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).
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:ltu-93607 |
| Date | January 2022 |
| Creators | Rincon, Jonathan |
| Publisher | Luleå tekniska universitet, Geovetenskap och miljöteknik, Luleå |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Licentiate thesis, comprehensive summary, info:eu-repo/semantics/masterThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | Licentiate thesis / Luleå University of Technology, 1402-1757 |
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