Norbotten, Sweden

Main commodities: Cu Au Fe
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The Tjårrojåkka Fe-Cu-Au occurrence is located approximately, 50 km WSW of Kiruna in the Norbotten district of northern Sweden. It is one of the best examples of spatially, and possibly genetically, related apatite-iron and copper-gold deposits in the region.

The regional tectonic setting is dominated by major crustal ductile deformation zones, the trends of which varies from NW-SE to pure N-S and NNW-SSE. The mineral occurrences of the Tjårrojåkka area however, appear to show a spatial relationship to a second order E-W fault, within a major NW-SE trending deformation zone.

The local bedrock is predominantly composed of supracrustal Svecofennian (~1.96 to 1.85 Ga), rocks intruded by younger and/or coeval plutonic rocks. The supracrustal rocks comprise intermediate to mafic volcanites (Porphyrite and Kirunavaara Group, respectively) which have been metamorphosed to amphibolite facies. Intrusive rocks range from gabbroic-dioritic to quartz-monzodioritic compositions. Several mafic and intermediate dykes intrude the metavolcanic rocks. The area has been strongly tectonised with at least three deformation events having been identified.

The Tjårrojåkka iron deposit is a typical Kiruna-type apatite-magnetite ore, while the Tjårrojåkka copper occurrence shows the same characteristics as most other epigenetic deposits in Norrbotten,

Regional and local sodic alteration (scapolitisation) is evident in the district, and is particularly intense in mafic extrusive and intrusive rocks. Potassic alteration, expressed as enrichment in K-feldspar and biotite, is developed in andesitic rocks and appears to be related to fracture/deformation zones.

Albitisation is present in proximity of the major Cu occurrence and is associated with the apatite-magnetite veins zone, which represents the "structural-footwall of the Cu occurrence.

The juxtaposition of albite and K-feldspar alteration within the host rocks, has resulted in an enrichment of Na, K, and Ba.   Fe and V were depleted in the altered zones and added in mineralised samples. REE were enriched in the system, with the highest concentrations accompanying the mineralisation.

The Fe-mineralisation occurs as an apatite-magnetite (Kiruna-type) deposit, with a massive magnetite core (60 to 67% Fe), surrounded by a magnetite breccia, containing 25% to 60% Fe. The host rock is an altered (albitic and potassic) andesite.

The Cu-mineralisation occurs within andesitic hosts and consists of chalcopyrite, magnetite and bornite with hematite, pyrite, chalcocite and covellite. The top of the mineralised body is located immediately beneath the bedrock surface. The deposit extends to a depth of ~450 m, is ~650 m long, and 10 to 60 m thick. A magnetite rich zone is recorded in proximity of the Cu-prospect and seems to be related to the albitic alteration.

Both the Fe and Cu mineralised bodies are elongated in an approximate SW-NE direction and dip almost vertically.

The Tjårrojåkka iron and copper deposits show comparable hydrothermal alteration minerals and paragenesis. Mineralogy and mineral chemistry of the principal alteration minerals, apatite, scapolite, feldspars, amphiboles and biotite, indicate a higher salinity and Ba/K ratio in the fluid related to the alteration in the apatite-iron occurrence compared to the copper deposit, where the minerals are enriched in F and S. The presence of hematite, barite, and SO4 in scapolite suggests more oxidising-rich conditions during the emplacement of the Tjårrojåkka-Cu deposit.

The copper deposit is estimated to contain 3.2 Mt @ 0.87% Cu.

The most recent source geological information used to prepare this summary was dated: 2005.    
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
   Selected References:
Edfelt A, Armstrong R N, Smith M and Martinsson O  2005 - Alteration paragenesis and mineral chemistry of the Tjarrojakka apatite-iron and Cu (-Au) occurrences, Kiruna area, northern Sweden: in    Mineralium Deposita   v40 pp 409-434
Sandrin A and Elming S A,  2007 - Physical properties of rocks from borehole TJ71305 and geophysical outline of the Tjarrojakka Cu-prospect, northern Sweden: in    Ore Geology Reviews   v30 pp 56-73

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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