Massive Sulfide Deposits Research Articles

Magnetite as a provenance and exploration tool for metamorphosed base-metal sulfide deposits in the Stollberg ore field, Bergslagen, Sweden

AbstractMagnetite is a common mineral in the Paleoproterozoic Stollberg Zn–Pb–Ag plus magnetite ore field (~6.6 Mt of production), which occurs in 1.9 Ga metamorphosed felsic and mafic rocks. Mineralisation at Stollberg consists of magnetite bodies and massive to semi-massive sphalerite–galena and pyrrhotite (with subordinate pyrite, chalcopyrite, arsenopyrite and magnetite) hosted by metavolcanic rocks and skarn. Magnetite occurs in sulfides, skarn, amphibolite and altered metamorphosed rhyolitic ash–siltstone that consists of garnet–biotite, quartz–garnet–pyroxene, gedrite–albite, and sericitic rocks. Magnetite probably formed from hydrothermal ore-bearing fluids (~250–400°C) that replaced limestone and rhyolitic ash–siltstone, and subsequently recrystallised during metamorphism. The composition of magnetite from these rock types was measured using electron microprobe analysis and LA–ICP–MS. Utilisation of discrimination plots (Ca+Al+Mn vs. Ti+V, Ni/(Cr+Mn) vs. Ti+V, and trace-element variation diagrams (median concentration of Mg, Al, Ti, V, Co, Mn, Zn and Ga) suggest that the composition of magnetite in sulfides from the Stollberg ore field more closely resembles that from skarns found elsewhere rather than previously published compositions of magnetite in metamorphosed volcanogenic massive sulfide deposits. Although the variation diagrams show that magnetite compositions from various rock types have similar patterns, principal component analyses and element–element variation diagrams indicate that its composition from the same rock type in different sulfide deposits can be distinguished. This suggests that bulk-rock composition also has a strong influence on magnetite composition. Principal component analyses also show that magnetite in sulfides has a distinctive compositional signature which allows it to be a prospective pathfinder mineral for sulfide deposits in the Stollberg ore field.

Sulfide texture and geochemistry of the Neoarchean Hongtoushan Cu-Zn deposit (NE China): Implication for mixed-state metamorphic remobilization

The Hongtoushan Cu-Zn deposit in the Neoarchean Qingyuan greenstone belt of the North China Craton is the oldest volcanogenic massive sulfide (VMS) deposit in China. The ore samples are classified by massive sulfide ores, disseminated sulfide ores, and sulfide-bearing quartz veins. Four types of massive sulfide ores are further identified. Type A massive ore, characterized by the granular quartz and euhedral dark mineral aggregates in the massive sulfides matrix, is interpreted as the result of partial melting of primary sulfides, and type B might record the process of partial melting and mechanical migration. Type C massive ore, formed by the recrystallization of type B massive ore, is characterized by coarse pyrite and pyrrhotite porphyroblasts. Type D massive ore undergoes deformation and upgrades by elements released during recrystallization. The relic anhydrite in type A massive ore is the preserve of the primary mineral from VMS mineralization. Most sulfide in massive ores has δ34S values closing to ∼ 0 ‰, showing magmatic sulfur characteristics. The intergrowth of pyrrhotite and magnetite with higher δ34S (5.5–8.3 ‰) is suggested to be the dissolution product of primary anhydrite. The sulfides from the tourmaline-bearing quartz veins have negative δ34S (-6.0 – −2.6 ‰) values, indicating that the sulfur was released from the desulfurization of massive pyrite. The ore remobilization is dominated by partial melting of sulfide and mechanical migration during the peak metamorphism. The fluid metasomatism is activated at the retrograde metamorphism. This mixed-state metamorphic remobilization plays a key role in the formation of metamorphosed massive sulfide ore and ore upgrading.

Polymetallic nanoparticles in pyrite from massive and stockwork ores of VMS deposits of the Iberian Pyrite Belt

This paper reports the first-ever study on nanoscale mineralogy in pyrite from the volcanogenic massive sulfide (VMS) deposits of the Iberian Pyrite Belt, southwestern Iberian Peninsula. It targeted colloform-textured grains formed at low temperature in the distal part of a polymetallic (Pb-Zn) massive sulfide lens hosted in felsic volcanoclastic rocks from the Masa Valverde deposit, and euhedral-textured grains (re)-deposited by higher temperature fluids in the Co-Au rich stockwork hosted in black shales of the Filón Norte orebody of the Tharsis deposit. The results acquired by a combination of techniques for mineral microanalysis and characterization (i.e., reflected light, FE-SEM, EPMA, LA-ICP-MS, HRTEM-STEM and TEM-EDS) show that trace amounts of metals (Au, Ag, As, Pb, Sb, Cu, Co) are incorporated as both lattice-bound and into nanoparticles (NPs). The mode of occurrence is strongly related with the evolutionary history of the mineralization. In the colloform pyrite collected from the massive sulfide lens, a rhythmic banding/oscillatory zonation with up to 3 wt% As, 5,000 ppm Pb, 1,070 ppm Sb and 750 ppm Cu is defined by the coexistence of several nano-sized layers (5 to 100 nm) and NPs (<100 nm) containing all these metals. The NPs include galena [PbS], tetrahedrite [(Cu,Fe)12Sb4S13)] and arsenopyrite [FeAsS] that exhibit euhedral and less frequently anhedral (i.e., droplet-like) morphologies being both randomly and preferentially oriented with respect to As-rich pyrite bands they are usually associated with. These features suggest formation of the NPs via direct deposition from the hydrothermal fluid(s) or low-temperature melts entrained in them as well as exsolution of trace elements originally dissolved in the As-rich pyrite structure. Additionally, some of these NPs are connected to late fractures disrupting the chemical zoning in colloform pyrite documenting a third genetic type of NPs related to late infiltration of fluids post-dating pyrite formation. In contrast, euhedral pyrite from the stockwork form well-developed homogeneous grains with discrete porous areas relatively depleted in Fe (45.20 wt%), and As (8,800 ppm) but enriched in Co (5,900 ppm). At the nanoscale, Co-enriched domains show patchy zoning defined by irregular distribution of Co– and As-rich bands of 200–500 nm in thickness. These nanometer Co– and As-rich bands are often disrupted by micron-to-nano-sized polycrystalline Au-Ag-Hg particles that fill voids in porous areas. Contact morphology anatomy between Co-rich pyrite and inclusions suggests that the Au-Ag-Hg particles are negative crystals occupying spaces originated in pyrite by coupled dissolution-reprecipitation reaction. Likewise, HRTEM observations along such pyrite-inclusion contacts show the existence of polycrystalline matrices in both pyrite and Au-Ag-Hg inclusions, the former consisting of nano-sized domains of arsenian pyrite and/or arsenopyrite in As-free pyrite and the Au-Ag-Hg inclusions made up of multiple crystal domains including nano-crystallites of Au0/Ag0 or electrum. Recognition of crystalline nanodomains and NPs in these polycrystalline matrices raises the possibility that Au NPs or nanomelts already present in the hydrothermal fluid catalyzed the formation of these heterogeneous crystals.

SANTORY: SANTORini’s Seafloor Volcanic ObservatorY

Submarine hydrothermal systems along active volcanic ridges and arcs are highly dynamic, responding to both oceanographic (e.g., currents, tides) and deep-seated geological forcing (e.g., magma eruption, seismicity, hydrothermalism, and crustal deformation, etc.). In particular, volcanic and hydrothermal activity may also pose profoundly negative societal impacts (tsunamis, the release of climate-relevant gases and toxic metal(loid)s). These risks are particularly significant in shallow (&amp;lt;1000m) coastal environments, as demonstrated by the January 2022 submarine paroxysmal eruption by the Hunga Tonga-Hunga Ha’apai Volcano that destroyed part of the island, and the October 2011 submarine eruption of El Hierro (Canary Islands) that caused vigorous upwelling, floating lava bombs, and natural seawater acidification. Volcanic hazards may be posed by the Kolumbo submarine volcano, which is part of the subduction-related Hellenic Volcanic Arc at the intersection between the Eurasian and African tectonic plates. There, the Kolumbo submarine volcano, 7 km NE of Santorini and part of Santorini’s volcanic complex, hosts an active hydrothermal vent field (HVF) on its crater floor (~500m b.s.l.), which degasses boiling CO2–dominated fluids at high temperatures (~265°C) with a clear mantle signature. Kolumbo’s HVF hosts actively forming seafloor massive sulfide deposits with high contents of potentially toxic, volatile metal(loid)s (As, Sb, Pb, Ag, Hg, and Tl). The proximity to highly populated/tourist areas at Santorini poses significant risks. However, we have limited knowledge of the potential impacts of this type of magmatic and hydrothermal activity, including those from magmatic gases and seismicity. To better evaluate such risks the activity of the submarine system must be continuously monitored with multidisciplinary and high resolution instrumentation as part of an in-situ observatory supported by discrete sampling and measurements. This paper is a design study that describes a new long-term seafloor observatory that will be installed within the Kolumbo volcano, including cutting-edge and innovative marine-technology that integrates hyperspectral imaging, temperature sensors, a radiation spectrometer, fluid/gas samplers, and pressure gauges. These instruments will be integrated into a hazard monitoring platform aimed at identifying the precursors of potentially disastrous explosive volcanic eruptions, earthquakes, landslides of the hydrothermally weakened volcanic edifice and the release of potentially toxic elements into the water column.

3D structural control and spatial distribution of Zn-Pb-Cu grades in the Palmeirópolis VMS deposit, Brazil

ABSTRACT The Palmeirópolis Zn-Pb-Cu volcanogenic massive sulfide deposit consists of four areas, presenting distinct features regarding host rocks, the geometry of ore bodies, hydrothermal alteration, deformation intensity, and metal proportions. The seven modeled Zn-Pb-Cu ore bodies occur mainly along with the contact between the Mesoproterozoic acid and basic metavolcanics within amphibolite facies. Some characteristics such as the relation of higher Zn-Pb and Cu grades to a higher proportion of acid and basic metavolcanic host rocks respectively, the same metamorphic grade and the gradational contact between volcanic host rocks, and distribution of alteration halo suggest that the original stratigraphy is still preserved. A smooth folding superposing the initial tight folds that define the ore bodies indicates at least two deformation events after the Zn-Pb-Cu mineralisation in the Palmeirópolis deposit. Finally, the geometry of the 3D ore bodies in Palmeirópolis are discussed against other VMS deposits around the world with 3D data available in terms of age, metamorphic, and deformation grades.

Mineralogy and geochemistry of clastic sulfide ores from the Talgan VHMS deposit, South Urals, Russia: Signatures of diagenetic alteration

Diagenetically altered thin-layered sulfide ores from the Talgan volcanic-hosted massive sulfide deposit (South Urals) represent an intercalation of thin sulfide and hyaloclastite layers up to 3 and 0.5 cm thick. Their mineralogy and trace element, including rare earth elements (REE), and S, C and O isotopic geochemistry are considered in this work. They occur at the slopes of ore bodies and pinch outside them within hyaloclastites and their thickness increases towards the flanks of the ore bodies. The sulfide layers are mostly composed of authigenic pyrite, which forms zoned nodules, anhedral aggregates, euhedral crystals and pseudomorphs after pyrrhotite crystals. The pyrite nodules and anhedral aggregates host inclusions of authigenic chalcopyrite, sphalerite, galena, barite, cotunnite, native gold, stromeyerite, tellurobismutite and hessite. The trace element content of sulfide layers widely varies and depends on the amount of non-sulfide minerals (chlorite, illite, calcite, quartz, rutile, scheelite), which formed as a result of alteration of dacitic hyaloclastite components mixed with sulfide clasts. The sulfide layers are enriched in REEs (up to 561 ppm) due to the presence of REE-bearing minerals (bastnaesite, parisite, synchysite, galgenbergite, REE-bearing xenotime), which do not occur in massive sulfide ores. A narrow range of δ34S values of pyrite (1.41–3.27 ‰) from sulfide layers is explained by equilibrium or kinetic dissolution–precipitation processes of redeposition of sulfide ore clasts during diagenetic processes. The δ13C values of bulk samples of sulfide layers (–5.29 to –17.89 ‰) indicate that the authigenic carbonates formed from pore fluids circulated in former organic-rich hyaloclastite layers. The δ18O values of the same samples (+4.00 to + 8.36 ‰) are higher compared to seawater δ18O values due to diagenetic isotopic exchange between the hyaloclastitic components and pore fluids at elevated temperatures of burial process. The positive δ34S–Mn, δ13C–Mn, δ13C–As, δ13C–Sb, δ18O–Mn and δ18O–U correlations reflect organic matter consumption during the evolution of authigenic minerals. Data presented in this study helps to define the origin of diagenetically altered layered sulfide ores in volcanic-hosted massive sulfide deposits and are important for understanding diagenetic REE accumulations in sulfide-rich sediments of these deposits.

Controls on groundwater selenium, arsenic and base metals in groundwater around a selenium-bearing volcanogenic massive sulfide deposit: constraints from stable isotopes, trace elements and redox controls

Understanding the controls on the behaviour of metalloids (Se, As) and metals (Cu, Zn, Pb) in natural aqueous systems is vital to interpreting hydrogeochemical data in environmental and mineral exploration applications. Geochemical, isotopic and redox measurements of a suite of groundwaters sampled from around the ABM zone of the Kudz Ze Kayah (KZK) volcanogenic massive sulfide (VMS) deposit in the Yukon, Canada are presented and contrasted with other case studies from a variety of mineral deposit types. This deposit has atypically high As (up to 4.3 wt%, average 2457 ppm) and Se (up to 2620 ppm, average 157 ppm) contents in the sulfide mineralization. As a relatively undisturbed deposit (unmined), it is an ideal site to study the mobility and solubility of trace metals in groundwaters. Herein we present field measurements (pH, dissolved oxygen, specific conductance, oxidation–reduction potential and temperature), major ion, trace element, anion (Cl, Br, SO 4 , PO 4 ), and stable isotope ( δ 2 H, δ 13 C DIC , δ 18 O, δ 18 O SO4 , δ 34 S) data. Waters are dominantly low-salinity HCO 3 to HCO 3 –SO 4 -type waters with variable sulfate (4.83 to 601 mg l −1 ), Ca (23–235 mg l −1 ) Mg (3.1–96.8 mg l −1 ), Na (0.30–66.9 mg l −1 ) and K (0.55 to 6.25 mg l −1 ) concentrations. These waters also have variable trace element concentrations that include As (0.01 to 148 µg l –1 ), Se (&lt;0.02 to 1.01 µg l –1 ), Fe (0.01 to 3.84 mg l −1 ), Zn (&lt;0.2 to 1070 µg l –1 ), Pb (&lt;0.01 to 8.4 µg l –1 ), Cu (0.03 and 24.5 µg l –1 ) and Sb (0.01 to 54.4 µg l –1 ). Some waters also have elevated concentrations (compared to most meteoric waters) of Nb (up to 0.3 µg l –1 ), Y (up to 1.42 µg l –1 ), Zr (up to 18 µg l –1 ), and the rare-earth elements (REEs) ( Σ REE up to 2.04 µg l –1 ). The δ 18 O (−22.8 to −20.9 ‰) and δ 2 H (−174 to −158 ‰), together with the δ 13 C DIC (−10.6 to +1.9 ‰), δ 34 S (+10 to +12 ‰) and δ 18 O SO4 (15.5 to −4.75 ‰) all suggest that local meteoric water has interacted with massive sulfide mineralization at the ABM zone. Our results demonstrate the requirement for the use of multiple techniques in hydrogeochemical studies, with dissolved concentrations of major and trace elements coupled with a suite of stable isotopes that help define a larger geochemical footprint for the KZK deposit. Water–mineral interaction between groundwater aquifers and VMS deposits like the ABM zone are distinctly different from dispersion halos described from other deposit types (i.e. Cu porphyry, unconformity U). Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues

Volcanology, geochemistry and geodynamic setting of the Neoarchean Sunrise volcanogenic massive sulfide deposit, Beaulieu River volcanic belt, Slave craton, Northwest Territories, Canada

The Sunrise volcanogenic massive sulfide (VMS) deposit is a banded, polymetallic Zn-Pb-Cu-Ag sulfide lens hosted by felsic volcanic rocks of the Neoarchean Beaulieu River volcanic belt in the western Slave craton in the Sunset Lake area of the Northwest Territories, Canada. With historic indicated resources of 1.52 Mt at 5.99% Zn, 2.39% Pb, 0.08% Cu, 262 g/t Ag, and 0.67 g/t Au—it is the largest known VMS deposit in the Northwest Territories.The footwall stratigraphy is interpreted to be the product of subaqueous, largely effusive, bi-modal volcanism with periods of pyroclastic eruptions and concomitant subsidence. It consists of basalt to basaltic-andesite lavas with minor associated volcaniclastic rocks, rhyolite lobe-hyaloclastite flows and rhyolite domes, and felsic volcaniclastic rocks. Though hosted within felsic volcaniclastic lithofacies, the mineralization is spatially associated with the thickest portions of a quartz-feldspar porphyritic lobe-hyaloclastite flow and rhyolite dome. Felsic tuff to lapillistone units, characterized by fine ash, pumice and broken crystal clasts indicate derivation from pyroclastic volcanism and deposition by eruption-fed density currents. Felsic tuff breccia units are characterized by block-sized fragments of quartz-feldspar porphyritic rhyolite and were deposited during mass wasting events along fault scarps or by the oversteepening of domes. Massive to stringer-style sulfide mineralization is dominantly within felsic (seldom heterolithic) tuff to tuff breccia units, but laterally discontinuous argillite units occur at the top of the footwall and commonly contain stringer to semi-massive sulfide mineralization, indicating a hiatus in volcanism before the onset of basaltic andesite lavas that form the hanging wall to the deposit.Volcanic stratigraphy and architecture, and the occurrence of a volcanogenic massive sulfide deposit, combined with major and trace element geochemistry and Nd, Hf, and Pb isotopic data indicate the volcanic rocks and the Sunrise deposit formed on rifted Mesoarchean crust.

The Potential of Cistus salviifolius L. to Phytostabilize Gossan Mine Wastes Amended with Ash and Organic Residues.

The São Domingos mine is within the Iberian Pyrite Belt, a mining district with large concentrations of polymetallic massive sulfide deposits. Mine waste heaps are considered extreme environments, since they contain high total concentrations of potentially hazardous elements (PHE), which contribute to inhibiting the development of most plants. Autochthonous plant species, such as Cistus salviifolius L., are able to grow naturally in this degraded environment, and may contribute to minimizing the negative chemical impacts and improving the landscape quality. However, the environmental rehabilitation processes associated with the development of these plants (phytostabilization) are very slow, so the use of materials/wastes to improve some physicochemical properties of the matrix is necessary in order to speed up the process. This work studied the effectiveness of the phytostabilization with C. salviifolius of gossan mine wastes from the mine of São Domingos amended with organic and inorganic wastes in order to construct Technosols. The mine wastes have an acid pH (≈3.5), high total concentrations of PHE and low concentrations of organic C and available nutrients. The best vegetative development occurred without visible signs of toxicity in the Technosols containing a mixture of agriculture residues. These treatments allowed the improvement of the soil-plant system providing a better plant cover and improved several chemical properties of mine wastes, helping to speed up the environmental rehabilitation.

Petrophysical Facies and Inferences on Permeability at Brothers Volcano, Kermadec Arc, Using Downhole Images and Petrophysical Data

Abstract Downhole data and cores collected during International Ocean Discovery Program (IODP) Expedition 376 at Brothers volcano, Kermadec arc, provide unprecedented, in situ views of volcanic facies and fluid pathways in an actively forming volcanogenic massive sulfide (VMS) ore deposit. Brothers volcano is a submarine caldera with extensive sea-floor hydrothermal alteration. Downhole data were collected in two holes: Hole U1530A at the NW Caldera and Hole U1528D at the Upper Cone. Textural analysis of microresistivity images in Hole U1530A provides a continuous image facies record that greatly improves findings based upon sporadic and partial (18%) core recovery. Between 90 and 214 meters below sea floor (mbsf), the heterogeneous image facies with local pattern variations is consistent with the volcaniclastic facies interpreted from cores. Between 232 and 445 mbsf, a volcanic facies was not recognizable in cores because of overprinting alteration, apart from five intervals of coherent lava flows that were less altered. Based on the fairly constant petrophysical data, Vp-porosity relationship, and presence of five to six coherent image facies intervals on the microresistivity image, we propose that the apparent volcaniclastic textures observed on cores and microresistivity images beneath 232 mbsf are dominantly lava flows. The change from volcaniclastic to dominant lava flow facies occurs over a transition zone (214–232 mbsf) where all petrophysical properties gradually change. In Hole U1528D, cores and petrophysical data show a similar transition from deep coherent lava flows to shallower, largely volcaniclastic sequences at ~270 mbsf. Down to 232 mbsf in Hole U1530A and 360 mbsf in Hole U1528D, the overall first-order downward decrease in porosity is interpreted to be caused by compaction and increased alteration intensity. Volcanic facies and fractures exert a second-order local control on petrophysical properties. Beneath 232 mbsf in Hole U1530A, the prolonged hydrothermal activity is inferred to have diminished local petrophysical property variations within the proposed lava flow-dominated rock package. High downhole fluid temperatures in Hole U1528D contrast with the moderate temperatures in Hole U1530A. Permeable zones show a mix of structural (inferred fault in Hole U1530A) and lithological controls in both holes. Some low-permeability layers and/or lithological interfaces possibly focus fluids laterally in higher-permeability layers, which may act as a trap for metal-rich fluids to form stratabound massive sulfides and deposits. Matrix is likely too low in permeability to conduct fluids but provides perfect conditions for the storage of supersaline brines. In Hole U1530A, located near active vents at the sea floor, the relatively low fluid temperature and the alteration overprint of moderate temperature demonstrate the high spatial and temporal variations at Brothers volcano. The implications of the new stratigraphy and controls on permeability proposed here for Brothers volcano include a better understanding of the following: (1) submarine volcanic eruption sequences, (2) permeability in active submarine volcanoes, and (3) the formation of volcanogenic massive sulfide deposits on (and near) the sea floor.

Seabed mining and blue growth: exploring the potential of marine mineral deposits as a sustainable source of rare earth elements (MaREEs) (IUPAC Technical Report)

Abstract The expected growth of the global economy and the projected rise in world population call for a greatly increased supply of materials critical for implementing clean technologies, such as rare earth elements (REEs) and other rare metals. Because the demand for critical metals is increasing and land-based mineral deposits are being depleted, seafloor resources are seen as the next frontier for mineral exploration and extraction. Marine mineral deposits with a great resource potential for transition, rare, and critical metals include mainly deep-sea mineral deposits, such as polymetallic sulfides, polymetallic nodules, cobalt-rich crusts, phosphorites, and rare earth element-rich muds. Major areas with economic interest for seabed mineral exploration and mining are the following: nodules in the Penrhyn Basin-Cook Islands Exclusive Economic Zone (EEZ), the Clarion–Clipperton nodule Zone, Peru Basin nodules, and the Central Indian Ocean Basin; seafloor massive sulfide deposits in the exclusive economic zones of Papua New Guinea, Japan, and New Zealand as well as the Mid-Atlantic Ridge and the three Indian Ocean spreading ridges; cobalt-rich crusts in the Pacific Prime Crust Zone and the Canary Islands Seamounts and the Rio Grande Rise in the Atlantic Ocean; and the rare earth element-rich deep-sea muds around Minamitorishima Island in the equatorial North Pacific. In addition, zones for marine phosphorites exploration are located in Chatham Rise, offshore Baja California, and on the shelf off Namibia. Moreover, shallow-water resources, like placer deposits, represent another marine source for many critical minerals, metals, and gems. The main concerns of deep-sea mining are related to its environmental impacts. Ecological impacts of rare earth element mining on deep-sea ecosystems are still poorly evaluated. Furthermore, marine mining may cause conflicts with various stakeholders such as fisheries, communications cable owners, offshore wind farms, and tourism. The global ocean is an immense source of food, energy, raw materials, clean water, and ecosystem services and suffers seriously by multiple stressors from anthropogenic sources. The development of a blue economy strategy needs a better knowledge of the environmental impacts. By protecting vulnerable areas, applying new technologies for deep-sea mineral exploration and mining, marine spatial planning, and a regulatory framework for minerals extraction, we may achieve sustainable management and use of our oceans.

Application of methods of structural petrophysical analysis for estimating metamorphogenic transformations of host rocks and ores of Dzhusa massive sulfide deposit (South Urals)

Based on a comparison of the chemical composition and a number of petrophysical and thermodynamic parameters of changed to varying degrees syn-ore and post-ore Devonian gabbroids of the Dzhusa pyrite-polymetallic deposit (South Ural), the principal possibility of quantifying the grade of their alteration and transformation related with the hydrothermal post-volcanic and dynamic metamorphism is shown.

Transformation of minerals and mobility of heavy metals during oxidative weathering of seafloor massive sulfide and their environmental significance

Seafloor massive sulfide (SMS) deposits have received widespread attention because of their potential as available metal resources. Deep-sea mining operations significantly increase the exposure of fresh sulfide to oxygenated seawater. Knowledge about mineral transformation and the fate of heavy metals during sulfide oxidation remains insufficient, which is unfavorable for eco-friendly deep-sea mining. Here, a series of partially or completely oxidized sulfide samples collected from the Yuhuang hydrothermal field, Southwest Indian Ridge, were examined for detailed mineralogical, geochemical, and morphological analyses. Models for mineral conversion and heavy metal mobility over time were established through the obtained results to assess the potential environmental impacts associated with deep-sea mining. The absence of hydrous ferric sulfates in the pure oxide samples suggests that they were transformed into iron (oxy)hydroxides after long-term exposure in seawater. There are also indications that amorphous iron (oxy)hydroxides dehydrated to layer-like goethite and that schwertmannite hydrolyzed to globular goethite. The microorganism-related morphology of secondary minerals strengthens the case that sulfide oxidation is a microbially mediated process. The enrichment of Cu, Zn, V, and U in oxidation products indicates that they can serve as effective purification agents to retain heavy metals originated from sulfide and seawater. Heavy metal contents display a progressively increasing trend in the oxide profiles, which can be well explained by our models for oxide crust accumulation. Because secondary minerals have excellent adsorption capability and mineral transformation is a reaction removal of sulfate radicals, we conclude that sulfide oxidation provides a sink for oceanic heavy metal cycles and a sulfur source in balancing the global biogeochemical sulfur cycle. In addition, mining SMS deposits containing a large quantity of Fe-bearing sulfide minerals or iron oxides from inactive hydrothermal fields are conducive to reducing environmental hazards and maintaining the economic value of remaining deposits.

Setting and formation of the earliest Neoproterozoic rifted arc Pingshui VMS deposit, South China

The Neoproterozoic Pingshui volcanogenic massive sulfide (VMS) deposit (Cu and Zn metals of 0.40 Mt) represents one of the best preserved VMS deposits in the northeastern margin of the Jiangnan Orogen, South China. This study reconstructs its magmatic and metallogenetic history and geodynamic evolution using new geological, whole-rock geochemical, and zircon U–Pb–Lu–Hf isotopic analyses. Two lithotectonic units are identified: the ore-hosting Pingshui Formation composed of a bimodal basalt-rhyolite suite and pyroclastic rocks, and the post-ore extrusive-intrusive assemblage including high-Mg basalt, Nb-enriched basalt, high-Mg diorite and felsic granitoids. The formation age of Pingshui Formation basalt to andesite is newly constrained at ∼977 ± 15 Ma by the least radiation-damaged zircon. The new and compiled data suggest that these post-ore rocks were generated during ∼932–904 Ma after a possible magmatic quiescence. In terms of geochemical characteristics, both the Pingshui Formation basalt to andesite (∼977 Ma) and late high-Mg basalt (∼921 Ma) are enriched in light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs, e.g., Nb, Ta, P, Ti, Zr and Hf). The late high-Mg diorite (∼932 Ma, MgO = 5.84–6.91%) has moderate (La/Yb)N ratios (13.7–14.1), resembling those of high-Mg andesites (HMA). These geochemical signatures indicate that they originated from a heterogeneous mantle wedge metasomatized by slab-derived fluids and melts. The Nb-enriched basalt (∼916 Ma) was derived from a mixture of OIB- and arc-like mantle sources as evidenced by relatively high Ti/V, Ti/Zr and Zr/Y ratios. The geochemical changes from a dominant subduction influence to asthenospheric involvement, corresponding to the mafic-intermediate rocks (977–921 Ma) and the Nb-enriched basalt (916 Ma) respectively, is indicative of a possible slab roll-back that triggered asthenospheric upwelling. Furthermore, the felsic rocks originated from partial melting of juvenile mafic lower crust or fractional crystallization of parental mafic melts. Their anomalously high temperatures of formation (over 950 °C), which are indicated by zircon saturation thermometry, suggest a long-lasting high heat flow environment. In summary, subduction of young oceanic crust and intra-arc rifting are likely mechanisms to account for the formation of the high temperature magmatic rocks and massive sulfide ores at Pingshui.

Au-rich bimodal-mafic type volcanogenic massive sulphide deposit associated with Jurassic arc volcanism from the Central Pontide (Kastamonu, Turkey)

The central part of the Pontide Orogenic Belt, located in northern Anatolia, is a segment of the Alpine-Himalayan orogeny. Çangaldağ Metamorphic Complex (CMC) occurs within this segment which consists of ensimatic island arc volcanics and deep sea sediments which occasionally cut cross by mafic sills/dykes. They were exposed to metamorphism under the greenschist facies conditions and remain in tectonic contact with each other. The Say yayla mineralization is one of the recently discovered volcanogenic massive sulfide (VMS) deposits in the CMC with a remarkable Au content. The mafic and felsic metavolcanic rocks are the host-rocks of the Say Yayla mineralization and the ages determined by U-Pb zircon grains of these felsic volcanic rocks range from 170 Ma to 165 Ma indicating Middle Jurassic time.At the 0.1% cut-off grade, 7.5 million tons of resource has been calculated with 0.75 ppm Au, 0.65 wt% Cu, and 0.35 wt% Zn grades. The Say Yayla mineralization consists of massive and semi-massive sulfide minerals and a mineral assemblage represented by predominantly pyrite and chalcopyrite and trace amounts of sphalerite, tennantite and galena. Average base and precious metal grades of the zones occur with >1 wt% Cu are 2 wt% for Cu, 0.7 wt% for Zn, 0.04 wt% for Pb and 1.5 g/t for Au.The sulfur isotope values (δ34S VCDT) range from 4.9‰ to 6.7‰ for pyrite grains and 4.2‰ was obtained from the one sphalerite sample. δ18O values for the quartz from quartz-rich ore samples were 10.6 ‰ and 11.7‰ δ18O (VSMOW)qtz. δ18O (VSMOW)fluid values for the ore-forming fluids vary between 0‰ and 2.4‰. Lead isotope compositions of the pyrite minerals were 18.148–18.150 (206Pb/204Pb), 15.548–15.550 (207Pb/204Pb) and 38.078–38.083 (208Pb/204Pb)The geological, geochemical, and isotopic data of the ore and host-rocks reveal that the mineralization is a bimodal-mafic type (Noranda type), which is classified into Cu-Zn group of volcanogenic massive sulfides. Geochemical and geochronological data from the wall rocks further show that mineralization was developed within an ensimatic island arc environment during the Middle Jurassic.

Geodynamic conditions of massive sulfide formation in the Magnitogorsk megazone

Research subject. Volcanism, rock geochemistry, geodynamics, and massive sulfide formation in the Magnitogorsk megazone (MMZ) of the Southern Urals in the Middle Paleozoic.Materials and Methods. Across the largest part of the massive sulfide deposits under investigation, the authors conducted route studies, including geological surveys of individual ore fields and quarries of deposits, core samples of deep wells and transparent sections. Representative analyses of petrogenic and microelements were performed using wet chemistry and ICP-MS in analytical centers in Russia and Europe. Along with the authors’ data, analytical materials published by Russian and foreign researchers were used. Geodynamic reconstructions were carried out taking into account regional data on gravics, thermal field, magnetometry, and seismic stu dies, including «Urseis-95».Results. The geodynamic reconstructions established that the main elements of the paleostructure of the Southern Urals in the Devonian were the subduction zone of the eastern dip and asthenospheric diapirs that penetrated into the «slab-window», which determined the type of volcanic belts, the composition and volume of volcanic rocks of pyrite-bearing complexes, and ore matter of pyrite deposits. The following geodynamic zones in the MMZ were identified: 1 – polychronous accretion prism; 2 – frontal and developed island arcs (D1e2–D2ef1); 3 – zone of back-arc spreading (D1e2); 4 – rear island arc (D2ef1).Conclusions. All investigated zones and ore areas are characterized by an autonomous development of volcanism, a special deep structure and a different composition, as well as by a different volume of massive sulfide deposits that vary in the Cu and Zn ratios and Pb, Ba, Au amounts. In the MMZ volcanic complexes, three groups of plume source basalts are distinguished. The results can be used in predictive-estimation and search operations for massive sulfide mineralization.

Mineral formation conditions in acid magmatic systems related to the formation of massive sulfide deposits of the Urals and Altai-Sayany area

Studies of melt inclusions in quartz indicate the similarity of acid magmatic systems of massive sulfde deposits in the Urals and Altai-Sayany region. The melts of normal alkalinity corresponding to rhyodacite and rhyolite compositions and related to the tholeiitic series are dominant in all the deposits considered. The magmas are characterized by the same type evolution with a decreasing content of main oxides (TiO2, Al2O3, FeO, MgO, CaO, Na2O, K2O) and an increasing SiO2 content. Our results show the accumulation of Cu in relatively low-H2O acidic melts of ancient (Cambrian) deposits of the Altai-Sayany region and low metal contents in the intermediate (Silurian–Devonian) and H2O-saturated magmas of the Urals. The youngest (Devonian) magmas of Siberia evolve simultaneously along these two directions. The analysis of melt inclusions in quartz suggests that the minimum contents of trace and rare earth elements are characteristic of the Silurian-Devonian acid melts of the Urals, with their maximum contents in the youngest (Devonian) magmas and the intermediate contents of ancient (Cambrian) magmatic systems of the Altai-Sayany region. The features of rare and rare earth element patterns in melt inclusions in quartz indicate the similarity of acid magmatic systems of massive sulfde deposits in the Urals and Altai-Sayany region with present-day suprasubduction melts in the ocean-continent transition zones. Computational modeling using data on melt inclusions in quartz confrms our previous conclusions (Simonov, Maslennikov, 2020) that the occurrence of contrasting (basic and felsic) volcanic complexes with massive sulfde deposits in the Urals and Altai-Sayany region is a result of evolution of basaltoid magmas. Keywords: conditions of mineral crystallization, basaltic-rhyolitic complexes, massive sulfde deposits, melt inclusions, quartz, acidic melts.

Nodular sillimanite rocks as field indicators to metamorphosed massive sulfide deposits

Nodular sillimanite rocks (NSR), some of which are spatially associated with massive sulfide deposits, consist of intergrowths of quartz, sillimanite (mainly fibrolite), and muscovite (up to 30 cm in length) that occur predominantly in Archean-Proterozoic metapelites, ortho- and para-gneisses, and metavolcanic rocks metamorphosed to the amphibolite/granulite facies. Such rocks are particularly abundant in central Colorado where they either enclose or occur stratigraphically above or below at least 10 metamorphosed Proterozoic Cu-Zn-(Pb-Au-Ag) deposits. A plot of NSR compositions in terms of SiO2/Al2O3 vs Na2O/K2O and a K2O-MgO-Na2O ternary diagram suggest that the protoliths of NSR spatially associated with sulfide occurrences in Colorado were predominantly shale, arenite, lithic arenite or greywacke. North American shale composite (NASC)-normalized rare earth element (REE) patterns of NSR associated with these deposits show compositions close to NASC values with flat patterns and slightly negative Eu anomalies, which also supports the concept of a sedimentary protolith. Such a protolith contrasts with NSR spatially associated with massive sulfide deposits elsewhere in the world that more commonly have volcanoclastic/igneous precursors. Mass-balance calculations of NSR from the Cotopaxi deposit (Colorado) show major and trace element mobility with mostly mass gains in K2O, MgO, Ba, Cu, Pb, and Zn, and depletions in CaO, and Na2O relative to their protolith (lithic arenite), an unaltered biotite-muscovite-feldspar gneiss. Although Al2O3 and SiO2 show both gains and losses, the mass gains are considerably larger for Al2O3. The gains in base metals (Cu, Pb and Zn), the enrichment of Cu and Zn (rather than Pb) that mimics the ore concentrations, the presence of gahnite (ZnAl2O4) in sillimanite nodules in some metallic deposits in Colorado, and the existence of chalcopyrite and pyrrhotite in NSR suggest the sedimentary protoliths were hydrothermally altered and that NSR, where spatially associated with sulfide deposits, represent zones of metamorphosed stratabound alteration zones. Nodular sillimanite rocks are easy to recognize in the field and constitute an exploration guide for massive sulfide deposits that were subjected to regional metamorphism at the amphibolite to granulite facies.

Characterization of hydrothermal fluids that alter the upper oceanic crust to spilite and epidosite: Fluid inclusion evidence from the Semail (Oman) and Troodos (Cyprus) ophiolites

Pervasive alteration of basaltic oceanic crust by heated seawater at greenschist facies conditions produces two contrasting hydrothermal rocks. “Spilites”, consisting of chlorite + albite + quartz ± actinolite ± epidote, occur typically with regional extents. Locally spilites are metasomatically transformed to “epidosites” consisting of epidote + quartz + titanite + hematite or magnetite. Both alteration types have been proposed as markers of deep hydrothermal upflow in sub-seafloor convection cells, and as sources of the ore metals in basalt-hosted seafloor massive sulfide deposits. Little direct evidence is available for the chemical compositions of these fluids in their states deep in the upflow zones prior to their discharge at the seafloor. To better characterize them we have conducted a field, petrographic and fluid inclusion study of the lavas, sheeted dikes and plagiogranites in the Semail ophiolite, with supporting samples from the Troodos ophiolite. Our results show that both the spilite- and epidosite-forming fluids were single-phase aqueous liquids during the hydrothermal alteration. At some sites their salinity is 3.1–3.2 wt.% NaCleq, which we take to represent the chlorinity of Cenomanian seawater in the Semail realm. At other sites salinities are as low as 2.4 wt.% NaCleq or as high as 5.7 wt.% NaCleq, attributable to liquid–vapor separation and partial remixing deep in the crust along the dew curve of seawater, prior to ascent of the fluids to the sites of fluid inclusion trapping. Hypersaline brines, often accompanied by vapor, are restricted to plagiogranites in both the Semail and Troodos ophiolites and they represent magmatic–hydrothermal fluids that pre-date and are genetically unrelated to the spilite and epidosite alteration. The volcanostratigraphic locations of the samples constrain their maximum depths to 1470–3600 m below seafloor during alteration. The range of possible fluid trapping pressures for all samples is 31–68 MPa. Trapping temperatures vary between sites from 145 to 440 °C for spilite fluids and 255 to 435 °C for epidosite fluids. Quantitative analyses of 12 elements in individual fluid inclusions by LA-ICP-MS define the chemical characters of the two alteration fluids. The Br/Cl ratio in the spilite fluid is the same as in modern seawater and the other elements fit expectations from seawater–basalt experiments at elevated temperature. Accordingly, concentrations of Li, B, Na, Cl, K, Br and Sr in the spilite fluid match those in modern black-smoker vent fluids in basaltic crust. Exceptions are Ca and Fe, which are enriched in the spilite fluid. As these elements may precipitate below or at the seafloor prior to vent sampling, we conclude that the spilite fluids are plausible feeders of basalt-hosted black-smoker vents. The epidosite fluid has broadly similar elemental concentrations to the spilite fluid, but vastly lower Fe, reflecting the highly oxidized state of epidosites. This suggests that epidosite fluids are incapabable of forming basalt-hosted seafloor massive sulfide deposits.

The Westwood Deposit, Southern Abitibi Greenstone Belt, Canada: An Archean Au-Rich Polymetallic Magmatic-Hydrothermal System—Part II. Hydrothermal Alteration, Mineralization, and Geologic Model

Abstract The Westwood deposit, located in the Archean Doyon-Bousquet-LaRonde mining camp in the southern Archean Abitibi greenstone belt, contains 4.5 Moz (140 metric t) of gold. The deposit is hosted in the 2699–2695 Ma submarine, tholeiitic to calc-alkaline volcanic, volcaniclastic, and intrusive rocks of the Bousquet Formation. The deposit is located near the synvolcanic (ca. 2699–2696 Ma) Mooshla Intrusive Complex that hosts the Doyon epizonal intrusion-related Au ± Cu deposit, whereas several Au-rich volcanogenic massive sulfide (VMS) deposits are present east of the Westwood deposit. The Westwood deposit consists of stratigraphically stacked, contrasting, and overprinting mineralization styles that share analogies with both the intrusion-related and VMS deposits of the camp. The ore zones form three distinct, slightly discordant to stratabound corridors that are, from north (base) to south (top), the Zone 2 Extension, the North Corridor, and the Westwood Corridor. Syn- to late-main regional deformation and upper greenschist to lower amphibolite facies regional metamorphism affect the ore zones, alteration assemblages, and host rocks. The Zone 2 Extension consists of Au ± Cu sulfide (pyrite-chalcopyrite)-quartz veins and zones of disseminated to semimassive sulfides. The ore zones are spatially associated with a series of calc-alkaline felsic sills and dikes that crosscut the mafic to intermediate, tholeiitic to transitional, lower Bousquet Formation volcanic rocks. The metamorphosed proximal alteration consists of muscovite-quartz-pyrite ± gypsum-andalusite-kyanite-pyrophyllite argillic to advanced argillic-style tabular envelope that is up to a few tens of meters thick. The North Corridor consists of auriferous semimassive to massive sulfide veins, zones of sulfide stringers, and disseminated sulfides that are hosted in intermediate volcaniclastic rocks at the base of the upper Bousquet Formation. The Westwood Corridor consists of semimassive to massive sulfide lenses, veins, zones of sulfide stringers, and disseminated sulfides that are located higher in the stratigraphic sequence, at or near the contact between calc-alkaline dacite domes and overlying calc-alkaline rhyodacite of the upper Bousquet Formation. A large, semiconformable distal alteration zone that encompasses the North Corridor is present in the footwall and vicinity of the Westwood Corridor. This metamorphosed alteration zone consists of an assemblage of biotite-Mn garnet-chlorite-carbonate ± muscovite-albite. A proximal muscovite-quartz-chlorite-pyrite argillic-style alteration assemblage is associated with both corridors. The Zone 2 Extension ore zones and associated alteration are considered synvolcanic based on crosscutting relationships and U-Pb geochronology and are interpreted as being the distal expression of an epizonal magmatic-hydrothermal system that is centered on the upper part of the synvolcanic Mooshla Intrusive Complex. The North and Westwood corridors consist of bimodal-felsic Au-rich VMS-type mineralization and alteration produced by the convective circulation of modified seawater that included a magmatic contribution from the coeval epizonal Zone 2 Extension magmatic-hydrothermal system. The Westwood Au deposit represents one of the very few documented examples of an Archean magmatic-hydrothermal system—or at least of such systems formed in a subaqueous environment. The study of the Westwood deposit resulted in a better understanding of the critical role of magmatic fluid input toward the formation of Archean epizonal intrusion-related Au ± Cu and seafloor/subseafloor Au-rich VMS-type mineralization.