The Role of Mineral Assemblages in the Environmental Impact of Cu-Sulfide Deposits: A Case Study from Norway

Metallic mineral deposits represent natural geochemical anomalies of economically valuable commodities but, at the same time, their weathering may have negative environmental implications. Cu-sulfide mineral deposits have been recognized as deposits with a particularly large environmental footprint. However, different Cu deposits may result in significantly different environmental impacts, mostly depending on weathering conditions, but also on geological characteristics (mineralogy, geochemistry, host-rock lithology) of the Cu mineralization. This study presents new mineral and geochemical data from the Repparfjord Tectonic Window sediment-hosted Cu deposits and the Caledonian volcanogenic massive sulfides (VMS) deposits. The deposits share similar mineral features, with chalcopyrite and bornite as the main ore minerals, but they differ according to their trace element composition, gangue mineralogy, and host lithology. The studied sedimenthosted Cu deposits are depleted in most toxic metals and metalloids like Zn, As, Cd, and Hg, whereas the Røros Caledonian VMS mineralization brings elevated concentrations of Zn, Cd, In, Bi, As, and Cd. The conducted leaching experiments were set to simulate on-land and submarine weathering conditions. A high redox potential was confirmed as the main driving force in the destabilization of Cu-sulfides. Galvanic reactions may also contribute to the destabilization of minerals with low rest potentials, like sphalerite and pyrrhotite, even under near-neutral or slightly alkaline conditions. In addition, the presence of carbonates under near-neutral to slightly alkaline conditions may increase the reactivity of Cu sulfides and mobilize Cu, most likely as CuCO3 (aq)

Environmental Aspects of Historical Ferromanganese Tailings in the Šibenik Bay, Croatia

The former manganese ferroalloy plant and the remaining tailings are affecting the quality of the environment in Šibenik Bay, Croatia, even though industrial activities ceased more than 25 years ago. This study has revealed that the main manganese mineral phases present in the recently collected tailings, as well as in the dust collected on the roof of the plant during the production period, are bustamite and Mn-oxides. The same type of Mn mineral phases was also found in recently collected sediments from Šibenik Bay. Detailed chemical and phase analyses (XRD, BCR sequential analysis, aqua regia and lithium borate fusion) of the dust sample revealed high manganese values (24.1%), while granulometric analysis showed that 50% of the particles are smaller than PM2.5. The influence of the tailings is visible in the sediment, but the concentrations of the potentially toxic elements determined by the sequential BCR analysis are within the legal limits. Some higher values (20.3 g/kg Mn, 595 mg/kg Pb and 494 mg/kg Zn) are detected in the tailings, which are still exposed to weathering and as such should be additionally monitored. On the other hand, this material contains a considerable number of elements that could be considered lucrative (∑ REE up to 700 mg/kg, Mn up to 23 g/kg, Fe up to 37 g/kg and Al up to 25 g/kg), opening the possibility of reuse and recovery

Late Palaeozoic fault-controlled hydrothermal Cu–Zn mineralisation on Vanna island, West Troms Basement Complex, northern Norway

The Vannareid–Burøysund fault is a major, brittle, normal fault in northern Norway, with cohesive fault rocks (cataclasites) that host Cu–Zn-bearing quartz-carbonate veins. The fault is exposed on the island of Vanna in the Neoarchaean to Palaeoproterozoic West Troms Basement Complex, separating variably deformed tonalitic gneisses in the footwall from mylonitised metasedimentary rocks and tonalites in the hanging wall. Radiometric dating (K–Ar illite) of normal fault movement along the Vannareid–Burøysund fault yielded a late Permian age, concurrent with incipient post-Caledonian continental rifting. The fault evolution and internal architecture of the Vannareid–Burøysund fault largely controlled the spatial distribution of mineralisation, and two main phases of the Cu–Zn mineralisation have been discerned. Early quartzsphalerite veins are deposited in the cataclastic fault core zone, where initial movement along the fault created a fluid conduit that allowed for fluid flow and sphalerite deposition. With subsequent movement and widening of the fault zone, a later and spatially more extensive generation of quartz-chalcopyrite veins were deposited in both the fault core and the damage zones. Fluid inclusion micro-thermometry revealed that the ore-forming fluids were highly saline aqueous solutions (20–37 wt.% NaCl + CaCl2) that carried base metals and sulphur. Further, the isotopic composition of hydrothermal carbonates indicates a magmatic source for the CO2. The structural data and obtained geochemical results indicate that the Cu–Zn mineralisation in the Vannareid–Burøysund fault was epigenetic and strongly controlled by extensional brittle faulting and cataclasis during early stages of post-Caledonian (Permian) continental rifting, thus providing a new model for exploration of post-Caledonian hydrothermal ore deposits in basement rocks of northern Norway

Iron isotopes constrain sub-seafloor hydrothermal processes at the Trans-Atlantic Geotraverse (TAG) active sulfide mound

Iron isotopic equilibration at the Trans-Atlantic Geotraverse hydrothermal field takes place over tens of thousands of years, with variable degrees of hydrothermal maturation throughout the active mound, according to iron isotope analyses of sulfide minerals. Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to the formation of seafloor massive sulfide deposits and to oceanic iron cycling, yet the nature of their relationship is poorly understood. Here we apply iron isotope analysis to sulfide minerals from the Trans-Atlantic Geotraverse (TAG) mound and underlying stockwork, 26 degrees N Mid-Atlantic Ridge, to trace hydrothermal processes inside an actively-forming sulfide deposit in a sediment-free mid-ocean ridge setting. We show that data for recently formed chalcopyrite imply hydrothermal fluid-mound interactions cause small negative shifts (<-0.1 parts per thousand) to the delta Fe-56 signature of dissolved iron released from TAG into the North Atlantic Ocean. Texturally distinct types of pyrite, in turn, preserve a delta Fe-56 range from -1.27 to +0.56 parts per thousand that reflects contrasting precipitation mechanisms (hydrothermal fluid-seawater mixing vs. conductive cooling) and variable degrees of progressive hydrothermal maturation during the >20 kyr evolution of the TAG complex. The identified processes may explain iron isotope variations found in fossil onshore sulfide deposits

Evolution of metal-bearing fluids at the Nussir and Ulveryggen sediment-hosted Cu deposits, Repparfjord Tectonic Window, northern Norway

The Palaeoproterozoic greenstone belts of Fennoscandia are metamorphosed and deformed volcanic and sedimentary rocks that formed in basins with a high base-metal ore potential. One of these, the Repparfjord Tectonic Window (RTW), is exposed in the Caledonides of northern Norway and contains several sediment-hosted Cu deposits including Nussir and Ulveryggen. The RTW is composed of mafic metavolcanic rocks (metabasalts, volcanoclastic metabreccia and metatuffite) intercalated with carbonate-siliciclastic sedimentary rocks (dolomitic marble, metasandstone to metapelite). This succession was deformed and metamorphosed up to greenschist to lower amphibolite facies during the Svecofennian Orogeny (c. 1.84 Ga). The Cu-mineralisation at the Nussir deposit is hosted by a dolomitic marble. It occurs mostly in the form of quartz-carbonate veins with chalcopyrite, bornite, chalcocite and covellite as the main ore minerals. In contrast, the Ulveryggen mineralisation is predominantly disseminated within a metasiliciclastic succession and dominated by chalcopyrite, bornite, chalcocite, covellite and neodigenite. Mineralogical, geochemical, stable isotope and fluid-inclusion studies provide insights into the evolution of the Cu-bearing fluids. A wide range in homogenisation temperatures (135–350°C at the Nussir deposit and 102–520°C at the Ulveryggen deposit) and fluid-inclusion salinities (from 0.35 up to 36 wt.% NaCl equivalents) suggest an evolving system with brines developed by subsurface evaporite dissolution. Fluid-inclusion and Cu-sphalerite geothermometry data constrain the temperature-pressure conditions of the Cu mineralisation in the Nussir deposit at 330–340°C and 1.1–2.7 kbars. High salinities at relatively high temperatures within the ore-bearing fluids imply that Cu was transported predominantly by Cu-chloride complexes. The interaction of ore-bearing fluids with carbonate-rich host lithologies is proposed as the main mechanism for deposition of the Cu mineralisation at Nussir. In contrast, at the Ulveryggen deposit the mineralisation was mostly controlled by dilution and cooling when ore-bearing fluids mixed with groundwaters. Locally, reaction of Cu-bearing fluids with sediment-hosted pyrite might also have triggered copper precipitation. Similar ranges of δ13C (- 0.9 to + 2.9‰ V-PDB) and δ18O (- 18.3 to - 15.9‰ V-PDB) values in carbonates from ore-bearing veins and underlying host dolomitic marbles reflect a carbonate rock-buffered system without a significant contribution of magmatic or hydrothermal CO2

Evolution of ore-forming fluids in a post-collisional porphyry Cu-Au system: A case study from the Bučim deposit, Republic of North Macedonia

The Bučim porphyry Cu-Au deposit is situated in the westernmost part of the Serbo-Macedonian Massif, Republic of North Macedonia. The deposit is hosted by Precambrian gneisses with tectonically imbedded rare lenses of Palaeozoic amphibolites. The mineralization is spatially associated with intrusions of andesitic to trachyandesitic magmatic bodies. The geochemical signature of the intrusions and their radiogenic age suggest that the Bučim porphyry Cu-Au deposit represents a product of the Oligocene/Early Miocene post-collisional magmatic activity. The Vršnik intrusion, the youngest among four intrusions at the Bučim deposit, has not been subjected to later magmatic overprints and was therefore selected for studying the evolution of ore-forming fluids in post-collisional porphyry Cu-Au systems. The Cu-Au mineralization is spatially associated with hydrothermal alteration assemblages within and around the Vršnik intrusion. The infiltration of hot, near-neutral, oxidized, and highly saline and metal-rich aqueous solutions developed a mineralized potassic alteration zone. The fluid inclusion study suggests the formation temperature and pressure of 600-645⁰C and 0.675 kbar, respectively. This alteration zone is characterized by the replacement of amphibole with biotite and crystallization of hydrothermal biotite, magnetite, and hematite within the fine-grained groundmass of the intrusion. The oxidation of ferrous to ferric iron in this alteration zone has been recognized as a possible trigger for sulfate reduction and the consequent deposition of sulfide mineralization. The fluid inclusion study reflects that the barren phyllic alteration zone represents a product of infiltration of hot and saline fluids with a high metal-transport capability. Anyhow, sericitization and silicification suggest a low pH that might have played a significant role in preventing Cu deposition. The stable isotope composition of carbonates associated with the phyllic alteration zone point to a contribution of magmatic CO2. The mineralized chlorite alteration zone is mainly well developed along the contact between the intrusion and surrounding gneisses and reflects conditions of a high water/rock ratio. The fluid inclusion assemblages composed exclusively of vapor-rich inclusions indicate fluid flashing, probably associated with the transition from the lithostatic to hydrostatic regime at the point when the system cooled down to approximately 400⁰C. The liquid + vapor fluid inclusion assemblages point to dilution and cooling episodes, apparently related to mixing of ore-bearing fluids and meteoric water. The decrease in temperature as well as the decrease in the fluid salinity are associated with the mobility of metals transported in forms of their chloride complexes, including Cu, Au and Ag. The barren argillic alteration zone was developed under the influence of relatively cold and diluted fluids, with very limited capability for transport of metals. The water/rock ratio was relatively high but lower comparing the chlorite alteration zone. The presented study revealed that development of hydrothermal alteration zones and evolution of ore-forming fluids in post-collisional porphyry Cu-Au systems are comparable with those known from subduction-related magmatic arcs

Evolution of ore-forming fluids in a post-collisional porphyry Cu-Au system: A case study from the Bučim deposit, Republic of North Macedonia

The Bučim porphyry Cu-Au deposit is situated in the westernmost part of the Serbo-Macedonian Massif, Republic of North Macedonia. The deposit is hosted by Precambrian gneisses with tectonically imbedded rare lenses of Palaeozoic amphibolites. The mineralization is spatially associated with intrusions of andesitic to trachyandesitic magmatic bodies. The geochemical signature of the intrusions and their radiogenic age suggest that the Bučim porphyry Cu-Au deposit represents a product of the Oligocene/Early Miocene post-collisional magmatic activity. The Vrˇsnik intrusion, the youngest among four intrusions at the Bučim deposit, has not been subjected to later magmatic overprints and was therefore selected for studying the evolution of ore-forming fluids in post-collisional porphyry Cu-Au systems. The Cu-Au mineralization is spatially associated with hydrothermal alteration assemblages within and around the Vrˇsnik intrusion. The infiltration of hot, nearneutral, oxidized, and highly saline and metal-rich aqueous solutions developed a mineralized potassic alteration zone. The fluid inclusion study suggests the formation temperature and pressure of 600-645⁰C and 0.675 kbar, respectively. This alteration zone is characterized by the replacement of amphibole with biotite and crystallization of hydrothermal biotite, magnetite, and hematite within the fine-grained groundmass of the intrusion. The oxidation of ferrous to ferric iron in this alteration zone has been recognized as a possible trigger for sulfate reduction and the consequent deposition of sulfide mineralization. The fluid inclusion study reflects that the barren phyllic alteration zone represents a product of infiltration of hot and saline fluids with a high metal-transport capability. Anyhow, sericitization and silicification suggest a low pH that might have played a significant role in preventing Cu deposition. The stable isotope composition of carbonates associated with the phyllic alteration zone point to a contribution of magmatic CO2. The mineralized chlorite alteration zone is mainly well developed along the contact between the intrusion and surrounding gneisses and reflects conditions of a high water/rock ratio. The fluid inclusion assemblages composed exclusively of vapor-rich inclusions indicate fluid flashing, probably associated with the transition from the lithostatic to hydrostatic regime at the point when the system cooled down to approximately 400⁰C. The liquid + vapor fluid inclusion assemblages point to dilution and cooling episodes, apparently related to mixing of ore-bearing fluids and meteoric water. The decrease in temperature as well as the decrease in the fluid salinity are associated with the mobility of metals transported in forms of their chloride complexes, including Cu, Au and Ag. The barren argillic alteration zone was developed under the influence of relatively cold and diluted fluids, with very limited capability for transport of metals. The water/rock ratio was relatively high but lower comparing the chlorite alteration zone. The presented study revealed that development of hydrothermal alteration zones and evolution of ore-forming fluids in post-collisional porphyry Cu-Au systems are comparable with those known from subduction-related magmatic arcs

Mineralogical distribution and genetic aspects of cobalt at the active Fåvne and Loki’s Castle seafloor massive sulfide deposits, Arctic Mid-Ocean Ridges

The demand for responsibly sourced cobalt has increased dramatically as a result of the global transition to ‘fossil-free’ electromobility. However, the distribution, mineralogical expressions and mechanisms of concentration of Co in different types of hydrothermal ore deposits remain poorly constrained, inhibiting resource assessments and exploration. Here we report Co and other metal concentrations in ores from the active Fåvne and Loki’s Castle seafloor massive sulfide (SMS) deposits located along the Mohns Ridge and assess some genetic aspects of Co. The assemblages from the recently discovered Fåvne deposit are dominated by either pyrrhotite-isocubanite or sphalerite, in both cases with abundant anhydrite and local Fe-oxides. They show high whole-rock Co concentrations (average 0.31 wt.%, up to 0.98 wt.%) and Co is enriched in the Cu-rich relative to the Zn-rich assemblages. No independent Co-minerals are observed; rather, Co is variably hosted in pyrrhotite (up to 1.03 wt.%), isocubanite (up to 0.71 wt.%), sphalerite (up to 0.14 wt.%) and magnetite (∼100 ppm). The assemblages from Loki’s Castle are dominated by pyrrhotite, isocubanite, sphalerite, amorphous silica and barite, and they exhibit distinctly lower Co concentrations in both whole-rock samples (average 62 ppm, up to 368 ppm) and in individual minerals (up to 152, 148 and 99 ppm in isocubanite, sphalerite and pyrrhotite, respectively). At both deposits, Co is interpreted to enter the Fe-, Cu-Fe- and Zn-sulfides and Fe-oxides via simple Co²⁺ ↔ (Fe,Zn)²⁺ substitutions and its mineralogical distribution reflects a combination of crystal-chemical controls (e.g., spin state compatibility between Co²⁺ and the divalent cation) and changing hydrothermal fluid conditions (e.g., temperature) during mineral formation. Based on a comparison with global SMS and VMS deposits, we suggest that the ‘diffuse’ high-temperature venting at Fåvne can in part explain the enrichment of Co in the surficial sulfides, whereas at Loki’s Castle more Co-rich sulfides might occur in the interior of the deposit. Furthermore, Fåvne and several Co-rich deposits elsewhere show evidence for the involvement of saline hydrothermal fluids with enhanced capacity to mobilize and transport Co during their evolution. While their future role as a source of Co and other critical commodities remains uncertain, active SMS deposits provide unique insights into the processes and conditions associated with formation of hydrothermal Co mineralization that will aid both deep-sea and onshore exploration

Palaeoproterozoic foreland fold-thrust belt structures and lateral faults in the West Troms Basement Complex, northern Norway, and their relation to inverted metasedimentary sequences

Palaeoproterozoic fold-thrust belt structures and steep, lateral shear zones characterize the foreland deformation of Neoarchaean basement tonalites in Vanna, West Troms Basement Complex, northern Norway. Low-grade par-autochthonous and allochthonous cover units (2.4–2.2. Ga) with sandstones and calcareous metapelites exist in separate areas of the foreland. They were formed as intracontinental rift- and/or deltaic shelf deposits, and subsequently intruded by a diorite sill at c. 2.2 Ga. The basement and cover units were folded and inverted along low-angle thrusts and steep reverse faults during two late/post Svecofennian (1.77–1.63 Ga) orthogonal shortening events (D1-D2). The D1 event involved NE-SW shortening, folding, ENE-directed thrusting, and dextral lateral shearing, controlled by pre-existing, N-S striking mafic dykes (c. 2.4 Ga) and basin-bounding normal faults. The D2 event involved SE vergent nappe translation, flat-ramp thrust propagation in a frontal duplex above a basement-seated detachment, and sinistral lateral reactivation in a partitioned orogen-parallel, transpressive setting. Hydrothermal fluid circulation affected all the shear zones. New aeromagnetic data show the basement-involved fold-thrust belt architecture well. The orthogonal Vanna Island fold-thrust belt styles of deformation resemble other inverted rift-basin deposits in northern Fennoscandia, deformed during the Svecofennian Orogeny (1.92–1.79 Ga), Alta-Kautokeino and Karasjok greenstone belts in northern Norway, Central Lapland, Peräpohja, Kittilä and Kuusamo belts of Finland, and in the Norrbotten province of Sweden. Westward younging of the orogenic events explain the younger age span of deformation on Vanna Islan

Stability of Cu-Sulfides in Submarine Tailing Disposals: A Case Study from Repparfjorden, Northern Norway

Mine tailings that were produced during the exploitation of the Ulveryggen siliciclastic sediment-hosted Cu deposit in northern Norway were disposed into the inner part of Repparfjorden from 1972 to 1978/1979. This study focuses on the mineralogy and geochemistry of the submarine mine tailings and underlying natural marine sediments from the inner part of Repparfjorden, as well as on the primary Ulveryggen ore. The ore mineralization from the neighboring Nussir carbonate sediment-hosted Cu deposit was studied too, due to the forthcoming mining of both deposits. Bornite and chalcopyrite are the major Cu-sulfides, and are characterized by low concentrations of potentially toxic elements including Cd, Hg, and As. The tailing material occupies the uppermost 9 cm of Repparfjorden sediments. It is characterized by predomination of a silty component with elevated Cu (up to 747.7 ppm), Ni (up to 87 ppm), and Cr (up to 417 ppm) concentrations. The high Cu concentration is related to the deposition of mine tailings. In contrast, Ni and Cr concentrations are close to those in naturally occurring stream sediments from the feeding river, Repparfjordelva, reflecting the compatibility of these elements with hosting mafic volcanics, which are widely spread in the Repparfjord Tectonic Window. Copper in the uppermost part of the sediments is bound to the acid-soluble fraction while Ni and Cr are bound to the residual fraction. Artificial placement of large masses of fine-grained material, i.e., smothering, resulted in a diminished biological activity and/or physical distortion of mostly benthic fauna, which was reflected in total organic carbon (TOC) values as low as 0.15% in the uppermost strata. Sulfide minerals are found both in natural marine sediments and in the mine tailings. They are generally well-preserved with an exception for chalcopyrite from the uppermost part of the submarine tailing, which shows signs of incipient weathering. Thermodynamic modeling confirmed that redox potential and pH are important factors in the weathering of sulfides. Available ligands contribute to the Cu speciation. In near-neutral to slightly alkaline conditions a presence of carbonates can lead to the mobilization of Cu in form of CuCO3 complexes