Synthesis of the Geological Evolution and Metallogeny of Finland

Hanski, Eero

doi:10.1016/b978-0-12-410438-9.00002-9

Cited by 8 publications

(3 citation statements)

References 84 publications

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“…Gently dipping nappe and overthrust structures, like those in Tuntsa (Figure 3a,b), are common also in juxtaposed Proterozoic formations [123,124]. Kyanite is commonly found in the Proterozoic metasedimentary rocks west of the Tuntsa Suite (Figure 1) [124][125][126] and similar clockwise cooling paths as in Tuntsa have been described from the Proterozoic rocks in Central Lapland and the Lapland Granulite Complex and its southern contact zone [121,124,127].…”

Section: Tectonic Implicationsmentioning

confidence: 72%

Paleoproterozoic Metamorphism of the Archean Tuntsa Suite, Northern Fennoscandian Shield

et al. 2020

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The Tuntsa Suite is a polymetamorphic Archean complex mainly consisting of metasedimentary gneisses. At least two strong metamorphic events can be distinguished in the area. The first took place at high temperatures in the Neoarchean at around 2.70–2.64 Ga, indicated by migmatisation and U-Pb ages of metamorphic zircon. During the Paleoproterozoic, metasedimentary gneisses were penetratively deformed and recrystallized under medium pressures producing staurolite, kyanite and garnet-bearing mineral assemblages. The suggested Paleoproterozoic PT path was clockwise where the temperature and pressure first increased to 540–550 °C and 6 kbar, crystallizing high Ca/low Mg garnet cores. The mineral compositions show that commonly garnet core was not in chemical equilibrium with staurolite but crystallized earlier, although garnet-staurolite-kyanite assemblages are common. The temperature and pressure increased to c. 650 °C and 8 kbars where staurolite and kyanite coexist. This was followed by decompression down to c. 550–600 °C and 3–4 kbars, shown by andalusite crystallization and cordierite formed in the breakdown of staurolite and biotite + kyanite. The observed garnet zoning where Mg increases and Ca decreases from the core to the rim was developed with both increasing and decreasing pressure, depending on the effective bulk composition. The U-Pb and Sm-Nd age determinations for monazite and garnet show that the Paleoproterozoic metamorphic cycle took place at 1.84–1.79 Ga, related with thrusting of the Lapland granulites onto the adjacent terranes and subsequent exhumation.

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Section: Tectonic Implicationsmentioning

confidence: 72%

Paleoproterozoic Metamorphism of the Archean Tuntsa Suite, Northern Fennoscandian Shield

et al. 2020

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“…For reasons presently not well understood, it appears that the slightly older magma influx has less potential to form major Ni sulfide ore deposits (cf. Weihed et al 2005;Hanski 2015). However, as the available database is relatively limited, it is difficult to assess the Ni sulfide prospectivity of these belts accurately.…”

Section: Volcanologymentioning

confidence: 99%

Geochemistry of komatiites and basalts in Archean greenstone belts of Russian Karelia with emphasis on platinum-group elements

et al. 2019

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Archean komatiites form an important host rock for Ni-Cu sulfide deposits in the world. In this study, we examined Archean komatiites and komatiitic basalts from four areas in the Vedlozero-Segozero greenstone belt and two areas in the Tikshozero greenstone belt, Russian Karelia, to constrain their Ni-Cu sulfide mineralization potential using chalcophile element geochemistry. The platinum-group element (PGE) concentrations in these Munro-type komatiitic rocks are at a level of other similar Sundersaturated komatiites and komatiitic basalts globally, with Pt and Pd concentrations in the range of 5-20 ppb and Pd/Ir varying from < 10 (komatiites) to > 15 (komatiitic basalts and basalts). Generally, the metals of the iridium-group elements (IPGEs; Ir, Ru, Os) show a compatible behavior, decreasing in abundance with decreasing MgO, whereas the metals of the palladium group (PPGEs; Pt, Pd, Rh) exhibit an incompatible behavior. The poor correlation between Ir and MgO suggests that olivine fractional crystallization is not the main control on the behavior of IPGE. In contrast, Ir, Ru, and Os show positive correlations with Cr, which is consistent with the compatible behavior of IPGEs in chromite or during the co-precipitation of chromite and platinum-group minerals (PGMs). Palladium, Cu, and Au have been variably mobile during alteration and metamorphism whereas Pt appears to have been less mobile. Some samples from the Khizovaara area show low (Pt/Ti) N ratios, low Ni, and high La/Sm and La/Nb, suggesting localized sulfide saturation in response to crustal contamination. However, the potential of the Russian Karelian greenstone belts for Ni-Cu sulfide mineralization is considered relatively low because most samples show neither enrichment nor depletion of chalcophile elements, and the paucity of dynamic lava channel environments, as indicated by the scarcity of olivine-rich adcumulates. In addition, there appears to be a lack of exposed sulfidic sedimentary rocks in the region.

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“…Paleoproterozoic volcanic terranes are known for their high gold content in a variety of different deposits such as orogenic lode, Au-volcanogenic massive sulphide (VMS), porphyries, iron oxide copper gold deposits (IOCG) and paleo-placers (Poulsen, 2000;Groves et al, 2003;Dubé et al, 2007;Goldfarb et al, 2010). The Trans-Hudsonian and Svecofennian orogens are good examples of the diversity of gold occurrences in Paleoproterozoic greenstone belts (Franklin et al, 2005;Dubé et al, 2007;Mercier-Langevin et al, 2011;Hanski, 2015;Pehrsson et al, 2016). In the Rhyacian part of the northern Guiana Shield, Milési et al (2003) recognized three types of primary gold deposits: (1) stratiform/stratabound gold-bearing tourmalinites, (2) mesothermal orogenic deposits along major faults/shear zones, and (3) paleoplacers (Fig.…”

Section: Introductionmentioning

confidence: 99%

Stratigraphic setting and timing of the Montagne d’Or deposit, a unique Rhyacian Au-rich VMS deposit of the Guiana Shield, French Guiana

Guiraud

Tremblay

Jébrak

et al. 2020

Precambrian Research

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In French Guiana, the Montagne d'Or gold deposit (5 Moz at 1.5 g/t Au) is located in the northern branch of the Rhyacian Paramaca Greenstone Belt. The sulphide deposit is hosted by a south-facing bimodal volcanic and volcaniclastic sequence that is highly strained and affected by a penetrative E-W striking and steeply southdipping foliation.The volcanic sequence is composed of three members, (1) the Lower unit in the stratigraphic footwall, (2) a bimodal mafic-felsic formation hosting the orebody, and (3) the Upper sedimentary and volcanic rocks unit in the stratigraphic hanging-wall. The bimodal formation is dominated by calc-alkaline felsic volcanic rocks in the west, interbedded/interdigitated with tholeiitic mafic rocks in the east. Pillowed mafic flows and graded-bedded felsic volcaniclastic rocks collectively indicate effusive to explosive volcanic activity in a submarine environment. The mineralization consists of thick and laterally extensive sulphide zones forming (1) stratiform sulphide disseminations, (2) structurally-transposed stringer stockworks, and (3) thin layers of deformed semi-massive sulphides. The gold-rich sulphide mineralization consists mainly of pyrite, pyrrhotite and chalcopyrite with minor sphalerite, magnetite, galena and arsenopyrite, hosted by chlorite-sericite-rich alteration zones mainly developed in the felsic tuff facies.U-Pb zircon geochronology shows that most of the Montagne d'Or volcanic and intrusive sequence has crystallized during a multi-cycle magmatic event, from ca. 2152 Ma to ca. 2130 Ma. A porphyry intrusion crosscutting the ore yields a U-Pb zircon age of 2117.6 ± 5.1 Ma, hence constraining a minimum age for the auriferous sulphide mineralization. This also indicates that the sulphide mineralization was coeval with arc magmatism, demonstrating the volcanogenic nature of the Montagne d'Or gold deposit.

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Synthesis of the Geological Evolution and Metallogeny of Finland

Cited by 8 publications

References 84 publications

Paleoproterozoic Metamorphism of the Archean Tuntsa Suite, Northern Fennoscandian Shield

Paleoproterozoic Metamorphism of the Archean Tuntsa Suite, Northern Fennoscandian Shield

Geochemistry of komatiites and basalts in Archean greenstone belts of Russian Karelia with emphasis on platinum-group elements

Stratigraphic setting and timing of the Montagne d’Or deposit, a unique Rhyacian Au-rich VMS deposit of the Guiana Shield, French Guiana

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