The grinding and flotation performance of Zn-Pb-Cu-Ag ores is highly sensitive to ore mineralogy, host rock composition, and textural variability, factors that are often overlooked in favour of bulk grade values. This study examines the Rävliden North Zn-Cu-Pb-Ag volcanogenic massive sulphide deposit (VMS) deposit in northern Sweden. Two main ore types are identified: massive sphalerite- and galena-rich ore and chalcopyrite-rich vein-dominated ore that coupled with host rock type led to further 6 sub-types. Mineralogical and textural characterisation of flotation feed and products, using Quantitative Evaluation of Minerals by Scanning Electron Microscopy (QEMSCAN®) and element to mineral conversion (EMC) based on multi-element chemical assays, reveals that fine-grained, sphalerite-dominated ore is more amenable to grinding and exhibit better liberation, enhancing flotation efficiency. In contrast, chalcopyrite-rich ore perform better in Cu-Pb flotation but is harder to grind due to its silicate-rich gangue (e.g., quartz). Minerals such as micas, amphiboles, and carbonates affect ore hardness, and ore mineralogy (sphalerite, galena, chalcopyrite and Ag mineralogy) directly affects flotation efficiency. Blending of poor grade and hard to grind (problematic) ores with better grade and softer to grind (fairly good to good) ore is recommended to improve concentrate quality. Precious, critical, and deleterious elements are mostly recovered in the chalcopyrite-galena flotation circuit in amalgams (Ag, Hg), dyscrasite (Ag, Sb), hessite (Ag), sulphosalts (Ag, Sb, Bi), native Bi, and tellurobismuthite (Bi). These minerals are fine-grained (< 20 µm) and poorly liberated, leading to recovery in both target and non-target flotation concentrates. Nevertheless, established metallurgical methods enable their efficient extraction maximising ore value. This study highlights the importance of process mineralogy for improved beneficiation in concentration circuits, and the understanding of by-products during processing of complex polymetallic ores.

Phanerozoic vein- and breccia-hosted Zn-Pb mineralisation in western Västerbotten forms a distinct mineral system which is superimposed on Palaeoproterozoic orogenic Au deposits of the Gold line and VMS deposits of the Skellefte district. Previous research on these deposits has focused on geochronological and fluid inclusion characteristics, whereas little data exist on sphalerite trace element chemistry. We present new LA-ICP-MS data from sphalerite in occurrences at Rävliden, Nyliden, Lagbäcken and Svärträsk, supplemented with SF-ICP-MS, SEM, SIMS, EPMA, SEM-CL and EBSD analyses.

Sphalerite-bearing veins crosscut all ductile fabrics and are mineralogically distinct from the VMS deposits. A polyphase is suggested by evidence for repeated events of brecciation and cementation by sphalerite, galena, calcite, zeolite, fluorite and quartz. Sphalerite displays oscillatory zoning, twinning, and evidence for recrystallisation and overgrowth. EBSD reveals subtle crystallographic misorientation and twin boundaries, which correlate spatially with preferential enrichment of Ga, Ge, Sb, and Cu along growth zoning and twinning. Presence of Ga- and Ge-rich nano inclusions are suspected and will be investigated using atom probe tomography (APT)

LA-ICP-MS contents in sphalerite reach 385 ppm Ge, 196 ppm Ga, 2700 ppm Cd, and 66.3 ppm In, and are among the highest reported in sphalerite from Sweden. In contrast, sphalerite from nearby VMS exhibit significantly lower values, which do not exceed 0.49, 53.7, 1644 and 113 ppm respectively. A systematic west-to-east zonation is observed, with higher Ge and Ga concentrations in sphalerite from western localities (e.g. Svärträsk and Lagbäcken) than eastern localities (Rävliden and Nyliden), coincident with an earlier identified T decrease from 150°C to 80°C based on available fluid inclusion data.

Stable (δ¹³C, δ¹⁸O, δ³⁴S) and Pb isotope data indicate precipitation from low-temperature, connate fluids, possibly mixed with organic-bearing fluids. Pb isotopic compositions are distinctly more radiogenic (²⁰⁷/²⁰⁴Pb ~16.2) than Skellefte VMS ores (²⁰⁷/²⁰⁴Pb ~15.1), consistent with Phanerozoic leaching of Pb from Paleoproterozoic rocks during either the opening of the Iapetus Ocean, the Timanian orogeny, or both.

The results indicate previously overlooked exploration potential for Ga-, Ge-, and In-endowed Zn mineralization. The fine-scale heterogeneity in trace element distribution in sphalerite highlights the need for high-resolution analytical workflows to inform studies assessing primary ore as well as by-product potential and tailings revalorization.

This research was carried out in the Impact Innovation programme Swedish Metals & Minerals, a joint initiative by the Swedish Energy Agency, Formas, and Vinnova, and within the ANR project Critical Metals in Orogens (ANR-23-CE01-0017). We thank as well the SFVE-A program 2024 for funding travels between France and Sweden and CAMM-CRM for additional support.

The Rävliden North volcanogenic massive sulfide (VMS) deposit, in northern Sweden underwent polyphase deformation and greenschist to lower amphibolite facies metamorphism during the Svecokarelian orogeny. This caused remobilisation and recrystallisation of ore minerals, whose composition was analysed using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) and electron probe microanalysis (EPMA). Sphalerite, chalcopyrite, and pyrrhotite chemistry mirrors zonation of undeformed VMS deposits. Chalcopyrite-rich mineralisation contains higher Cu, Co, In, and lower Mn concentrations than sphalerite-rich mineralisation. Besides galena, Ag occurs in sulfosalts, tellurides, antimonides, and amalgams, which possibly formed through exsolutions from α-galena in syn- to post-tectonic structures. LA-ICP-MS imaging shows Ag-rich minerals in early syngenetic pyrite, in contrast to syn-metamorphic pyrite, indicating remobilisation during deformation. Despite sampling effects accounted for through linear mixed effects (LME) modelling, the results indicate that syn-metamorphic recrystallisation and remobilisation did not lead to substantial compositional changes in ore minerals. Instead, these processes partitioned Ga between sphalerite and chalcopyrite and enriched Ag, Cd, and Sb in minerals associated with younger parageneses. Zeolite-bearing veins in the hanging wall host sphalerite with the highest Ga, Ge, Cu, and Sb contents and galena with the lowest Bi, Te, and Tl contents. An origin potentially linked to far-field effects of the opening of the Iapetus Ocean or waning Timanian orogeny is discussed based on similarities to other vein- and breccia-hosted Zn Pb deposits in Northern Sweden. This study provides the first multiple-mineral in-situ trace element dataset for a VMS deposit in the Skellefte district, enhances understanding of element redistribution during metamorphism, and identifies remobilised elements potentially vectoring mineralisation at depth. Moreover, this study enables tracing of penalty and by-product elements in downstream beneficiation processes.

Volcanogenic massive sulfide (VMS) deposits belong to the most significant sources of base and precious metals such as Zn, Cu, Pb, Ag, and Au, as well as critical elements such as In, Ga, Ge, Sb, and Bi. Deformation and metamorphism of VMS deposits complicate their exploration and beneficiation. Examples are found in the Skellefte district, northern Sweden, where VMS deposits formed and underwent polyphase deformation (D1, D2, D3) during the 2.0–1.8 Ga Svecokarelian orogeny, imparting structural and mineralogical complexity at various scales. Presence of highly conductive graphitic strata in the host succession complicates direct detection using conventional electromagnetic geophysical techniques, necessitating a larger emphasis on geological and geochemical criteria to guide exploration. This study addresses these challenges by providing an integrated mineralogical, chemical, and textural characterisation of the Rävliden North Zn–Cu–Pb–Ag VMS deposit in the Skellefte district. 

Rävliden North is hosted at the transition between 1.89–1.88 Ga metavolcanic rocks of the Skellefte group and overlying 1.88–1.87 Ga, predominately metasedimentary rocks of the Vargfors group. Massive to semi-massive sphalerite, pyrrhotite, galena, pyrite occurs structurally and stratigraphically above chalcopyrite, pyrrhotite, pyrite-dominated mineralisation. Petrographic and structural analysis reveals textural evidence of sulfides hosted in ductile to brittle structures (e.g. foliations, boudinage, durchbewegt ore, piercement veins, tension gashes, breccia, and veinlets), indicative of polyphase remobilisation. Microanalysis show that sphalerite and chalcopyrite retain a zonation comparable with unmetamorphosed VMS, with enrichment of Cu, Co, and In in chalcopyrite-rich mineralisation. Limited syn-metamorphic redistribution of trace elements occurred beyond partitioning between coexisting sulfides. In-situ δ34S analyses indicate limited isotopic fractionation, with δ³⁴S values tightly constrained at 0 ± 2‰, consistent with a volcanic sulfur source. Meanwhile, variable δ114Cd, δ66Zn, δ56Fe and Zn/Cd ratios in sphalerite suggest an importance of mass-dependent kinetic fractionation with lighter isotopes precipitating near a high-temperature source, albeit volcanic source rocks akin to the Skellefte group can be pinpointed based on Pb isotopes. 

Overprinting, late-Svecokarelian sulfide assemblages (sphalerite, galena, Ag-rich sulfosalts) occur in quartz veins and sulfide-cemented breccia that crosscut ductile fabrics in the hanging wall. These host sphalerite and galena enriched in Cd, Ag, and Sb, and exhibit δ34S values consistent with recycling of syn-sedimentary sulfides, originally formed via sulfate reduction under anoxic deep-ocean conditions. Post-Svecokarelian mineralisation associated with calcite or zeolite (laumontite, heulandite and wairakite) veins and breccia crosscut all ductile fabrics. Distinctive colour-zoned sphalerite with oscillatory trace-element distribution in twins (enriched in Ga, Ge, Cu, Sb) together with δ114Cd, δ66Zn, δ56Fe, Zn/Cd, δ34S, δ15C and δ18O indicate a low-temperature (~150 °C) system involving reduced meteoric to connate water. Mineralogical and Pb isotopic similarities to nearby vein- and breccia-type Zn-Pb deposits indicate derivation from a juxtaposed mineral system at c. 0.5 Ga, linked to far field effects during opening of the Iapetus Ocean or the Timanian orogeny. Future research should test exploration vectors derived from hanging wall mineralisation, perhaps by correlating bulk-rock geochemical proxies with mineral-scale chemistry.

The classification of Rävliden North’s VMS mineralisation based on dominant sulfides, host lithology, and textures allowed the investigation of mineral processing performance. Massive sphalerite-rich mineralisation hosted in amphibole and mica rich rocks differ markedly in grindability and flotation response compared to chalcopyrite-rich veinlets in more quartz-rich rocks. Recovery and concentrate quality for Zn, Cu, and Pb are controlled by mineralogy, liberation and grain size, while trace and critical elements (Ag, Sb, Bi, Cd, Hg, Tl, As) recovery depends on liberation and inter-locking associations with sulfides and sulfosalts. The results allow optimisation of blending protocols that could help enhance recoveries, mitigate deleterious elements, and facilitate exploitation of future by-products such as Bi and Sb. Future research should develop geometallurgical models that capture deposit-scale variability and strategies to recover critical metals as by-products.

The Skellefte district in northern Sweden hosts many volcanogenic massive sulfide (VMS) deposits and is considered one of the most important European mining districts for Cu, Zn, Pb, Ag, and Au. The volcanic and sedimentary rocks that the VMS deposits are hosted in were deformed during the Svecokarelian orogeny, with three documented regional deformation phases. These events imparted a distinct attitude and geometry to the deposits, their host succession, and discordant zones of synvolcanic hydrothermal alteration. Few studies have investigated the detailed deformation effects on the sulfide minerals.

In this contribution, we document the structural characteristics and remobilization history of mineralization at the Rävliden North Zn-Pb-Cu-Ag deposit—one of the most important recent discoveries in the district consisting of 8.5 million tonnes (Mt) grading 1.01% Cu, 3.45% Zn, 0.53% Pb, 78.60 g/t Ag, and 0.23 g/t Au. At Rävliden, massive to semimassive sphalerite-rich mineralization with lesser pyrrhotite, galena, pyrite, and silver minerals occurs structurally above stringer-type mineralization dominated by chalcopyrite, pyrrhotite, and pyrite. These mineralization types exhibit evidence of deformation and remobilization such as (1) sulfide-alignment parallel to tectonic foliations; (2) rounded wall-rock tectonoclasts in a ductile deformed sulfide matrix (“ball ore” or durchbewegt ore); and (3) sulfides in tension gashes, strain shadows, piercement veins, and late, straight veinlets crosscutting tectonic fabrics. These features are attributed to polyphase deformation during the D1, D2, and D3 events at temperature ranging from 200° to 550°C. Remobilization of sulfides was mostly within the bounds of the main mineralization (i.e., 10–100 m), with few local external occurrences. A combination of solid-state and fluid-assisted remobilization processes are inferred.

Rare brittle veinlets and zeolite-cemented breccias with sphalerite, galena, and silver minerals occur in the stratigraphic hanging wall, where they crosscut all Svecokarelian structures. This mineralization type is highly reminiscent of Phanerozoic low-T vein- and breccia-hosted Pb-Zn deposits of the Lycksele-Storuman area west of Rävliden North, which have been linked to far-field effects associated with the opening of the Iapetus Ocean (0.7–0.5 Ga). We suggest that this Zn-Pb mineralizing event led to the formation of the late sulfide-zeolite veinlets and breccias at Rävliden North, and that elements such as Ag and Sb within this mineralization were locally remobilized from Rävliden.

Lithofacies logging from Rävliden North in the Skellefte district is presented, and the use of lithostratigraphic names in deposit scale mapping is discussed. The authors conclude that while Skellefte district nomenclature can be applied, it cannot preserve the level of detail relevant to exploration

The Rävliden North volcanogenic massive sulphide (VMS) deposit and its host rocks exhibit a shared history of metamorphism during the 1.88–1.86 Ga deformation phases of the Svecokarelian orogeny. Predominantly internal sulphide remobilisation produced minor modifications to the overall pre-metamorphic trace element distribution including remobilisation. Post-Svecokarelian sulphide-bearing zeolite- and calcite veinlets cross-cut the stratigraphic hanging wall suggesting mobilisation of sulphides in a fluid phase during an overprinting later event unrelated to the VMS mineralisation.

The discovery of new mineral deposits is essential to meet the increasing demand for metals in our society. The Skellefte mining district in Northern Sweden is one of the main producers of polymetallic ores of Cu, Zn, Pb,Ag, Au, and Te in Europe. Discovery of new deposits in the Skellefte district has become increasingly challenging due to exhaustion of near surface deposits, and general difficulties when applying traditional exploration methods at depth. This has stimulated an interest in alternative methods, such as utilizing the trace element chemistry of sulphide minerals (e.g. pyrite) in metasedimentary and metavolcanic rocks to vector in on massive sulphide deposits. Meanwhile, there is a near complete paucity of trace element data from the massive sulphide deposits of the Skellefte district, and a global shortage of data from Palaeoproteroizoic, polydeformed and metamorphosed volcanogenic massive sulphide deposits (VMS).

The Rävliden North Zn-Pb-Cu-Ag VMS deposit in the western most part of the Skellefte district, offers a great opportunity for combine in-situ trace element studies with paragenetic analysis to assess if vectors to mineralisation can be defined, and the effects of deformation and metamorphism. The deposit is hosted at the transition from the mainly felsic metavolcanic rocks of the Skellefte group to the mainly pelitic metasedimentary and mainly mafic – intermediate metavolcanic rocks of the Vargfors group. Rävliden North was significantly affected by deformation and greenschist – lower amphibolite facies metamorphism during the 1.88 – 1.86 Gadeformation phases of the Svecokarelian orogeny. Sphalerite-rich mineralisation associated with pyrrhotite, galena, pyrite and Ag-minerals is situated structurally and stratigraphically above stringer-type chalcopyrite-richmineralisation with lesser pyrrhotite, pyrite and minor amounts of Ag-minerals. Analysis of the textural and structural paragenesis of the mineralisations in the deposit show that sulphides range from aligned sub-parallel to three foliations (SC, S2, S2L), to hosted by tectonic structures such as tension gashes, piercement veins, veinlets, breccias and plastically deformed sulphide ore with rounded tectonoclasts (‘ball ore’). Sulphide occurrences associated with quartz veinlets and sulphide-cemented breccias cross-cutting poly-stage ductile structures could be the result of remobilisation under brittle conditions during the late stages of the Svecokarelian orogeny or afterwards. In-situ minor and trace element data from sphalerite, pyrite, sulphosalts, tellurides, antimonides and amalgams indicate trace element distribution patterns that can be related to primary ore formation followed by subsequent redistribution during the main phases of metamorphism and deformation.

Sphalerite from the stringer-type chalcopyrite-rich mineralisation has a higher In, Co, Cu content, and a lower Mn content compared with sphalerite from the sphalerite-rich mineralisation. This trace element zonation resembles that of common VMS deposits, and is thus interpreted as retained from primary mineralisation. The Feand Cd content in sphalerite shows little variation in the sphalerite-rich mineralisation compared with the chalcopyrite-rich mineralisation, and do not exhibit any systematic variation relative to deformation textures. This can be explained by syn-metamorphic recrystallisation that could have equilibrated the composition of sphalerite. Sulphosalts, tellurides, antimonides, and amalgams are associated with galena and chalcopyrite in syn- to post-tectonic structures relative the main phase of deformation. The Ag-mineralogy seem to have formed during the retrograde phase of metamorphism as exsolutions from α-galena when temperatures decreased from 500 to 200C. However, LA-ICP-MS imaging of pyrite grains reveal co-precipitation of early syngenetic pyrite, base metalsulphides, and silver-rich minerals, and subsequent syn-metamorphic pyrite growth and remobilisation of the latter. This suggest that besides causing a significantly higher Ag content in paragenetically younger mineralisation types, syn-metamorphic remobilisation may have not extensively modified the mineralisations at Rävliden North.

Sphalerite associated with low temperature Ag-sulphosalt-, zeolite- and calcite-bearing veinlets and breccias in the stratigraphic hanging wall contain the highest contents of Ga, Ge, Sb and Cu in the area. Comparison with sphalerite in similar style of mineralisation in the Lycksele-Storuman area, west of Kristineberg, suggest a contemporaneous origin. They possibly formed as a result of a mineralising event related to the opening of the Iapetus Ocean (0.7 – 0.5 Ga) or the waning stages of the Timanian orogeny (0.6 – 0.5 Ga). Although unrelated to the VMS deposit, the late-stage veins in the stratigraphic hanging wall of Rävliden North can still be of some aid during mineral exploration as they likely contain some components that were sourced locally via remobilisation (e.g. Ag and Sb).

Remobilisation of sulphides in metamorphosed volcanic-hosted massive sulphide deposits has been investigated in many VMS districts with regards to scale, mineral assemblages, texture and relative competence of minerals under certain p-t conditions (Gilligan & Marshall, 1987; Marshall & Gilligan, 1987). Examples of syn-tectonic remobilisation can be found at the Rävliden Norra (RVN) volcanic-hosted massive sulphide in the Skellefte district. At Rävliden, polymetallic sulphide mineralization occurs at the transition from meta-volcanic rocks of the Skellefte group rocks to the overlying Vargfors group, comprising volcaniclastic metasedimentary rocks and graphitic shales. This contribution details features of mesoscale (0.1-50 cm) remobilisation of sulphides, such as sulphide-rich veins, tension gashes, ball-ore, massive sulphides with cataclastic texture, and micro-scale features such as infilling of pressure shadows, displaying evidences of brittle and ductile deformation. Sulphide-rich veins containing sphalerite, galena, and a relative high content of Ag-sulphosalts (e.g. freibergite, pyrargyrite, pyrostilpnite) are hosted in the hanging wall (HW) of the RVN mineralization. Brittle deformation is shown in accessory quartz and calcite as bulging recrystallization, grain boundary migration and deformation lamellae or twinning. Ductile expressions include ball-ore (i.e. “durchbewegung”) textures, typically made up of two components, one composed of clasts of graphite shale or tremolite-, actinolite-, talc-altered meta-volcanic rocks and the other comprising a matrix of massive sulphide mineralization. In the massive sulphide matrix of sphalerite, chalcopyrite or pyrrhotite, micro-scale tension gashes and/or pressure shadows occur around clasts infilled by pyrrhotite, chalcopyrite, galena, freibergite, boulangerite, or gudmundite. A similar mineralogy is observed in ore lenses in the ore zone, comprising sphalerite, galena and Ag-Sb-As sulphosalts, hosted structurally above chalcopyrite + pyrrhotite stringer zones in the footwall (FW). Sulphosalts and galena present a high silver content relative to other VMS deposits in the district. This is evidenced by SEM and EMPA analysis in both HW and FW ore lenses. Argentopyrite, sternbergite and stephanite are also locally present in the HW as minor silver species hosted in veins. Inclusions of freibergite in galena contain Ag with average values of 18.4 wt. % in the HW (n=5), 18 wt. % in the massive sphalerite and ball-ore (n= 15), and 20.2 wt. % in the chalcopyrite + pyrrhotite stringer zone (n= 5). Similarly, Pb is 0.2 wt. %, 0.3 wt. %, and 0.4 wt. %, respectively. For sphalerite, Fe is on average 8.0 wt. % (n=3), 7.4 wt. % (n = 11), and 8.3 wt. % (n=3), respectively. Our preliminary results suggest that mineralization in the HW is remobilized from the main ore and textural relationships support a hypothesis that remobilisation involved a relative silver-enrichment in paragenetically later assemblages. At least two stages of deformation in the deposit can be recognized. In the first stage, sphalerite- and chalcopyrite-rich mineralization was deformed along with tremolite and talc to form a S1 foliation. The second stage involved folding of S1, and remobilisation of galena, chalcopyrite and Ag-Sb-As sulphosalts as veins or breccia infill in the HW or filling tension gaps or ball-ore, in the FW. These are often parallel to S2 crenulation or axial planes.