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Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland

Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland
Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland
The Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.
Boron isotopes, Cobalt, Finland, Juomasuo, Orogenic gold, Sulfur isotopes, Trace elements
0026-4598
1195-1222
Vasilopoulos, Mikael
e353b16f-62d9-4482-9790-7e5f81d896ec
Molnar, Ferenc
047903e5-e09b-4e6a-b15d-47c21dcb645a
O'Brien, Hugh
607db8d7-1340-4d42-89d0-a3ead1edd221
Lahaye, Yann
c61dcfef-2527-4f1b-b74c-6c3cad860fd0
Lefebvre-Desanois, Marie
b9ca8d27-8ab9-4a72-b4e4-39defc53aa85
Richard, Antonin
c0ebf47e-421c-4e81-acae-aa3788b2217e
Andre-Mayer, Anne-Sylvie
5bb66a9e-cc3a-40d7-a766-1adb0c1fd584
Ranta, Jukka-Pekka
194ddf1a-50b3-4bc0-8715-79cf126023df
Talikka, Matti
f794998d-c882-45f3-8202-9a1d76b640c1
Vasilopoulos, Mikael
e353b16f-62d9-4482-9790-7e5f81d896ec
Molnar, Ferenc
047903e5-e09b-4e6a-b15d-47c21dcb645a
O'Brien, Hugh
607db8d7-1340-4d42-89d0-a3ead1edd221
Lahaye, Yann
c61dcfef-2527-4f1b-b74c-6c3cad860fd0
Lefebvre-Desanois, Marie
b9ca8d27-8ab9-4a72-b4e4-39defc53aa85
Richard, Antonin
c0ebf47e-421c-4e81-acae-aa3788b2217e
Andre-Mayer, Anne-Sylvie
5bb66a9e-cc3a-40d7-a766-1adb0c1fd584
Ranta, Jukka-Pekka
194ddf1a-50b3-4bc0-8715-79cf126023df
Talikka, Matti
f794998d-c882-45f3-8202-9a1d76b640c1

Vasilopoulos, Mikael, Molnar, Ferenc, O'Brien, Hugh, Lahaye, Yann, Lefebvre-Desanois, Marie, Richard, Antonin, Andre-Mayer, Anne-Sylvie, Ranta, Jukka-Pekka and Talikka, Matti (2021) Geochemical signatures of mineralizing events in the Juomasuo Au–Co deposit, Kuusamo belt, northeastern Finland. Mineralium Deposita, 56 (6), 1195-1222. (doi:10.1007/s00126-020-01039-8).

Record type: Article

Abstract

The Juomasuo Au–Co deposit, currently classified as an orogenic gold deposit with atypical metal association, is located in the Paleoproterozoic Kuusamo belt in northeastern Finland. The volcano-sedimentary sequence that hosts the deposit was intensely altered, deformed, and metamorphosed to greenschist facies during the 1.93–1.76 Ga Svecofennian orogeny. In this study, we investigate the temporal relationship between Co and Au deposition and the relationship of metal enrichment with protolith composition and alteration mineralogy by utilizing lithogeochemical data and petrographic observations. We also investigate the nature of fluids involved in deposit formation based on sulfide trace element and sulfur isotope LA-ICP-MS data together with tourmaline mineral chemistry and boron isotopes. Classification of original protoliths was made on the basis of geochemically immobile elements; recognized lithologies are metasedimentary rocks, mafic, intermediate-composition, and felsic metavolcanic rocks, and an ultramafic sill. The composition of the host rocks does not control the type or intensity of mineralization. Sulfur isotope values (δ34S − 2.6 to + 7.1‰) and trace element data obtained for pyrite, chalcopyrite, and pyrrhotite indicate that the two geochemically distinct Au–Co and Co ore types formed from fluids of different compositions and origins. A reduced, metamorphic fluid was responsible for deposition of the pyrrhotite-dominant, Co-rich ore, whereas a relatively oxidized fluid deposited the pyrite-dominant Au–Co ore. The main alteration and mineralization stages at Juomasuo are as follows: (1) widespread albitization that predates both types of mineralization; (2) stage 1, Co-rich mineralization associated with chlorite (± biotite ± amphibole) alteration; (3) stage 2, Au–Co mineralization related to sericitization. Crystal-chemical compositions for tourmaline suggest the involvement of evaporite-related fluids in formation of the deposit; boron isotope data also allow for this conclusion. Results of our research indicate that the metal association in the Juomasuo Au–Co deposit was formed by spatially coincident and multiple hydrothermal processes.

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More information

e-pub ahead of print date: 19 January 2021
Published date: August 2021
Additional Information: Funding Information: We would like to thank John Slack, Dan Kontak, and Pasi Eilu for their constructive comments that helped improve the quality of the text. The Ion Probe Nancy Team is warmly acknowledged for their help with the SIMS analyses at the CRPG laboratory. Funding Information: Open Access funding provided by University of Oulu including Oulu University Hospital. This work was financially supported by grants from the Vilho, Yrjö, and Kalle Väisälä Foundation; the K.H. Renlund Foundation; the Finnish Cultural Foundation; the Horizon 2020 NEXT project; and the Academy of Finland #281670–MinSysPro project. Publisher Copyright: © 2021, The Author(s).
Keywords: Boron isotopes, Cobalt, Finland, Juomasuo, Orogenic gold, Sulfur isotopes, Trace elements

Identifiers

Local EPrints ID: 449911
URI: http://eprints.soton.ac.uk/id/eprint/449911
ISSN: 0026-4598
PURE UUID: 6d22b434-2065-4b05-9a25-a94bd387d110
ORCID for Marie Lefebvre-Desanois: ORCID iD orcid.org/0000-0002-3173-3114

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Date deposited: 25 Jun 2021 16:30
Last modified: 17 Mar 2024 04:07

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Contributors

Author: Mikael Vasilopoulos
Author: Ferenc Molnar
Author: Hugh O'Brien
Author: Yann Lahaye
Author: Marie Lefebvre-Desanois ORCID iD
Author: Antonin Richard
Author: Anne-Sylvie Andre-Mayer
Author: Jukka-Pekka Ranta
Author: Matti Talikka

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