Hydrothermal alteration and host rock characteristics of the Rautuoja Iron oxide-Copper-Gold deposit

• Main Author: Ullgren, Aki
• Other Authors: Helsingin yliopisto, Matemaattis-luonnontieteellinen tiedekunta, Geotieteiden ja maantieteen laitos, University of Helsinki, Faculty of Science, Department of Geosciences and Geography, Helsingfors universitet, Matematisk-naturvetenskapliga fakulteten, Institutionen för geovetenskaper och geografi
• Format: Master Thesis
• Language: English
• Published: Helsingfors universitet 2013
• Subjects: Geology; Geologia; Geologi; Haparanda; Kolari; Pajala; Savukoski; Wall Rocks
• Online Access: http://hdl.handle.net/10138/230472

The Rautuoja deposit lies at the contact of the ca. 1.86 Ga Haparanda Group Monzonite-Diorite intrusions and the Savukoski Group supracrustal rocks. The deposit is adjacent to the SSW-NNE trending shear zone that is a part of the Kolari-Pajala shear structure. The deposit consists of disseminated type Fe-Cu-Au mineralization. The deposit also contains skarn-hosted magnetite lenses and bands. The hanging wall rocks consist of monzonites and hydrothermally altered diorites and the footwall rocks consist of hydrothermally altered metavolcanic rocks. The deposit also contains strongly albitized rocks, referred to as albitites. The deposit also contains quartz veins that are located in the proximal ore zone. The quartz veins have correlation with the Au and Cu grades.The main oxide mineral in the deposit is magnetite, and the main sulphide minerals are pyrite, chalcopyrite and pyrrhotite. Native gold can be found with pyrite and chalcopyrite. Rock types associated with the Rautuoja deposit are categorized to five different lithologies: monzonite, diorite, albitite, skarn and amphibolite. The main alteration minerals in the Rautuoja deposit are albite, magnetite, biotite, clinoamphiboles (tremolite, actinolite, hornblende), potassium feldspar, quartz and sulphides (chalcopyrite, pyrite, pyrrhotite). Minor alteration minerals include apatite, titanite, chlorite, carbonate, epidote, andradite and hematite. Alteration textures are variable and primary textures are destroyed mostly due intense alteration. Hydrothermal alteration in the Rautuoja IOCG deposit consists of sodic, potassic, calcic-iron, silicic and late calcic alteration stages. Primary rock types in the Rautuoja deposit were distinguished by Zr-TiO2, Zr-Al2O3 and TiO2- Al2O3 ratios. Textural-based protolith recognition is controversial because the alteration has destroyed most of the primary textures in the host rocks. The trend that can be distinguished in the immobile element ratios indicates different origins for the diorite and monzonite in the Rautuoja ...