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Does different metal endowment in orogenic Au deposits (Pohjanmaa Belt, western Finland) form during different tectonic events?

The Pohjanmaa Belt in western Finland hosts orogenic Au deposits with enrichment in base metals, such as the Jouhineva Cu-Co-Au-Ag deposit (0.448 Mt at 0.811% Cu, 0.182% Co, 0.88 ppm Au, and 7.864 ppm Ag measured reserves). It is located 3 km NW of the Au-only Huhta occurrence along the same NNW-trending fault. We test if the different metal association in both deposits is related to temporally and structurally different mineralization events. Four deformation events are distinguished: D1 formed a now EW- and NW-trending S1, which is transposed during subsequent deformation; D2 folded S1 into a NW-SE to NNW-SSE trending S2 crenulation cleavage; D3 refolded S2 into close to isoclinal folds and generated a NNW-SSE trending, axial planar S3; D4 formed a centimeter-spaced, EW-trending S4 foliation. Huhta hosts syn-D3 Lö-Apy-Au-Qtz veins with multiple stages of sulfide, arsenide, and sulfarsenide mineralization. Jouhineva hosts syn-D3 Apy-Au-Ccp-Qtz and syn-D4 Ccp-Au-Qtz veins. Titanite U-Pb and structural data indicate synchronous formation of Lö-Apy-Au-Qtz veins in Huhta and Apy-Au-Ccp-Qtz veins in Jouhineva at 1850-1820 Ma during D3. Thus, the different mineralogy and metal endowments formed during the same tectonic event during the Svecofennian Orogeny. Only Jouhineva hosts additional Cu-Au mineralization that formed later during the retrograde evolution. The different metal association in both occurrences may be explained by different metal and fluid sources and compartmentalized fluid migration, distinct mineralization events during the 30 m.y. evolution that cannot be resolved by titanite geochronology, or different precipitation mechanisms although host rocks and PT conditions are similar.

Details

Author
Andressa de Araujo Silva1, Simon Hector1, Clifford Patten2, Aratz Beranoaguirre3, Elisabeth Eiche1, Benjamin F. Walter4, Jochen Kolb1
Institutionen
1Institute of Applied Geosciences (AGW), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany;Laboratory for Environmental and Raw Materials Analysis (LERA), AGW, KIT, Karlsruhe, Germany; 2Institute of Applied Geosciences (AGW), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany;Laboratory for Environmental and Raw Materials Analysis (LERA), AGW, KIT, Karlsruhe, Germany;Institute of -Mineralogy and Petrography, University of Innsbruck, Austria; 3Institute of Applied Geosciences (AGW), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany;Laboratory for Environmental and Raw Materials Analysis (LERA), AGW, KIT, Karlsruhe, Germany;Institute of Geosciences, Goethe University Frankfurt, Germany; 4Institute of Applied Geosciences (AGW), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany;Laboratory for Environmental and Raw Materials Analysis (LERA), AGW, KIT, Karlsruhe, Germany;Eberhard Karls University Tübingen, Department of Petrology and Mineral Resources, Germany
Veranstaltung
GeoSaxonia 2024
Datum
2024
DOI
10.48380/d8dd-h973