Sulfide Deposits Research Articles

Evaluation of compatibility between formation and Injection water into the Reservoir Rock

Scale deposition represents a critical challenge encountered in water injection systems. The objective of this study is to assess the compatibility between the candidate smart water and the formation water in an oil reservoir rock sample. To achieve this, water samples were collected and analyzed to evaluate the extent of deposit formation under varying temperature and pressure conditions. Additionally, the study also examined the combined influence of temperature and pressure on deposit formation. The results indicated that as the temperature increased, there was a decrease in the concentration of sulfate in the seawater. Taking into account the low concentration of barium (zero) in seawater and the unchanged strontium concentration, the decrease in sulfate concentration can be attributed to the deposition of calcium sulfate. Contrarily, in various ratios of smart water, the sulfate concentration has shown an increase with rising temperatures. This can be attributed to the transformation of sulfite present in the formation water into sulfate due to the influence of temperature. The presence of a low concentration of barium in the formation water resulted in insignificant changes in sulfate concentration due to the precipitation of barium sulfate. Additionally, despite the high concentration of strontium, strontium sulfate deposition did not occur, possibly due to the solubility product constant. The analysis of different smart water ratios under various pressures at ambient temperature revealed that pressure had a minimal effect on the solubility of sulfate and calcium salts. During the sediment analysis, no evidence of strontium sulfate sediment formation was observed. However, the analysis indicated a high possibility of iron sulfide and iron oxide deposits forming. Ultimately, under the experimental conditions, significant sediment formation was not observed.

Re-distribution and upgrade of metals induced by the superimposition of later magmatic fluids in the Archean Hongtoushan VMS deposit, NE China

The Hongtoushan copper-zinc deposit is a highly metamorphosed Archean volcanogenic massive sulfide deposit (VMS) in China. After metamorphism, the deposit underwent later fluid superimposition, which is of significance for the re-distribution of metals and upgrading ores. However, the hydrothermal modification mechanism and fluid source remain unclear due to the difficulties in accurately recognizing the mineral textures and assemblages formed by hydrothermal modification. In this study, the mineral texture was investigated to identify the modification mechanism of later fluid and in situ sulfur isotope and trace elements of chalcopyrite were tested to track the source of later fluid and metals. The dominant assemblage formed by superimposed fluid consisted of pyrite, chalcopyrite, sphalerite, minor galena, magnetite, calcite, anhydrite, and hydrothermal alteration minerals, i.e. sericite and chlorite. These minerals infilled the fractures in early pyrite porphyroblasts or precipitated along the grain boundary. Additionally, the pre-existing sulfides were corroded by these minerals. They exhibited replacement and porous textures, indicating that the superimposed fluids resulted in a dissolution-reprecipitation process and formed new sulfides. The hydrothermal metasomatism produced the sericitization of plagioclase and chlorization of biotite, which concurrently liberated silica to form silicification. These interactions suggested that the hydrothermal fluid is acid fluid. The chlorite geothermometer defined the formation temperature of 226–279°C, implying that the superimposed fluid has a moderate temperature. The chalcopyrite precipitated from superimposed fluid either coexisted with pyrite (Ccp 2a) or magnetite (Ccp 2b). The sulfur isotope of Ccp 2a defined a closing zero range (0.75–2.41‰), demonstrating the superimposed fluids were derived from magmatic fluids. In contrast, the Ccp 2b enriched heavy sulfur with a δ34S range of 4.10–8.63‰, which was attributed to the oxidation of fluids. Partial ferrous ions were oxidized to ferric iron, and ferrous and ferric iron precipitated as magnetite. The mineral assemblage changed from chalcopyrite + pyrite, followed by magnetite + chalcopyrite + pyrite, to magnetite + pyrrhotite, representing the local increase of the oxidation state of hydrothermal systems. During the oxidation process, the oxygen fugacity of the superimposed fluid decreased, whereas the pH increased. These results provide crucial evidence on the re-distribution pattern of metals and the post-hydrothermal modification process in the Hongtoushan Cu-Zn deposit.

A New Discovery of Cu Mineralization in the North Qaidam, Tibet via Log-Ratio, Robust Factor Analysis, and Spectrum–Area Modeling

The Qinghai–Tibet Plateau, abundant in mineral resources, is a treasure trove for geological explorers. However, exploration has been hindered by the presence of dense vegetation, weathering layers, and desert cover, particularly in the North Qaidam region. As a result, there is an urgent need to develop efficient geochemical composition methods. In a study of stream sediment geochemical data from the Lüliangshan area of the North Qaidam, the log-ratio transformation was used for data processing, Robust Factor Analysis (RFA) was used for model construction, and the spectrum–area (S-A) model was used for anomaly separation. The outcomes identified two distinct groups of element combinations associated with mineralization. The first group consisted of Au + Ag + Pb + Sb + Hg linked to tectonic-altered rock-type Au (antimony) deposits, while the second group consisted of Cu + Zn + Co and was closely associated with Cu-Ni sulfide deposits. The S-A fractal filtering technique amplified weak anomalies and minimized the area of anomalies against strong backgrounds. The study successfully detected substantial Cu mineralization in the source areas of geochemical anomalies in the Lüliangshan region. Consequently, the log-ratio–RFA–S-A fractal model has been proven to be an effective combination of methods for identifying and extracting geochemical anomalies from stream sediment samples and for mineral exploration in covered areas.

Sulfur isotopes in Archaean crustal reservoirs constrain the transport and deposition mechanisms of nickel-sulfides in komatiites

Assimilation and prolonged suspension of crust-derived sulfide liquid in komatiites are essential to form Ni-rich mineralisation. Evaluating the spatial relationship between komatiite-hosted Ni mineralisation and crustal S sources may thus provide insights into mechanisms of transport, metal enrichment and deposition of assimilated sulfide liquid. This study applied facies analysis and S isotopes to sulfides in Ni-mineralised komatiites and stratigraphically underlying bimodal volcanic-volcaniclastic and sedimentary rocks, which formed during rifting in the Agnew-Wiluna Greenstone Belt, Western Australia. The results revealed a lateral variation from rift-distal sedimentary sulfides, through sulfidic BIF, to rift-proximal VMS-style sulfides, the latter of which was predominantly assimilated by komatiites. Both crustal and komatiite-hosted sulfides were overprinted by granite-related skarn alteration during later basin inversion. Spatial S isotopes correlation revealed that Ni mineralisation in komatiites predominantly formed < 5 km from their crustal S sources, excluding long lateral transport as the main metal enrichment mechanism. Rather, metal enrichment likely happened through multiple cycles of sulfide entrapment and entrainment in lava flow vortices that formed in the wake of topographic steps represented by syn-rift faults. These faults were the main loci for pre-existing crustal weaknesses, hydrothermal fluid circulation, and VMS-style sulfide deposition, which were subsequently utilised by komatiites for enhanced thermo-mechanical erosion and crustal sulfide assimilation. This study shows that proximity to the syn-rift faults was the dominant control on the formation of komatiite-hosted Ni–sulfide mineralisation, regardless of substrate lithology. The S isotope signatures of crustal sulfides may be used as a proxy to identify syn-rift faults in highly deformed terranes.

Flexible highly conductive melamine foam/copper sulfide has both electrical heating and pressure sensing properties

The increasing advancements in science and technology have led to a growing demand for wearable products. In this paper, copper sulfide/melamine foam composites were prepared by chemical deposition of copper sulfide on the melamine foam skeleton. The effects of different deposition amount of copper sulfide on its microstructure, and electrical conductivity were studied. The results showed that the composite had good electrical conductivity and flexibility when the reaction solution concentration was 1 wt.%. The material can be used as an electric heater, the surface of the material can be heated to 145°C under the low voltage of 4 V, and the material can also be used as a flexible pressure sensor with a high sensitivity of 0.385 kPa−1 and a stability of more than 2000 cycles. Materials based on flexible copper sulfide/melamine foams can be used for electric heaters and flexible pressure sensor, which will make them promising applications in wearable products.

Geology and structural setting of the undiscovered Amgififa volcanogenic massive sulfide (VMS) deposit in the southwestern part of the Haya Terrane, Arabian-Nubian Shield, Sudan

The knowledge about the Amgififa deposit in the Haya Terrane of the Arabian-Nubian Shield (ANS)in Sudan is limited due to the geological and structural features of this deposit are hidden beneath Quaternary deposits. This study reveals the characteristics of this deposit through systematic mapping (from trenches, drill holes, and artisanal mining pits), structural analysis, whole-rock geochemistry, and SHRIMP U-Pb zircon age dating. The results suggest that the deposit originated during the Neoproterozoic, with compelling evidence of bimodal–mafic volcanogenic massive sulfides (VMS) that evolved in a localextensional setting. Structural developments were associated with the NW-SE collisions between the Haya and Gebeit terranes, which occurred during the amalgamation of the ANS. A comparison between our study area and the Ariab mining area revealed several similarities, suggesting a regional correlation. In this study, we present a four-stage deformation model to provide insights into the geological history of the Amgififa deposit, which is affected by the tectonic evolution of the ANS. This study not only enhances our understanding of the tectonic chronology of the ANS in the study area, but also offers valuable insights into the mechanisms of regional mineralization. Notably, our study can strengthen the overall understanding of the Amgififa deposit in the ANS context and be used as a foundation for improving future mineral-exploration techniques in the region.

Potential controls on magmatic Ni-Cu sulfide mineralization in orogenic belts: Constraints from mineral compositions of the Huangshandong and Erhongwa intrusions in eastern Tianshan, NW China

Numerous Permian mafic-ultramafic intrusions are situated in the eastern Tianshan Orogen at the southern margin of the Central Asian Orogenic Belt. These intrusions demonstrate a diverse range of magmatic Ni-Cu sulfide mineralization. Notably, the Huangshandong intrusion hosts a large Ni-Cu sulfide deposit, whereas the Erhongwa intrusion lacks any economically significant sulfide mineralization. Both intrusions exhibit similar lithologies and mainly consist of lherzolite, gabbro, gabbronorite and diorite.To elucidate the controlling factors influencing the disparity in mineralization between two intrusions, analyses were conducted on the compositions of olivine, spinel, pyroxene and amphibole. Olivine grains from the Erhongwa lherzolite have lower Ni (361–943 ppm) contents than those from Huangshandong layered lherzolite (Ni 684–864 ppm) and Huangshandong massive lherzolite (Ni 1218 to 1878 ppm). This discrepancy may be attributed to early sulfide separation occurring at greater depths. Modeling results indicated that for the Huangshandong mantle source, 1 % slab-derived melts and 2 % slab-derived fluids were incorporated; conversely, for the Erhongwa mantle source, approximately 2.5 % slab-derived melts and 0.5 % slab-derived fluids were added.Parental magmas of the Erhongwa intrusion exhibit higher oxygen fugacity and water contents than those of the Huangshandong intrusion. Specifically, the magma of the Erhongwa intrusion undergoes magma evolution within a shallow magma chamber, whereas the magma of the Huangshandong intrusion gains sulfide saturation within a deep magma chamber. This research suggests that factors including mantle source features, suitable timing for sulfide separation, and depth of magma chamber are essential for Ni-Cu sulfide mineralization in mafic-ultramafic intrusions in convergent margin setting.

Numerical Simulation of the Self‐Organizational Origin of Concentrically Zoned Aggregates of Siderite and Pyrite in Sediment‐Hosted Massive Sulfide Deposits

AbstractConcentrically zoned pyrite aggregates (CZPA) are common in sediment‐hosted massive sulfide (SHMS) deposits and have been widely used to interpret the ore‐forming processes. There is considerable uncertainty, however, over the formation of aggregates that are oscillatorily zoned and contain randomly‐orientated pyrite microcrystals. Guided by the results of examination of the micro‐textures of CZPA and in‐situ chemical analyses, we conducted a quantitative diffusion‐reaction simulation to assess the mechanism of CZPA formation. Our study shows that oscillatory zoning results from the feedback between the diffusion of reactants and the nucleation‐growth of Fe‐sulfides. Externally derived Fe2+ diffuses into the early diagenetic sediments containing decomposing organic matter (2CH2O + SO42− = 2HCO3− + H2S) and reacts with H2S to form a pyrite layer via an intermediate pathway (Fe2+ + H2S → FeS + 2H+, FeS + H2S → FeS2 + H2). This growth of pyrite layers depletes the local concentration of reactants and suppresses nucleation until the diffusive reaction front advances and another layer is formed. Intermediate phases, for example, mackinawite, nucleate instead of pyrite, because of their greater ease of nucleation due to the low surface tension, and lead to the domination of nucleation over growth. The nucleation of mackinawite and occurrence of siderite in the CZPA are consistent with a low temperature, high pH, anoxic early diagenetic environment. Our study demonstrates that CZPA in SHMS deposits are formed by intrinsic self‐organizational processes rather than by extrinsic changes of ore‐forming fluids. The CZPA in SHMS deposits are thus indicative of their diagenetic origin with Fe2+ infiltrated and diffused from hydrothermal fluids into the sediments.

Geochemical Signatures of Mafic Volcanic Rocks in Modern Oceanic Settings and Implications for Archean Mafic Magmatism

Abstract Greenstone belts are dominated by mafic volcanic rocks with geochemical characteristics that indicate a range of possible geodynamic influences. Many analogies with modern tectonic settings have been suggested. Increasing exploration of the modern oceans and comprehensive sampling of volcanic rocks from the sea floor are now providing unique opportunities to characterize different melt sources and petrogenesis that can be more closely compared to greenstone belts. In this study, we have compiled high-quality geochemical analyses of more than 2,850 unique samples of submarine mafic volcanic rocks (&amp;lt;60 wt % SiO2) from a wide range of settings, including mid-ocean ridges, ridge-hotspot intersections, intraoceanic arc and back-arc spreading centers, and ocean islands. The compiled data show significant geochemical variability spanning the full range of compositions of basalts found in greenstone belts. This diversity is interpreted to be due to variable crustal thickness, dry melting versus wet melting conditions, mantle mixing, and contamination. In particular, different melting conditions have been linked to mantle heterogeneity, complex mantle flow regimes, and short-lived tectonic domains, such as those associated with diffuse spreading, overlapping spreading centers, and triple junctions. These are well documented in the microplate mosaics of the Western Pacific. Systematic differences in mafic volcanic rock compositions in modern oceanic settings are revealed by a combination of principal components analysis and unsupervised hierarchical clustering of the compiled data. Mafic volcanic rocks from most arc-back arc systems have strongly depleted mantle signatures and well-known subduction-related chemistry such as large ion lithophile element (LILE) enrichment in combination with strong negative Nb-Ta anomalies and low heavy rare earth elements (HREEs). This contrasts with mafic volcanic rocks in Archean greenstone belts, which show no, or at least weaker, subduction-related chemistry, a less depleted mantle, less wet melting, and variable crustal contamination. The differences are interpreted to be the result of the lower mantle temperatures, thinner crust, and subduction-related processes of present-day settings. However, mafic rocks that are geochemically identical to those in Archean greenstone belts occur in many modern back-arc basins, including the Lau basin, East Scotia ridge, Bransfield Strait, and Manus basin, which are characterized by fertile mantle sources, high heat flow, and complex spreading regimes typical of small-scale microplate mosaics. These types of settings are recognized as favorable for volcanogenic massive sulfide (VMS) deposits in modern and ancient greenstone belts, and therefore the particular geochemical signatures of the mafic volcanic rocks are potentially important for area selection in base metal exploration.

Ab Initio Molecular Dynamics Simulations and Vibrational Frequency Calculations of Species in Liquid-Liquid Phase Separated MgSO4 Solution at 543 K

The transport of sulfate-bearing brines is closely relevant to mineralization of sulfide deposits as metal-sulfate complexes exist in hydrothermal fluids. Liquid-liquid phase separation evidently occurs in various metal-sulfate systems with transport and precipitating different from homogeneous fluids. Previous studies have revealed a new species with a Raman peak at ~1020 cm-1 in rich concentration phase of liquid-liquid phase separated MgSO4 solution, and it was interpreted as chain structure polymers. Ab initio molecular dynamics simulations (AIMD) and autocorrelation functions for frequency calculation have been performed to disclose the speciation. The results show that more Mg2+ ions surrounding a SO42- anion lead to higher wavenumber of Raman peaks, which indicates the formation of complicate clusters with ion associations similar to kieserite. Besides, the splitting peaks of v-980 Raman bands at ~980, 990, and 1005 cm-1 in homogeneous solution represent more monodentate Mg-Os (Os: O of SO42-) associations instead of certain species, which favors the formation of prenucleation clusters. Furthermore, bidentate Mg-SO4 ligand is less stable than monodentate ligands at 543 K by applying free energy calculations. Our findings give atomic level recognition of concentrated phase in liquid-liquid phase separated MgSO4 fluids and theoretical explanation of the 980 cm-1 Raman peak shifting, which will further inspire understandings on nucleation processes of hydrated sulfate minerals and Raman spectra resolving of other sulfate systems.

Structural controls on the location of hydrothermal activity at the inside corner revealed by stress state

The increased hydrothermal activity at the inside corners is interpreted to be controlled by the high-permeability detachment faults at mid-ocean ridges. Paradoxically, no hydrothermal activity is confirmed to be located at the detachment terminations, where the permeability is theoretically maximal. Here, we use a numerical model to investigate the stress state of the Longqi hydrothermal field and Trans‐Atlantic Geotraverse (TAG) hydrothermal field, which are both located on the hanging wall of a detachment fault rather than at detachment terminations. Our results show that the maximum horizontal stress SHmax at the inside corner is deviated from the observed spreading direction by more than 45°. Meanwhile, shear strain is much higher at the insider corner and the distributions of maximal shear strain is consistent with locations of hydrothermal field. We speculate that regional stress rotation and shear strain enhance the regional permeability of the shallow crust, facilitate hydrothermal circulation on the hanging wall and therefore control the location of the hydrothermal field. Our model provides a potential mechanism for the location of the hydrothermal activity in similar geological settings and therefore provides an important constrain for the exploration of seafloor massive sulfide deposits in the future.

Contrasting Cu mineralization styles across the Dananhu Arc, Eastern Tianshan: insights from the geochronology, geochemistry, and Sr–Nd–Hf isotopes of Carboniferous arc rocks

ABSTRACT The tectonic regime is an important factor controlling the formation of ore deposits, and magmatic rocks generated in different tectonic regimes are characterized by contrasting ore affinities and mineralization styles. A series of early Carboniferous volcanogenic massive sulphide (VMS) deposits occur in the western segment of the Dananhu Arc in the Central Asian Orogenic Belt. In contrast, coeval magmatic rocks in the middle segment are devoid of VMS copper mineralization but host porphyry copper deposits. However, the relationship between tectonic setting and mineralization still needs to be clarified. Herein, we synthesize the new and existing geochemical data of the Carboniferous arc rocks of the Dananhu Arc, showing diverse arc magmatism and contrasting Cu mineralization styles in the western and middle segments. Magmatic rocks in the western segment are consistent with normal island arc origin. In contrast, magmatic rocks in the middle segment of the Dananhu Arc have adakite-like affinities. The magmatic rocks in the western segment were derived from the partial melting of the juvenile lower crust triggered by slab rollback in an extension setting. In contrast, the rocks in the middle segment originated from partial melting of the subducted slab that was triggered by flat subduction. The extension setting coupled with high temperature magmatic activity induced the circulation of the hydrothermal fluids, which were critical to the development of the Xiaorequanzi VMS deposit. Copper would become progressively enriched in the fractionating melt under the high–fO2 condition, and the compressional regime caused by flat subduction reduces the ‘leakage’ of hydrothermal fluids, which are favourable for the formation of the porphyry mineralization in the middle segment. It is, therefore, evident that variations in the tectono-magmatic setting across the Dananhu Arc played an important role in generating the diversity of Cu deposit types and variable ore affinities throughout the Eastern Tianshan.

Mapping Ni-Cu-Platinum Group Element-Hosting, Small-Sized, Mafic-Ultramafic Rocks Using WorldView-3 Images and a Spatial-Spectral Transformer Deep Learning Method

Abstract Mafic-ultramafic intrusive complexes possess a considerable capacity for hosting Ni-Cu-platinum group element (PGE) sulfide deposits. However, the mapping of small outcrops over large areas by field surveys is time-consuming. In this study, WorldView-3 (WV-3) data with moderate spectral and very high spatial resolution were employed for mapping mafic-ultramafic units using spectral indices and the spatial-spectral transformer (SSTF) deep learning method in the Luotuoshan area of Beishan, Gansu Province, China. Based on representative reflectance signatures extracted from imagery of known locations, false-color composites of three-band ratios and a newly proposed short-wave infrared (SWIR) spectral index provided reasonable delineation of mafic-ultramafic rocks. The SSTF method facilitated mapping the occurrence of small mafic-ultramafic outcrops and defining much clearer boundaries, particularly for tiny units at meter scale. Moreover, the SSTF method is not sensitive to the occurrence of carbonate lenses that may affect the reflectance of outcrops. Field investigation and laboratory sample analyses confirmed the occurrence of mafic and ultramafic rocks with substantial metallic mineral potential in this area. Seven prospects were confirmed to be related to mafic-ultramafic intrusions during field validation, four of which contained metallic minerals such as chalcopyrite, pentlandite, pyrite, and chromite in the samples observed by scanning electron microscopy and energy dispersive spectrometry. This study proves that the spectral indices and SSTF deep learning method applied on WV-3 multispectral data are useful for discriminating small-sized mafic-ultramafic intrusive rocks (&amp;lt;100 m) for prospecting of local mineralization.

Distribution of chalcophile elements during crystallisation and alteration of magmatic Ni-Cu-Co sulfide deposits in the anorthositic Espedalen Complex, Norway: pentlandite as an indicator for tracking metal tenors

Distribution of chalcophile elements during crystallisation and alteration of magmatic Ni-Cu-Co sulfide deposits in the anorthositic Espedalen Complex, Norway: pentlandite as an indicator for tracking metal tenors

Copper sulfide deposition and remobilisation triggered by non-magmatic fluid incursion in the single-intrusion Tongchang porphyry system, SE China

Porphyry ore deposits are a major source of base and precious metals. Likewise, they bear important fingerprints for understanding magmatic / hydrothermal processes in the convergent margin. For many decades, the sources of non-magmatic fluid and its role in sulfide mineralization in the porphyry hydrothermal systems have been equivocal. The Tongchang porphyry deposit, which is a single intrusive system with a well-established fluid history, is investigated to reconstruct its hydrothermal process that contributed to the ore formation. In-situ oxygen and strontium isotopes in hydrothermal quartz and anhydrite revealed a coexistence of magmatic and non-magmatic fluid reservoirs. The granodiorite—derived magmatic fluid and external groundwater were spatially separated by a hydrologically impermeable shell formed by retrograde mineral deposition (mainly quartz). The location of the impermeable shell coincided with a brittle-ductile transition (BDT) interface established in the host phyllite in response to latent heating by the cooling magmas. It is inferred that the ductile phyllite beneath the impermeable shell may have entrained some amounts of groundwater and remnant metamorphic fluid. The early fluid stage was dominated by the magmatic fluids, forming disseminated chalcopyrite and barren quartz veins in the potassic-altered ductile granodiorite at high temperatures (> 500 °C). The next stage (early-intermediate) was also driven by the circulation of the magmatic fluids, but in a largely brittle zone formed in-between the impermeable shell and the retreated BDT interface (similar to the so-called “carapace” in the orthomagmatic models). In this stage the formation of pyrite and chalcopyrite veins together with chloritic alteration at temperatures of 400–350 °C occurred. The late-intermediate stage was marked by incursion of the trapped non-magmatic fluids due to rupturing of the enlarged carapace. Mixing of the non-magmatic fluids and the magmatic fluids led to deposition of a major phase of vein-type Cu sulfide at temperatures of 350–300 °C. The late fluid stage was characterized by breaching of the impermeable shell in response to volumetric contraction of the fluid system, leading to excessive infiltration of groundwater and ore remobilization. Based on the Tongchang model, six generic fluid models are proposed for porphyry ore deposits that differ in availability of non-magmatic components as well as intrusive histories. The models can account for variabilities in ore and alteration styles found in porphyry ore deposits globally.

Two new melanodrymiid snails from the East Pacific Rise indicate the potential role of inactive vents as evolutionary stepping-stones

Since their discovery in 1977, animals specialized to life in active deep-sea hydrothermal vents have been the focus of many studies. Inactive spires in the vent periphery, however, have received little attention. Recent shifts of deep-sea mining interests from active vents to inactive sulphide deposits have led to an urgent need to characterize the inactive vent fauna. Here, we report two new species of the vent-endemic genus Melanodrymia that are apparently specific to surfaces of inactive sulphides on the East Pacific Rise. Melanodrymia laurelin sp. nov. and M. telperion sp. nov. are easily distinguished from other congeners by shell shape and sculpture; their standings as distinct species are supported by molecular analyses using the mitochondrial cytochrome c oxidase subunit I (COI) gene. They were collected together with numerous specimens of M. galeronae, another species originally described some distance away from active vents. Phylogenetic reconstruction indicates Melanodrymia species living in active vents likely evolved from ancestors specializing in inactive spires, and in turn from sunken wood. Our findings add to the growing evidence that inactive sulphides host unique species, bolstering the need to better understand these systems before any anthropogenic exploitation takes place. https://zoobank.org/urn:lsid:zoobank.org:pub:D8E8EB3F-B246-4962-B70C-1CD94AEB134D

Hidden Markov model for spatial analysis of three-dimensional mineralization distribution: Insights into magma flow and mineral exploration targets in the Jinchuan Ni-Cu-(PGE) sulfide deposit, China

The spatial distribution of mineralization includes significant clues about the magma/fluid flow process for ore formation. However, given the complex nature of the ore-forming process and its weak signature in the mineralization data, revealing the magma/fluid flow process in their mineralization footprint presents a considerable challenge. In this paper, we present a hidden Markov model (HMM) for the analysis of three-dimensional (3D) spatial distribution of mineralization. The HMM assumes the magma flow is a Markov process that is “hidden” in the “observable” mineralization features. Under this setting, the HMM quantifies the states of magma flow and links them as a whole in a probabilistic manner. This allows for the comprehensive combination of mineralization information, facilitating holistic inference of magma flow hidden in the mineralization signal. Based on the maximum likelihood principle, the magma trajectories and the associated injection points are inferred from the HMM. The proposed model is applied to spatial analysis of the mineralization in the world-class Jinchuan Ni-Cu-(PGE) magmatic sulfide deposit in NW China. Based on the 3D mineralization data interpolated from drill assays, the HMM infers magma trajectories and the associated injection points at Jinchuan, which indicate the Jinchuan deposit was formed by a multiple magma conduit system that comprises four independent injection points of magma ingress. According to the identified magma trajectories and injection points, four sites beneath the injection points and along the extension of magma trajectories are considered promising for future mineral exploration. With the insights gained from this case study, the proposed HMM can serve as an effective tool in the exploration information system to unveil magma/fluid flow history and guide exploration efforts toward concealed, deep-seated mineralization.

Paleovolcanism and the prospecting indicators and outlooks for discovery of new economic-grade copper-zinc massive sulfide ore deposits in the Verkhneuralsk ore region, Southern Urals

The principal regularities of distribution of the VMS type mineralization in the Verkhneuralsk ore region in the Southern Urals are characterized. Metallogenic factors of the first kind (stratigraphic, magmatic, lithological, and tectonic) and of the second kind (geotectonic and paleovolcanic) are&#x0D; shown. A combined convective-postmagmatic ore formation model for the VMS is briefly described, that takes into account a genetic relationship of the VMS ore formation to silicic magmatism of the basalt-rhyolite (“contrast”) volcanic formation, four types of such relationship being distinguished, the spatial, temporal, energetic, and compositional ones. The geological, geochemical, and geophysical prospecting indicators for the Ural type VMS mineralization are presented separately for various classes of forecasting metallogenic areas (ore regions, ore clusters, and ore fields and deposits). In the southern portion of the ore district, a site promising for revealing a new ore deposit has been identified, for which the category P2 forecasted resources have been estimated and a recommendation has been given for the geological exploration.

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.

Lithospheric hydrous pyroxenites control localisation and Ni endowment of magmatic sulfide deposits

Lithospheric hydrous pyroxenites control localisation and Ni endowment of magmatic sulfide deposits