Massive Sulfide Research Articles

Atmosphere and biological impact during sulfide formation in the Archean Central-Vozhma sulfide deposit (Karelia)

Relevance. The need of new knowledge about the early stages of the Earth. Sulfur isotope analysis of sulfide minerals is a powerful tool to understand the processes during the Archaean and Paleoproterozoic. Combined with other data, isotope geochemistry provides an insight into sulfur sources of sulfides from ancient sulfide volcanosedimentary deposits; geochemical factors affecting Archaean sulfide volcanosedimentary ore formation; adjust genetic models and determine the degree of influence of bacteria on the mineral formation. Aim. To identify the sources of sulfur during the formation of sulfide deposits via isotope analysis, and to evaluate bacteria affect mineral formation. Objects. They were obtained from the core of boreholes of Mesoarchaean volcanosedimentary sulfide Central-Vozhma deposit, being a part of the Sumozersko-Kenozersky greenstone belt of the Karelian craton. Methods. Mineralogical studies of rock and ore samples were carried out using optical microscopy; scanning electron microscopy and energy dispersive X-ray spectroscopy. The ratios of four stable sulfur isotopes were analyzed in sulfide minerals of the deposit (33S/32S, 34S/32S, 36S/32S). Results. The results obtained demonstrated the polygenic source of sulfur in sulfides. The sulfides have both positive and negative Δ33S values, indicating the presence of atmospheric sulfur formed under UV photolysis during mineral formation. Sulfide minerals include the following components: Seawater sulfate sulfur of photolytic genesis showed a negative anomaly Δ33S (∼ –0.4‰). It was the source of authigenic pyrite. Sulfides crystallized as a result of biological sulfate reduction demonstrated a narrow range of δ34S values (–2.64‰˂0˂+4.27‰). Elemental sulfur of photolytic genesis mobilized from the host sedimentary rocks by hydrothermal fluids. This sulfur, with a positive Δ33S anomaly (up to +1.6‰) took part in the massive sulfide ores formation.

Effects of deep magmatic degassing and shallow seawater circulation on trace element and sulfur cycling in submarine hydrothermal systems: Insights from the Shijuligou analog, North China

Limited access to modern subseafloor sulfides hampers our understanding of the link between magmatic volatile influx and the cycling of trace elements and sulfur, as well as the effect of the subsequent shallow seawater circulation on these processes. Hence, we studied a well-preserved fossil analog of submarine hydrothermal systems – the Shijuligou volcanogenic massive sulfide (VMS) deposit from the North Qilian Mountains in North China to examine variations in elements and isotopes of subseafloor sulfides vertically.The vertical distribution of trace elements in subseafloor sulfides is strongly controlled by temperature gradients and redox states during the interaction between hot fluids and seawater beneath the paleo-seafloor. While the enrichment of elements like As, Sb, and Au (median: 1335, 43.7, and 0.30 ppm, respectively, n = 21) and negative δ34S values (mean: −3.07 ‰, n = 7) of euhedral pyrites in the jasper, along with the precipitation of high sulfidation minerals (e.g., enargite), suggest the input of magmatic volatiles into hydrothermal systems. During the shallow seawater-hydrothermal circulation, pyrites in the veined and stockwork zones exhibit distinctly elevated δ34S values (up to 15.74 ‰), accompanied by increased concentrations of wall-rock-derived elements (e.g., Cu, Ni, Si, and Ti) and low-temperature-responsive elements (e.g., Pb, Zn, and Cd). Sulfur isotopes of sulfides vary significantly from the surface to the deep ore zones, ranging from −3.36 to 19.84 ‰ (mean: 9.25 ‰, n = 37). The negative δ34S values of pyrites at the paleo-seafloor are due to the addition of H2S derived from the disproportionation of magmatic SO2. The increased δ34S values of stockwork and disseminated sulfides at depth are attributed to the progressive reduction of seawater sulfates by ferrous iron released from the alteration of fresh basalts. The trace elemental and isotopic characteristics of sulfides suggest the Shujuligou VMS deposit resembles the fossil analog of immature, subduction-related submarine hydrothermal systems.

Assessment of atmospheric pollution by potentially toxic elements in the urban areas of the Riotinto mining district

Ore mineralizations in bedrock and their exploitation may have a negative impact on air quality of surrounding urban areas and, subsequently, on human health. This study uses lichens as bioindicators of atmospheric pollution to evaluate the spatial distribution of potentially toxic elements (PTEs) in the towns close to the massive sulfide deposits of the Iberian Pyrite Belt (IPB) in SW Spain. Altogether 89 native lichen samples of Xanthoria parietina were collected from the mining towns, control towns out of the reach of the mining activity, as well as from distal sampling sites. The samples were analyzed for 29 elements after acid digestion. The concentrations for Co, Ni, Cu, Zn, As, Rb, Mo, Cd, Sn, Sb, Cs, Ba, W, Tl, Pb, S, and Fe are significantly higher in the mining towns in comparison to the control towns. The ore mineral-associated PTEs, including Cu, Zn, As, Ba, and Pb, exhibit extreme concentrations in the urban areas close to the mining activity, and particularly in the small settlement of La Dehesa next to the mineral processing plant and the tailings pond. The distal samples confirm the decrease in the concentrations of all PTEs, and these samples present similar values as in the control areas. The results, point at increased bioaccumulation of PTEs in the lichen thalli of the adjacent urban areas, suggesting that the air quality of the adjacent urban areas is locally impacted by the massive polymetallic sulfide deposits which is enhanced by the mining activity. Therefore, monitoring the urban air quality is recommended.

GOLD ENRICHMENT MECHANISM IN MID-OCEAN RIDGE HYDROTHERMAL SYSTEMS: AN EXAMPLE FROM THE LONGQI HYDROTHERMAL FIELD ON THE ULTRASLOW-SPREADING SOUTHWEST INDIAN RIDGE

Abstract In mid-ocean ridge (MOR) hydrothermal systems, the gold grade of sea-floor massive sulfides (SMSs) is negatively correlated with the spreading rate of the ridge. Previous investigations have addressed the distribution of gold in sulfides from hydrothermal fields hosted by ultramafic rocks. In contrast, the gold enrichment mechanisms in sulfides from hydrothermal fields hosted by mafic rocks in ultraslow-spreading ridge environments are less well constrained. The basalt-hosted Longqi hydrothermal field, located on the classic ultraslow-spreading Southwest Indian Ridge, provides an opportunity to examine gold enrichment mechanisms in such an environment. Two ore-forming stages are identified in chimney fragments: anhydrite + barite + colloidal/porous pyrite (Py1) + marcasite + fine-grained sphalerite (stage 1); euhedral-subhedral pyrite (Py2) + coarse-grained sphalerite + chalcopyrite + isocubanite (stage 2). Py1 is usually overgrown by marcasite, which is in turn enclosed by Py2. Py2 coexists with coarse-grained sphalerite and chalcopyrite. Abundant native gold nanoparticles occur in Py1 or at the transition zone between Py1 and Py2. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analysis suggests that Py1 contains higher Mo, V, Sn, and Pb and lower As, Co/Ni, and Se/Tl values compared to Py2. In situ LA-multicollector (MC)-ICP-MS analyses show that Py1 has a higher mean δ34S (+7.1‰) value than Py2 (+6.6‰). Sulfur primarily derives from MORB and seawater sulfate, of which the proportion of sulfur from seawater sulfate is between 20.5 and 47.6%. Textures, mineral assemblages, and trace element contents of sulfides indicate that the degree of mixing between hydrothermal fluids and seawater decreases as the chimney grows and is accompanied by a gradual increase in temperature. Based on data compiled from 41 hydrothermal fields hosted by basalt, the large range of sulfide δ34S from slow- and ultraslow-spreading MORs may be attributed to the wide range of sulfur sources (e.g., leaching from MOR basalt, thermochemical reduction of seawater sulfate, magma degassing, and bacterial activity), fluid-basalt interaction, and redox state (CH4/CO2 ratios). Prolonged fluid-basalt interaction and the type of chimneys, such as beehive chimneys, may lead to higher gold grades in hydrothermal fields. Moreover, low H2S content may be an important contributor to gold enrichment in basalt-hosted SMS deposits in ultraslow-spreading MOR environments.

Extent and survival of zoned pyroxene within intrusions hosting magmatic sulfides: Implications for zoned pyroxene as a prospectivity indicator

AbstractChromium-zoning patterns in pyroxene from the economically significant Ni-Cu sulfide deposits at Nova-Bollinger (Western Australia) and Kevitsa (Northern Finland) were investigated using XRF mapping, automated mineralogy, and EPMA analyses. At Nova-Bollinger, complex Cr-zoning patterns are found widely throughout the cumulus orthopyroxene and clinopyroxene within the Lower Intrusion, a small chonolith that hosts the vast extent of the sulfide mineralisation. Cumulus pyroxenes with visible sector and abrupt zonation patterns have been found up to 150 m vertically away from the massive sulfide ore. Complex zoning patterns are observed throughout the Kevitsa intrusion, in the form of strong oscillatory zoning in cumulus clinopyroxene and sector zoning in idiomorphic orthopyroxene oikocrysts. Kevitsa pyroxenes show varying degrees of hydration, leading to epitaxial replacement by amphibole. Cr zonation is visible through the early stages of this alteration, with preservation enabled by the presence of Cr-rich epitaxial amphibole; however, the remnant zoning is lost as the amphibole alteration progresses. Results suggest that Cr zonation in pyroxene may be an effective indicator of dynamic recharged conduits and therefore an indicator of favourable conditions for metal enriched magmatic sulfide ore formation. Such indicators have significant vertical extent from the ore body and can survive partial alteration, which makes them a useful tool for prospectivity assessment of drilled intrusions. Furthermore, our data show that there is potential for complexly zoned pyroxene to be used as an ex-situ prospectivity indicator in glacial till.

Insights into the indium enrichment of the Ashele VMS Cu-Zn deposit, Altay, NW China

Indium (In) is a critical metal used in the photovoltaic and semiconductor industries, which have exhibited extraordinary growth in demand. Indium is produced as a by-product of mining from different ore deposits (e.g., epithermal, sediment-hosted, and skarn). Volcanogenic massive sulfide (VMS) deposits are an important source of In; however, the mechanism of In enrichment is not fully understood. Here, we combine mineralogy with in situ trace element and S-Pb isotope geochemistry to reveal the enrichment of indium in the Ashele VMS Cu-Zn deposit (1.08 Mt. Cu, 0.43 Mt. Zn) located in Altay, NW China. The Ashele deposit is hosted in the metamorphosed Devonian felsic-bimodal volcanic rocks. This deposit consists of seafloor hydrothermal, metamorphic hydrothermal, and supergene stages. The seafloor hydrothermal stage comprises macro-scale Cu-rich bands (chalcopyrite, pyrite, and minor sphalerite) and Zn-rich bands (sphalerite, pyrite, and minor chalcopyrite). Indium is mainly hosted by chalcopyrite (mean 178 ppm) and sphalerite (mean 214 ppm) and occurs in the lattice. Mineral assemblages and trace element geochemistry suggest that the Cu-rich bands were deposited under high temperatures (> 300–350 °C) and sulfur fugacity (−7.2 to −4.9), whereas the Zn-rich bands were formed under lower temperatures (180–220 °C) and sulfur fugacity (−15.7 to −11.5). The interlayered Cu-rich and Zn-rich bands may reflect the oscillating temperature and sulfur fugacity variations. In situ S isotopic compositions of sulfides cluster within two ranges: 1–3 ‰ and 3–6 ‰, suggesting two endmembers: volcanic origin and reduced seawater sulfate. Pb isotopic ratios are similar to those of the host volcanic rocks, indicating that the metals may be derived from the felsic volcanic system. During metamorphism, the indium may be retained, but Cu contents of sphalerite become more homogeneous. Most In-rich VMS deposits worldwide are hosted by the felsic-dominant system in island arc and back-arc settings. These tectonic settings are conducive to the production of felsic volcanic systems, which are more likely to contain In mineralization. This study highlights the enrichment mechanism of indium in VMS deposits and suggests that the South Altay could become an important source of In.

Study on the influence of collecting parameters of deep-sea seafloor massive sulfide on ore collecting characteristics

The commercialization of deep-sea mining has put forward strict requirements for ore collection output, ore collection efficiency, and environmental disturbance. However, the research of seafloor massive sulfide collection is in the initial stage. The influence of ore-collecting working parameters on the ore-collecting performance is not clear. In order to realize the commercial exploitation of deep-sea minerals, it is urgent to carry out the analysis and research on the influence of ore-collecting parameters on ore-collecting characteristics. The computational fluid dynamics-discrete element method is adopted in this paper to carry out numerical simulation research. Through the qualitative and quantitative analysis method, the influence law of six ore collecting parameters on ore collecting characteristics was analyzed. On this basis, the prediction model of ore-collecting characteristics and the optimal selection of ore-collecting parameters are proposed. Through the research, it is suggested to select 133.2 kg/s flow suction for ore collecting hard pipe; 60 rpm rotation speed is recommended for the mining head. It is recommended to select mining areas with the mineral density of 3000 kg/m3 for collection. The collection stage should be broken as far as possible to the 25 mm chip size. The recommended cutting depth is 224 mm if the strength and system metrics are met. The research of this paper provides a theoretical basis for the practice of deep-sea ore collection and has guiding significance for the selection of ore collection parameters, structural optimization design, and other engineering problems.

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.

Сопоставление пространственного положения рудных объектов глубоководных полиметаллических сульфидных руд и глубинного строения мантии по геофизическим полям в северном приэкваториальном сегменте Срединно-Атлантического хребта

A comparison of geophysical data along the segment of the Mid-Atlantic Ridge (MAR) between 10° N and 25° N and seafloor massive sulfides (SMS) ore objects revealed a number of regularities and relationships in their spatial distribution. SMS are grouped in areas with the following features: near subvertical «microplumes», into which the single axial anomaly of the MAR, determined by the seismotomographic model UU-P07, splits; maximums of Bouguer anomalies between the Vema and Kane transform faults, corresponding to dense mantle volumes and minimal magmatic debit; a pronounced alternation of spatiotemporal «voids» and «bands» of seismicity with a step of ~1.5°, comparable to the near-surface δVp minima; inversion of spreading rates asymmetry from east of the MAR to the west within 20° N and 24° N south of the Kane fault with nontransform south-oriented offsets; areas with positive correlation of the Bouguer anomalies and topography between 19° N and 22° N. The relation of SMS with the specified features of geophysical data forms a predictive basis for this type of objects.

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.

Relationships between hydrogeochemistry and diatoms in acid mine drainage affected media: The case of Iberian pyrite belt; functioning models for an all metallogenetic province

The Iberian Pyritic Belt (IPB) is one of the most important metallogenic provinces, which hosts massive sulfides and extends over 230 km from Canal Caveira-Lousal in Portugal to Gerena (near Seville) in Spain. It has 88 active and inactive mines only in the Spanish part and near 30 in Portugal that generate Acid Mine Drainage (AMD) pollution to the main river basins, Corona, Roxo (Portugal), Odiel, Tinto, Guadiamar (Spain) and Chanza-Guadiana (Portugal/Spain) and consequenty to the 35 acidic sampling sites, 14 in Portugal and 21 in Spain, selected for this unique study. The physico-chemical parameters of waters (EC, Eh, pH, Al, As, Cd, Co, Cu, Fe, Mn, Ni, Pb, Zn, SO42−), acidic diatoms (%Pinacid) and diatom diversity (N°sps) were determined in the laboratory. Then, the results were integrated in a database with 16 variables and 35 sampling points to be statistically analyzed by factor and cluster analysis. In the first, for the 35 sampling sites, it showed a clear inexistence of ecological barriers, exposing how could distantly sampling points be paired together. The last, allowed the pollution–biota interaction models formulation governed by 2 factors: 1-Unrestored Mining Surfaces and 2-WFD (Water Framework Directive) exceeding limits. Dispersion diagram showed that although the unrestored mining surface increases, starting from a certain concentration of contaminants, salts begin to precipitate: the AMD process increases but the WFD does not. There are numerous works in the scientific literature aimed to define diatom-hydro-geo-chemistry interrelationships, but none that covers an entire metallogenetic province where ecological barriers could exist, conditioning the diatom species and groups evolution and distribution in an acidic (pH: 1.90–4.43) environment.

Numerical study of the coupling collection flow field and collecting mechanism of swirling flow and negative pressure suction flow in deep sea mining

The ore collection mechanism of seafloor massive sulfide has not been paid enough attention. In order to achieve collection efficiency, it is necessary to study the ore collection mechanism. Aiming at the ore collection model of the 'KTII' deep-sea mining vehicle, this paper carried out the analysis of the flow field characteristics of the coupled collection, the swirling flow collection and the negative pressure suction flow collection, and the role of each power source in the ore collection process. Finally, the relationship between swirling flow and negative pressure suction flow in the ore collection process is summarized, and the ore collection mechanism is analyzed. The results show that the rotation of the mining head will produce swirling flow, triggering the "inward winding effect", which can ensnare the ground surface fluid into the virtual cutting rotary cavity. The negative pressure suction flow of the collecting hard pipe can suction the liquid in the small-scale range of the throat surface. However, swirling flow and negative pressure suction flow both have advantages and disadvantages in collecting and the two power sources are complementary and inseparable. The research results of this paper have certain guiding significance for the engineering practice of deep-sea mining.

Compositional balance analysis for Cu–Zn(±Co) geochemical anomaly mapping in Trøndelag county, Norway

Trøndelag county has been recently the focus of a new mineral exploration wave given its well-known base metal mineralization potential associated with the occurrence of volcanogenic Cu–Zn (±Co ± Ag ± Au) massive sulfide deposits (VMS). This study evaluates a regional low-density soil sampling survey by implementing principal component analysis (PCA), and compositional balance analysis (CoBA) to target prospective areas for base metal mineralization. Principal component analysis indicates a dominant base metal mineralization signature characterized by a correlation between As and Cu–Cr–Co–Ni, which is consistent with the occurrences of mafic metavolcanic and associated low K–Ca metasedimentary rocks. However, several other Cu–Zn occurrences hosted in K- and/or Ca-rich (meta-)sedimentary (e.g., Røros districts) and felsic (meta-)igneous lithologies have been overlooked by this approach. Data- and knowledge-driven balances (i.e., isometric log-ratios) were then constructed to enhance these “weaker” Cu–Zn (±Co) mineralization fingerprints. Most of the data-driven balances (dcobals) are shown to be very noisy, and less useful for base metal geochemical anomaly mapping compared to their more coherent knowledge-driven counterparts (kcobals). However, the kcobals (e.g., for Cu, Zn and Co) highlight relatively large anomalous areas, which makes them less practical if used as individual exploration vectors. To further define zones of economic interest, common anomalous areas (defined as kcobal >75th percentile) have been filtered out from selected kcobal pairs. This has resulted in the identification of several prospective areas that correspond with 15%–20% of the Trøndelag county.This study not only explores the combined use of CoBA and PCA for detecting base metal anomalies, but also elaborates on some factors that can affect the interpretation and performance of multivariate approaches (e.g., mineralization/alteration extension versus survey resolution, geological framework, and deposit type). The visualization and implementation of CoBA presented in this paper aim to improve geoscientists’ understanding of the reach and limitations of using isometric log-ratios for mineral exploration studies.

Geochemical characteristics of Neoproterozoic metavolcanic rocks of Ariab Auriferous Volcanogenic Massive Sulfide deposit, Red Sea hills, North-East Sudan

The Ariab volcanogenic massive sulfide (VMS, ∼118.3 Mt with >2 Moz Au recovered) district is part of the Ariab-Arbaat belt located in the Haya terrane, Red Sea Hills, Northeast Sudan. The gold-bearing gossan and VMS deposits are mainly hosted by Neoproterozoic bimodal volcanic succession. The petrogenesis, age dating, metallogenic evolution, and tectonic environment as well as the relationship between the metals occurrences and hosting materials remain poorly constrained and controversial. The study aims to investigate the geochemical characteristics of metavolcanic rocks of Ariab Auriferous Volcanogenic Massive Sulfide. XRF and ICP-MS techniques were employed to analyze major, trace, and rare earth elements content. The metavolcanics composition of Ariab VMS hosting rocks ranging from basalt to rhyolitic lava with variable pyroclastics. The chemical affinity varies from sub-alkaline tholeiitic to calc-alkaline nature, raising an argument against the possibility of fractional crystallization. The Ariab VMS metavolcanics were likely formed in the intra-oceanic arc tectonic environment. Ariab mafic lava is characterized notably by high Cr and Ni concentrations. The negative and positive anomalies in trace element profiles are typically ocean island basalt patterns, implying minimal crustal contamination. The geochemical results of dacitic and rhyolitic rocks reveal an assimilation-fractional-crystallization process, including the possibility that plagioclase-rich restite was formed in the parent magma source with a significant contribution from the old crust. The mobility of elements such as Zn, Cu, Pb, Ag, Au, As, and Co complicates the determination of their primary abundances. The partitioning behavior of REEs, the geochemical signatures of chalcophile elements, and their associations with VMS deposits, underscores the complex interaction between igneous processes and subsequent hydrothermal alteration.

Ore Remobilization History of the Metamorphosed Rävliden North Volcanogenic Massive Sulfide Deposit, Skellefte District, Sweden

Abstract The Skellefte district in northern Sweden hosts many volcanogenic massive sulfide (VMS) deposits and is considered one of the most important European mining districts for Cu, Zn, Pb, Ag, and Au. The volcanic and sedimentary rocks that the VMS deposits are hosted in were deformed during the Svecokarelian orogeny, with three documented regional deformation phases. These events imparted a distinct attitude and geometry to the deposits, their host succession, and discordant zones of synvolcanic hydrothermal alteration. Few studies have investigated the detailed deformation effects on the sulfide minerals. In this contribution, we document the structural characteristics and remobilization history of mineralization at the Rävliden North Zn-Pb-Cu-Ag deposit—one of the most important recent discoveries in the district consisting of 8.5 million tonnes (Mt) grading 1.01% Cu, 3.45% Zn, 0.53% Pb, 78.60 g/t Ag, and 0.23 g/t Au. At Rävliden, massive to semimassive sphalerite-rich mineralization with lesser pyrrhotite, galena, pyrite, and silver minerals occurs structurally above stringer-type mineralization dominated by chalcopyrite, pyrrhotite, and pyrite. These mineralization types exhibit evidence of deformation and remobilization such as (1) sulfide-alignment parallel to tectonic foliations; (2) rounded wall-rock tectonoclasts in a ductile deformed sulfide matrix (“ball ore” or durchbewegt ore); and (3) sulfides in tension gashes, strain shadows, piercement veins, and late, straight veinlets crosscutting tectonic fabrics. These features are attributed to polyphase deformation during the D1, D2, and D3 events at temperature ranging from 200° to 550°C. Remobilization of sulfides was mostly within the bounds of the main mineralization (i.e., 10–100 m), with few local external occurrences. A combination of solid-state and fluid-assisted remobilization processes are inferred. Rare brittle veinlets and zeolite-cemented breccias with sphalerite, galena, and silver minerals occur in the stratigraphic hanging wall, where they crosscut all Svecokarelian structures. This mineralization type is highly reminiscent of Phanerozoic low-T vein- and breccia-hosted Pb-Zn deposits of the Lycksele-Storuman area west of Rävliden North, which have been linked to far-field effects associated with the opening of the Iapetus Ocean (0.7–0.5 Ga). We suggest that this Zn-Pb mineralizing event led to the formation of the late sulfide-zeolite veinlets and breccias at Rävliden North, and that elements such as Ag and Sb within this mineralization were locally remobilized from Rävliden.

In Situ Sulfur Isotope Geochemistry Using Secondary Ion Mass Spectrometry of Sulfides in the ABM Replacement-Style Volcanogenic Massive Sulfide Deposit, Finlayson Lake District, Yukon, Canada

Abstract The ABM deposit is a bimodal-felsic, replacement-style volcanogenic massive sulfide deposit located in the Finlayson Lake district, Yukon, Canada, that is hosted by back-arc-affinity felsic volcanic rocks of the Yukon-Tanana terrane. Massive sulfide mineralization occurs as a series of stacked and stratabound lenses subparallel to the volcanic stratigraphy, surrounded by an envelope of pervasive white mica and chlorite alteration. Three major mineral assemblages occur: (1) a pyrite-sphalerite assemblage enriched in Zn-Pb-As-Sb-Ag-Au that formed at temperatures ∼200–270 °C, (2) a pyrite-chalcopyrite-magnetite-pyrrhotite assemblage enriched in Cu-Bi-Se-Co that formed at temperatures ∼300–350 °C, and (3) a chalcopyrite-pyrrhotite-pyrite stringer assemblage formed at temperatures >300 °C. In situ analysis of the sulfur isotopic ratios (δ34S) using secondary ion mass spectrometry has been performed on sulfides (pyrite, pyrrhotite, chalcopyrite, galena, and arsenopyrite) from samples representative of the major mineral assemblages. The δ34S results range between +4.0 and +12.5‰. The pyrite-sphalerite assemblage has an average δ34S value of +6.6 ± 1.8‰ (n = 31), whereas the higher temperature assemblages have an average δ34S value of +9.9 ± 1.4‰ (n = 59). Examination of the δ34S values of adjacent mineral pairs shows that the sulfides were formed under disequilibrium conditions and were not significantly altered or re-equilibrated by greenschist facies metamorphism that affected the ABM deposit post-volcanogenic massive sulfide formation. The observed range of δ34S values suggests that H2S derived from thermochemical sulfate reduction of seawater sulfate and/or an igneous sulfur source as the likeliest sources of S for the sulfides in the ABM deposit. Modeling of thermochemical sulfate reduction of contemporaneous Late Devonian seawater sulfate (δ34S ∼ +25‰) at temperatures estimated for the fluids forming the ABM deposit mineral assemblages (200–350 °C) shows that the reduction of 5–30% of the seawater sulfate would result in isotopic signatures similar to those observed at the ABM deposit. This model also explains the distribution of δ34S values across the mineral assemblages, as thermochemical sulfate reduction at higher temperatures (350 °C) results in more isotopically positive δ34S values. Modeling of mixing lines between thermochemical sulfate reduction at different temperatures and an igneous sulfur source suggests that leaching of magmatic/volcanic rocks also acted as a source of sulfur and was a likely a major contributor (70–95%) to the hydrothermal fluid system at the ABM deposit.

Corundum in Sulfide Ore at the Thompson Mine, Manitoba, Canada: An Unusual Occurrence of Cr- and Ni-Bearing Corundum

Abstract A novel type of corundum host environment is described from the Thompson Mine, northern Manitoba, where corundum occurs within a high-grade metamorphic reaction zone between boudinaged metaperidotite bodies, sulfide ore, and Al-rich pelitic schist of the Pipe Formation (Ospwagan Group). Zoned corundum porphyroblasts, up to 20 mm across, contain coevally formed sulfide inclusions, zircon, rutile, abundant exsolved rutile needles, and secondary sulfide inclusions formed within fractures. Retrograde alteration products of corundum include greenish muscovite (in contact with the schist) and diaspore (in contact with sulfides). The median concentrations of trace elements in Thompson corundum are as follows (in µg/g): 119 Mg, 1720 Ti, 69.9 V, 390 Cr, 8.2 Mn, 1924 Fe, 9.1 Ni, and 106 Ga. The geochemical signature of Thompson corundum (enrichment in Fe, Cr, and Ni) resembles that of ruby in other metamorphic and metasomatic mafic-ultramafic-hosted deposits, and the Cr concentration is comparable to the low range of rubies. Thompson corundum contains high Ni concentrations relative to most Cr-enriched corundum occurrences, a result of formation in an exceptionally Ni-rich environment. The high abundance of exsolved rutile inclusions imparts a dominantly brownish-gray color to the corundum, which precludes it from being of gem quality. Chromium-bearing corundum has been suggested as a possible indicator mineral for metamorphosed massive sulfide deposits, however, it is an indirect indicator that risks yielding false positives. Further investigation into Ni concentrations in corundum, a potential indicator of formation in a Ni-rich environment, is recommended.

Factor analysis in residual soils of the Iberian Pyrite Belt (Spain): comparison between raw data, log-transformation data and compositional data

The Iberian Pyrite Belt (IPB) is a metallogenic province in SW Spain and Portugal hosting the largest concentration of massive sulfide deposits worldwide. Exploration campaigns in both the Spanish and Portuguese sectors of the IPB have increased recently due to the rise in metal prices. Within this framework, distinguishing geochemical features associated with natural phenomena and isolating geogenic anomalies from anthropogenic ones can pose a challenge. This contribution uses the residual soil geochemical database of the IPB (Spain) to examine numerous variables, encompassing major, minor and trace elements. Some of these variables commonly exhibit high correlations owing to consistent geochemical behaviour. However, the influence of anthropogenic factors tends to elevate data variability, occasionally masking the natural relationships that govern their distributions. We apply different treatments of data to develop factor analysis using log-transformed data, and centred log-ratio (clr) transformed data to compare and improve the geochemical interpretation of this important zone. Factor analysis has been developed with these results to compare with previously published research on factor analysis in raw data. Factor score interpolated maps were also generated using both lognormal and clr-transformed data to visualize better the distribution and the different geochemical associations in the IPB. This study shows the importance of the different data treatments and the improvement of the clr-transformed multivariate analysis to reduce the dilution or overestimation of the results of some elements that cause erroneous interpretations of the data.

Tellurium Transport and Enrichment in Volcanogenic Massive Sulfide Deposits: Numerical Simulations of Vent Fluids and Comparison to Modern Sea-Floor Sulfides

Abstract Volcanogenic massive sulfide deposits may represent a significant future source of Te, which is a critical element important for the green energy transition. Tellurium is enriched in these settings by up to 10,000 times over its crustal abundance, indicating that fluids in sea-floor hydrothermal systems may transport and precipitate Te. The major element composition of these hydrothermal fluids is controlled by fluid-rock interaction and is well documented based on experimental, modeling, and natural studies; however, controls on Te mobility are still unknown. To better understand Te enrichment in this deposit type, numerical simulations of the mafic-hosted Vienna Woods and the felsic-hosted Fenway sea-floor vents in the Manus basin were performed to predict Te mobility in modern sea-floor hydrothermal vent fluids and Te deposition during sulfide formation. These simulations demonstrate that the mobility of Te in sea-floor hydrothermal systems is primarily controlled by fluid redox and temperature. Tellurium mobility is low in reduced hydrothermal fluids, whereas mobility of this metal is high at oxidized conditions at temperatures above 250°C. Numerical simulations of the reduced vent fluids of the mafic-hosted Vienna Woods site at the back-arc spreading center in the Manus basin yielded Te concentrations as low as 0.2 ppt. In contrast, the more oxidized model fluids of the felsic-hosted Fenway site located on Pual Ridge in the eastern Manus basin contain 50 ppt Te. The models suggest that Te enrichment in these systems reflects rock-buffer control on oxygen fugacity, rather than an enriched source of Te. In fact, the mafic volcanic rocks probably contain more Te than felsic volcanic rocks. The association of elevated Te contents in the felsic-hosted Fenway system likely reflects magmatic volatile input resulting in lower pH and higher Eh of the fluids. More generally, analysis of sulfide samples collected from modern sea-floor vent sites confirms that redox buffering by the host rocks is a first-order control on Te mobility in hydrothermal fluids. The Te content of sulfides from sea-floor hydrothermal vents hosted by basalt-dominated host rocks is generally lower than those of sulfides from vents located in felsic volcanic successions. Literature review suggests that this relationship also holds true for volcanogenic massive sulfides hosted in ancient volcanic successions. Results from reactive transport simulations further suggest that Te deposition during sulfide formation is primarily temperature controlled. Modeling shows that tellurium minerals are coprecipitated with other sulfides at high temperatures (275°–350°C), whereas Te deposition is distinctly lower at intermediate (150°–275°C) and low temperatures (100°–150°C). These predictions agree with geochemical analyses of sea-floor sulfides as Te broadly correlates positively with Cu and Au enrichment in felsic-hosted systems. The findings of this study provide an important baseline for future studies on the behavior of Te in hydrothermal systems and the processes controlling enrichment of this critical mineral in polymetallic sulfide ores.

Application of Machine Learning to Research on Trace Elemental Characteristics of Metal Sulfides in Se-Te Bearing Deposits

This study focuses on exploring the indication and importance of selenium (Se) and tellurium (Te) in distinguishing different genetic types of ore deposits. Traditional views suggest that dispersed elements are unable to form independent deposits, but are hosted within deposits of other elements as associated elements. Based on this, the study collected trace elemental data of pyrite, sphalerite, and chalcopyrite in various types of Se-Te bearing deposits. The optimal end-elements for distinguishing different genetic type deposits were recognized by principal component analysis (PCA) and the silhouette coefficient method, and discriminant diagrams were drawn. However, support vector machine (SVM) calculation of the decision boundary shows low accuracy, revealing the limitations in binary discriminant visualization for ore deposit type discrimination. Consequently, two machine learning algorithms, random forest (RF) and SVM, were used to construct ore genetic type classification models on the basis of trace elemental data for the three types of metal sulfides. The results indicate that the RF classification model for pyrite exhibits the best performance, achieving an accuracy of 94.5% and avoiding overfitting errors. In detail, according to the feature importance analysis, Se exhibits higher Shapley Additive Explanations (SHAP) values in volcanogenic massive sulfide (VMS) and epithermal deposits, especially the latter, where Se is the most crucial distinguishing element. By comparison, Te shows a significant contribution to distinguishing Carlin-type deposits. Conversely, in porphyry- and skarn-type deposits, the contributions of Se and Te were relatively lower. In conclusion, the application of machine learning methods provides a novel approach for ore genetic type classification and discrimination research, enabling more accurate identification of ore genetic types and contributing to the exploration and development of mineral resources.