Massive Sulfide Research Articles

Experimental study on the influence of cutting parameters on cutting characteristics of deep-sea seafloor massive sulfide

The research of seafloor massive sulfide cutting characteristics is in the initial stage, and experimental methods are rarely used to conduct research. In addition, the mechanism of cutting parameters influencing cutting characteristics is not clear. In order to clarify the influence mechanism, the influences of cutting depth and cutting velocity on cutting characteristics are studied experimentally. It is found that with the increase of cutting depth, the load fluctuation is more severe, the breaking yield is increased, the size of the chip is increased, the powdered percentage is decreased, and the externally expanded breaking zone of rock is wider. However, the cutting depth has little effect on the cutting angle, and the breaking angle is between 48° and 61°. With the increase in cutting velocity, the number of load fluctuations per unit of time increases significantly, and the size of the chip decreases. However, the breaking yield, powdered percentage, breaking angle and external expansion area remain basically unchanged. The research is of guiding significance to the optimization of the mining head structure and the selection of cutting parameters.

Relative timing and controls on advanced argillic and conventional alteration of the Neoarchean Onaman volcanogenic massive sulfide deposit, Ontario, Canada

Relative timing and controls on advanced argillic and conventional alteration of the Neoarchean Onaman volcanogenic massive sulfide deposit, Ontario, Canada

Multi-stage magma emplacement in the western end of the Jinchuan Ni[sbnd]Cu sulfide deposit, NW China, and mineral exploration strategy based on exploration data

The western intrusion of the world-class Jinchuan NiCu sulfide deposit consists of fine-grained and coarse-grained binary lithofacies units. However, recent exploration has revealed two layers of net-textured sulfides in the fine-grained unit at the western end of the Jinchuan intrusion, adding complexity to the genesis of sulfide mineralization. We measured chalcophile elements and collected exploration data on Cu and Ni content to investigate their genesis and prospecting potential. The lower fine-grained subunits, comprising a layer of disseminated sulfides (DS-1) in the bottom and overlain by massive sulfide (MS) and olivine-sulfide cumulates (NTS-1), were overlain by the upper fine-grained subunits disseminated sulfides (DS-2) with a core of net-textured sulfides (NTS-2). The coarse-grained lherzolite with disseminated sulfides (DS-3) sharply cut through the upper subunit. All disseminated samples have Cu/Pd ratios (11,414–128,626) that exceed the mantle range. Additionally, the Pd/Ru ratios of DS-1 (1.26–13.2) are the lowest, followed by DS-2 (3.69–13.5), and highest in DS-3 (2.80–33.6). The exploration data indicate that the Ni and Cu contents and Cu/(Cu + Ni) ratios are significantly higher in DS-3 than in DS-2, while DS-1 shows more dispersed. The NTS-1 exhibits significant Ir and Ru depletion, with Cu/(Cu + Ni) decreasing with depth, eventually encountering Ir and Ru-riched MS. In addition, NTS-2 shows partially Ir depletion but Ru non-depletion, and Cu/(Cu + Ni) increases with depth. These signatures suggest that the lower and upper subunits, along with the coarse-grained unit, formed from platinum-group elements (PGE) in increasingly depleted magma, likely resulting from prior sulfide segregation before emplacement. Furthermore, the differences in Ir and Ru depletion and the variation in the Cu/(Cu + Ni) trend with depth between NTS-1 and NTS-2 were explained by the migration direction of fractional sulfide liquid during sulfide fractionation. We propose that the western end of the Jinchuan intrusion was formed by multi-stage magma emplacement. The strong correlation between exploration data (Ni, Cu, and Cu/(Cu + Ni)) and various sulfide mineralization layers suggests that delineating the spatial range of each sulfide mineralization could provide valuable information for deep mineral prospectivity mapping.

Bio-mediated enhancement of supergene copper mineralization: Evidence from Cu isotope geochemistry

The relationship between microbial activity and the supergene modification of ore systems has been a major subject of debate. Here, we present isotopic evidence of microbial-driven secondary copper mineralization in the active cementation zone of the Las Cruces deposit, a volcanogenic massive sulfide deposit located in Iberian Pyrite Belt, Spain. Copper isotopic data show that the lower isotopic ratios (δ65Cu ≈ −9.2 ± 0.11 ‰, the lowest value measured worldwide in a supergene environment) are found in the upper part of the cementation zone, the same zone where the maximum copper grades are found and where there is direct evidence of extremophilic microbial activity. There is a tendency towards higher values downwards through the cementation zone (−9.2 ± 0.11 ‰ to + 1.67 ± 0.11 ‰ δ65Cu) and upwards into the former Cu-depleted gossan that originally capped the cementation zone (−7.79 ± 0.11 ‰ to −1.32 ± 0.11 ‰ δ65Cu). As microbes preferentially sequester the lighter isotope when incorporating intracellular Cu, this distribution indicates that microbes played a major role in the formation of the high-grade zones. Water arrives to the deposit enriched in isotopically heavy copper, likely because it has leached other ore bodies upstream. δ65Cu values of water currently flowing into the system are remarkably more positive than those in the ore, indicating that microbial activity is a major cause of copper isotope fractionation. At least half of the copper transported by the incoming waters remains within the ore body. Our best interpretation is that the large and high-grade cementation zone at Las Cruces is of biogenic origin, and that the primary mineralization acted as a trap for copper transported by groundwater, leading to the formation of an exotic mineralization distal to sub-eroded massive sulfides located upstream.

Sulfur and metal mobilization during the life cycle of an oceanic core complex: Implications for seafloor massive sulfide deposits formation at slow and ultra-slow spreading ridges

Seafloor massive sulfide (SMS) deposits at slow and ultra-slow spreading ridges are often spatially related to, or hosted in oceanic core complexes (OCCs). The specific oceanic crust architecture, magmatism, hydrothermal fluid circulation and lithologies at OCCs, however, imply different S and metal (e.g. Cu, Zn, Co, Ni) fluxes relative to well-structured oceanic crust at-fast spreading ridges and which are not yet fully constrained. The study of S and metal distribution in the ODP Hole 735B deep drill core from the Atlantis bank allows to understand these fluxes along detachment faults and to better constrain the source zone of S and metals for OCC-related SMS deposits. Significant depletion of S, Cu, Zn and Ni are observed within the upper 250 m of the drill core where intense deformation and hydrothermal fluid circulation occurred. During the complex tectono-magmatic-hydrothermal evolution of the Atlantis Bank, four important stages are recognized for S and metal mobilization: 1) magmatic stratification leading to a higher proportion of sulfide-rich and S, Cu, Zn and Co fertile oxide gabbros in the root zone of the Atlantis Bank detachment, 2) high temperature ductile deformation leading to magmatic sulfide reworking and onset of sulfide leaching with limited metal mobilization, 3) extensive sulfide leaching and metal mobilization during amphibolite to greenschist facies metasomatism and, 4) late stage secondary sulfide precipitation and S enrichment during low temperature fluid circulation. Mass balance calculations from the source zones of the Atlantis Bank detachment highlights that metal mobilization during hydrothermal alteration of gabbroic rocks along detachment faults can fully account for the formation of OCC-related SMS deposits at slow and ultraslow spreading ridges. The Atlantis Bank detachment system, however, is gabbroic-dominated and represent the magmatic end-member of OCCs and further work is necessary for understanding metal fluxes in ultramafic-dominated detachment systems.

The occurrence of cobaltite nanoparticles in pyrite from the De’erni deposit, NW China

Cobalt (Co) is a critical metal that occurs in many types of deposits, Co minerals and sulfide hosts are the main forms of Co occurrence. Pyrite is the most important cobalt-bearing mineral in the De’erni Cu-Zn-Co ultramafic-hosted volcanogenic massive sulfide deposits. However, the occurrence and enrichment of Co in pyrite remain unclear. In this study, a combination of LA-ICP-MS and STEM techniques was employed to conduct a detailed mineralogical investigation of pyrite in the De’erni deposit. The results revealed significant variations in cobalt content among pyrite samples from different mineral assemblages. Pyrite associated with magnetite (Mag), pyrrhotite (Po), chalcopyrite (Ccp), arsenopyrite (Apy), and bornite (Bn) (Py-Mag-Po-Ccp-Apy-Bn suite of mineral assemblages) exhibited the highest cobalt content, which ranged from 672.6 ppm to 2007 ppm. Cobalt occurs in two forms in the pyrite from the De’erni deposit: as cobaltite nanoparticles (NPs) and as a substitute for iron (Fe) in the pyrite lattice. The enrichment mechanism of cobalt in pyrite was explored at the deposit and mineral scales. The results indicate that a decrease in ore-forming fluid temperature and an increase in cobalt content may be significant factors contributing to cobalt enrichment at the deposit scale. Lattice defects may play a crucial role in cobalt enrichment within the pyrite lattice. Furthermore, the discovery of cobaltite NPs in pyrite could provide new insights for explaining the complex zonation of the cobalt element in pyrite.

Combined effect of magmatic fluid–seawater mixing and host rock alteration on the formation of gold-enriched massive sulfides in the Forecast vent field, southern Mariana Trough

Massive sulfides and sulfide-bearing breccia were collected from the Forecast vent field in the southern Mariana Trough. These samples exhibit varying degrees of hydrothermal alteration and/or mineralization, with the former type having significant enrichments in Au (up to 101 ppm). In this study, detailed analyses of mineralogy, geochemistry, S isotope, and fluid inclusion were conducted to understand the unusual Au-rich mineralization. Mineralogical investigations and geochemical analyses (LA–ICP–MS and EPMA) of dominant sulfide minerals indicate that electrums, the main phase of Au mineralization, are characterized by two different generations based on mineralogical relationships and fineness. Early-stage high fineness electrums (930–981 ‰) are associated with sphalerite under relatively high-temperature fluid conditions, whereas galena is main host mineral related to late-stage low fineness electrums (773–868 ‰). Sphalerite geothermometry (231–264 °C), the occurrence of colloform textured sulfides, and microthermometric characteristics of fluid inclusions (Th = 220–304 °C; Salinity = 1.4–6.6 wt% NaCl equivalent; a general trend of decreasing salinity with decreasing Th) indicate that significant decreases in H2S activity, attributed to seawater dilution and rapid precipitation of sulfide minerals, facilitated the efficient destabilization and deposition of Au transported as sulfide complexes from hydrothermal fluids. In particular, the lower 34S values (+0.2 ‰ to + 1.3 ‰) of sulfides compared to those of arc/back-arc lavas (δ34S = +5‰ to + 11 ‰), along with the prevalence of CO2 in the vapor phase of fluid inclusions, reflect that the significant contribution of magmatic volatile influx supplied most of the sulfur and metals (including Au) to the Forecast hydrothermal fluids. Additionally, the abundance of montmorillonite and varying proportions of sulfide and gangue minerals observed in hydrothermal samples suggest that the chemical buffering of fluids by associated substrates and/or sediments could be another significant factor in promoting Au-rich mineralization. Therefore we conclude that the combination of magmatic fluid–seawater mixing and host rock alteration plays an important role in the formation of Au-enriched massive sulfides in the Forecast vent field.

Classification of volcanogenic massive sulfide deposits in North Qilian, China: Evidenced from lithostratigraphy and geodynamic setting

Volcanogenic massive sulfide (VMS) deposits are widely distributed both geographically and temporally, occurring from ancient Archean cratons to modern submarine volcanic environments, with a notable surge during the Paleozoic era. The North Qilian orogenic belt in China is a prominent Paleozoic VMS metallogenic province, shaped by complex geological processes such as the opening of the Qilian Ocean, oceanic subduction, and arc-continent collision. Previous research has constrained the timing of VMS mineralization in the North Qilian to between 440 and 470 Ma, identifying two primary deposit types: Kuroko-type and Cyprus-type. However, ongoing debates persist regarding the classification and geodynamic framework of these VMS deposits. The recent surge in international research on VMS deposit classification and tectonic settings has prompted a reassessment of VMS mineralization within the North Qilian belt. This study revisits the geological and geochemical characteristics of VMS deposits in the region, identifying two distinct types: Mafic VMS deposits and Bimodal-Felsic VMS deposits. Furthermore, the metallogenic dynamics of the Shijuli, Jiugequan, and Baiyinchang deposits have been re-evaluated in the context of the structural evolution and contemporary interpretations in this area.

The Fate of “Immobile” Ti in Hyaloclastites: An Evidence from Silica–Iron-Rich Sedimentary Rocks of the Urals Paleozoic Massive Sulfide Deposits

The formation of Paleozoic silica–iron-rich sedimentary rocks in the Urals volcanic-hosted massive sulfide (VHMS) deposits is considered a result of seafloor alteration of hyaloclastites mixed with calcareous/organic or sulfide material. These rocks host various Ti mineral phases pointing to the transformation of precursor metacolloidal TiO2 phases to disordered anatase during seafloor alteration of hyaloclastites, which was later converted to globules and clusters and further to diagenetic rutile. The LA-ICP-MS analysis showed that the Ti content of hyaloclasts partly replaced by finely dispersed Si–Fe aggregates increases to 540–2950 ppm and decreases (<5 ppm) in full Si–Fe pseudomorphs after hyaloclasts. LA-ICP-MS element mapping reveals the enrichment in V, U, Cr, W, Nb, Pb, and Th of the anatase globules and the local accumulation of Zr, Y, and REE on their periphery. Corrosive biogenic textures in the outer zones of some hyaloclasts and biomorphic aggregates in rocks contain anatase particles in assemblage with apatite indicating the biophilic properties of Ti. This work fills the knowledge gaps about Ti mobilization during low-temperature seafloor alteration of hyaloclastites in VHMS deposits.

A deep-sea stalked tunicate Culeolus suhmi Herdman (1881) (Ascidiacea: Pyuridae) from the Central Indian Ridge

The deep-sea stalked tunicate species Culeolus suhmi has reported a near the off-axis of a seamount in the Mid-Ocean Ridge sector of the Central Indian Ridge. The megabenthic communities were collected using a benthic sledge from depths between 2140 and 2348 m. This species identification was based on morphological characteristics, and the evolutionary placement was determined using a molecular study of the 18S rRNA gene. This analysis supported the monophyly of the clade belonging to the family Pyuridae. This study is part of a baseline assessment of the environment and benthic ecology, and it will assist in evaluate the impact of future massive sulphide exploitation in the Indian Ocean.

Research on the Collection Characteristics of a Hydraulic Collector for Seafloor Massive Sulfides

Ore collection is very important in deep-sea mining for seafloor massive sulfide (SMS). In view of the characteristics of SMS ores produced by mechanical crushing, which contain coarse particles and a wide particle size distribution, in-depth research on the collection process with a device combining a rotary crushing head and a flat suction mouth was conducted. In this paper, solid–liquid two-phase flow in the hydraulic collection process with a drum rotation is carried out using the computational fluid dynamics-discrete element method (CFD-DEM), and the flow field characteristics and particle motion characteristics are analyzed. The results indicate that particles with a maximum diameter of 20 mm can be effectively collected when the suction velocity is 3 m/s. The collection process of SMS mainly goes through three stages: particle disturbance start-up, partial particle influx, and stable collection. In addition, the appropriate drum speed facilitates the collection of SMS ore. Finally, the correctness of the numerical method was assessed using similarity experiments. This work can be used to guide the design of underwater mining equipment.

Resistivity anomalies in the shallow and deep crust beneath West Tasmania from a broadband magnetotelluric 2D transect

West Tasmania has a complex geological history, including a Cambrian tectonic collision and related orogenesis, which formed ore deposits in a volcanic hosted massive sulfide (VHMS) setting. While the topography and dense vegetation covering the area presents challenges for on-ground investigations, the area is relatively well-studied such that 3D geological models are available. This contribution presents results of a broadband magnetotelluric (MT) 2D transect across the area (∼30 stations over a ∼ 80 km line, deployed in early 2016) that enables a combined interpretation of regional-scale geoelectric and geological structures. After accounting for noise, distortion and geoelectric strike; we produce 2D resistivity models using OCCAM2D inversion. We infer low resistivity anomalies in the shallow ( < 3 km ), mid (3–8 km) and deeper crust. Along this MT transect the shallow and mid crust low resistivity zones correspond to major crustal faults. Deep low resistivity features in the east of the transect suggest fluid pathways associated with metamorphism along the western boundary of the Tyennan block during the Cambrian Tyennan Orogeny, while others potentially represent the metasomatism of lower crustal rocks and fluid pathways converging into the mid crust.

Petrogenesis and Ni–Cu–(PGE) prospectivity of the Mount Ayliff Complex in the Karoo Igneous Province: new insights from the Ingeli and Horseshoe lobes

The Mount Ayliff Complex comprises five cognate mafic–ultramafic bodies emplaced along the southern margin of the Kaapvaal Craton. This study examines the Ingeli and Horseshoe lobes and assesses their magmatic sulfide prospectivity with respect to the Insizwa lobe, which hosts massive sulfides at its Waterfall Gorge occurrence. The Ingeli lobe consists of 465 m of olivine–chromite cumulates overlain by 340 m of (olivine-)gabbronorite, while the Horseshoe lobe consists of 45 m of olivine gabbronorite overlain by 5 m of gabbro. The Ingeli lobe possesses sparsely disseminated sulfides at its mafic–ultramafic transition, whereas disseminated sulfides are present throughout the Horseshoe lobe. A petrogenetic model is proposed, where magma accumulated and fractionated nickeliferous olivine and chromite in an upper-crustal staging chamber hosted by Proterozoic basement rocks. Magma then ascended and deposited olivine–chromite cumulates at the level of the complex. Prolonged magma flux in the staging chamber facilitated the assimilation of basement rocks, triggering sulfide saturation and the crystallization of Ni-poor olivine. Contaminated magma then ascended and interacted with pre-existing cumulates, depositing sulfide melt that may have backflowed as magmatic activity waned. Basaltic magma then flowed over the ultramafic cumulates, depositing disseminated sulfides whilst undergoing closed-system fractionation. Basal depressions and underlying feeder structures are the most prospective locations for magmatic sulfide mineralization.

Synchronous felsic volcanism and carbonate sedimentation as a setting for VMS deposits localization at the Salair terrane, NE Central Asian Orogenic Belt

The Salair terrane located in the northern part of the Central Asian Orogenic Belt (CAOB) contains many epithermal deposits including volcanogenic massive sulphide (VMS) deposits. The host rocks mainly consist of felsic volcanic rocks such as lavas, volcanic breccias and tuffs that associated with thick strata of carbonates. In this study, we present zircon U–Pb ages, whole rock geochemistry, and Nd isotope data from the volcanic rocks, and results of geochemical and isotope (Sr, C, O) studies of carbonates to constrain their age and petrogenesis, and to characterize the tectonic setting. Zircon U–Pb dating reveals that the ore-bearing felsic lavas have age of 519.3 ± 1.9 Ma, while the felsic tuffs have age of 516.0 ± 0.9 Ma. These volcanic rocks are characterized by high SiO2 and Na2O contents, enrichment in light rare-earth elements, remarkable negative Eu anomalies, and pronounced depletion in Nb, Ta, P, and Ti. They have depleted ɛNd(t) values ranging from +4.9 to +6.3, and young two-stage Nd model ages (from 0.82 to 0.64 Ga). The felsic volcanic rocks from the Salair terrane are interpreted as highly evolved I-type magmatic rocks that might be produced by high degree partial melting of juvenile lower crust without a significant contribution of ancient crust and without crustal reworking.Felsic volcanism was accompanied by the formation of thick strata of carbonates. These carbonates are marine limestones with Mg/Ca ratios less than 0.007, δ18O(SMOW) values from 17.1 to 23.8 ‰ and δ13C(PDB) values between –0.9 and +0.9. Their Sr isotope composition varies in a narrow range within 0.70844–0.70859 that interpreted as representing proxy for coeval seawater. These values are consistent with depositional ages of 520–510 Ma and confirms the synchronicity of the formation of carbonates and felsic volcanism. Based on the regional geology and geochemistry, the ore-host rocks of the Salair terrane were formed in the back-arc setting where the marine transgression occurred as a result of graben subsidence. It is important for better understanding epithermal deposits in the northern CAOB and might provide new insights about prospecting the VMS deposits in similar tectonic settings.

The flotation of magmatic sulfides transfers Cu-Au from magmas to seafloor massive sulfide deposits

Copper and gold-rich seafloor massive sulfide deposits formed in intra-oceanic subduction settings are typically associated with hydrous and oxidized magmas, but processes leading to their formation remain controversial. Sulfide-bubble interaction has been suggested to play an important role in metal transfer from magmas to seawater-derived hydrothermal fluids. Here we use textural observations of magmatic sulfides, geochemical numerical models of chalcophile element concentrations, and numerical models of magmatic sulfide growth within a mafic to felsic submarine magmatic suite (Fatu Kapa, SW Pacific) associated with copper-gold-rich seafloor massive sulfide deposits. We demonstrate that concomitant sulfide and aqueous fluid formation at the andesitic stage results in floating sulfide-bubble compound drops in magmas, which play a crucial role in the transfer of copper and gold toward the surface. We emphasize that late sulfide saturation in copper-gold-rich intra-oceanic subduction-derived felsic magmas favors upward sulfide transfer via flotation.

Whole rock lithogeochemical analysis of the Mount Read Volcanics: a new tool for geochemical exploration

The Mount Read Volcanics (MRV) of western Tasmania is a belt of Middle to Late Cambrian submarine volcanics and volcaniclastics and one of the major base and precious metal provinces within Australia. Exploration success in the MRV has been in decline in recent years due to a variety of challenges including intensely altered rocks with complex stratigraphy and lithofacies variation, and a lack of accessible outcrop. As a result, local and regional mapping of the MRV is often restricted to Group-level stratigraphy, rendering geological mapping ineffective for identifying decametre-scale mine stratigraphy. Surface rock chip and drill hole samples were collected and analysed using commercially available geochemical assays to create a regional geochemical dataset of the MRV, covering the entire province and all major stratigraphic units. From these data, a lithogeochemical methodology was developed, utilizing Ti/Nb and V/Sc systematics that effectively characterizes the samples according to composition and magmatic processes. This method is shown to be robust to biases due to alteration and lithofacies, eliminating the need for highly selective sampling or extensive data filtering. To demonstrate the utility of this method in an exploration context, data from the K-lens of the Rosebery polymetallic volcanic-hosted massive sulfide (VHMS) deposit was used as a case study. Using Ti/Nb–V/Sc systematics, a rock composition classification was developed that allowed for discrimination of the footwall, hanging wall and host stratigraphy of the Rosebery mine sequence. A geochemical fingerprint for the footwall stratigraphy to mineralization was developed, and by correlating this signature to the regional unclassified samples, geochemical analogues for the Rosebery footwall were readily identified. This approach rapidly reduces the exploration search space and provides valuable information for future mineral exploration. The methodology is applicable in other terrains; however, appropriate orientation studies are required to investigate potential biases due to lithofacies, alteration and mineralogical variability.

Updating Geological Information about the Metallogenesis of the Iberian Pyrite Belt

The Iberian Pyrite Belt (IPB) represents one of the largest districts of volcanogenic massive sulfide (VMS) deposits in the world, and is a critical source of base metals (Cu, Pb, and Zn) for Europe. Confirmed resources exceed 1700 Mt of massive sulfides with grades of around 1.2% Cu, 1% Pb, and 3% Zn as well as more than 300 Mt of stockwork-type copper mineralization. Significant resources of Sn, precious metals (Au and Ag), and critical metals (Co, Bi, Sb, In, and Se) have also been evaluated. The genesis of these deposits is related to a complex geological evolution during the late Devonian and Mississippian periods. The geological record of such evolution is represented by three main lithological units: Phyllite–Quartzite Group, the volcano–sedimentary Complex (VSC), and the so-called Culm Group. The sulfide deposits are located in the VSC, associated with felsic volcanic rocks or sedimentary rocks such as black shales. The massive sulfide deposits occur as tabular bodies and replacement masses associated with both volcanic and sedimentary rocks. Their mineralogical composition is relatively simple, dominated by pyrite, chalcopyrite, sphalerite, and galena. Their origin is related to three evolutionary stages at increasing temperatures, and a subsequent stage associated with the Variscan deformation. The present paper summarizes the latest developments in the IPB and revises research areas requiring further investigation.

A newly recognised mafic sill-hosted Ni-sulfide deposit emplaced during the 2.4 Ga Widgiemooltha dike swarm event, Eastern Goldfields, Western Australia

AbstractThe Cathedrals Ni-Cu prospect, located at the western margin of the Eastern Goldfields of the Yilgarn Craton, is hosted within a mafic intrusion interpreted as a sill complex. U-Pb dating of apatite from the sill yielded a crystallisation age of 2336 ± 64 Ma, inferring an association of sill emplacement and Ni mineralisation related to emplacement of the c. 2400 Ma Widgiemooltha dike swarm. The sill is typically differentiated into a lower olivine orthocumulate layer overlain by a dolerite unit containing xenoliths of partially assimilated granitoids in its upper portion. The latter is interpreted to be the result of stoping and melting of the granitic hanging wall, thereby creating a gravitationally stable buoyant melt layer beneath the top contact. Ni-Cu-Fe sulfides are increasingly abundant towards the base of the sill, ranging from globular disseminated sulfides to net-textured and massive sulfides at the basal contact. The presence and orientation of sulfide globule-bubble pairs indicates a primary near-horizontal orientation. Massive sulfides commonly exhibit a loop texture with pyrrhotite grains surrounded by pentlandite and chalcopyrite. Despite the variety of sulfide textures, sulfur isotopes have a homogeneous mantle-like signature without significant mass independent fractionation. Mineral chemistries that indicate sulfide prospectivity in larger intrusions do not work as effectively in this small sill, therefore new indicators may need to be developed to explore for similar deposits. To date, there are no other known magmatic deposits of this age in Australia. Sills of this age may be more prospective than previously recognised.

Mineralogy and sulfur isotopic compositions of sulfides from Yunzang (25.3°S) hydrothermal field, South Mid-Atlantic Ridge: Implications for formation mechanism and maturation of sulfide chimneys

A newly discovered hydrothermal field, named Yunzang and predominantly hosted by mafic rocks, was recently identified at 25.3°S on the South Mid-Atlantic Ridge (SMAR). This is the first report on the sulfide mineralogy and sulfur isotopic composition of sulfide chimney and massive sulfide ores collected from Yunzang field, SMAR. Based on mineralogical morphology, texture, crystallinity, assemblage and zonation, five specific stages of mineralization can be divided for the sulfide chimney at Yunzang. These stages range from low- to high-temperature hydrothermal conditions, along with an additional stage of seafloor weathering. The observed variations in morphology and crystallinity from low- and medium-temperature stages to high- and high- to medium-temperature stages suggest an evolution in the ore-forming conditions. Initially, the environment was characterized by instability and low-temperature conditions, with significant seawater influx. Subsequently, there was a shift towards a more stable regime dominated by high-temperature ore-forming fluid condition. The positive δ34S values of all the sulfides from Yunzang hydrothermal field suggest 79–92 % and 69–79 % of sulfur were generated from the leaching of basalt for sulfide chimney and massive sulfide, respectively, the rest sulfur were from reduced seawater sulfate. The δ34S values of massive sulfide (3.5–6.8 ‰, average = 5.1 ± 0.9 ‰) are mostly higher than that of sulfide chimney (1.1–4.5 ‰, average = 2.8 ± 0.8 ‰) are mainly caused by sub-surface reactions between preexisting sulfate and re-circulating fluid. An incremental increase of δ34S values from the external edge to the interior orifice indicating the Yunzang chimney maturation is relatively lower and the duration of hydrothermal activity was short. These results enrich our comprehension of mineralization in the seafloor hydrothermal system.

Geochronology and metallogenic mechanism of the Ashele copper–zinc deposit in the Altay, Xinjiang, Northwest China: Insights from pyrite Re–Os dating, trace elements and sulfur isotopes

The Ashele Cu–Zn deposit is the largest volcanogenic massive sulfide (VMS) type deposit in the Xinjiang Central Asian Orogenic Belt (XCAOB). This deposit is located in the Devonian volcanic–sedimentary basin on the South Altay, Xinjiang. The Nos. I and II mineralized belts are the largest in the ore district consist of two parts: concordant massive sulfide lenses and discordant vein-type sulfide mineralization. This study mainly focuses on the mineralization during the submarine exhalative–sedimentary period. In situ trace element analysis showed that sphalerite is an important host for In and Cd, and tennantite is the main host for Au, Ag, As, Cd, Sb, Zn, Bi, and Se in base metal sulfides system. The concentration fluctuation of Bi and Se may be caused by galena. Pyrite and chalcopyrite are not enriched with specific elements, except for occasional inclusions of other minerals. Seven stratified pyrite samples display a Re–Os weighted average age of 389.1 ± 9.9 Ma (MSWD = 0.15). This data can represent the formation time of the No. I mineralized belt. The geothermometer of sulfur isotope shows sulfide mainly formed at 113 to 362 °C (avg. 214 °C), and sphalerite formed at 133 to 194 °C (avg. 175 °C) based on GGIMFis geothermometer. The δ34S values are between −1.84 to 5.51 ‰, suggestting sulfur mainly comes from magmatic sulfur, followed by seawater sulfate.