University of Oulu

Makkonen, Hannu V.; Tuisku, Pekka (2020) Geology and crystallization conditions of the särkiniemi intrusion and related nickel-copper ore, central Finland – implications for depth of emplacement of 1.88 ga nickel-bearing intrusions. Bulletin of the Geological Society of Finland, 92(2), 111-130, https://doi.org/10.17741/BGSF/92.2.003

Geology and crystallization conditions of the Särkiniemi intrusion and related nickel-copper ore, central Finland : implications for depth of emplacement of 1.88 Ga nickel-bearing intrusions

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Author: Makkonen, Hannu V.1; Tuisku, Pekka2
Organizations: 1Suomen Malmitutkimus Oy, Leimaajantie 7, FI-70150 Kuopio, Finland
2Oulu Mining School, P.O.Box 8000, FI-90014 University of Oulu, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 2.5 MB)
Persistent link: http://urn.fi/urn:nbn:fi-fe2021050428702
Language: English
Published: The Geological Society of Finland, 2020
Publish Date: 2021-05-04
Description:

Abstract

Several Ni-Cu deposits occur within the Kotalahti area, central Finland, in proximity to an Archaean gneiss dome surrounded by a Palaeoproterozoic craton-margin supracrustal sequence comprising quartzites, limestones, calc-silicate rocks, black schists and banded diopside amphibolites. The geology of the area and age of the Ni-bearing intrusions (1.88 Ga) are similar to the Thompson Ni belt in the Canadian Trans-Hudson Orogen. The small mafic-ultramafic and Ni-Cu -bearing Särkiniemi intrusion, closely associated with the Archaean basement core of the Kotalahti Dome, is composed of a western peridotite and eastern gabbro body, both of which are mineralized. The eastern gabbro has a contact aureole several meters thick, consisting of orthopyroxene +/- cordierite bearing hornfels between the intrusion and the migmatites. Geochemically, the Särkiniemi intrusion shares many features in common with other Svecofennian mafic-ultramafic intrusions, including crustal contamination and nickel depletion. The related Ni-Cu deposit has a low Ni/Co value (15) and low nickel content in the sulphide fraction (2.8 wt.%), together with a low estimated magma/sulphide ratio of around 170. Svecofennian 1.88 Ga mafic-ultramafic intrusions occur in terrains of variable metamorphic grade (from low-amphibolite to granulite facies) and are likely to represent emplacement at different crustal depths. Multi-equilibrium thermobarometry indicates that the contact aureole at Särkiniemi reached equilibrium at pressures of 4.5–6 kbar (15–20 km depth) and temperatures of 600–670 °C. Combined with the results of earlier research on the Svecofennian intrusions, this study indicates that a depth of 15–20 km crustal level was favourable, along with other critical factors, for nickel sulfide deposition at 1.88 Ga.

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Series: Bulletin of the Geological Society of Finland
ISSN: 0367-5211
ISSN-E: 1799-4632
ISSN-L: 0367-5211
Volume: 92
Issue: 2
Pages: 111 - 130
DOI: 10.17741/BGSF/92.2.003
OADOI: https://oadoi.org/10.17741/BGSF/92.2.003
Type of Publication: A1 Journal article – refereed
Field of Science: 1171 Geosciences
Subjects:
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