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.

The Rävliden Norra VMS deposit, represents one of the most important new discoveries in the Skellefte district (SD) in this decade. The mineralization is hosted at the transition between Skellefte group rocks (SG), dominated by coherent rhyolitic and dacitic meta-volcanic rocks, and the Vargfors group (VG), composed of metasedimentary graphitic shale interbedded with crystal-rich, monomictic to polymictic, clast-supported mass flow deposits. The ore lenses contain massive sphalerite + galena + pyrite + pyrrhotite + chalcopyrite ± Ag-Sb-Pbsulphosalts, structurally and stratigraphically above chalcopyrite + pyrrhotite stringer mineralization. The hanging wall rocks (VG) host pyrite + pyrrhotite ± arsenopyrite mineralization. Alteration in the footwall rocks, consists of sericite, chlorite, quartz, pyrite, tremolite, actinolite, carbonate and talc. The hanging wall is less altered with limited sericite or chlorite associated with minor carbonate alteration. Post ore modifications occur as, e.g. sulphides in pressure shadows, infilling of syntectonic tension gashes, “durchbewegung” texture, and sulphide-rich veins that crosscut hanging wall rocks. Significant changes in the distribution and deportment of trace and precious elements within the deposit are evident, however the implications of these on mineral processing performance and exploration vectoring has not previously been assessed in other VMS deposits in the SD. To this end, the presence of pyrite and remobilised sulphides in both hanging wall and footwall of the Rävliden Norra mineralizations, provides an opportunity to evaluate enrichment or depletion of elements hosted in the sulphide lattices or as inclusions using LA-ICP-MS. In-situ SIMS analyses in sulphide phases will allow discrimination between sedimentary and hydrothermal sulphur in the system. An investigation into the deportment of In, Ga and Ge in sphalerite and galena, will be the first assessment of these critical elements in a VMS deposit in the SD. Ultimately, integration of elemental distribution and mineral features, such as modal mineralogy, liberation degree, and grain size, with processing variables, e.g. mineral recovery, grade or flotation kinetics; will provide a better understanding of the ore performance during concentration and beneficiation.

The Colombian Andes are the product of the interaction of terranes with different geological affinity, such as the Western Cordillera, which is made up of blocks of oceanic affinity, that have been accreted to the western boundary of pre-existing terranes with continental affinity. The study area is geologically dominated by the Sabanalarga Batholith, which has at least two facies, gabro-diorite and tonalitie-granodiorite, that intrude the Barroso Formation. Both units have been affected strongly by regional faults generating large areas of mylonites closely related with hydrothermal alterations and mineralization occurrences. Due the clear intrusive relationship between the Sabanalarga Batholith and Barroso Formation, and due the Cauca-Almaguer fault cuts both units without separating them, it is suggested that the Terranes Theory must be reconsidered in this part of the country, because the Cauca-Almaguer fault do not correspond to the boundary between Calima Terrane and the terranes Arquía and Quebradagrande.

Los Andes Colombianos son el producto de la interacción de terrenos de diferente afinidad geológica, como la Cordillera Occidental, conformada por bloques de afinidad oceánica acrecionados al límite occidental de terrenos preexistentes de afinidad continental. La zona de estudio está dominada geológicamente por el Batolito de Sabanalarga, el cual presenta al menos dos facies, una gabróica-diorítica y una tonalítica-granodiorítica, que intruyen a la Formación Barroso. Ambas unidades se presentan intensamente afectadas por fallas regionales, dando origen a extensas zonas de milonitas íntimamente relacionadas con mineralizaciones y alteraciones hidrotermales. Dada la clara relación intrusiva entre el Batolito de Sabanalarga y la Formación Barroso, y que la Falla Cauca-Almaguer corta a ambas unidades sin separarlas, se sugiere que la Teoría de Terrenos debe ser replanteada en esta parte del país, pues la falla Cauca-Almaguer no correspondería al límite entre el Terreno Calima y los Terrenos Arquía y Quebradagrande.