Sedimentary Exhalative Research Articles

A Comprehensive Geophysical Exploration of Sedimentary Exhalative Deposits: An Example from the Huaniushan Lead–Zinc–Silver Polymetallic Deposit in Gansu, China

The Huaniushan lead–zinc–silver deposit is a hydrothermal sedimentary exhalative deposit (SEDEX), and the mining area has complex geological conditions, with the main tectonic structure being the Huaheitan–Shuangfengshan Fault (F3), which controls the distribution of strata and magmatic rocks. Since the discovery of the Huaniushan lead–zinc–silver deposit, diverse interpretations of its genesis and metallogeny have been proposed, making it challenging to establish a definitive geological explanation. Moreover, using a single geophysical exploration method relies on limited rock physical parameters, making it difficult to effectively characterize underground structures. The combined use of multiple geophysical methods can effectively integrate the geophysical characteristics of different rock physical parameters, reducing the multiplicity and uncertainty of the inverse interpretation of geophysical data. The comprehensive interpretation of three-dimensional inversion based on various geophysical data, the construction of geological–geophysical models on geological grounds, the establishment of hidden ore exploration and positioning, and the rapid evaluation of geophysical technological systems are the current research trends in mineral exploration. In light of this, in this study, we conducted research on the three-dimensional inversion interpretation of gravity and magnetoelectric exploration data of the Huaniushan sedimentary exhalative lead–zinc–silver polymetallic deposit and constructed a three-dimensional geological–geophysical model of the study area based on the obtained three-dimensional physical structure of the underground density, magnetization intensity, resistivity, and polarizability of the study area, in combination with related geological and drilling hole data. Finally, we comprehensively interpreted the favorable mineralization sites in the study area.

Sedimentary exhalative Pb-Zn deposit model of the Ban Lin – Phia Dam ore range, Vietnam

Purpose. The aim of this study is to construct a typical ore model for Pb-Zn ore range in Ban Lin – Phia Dam and to compare it with the existing ones. The model is constructed based on three main elements of the mineral generation process, such as formation environment, generated-ore fluid source, and deposited-ore mechanism. The obtained results are aimed at determining and predicting the resource of sedimentary exhalative (SEDEX) Pb-Zn ore deposit in Vietnam. Methods. To comprehend the characteristics of the SEDEX Pb-Zn ore deposits in the Ban Lin – Phia Dam area, we employ a combination of approaches that include mineralography to determine the composition and tectonic structure of rocks and ore, inclusion analysis to determine the temperature and inclusion composition, Pb isotopic analysis and stable S isotopic analysis to explore the environment and sources of ore-forming materials. Findings. The sedimentary exhalative (SEDEX) Pb-Zn ore deposit arises from the dissolution of metal-rich salt deposits due to heating at shallow depths (several kilometers). Subsequently, this fluid migrates through faults and fractures to preferred locations where galena and sphalerite precipitate alongside sedimentary basin deposition. Originality. SEDEX ore deposits have been extensively studied in various regions of the world. Although there are multiple theories regarding their origin, including explosion, biological debris accumulation, and surface replacement, each model has its own distinct advantages and limitations in explaining the genesis and development of SEDEX ore deposits. Practical implications. The acquired findings are intended to identify and predict the resources of sedimentary exhalative Pb-Zn ore deposits in Vietnam.

Alteration Zones as Exploration Parameters for Stratiform Pb-Zn-Ag-Ba Deposits in the Graz Paleozoic (Eastern Alps, Austria)

AbstractIn the Graz Paleozoic in the Eastern Alps (Austria), stratiform Pb-Zn-Ag-Ba deposits have been mined in the past. They are classified as sedimentary-exhalative (SEDEX) deposits and are hosted by polyphase deformed greenschist facies metasediments and volcanics of the Schönberg Formation (Schöckel nappe; Drauzug-Gurktal nappe system), which is upper Silurian to Lower Devonian in age. The stratiform ore horizons are dominated by galena, sphalerite, barite, pyrite, pyrrhotite, and magnetite and are accompanied by chalcopyrite, arsenopyrite, fahlore, pyrargyrite, tetradymite, cobaltite, ullmannite, breithauptite, electrum, and others. The project MRI_SEDEXPOT investigates these deposits to evaluate their exploration potential by focusing on hydrothermal alteration zones occurring in the footwall and hanging wall of the ore. Such alteration zones are globally used as exploration tools not only for SEDEX deposits. The investigated alteration zones show distinct mineralogical and geochemical characteristics. They contain Fe rich carbonates and chlorite, K‑ and Ba-feldspars, Ba bearing white mica, fluorapatite, REE and HFSE minerals. Disseminated sulphides are widespread, and albitization is typical below sulphide rich horizons. Geochemical profiles correlate well with the observed mineralogy. Ongoing investigations of these alteration zones should lead into defining proximity indicators to the ore and evaluation of the exploration potential of the stratiform Pb-Zn-Ba-Ag deposits of the Graz Paleozoic.

Characterization of Co-bearing pyrite from the SEDEX Tuolugou Co(Au) deposit, northern Qinghai-Tibet Plateau, China

The Tuolugou sedimentary-exhalative (SEDEX) Co-Au deposit is located in the eastern Kunlun metallogenic belt of the northern Qinghai-Tibet Plateau in China. Pyrite is the prevalent Co-hosting sulfide mineral that occurs in the Tuolugou deposit. In this study, we investigated mineral characteristics of Co-bearing pyrite and effect of Co on crystal structure of the pyrite to obtain a better understanding of Co mineralization. Three pyrite generations were identified, including Co-barren pyrite (Py-1, formed during the early mineralization stage I, with Co content of 1-3844 ppm), Co-rich pyrite (Py-2, formed during the sedimentary-exhalative stage II, Co content 15–36522 ppm), and Co-rich pyrite (Py-3, formed during metamorphic stage III, with Co contents of 448–10505 ppm in Py-3A, and 1371–14904 ppm in Py-3B). As Co enters the pyrite structure, it is discovered that the octahedrons in pyrite is twisted and tilted, the lattice parameters (a0) rise, and the sulfur atom positions alter. The Co-rich Py-2 shows a similar REE and trace element distribution as those in quartz albitite, which indicates that Co mineralization is related to SEDEX genesis. Subsequent metamorphism resulted in additional Co enrichment. This detailed study of Co-bearing pyrite provides insights on the details of isomorphism Co in pyrite similar to the situation of this deposit as medium–low Co grade.

Discrimination of Pb-Zn deposit types using the trace element data of galena based on deep learning

Different types of ore deposits exhibit distinct metal sources, physicochemical conditions, and ore-forming processes. Galena, a key sulfide in Pb-Zn deposits, possesses trace elements that may be utilized for classifying Pb-Zn deposit types. Presently, research on classifying ore deposit types based on trace elements in galena is sparse, and there is a lack of robust methods for distinguishing Pb-Zn deposit types using these trace elements. In this study, we demonstrate that a deep learning algorithm, based on the trace elements in galena, can be effectively utilized for classifying Pb-Zn deposit types. The model training process utilized UMAP for visualization, and the evaluation was conducted using multiple statistical metrics, confusion matrices, and ROC curves. Finally, by dissecting the ’black box’ with the UMAP algorithm, we established a comprehensive set of analysis methods for discriminating deposit types: discrimination-visualization-evaluation-dissection. A dataset comprising 828 LA-ICP-MS analyses of galena from 34 Pb-Zn deposits worldwide was curated from peer-reviewed sources. It includes data on 7 elements (Se, Ag, Cd, Sn, Sb, Tl, and Bi) across 7 deposit types: carbonate replacement deposits (CRD), epithermal, mississippi valley type (MVT), sedimentary exhalative (SEDEX), skarn, volcanogenic massive sulfide (VMS), and vein-type deposits. Initially, we selected the UMAP algorithm from three visualization methods (PCA, t-SNE and UMAP), for its ability to balance global and local structures in visualizing the internals of the deep model. Subsequently, we developed a deep learning model (1D-CNN) for deposit type classification. Various evaluation metrics and visual analyses indicate exceptional performance of our model, achieving an overall accuracy of 99.18 % on the test set. Finally, the SHAP algorithm was used to analyze the importance of trace elements in galena for different deposit types. Elements such as Sn, Tl, and Bi were found to be particularly significant in classifying deposit types, confirming the influence of multiple elements in Pb-Zn deposits within galena. Therefore, we conclude that deep learning algorithms can effectively identify Pb-Zn deposit types, offering new insights into the study of galena.

Sulfide Remobilization in the Metamorphosed Kayad Sedimentary Exhalative Zn-Pb Deposit, Western India: Evidence from Mode of Occurrence, Texture, Hydrothermal Alteration Features, and Trace Element Chemistry

Abstract The Kayad Zn-Pb deposit, situated within the Proterozoic Aravalli-Delhi fold belt in western India, is primarily characterized by sphalerite and galena along with pyrrhotite and chalcopyrite. The mineralization occurs as disseminated ores in quartzite, disseminated/laminated and massive ores in quartz-mica schist, and in pegmatite and quartz veins. The laminated ores conform to the regional schistosity and folding, whereas the massive Zn-Pb ores postdate the pervasive tectonic fabric, accumulating at the fold hinges. The massive ore is characterized by durchbewegung texture, discrete blebs of galena and chalcopyrite in a sphalerite matrix with low interfacial angles, and discrete intergrowths of sulfides and sulfosalts such as pyrargyrite, gudmundite, Ag-tetrahedrite, and breithauptite. Geochemical analyses of sulfides reveal microinclusions of sulfosalts comprising Ag, Sb, Cu, Tl, and As, which are regarded as low-melting chalcophile elements (LMCEs). Hydrothermal alteration is insignificant in the laminated and massive ores but prominent around Fe-Cu ± Zn-Pb and Zn-Pb ± Fe-Cu veins. The alteration assemblages in these veins evince a pervasive K + Na ± Fe alteration, later overprinted by a subsidiary Ca ± Na alteration. We interpret the laminated/disseminated ores to be of syndiagenetic sedimentary-exhalative (SedEx) origin formed within an euxinic basin. Conversely, the textural features, mineralogical composition, lack of associated hydrothermal alterations, and evident structural influence on the emplacement of the massive ores suggest they have been remobilized both via plastic flow and by sulfide partial melting. Temperature estimates of up to 650°C, derived from Ti-in-biotite geothermometry of the metamorphosed host rocks, indicate lower-middle amphibolite facies conditions during regional metamorphism. The initiation of melting at these temperatures was promoted by the desulfurization of pyrite to pyrrhotite in quartz-mica schist, aided by melting point depression due to the presence of LMCEs like Ag, Sb, and As.

New insights into the origin and depositional setting of the Haerdaban Pb[sbnd]Zn deposit, Chinese western Tianshan: Evidence from geology, chert geochemistry, and detrital zircon U[sbnd]Pb geochronology

The Haerdaban PbZn deposit (with an ore reserve of 10.93 Mt. at 1.0–25.65 % Zn and 0.7–12.29 % Pb) is hosted in weakly metamorphosed clastic‑carbonate rocks from the Proterozoic Haerdaban Group. It represents a significant addition of the sediment-hosted PbZn deposits in the Yili block, Chinese western Tianshan. Currently, there are ongoing debates regarding its genesis, with a particular focus on the crucial metallogenic mechanism (syngenetic sedimentary exhalation or epigenetic reworking) responsible for the primary sulfide mineralization. Mineralization at Haerdaban primarily occurs as banded to stratiform ore layers or lenses conformably sandwiched in their host rocks. Vein and stockwork ores occur locally below the stratiform ore layers. A syn-sedimentary fault trending SN was identified based on abrupt lateral changes in lithofacies and thickness of the stratigraphic units. The ore mineralogy is dominated by sphalerite, galena, quartz, and dolomite, with a small amount of pyrite, barite, and organic matter. Detrital zircon LA-ICP-MS UPb dating of the Haerdaban siltstones obtained a maximum depositional age of about 604 Ma. Their geochemical composition similar to the passive continental margin signatures, with rare earth element (REE) patterns enriched in LREE and negative Eu anomalies (Eu/Eu* = 0.50–1.14). Stratiform beds of chert that host disseminated ores have relatively high contents of hydrothermal components (e.g., Ba, Zn), with apparent positive Eu anomalies (Eu/Eu* = 7.38–49.34) and negligible negative Ce anomalies (Ce/Ce* = 0.85–0.98). They are thus interpreted to be hydrothermal sedimentary rocks (exhalites) deposited in a suboxic-anoxic environment proximal to the hydrothermal vents. Integrated geological and geochemical evidence indicates that the Haerdaban PbZn deposit is a typical vent-proximal sedimentary exhalative (SEDEX) deposit formed in a Neoproterozoic Sinian (Ediacaran) passive continental margin rift basin. Post-depositional metamorphism and deformation in the Paleozoic may have caused partial remobilization of primary ores but did not significantly alter the morphology of the orebodies. Furthermore, establishing a genetic model for the Haerdaban deposit has important implications for the exploration of similar deposits preserved in the equivalent stratigraphy within the Chinese western Tianshan region.

Genesis of the Dongtangzi Zn-Pb Deposit of the Fengxian–Taibai Ore Cluster in West Qinling, China: Constraints from Rb-Sr and Sm-Nd Geochronology, and In Situ S-Pb Isotopes

The large Dongtangzi Zn-Pb deposit is located in the southwest of the Fengxian–Taibai (abbreviated as Fengtai) ore cluster in the west Qinling orogen. The origin of the deposit is controversial, positing diverse genesis mechanisms such as sedimentary-exhalative (SEDEX), sedimentary-reformed, and epigenetic-hydrothermal types. This study combines systematic ore geology observations with high-precision Rb-Sr and Sm-Nd ages of 211 Ma and in situ S-Pb isotopes to constrain the timing and origin of mineralization. In situ S-Pb isotopic studies show that the sulfide ores display a narrow range of δ34S values from 1.1‰ to 10.2‰, with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 18.07 to 18.27, 15.64 to 15.66, and 38.22 to 38.76, respectively. On the other hand, pyrites of the sedimentary period and the granite porphyry dike have δ34S values ranging from 15.8 to 21.4‰ and from 2.1 to 4.3‰ (with 206Pb/204Pb ratios of 18.09 to 18.10, 207Pb/204Pb ratios of 15.59 to 15.61, and 208Pb/204Pb ratios of 38.17 to 38.24), respectively. The above-mentioned S-Pb isotopic compositions indicate that the metallic materials involved in ore formation originated from a mixture of Triassic magmatic hydrothermal fluid and metamorphic basement. By integrating the regional geology, mineralization ages, and S-Pb isotopic studies, we propose that the Dongtangzi Zn-Pb deposit is the product of epigenetic hydrothermal fluid processes, driven by Late Triassic regional tectono-magmatic processes.

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.

Infrared microthermometry of fluid inclusion in sphalerite: A case study of the Xinqiao deposit in the Middle–Lower Yangtze metallogenic belt

Infrared microthermometry allows direct measurement of fluid inclusions hosted in opaque ore minerals and can provide direct constraints on the evolution of ore-forming fluids. This study presents infrared microthermometry of spherite-hosted fluid inclusions from the Xinqiao deposit in the Middle-Lower Yangtze Metallogenic Belt and sheds new light on the ore genesis of the deposit. Considering that infrared light may lead to non-negligible temperature deviations during microthermometry, some tests were first conducted to ensure the accuracy of the microthermometric measurements. The measurement results indicated that using the lowest light intensity of the microscope and inserting an optical filter were effective in minimizing the possible temperature deviations of infrared microthermometry. All sphalerite-hosted fluid inclusions from the Xinqiao deposit were aqueous. They show homogenization temperature ranging from ~200 to 350 °C, but have two separate salinity groups (1.0–10% and 15.1–19.2% NaCl equivalent). The low-salinity group represents sedimentary exhalative (SEDEX)-associated fluids, whereas the high-salinity group results from modification by later magmatic hydrothermal fluids. Combined with published fluid inclusion data, the four-stage fluid evolution of the Xinqiao deposit was depicted. Furthermore, our data suggest that the Xinqiao deposit was formed by two-stage metallogenic events including SEDEX and magmatic-hydrothermal mineralization.

Genetic modeling and prospecting criteria: An example of syngenetic vs. epigenetic ore formation

The paper presents the importance of mineral deposit modeling, based on the elucidation of key elements of its origin, for the development of reliable criteria for prospecting of new deposits and orebodies of this type. On the example of the Kremikovtsi carbonate-hosted IF-barite-polymetallic deposit, it is shown that the adoption of a well-grounded syngenetic or epigenetic concept for its origin is crucial for successful prospecting activity. Based on the developed model for a sedimentary-exhalative (SEDEX) origin of the deposit (i.e. syngenetic to the carbonate host), the key factors controlling ore formation are specified, and an optimal strategy for future prospecting in the region is proposed.

Determining the ore-forming processes of Dongshengmiao Zn-Pb-Cu deposit: Evidence from the linear discriminant analysis of pyrite geochemistry

The orogenic base metal deposits gain more and more attentions in recent years. The ore-forming fluids associated with these deposits are enriched in reduced sulfur and have low salinity. Since this kind of fluid has low affinity to transport base metals, pre-enrichment of sulfide should take place during the formation of orogenic base metal deposits. The Dongshengmiao Zn-Pb-Cu deposit, which is located in the northern margin of the North China Block, was considered as orogenic base metal deposit, and a two-stage mineralization process was proposed by previous researchers, but other researchers proposed that the Dongshengmiao is a typical sedimentary exhalative (SEDEX) deposit. Even though the tectonic environment, fluid inclusion, geochronology and isotopic geochemistry have been widely investigated in the Dongshengmiao, its genesis is still under debate, and new data or proof should be presented to decipher the genesis model of the Dongshengmiao deposit. In this study, linear discriminant analysis (LDA), one of the commonly used machine learning methods, was employed to discriminate the genesis of pyrite in the Dongshengmiao deposit based on the trace element concentrations analyzed by LA-ICP-MS. The LDA results demonstrate that nearly all the early-stage fine-grained pyrites (Py1) show the same geochemical features as the pyrites from volcanic hosted massive sulfide (VHMS), whereas most of the late-stage recrystallized pyrite (Py2) is of orogenic origin. The Mesoproterozoic submarine volcanic activities resulted in pre-enrichment of sulfide with VHMS geochemical signature in the rocks hosting Dongshengmiao deposit. The pre-enriched sulfides were subsequently remobilized during the subsequent metamorphism in the early Cretaceous, leading to the formation of giant an orogenic base metal 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.

Geology, Pb and S Isotope Geochemistry, and Genesis of the Na Bop-Pu Sap Lead-Zinc Deposit in the Cho Don area, Northeastern Vietnam

The Na Bop-Pu Sap Pb-Zn ore bodies represent a typical vein-type lead-zinc deposit situated in the Cho Don area and are currently being extracted for their lead and zinc resources. This deposit is characterized by its significant scale and quality and is considered one of the prominent lead-zinc deposits in the Cho Don area. Despite its significance, this deposit has not received adequate attention, resulting in limited knowledge of its geology, mineralization, and deposit genesis model. To address this knowledge gap, our study utilized several methodologies, including field surveying, ore mineral analysis under a microscope, and S and Pb isotopic geochemistry. By employing these approaches, we were able to obtain specific insights into the origin of mineralization and the deposit model. Our field survey suggests that the ore deposits are formed as Pb-Zn-bearing veins along Devonian shale, claystone, and limestone faults. Microscopic analyses of the veins reveal the presence of galena, sphalerite, chalcopyrite, pyrite, arsenopyrite, and pyrrhotite as ore minerals, and quartz, calcite, dolomite, and chalcedony as gangue minerals. Sulfur-isotope values (δ34SCDT) of galena 5.3 to 0.1‰ (average 2.8‰), sphalerite 6.8 to 2.5‰ (average 5.3‰), and pyrite 5.8 to 4.1‰ (average 4.9‰) indicate that the sulfide mineralization may be related to a deep source, possibly originating from magmatic activity in the region and contaminated by carbonate-bearing marine sedimentary rocks. Lead-isotope studies indicate a model age of 598-424 Ma for the lead reservoir, consistent with the possible presence of local source rocks containing sulfur. The lead and sulfur in the ore veins were probably contaminated by Devonian carbonate-bearing marine sedimentary rocks and leached from Neoproterozoic to Cambrian magmatic activity. The lead-zinc deposits in Na Bop-Pu Sap do not display any Mississippi valley-type (MVT) or Sedimentary exhalative (SEDEX) lead-zinc deposit characteristics, as they appear to be related to shear zone-hosted lead-zinc deposits.

Supergene Hydrous Sulfates in the Tuolugou Co-Au Deposit, Northern Qinghai–Tibet Plateau: Implications for Genetic Mechanism and Exploration

Supergene hydrous sulfate minerals form through the oxygenation and weathering of primary sulfides. In the Qinghai–Tibet Plateau region, with an alpine and dry environment, hydrous sulfate minerals oxidized from pyrite-bearing ore bodies provide important clues regarding the mineralization and environment. The Tuolugou sedimentary-exhalative (SEDEX) Co-Au deposit is located in the East Kunlun metallogenic belt of the northern Qinghai–Tibet Plateau in China. In the mining district, pyrite is the prevalent Co-hosting sulfide mineral, and is partially exposed on the surface to weathering and oxidation. Herein, we document the mineral assemblages in the supergene oxidation zone in the Tuolugou deposit, probe the genesis of supergene assemblage, and explore the implications for exploration. Three zones can be recognized in the oxidation zone of the Tuolugou deposit, including the outer zone (natrojarosite), intermediate zone (rozenite and aplowite), and inner zone (roemerite and melanterite). The mechanism of oxidation under aerobic and anaerobic conditions, as well as zoning with different oxidation degrees, are described in detail. Hydrous sulfates such as natrojarosite can be used as possible indicators of the exploration of albitite-related SEDEX deposit in this region.

Geochemical discrimination of pyrite in diverse ore deposit types through statistical analysis and machine learning techniques

Abstract Pyrite is a ubiquitous mineral in many ore deposits and sediments, and its trace element composition is mainly controlled by temperature, oxygen fugacity, pH, compositions of fluids, and host rock composition. A discriminant analysis (DA), based on multi-element compositions of pyrite, distinguishes iron oxide-apatite (IOA), iron oxide copper-gold (IOCG), skarn Cu-(Fe), porphyry Cu-Mo, orogenic Au, volcanic-hosted massive sulfide (VMS), sedimentary exhalative (SEDEX) deposits, and barren sedimentary pyrite. Testing of the DA classifier yields an accuracy of 98% for IOA, 96% for IOCG, 91% for skarn Cu-(Fe), 94% for porphyry Cu-Mo, 87% for orogenic Au, 84% for VMS, 96% for SEDEX, and 85% for barren sedimentary pyrite. Furthermore, neural network, support vector machine, and random forest, were performed for selecting the optimum classifier more accurately. In these three techniques, the support vector machine yielded the highest overall accuracy (98% for IOA, IOCG, skarn Cu-Fe, and porphyry Cu-Mo, and 97% for orogenic Au, VMS, SEDEX, and barren sedimentary pyrite) and thus is an appropriate technique in predicting pyrite types.

Classification of Polymetallic Ore-Forming Processes and Transitional VMS–SEDEX–MV-type: the Example of the Giant Ozernoe Deposit in Transbaikalia, Russia

This article discusses the general classification approaches and key features of different families of polymetallic deposits, with particular attention to the largest in Eurasia Ozernoe polymetallic deposit located in Western Transbaikalia and thoroughly explored 50 years ago. The main groups (or families) of polymetallic deposits in the English-language literature are identified by brief names: volcanogenic massive sulphide (VMS), sedimentary exhalative (SEDEX), and Mississippi Valley type (MVT). Within these three families of deposits, there are many additional types/subtypes, a large number of which are mostly due to the incompleteness and inconsistency of accumulated knowledge on the genesis of polymetallic deposits. Overall, all Pb–Zn(Ag,Cu) deposits—both those that are considered syngenetic, forming on and near the seafloor (VMS and SEDEX), and epigenetic low-temperature ones (MVT)—demonstrate a wide range of features that distinguish and bring together these families. This also applies to the types and subtypes of mineral deposits identified within them. One of the most complex objects for geological–genetic classification is the Ozernoe deposit studied by the authors, which, in terms of the nature of the host rocks, is intermediate between the end members of all three families: SEDEX, VMS and MVT. The deposit is localized in volcanic–carbonate–terrigenous rocks of the Cambrian Oldynda formation, but the age and stratigraphic affiliation of the ore-bearing series remain a matter of debate. The Ozernoe deposit is a combination of massive sulfide and siderite ore beds, ore breccia horizons, low-carbonate aleuropelite members, limestones, fine detrital tuffites, lavas, and tuffs. The sulfide bodies are confined to several stratigraphic levels, and the main productive unit thickness reaches 230 m. The thickness is comprised of 12 mineral lodes, a series of stratified ore bodies separated by gangue layers of sedimentary and volcaniclastic rocks. The primary ore minerals are pyrite, sphalerite, and galena, while the minor minerals include magnetite, chalcopyrite, marcasite, tetrahedrite, and arsenopyrite. There are two main theories regarding the origin of the ore: volcanogenic–sedimentary and hydrothermal–metasomatic. The hydrothermal–sedimentary theory remains the prevailing hypothesis, but there are many indications that epigenetic hydrothermal–metasomatic and dynamic metamorphic processes have contributed to the formation of the deposit. These include the appearance of sulfide–quartz and quartz–carbonate–sulfide veins and vein zones in fine-grained “layered” ores, with large crystalline sphalerite and galena; multiple signs of ore recrystallization, including the formation of pyrite porphyroblasts and arsenopyrite metacrystals; and the formation of solid pyrrhotite and pyrrhotite–magnetite ores with a lenticular-striped, gneissic structure. These observations suggest that different processes, both hydrothermal–sedimentary and metamorphogenetic–metasomatic, were involved in the formation of the Ozernoe deposit. In other words, primary hydrothermal–sedimentary ores were redeposited by late hydrothermal solutions. Nevertheless, many issues concerning the genesis of the Ozernoe deposit remain unresolved.

Trace elements of sulfides in the Dengjiashan Pb–Zn deposit from West Qinling, China: Implications for mineralization conditions and genesis

Dengjiashan is a large‐scale Pb–Zn deposit discovered in the western part of the Xicheng ore field within the West Qinling metallogenic belt. Information regarding the distribution and occurrence of trace elements in ore minerals and mineralization, as well as the genesis of this deposit, remains scarce. Laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS) analysis and elemental mapping were used to determine the distribution and occurrence of trace elements in the sulfide minerals of the Dengjiashan deposit, as well as delineate the process of its genesis. Our results showed that the trace elements enriched in the different sulfides were significantly different. Sphalerite is the main carrier mineral of the scattered elements Cd, Ge and Ga. Based on the trace element content and ratio, principal component analysis and colour of the sphalerite and pyrite, the deposit likely formed in a medium‐temperature environment. The comparative analysis of trace elements from multiple deposits of different origins, combined with the geological characteristics and distribution of sulfide trace elements, suggests that Dengjiashan is a sedimentary exhalative (SEDEX)‐type deposit. As the metallogenic process had a closer relationship to medium‐low temperature hot brine and later tectonic metamorphic hydrothermal fluid, than with magmatic hydrothermal fluid, the deposit is likely of non‐magmatic SEDEX–hot brine superimposed transition origin. This study provides additional insight on the distribution of trace elements in the sulfide minerals of the Dengjiashan deposit, as well as the processes that led to its formation, and may further facilitate ongoing and future key metal prospecting and exploration efforts.

Redetermination of the Depositional Age of the Haerdaban Group in the Northern Margin of the Yili Block, Western Tianshan, NW China: Implications for Regional Tectonics and Pb‐Zn Mineralization

AbstractThe Yili Block in the Western Tianshan orogen is a key area for understanding the early crustal formation and evolution of the Central Asian orogenic belt, due to the widely‐distributed Precambrian rocks. Also, it hosts a lot of medium– to large‐scale sedimentary exhalative (SEDEX) Pb‐Zn deposits that mainly occur in Proterozoic metamorphosed clastic‐carbonate rocks. In this study, LA‐ICP‐MS U‐Pb analyses were carried out on detrital zircons in siltstones of the Precambrian Haerdaban Group in the Haerdaban Pb‐Zn deposit and magmatic zircons in the diorite dyke that cuts through the strata and orebodies. The maximum depositional age of the siltstones was determined to be about 604 Ma, the diorite having formed at approximately 500 Ma. As such, the Haerdaban Group was most likely formed in the Neoproterozoic Sinian, rather than the previously considered Mesoproterozoic Changchengian. Detrital materials of the Haerdaban Group were mostly derived from the Nanhua–Sinian mafic dykes and granitic rocks around Lake Sayram at the northern margin of the Yili Block. It is proposed that the Yili Block, together with the Kazakhstan and Central Tianshan blocks and the Tarim Craton, might all pertain to the same Rodinia supercontinent, which has great potential for targeting large to super‐large SEDEX Pb‐Zn deposits.

Sulfide anatexis during high-grade metamorphism: a case study from the Bodenmais SEDEX deposit, Germany

Many sedimentary-exhalative (SEDEX) sulfide deposits have been subject to regional metamorphism and, if the metamorphic grade was high enough, this could have resulted in sulfide anatexis. Although experiments and textures indeed showed that some deposits were partially molten, there is an ongoing debate as to the extent to which metamorphosed ore deposits were molten. Since some SEDEX deposits underwent amphibolite to granulite facies metamorphism, not only sulfides but also the host silicate rocks should have reached anatectic conditions. Due to the two immiscible silicate and sulfide melts, the formation of typical mingling and emulsion textures, as already known from magmatic sulfide deposits, should form. To test this hypothesis, we investigate sulfide-silicate textures from the granulite-facies Bodenmais SEDEX deposit (Germany). Textures from Bodenmais are similar to magmatic sulfide deposits including sulfide-matrix breccia, emulsion textures, pegmatitic leucosomes, and massive sulfides overlain by net-textured intergrowths of refractory quartz, which is interpreted to be a relic of silicate anatexis. Minerals crystallized during the interaction of both immiscible melts differ in their chemistry compared to the same minerals found in the adjacent migmatitic host rocks: for example, garnet in sulfides is Mn-rich (spessartine), but Fe-rich (almandine) in the migmatites and sulfide-enclosed cordierite is more enriched in Mg (Mg/(Mg + Fe): 0.84) than migmatitic cordierite (Mg/(Mg + Fe): 0.54). The textures themselves, their spatial arrangement within the deposit, the differences in mineral chemistry, and the observed crystallization sequence provide unequivocal evidence that the sulfides at Bodenmais were molten to a large extent under granulite facies conditions.