Mineral Resources on Svalbard

NHM researcher: Nigel J. Cook and Tom V. Segalstad

This page in Norwegian

Cook has focussed on the mineralogy of some metalliferous deposits in Spitsbergen. Ores of zinc and lead occur within rocks of the Proterozoic Hecla Hoek Complex (HHC) along the west coast. The deposits of Kapp Mineral and Sinkholmen are hosted within low-grade metamorphic rocks, but close to Tertiary fault zones separating the HHC from younger Paleozoic successions. At Kapp Mineral, sphalerite and galena occur within a brecciated carbonate phyllite several m in width and containing crosscutting cm-scale calcite veins; many are barren, others contain sphalerite+galena. High-grade Zn-ore has been mined from Sinkholmen, a small island in Bellsund ( Picture 3 ), a massive breccia of rock fragments cemented by sphalerite, quartz, calcite and fluorite. Pyrite, chalcopyrite, galena, bornite, idaite, chalcocite, digenite, covellite and Ag-tetrahedrite are also present. Field relationships suggest a replacement origin. Both occurrences are hosted by rocks affected by the Paleogene West Spitsbergen orogen and are likely to be Tertiary or younger in age.

Quaternary volcanic centres (Bockfjorden Volcanic Complex, BVC) are aligned along the N-S trending Breibogen fault in NE Spitsbergen, separating Devonian units from HHC basement. Sigurdfjell ( Picture 4 ) is a 4.5 km long ridge of coarsely-bedded pyroclastics and rare alkaline basalts penetrated by explosion vents. The Sigurdfjellet mineral occurrence, on the southern flank of the stratavolcano, about 1 km from the peak, comprises Cu-stained boulder float with moderate amounts of base-metal sulfides (chalcopyrite, tennantite, bornite, chalcocite, digenite, covellite). Although the mineralisation may relate to the Quaternary volcanic episode, the ores are clearly associated with major N-S-trending faults that separate HHC basement from the Devonian successions, suggesting that mineralisation at Sigurdfjell either pre-dates volcanism or possibly represents reworking of pre-existing ore.

Paleozoic sedimentary units unconformably overlie and are overthrust onto an older blueschist-eclogite complex in Oscar II Land. Cr-mica -bearing dolostones within the metamorphic complex correspond to hydrated ultrabasic rocks of the lower-grade unit of the Motalafjellet Metamorphic Complex. Together with other highly-altered rocks, these have been described by the Russian teams who discovered the deposits as 'listwænites'. Ore occurrences, as both veins and impregnations, containing galena, sphalerite, chalcopyrite, subordinate tetrahedrite-tennantite, millerite, arsenopyrite and anomalous precious metals, are found associated with these rocks south of St. Jonsfjord. Cu-dominant base-metal mineralisation is well-exposed in boulders on the NW side of Motalafjellet ( Picture 5 ). The mineralisation is dominated by fine-grained jordanite, subordinate chalcocite, chalcopyrite and tetrahedrite, altered to azurite and malachite.

Svalbard contains several other tantalising examples of mineralization which urgently need additional study in order to understand their origin. The Farmhamna hematite ores, for example ( Picture 6 ) are clearly post-Carboniferous and epigenetic. Could these too be related to Tertiary volcanism or hot spring activity?

Numerous hydrothermal vein fillings of calcite [magnesian], dolomite, barite, sphalerite, galena; fluorite; chalcopyrite; witherite, strontianite; and occasional late quartz with barite and dolomite (general crystallizing sequence) occur at Bjørnøya [B] (74°N) and along the western part of Spitsbergen (77-79°N) in the Svalbard archipelago of the Arctic. As part of their study of the geochemistry of hydrothermal mineralizing systems at Spitsbergen and Bear Island, Segalstad and co-workers have used stable and radiogenic isotope data to identify the sources of metals in the ores.

Most veins occur in Late Precambrian to Ordovician sandy and calcareous sedimentary rocks. Some veins occur in Late Devonian to Early Permian siliciclastic Red Bed deposits. Barite veins also occur in Devonian strata on N Spitsbergen at Sigurdfjellet with a Cu-Pb-sulphide assemblage, and at Zeipeldalen ( Picture 7 ) and Ridderborgen without sulphides. All veins are spatially (and genetically?) related to large-scale post-Devonian faults. The age and genesis of these veins are unknown. Segalstad et al. (2006, 2008) have found these epigenetic vein fillings cutting sedimentary strata through the complete stratigraphy, from Late Precambrian through Permian; hence field evidence shows a Triassic or younger age. The heat source may have been the adjacent Tertiary Vestbakken volcanism associated with the Atlantic rifting.

The fluid inclusions found are, unfortunately, too small for microthermometry. δ¹⁸O of a coexisting calcite - dolomite assemblage yielded an equilibrium temperature of 180°C for a vein at Bjørnøya. δ³⁴S in all sulfides range -0.6 to 12.7‰; in all barites 13.4 to 27.0‰. Coexisting sulfides - barite show ∆³⁴S of -0.2 to 26‰; no equlibrium values, as expected from the relatively low hydrothermal temperature. Bjørnøya and Spitsbergen show different δ³⁴S. Bjørnøya barites have high δ³⁴S like Precambrian - Ordovician seawater, as expected from the local Hecla Hoek wallrocks. Computed δ³⁴S of H₂S in equilibrium with sulphides reach the value of Permian evaporites, a possible source of S. Similar low δ³⁴S is found at Sigurdfjell and Sinkholmen in Spitsbergen. Barite from Ridderborgen and Zeipeldalen show intermediate δ³⁴S like their wallrock Devonian sulphate. Early vein carbonates at Bjørnøya show high δ¹⁸O and δ¹³C like for wallrocks; later vein carbonates show low δ¹⁸O and δ¹³C, indicating mixing with a different fluid carrying oxidized coal. A deep crustal fluid with metals, Ba, and Cl, mixed with a descending fluid carrying dissolved evaporite sulphate, partly reduced to H₂S by local coal beds; depositing the vein barite and metal sulphides.

Galena Pb isotopes from Bjørnøya and Sigurdfjell give two ²⁰⁶Pb/²⁰⁴Pb populations, 18.180 and 18.346. In spite of a huge hydrothermal system, fluids must have leached a relatively homogeneous source within a short time. The vein Pb source was eroded Caledonian crust, homogenized during transport to Devonian sedimentary basins. The hydrothermal fluids leached Pb while percolating towards lower stratigraphic levels, precipitating galena with sphalerite and barite in fractures. The bimodal isotopic pattern can be explained by two hydrothermal cells of slightly different sizes, activated shortly after each other.

 Publications

Cook, N.J., Kjærnet, T. (2008): Mineralogy and paragenesis of selected base metal deposits, NW Spitsbergen, Svalbard. 33^rd International Geological Congress, Oslo, August 6 th - 14 th 2008, Abstract CD-ROM.

Segalstad, T.V. 2008: Metallogeny of the Arctic Region - Convener's Introductory Lecture . 33^rd International Geological Congress, Oslo. 8 Aug. http://folk.uio.no/tomvs/Metallogeny-Arctic_IGC33.pdf

Segalstad, T.V., Sundblad, K. & Kjærnet, T. 2006: Stable isotope evidence for Ba-Pb-Zn vein mineralizations by fluid circulation in the sedimentary basin at Svalbard. Geological Survey of Finland Bulletin, Special Issue 1 , 143.

Segalstad, T.V., Sundblad, K. & Kjærnet, T. 2008: Metallogeny of Pb-Zn-Ba vein mineralizations in Svalbard, Norwegian Arctic. 33^rd International Geological Congress, Oslo. 8 Aug.

Sundblad, K., Andersen, T., Kjærnet, T., Segalstad, T.V., Aasum, L. & Wernigsen, C. 2006: Source of lead in Mesozoic baryte-galena-sphalerite mineralization at Svalbard. Geological Survey of Finland Bulletin, Special Issue 1 , 157.