Sulfide trace elements, isotope geochemistry and lithogeochemical characteristics of orogenic gold deposits with typical and atypical metal associations from northern Finland
Thesis event information
Date and time of the thesis defence
Place of the thesis defence
Auditorium L5, Linnanmaa
Topic of the dissertation
Sulfide trace elements, isotope geochemistry and lithogeochemical characteristics of orogenic gold deposits with typical and atypical metal associations from northern Finland
Doctoral candidate
Master of Science Mikael Vasilopoulos
Faculty and unit
University of Oulu Graduate School, Faculty of Technology, Oulu Mining School
Subject of study
Geosciences
Opponent
Professor Christoph Beier, University of Helsinki
Custos
Docent Jukka-Pekka Ranta, University of Oulu
Sulfide trace elements, isotope geochemistry and lithogeochemical characteristics of orogenic gold deposits with typical and atypical metal associations from northern Finland
Orogenic gold deposits are one of the most economically important gold deposit types. These hydrothermal deposits are formed by complex large-scale processes, with gold typically being the only metal enriched in economically significant concentrations. A category of gold deposits that are also enriched in base metals occur in some provinces dominated by orogenic gold deposits and have been termed as orogenic gold deposits with an atypical metal association. The Paleoproterozoic Central Lapland and Kuusamo belts of northern Finland host several examples of orogenic gold mineralization, with roughly half of the known orogenic gold occurrences in the Central Lapland belt and most of the occurrences in the Kuusamo belt classified as orogenic gold deposits with an atypical metal association.
The aim of this PhD study is to combine several geochemical methods with mineralogical observations with the purpose of investigating the evolution of hydrothermal processes that led to the formation of orogenic gold deposits in northern Finland. The research targets of this study include: the Juomasuo Au-Co deposit from the Kuusamo belt, and the Hirvilavanmaa Au-only and Naakenavaara Cu-Co-Ni-Au deposits from the Central Lapland belt. This study presents geochemical characteristics from tourmaline and sulfide minerals, several geochemical applications based on lithogeochemical data, and U-Pb ages from hydrothermal xenotime and monazite.
The combination of study geochemical study methods based on lithogeochemical and mineral chemical data proved to be very useful in understanding the hydrothermal processes behind the formation of the three studied deposits. Results of this study indicate that the atypical Juomasuo and Naakenavaara deposits were formed by multiple and spatially coincident hydrothermal processes, with a late Au-rich stage overprinting earlier base metal-rich ore.
Results of U-Pb dating indicate that the Naakenavaara and Hirvilavanmaa deposits in the Central Lapland belt were formed during late (between approximately 1.82–1.75 Ga) stages of the Svecofennian orogeny. Geochemical characteristics from these two deposits point towards a different source of ore-forming components with a metasedimentary and mafic metavolcanic rock source indicated for Naakenavaara and Hirvilavanmaa, respectively.
The aim of this PhD study is to combine several geochemical methods with mineralogical observations with the purpose of investigating the evolution of hydrothermal processes that led to the formation of orogenic gold deposits in northern Finland. The research targets of this study include: the Juomasuo Au-Co deposit from the Kuusamo belt, and the Hirvilavanmaa Au-only and Naakenavaara Cu-Co-Ni-Au deposits from the Central Lapland belt. This study presents geochemical characteristics from tourmaline and sulfide minerals, several geochemical applications based on lithogeochemical data, and U-Pb ages from hydrothermal xenotime and monazite.
The combination of study geochemical study methods based on lithogeochemical and mineral chemical data proved to be very useful in understanding the hydrothermal processes behind the formation of the three studied deposits. Results of this study indicate that the atypical Juomasuo and Naakenavaara deposits were formed by multiple and spatially coincident hydrothermal processes, with a late Au-rich stage overprinting earlier base metal-rich ore.
Results of U-Pb dating indicate that the Naakenavaara and Hirvilavanmaa deposits in the Central Lapland belt were formed during late (between approximately 1.82–1.75 Ga) stages of the Svecofennian orogeny. Geochemical characteristics from these two deposits point towards a different source of ore-forming components with a metasedimentary and mafic metavolcanic rock source indicated for Naakenavaara and Hirvilavanmaa, respectively.
Last updated: 23.1.2024