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Source of metals and fluids in orogenic Au deposits with atypical metal association: Insights from the Pohjanmaa Belt, Finland

Orogenic Au deposits formed in metamorphic belts over most of the Earth history and the genetic models developed since the three last decades aim to provide a general model for these gold-only deposits. However, some deposits, known as orogenic gold deposits with atypical metal associations, show enrichment in base and critical metals, mainly Cu, Co, sometimes Ni, Sb, U and (REE) that are not explained by the current models (i.e. metamorphic devolatilisation, subcrustal fluids, magmatic-hydrothermal model). The Pohjanmaa Belt in western Finland hosts both typical and atypical gold mineralization and is a natural laboratory to decipher the genesis of orogenic Au-Cu-Co-Ni deposits and establish a genetic deposit model including both type of deposits. This study explores the origin and nature of the mineralizing fluids and precipitation mechanisms by combining multiple methods as follows:

(1) microthermometry and in-situ geochemistry on well preserved primary fluid inclusion assemblages;

(2) whole rock geochemistry for basic geochemical characterization and identification of metal enrichments in hydrothermal alteration zones;

(3) in-situ geochemistry on hydrothermal mineral separates (amphibole, biotite, chlorite, sericite) to highlight potential sources of fluid and metals;

(4) Halogen ratios (Cl, Br, I) for identification of potential fluid sources, including evaporites;

(5) In-situ S isotope analysis and geochemistry of sulfides to characterize the S source, redox-related precipitation mechanisms and link with the mineralizing fluids.

Details

Author
Regina Albrecht1, Simon Hector1, Jochen Kolb1, Benjamin Walter2
Institutionen
1Institute of Applied Geosciences, Geochemistry and Economic Geology, Karlsruhe Institute of Technology, Germany; 2Eberhard Karls University Tübingen, Petrology and Mineral Resources, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/20j4-df14