Massive Sulfide Mineralization Research Articles

Trace Element and Sulfur Isotope Signatures of Volcanogenic Massive Sulfide (VMS) Mineralization: A Case Study from the Sunnhordland Area in SW Norway

The Sunnhordland area in SW Norway hosts more than 100 known mineral occurrences, mostly of volcanogenic massive sulfide (VMS) and orogeny Au types. The VMS mineralization is hosted by plutonic, volcanic and sedimentary lithologies of the Lower Ordovician ophiolitic complexes. This study presents new trace element and δ34S data from VMS deposits hosted by gabbro and basalt of the Lykling Ophiolite Complex and organic-rich sediments of the Langevåg Group. The Alsvågen gabbro-hosted VMS mineralization exhibits a significant Cu content (1.2 to >10 wt.%), with chalcopyrite and cubanite being the main Cu-bearing minerals. The enrichment of pyrite in Co, Se, and Te and the high Se/As and Se/Tl ratios indicate elevated formation temperatures, while the high Se/S ratio indicates a contribution of magmatic volatiles. The δ34S values of the sulfide phases also support a substantial influx of magmatic sulfur. Chalcopyrite from the Alsvågen VMS mineralization shows significant enrichment in Se, Ag, Zn, Cd and In, while pyrrhotite concentrates Ni and Co. The Lindøya basalt-hosted VMS mineralization consists mainly of pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V, and Tl. The δ34S values of sulfides and the Se/S ratio in pyrite suggest that sulfur was predominantly sourced from the host basalt. The Litlabø sediment-hosted VMS mineralization is also dominated by pyrite and pyrrhotite. Pyrite is enriched in As, Mn, Pb, Sb, V and Tl. The δ34S values, which range from −19.7 to −15.7 ‰ VCDT, point to the bacterial reduction of marine sulfate as the main source of sulfur. Trace element characteristics of pyrite, especially the Tl, Sb, Se, As, Co and Ni concentrations, together with their mutual ratios, provide a solid basis for distinguishing gabbro-hosted VMS mineralization from basalt- and sediment-hosted types of VMS mineralization in the study area. The distinctive trace element features of pyrite, in conjunction with its sulfur isotope signature, have been identified as a robust tool for the discrimination of gabbro-, basalt- and sediment-hosted VMS mineralization.

Magmatic evolution of the Kolumbo submarine volcano and its implication to seafloor massive sulfide formation

Seafloor massive sulfides form in various marine hydrothermal settings, particularly within volcanic arcs, where magmatic fluids may contribute to the metal budget of the hydrothermal system. In this study, we focus on the Kolumbo volcano, a submarine volcanic edifice in the central Hellenic Volcanic Arc hosting an active hydrothermal system. Diffuse sulfate-sulfide chimneys form a Zn-Pb massive sulfide mineralization with elevated As, Ag, Au, Hg, Sb, and Tl contents. These elements have similar behavior during magmatic degassing and are common in arc-related hydrothermal systems. Trace-element data of igneous magnetite, combined with whole rock geochemistry and numerical modelling, highlights the behavior of chalcophile and siderophile elements during magmatic differentiation. We report that, despite early magmatic sulfide saturation, chalcophile element contents in the magma do not decrease until water saturation and degassing has occurred. The conservation of chalcophile elements in the magma during magmatic differentiation suggests that most of the magmatic sulfides do not fractionate. By contrast, upon degassing, As, Ag, Au, Cu, Hg, Sb, Sn, Pb, and Zn become depleted in the magma, likely partitioning into the volatile phase, either from the melt or during sulfide oxidation by volatiles. After degassing, the residual chalcophile elements in the melt are incorporated into magnetite. Trace-element data of magnetite enables identifying sulfide saturation during magmatic differentiation and discrimination between pre- and post-degassing magnetite. Our study highlights how magmatic degassing contributes to the metal budget in magmatic-hydrothermal systems that form seafloor massive sulfides and shows that igneous magnetite geochemistry is a powerful tool for tracking metal-mobilizing processes during magmatic differentiation.

Geology and Lithogeochemistry of the Paleoproterozoic Flambeau Cu-Zn-Au Volcanogenic Massive Sulfide Deposit, Wisconsin, USA

Abstract The Paleoproterozoic Flambeau Cu-Zn-Au deposit in northwestern Wisconsin is the only volcanogenic massive sulfide (VMS) deposit to reach production in the Pembine-Wausau terrane of the Penokean orogen, despite the discovery of more than 150 million tonnes of mineralization within 14 deposits since the 1970s. Renewed exploration interest in the region and need for critical minerals has highlighted the importance of the VMS deposits in the region and the need for an improved understanding of their geologic setting. This study examined and sampled 50 drill cores from the Flambeau deposit stored at the Wisconsin state core repository to determine the volcanic, hydrothermal, and tectonic setting of the deposit. The least altered units at the deposit are metadacite and quartz-augen schists that are interpreted to be rapidly emplaced felsic to intermediate crystal-rich tuffs and lapilli tuffs. There are also chlorite ± garnet schists that are interpreted to be mafic sills and/or small flows. The main altered unit is biotite ± andalusite ± white-mica schist that contains porphyroblasts of biotite and/or andalusite that replace the intermediate volcaniclastic units. The ore horizon contains massive sulfide, metachert, and semimassive mineralization within a quartz–white-mica schist. Stratigraphic relationships and chemostratigraphy structurally above and below the ore horizon indicate that the strata are overturned. Despite structural and metamorphic destruction of microtextural evidence, evidence for lateral mineralizing fluid flow in rapidly emplaced, permeable volcanic units, interlayered impermeable to semipermeable units, and macrotextural evidence for lit-par-lit replacement of tuffaceous layers indicate that the Flambeau ores are replacement-style mineralization. Trace element systematics reveal that mafic rock and intermediate rocks are calc-alkalic with low Ti/V values, characteristic of arc environments. Felsic rocks are calc-alkalic, depleted high field strength element (HFSE), FI- to FII-type rhyolites that are also consistent with an arc environment. These lithogeochemical characteristics are similar to those of modern mature oceanic-arc settings. This setting contrasts with other host rocks at nearby deposits (e.g., Lynne, Back Forty) that have petrogenetic evidence for the presence of older Archean basement (i.e., continental crust). Therefore, the geology of the Flambeau deposit highlights the variability of VMS-forming environments within the Penokean orogen and has important local and regional implications for other VMS deposits globally.

Nature and Origin of a Massive Sulfide Occurrence in the Karrat Group: Evidence for Paleoproterozoic VMS Mineralization in Central West Greenland

Abstract Mafic volcanic rocks of the Kangilleq Formation of the Paleoproterozoic Karrat Group host volcanogenic massive sulfide (VMS) mineralization in the area of central Kangiusap Kuua, central West Greenland. The mafic volcanic rocks display evidence of subaqueous, effusive eruption and redeposition by mass debris flows generated along fault scarps on the sea floor. A zone of semiconformable quartz alteration and disconformable chlorite alteration within hydrothermal breccias and mafic tuff breccias near the top of the volcanic sequence is interpreted to reflect a synvolcanic hydrothermal system. Conformable, massive to semimassive, and discordant, stringer-style sulfide mineralization is hosted within the quartz- and chlorite-altered volcanic rocks. The massive to semimassive sulfide mineralization is ~10 m thick and crops out along strike for ~2,000 m. The stringer zone is ≤10 m thick with individual sulfide stringers ranging in width from 5 to 90 cm. All sulfide zones are dominated by coarse pyrrhotite and pyrite, with trace amounts of sphalerite and chalcopyrite. The pillow lavas are subalkaline with geochemical characteristics typical of modern transitional to tholeiitic mid-ocean ridge or back-arc basin basalt. Trace element and Nd isotope data suggest that these lavas erupted in an epicratonic, back-arc basin. Characteristics of the host rocks indicate a period of localized rifting, volcanism, and VMS formation during genesis of the Karrat Group, which is dominated by siliciclastic rocks.

Two new bamboo corals species (Octocorallia: Keratoisididae) from the seamounts of slow-spreading Central Indian Ridge

Bamboo corals are a subclass of cnidarian anthozoans in the family Keratoisididae Gray, 1870. Most of the bamboo coral species are known from the Pacific and Atlantic Oceans. This study reports on two new species of bamboo corals (Dokidisis krishanani sp. Nov. and Adinisis oblonga sp. Nov.) from the Central Indian Ridge (CIR) system seamounts, using morphological and genetic (MutS) data to compare with existing species. They are distributed globally in shallow and deep waters, and having complex body structure. It is part of a baseline environmental and benthic biological evaluation. All the data will help identify the long-term effects of massive sulphide mining in the Indian Ocean. The two novel species were used to collect information on distinguishing morphological characteristics that vary significantly from the sibling species. Considering the recently published literature, the discovery of new biological species, and sampling efforts, we hypothesise that many more octocoral species are yet to be discovered, particularly in the seamount of CIR and SWIR regions.

Random forest classification for volcanogenic massive sulfide mineralization in the Rouyn-Noranda Area, Quebec

Random forest (RF) classification was applied to 37 predictor maps (vectors to mineralization) producing a Mineral Prospectivity Map (MPM) for volcanogenic massive sulfide (VMS) mineralization in the Noranda District, Abitibi subprovince, which is host to ∼ 20 VMS deposits and numerous subeconomic occurrences. The predictor maps were created using geological, geochemical, and geophysical data, and the known VMS deposits were used to train the RF classifier. The RF model was applied on two regions of interest (ROI) to investigate the effect of different sized ROIs on the results. Five sets of balanced and unbalanced training data were used in the experiments to examine the sensitivity of RF to different sets of training data. The probability/prospectivity maps showed very high success rate of classification with regard to training data particularly for the training sets with higher ratio of non-deposits/deposits. Accuracy assessment of classification maps using cross-validation also showed very high accuracy when assessed by the training data in all experiments again giving a higher accuracy for the training sets with higher ratios of non-deposits/deposits, however the later showed very low accuracy when applying k-fold cross-validation or when assessed by 15 VMS showings used as the test data indicating an overfitting problem with the unbalanced data. In most of the experiments, principal component 4 (PC4) of geochemical analysis, proximity to synvolcanic tonalite-trondhjemite-granodiorite (TTG) intrusions, lithology, and sericite alteration maps showed higher predictive power. The importance of individual variables changed when the ROI was changed to a smaller area suggesting that RF is sensitive to the study area.

Quaternary Seabed Sediment Characteristics as an indication of VMS-mineral deposits at the South Banda Basin and its surroundings, Indonesia

The South Banda back-arc basin is a morphotectonic environment that is part of the South Banda Basin, characterized by a flat morphology with depths ranging from 5000m to 6000m. The purpose of this paper is to analyze and relate morphometric aspects to the Quaternary seabed sediment deposits deposited in an active tectonic basin in the Banda Sea area, including information on the type of sediment and its distribution as well as its relation to volcanic hosted-massive sulfide (VHMS) or volcanogenic massive sulfide (VMS) mineral deposits. The seabed lithofacies in the Banda Arc area were deposited in several morphotectonic environments. The types of deposits that are deposited are pelagic, and hemipelagic deposits including turbidite and volcanic origin deposits. Volcanic deposits consist of gravel, sand, muddy sand, and silt which are classified very poorly to moderately well sorted. The grain composition is volcanic lithic, feldspar, augite, hypersthene, and enstatite which are commonly found in volcanic arcs and troughs. Groups of volcanic grains composed of pyroxene andesite, pumice, and tuffite or siliceous gravel, distributed in the northern and the middle of the volcanic arc area are interpreted to originate from the Banda volcanic complex and the Seram-Gorong islands.

Ultramafic-Hosted Ni-Cu-Co-(As) Mineralization from an Ancient Oceanic Transform Fault Zone in the Troodos Ophiolite, Cyprus: An Analogue for Ultramafic Sea-Floor Massive Sulfide Mineralization?

Abstract Accumulations of sulfide minerals that are enriched in Ni-Cu-Co-(As) occur as sea-floor massive sulfide (SMS) deposits associated with ultramafic rock types on the sea floor and in ophiolite terranes as Outokumpu-type mineralization. In this study we focus on similar mineralization at Lakxia tou Mavrou in the Limassol Forest Complex of Cyprus, which represents the on-land exposure of an oceanic transform fault zone preserved within the Troodos ophiolite. Mineralization here consists of massive lenses of pyrrhotite associated with veins of isocubanite, chalcopyrite, Co pentlandite, and chrome spinel hosted in serpentinized mantle peridotite. We reexamine the field context of mineral occurrences and use in situ mineral chemistry, element mapping, and sulfur isotope ratios (δ34S) to constrain metal sources and provide an updated paragenetic model for Lakxia tou Mavrou. Highly variable S/Se ratios (304–108,571), a depletion in platinum group elements relative to mantle values, and an average δ34S value of –3.7 ± 2.4‰ (1σ, n = 17) in sulfide minerals support a hybrid hydrothermal and magmatic origin for the mineralization. Metals at Lakxia tou Mavrou were sourced from both the serpentinization of peridotites and from crosscutting intrusions, with later intrusions into the already serpentinized mantle lithosphere host providing a heat source to drive prolonged hydrothermal circulation. The reexamination of the field context of mineralization shows that the Ni-Cu-Co-(As) mineralization at Lakxia tou Mavrou originally formed because of the fault-guided intrusion of hot primitive magma bodies into serpentinized shallow mantle lithosphere in the active domain of an ocean-floor transform fault zone. The mineralization was subsequently partially disrupted by structures related to emplacement of the Troodos ophiolite. We show that the relationship between serpentinization, magmatism, and hydrothermal circulation at Lakxia tou Mavrou can be used to understand the formation of ultramafic-hosted SMS deposits in transform fault and other ultramaficdominated slow- and ultraslow-spreading mid-ocean ridge settings.

A new deep-water coral species Telestula ridgensis sp. nov (Scleralcyonacea: Sarcodictyonidae) from the seamount of the Central Indian Ridge.

Telestula ridgensis sp. nov. is a deep-sea octocoral species collected from the Central Indian Ridges (CIR) seamount. The megabenthic communities were sampled from the depths between 1917 and 2053 m using a benthic sledge. It forms part of a baseline environmental and benthic ecological assessment. All these data will be functional in assessing the impact of future massive sulfide mining in the Indian Ocean. We describe a new octocoral species based on integrative taxonomic methods through morphological comparison and molecular phylogenetics. The sclerome of the new species consists of short, stellate plates, crosses, and irregularly shaped and branching forms with dense tubercular ornamentation. The polyp sclerites are arranged in longitudinal rows underneath the tentacles. Two mitochondrial DNA genes (mtMutS and COI) and one ribosomal nuclear DNA gene (28S rRNA) were sequenced to separate the new species. The phylogenetic analyses strongly support the placement of new species in the genus Telestula clade.

Seismic Imaging of Mineral Exploration Targets: Evaluation of Ray- vs. Wave-Equation-Based Pre-Stack Depth Migrations for Crooked 2D Profiles

Seismic imaging is now a well-established method in mineral exploration with many successful case studies. Seismic data are usually imaged in the time domain (post-stack or pre-stack time migration), but recently pre-stack depth imaging has shown clear advantages for irregular/sparse acquisitions and very complex targets. Here, we evaluate the effectiveness of both ray-based and wave-equation-based pre-stack depth imaging methodologies applied to crooked-line 2D seismic reflection profiles. Seismic data were acquired in the Kylylahti mining area in eastern Finland over severely folded, faulted and subvertical Kylylahti structure, and associated mineralization. We performed 3D ray-based imaging, i.e., industry-standard Kirchhoff migration and its improved version (coherency migration, CM), and wave-equation-based migration, i.e., reverse time migration (RTM) using a velocity model built from first-arrival traveltime tomography. Upon comparing the three different migrations against available geological data and models, it appeared that CM provided the least noisy and well-focused image, but failed to image the internal reflectivity of the Kylylahti formation. RTM was the only method that produced geologically plausible reflections inside the Kylylahti formation including a direct image of the previously known shallow massive sulfide mineralization.

Impacts of the first deep-sea seafloor massive sulfide mining excavation tests on benthic communities

Japan undertook the first ever tests of deep-sea seafloor massive sulfide (SMS) excavation in 2017 in the Okinawa Trough. This study examines infauna from several nearby stations before and up to 3 yr after disturbance. Distance from excavation, current direction, seafloor topography, and modeled and observed deposition were used to classify the level of impact of each station. Metal concentrations were analyzed, as were nanofauna (2-32 µm), meiofauna (32-300 µm), and macrofauna (>300 µm). Elevated Cd, Pb, Hg, Zn, Fe, and Cu were confirmed as indicators of sedimentation from the SMS extraction. Benthic communities appeared altered by the disturbance test, with different size classes showing different levels of response and recovery. Nanofaunal and meiofaunal abundances appeared to take several weeks to show impacts from the disturbance and may have returned to pre-test levels within 1 yr, but changes to nematode community structure persisted longer. In contrast, macrofaunal abundances and diversity appeared to decrease immediately, and possibly remained depressed compared to pre-test levels at impacted sites at least 3 yr later. In addition, meiofaunal nematode:copepod ratio and macrofaunal percent composition of polychaetes, along with several nematode taxa, may serve as useful bioindicators of SMS mining. The small scale of disturbance requires caution when extrapolating to full-scale mining, but these results suggest current direction and topography greatly influence the extent of mining impacts; in addition, several metals may be useful for identifying the mining footprint. Biological results indicate that larger macroinfauna may be less resistant and resilient to mining impacts than smaller meiofauna and impacts from even small-scale mining activities may persist for at least 3 yr.

Geologic setting of the Pueblo Viejo Au–Ag–Cu-(Zn) mining district, Dominican Republic - Links to volcanic domes and volcanogenic massive sulfide mineralization

Geologic mapping at the Pueblo Viejo Au–Ag–Cu-(Zn) mine, Dominican Republic, and across the surrounding Pueblo Viejo district, reveals the geologic setting at the time of mineralization. Ore deposits consisting of disseminated sulfide, bedded massive sulfide, and high-grade massive sulfide veins formed (∼112 Ma) in a volcanic dome field during a period of extension across an emergent, intraoceanic island arc. Geologic maps reveal the links between volcanic domes and structure, hydrothermal alteration and mineralization, and ore deposits and gossans. Whole-rock geochemical data establish a tholeiitic signature for Early Cretaceous magmatism including the volcanic dome field. Northerly-striking, high-angle faults controlled the emplacement of volcanic domes and served as feeders for hydrothermal solutions. The largest ore deposits formed in a subsiding, marginal marine, volcano-sedimentary basin. Stacked intervals of bedded massive sulfide mineralization indicate that the basin was subsiding while mineralization was underway. Calc-alkaline dikes and plutons in the Pueblo Viejo district intruded at ∼88 Ma, well after mineralization had ended. Low-angle reverse faulting, greenschist facies metamorphism, and milky quartz veining and replacement were also Late Cretaceous (post-mineral) events. Ore deposits in the Pueblo Viejo district are best described as hybrid epithermal – VMS deposits, formed during a period of Early Cretaceous extension, tholeiitic volcanism, and volcanic dome emplacement in a shallow, marginal marine environment. Exploration for Au–Ag–Cu-(Zn) deposits like Pueblo Viejo should focus on intraoceanic island arcs, tholeiitic volcanic dome fields, extensional volcano-sedimentary basins, and VMS mineral occurrences.

Bi-Ag-Sulfosalts and Sulfoarsenides in the Ruwai Zn-Pb-Ag Skarn Deposit, Central Borneo, Indonesia

The Ruwai skarn deposit is located in the Schwaner Mountain complex within the central Borneo gold belt and is currently considered the largest Zn skarn deposit in Indonesia. The deposit has been known to host Zn-Pb-Ag mineralization in the form of massive sulfide ore bodies; however, the occurrence of Ag-bearing minerals has not been identified yet. This study documents the mineralogical characteristics of several Bi-Ag sulfosalts and sulfoarsenides, as well as their chemical compositions. Ten Bi-Ag sulfosalts were identified, including native bismuth, tetrahedrite, cossalite, tsumoite, bismuthinite, joseite-B, Bi6Te2S, Bi-Pb-Te-S, Bi-Ag-S, and Bi-Te-Ag. Three sulfoarsenides were identified, including arsenopyrite, glaucodot, and alloclasite. The occurrence of Bi-Ag sulfosalts is typically associated with massive sulfide mineralization, although tsumoite can also be found associated with massive magnetite. In terms of sulfoarsenides, both arsenopyrite and glaucodot are associated with massive sulfide mineralization, whereas alloclasite is associated with massive magnetite mineralization. The Bi-bearing minerals are characterized by irregular, bleb-like texture or patch morphology, and occur either as free grains or inclusions within sulfides, such as galena or pyrite. Tetrahedrite typically has an anhedral shape with a rim or atoll texture surrounding sphalerite or galena. In contrast, sulfoarsenides are typically found as euhedral–subhedral grains where glaucodot typically is rimmed by arsenopyrite. Both Bi-Ag sulfosalt and sulfoarsenides were formed during the retrograde stage under high oxidation and a low sulfidation state condition. The ore-forming temperature based on arsenopyrite geothermometry ranges from 428 °C to 493 °C.

New insights into the petrogenesis of rhyolites and evolution of volcanic‐hosted massive sulphide mineralization from shallow borehole core, Betul Belt, Central India

Shallow borehole drilling has been conducted at the Sarni area of Betul Belt, Central India to understand the subsurface geology and nature of mineralization. The predominant lithounits are ferruginous quartzites, felsic volcanic rocks, and with minor intrusions of amphibolites. The encountered felsic volcanic rocks are rhyolites varying from pink (rich in K‐feldspar) to grey (rich in Na‐feldspar and amphiboles). The rhyolitic rocks have undergone intense hydrothermal alteration. The alteration zones are defined by the presence of biotite‐chlorite‐garnet‐gahnite; biotite‐sericite‐chlorite‐anthophyllite and anthophyllite‐actinolite‐tremolite‐carbonate mineral assemblages. Sulphide pits, highly leached zones with occasional bluish tinges, limonitic patches are present in the felsic volcanic rocks, followed by semi‐massive to disseminated sulphide mineralization indicative of Kuroku‐ type Zn–Cu–Pb volcanic‐hosted Massive Sulphide (VHMS) mineralization. Scanning electron microscope and energy‐dispersive x‐ray spectroscopy studies documented sphalerite, pyrite, chalcophyrite, arsenopyrite, pyrrhotite, and minor Au–Ag phases. The Sarni rhyolites exhibit chalcopyrite disease in sphalerite, replacement, and overgrowth ore‐textures. The high HFSE, low Zr/Y ratio, pronounced negative Eu anomalies characterize the felsic volcanic rocks as FIIIb type with high zircon saturation temperatures of 856–931°C. These rhyolites are formed at a back‐arc rift setting in an ensialic island‐arc tectonic regime. The synvolcanic structures facilitated the magma ascent to the surface. The hydrothermal circulation due to adequate heat flow in the back‐arc rift environment, in an episodic multicyclic process provided sufficient time for accumulation of sulphides from the seafloor, which was later deposited to form a VHMS mineralization. We also report tungsten (W) mineralization in the quartz veins of these felsic volcanic rocks. It is suggested that the felsic magma has interacted with metasedimentary sequences and assimilated W‐ore bearing fluids, and during remobilization in the later stages of tectonic activity enabled the deposition of tungsten in these quartz veins.

A tale of elemental accumulation and recycling in the metamorphosed Keketale VMS-type Pb-Zn deposit, Altai Mountains

The elemental accumulation and recycling in the metamorphosed Keketale VMS-type Pb-Zn deposit of the Altai Mountains are presented in this study. Based on detailed fieldwork and microscopic observation, the formation of the deposit involved syngenetic massive sulfide mineralization and epigenetic superimposed mineralization. Different generations of iron sulfides (i.e., pyrite and pyrrhotite) with contrasting textural, elemental, and sulfur isotopic features were generated in primary mineralization (including hydrothermal iron sulfides, colloform pyrite) and secondary modification (including annealed iron sulfides, oriented iron sulfides, and vein-pyrite). It is revealed that the spatial variation in textures and elements of hydrothermal iron sulfides depends on the inhomogeneous fluid compositions and varied environment in VMS hydrothermal system. Both leached sulfur from the footwall volcanic rocks and reduced sulfur by the TSR process are regarded as important sulfur sources. Furthermore, large sulfur isotopic fractionation and negative δ34S values were mainly caused by varied oxygen fugacity, and to a lesser extent, temperature fluctuation. The epigenetic polymetallic veins that contain sulfides and sulfosalts (e.g., jordanite-geocronite, bournonite-seligmannite, boulangerite) were considered as the products of metamorphic fluid scavenged the metal-rich strata. All things considered, it is indicated that two episodes of fluid with distinct origins were essential for the formation of the deposit. The predominant evolved seawater along with subordinate magmatic fluid mobilized metals from volcanic rocks and precipitated massive sulfides near the seafloor are vital for primary mineralization. The metamorphic fluid remobilized metals (i.e., FMEs: fluid mobile elements, e.g., Pb, As, Sb) from neighboring volcanic and pyroclastic rocks and destabilized them within the fractured zone are responsible for secondary mineralization, which enhances the economic value of the deposit. Accordingly, metal-rich Devonian strata had been successively swept by different origins of fluid, leading to progressively elemental enrichment and the formation of a large deposit. Furthermore, the current study enlightens that FME-bearing veins with economic benefits can be discovered near the metamorphosed VMS deposits.

Perspectives on exploration and extraction of seafloor massive sulfide deposits in Norwegian waters

Abstract We present a stochastic dynamic simulation model for exploration and extraction of seafloor massive sulfide (SMS) mineral deposits on the Norwegian Continental Shelf (NCS). The model is developed based on selected industry knowledge, expectations, and perceptions elicited through a participatory systems mapping session with 82 participants and 20 in-depth interviews with experts from industry, academia, and the public policy sector. Using the model, we simulate the expected ranges of resource- and economic potential. The simulation results indicate an expected commercial resource base of 1.8 to 3 million tons of copper, zinc, and cobalt, in which copper makes out the most significant part. Relating to the expected commercial resource base, we highlight a discrepancy between academic and industrial expectations, in which the academic expectations are more conservative than the industrial expectations. The corresponding net present values lie in the range of a net present loss of 970 million USD up to a net present gain of 2.53 billion USD, in which the academic expectations are projected to yield a negative net present value, while the industrial expectations are projected to yield a positive net present value. Closer investigation of the results reveals that one of the main challenges regarding SMS exploration and extraction is the initial exploration costs associated with coring operations. These costs are expected to be high with today’s exploration technology. Moreover, they occur relatively early in time compared to revenue-generating activity, which has a significant negative impact on the net present value of the industry due to discounting. Thus, a key focus of the industry should be to find ways to reduce the costs associated with coring operations and/or the time it takes from initial exploration to extraction and generation of revenue.

S and Pb isotope characteristics and fluid inclusions of the metamorphic rock hosted massive sulfide mineralization at the village of Başçatak (Yozgat province, Turkey) in the Central Anatolian Crystalline Complex

S and Pb isotope characteristics and fluid inclusions of the metamorphic rock hosted massive sulfide mineralization at the village of Başçatak (Yozgat province, Turkey) in the Central Anatolian Crystalline Complex

Ultramafic-hosted volcanogenic massive sulfide deposits from Cuban ophiolites

Ultramafic-hosted volcanogenic massive sulfide deposits (UM-VMS) located in the Havana-Matanzas ophiolite (Cuba) are the only known example of this type of mineralization in the Caribbean realm. UM-VMS from Havana-Matanzas are enriched in Cu, Ni, Co, Au, and Ag. The mineralization consists of massive sulfide bodies mostly composed of pyrrhotite and hosted by serpentinized upper mantle peridotites. Chemical composition of unaltered cores in Cr-spinel grains found within the massive sulfide mineralization and in the peridotite host indicates formation in the fore-arc region of the Greater Antilles volcanic arc. A first stage of serpentinization probably took place prior to the sulfide mineralization event. The UM-VMS mineralization formed by the near-complete replacement of the silicate assemblage of partially serpentinized peridotites underneath the seafloor. The sequence of sulfide mineralization has been divided into two stages. The first stage is characterized by a very reduced hydrothermal mineral assemblage consisting of pyrrhotite, Co–Ni–Fe diarsenides, chalcopyrite, Co-rich pentlandite, and electrum. In the second stage, pyrite and Co–Ni–Fe sulfarsenides partially replaced pyrrhotite and diarsenides, respectively, under a more oxidizing regime during the advanced stages of ongoing serpentinization. The proposed conceptual genetic model presented here can be useful for future exploration targeting this type of deposit in the Caribbean region and elsewhere.

High-Precision CA-ID-TIMS U-Pb Zircon Geochronology of Felsic Rocks in the Finlayson Lake VMS District, Yukon: Linking Paleozoic Basin-Scale Accumulation Rates to the Occurrence of Subseafloor Replacement-Style Mineralization

Abstract Felsic igneous complexes and associated volcano-sedimentary rocks in continental back-arc environments host large-tonnage and/or high-grade volcanogenic massive sulfide (VMS) deposits. The emplacement mechanisms, style, and preservation of these deposits is thought to be partially dependent on depositional rates of the host lithofacies (i.e., discrete volcanic eruptions) relative to the setting of massive sulfide genesis on the seafloor as mounds and/or via subseafloor replacement of existing strata. The localization and occurrence of subseafloor replacement-style VMS deposits is therefore strongly influenced by the characteristics of the volcano-sedimentary facies in the hosting basin and the rates of their emplacement; the latter are poorly constrained in the literature due to the difficulty of obtaining high-precision dates that make this possible in Phanerozoic and older rocks. New high-resolution U-Pb geochronology and detailed regional stratigraphic investigation indicate that Devonian-Mississippian volcanic rocks and associated VMS mineralization in the Yukon-Tanana terrane in the Finlayson Lake district, Yukon, Canada, were erupted or emplaced during distinct time periods (ca. 363.3, 362.8, and 355.2 Ma) in two discrete submarine basins: the Kudz Ze Kayah formation and the Wolverine Lake group. The VMS deposits in both settings are contained within intrabasinal rocks that accumulated at rapid rates of ~350 to 2,000 m/m.y. over 0.6 to 1.4 m.y. Locally, these rates reach peak rates up to 7,500 m/m.y. in the Wolverine Lake group, which are interpreted to reflect facies deposition by mass transport complexes or turbidity currents. These new dates indicate that rapid accumulation of volcanic rocks in the back-arc basins was critical for localizing subseafloor replacement-style mineralization and the development of the Zn-enriched GP4F, Kudz Ze Kayah, and Wolverine VMS deposits. Rapid depositional processes observed in these deposits and their host basins are interpreted to have an important role in developing highly porous and permeable, water-saturated lithofacies that provide optimal conditions for enhancing zone refining processes and subsequent preservation of massive sulfide mineralization, which are key in the development of high-grade and large-tonnage VMS deposits. It is herein suggested that quantitative basin-scale accumulation rates, as a result of new U-Pb geochronological methods and increased precision combined with detailed stratigraphic and facies analysis, may provide important perspectives on the formation of continental back-arc basins and the localization of VMS deposits in other continental margin environments globally.

Geology, Geochemistry, and Geochronology of the Giant Rio Tinto VMS Deposit, Iberian Pyrite Belt, Spain

Abstract The Rio Tinto deposit is a giant volcanogenic massive sulfide deposit (VMS) that contains more than 500 Mt of pyrite-rich massive sulfides and more than 2 Gt of mineralized stockwork. Three broad lithostratigraphic groups occur in the regional stratigraphy: the phyllite-quartzite group, the volcano-sedimentary complex, and the Baixo Alentejo Flysch Group. These three major packages reflect the evolution of a depositional environment from a stable platform to deposition in pull-apart continental basins during oblique subduction and collision and coeval synorogenic flysch sequence. The volcano-sedimentary complex, which hosts massive sulfide mineralization at Rio Tinto, can be divided into four major units: (1) the Mafic Siliciclastic Unit, (2) the Lower Sedimentary Unit, (3) the Felsic Unit, and (4) the Upper Sedimentary Unit. The Felsic Unit is further subdivided based on new U-Pb zircon geochronology into three distinct subunits. Felsic Unit I (ca. 356 Ma) includes dome complexes dominated by rhyodacite and reflects the onset of felsic magmatism in the region. Felsic Unit II (ca. 352–348 Ma) represents the main interval of volcanic activity, also dominated by rhyodacite domes and related aprons, and is associated with widespread VMS mineralization. Felsic Unit III (ca. 340 Ma) reflects a late pulse of rhyolitic volcanism. Massive sulfides occur as two different styles of mineralization: (1) replacive ores as discordant pipes hosted by glass-rich felsic rocks and enclosed by a large zone of stockwork-like mineralization and (2) overlying shale-hosted exhalative mineralization in small anoxic basins, probably formed during the collapse of the volcanic domes of Felsic Unit II in the Middle-Late Tournaisian. New lithogeochemical data illustrate two types of mafic rocks in the Mafic Siliciclastic Unit: a basaltic andesite and a high–Ti-Zr basalt, both of tholeiitic affinity. Using immobile element ratios (heavy rare earth elements [HREEs], Al, Y, Zr, and Ti) of the Felsic Unit, fundamental differences have been recognized between the subunits. The unmineralized Felsic Unit I is characterized by high Zr content (225–300 ppm) and a pronounced Eu negative anomaly, and probably represents the most fractionated rocks. Felsic Unit II is characterized by Zr values between 50 and 200 ppm. The low Zr values of the mineralized unit contrast with the typically high Zr values of the felsic rocks related to volcanogenic massive sulfides elsewhere and, at a regional scale, can help to discriminate potentially fertile domes from barren volcanism.