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Bleikvassli

Norway

Main commodities: Zn Pb Cu
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The Bleikvassli massive sulphide lead-zinc-copper deposit is located in northern Norway, 50 km south of the Arctic Circle, 70 km SSW of Mo i Rana, 300 km NE of Trondheim and 30 km west of the Swedish border.

The deposits at Bleikvassli are hosted within the Scandinavian Caledonides, a belt of Neoproterozoic to early Palaeozoic rocks emplaced as a series of thrust nappes (Roberts and Gee 1985; Hacker and Gans 2005), that overlie the Palaeoproterozoic rocks of the Fennoscandian Shield and constitute the northernmost section of the composite Caledonian-Appalachian belt in Scandinavia and eastern North America (Grenne et al., 1999).

The nappes forming the Caledonides have been grouped into four main allochthons, the Lower, Middle, Upper, and Uppermost Allochthons (Roberts and Gee 1985). The Bleikvassli deposit is hosted by a highly deformed Proterozoic pelitic, quartzo-feldspathic and amphibolitic rocks of the Kongsfjellet Group in the Rödingsfjället Nappe Complex of the Uppermost Allochthon.

The deposit is hosted by the upper Kongsfjellet Group, within an ~1 km thick unit referred to as the "Mine Sequence", which contains a heterogeneous succession of metasedimentary rocks, primarily composed of garnet-mica, kyanite, graphite and calcareous schists, marbles, quartzites, feldspathic gneisses and amphibolites. The orebody is contained within the lower Mine Sequence, which is dominated by feldspathic gneisses and quartzites. The upper Mine Sequence is more schistose and contains more marble and calcsilicate rocks. A Neoproterozoic age for the hosts is indicated by intrusive relationships.

The massive sulphides were stratabound within lithologies comprising garnet-mica schist with interlayers of quartzite, graphite schist, calcareous mica schist and amphibolite.   In the vicinity of the ore the hosts were staurolite-kyanite gneisses and microcline gneisses, interpreted to represent metamorphosed felsic tuffs.

Ore was developed over a strike length of 1500 m with an average width of 20 to 25 m, dipping 40 to 90° to the NW. It comprised a series of interconnecting and branching lenses of massive sulphides concordant with the schistosity, divided into southern, northern and northernmost ore lenses, connected by a zone of disseminated sulphides. The major axes of these elongated lenses plunge NE. The southern lens has a sharp (probably tectonic) termination, while the northernmost lens continues below Lake Bleikvatn. A 500 m segment of the southern lens outcrops where the orebody reaches its maximum thickness of 15 m. In the northern lens, the ore is typically 2 to 3 m thick. Thickness variations may be due to post-ore deformation, as the deposits have been isoclinally folded and extensively sheared.

The orebody is composed of individual lenses of massive sulphide, intimately interlayered and generally concordant with the wall rocks. Three types of ore have been recognised,
i). massive pyrite - which commonly contain sphalerite, galena and chalcopyrite, with minor arsenopyrite, and Cu-, Pb- and Ag-bearing sulphosalts and rare magnetite. This is the dominant type and is mainly in the footwall;
ii). massive pyrrhotite, which contains the same assemblage of other sulphides, although chalcopyrite is more abundant than in the pyrite ores; and
iii). veinlets in the wall rocks, primarily the hanging wall, occurring as veins and pods within 5 m of the orebody, composed of the same sulphides as in the two massive sulphide ore types.;

The deposit was discovered in 1917, with production commencing in 1952 based on a reserve of 2.6 Mt @ 2.4% Pb, 4.2% Zn, 0.22% Cu, 17% S.
Production between 1957 and 1997 totalled 5.0 Mt @ 4.0% Zn, 2.0% Pb, 0.15% Cu (Bjerkgård, 1999).

The most recent source geological information used to prepare this summary was dated: 1989.     Record last updated: 22/11/2012
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Cook N J, Spry P G, Vokes F M  1998 - Mineralogy and textural relationships among sulphosalts and related minerals in the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway: in    Mineralium Deposita   v34 pp 35-56
Rosenberg F M, Spry P G, Jacobson C E, Cook N J, Vokes F M  1998 - Thermobarometry of the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway : in    Mineralium Deposita   v34 pp 19-34
Rosenberg J L, Spry P G, Jacobson C E and Vokes F M  2000 - The effects of sulfidation and oxidation during metamorphism on compositionally varied rocks adjacent to the Bleikvassli Zn-Pb-(Cu) deposit, Nordland, Norway: in    Mineralium Deposita   v35 pp 714-726


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