| Summary: | The Salmijärvi deposit in northern Norrbotten, Sweden, is a satellite to the giant Aitik deposit and sets 600 m towards the south of Aitik. A recent expansion program in Aitik included the opening of the Salmijärvi mine to meet the increased production demand of 36Mt of ore annually. The new deposit adds 115 Mt of ore to the total resources of Aitik (747 Mt) and expands the mine life with 19 years. This study describes the geology of the Salmijärvi deposit with emphasis on veins, especially mafic veins with a light halo containing abundant ore minerals that are typical of this locality. The information is based on field mapping, drill-core logging, light microscopy, and microprobe analysis. The rocks of Salmijärvi belong to the Porphyrite group and the Kiruna Porphyry group described by Martinsson et al. (1995) and are metamorphosed to amphibolite facies. Several rock units are recognized including amphibole-biotite gneiss, biotite-amphibole gneiss, K feldspar-altered amphibole-biotite gneiss, biotite gneiss, amphibolite, hornblende-banded gneiss, and quartz diorite. The mineralogy is dominated by plagioclase and amphibole with additional biotite, minor quartz and traces of sphene. The deposit is strongly characterized by dark veins composed mainly of magnesio-hornblende making the interior of the veins, and plagioclase forming the surrounding light rims. Ore minerals are chalcopyrite and pyrite containing trace amounts of gold and silver. The ore minerals in the dark veins are generally of larger grain size and surrounded by an oxide rim, while the ore minerals in the matrix have smaller grain size and lack oxide rims. The fluids forming the dark veins has been suggested to be the result of regional metamorphism in addition to the movement of major crustal structure. However, a mafic constituent cannot been excluded. The source of metals in dark veins has not been identified in this study but remobilization of the primary mineralization is suggested as a probable scenario. The Salmijärvi deposit is most likely ...
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