Petrographic, mineralogical and geochemical study of the Mäkärä Au-Fe mineralization, Tanaelv belt, northern Finland

• Main Author: Vesilahti, V. (Ville)
• Format: Master Thesis
• Language: English
• Published: University of Oulu 2016
• Subjects: Geotieteiden koulutusohjelma; Northern Finland; Lapland
• Online Access: http://jultika.oulu.fi/Record/nbnfioulu-201701031025

Abstract. The Mäkärä mineralization is located in the Tanaelv Belt next to the Lapland Granulite Belt. It is a hydrothermal vein-type deposit enriched in gold and iron. The aim of this study was to provide a geological and mineralogical overview of the mineralization and classify the associated rock types and their alteration styles. In addition, a formation model, mineral paragenesis and possible classification of the mineralization are discussed. Geochemical data, hand samples and thin sections were provided by the Geological Survey of Finland (GTK). A total of 20 thin sections were selected for petrographic study, which was done in Oulu Mining School. In addition, chemical analysis was made on selected minerals from 11 thin sections with a field emission scanning electron microscope (FESEM) in the University of Oulu. Geochemical data were utilized in studying the correlation of different elements with gold. A lithological map and a W-E cross section were compiled from the research area using geophysical, drilling and bedrock observation data of GTK. The results of petrological, geochemical and FESEM studies showed that the major vein minerals are hematite, quartz, pyrite, and magnetite. Multiple vein generations with variable mineral assemblages were recognized. The major rock types hosting ore-bearing veins are arkose- and granite gneisses, arkose quartzite, and amphibolite. Sericite, quartz, propylitic, carbonate and limonite alterations were observed. Gold occurs as native microscopic (≤20 µm) grains and is hosted by pyrite and limonite in ore veins. Silver and iron were detected in gold grains in FESEM analyses. In whole-rock compositions, gold correlates with silver, bismuth, iron, tellurium, and tungsten. The results also suggest that gold has been remobilized after brittle deformation and/or vein recrystallization. The Mäkärä mineralization could not be assigned to any specific gold deposit class. The most feasible analogues are distal granitoid-related IRG, IOCG, or epithermal Au ± Ag occurrences ...