| Summary: | The Nautanen deposit in northern Sweden, which was mined in the beginning of the 20th century, is regarded as an IOCG deposit. It is located within the Nautanen deformation zone (NDZ), which generated a steep, almost vertical, tectonic structure, with later shearing and faulting, which created an offset of the NDZ. The alteration and deformation are so intense and pervasive in the NDZ that it is difficult to interpret the original character of the rocks. The Lina River fault splits the Nautanen area in two; to the east of the fault are the metavolcanoclastics and meta-arenites of the Muorjevaara formation, together with the Lina granite. To the west and south of the fault are granites, gabbros and the Kiruna Porphyries. The mineralization in this area consists of chalcopyrite-pyrite, minor magnetite, pyrrhotite and traces of bornite and is mainly disseminated, but it also occurs in structurally controlled small-scale microfractures. Garnets occur frequently in the area together with the mineralization.The aim of this study is to determine if multiple phases of garnet are present, to deduce the P-T conditions of the garnet formation and to determine if there is a relationship between the mineralization and the garnet occurrence. Petrographic studies and SEM/Microprobe work have been performed to investigate the chemistry of the garnets and geothermobarometrical calculations to deduce the P-T conditions. Cataloguing the garnets has been done to distinguish their variety and distribution at Nautanen. Garnet occurs in all rock types in Nautanen, especially in the various types of biotite-gneiss. The areas close to and/or within the mineralization contain more and larger garnets, which occur in combination with strong biotite/sericite alteration. It is rare to find Cu-mineralization in this area in a garnet-absent rock. Most of the garnets in Nautanen are euhedral and vary in size from tiny (<3mm) up to 10 cm in size, but the most common size is small (3-5mm). The garnets are rich in spessartine with almandine, ...
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