of paired carbonate geochemistry and U-Pb geochronology in drawing links between tectonic events, fluid expulsion and the waxing and waning of mineralization potential in foreland basins. The results of this study challenge our understanding of timescales in MVT systems and imply that anomalous metal enrichment in basinal fluids over a short temporal interval is not a necessary precondition to form economic-sized, sediment-hosted Zn-Pb deposits. Rather, it is the coexistence of a focused fluid flow in an interconnected aquifer with suitable metal depositional mechanisms over a prolonged period of time (106–107 yr) that allows precipitation of economic amount of base metals at a specific site in the upper crust.

Deposit type discrimination based on trace elements in sphalerite

Sphalerite can form in different geological environments and is the main ore mineral of most Pb-Zn deposits. Trace elements in sphalerite combined with machine learning (ML) methods have been used for deposit type discrimination. However, the performance of different multivariate and ML methods is not systematically compared. Here more than four thousand laser ablation inductively coupled plasma mass spectrometry data from more than one hundred deposits were compiled and investigated by different multivariate and ML methods. Unsupervised multivariate and ML methods including principal component analysis (PCA) and t-distributed stochastic neighbor embedding (t-SNE), and supervised multivariate and ML methods including partial least squares-discriminant analysis (PLS-DA), logistic regression (LR), support vector machine (SVM), K-nearest neighbors (KNN), random forest (RF), naïve Bayes (NB), and neural network (NN) are used to classify deposit types. The models are constructed for five deposit types, Mississippi Valley-type (MVT), Volcanogenic Massive Sulfide (VMS), sedimentary exhalative (SEDEX), Epithermal, and Skarn deposits, based on twelve elements in sphalerite, Fe, Pb, Mn, Co, Cu, Ga, Ge, Ag, Cd, In, Sn, and Sb.The PCA and PLS-DA methods show similar clustering results, where Epithermal, MVT, SEDEX, and Skarn deposits can be separated from other deposit types. The t-SNE method is only efficient in discriminating MVT, SEDEX, and Epithermal deposits. The KNN, RF, and NN methods show better performance than LR, SVM, and NB in terms of average accuracy and precision. The PCA, t-SNE, and PLS-DA methods have advantages in data visualization, whereas KNN, NN, and RF methods are more suitable for classification tasks. Feature importance analyses of the PLS-DA and RF methods show that the most important discriminant elements in the classification are Ge, Mn, In, Sn, Ga, and Sb. The models based on PCA, PLS-DA, KNN, NN, and RF are used to predict sphalerite samples with uncertain origins. All the models give similar classification results for deposit types, which are consistent with the ore-forming geological setting. The multivariate and ML models, including discrimination diagrams of PCA and PLS-DA, can be used as the first screening for the type of Pb-Zn mineralization in mineral exploration.

The world-class carbonate-hosted Fankou Zn-Pb deposit in China. Part II. Alterations: C-O isotopic halos footprint the nature and transfer pathway of ore-fluids, and quantitative water-rock interaction process

The giant Fankou Zn-Pb deposit (more than 10 Mt Zn + Pb metals, grading at 15 %), situated in northern margin of the Quren Basin, is one of the largest Zn-Pb deposits in China. The stratiform orebodies are jointly bounded by both the strata (in the specific layers of Middle to Upper Devonian Donggangling and Tianziling carbonate sequences) and the fault system (a three-order thrusting fault system). Ore textures of carbonate dissolution, replacement-infilling and cementation are widespread in Fankou, analogous to a MVT (Mississippi Valley-type) deposit. Owing to the poorly developed fluid inclusions, the nature of the Fankou ore fluids remains indeterminate. To address this problem, we herein utilize micro-petrography, carbon-oxygen (C-O) isotopes and quantitative isotopic exchange modelling to trace the ore-fluids and water-rock interaction process. A total of ninety-three (93) carbonate samples, covering the majorities of stratigraphic horizons, planar locations, and various alteration intensities, were systematically collected. Micro-petrography reveals the primitively sedimentary bioclastic limestone suffer from heterogeneous dolomitization and carbonatization followed by massive Zn-Pb precipitation. These carbonate samples display a widely-ranged, δ18O- and δ13C-depleted isotope signature (δ18O = 12.57 to 23.82 ‰, δ13C = −7.79 to −0.46 ‰), relative to normal marine carbonates (δ18O = 25 ‰, δ13C = 0 ‰). Further modelling of isotopic exchange indicates a low-temperature (100 to 250 °C), δ18O-depleted (−3 to 7 ‰) and δ13C-depleted (−10 to −7‰) ore fluid equilibrated with the host rock by a relatively low water-rock ratio (W/R = 1 to 10). In terms of space, we identified a relatively decreasing trend of δ18O and δ13C isotopic compositions of carbonates, from southeast to northwest, and from bottom to up. Based upon the previous structural analysis, we interpret that the δ18O and δ13C isotopic distribution patterns are caused by a northwestwards transfer pathway of ore-fluids along the thrusting fault system, and the metalliferous, δ18O- and δ13C-depleted fluids are sourced from the interior of the Quren Basin. Collectively, we clarify the deep southeastern part of the Fankou Zn-Pb deposit and the interiors of the Quren Basin is the favorable exploration target in future.

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).

Enrichment of Mississippi Valley-type (MVT) deposits in the Tethyan domain linked to organic matter-rich sediments

Enrichment of Mississippi Valley-type (MVT) deposits in the Tethyan domain linked to organic matter-rich sediments

Geology, fluid inclusions and C−O−S−Pb isotopic compositions of the Chahmileh Pb-Zn deposit, Central Iran: Implications for ore genesis

AbstractThe Chahmileh Pb–Zn deposit, located northwest of the Central Iran Zone, is a sediment-hosted Pb–Zn deposit in the ‘Yazd-Anarak Metallogenic Belt’. It is hosted in Middle Triassic carbonate rocks and is mainly controlled by NW-trending faults. The main ore minerals are galena and sphalerite with minor chalcopyrite, pyrite, and quartz, dolomite, along with minor calcite and baryte as gangue minerals. Cerussite, hemimorphite, wulfenite, mimetite, smithsonite, malachite and iron oxy-hydroxides are the main non-sulphide ore minerals. The main styles of mineralization are vein-veinlet, breccia, disseminated and replacement in association with silicification and dolomitization. Microthermometry of fluid inclusions in dolomite and quartz indicates that the ore precipitated from a warm to hot basin-derived saline fluid. Dolomite samples have δ13CVPDB and δ18OVSMOW values of −0.99 to +1.99‰ and +20.74 to +25.48‰, respectively, and are plotted in the marine carbonate rocks field. These isotopic values suggest that CO2 in the hydrothermal fluids mainly originated from marine carbonate rock. The δ34S values range from +6.3 to +8.2‰ for galena, +5.9 to +6.2‰ for sphalerite, +1.4 to +3.4‰ for chalcopyrite and +15.0 to +17.4‰ for bayite are compatible with a predominant thermochemical sulphate reduction process, and with sulphur sourced from Triassic seawater. Galena samples have a homogeneous Pb isotopic composition that is indicative of a continental crustal reservoir as the main source of lead and probably for the other ore metals. Based on geology, mineralogy, texture and fluid characteristics, the Chahmileh deposit is classified as a carbonate-hosted Mississippi Valley-type deposit.

Continental evaporites as brine sources for formation of SEDEX and MVT deposits: Implications from boron isotope compositions of tourmaline

In this study, the boron isotopic composition of Paleoproterozoic seawater is reconstructed using δ11B of tourmaline from the Paleoproterozoic Pb-Zn deposits of Rajpura-Dariba, Zawarmala, and Rampura-Agucha in the Aravalli-Delhi Fold Belt (ADFB) as well as non-mineralized tourmaline bearing metapelites from the Mangalwar Complex (MC) and Gangpur Schist Belt (GSB). This is then used to constrain the source of the mineralizing fluids in Sedimentary Exhalative (SEDEX)- and Mississippi Valley Type (MVT)-deposits. Based on textural relations and chemical variations, tourmaline in the Rajpura-Dariba and Zawarmala deposits can be grouped into two generations: syn-mineralization Tur-I and metamorphic Tur-II. In contrast, a single generation of metamorphic tourmaline is identified in the Rampura-Agucha deposit and in the MC. Tur-I from Rajpura-Dariba has XMg of 0.14–0.56, while Tur-II is more magnesian (XMg = 0.58–0.77). Similarly, Tur-I from Zawarmala has a wide compositional range (XMg = 0.22–0.67), whereas Tur-II is Mg-rich (XMg = 0.39–0.67). Tourmalines from Rampura-Agucha and MC are also magnesian (XMg = 0.66–0.70 and 0.59–0.69, respectively). The δ11B values of syn-ore tourmaline from Rajpura-Dariba and Zawarmala vary between −18.8‰ and −16.1‰, and between −6.6‰ and −4.0‰, respectively. Metamorphic tourmalines from Rajpura-Dariba, Zawarmala, Rampura-Agucha and MC have δ11B values between −19.1‰ and −7.7‰.The δ11B of the pelitic sediments in Rajpura-Dariba, Rampura-Agucha, the MC and the GSB were estimated from the δ11B of metamorphic tourmaline hosted in them using mass balance constraints and P-T pseudosection modelling. Applying the B-isotope fractionation factor between Miocene shale and modern clay (Δ11Bmiocene shale − modern clay = −3.8‰ to −2.2‰) to the modelled δ11B of post-diagenetic protoliths of the metapelites, the δ11B of marine sediments for these basins were constrained between −15.1‰ and −10.2‰. Subsequently, using the B-isotope fractionation factor between modern clay and seawater (Δ11Bmodern clay − modern seawater = −45.2‰ to −40.8‰), the δ11B of Paleoproterozoic seawater is estimated to have been between +27.3‰ and +33.4‰.The isotopically light δ11B of syn-mineralization tourmaline from Rajpura-Dariba and Zawarmala (−18.8‰ to −16.1‰ and −6.6‰ to −4.0‰, respectively), and worldwide SEDEX/MVT-type deposits in general (a median value of −9.6‰; compilation of Trumbull et al., 2020), implies that the B was most likely sourced from continental evaporites and not evaporated seawater and/or connate brine. Dissolution of early rift-related continental evaporites most likely act as a major source of basinal brines for the formation of SEDEX/MVT deposits during the sag-phase of basin development.

Supernormal enrichment of cadmium in sphalerite via coupled dissolution-reprecipitation process

Supernormal enrichment of cadmium in sphalerite is frequently observed in some sedimentary-hosted zinc-lead deposits, although related fluid process remains unconstrained. At the Jinding Mississippi Valley-type deposit, a considerable portion of cadmium has been remobilized from early sphalerite through coupled dissolution-reprecipitation reaction to form high-grade ores. Here we report natural occurrence of various sulfide nanoparticles and related textures in sphalerite that help document this process. A nanoscale study by transmission electron microscopy provides a rare glimpse of phase transition of cadmium from lattice-bond impurity, composition anomaly along planar defects, aggregates of hexagonal cadmium sulfide nanoparticles, to crystalline greenockite inclusions. Such a process may be mediated by oxidative dissolution on early-formed cadmiferous sphalerite during injection of cadmium-rich oxidative acidic fluids. This study provides an alternative mechanism versus exclusively solid-state diffusion for dispersed elements’ redistribution in hydrothermal ore deposits. It also sheds light on artificial synthesis of II-VI semiconductor nanomaterials by similar methods.

Re-examination of the Aïn Allegua-Aguiba celestite-Pb-Zn salt diapir-related Mississippi Valley-type deposits (Nappes zone, Northwestern Tunisia): New conceptual model

The celestite-rich and Pb-Zn-poor Aïn Allegua deposits are located at the northeastern extremity of the Dougas diapir in the Nappes zone of northern Tunisia. The Sr-Ba-Zn-Pb mineral system studied in this paper is enclosed in a Triassic breccia, labeled cap rock, located between the Triassic diapir and the surrounding Cretaceous to Lutetian marine sediments. It consists of evaporite dissolution float breccia where Triassic dolostone clasts are floating in a Triassic matrix of anhydrite and argillites. Five mineralizing stages are recognized, which are from early to late: celestite (stage 1); hydrothermal dolomite (stage 2); crosscutting galena-barite or sphalerite-galena-barite-calcite (stage 3); (4) fracture and karst filled by barite, celestite, and galena (stage 4); and late supergene mineralization (strontianite, smithsonite, and cerussite) (stage 5). The present study shows that the celestite and Pb-Zn mineralization formed from the circulation in the cap rock of at least three fluids: (1) fluid A (100–150 °C; 10 to 25 wt% NaCl eq.) deposited the celestite; (2) fluid B (125 to 185 °C; 29 to 34 wt% NaCl eq.) deposited the hydrothermal dolomite, and (3) fluid C (temperatures around 90 °C; 14 to 22 wt% NaCl eq.) deposited the calcite that accompanied sphalerite and galena precipitation. The δ34S values for sphalerite and galena fall within a narrow range from + 10.4‰ to + 18.9‰ (avr. 13‰) indicating a homogeneous source of sulfur. The δ34S values of celestite and barite are also relatively homogeneous from + 14.7 to + 23‰ (ave. + 16.5‰) and match those of Tunisian Triassic gypsum and Triassic marine sulfates (δ34S = +15‰). The temperature of deposition together with sulfur isotope data indicate that the reduced sulfur in sulfides was derived through thermochemical sulfate reduction of Triassic sulfate. The lead isotopes in galena show that Pb, and probably Zn and Ba were extracted from the upper crustal rocks. Part of the strontium is derived from the Triassic anhydrite and the other part is probably transported to the cap rock in formation waters. The tectonic setting, the carbonated nature of the host rocks, the epigenetic style of the mineralization, and the mineral associations, together with fluid inclusions data and sulfur and lead isotopes show that the Aïn Allegua deposit belongs to the diapir-related Mississippi Valley-type (MVT) deposits of the Eastern Maghreb salt diapirs province, that formed, as the most of the MVT deposits and districts in the world, from basinal brines with no mixing with metamorphic and/or magmatic fluid or involvement of a heat source from a concealed sill or magmatic intrusion.

Neoproterozoic Zn-Pb mineralization in the world-class Sichuan-Yunnan-Guizhou Zn-Pb triangle, southwest China: Insights from apatite geochemistry and in situ sericite Rb-Sr geochronology of the Daxiao deposit

The Sichuan-Yunnan-Guizhou (SYG) zinc-lead triangle, located in southwestern China, is an important producer of zinc, lead, silver, and critical raw metals such as germanium. In this region, most Zn-Pb deposits hosted in the later Ediacaran to Permian carbonate rocks are believed to be Mississippi Valley-type (MVT) deposits, while the origin of the Zn-Pb deposits found in the Mesoproterozoic basement remains controversial. To address this gap, our study conducted in situ LA-ICP-MS/MS muscovite Rb-Sr dating and apatite major, trace and Sr isotope analysis on the Daxiao deposit hosted in the Mesoproterozoic basement. The in situ Rb-Sr dating of sericite yielded a Neoproterozoic age of 766 ± 31.3 Ma, challenging the previously proposed Indosinian orogen-related MVT model. Instead, it links the formation of this deposit to an extensional setting that coincided with the breakup of the Rodinia. We identified a specific type of apatite, recognized as ore-stage apatite based on texture and analyzed composition, within the deposit. The ore-stage apatite exhibits high 87Sr/86Sr ratios (ranging from 0.78384 to 0.81082), similar to those of the Archean basement rocks.Based on our study and previous data, we proposed a new genetic model for the Daxiao Zn-Pb deposit, and possibly other basement-hosted Zn-Pb deposits in the SYG triangle. During the Neoproterozoic (∼766 Ma), the study area experienced an extensional setting characterized by crustal thinning and magmatic activity resulting from the breakup of the Rodinia. Basinal brines infiltrated the deep Archean basement along faults and were heated to high temperatures by magma and/or high geothermal gradients. These hot brines continuously extracted Pb, Zn from the Archean basement and migrated upward into the Mesoproterozoic host rock, where they precipitated lead–zinc ores in favorable structural positions. The Daxiao Zn-Pb deposit, along with the coexisting sediment-hosted stratabound copper (SSC) deposits, basement-hosted gold and uranium deposits, and late sulfide mineralization in the iron oxide-copper–gold (IOCG) deposits, suggests a Neoproterozoic regional mineralization event associated with the breakup of Rodinia. Our study also highlights the potential of using in situ sericite Rb-Sr dating to precisely determine the age of other hydrothermal ore deposits, such as Carlin-type Au deposits, which have long been a subject of uncertainty.

LA-ICP-MS Trace Element Geochemistry of Sphalerite and Metallogenic Constraints: A Case Study from Nanmushu Zn–Pb Deposit in the Mayuan District, Shaanxi Province, China

The Nanmushu Zn–Pb deposit is a large-scale and representative deposit in the Mayuan ore field on the northern margin of the Yangtze Block. This study investigates the trace element geochemistry of sphalerite from this deposit using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). The results show that the main trace elements in sphalerite include various trace elements, such as Mn, Fe, Cu, Ga, Ge, Ag, Cd, Pb, Co, Hg, Tl, In, Sn, and Sb. Among them, Ag, Ge, Cd, and Cu are valuable components that may be recovered during mineral processing or smelting techniques. The histograms, LA-ICP-MS time-resolved depth profiles, and linear scan profiles indicated that most trace elements occur in sphalerite as isomorphs, while partial Pb, Fe, and Ag occur as tiny mineral inclusions. The correlation diagrams of trace elements revealed that Fe2+, Mn2+, Pb2+, and Tl3+ can substitute Zn2+ in sphalerite through isomorphism. In sphalerite, Cd2+ and Hg2+ together or Mn2+, Pb2+, and Tl3+ together can replace Zn2+, i.e., ((3Mn, 3Pb, 2Tl)6+, 3(Cd, Hg)2+) ↔ 3Zn2+. Moreover, there is a mechanism of Ge4+ with Cu+ or Ga3+ with Cu+ replacing Zn2+ in the Nanmushu deposit, i.e., Ge4+ + 2Cu+ ↔ 3Zn2+ or 2Ga3+ + 2Cu+ ↔ 4Zn2+. Furthermore, the trace element compositions indicate that the Nanmushu Zn mineralization occurred under low-temperature conditions (<200 °C) and should be classified as a Mississippi Valley-type (MVT) deposit. This study provides new insights into the occurrence and substitution mechanisms of trace elements in sphalerite and the metallogenic constraints of the Nanmushu deposit.

Impact of deformation and metamorphism on sphalerite chemistry – Element mapping of sphalerite in carbonate-hosted Zn-Pb sulfide deposits of the Kootenay Arc, southern British Columbia, Canada and northeastern Washington, USA

Sphalerites from the Kootenay Arc in British Columbia and Washington State were selected to represent three types of carbonate-hosted massive sulfide deposits, including Mississippi Valley-type (MVT), Irish-type, and fracture-controlled replacement type (FCR). These deposits were variably deformed and metamorphosed during the Cordilleran orogen. Laser ablation inductively coupled plasma mass spectrometric (LA-ICP-MS) analyses of the trace element distributions within the sphalerites are combined with petrography and sulfur isotope analyses to evaluate the influence of primary trace element signatures, along with the variable influence of post-ore metamorphism and deformation on sulfide remobilization and trace element redistribution.Mississippi Valley-type (Josephine orebodies) and Irish-type (Yellowhead orebodies) at Pend Oreille mine are only weakly deformed and recrystallized, so their sulfide minerals commonly retain primary ore textures. The sphalerite from the Irish-type deposit has positive narrow range of δ34S values (17.9–20.5‰, mean 19.2‰), and it is enriched in Ge, Tl and Pb, but depleted in Cd, Mn, and Cu relative to MVT and FCR deposits. Germanium is concentrated in dark-brown acicular-colloform bands where micro-inclusions of a germanium oxide mineral (argutite (GeO2)) and galena have been detected. Other MVT deposits of the Kootenay Arc (Reeves MacDonald, Jersey-Emerald, HB, Jackpot-Lerwick, Duncan) are more deformed and metamorphosed than the Irish-type deposit of the Pend Oreille mine and primary ore textures are only locally preserved. There is a progressive increase in deformation and degree of recrystallization from Reeves MacDonald, located away from intrusions, to deposits within the contact metamorphic aureoles of intrusions (HB, Jersey-Emerald, Jackpot-Lerwick). Sphalerite from the least metamorphosed Reeves MacDonald deposit has high Cd, Ga, Pb, and Tl contents, high Cd/Ge and Ga/In values, and the lowest δ34S values (7.4 to 11.1‰, mean 8.8‰). In contrast, sphalerites from contact metamorphosed HB, Jersey-Emerald and Jackpot-Lerwick deposits have higher δ34S values (13.3 to 28.5‰, mean 19.2‰), are enriched in Mn and Fe, with higher Zn/Cd and Mn/Fe values relative to Reeves MacDonald deposit. These enrichments and fractionations correspond to the breakdown of pyrite and pyrrhotite and the thermal annealing of sphalerite caused by contact metamorphism. Sulfide minerals from the FCR deposit (Abbott-Wagner) are undeformed (except for microfractures) and only weakly recrystallized. Sphalerite from the FCR Abbott-Wagner deposit is enriched in Cu, Ga, In, and Sn as primary source signatures relative to sphalerite from MVT and Irish-type deposits. This reflects the more complex mineral assemblage of galena, sphalerite, pyrite, chalcopyrite, and tetrahedrite in this deposit. The presence of chalcopyrite and tetrahedrite is consistent with a higher-temperature origin of the FCR deposit relative to the lower-temperature MVT and Irish-type deposits.This study demonstrates that the high spatial resolution of in-situ LA-ICP-MS analyses of trace element within sphalerites, in combination with petrography and other analytical techniques (e.g., electron microprobe, secondary ion mass spectrometry, field emission scanning electron microscopy) characterizes the behavior and distribution of trace elements in sphalerite for three deposit types and variable conditions of regional and contact metamorphism. Understanding the effects of metamorphism and deformation on trace elements can be very useful in exploration for deposits rich in critical metals.

Genesis of the carbonate-hosted zinc–lead deposits in the southwestern Yangtze Craton, SW China: Insights from the Maoping deposit

The southwestern Yangtze Craton represents one of the world's largest zinc–lead provinces and contains over 26 million tons of zinc–lead resources. It comprises more than four hundred carbonate-hosted zinc–lead deposits with various sizes; however, genesis of the deposits has long been debated and still remains controversial, due to a lack of comprehensive understanding on the geology and metallogeny. Located in the north of the area, the giant Maoping zinc–lead deposit (Zn + Pb: 3 Mt @ 10–30 wt%) provides an ideal objective to illustrate this issue. In this paper, we conduct detailed field geological investigation at Maoping and present new in situ LA–ICP–MS data of sulfur and lead isotopes and trace elements from 25 sulfide samples. The δ34S values of the sulfides vary from −22.8 ‰ to +22.5 ‰, and the ratios of 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb of the sulfides vary in ranges of 18.247–18.767, 15.712–15.768, and 38.548–39.435, respectively. Combined with previous studies, we interpret that reduced sulfur is likely sourced from marine sulfates in the carbonate of the Upper Devonian Zaige Formation, and ore metals are mainly derived from the Neoproterozoic basement and the Zaige Formation carbonate. Titanium, Cr, Mn, Co, Ni, Cu, Zn, Ge, As, Se, Ag, Cd, Sb, and Pb are enriched in pyrite within the Maoping deposit, and low abundances of Co and Ni (0.01 × 10−6–21.09 × 10−6) and low Co/Ni ratios (0.04–4.95) in pyrite constrain its low-temperature hydrothermal origin. New geological and geochemical data demonstrate that geology, mineralization, and geochemistry of the Maoping deposit coincide with those of the Mississippi-Valley type (MVT) deposits worldwide. Together with previous studies, we suggest that genesis of the carbonate-hosted zinc–lead deposits in the southwestern Yangtze Craton resemble the MVT deposits.

The world-class carbonate-hosted Fankou Zn-Pb deposit in China. Part I. Structural analysis: Evolutionary three-order thrusting structures control on the localization of Zn-Pb orebodies

The Fankou giant deposit (with exceeding 10 Mt Zn + Pb metals, grading at 15 wt%) is a carbonate-hosted, stratabound Zn-Pb deposit in the northern Quren Basin, South China. Lenticular, stratiform and wedge-shaped orebodies are strictly hosted in specific layers of Upper Devonian to Lower Carboniferous carbonate sequences along a series of NE and NNE trending faults. Previous ore geological and geochemical studies proposed that the Fankou can be analogous to a Mississippi Valley-type (MVT) deposit, but how the evolution of complex fault system controls ore-forming fluids migration, metals accumulation and orebodies localization remains unclear. To address this question, we conducted a deposit-scale structural analysis based on the geological mapping, underground works, and diamond drills logging. We identified three-order structures gradually growing in the Fankou deposit, including: 1) The first-order fault represented by F203 is a NW-striking thrust fault penetrating basement and acts as a major conduit for ultimate hydrothermal fluids migrations from depth; 2) The second-order faults include a spectrum of NNW-striking faults F2, F3, F4, F4, F5, F6, F7, F8 and F9. They are intersected with F203 in depth, and soon before and synchronous activities with Zn-Pb mineralization; 3) The third-order faults contain a series of NNE-striking F100, F101 and F102 with limited scale, which is subordinate to second-order faults and control the terminal localization of Zn-Pb orebodies. Collectively, we conclude that the evolutionary three groups of deposit-scale faults, derived from the regional NE-striking Wuchuan-Sihui Fault, jointly control the ore-forming fluids migrations from deep to shallow and from SE to NW in space. It is noteworthy that the second- to third-order faults act as the direct metal precipitation space when the upwards metalliferous fluids replaced with the favorable lithological layers. Therefore, we highlight that the southeast part of the mining area, where the metalliferous fluids came from, is a promising exploration target area in future.

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.

Trace Elements of Gangue Minerals from the Banbianjie Ge-Zn Deposit in Guizhou Province, SW China

There are many dispersed element-rich Pb-Zn deposits hosted by Paleozoic carbonate rocks in the Middle-Upper Yangtze Block, China. The origin and nature of the ore-forming fluids that formed them are still much debated (syngenetic vs. epigenetic). The Banbianjie Ge-Zn deposit is located in the southeastern margin of the Yangtze Block, SW China. It is a newly discovered medium-sized Zn (Zn metal reserves > 0.39 Mt, @1.78%–9.5% Zn) and large-scale Ge deposit (Ge metal resources > 900 t, @100 × 10−6–110 × 10−6 Ge) in the Western Hunan–Eastern Guizhou Pb-Zn metallogenic belt, SW China. Gangue minerals in the Banbianjie deposit are very developed, including calcite, dolomite and barite, which are closely associated with sulfides. Hence, the trace elements of gangue minerals could be used to trace the nature, source and evolution of ore-forming fluids, and the ore genesis of this deposit can be discussed. These gangue minerals are nearly horizontally distributed in the plot of La/Ho-Y/Ho, suggesting that they are the products of the same hydrothermal fluids. The total rare earth element (∑REE) contents from calcite and dolomite to barite show an increasing trend, indicating that the REEs in the ore-forming fluids were mainly enriched in barite. Hence, the ∑REE of barite can approximately represent the ΣREE of the hydrothermal fluids, which are quite similar to those of the underlying strata, indicating that the ore-forming fluids were likely originated from and/or flowed through them. The Eu anomalies from dolomite (Eu/Eu* = 0.33–0.66) to calcite (Eu/Eu* = 0.29–1.13) and then to barite (Eu/Eu* = 1.64–7.71) show an increasing trend, suggesting that the ore-forming fluids experienced a shift in the ore-forming environment from reduced to oxidized. Hence, the source of the Banbianjie Ge-Zn deposit is the underlying strata, and the ore-forming physical–chemical condition has experienced a transition from reduction to oxidation during the Ge-Zn mineralization. The ore genesis of the Banbianjie Ge-Zn deposit is most likely a Mississippi Valley-type (MVT) deposit.