University of Oulu

Vasilopoulos, M., Molnár, F., Ranta, J.-P., & O’Brien, H. (2023). Mineralogical, lithogeochemical and sulfide trace element characteristics of the Hirvilavanmaa Au-only and the base metal-rich Naakenavaara orogenic gold deposits in the Central Lapland belt, northern Finland. Journal of Geochemical Exploration, 244, 107132. https://doi.org/10.1016/j.gexplo.2022.107132

Mineralogical, lithogeochemical and sulfide trace element characteristics of the Hirvilavanmaa Au-only and the base metal-rich Naakenavaara orogenic gold deposits in the Central Lapland belt, northern Finland

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Author: Vasilopoulos, Mikael1; Molnár, Ferenc2; Ranta, Jukka-Pekka1;
Organizations: 1Oulu Mining School, University of Oulu, P.O. Box 3000, 90014 Oulu, Finland
2Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 50 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2022120569352
Language: English
Published: Elsevier, 2023
Publish Date: 2022-12-05
Description:

Abstract

The Hirvilavanmaa (Au-only) and Naakenavaara (Cu-Co-Au-Ni) deposits, located only 5 km apart in the Paleoproterozoic Central Lapland belt (CLB) in northern Finland, represent two types of orogenic gold mineralization that dominate the CLB: (1) Au-only and (2) Au with atypical metal association, respectively. In this study, we compare these deposits in order to pinpoint the origin of differences in their metal associations. The pyrite-rich Hirvilavanmaa and the pyrrhotite- and chalcopyrite-rich Naakenavaara deposits are hosted primarily by ultramafic metavolcanic and metasedimentary rocks respectively. Similarities in the deposits include pre-ore albitization of host rocks and ore mineralization-related carbonate and chlorite alteration and quartz‑carbonate veins. Ore-related sericite and biotite alteration is prominent only at Naakenavaara. Pyrite and chalcopyrite from the two deposits have a distinct trace element geochemistry; pyrrhotite from Naakenavaara hosts significant Co and Ni concentrations. At Hirvilavanmaa, three pyrite generations with distinct Co/Ni ratios represent the gradual evolution of ore deposition. Hirvilavanmaa can be confidently classified as an orogenic Au deposit with evidence pointing to a mafic metavolcanic rock source for the ore-forming components. At Naakenavaara, our results reveal a complex evolution involving two distinct but spatially coincident mineralizing events. The earliest base metal-rich event started as Co-rich and gradually developed into the main Cu-rich stage; two pyrite types (mean Co/Ni ratios of 12.5 and 762 respectively) are associated with these stages. Subsequently ore zones were overprinted locally by an orogenic Au event that deposited pyrite with low Co/Ni ratios (mean of 0.3). The presence of late gold deposition overprinting earlier base metal-rich ore fits with observations from other base metal‑gold deposits from northern Finland.

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Series: Journal of geochemical exploration
ISSN: 0375-6742
ISSN-E: 1879-1689
ISSN-L: 0375-6742
Volume: 244
Article number: 107132
DOI: 10.1016/j.gexplo.2022.107132
OADOI: https://oadoi.org/10.1016/j.gexplo.2022.107132
Type of Publication: A1 Journal article – refereed
Field of Science: 1171 Geosciences
Subjects:
Funding: This work was financially supported by grants from the Vilho, Yrjö, and Kalle Väisälä Foundation, the K.H. Renlund Foundation and the Finnish Cultural Foundation.
Copyright information: © 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).
  https://creativecommons.org/licenses/by/4.0/