Garnet Occurrence and its Relationship to Mineralization at the Nautanen Deposit, Northern Sweden
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
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, and there are also examples of Ca-rich spessartine. The majority of the garnets contain inclusions, mainly Qz and Bt, but some rare garnets also contain minor Py and Mag. The inclusions exhibit both pre- and syn-kinematic textures, but since no Cu-mineralization occurs within the Garnets, it implies that the Cu could have originated from a younger event than the garnet formation. An estimate of 630-680˚C at a pressure of 6.5 kbar has been obtained for the conditions of garnet-rim formation based on GB-GBPQ and Thermocalc calculations from three different thin section samples containing Grt, Bt and Pl.
Place, publisher, year, edition, pages
2015. , 84 p.
IdentifiersURN: urn:nbn:se:ltu:diva-59060Local ID: f97091bd-3bd8-4926-834c-81e2994e59ffOAI: oai:DiVA.org:ltu-59060DiVA: diva2:1032448
Subject / course
Student thesis, at least 30 credits
Natural Resources Engineering, master's
Validerat; 20150410 (global_studentproject_submitter)2016-10-042016-10-04Bibliographically approved