Volcanogenic 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.

Discriminating Superimposed Alteration Associated with Epigenetic Base and Precious Metal Vein Systems in the Rouyn-Noranda Mining District, Quebec; Implications for Exploration in Ancient Volcanic Districts

Abstract The Rouyn-Noranda mining district of Quebec contains 20 Cu-Zn (±Au ±Ag) volcanogenic massive sulfide (VMS) deposits, including the giant and gold-rich Quemont and Horne deposits. Mineralized epigenetic veins are also present, but their origin and relative timing remain enigmatic. The nature and extent of their alteration signatures and the effect of their superposition on district-scale alteration patterns is unknown. The VMS-related quartz-sulfide Cu-Zn-Ag veins have δ18Oquartz values of 8.5 ± 0.8‰, reflecting δ18Ofluid compositions of –0.4 to 3.1‰ (250°–350°C) that are typical of Archean seawater. They are associated with a proximal Fe-rich chlorite alteration and marginal spotted sericite-chlorite alteration with whole-rock δ18O values of 2.9 to 5.9‰ and are interpreted to have formed within the structurally controlled discordant upflow zones of a VMS hydrothermal system. Younger gold-bearing quartz-carbonate veins were emplaced along mechanical anisotropies created by mafic dikes during north-south compression and the formation of regional E-trending faults, folds, and cleavage. They are characterized by δ18Oquartz values of 11.3 ± 0.8‰, reflecting δ18Ofluid compositions of 2.4 to 5.9‰ (250°–350°C), typical of a metamorphic fluid, possibly mixed with a lower δ18O upper crustal fluid. They are associated with ankerite, calcite, muscovite, chlorite, albite, and quartz ± hematite alteration with whole-rock δ18O values of 5.8 to 10.3‰. Chemical abrasion-isotope dilution-thermal ionization mass spectrometry (CA-ID-TIMS) U-Pb zircon ages for two tonalite intrusions constrain the maximum age of the Cu-Zn-Ag veins to 2697.6 ± 0.7 Ma and the minimum age to 2695.3 ± 1.0 Ma, which is also the maximum age of the gold quartz-carbonate veins. Superposition of alteration related to the gold quartz-carbonate veins on previously chlorite- and sericite-altered rocks has resulted in mixed alteration signals with whole-rock δ18O values of ~6 to 8‰ that have perturbed and masked regional alteration patterns related to older VMS mineralization, such as those found in the Quemont and Horne deposits. These results indicate that defining alteration vectors in camps that have superimposed hydrothermal systems requires full consideration of the hydrothermal history of the camp, and if such constraints are lacking, whole-rock δ18O values should not be used as a stand-alone exploration method.

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.

Lead isotopes in New England (USA) volcanogenic massive sulfide deposits: implications for metal sources and pre-accretionary tectonostratigraphic terranes

Lead isotope values for volcanogenic massive sulfide (VMS) deposits provide important insights into metal sources and the nature of pre-accretionary tectonostratigraphic terranes and underlying basements. Deposits of this type in New England formed in diverse tectonic settings including volcanic arcs and backarcs, a supra–subduction zone arc, a rifted forearc foreland basin, and a rifted continental margin. Following VMS mineralization on or near the seafloor, components of the tectonostratigraphic assemblages—volcanic ± sedimentary rocks, coeval intrusions, sulfide deposits, and underlying basements—were diachronously accreted to the Laurentian margin during the Paleozoic. Lead isotope data for galena show relatively large ranges for 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb. Evaluation of potential lead sources, using for comparison Pb-isotope data from modern and ancient settings, suggests that principal sources include the mantle, volcanic ± sedimentary rocks, and deeper basement rocks. Integration of the Pb-isotope values with published data such as Nd isotopes for the volcanic rocks and from deep seismic reflection profiles points to the involvement of several basements, including those of Grenvillian, Ganderian, Avalonian, and West African (and (or) Amazonian) affinity. Clustering of Pb-isotope data for VMS deposits within individual Cambrian and Ordovician volcanic and volcanosedimentary settings, delineated by differences in 206Pb/204Pb and µ (238U/204Pb) values, are consistent with lead derivation from at least four and possibly five different tectonostratigraphic assemblages with isotopically distinct basements. Collectively, our Pb-isotope data for New England VMS deposits provide a novel window into the nature of subarc basement rocks during pre-accretionary sulfide mineralization outboard of Laurentia during early Paleozoic time.

Microstructure, trace element systematics and in-situ sulfur isotopes of multistage sulfides in the Kalatag district (East Tianshan, NW China): Implications for formation of arc-hosted VMS deposit

The Early Paleozoic arc-hosted volcanogenic massive sulfide (VMS) deposits in the Kalatag arc are well-known for their well-preserved and high-grade Cu–Zn sulfide mineralization in the East Tianshan. Unfortunately, there is a puzzle on the ore-forming fluid and metal source as well as physicochemical condition of metallogenic process of these arc-hosted VMS Cu–Zn deposits. The Huangtupo was firstly reported Early Paleozoic arc-hosted VMS Cu–Zn deposit (300Kt@1.49 % Cu; 280Kt@3.51 % Zn) in the East Tianshan. In order to better recognize the physicochemical condition and formation processe of arc-hosted VMS deposits, this research takes the Huangtupo deposit as an example, combining the microstructure, in-situ sulfur isotope and trace element composition of multistage sulfides to conduct a comprehensive study. In the Huangtupo deposit, the overall mineralization process is divided into syndepositional mineralization stage, hanging-wall massive mineralization stage and channel hydrothermal stage according to the main mineral interpenetration relationship and horizon relationship. Pyrite can be divided into five types in the Huangtupo Cu–Zn deposit: 1) subhedral to anhedral pyrite in the silicious exhalite (Py1); 2) colloform pyrite in the hanging-wall massive pyrite + barite + sphalerite zone (Py2); 3) subhedral pyrite in the hanging-wall massive pyrite + chalcopyrite + sphalerite ± magnetite zone (Py3); 4) fine-grained (or disseminated) pyrite in the footwall pyrite + chalcopyrite + sphalerite stage (Py4); 5) euhedral pyrite in the footwall quartz + pyrite + chalcopyrite stage (Py5). Two types of chalcopyrite are identified, including hanging-wall massive chalcopyrite (Ccp1) and footwall stockwork chalcopyrite (Ccp2). In addition, three generations of sphalerite could be identified, namely (1) hanging-wall massive pyrite + barite + sphalerite zone (Sp1); (2) hanging-wall massive pyrite + chalcopyrite + sphalerite ± magnetite zone (Sp2); and (3) footwall pyrite + quartz + sphalerite + chalcopyrite stage (Sp3). In the upper massive orebody, LA–ICP–MS in-situ microanalysis shows that pyrite is enriched in Cu, Zn, Au, Ag, Pb, Sb, and Tl, while it is poor in Co, Ni, Se, Te, Ti, and Sn, indicating that it was formed in a metal-rich, medium–high temperature and more oxidizing hydrothermal environment. By contrast, pyrite from the footwall stockwork orebody contains low Au, Ag, Cu, Zn, Pb, Sb, Tl and high Co, Se, Te, Ti content, indicating that it is formed in the hydrothermal environment with a high temperature, reduction and trace metal deficit signature. Trace element compositions of sphalerite suggest that Fe, Mn, Ag, Se, In, Ge, and Ga are present as lattice. By contrast, Sn, Pb, Tl, and Bi are present as mineral microinclusions. The mineralization temperature is determined by sphalerite geothermometer (GGIMFis) and shows a decreasing trend from footwall stockwork mineralization to hanging-wall massive mineralization. Comparing with sphalerite, chalcopyrite is enriched in Ge, Ag, Zn, Se, Sn, and Cd, relatively poor in In and Ga. The integrated in situ sulfur isotopic (δ34S) composition and trace metal content of sulfides suggest that ore-forming material is most likely derived from a combination of host volcanics and seawater. In addition, the thermochemical sulfate reduction is also a key factor affecting sulfur isotope fractionation. Overall, the trace element compositions of multistage sulfides are robust monitor of the complex hydrothermal process and effectively reconstruct the metal enrichment process during the formation of arc-hosted VMS mineralization system.

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.

Interaction Between Mineralization and Rock Magnetization: New Constraints From a Silurian‐Lower Devonian Volcanogenic Massive Sulfide (VMS) Deposit

AbstractThe unclear relationship between mineralization, hydrothermal alteration, and rock magnetization in volcanogenic massive sulfide (VMS) deposits limits us from fully understanding the magnetic anomalies and remagnetization process in this type of deposit. We address the issue by conducting systemic paleomagnetic, rock magnetic, petrographic, and X‐Ray diffraction studies in the Dapingzhang VMS deposit on the northwestern Indochina Block. Magnetite is the dominant magnetic carrier of hydrothermally altered surrounding rocks and orebody. Magnetite consumption and secondary magnetite formation occurred at different stages and types of hydrothermal alteration. The overall decrease in magnetite concentration from chloritization via silicification to mineralization implies that the magnetite was mostly consumed during hydrothermal alterations. Secondary single domain magnetite, which can carry a remagnetization direction, is proposed to be formed during illitization via the smectite‐to‐illite transformation. Secondary superparamagnetic magnetite, which was most likely formed during the late stage of chloritization, is unable to carry the stable characteristic remanent magnetization. The site‐mean direction of high‐temperature and high‐coercivity components is Dg/Ig = 324.5°/43.1°, and kg = 35.1, with α95 = 6.8° before tilt correction, and Ds/Is = 316.2°/37.6°, and ks = 16.4, with α95 = 10.1° after tilt correction, with a negative fold test. However, plate reconstruction is limited by the uncertainty of the tilting process following mineralization and the possibility of remagnetization during burial alteration. Therefore, this study provides a mechanism for rock magnetic variation and remagnetization during VMS mineralization.

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.

District-Scale VMS to Porphyry-Epithermal Transitions in Subduction to Postcollisional Tectonic Environments: The Artvin Au-Cu District and the Hod Gold Corridor, Eastern Pontides Belt, Turkey

Abstract Porphyry, epithermal, and volcanogenic massive sulfide (VMS) deposits can form together in the same mineral district in convergent margin environments. Their spatial association and superposition indicate evolving tectonic settings. The Artvin Au-Cu district is one of the major clusters of VMS bimodal-felsic, porphyry, and epithermal deposits in the Eastern Pontides belt in northeast Turkey. Whereas ore-forming processes, timing, and tectonic setting of VMS mineralization are well defined in Artvin, those for porphyry and epithermal mineralization remain less constrained. Our district-scale field study focused on the Hod gold corridor in the Artvin district, which is defined by the NE-trending alignment of the recent Au-Cu mineral discoveries (~205 t Au; ~0.33 Mt Cu; e.g., Hod Maden, Ardala-Salinbaş, and Taç-Çorak) that include Au-rich porphyry, highand intermediate-sulfidation epithermal, carbonate-replacement, and hybrid VMS-epithermal mineralization styles. Our new U-Pb, 40Ar/39Ar, and Re-Os geochronological results interpreted with previously compiled data show that magmatism in the Artvin district formed in the Carboniferous (358–325 Ma), Jurassic (182–174 Ma), Late Cretaceous (92–78 Ma), Eocene (51–40 Ma), and Oligocene (30 Ma). Porphyry and epithermal mineralization along the Hod gold corridor peaked in the Early (~113 Ma; Berta prospect) and Late Cretaceous (~86.5-82 Ma; e.g., Taç and Çorak deposits) and Eocene (~50 Ma; e.g., Ardala deposit), whereas VMS bimodal-felsic mineralization only formed in the Late Cretaceous (~91–85 Ma). Therefore, we interpret that the Hod gold corridor was a long-lived, deep crustal-scale structural feature along which the successive magmatic and mineralization events were emplaced. In addition, the timing of porphyry Cu-Mo mineralization can significantly (>20 Ma) postdate the crystallization age of the intrusive host rocks in the Artvin district, such as at Berta and Balcılı camp, which emphasizes the importance of dating mineralization directly to correctly attribute the tectonic setting. The distribution of Late Cretaceous mineral occurrences suggests a possible eastward temporal evolution from VMS (~91–85 Ma) to epithermal-porphyry systems (~86.5–82 Ma), transitioning from back-arc to arc settings at the onset of the Northern Neotethyan oceanic slab rollback and accompanied by increasingly elevated gold content eastwards across the Artvin district.

Ore forming and reworking processes in the Xitieshan Pb–Zn deposit, Qinghai Province, China: Constraints from in situ trace-element and S isotope compositions of sulfides

Although volcanogenic massive sulfide (VMS) deposits always form in extensional settings, many have been reworked by metamorphism, deformation, and the circulation of hydrothermal fluids during subsequent accretionary events. The genesis of VMS deposits has been well documented, however, the mechanisms that rework the mineralization have been relatively poorly constrained. An understanding of these mechanisms, though, is critical to the development of robust mineral deposit models as they are capable of remobilizing ore-forming metals. The Xitieshan Pb–Zn deposit, located in Qinghai Province, western China, is the third largest Pb–Zn deposit in China, with a total Pb–Zn metal reserve of 6.4 million tons. The occurrence of laminated and non-laminated orebodies in the Xitieshan deposit make it an ideal candidate to i) constrain the effects of metamorphic and hydrothermal processes on remobilization of metals in these base-metal systems, and ii) assess the genetic nature of this deposit. This is accomplished here by integrating new S isotope data and trace-element chemistry of sulfides from laminated ores with previous information on regional and deposit geology, and deformation characteristics preserved by the mineralized system. The S isotope composition of pyrite and sphalerite grains from laminated ores are consistently positive and range from 2.08 ‰ to 5.81 ‰, indicative of mixing of reduced sulfur from three distinct sources — volcanic rocks, seawater and thermochemical reduced sulfate, which is typical of VMS deposits globally. Greigite (Fe3S4) grains in laminated ores exhibit oscillatory zonation with respect to Cu, Co, Mn, Sb, and Tl concentrations; such compositional variations indicate that at least some of the primary VMS mineralization characteristics have been preserved despite subsequent reworking by metamorphism, deformation, and hydrothermal circulation. Combined with the results of previous studies, a two-stage genetic model is proposed for the formation and modification of the Xitieshan Pb–Zn deposit — i) initial formation of the primary Pb–Zn mineralization with minor of Cu, and ii) subsequent metamorphism and hydrothermal reworking of the deposit, which did not completely destroy the textural and chemical characteristics of the primary mineralization.

Origin of the Neoarchean VMS-BIF Metallogenic Association in the Qingyuan Greenstone Belt, North China Craton: Constraints from Geology, Geochemistry, and Iron and Multiple Sulfur (δ33S, δ34S, and δ36S) Isotopes

Abstract The association of volcanogenic massive sulfide (VMS) deposits and Algoma-type banded iron formations (BIFs) in many Precambrian terranes indicates a link between submarine hydrothermal processes, seawater chemistry, and chemical sedimentation. The Neoarchean (~2.55 Ga) Qingyuan greenstone belt VMS-BIF metallogenic association, located on the north margin of the North China craton, is a typical example of such an association. The stratigraphy of the Qingyuan greenstone belt includes three units (from the oldest to youngest): (1) the Shipengzi Formation, composed of tholeiitic-transitional arc basalts with negative Nb anomalies, interlayered normal mid-ocean ridge basalts (N-MORBs) and FI-type dacites, and BIFs; (2) the Hongtoushan Formation, consisting of polycyclic bimodal suites of N-MORB-type basalts and FII-type dacites, as well as VMS mineralization and minor BIFs; and (3) the Nantianmen Formation, composed of schist, quartzite, and marble with minor basalts and BIFs. Positive Fe isotope compositions (δ56Fe of 0.48–0.69‰) for magnetite in the silicate BIF of the Shipengzi Formation indicate partial oxidation of aqueous Fe(II). Using a dispersion-reaction model, the relatively high δ56Fe values (0.72–1.04‰) estimated for primary ferric (oxyhydr)oxides in this BIF constrain local dissolved O2 contents of the Neoarchean surface ocean to 10–4 to 10–3 μmol/L. By comparison, negative δ56Fe values for magnetite (–0.83 to –0.65‰) in silicate BIFs of the Hongtoushan Formation and the Nantianmen Formation suggest deposition from a residual water column that was depleted in 56Fe. Following the formation of the bulk of the VMS deposits in the Hongtoushan Formation, a significant change to positive magnetite δ56Fe values (0.79–1.04‰) occurs in the youngest sulfide-bearing BIF in the Nantianmen Formation. This implies that the VMS-related hydrothermal vents injected a large mass of unfractionated ferrous iron into the ocean. Negative Δ33S anomalies in sedimentary pyrite of bedded VMS ores (avg of –0.08 ± 0.007‰, n = 6) and sulfide-bearing BIFs (avg of –0.06 ± 0.007‰, n = 3) of the Qingyuan greenstone belt, along with mass-independent fractionations (with an average Δ36S/Δ33S ratio of –1.1 ± 0.3), are best explained by incorporation of seawater sulfate of atmospheric photochemical origin during their formation. The systematic differences in whole-rock geochemistry and Δ33S values for different types of VMS ores imply variable seawater sulfate contributions to their mineralization. Our results are consistent with global anoxic conditions during the Neoarchean to Paleoproterozoic transition (i.e., at 2.5 Ga), and confirm that formation of the VMS-BIF metallogenic association took place in dominantly anoxic, ferruginous basins at different depths, with the VMS-related hydrothermal system contributing significant Fe to the deposition of BIFs.

Lithostratigraphy, Lithogeochemistry, and Tectono-Magmatic Framework of the ABM Replacement-Style Volcanogenic Massive Sulfide (VMS) Deposit, Finlayson Lake District, Yukon, Canada

Abstract The Upper Devonian ABM deposit is a bimodal-felsic, replacement-style volcanogenic massive sulfide (VMS) deposit within the Finlayson Lake district in Yukon, Canada. The deposit is hosted by predominantly felsic volcanic rocks of the upper Kudz Ze Kayah formation that were deposited in an active back-arc basin in three sequences consisting of interbedded felsic volcaniclastic rocks and argillites, and felsic lava flows and domes, and felsic and mafic sills. The felsic rocks fall into two groups, Felsic A and Felsic B (FA and FB), based on immobile elements and their ratios. Relative to the FB group, the FA group has high Zr concentrations (>550 ppm) and generally higher contents of high field strength elements. The FA/FB chemostratigraphy roughly coincides with the lithostratigraphic sequences. Sequence 2 hosting the mineralization consists of FB felsic rocks; the hanging-wall Sequence 3 and footwall Sequence 1 felsic rocks have FA signatures. An argillite lens, recording a period of volcanic quiescence, occurs at the upper contact of Sequence 2. From reconstruction of the basin architecture, two sets of synvolcanic faults are inferred. The synvolcanic faults were interpreted based on thickness changes of volcanosedimentary units and the distribution of coherent rocks. During breaks in volcanism, synvolcanic faults acted as conduits for upwelling hydrothermal fluids, which were diverted laterally into unconsolidated volcaniclastic rocks and formed the replacement-style VMS mineralization. Although the mineralized lenses are hosted by FB felsic rocks, their replacement-style nature implies that the mineralizing processes occurred during the break in volcanism and were genetically associated with the overlying FA felsic volcanic rocks.

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.

Age and Chemostratigraphy of the Finlayson Lake District, Yukon: Implications for Volcanogenic Massive Sulfide (VMS) Mineralization and Tectonics along the Western Laurentian Continental Margin

Abstract The Yukon-Tanana terrane in the Finlayson Lake district, Yukon, represents one of the first arc–back-arc systems that formed adjacent to the Laurentian continental margin in the mid-Paleozoic. Back-arc rocks contain many large and high-grade volcanogenic massive sulfide (VMS) deposits. This study integrates U-Pb zircon geochronology, lithogeochemistry, and Hf-Nd isotopes to establish precise controls on tectonomagmatic activity adjacent to the western Laurentian margin in the Late Devonian to Early Mississippian. High-precision chemical abrasion- (CA-) ID-TIMS U-Pb zircon geochronology defines coeval arc (ca. 363.1 to 348 Ma) and back-arc (ca. 363.3 to 355.0 Ma) magmatism in the Finlayson Lake district that intruded continental crust of Laurentian affinity (e.g., Snowcap assemblage). Mafic and felsic rocks display geochemical and isotopic characteristics that are consistent with being formed from mixtures of depleted asthenosphere and enriched lithospheric mantle sources. These melts variably entrained Laurentian continental crust via high-temperature crustal melting due to basaltic underplating. The high-temperature back-arc felsic magmatism occurs at specific time periods coinciding with VMS deposits and supports previous genetic models for VMS mineralization that suggest elevated heat flow and hydrothermal circulation were due to regional-scale rift-related magmatism rather than from local subvolcanic intrusions. The short timescales and transient nature of tectonomagmatic events in the Finlayson Lake district suggest that rapid and complex subduction initiation of oceanic and continental crust fragments facilitated coeval compression, extension, and magmatism in the arc and back-arc regions. We thus reevaluate the presently accepted tectonostratigraphic framework of the Finlayson Lake district and suggest revised interpretations that shed light on VMS depositional environments and a possible broader association with the ca. 358 Ma Antler Orogeny. Results of this study have implications for incipient tectonics, magmatism, and mineralization along the western Laurentian continental margin and other orogenic belts globally.

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.

Exploration-resource assessment of productive felsic volcanic centers in the Paleoproterozoic Penokean Volcanic Belt of northern Wisconsin, Michigan and east-central Minnesota, USA

Five productive felsic volcanic centers have been identified in the Paleoproterozoic Penokean Volcanic Belt (PVB). Each center hosts at least one potentially economic polymetallic volcanogenic massive sulfide (VMS) deposit. To date, these drill-defined (inferred + indicated + measured) resources collectively contain over 93 million tonnes of VMS-style, base (Cu, Pb, Zn) and precious metal (Ag, Au) mineralization including nearly 4 million ounces of gold. This does not include smaller, less defined (mostly inferred) deposits in the belt that would increase the total to at least 150 million tonnes. From this resource base only 1.73 million tonnes of actual ore production has occurred. However, previous positive feasibility studies completed on the Crandon (1994), Lynne (1995) and most recently (2020) Back Forty deposits verify a total of approximately 44 million tonnes, or 47% of the total drill-defined resource base, are potentially minable reserves. Currently the PVB resource base remains as unrealized new wealth.Mineral resource assessments completed in 1996 and 2007 collectively suggest there is a high probability of at least 4 to 22 (average ~13) or more VMS deposits remaining to be discovered in the Ladysmith-Rhinelander complex and to a lesser extent the Wausau complex of the PVB. These newly discovered VMS deposits will fill out the tonnage distribution for this belt by following a natural geometric (log normal) progression consistent with established grade-tonnage models. It is postulated that among these will be one giant (>100 million tonnes) deposit. If verified, potentially economic VMS mineralization hosted by the PVB would be comparable to other productive Paleoproterozoic greenstone belts in the Canadian Shield such as Flin Flon (>200 million tonnes) or even approach that of the prolific Neoarchean Abitibi (~775 million tonnes).Exploration to date suggests that many of these undiscovered VMS deposits will be identified in five, highly permissive felsic volcanic centers. These centers, which comprise less than 2% of the known belt, are distributed within the Highway 8 intra-arc rift basin of the 1,880 to 1,860 Ma old Ladysmith Rhinelander volcanic complex. Exact aerial boundaries are poorly defined. However, extrapolation of geophysical, drill hole and rare outcrop data provides a reasonable estimate. Each productive center is stratigraphically associated with major, district-scale, commonly mineralized, meta-argillite formations or formational groups. Felsic centers are identified in the Wausau complex but have thus far been barren of significant VMS-style mineralization as is the adjacent Wausau basin.Future exploration for new VMS deposits should be focused within the productive felsic centers where a number of prospective targets and prospects have been previously identified. Other significant felsic centers likely exist within the Highway 8 basin particularly in Cambrian sandstone-covered areas along the western and eastern margins of the belt. Additionally, at least one felsic center may be present in the Milaca complex which could have VMS potential.Of particular note is the VMS potential of a second mostly Cambrian sandstone-covered, greenstone belt in the Marshfield subterrane (Eau Claire complex). Geophysical data suggest possible back-arc or intra-arc rift basins may be present and historical drilling has identified at least one VMS occurrence. This highly prospective volcanic complex is essentially new hunting ground with its own deposit tonnage distribution of potentially supergene-enriched VMS deposits. Based on criteria set out in a 2007 mineral assessment, this belt has the potential to host at least 1 to a maximum of 15 deposits.

Potential for Volcanogenic Massive Sulfide Mineralization at the A6 Anomaly, North-West British Columbia, Canada: Stratigraphy, Lithogeochemistry, and Alteration Mineralogy and Chemistry

The Middle Jurassic A6 Anomaly is located 30 km southeast of Eskay Creek, north-central British Columbia and consists of thick, altered felsic igneous rocks overlain by a mafic volcano-sedimentary package. Lithogeochemistry on igneous rocks, X-ray diffraction on altered felsic units, and electron probe microanalysis and secondary ion mass spectrometry on illite and quartz were applied to explore the volcanogenic massive sulfide (VMS) potential, characterize alteration, and determine fluid conditions at the A6 Anomaly. Lithogeochemistry revealed calc-alkaline rhyodacite to trachyte of predominantly FII type, tholeiitic basalts with Nb/Yb < 1.6 (i.e., Group A), and transitional to calc-alkaline basalts and andesites with Nb/Yb > 2.2 (i.e., Group B). The felsic units showed weakly to moderately phyllic alteration (quartz–illite with minor orthoclase and trace chlorite–pyrite–calcite–barite–rutile). Illite ranged in composition from illite/smectite (K = 0.5–0.69 apfu) to almost endmember illite (K = 0.69–0.8 apfu), and formed from feldspar destruction by mildly acidic, relatively low temperature, oxidized hydrothermal fluids. The average δ18O composition was 10.7 ± 3.0‰ and 13.4 ± 1.3‰ relative to Vienna Standard Mean Ocean Water for illite and quartz, respectively. Geothermometry involving illite composition and oxygen isotope composition on illite and quartz yielded average fluid temperatures of predominantly 200–250 °C. Lithogeochemical results showed that the A6 Anomaly occurred in a late-Early to Middle Jurassic evolving back-arc basin, further east then previously recognized and in which transitional to calc-alkaline units formed by crustal assimilation to enriched Mid-Ocean Ridge Basalt (EMORB) (i.e., felsic units, Group B), followed by thinning of the crust resulting in tholeiitic normalized MORB basalts (i.e., Group A) with a minor crustal component. The alteration assemblage is representative of distal footwall alteration, and metal transport in this zone was limited despite favorable temperature, pH, and redox state, indicating a metal depleted source (i.e., felsic units).

Evolution of the Garmab-e-Paein native copper-rich volcanogenic massive sulfide deposit from northeast Iran: Insights from sulfur isotope and chlorite chemistry

The Garmab-e-Paein Cu-Ag volcanogenic massive sulfide (VMS) deposit occurs as stratiform and stratabound orebody within a specific stratigraphic horizon in a Late Cretaceous volcano-sedimentary sequence of the Sabzevar zone, northeast Iran. The host rocks to mineralization are andesitic-trachyandesitic volcanic and volcaniclastic rocks. Based on textural and mineralogical studies, the VMS mineralization is comprised of four ore facies: 1) vein-veinlets (stringer) containing chalcopyrite, pyrite and minor magnetite, 2) massive ore, dominated by pyrite and minor chalcopyrite, 3) bedded ore containing laminated pyrite, and 4) exhalite containing Fe-Mn oxide-hydroxides such as hematite, psilomelane and pyrolusite. Wall rock alteration styles are chloritic, minor silicic and secondary argillic. There is a distinct metal zonation in the massive sulfide orebody; Au, Pb, As, and Ag contents and the Cu/Zn ratio increase vertically from the stringer to the massive facies, but decrease laterally from the stringer to the bedded facies. Zinc and Mn increase from the stringer to the bedded ore facies. Sulfur isotope values for pyrite range from −1.7 to +5.1‰, with average +1.4‰. The δ34S values of massive ore facies (−1.7 and +2.7‰) increase downward toward the stockwork (+2.2 to +4.3‰) and laterally outward toward the bedded (+5.1‰) zones. The near-zero sulfur isotope values indicate that most of the sulfur was derived from leaching of underlying host volcanic rocks by hydrothermal fluids circulating in the high temperature reaction zone.Extensive disseminations and vein-veinlets of native copper mineralization formed within the hanging wall Late Cretaceous volcanic rocks and younger Paleocene conglomerates. The native copper mineralization is accompanied by chlorite and zeolite alteration, and both formed after formation of the Garmab-e-Paein VMS deposit during diagenesis, burial metamorphism and uplift. The deposit is now potentially economic due to the native copper mineralization.Two generations of chlorite are observed in the deposit: Chl-I is accompanied pyrite and chalcopyrite, in the VMS mineralization system, and the second Chl-II occurs along with zeolite and native copper mineralization. The EPMA results show that Chl-I is more Fe-rich than Chl-II.

Refining the Paleoproterozoic tectonothermal history of the Penokean Orogen: New U-Pb age constraints from the Pembine-Wausau terrane, Wisconsin, USA

Abstract An enduring problem in the assembly of Laurentia is uncertainty about the nature and timing of magmatism, deformation, and metamorphism in the Paleoproterozoic Wisconsin magmatic terranes, which have been variously interpreted as an intra-oceanic arc, foredeep or continental back-arc. Resolving these competing models is difficult due in part to a lack of a robust time-frame for magmatism in the terranes. The northeast part of the terranes in northern Wisconsin (USA) comprise mafic and felsic volcanic rocks and syn-volcanic granites thought to have been emplaced and metamorphosed during the 1890–1830 Ma Penokean orogeny. New in situ U-Pb geochronology of igneous zircon from the volcanic rocks (Beecher Formation), and from two tonalitic plutons (the Dunbar Gneiss and Newingham Tonalite) intruding the volcanic rocks, yielded crystallization ages ranging from 1847 ± 10 Ma to 1842 ± 7 Ma (95% confidence). Thus, these rocks record a magmatic episode that is synchronous with bimodal volcanism in the Wausau domain and Marshfield terrane farther south. Our results, integrated with published data into a time-space diagram, highlight two bimodal magmatic cycles, the first at 1890–1860 Ma and the second at 1845–1830 Ma, developed on extended crust of the Superior Craton. The magmatic episodes are broadly synchronous with volcanogenic massive sulfide mineralization and deposition of Lake Superior banded iron formations. Our data and interpretation are consistent with the Penokean orogeny marking west Pacific-style accretionary orogenesis involving lithospheric extension of the continental margin, punctuated by transient crustal shortening that was accommodated by folding and thrusting of the arc-back-arc system. The model explains the shared magmatic history of the Pembine-Wausau and Marshfield terranes. Our study also reveals an overprinting metamorphic event recorded by reset zircon and new monazite growth dated at 1775 ± 10 Ma suggesting that the main metamorphic event in the terranes is related to the Yavapai-interval accretion rather than the Penokean orogeny.

Rift structures and magmatism focus VMS and gold mineralisation in the Paleoproterozoic Bryah Rift Basin, Australia

• Geophysical interpretation reveals syn -rift structures and magmatic centres. • Magmatic centres control syn -rift VMS and post-rift orogenic gold mineralisation . • Long-lived structures favour high endowment mineralisation. The interaction of structure development and magmatism in rift-settings provides systemic controls on the emplacement of ore deposits both during rifting and subsequently, and a knowledge of these may help to predict better the likely locations of major deposits. The Paleoproterozoic Bryah Rift Basin includes substantial mafic magmatism and deep-crust penetrating structures and possesses syn -rift volcanogenic massive sulphide (VMS) and later gold mineralisation, providing a good opportunity to study interactions between magmatism, structures, and mineralisation. The volcano-sedimentary Bryah Group was deposited in a continental rift developed within the broader Yerrida Basin on the northern margin of the Yilgarn Craton at ca. 2030 Ma. Multi-scale interpretation and forward modelling of gravity and magnetic data were applied to characterise the magmatic and structural patterns of the Bryah Group, enabling a better understanding of its tectono-magmatic development and controls on VMS and gold mineralisation. The interpretation highlights the bounding extensional faults and the inward-deepening structural pattern of the Bryah Rift Basin that reflects the initial rift geometry. Deep-rooted gravity sources show magmatism focused in the southern-central part of the basin, where mafic rocks' thickness can reach more than 10 km. At shallower levels, the rift magmatism extends in three east to east-northeast trending magmatic corridors with an en-echelon arrangement along the rift, oblique to major structures. These magmatic corridors have an intrinsic relationship with the internal structure of the rift. VMS mineralisation associated with mafic magmatism shows a spatial connection with magmatic corridors and major syn -rift faults, whereas VMS mineralisation associated with felsic volcanic rocks is related with off-axis volcanism and regional pre-rift faults. Later orogenic gold mineralisation is also spatially associated with the borders of the magmatic centres and rift faults, despite occurring ~200 Ma later. These associations suggest that primary rift architecture has substantially focused syn -rift VMS mineralisation and also later gold mineralisation, as a consequence of rheological and compositional contrasts.