Tapio Halkoaho - Academia.edu (original) (raw)
Papers by Tapio Halkoaho
Mineralium Deposita, Jan 23, 2020
The Kiviniemi mafic intrusion, near the eastern margin of the Paleoproterozoic Central Finland Gr... more The Kiviniemi mafic intrusion, near the eastern margin of the Paleoproterozoic Central Finland Granitoid Complex, is both spatially and temporally associated with post-kinematic Fe-TiP enriched Svecofennian orogenic mafic magmatism. The main rock types in this small (~15 ha) intrusion are garnet-bearing fayalite ferrodiorite, leucoferrodiorite, ferromonzodiorite, and pyroxene diorite. The garnet-bearing fayalite ferrodiorite and leucoferrodiorite contain 50-281 ppm Sc, 275-5600 ppm Zr, and 58-189 ppm Y (n = 42), delineating a mineralized deposit some 2.5 ha in extent. Overall, these rocks show an evolved (ironenriched) tholeiitic character; low values of Ni (< 20-40 ppm), Cr (< 20 ppm), and Cu (< 20-80 ppm); and high contents of Zn (213-700 ppm). The rock-forming minerals in the ferrodioritic rocks are (ferro)hedenbergite, plagioclase (~An 40), ferropargasite and ferroedenite, almandine garnet, and fayalite (Fo 1-4). Accessory minerals include zircon, ilmenite, fluorapatite, biotite, pyrite, pyrrhotite, potassium feldspar, grunerite, and clinoferrosilite. Some relict cumulate textures have been preserved, but primary magmatic features have largely been overprinted by strong recrystallization and corona formation. The main carriers of Sc are amphibole, clinopyroxene, and apatite. The remarkably strong enrichment of Sc in ferromagnesian silicates and apatite, rather than in specific Sc-minerals, implies magmatic enrichment. Post-kinematic mafic intrusions in central Finland constitute a bimodal association with co-existing granitoid counterparts. The Kiviniemi mafic intrusion is associated with a coarse megacrystic granite and the two rock type display mingled contacts, indicative of contemporaneity of the two magmas. This conclusion is in accord with the coincident U-Pb zircon ages for the ferrodiorite, at 1857 ± 2 Ma (multigrain ID-TIMS) and the megacrystic granite, at 1860 ± 7 Ma (single-crystal LA-MC-ICP-MS). The initial εNd value of the ferrodiorite and the granite are + 0.1 and − 2.5, respectively. These Nd isotope compositions probably reflect a chondritic mantle source for the ferrodiorite and suggest incorporation of some Archaean crustal material into the granite in the course of magmatic evolution. The resource estimation calculated for Kiviniemi intrusion by using 40 g/t Sc cut off value is 13.4 Mt of rock with an average grade of 162.7 g/t scandium, 1726 g/t zirconium, and 81 g/t yttrium.
The Fennoscandian School of Ore Genesis in Layered Intrusions, 2021
The Junttilanniemi layered intrusion is located in the Kainuu region, Finland. The intrusion cont... more The Junttilanniemi layered intrusion is located in the Kainuu region, Finland. The intrusion contains three main units: marginal series, layered series and granophyre. The layered series being further divided into three megacyclic units (MCUs). Quite recently, during year 2010, Geological Survey of Finland (GTK) located from the Junttilanniemi intrusion a new reef-type platinum-group element (PGE) enrichment of the 2.44 Ga Fennoscandian layered intrusion.
International Journal of Earth Sciences, 2016
providing resources for the field and laboratory work. The Nordsim facility is financed and opera... more providing resources for the field and laboratory work. The Nordsim facility is financed and operated under an agreement between the research councils of Denmark, Norway and Sweden, the Geological Survey of Finland and the Swedish Museum of Natural History. This is Nordsim contribution no. 448. The staff of the Nordsim laboratory, Martin Whitehouse, Kerstin Lindén and Lev Ilyinsky, and the staff of the Isotope laboratory of the Geological Survey of Finland, Hugh O'Brien, Yann Lahaye and Leena Järvinen, are thanked for the sample preparation and technical assistance. Tom Andersen is acknowledged for providing program to handle the LAMC-ICPMS data. Comments from reviewers Stefan Claesson and Mike Fowler and editorial work by Victoria Pease are highly appreciated.
Mineralogy and Petrology, 1990
Teilen von Megazyklus III entwickelt sein. PGE Anreicherungen sind entweder an Sulfide (haupts/ic... more Teilen von Megazyklus III entwickelt sein. PGE Anreicherungen sind entweder an Sulfide (haupts/ichlich Pyrit-Kupferkies-Pentlandit) oder an disseminierten Chromit gekniipft. Der letztere Vererzungstyp ist durch h6here Gehalte gekennzeichnet. Wfihrend der Intrusion der Magmen des Megazyklus IV kam es zu einer Magmenmischung zwischen diesen und/ilteren Magmen. Es kann angenommen werden, dab dieses "Magma-mixing" fiir die Ausfgllung und Anreicherung der PGE's in den Sulfiden, die in den tieferen Anteilen der Olivin-Kumulate auftreten, verantwortlich zu machen ist und der Grund fiir diese disseminierte an Sulfide gebundene Vererzung ist. Das Eindringen mfichtiger neuer Magmensch~be und die Ausbreitung dieses Magmas fiber die obersten, bereits konsolidierten Gabbro-Kumulate des Megazyklus III, verursachten eine lokal intensive Erosion in diesen obersten bereits kristaltisierten Lagen. L~ingliche Spaltensysteme und/oder Einsenkungen,/ihnlich wie bei St6rungen, wurden angelegt. In diesen Spaltensystemen und Einsenkungen sammelte sich filtere Schmelze, die an Elementen der Platingruppe angereichert war. Sie bildete die an disseminierten Chromit gebundene Vererzung im SJ Reef.
Journal of Geological Society of India, 1996
Electron Microprobe studies on BIF from Kudremukh area have indicated the presence of Ag-Bi- and ... more Electron Microprobe studies on BIF from Kudremukh area have indicated the presence of Ag-Bi- and Pb-Tellurides in association with other sulphides
The 2444 Ma Penikat layered ultramafic-mafic intrusion in northern Finland contains at least six ... more The 2444 Ma Penikat layered ultramafic-mafic intrusion in northern Finland contains at least six platinumgroup element (PGE) enriched horizons, including the SJ, AP and PV reefs, each with 4 to >10 ppm Pt+Pd over a width of between 10 m. The mineralisation formed by orthomagmatic processes as indicated by strong positive correlations between Pt and Ir contents. Subdued stratigraphic variation in incompatible trace element ratios and Nd isotope ratios indicates that mixing of magmas of distinct lineage, or in situ contamination with country rocks, was not required to form the PGE reefs. There is also no evidence for addition of external sulphur to the magma, based on S/Se ratios at, or below, primitive mantle levels. Instead, sulphide melt saturation was likely reached in response to silicate fractionation of a siliceous highmagnesium basalt. We propose that the SJ reef formed through hydrodynamic sorting of crystal mushes, hereas the AP and PV reefs formed through tectonically in...
The Fennoscandian School of Ore Genesis in Layered Intrusions. Online Workshop 2, 2022
The Penikat layered intrusion is located in southwest Lapland, Northern Finland. The intrusion co... more The Penikat layered intrusion is located in southwest Lapland, Northern Finland. The intrusion contains two main units: the marginal series and layered series, the layered series being further divided into five megacyclic units (MCUs). The intrusion contains three major PGE-enriched zones. The middle one, termed Ala-Penikka PGE reef contains a large PGE enriched pothole structure.
Bulletin of the Geological Survey of Finland
The structure of the Archaean Kuhmo greenstone belt, which forms the central portion of the Tipas... more The structure of the Archaean Kuhmo greenstone belt, which forms the central portion of the Tipasjärvi-Kuhmo-Suomussalmi (TKS) greenstone complex in eastern Finland, is essentially a regional scale, northerly trending synclinorium. It was deformed and metamorphosed during several phases of deformation, youngest of which was dated as Proterozoic. Migmatized banded amphibolites, originally Fetholeiitic in composition, and intermediate and felsic volcanic rocks are interpreted as the oldest preserved supracrustal rock units, and are between 3100-2900 Ma in age. They are transected by and occur as enclaves within felsic and intermediate tonalite-trondhjemite-granodiorite (TTG) intrusions, which were deformed and metamorphosed during the D 2/M 2 event at 2843±18 Ma, when the U-Pb isotope systematics of the TTG complex were homogenized. The lowermost stratigraphic unit of the TKS greenstone complex proper is composed of felsic to intermediate volcanic rocks, which have yielded zircon ages...
Undiscovered resources of copper, zinc, lead, gold and silver in volcanogenic massive sulphide (V... more Undiscovered resources of copper, zinc, lead, gold and silver in volcanogenic massive sulphide (VMS) deposits, undiscovered resources of copper, molybdenum, gold and silver in porphyry copper deposits, and undiscovered resources of copper, zinc, nickel and cobalt in Outokumpu-type deposits were estimated down to the depth of one kilometre in the bedrock of Finland using the threepart quantitative assessment method. Grade-tonnage models were constructed for felsic, bimodal-mafic and mafic VMS deposits using data from known Fennoscandian deposits. A grade-tonnage model for porphyry copper deposits was constructed using global data from Precambrian deposits. For the Outokumpu-type deposits, a grade-tonnage model was developed using data from wellknown deposits within the Outokumpu area. Thirty-one permissive tracts were delineated for VMS deposits, 10 for porphyry copper deposits, and one for Outokumpu- type deposits. The VMS tracts cover an area of 41,600 km2, the porphyry copper trac...
Mineralogy and Petrology, 1990
Bulletin of the Geological Society of Finland, 2016
We document a new and unusual occurrence of patterns of protruding spheroidal weathering develope... more We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of "normal spheroidal weathering" sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo 87.5), which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. %) are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96) formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts) during a deuteric (autometasomatic) alteration. In contrast, oikocrystic Opx (En 86.0) is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr) are observed. We infer that (1) the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2) Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3) The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions.
The Canadian Mineralogist, 2002
is a new parkerite-type sulfide discovered in the Penikat layered complex, Finland. It occurs in ... more is a new parkerite-type sulfide discovered in the Penikat layered complex, Finland. It occurs in altered pyroxenite in the Kirakkajuppura deposit in association with actinolite and clinochlore, accessory chromite, various platinum-group minerals [vysotskite, zvyagintsevite, cuprorhodsite-(ferrorhodsite)-malanite, laurite-erlichmanite, irarsite, keithconnite, unusual Pb-(Pd)-rich thiospinels of Cu, Fe, Rh and Ir, unnamed Pd 9 PbO 10 and Rh(Ni,Fe,Cu) 2 S 3 ], Pd-rich gold, and minor base-metal sulfides (chalcopyrite, bornite and millerite). Laflammeite occurs as individual subhedral to euhedral crystals up to 0.3 mm in size, and in intergrowths with Pt-Ni-poor vysotskite. Laflammeite is opaque and cream-colored with a brownish tint in reflected light in air. The anisotropy is weak, from brownish gray to grayish brown. The bireflectance is weak; pleochroism was not observed. Reflectance percentages in air (and in oil) are,
The Palaeoproterozoic Penikat layered intrusion in northern Finland contains at least six platinu... more The Palaeoproterozoic Penikat layered intrusion in northern Finland contains at least six platinum-group element (PGE) enriched horizons exposed along >20 km of strike, amongst them the SJ reef, with 3-7 ppm Pt+Pd over a width of 1-2 m. Important PGE enrichments also occur in the PV reef (avg. 2.6 ppm Pd, 4 ppm Pt over 1.1 m) and AP1 reef (avg. 6.2 ppm Pd, 1.7 ppm Pt over 0.7 m0. The PGE reefs formed by predominantly orthomagmatic processes. Late-magmatic fluids played no significant role in concentrating PGE. Subdued stratigraphic variation in incompatible trace element ratios (Ce/Sm mostly 5-10) and Nd isotope compositions (eNd -3 to -1) indicate that mixing of distinct magmas, or in situ contamination with country rocks, was not required to form the reefs. There is also no evidence for addition of external sulphur, based on S/Se ratios at, or below, primitive mantle levels. Instead, we propose that sulphide melt saturation was reached in response to magma fractionation, and th...
The Kirakkajuppura platinum-group-element (PGE) deposit, in the Penikat layered complex, Finland,... more The Kirakkajuppura platinum-group-element (PGE) deposit, in the Penikat layered complex, Finland, is associated with the low-sulfide Sompujiirvi PGE reef, located near the contact between ultramafic and gabbroic cumulates, close to the country rocks. The deposit is unique among PGE deposits in layered intrusions as it displays, on a relatively small scale, very high bulkrock concentrations of PGE (up to >0 5 kg/t total PGE) aLong with a low content of S and Cr, e.g.,\fcn 224 ppm. 108 ppm S and 0.8 wt.% Cr; (Pd + Pt)/(Os + Ir + Ru) = 93.9 and Pd/ft = 3.0 (mean of four whole-rock analyses). The platinum-group minerals (PGM), predominantly Pt-Ni-poor vysotskite-braggite, zvyagintsevite and a Pd-Pb oxide, mainly occur in altered pyroxenite, among grains of Mg-rich actinolite and clinochlore, as unusually large veinlerlike or chain-like aggregates up to -1 cm in length. In agreement with the whole-rock data, the PGM do not show a close relationship with base-metal sulfides (8M,9) and ...
Mineralogy and Petrology, 2020
Several mafic-ultramafic layered intrusions were emplaced in the Fennoscandian Shield during wide... more Several mafic-ultramafic layered intrusions were emplaced in the Fennoscandian Shield during wide-spread mantle-sourced magmatism at 2.5–2.4 Ga. The Näränkävaara intrusion (surface area 5 × 30 km 2 ), northeastern Finland, contains a 1.5–2 km thick basal dunite (not dated), and a 1.5 km thick layered series (2436 ± 5 Ma). A newly discovered marginal series between the basal dunite and the layered series indicates that the basal dunite is older, and highlights the need for further study on their relationship. Along its southern basement contact, the basal dunite contains a 200–300 m thick zone of olivine ortho- and mesocumulates, but the bulk of it is composed of olivine adcumulates and lesser olivine-orthopyroxene heteradcumulates. Based on whole-rock geochemistry, the basal dunite is divided into a low-Fe zone (average FeO t 10.2 wt% and Ni 2250 ppm) and a high-Fe zone (average FeO t 12.5 wt% and Ni 1700 ppm). Both zones have high MgO (32–47 wt%) and varying Cr (830–5160 ppm) and A...
Mineralium Deposita, Jan 23, 2020
The Kiviniemi mafic intrusion, near the eastern margin of the Paleoproterozoic Central Finland Gr... more The Kiviniemi mafic intrusion, near the eastern margin of the Paleoproterozoic Central Finland Granitoid Complex, is both spatially and temporally associated with post-kinematic Fe-TiP enriched Svecofennian orogenic mafic magmatism. The main rock types in this small (~15 ha) intrusion are garnet-bearing fayalite ferrodiorite, leucoferrodiorite, ferromonzodiorite, and pyroxene diorite. The garnet-bearing fayalite ferrodiorite and leucoferrodiorite contain 50-281 ppm Sc, 275-5600 ppm Zr, and 58-189 ppm Y (n = 42), delineating a mineralized deposit some 2.5 ha in extent. Overall, these rocks show an evolved (ironenriched) tholeiitic character; low values of Ni (< 20-40 ppm), Cr (< 20 ppm), and Cu (< 20-80 ppm); and high contents of Zn (213-700 ppm). The rock-forming minerals in the ferrodioritic rocks are (ferro)hedenbergite, plagioclase (~An 40), ferropargasite and ferroedenite, almandine garnet, and fayalite (Fo 1-4). Accessory minerals include zircon, ilmenite, fluorapatite, biotite, pyrite, pyrrhotite, potassium feldspar, grunerite, and clinoferrosilite. Some relict cumulate textures have been preserved, but primary magmatic features have largely been overprinted by strong recrystallization and corona formation. The main carriers of Sc are amphibole, clinopyroxene, and apatite. The remarkably strong enrichment of Sc in ferromagnesian silicates and apatite, rather than in specific Sc-minerals, implies magmatic enrichment. Post-kinematic mafic intrusions in central Finland constitute a bimodal association with co-existing granitoid counterparts. The Kiviniemi mafic intrusion is associated with a coarse megacrystic granite and the two rock type display mingled contacts, indicative of contemporaneity of the two magmas. This conclusion is in accord with the coincident U-Pb zircon ages for the ferrodiorite, at 1857 ± 2 Ma (multigrain ID-TIMS) and the megacrystic granite, at 1860 ± 7 Ma (single-crystal LA-MC-ICP-MS). The initial εNd value of the ferrodiorite and the granite are + 0.1 and − 2.5, respectively. These Nd isotope compositions probably reflect a chondritic mantle source for the ferrodiorite and suggest incorporation of some Archaean crustal material into the granite in the course of magmatic evolution. The resource estimation calculated for Kiviniemi intrusion by using 40 g/t Sc cut off value is 13.4 Mt of rock with an average grade of 162.7 g/t scandium, 1726 g/t zirconium, and 81 g/t yttrium.
The Fennoscandian School of Ore Genesis in Layered Intrusions, 2021
The Junttilanniemi layered intrusion is located in the Kainuu region, Finland. The intrusion cont... more The Junttilanniemi layered intrusion is located in the Kainuu region, Finland. The intrusion contains three main units: marginal series, layered series and granophyre. The layered series being further divided into three megacyclic units (MCUs). Quite recently, during year 2010, Geological Survey of Finland (GTK) located from the Junttilanniemi intrusion a new reef-type platinum-group element (PGE) enrichment of the 2.44 Ga Fennoscandian layered intrusion.
International Journal of Earth Sciences, 2016
providing resources for the field and laboratory work. The Nordsim facility is financed and opera... more providing resources for the field and laboratory work. The Nordsim facility is financed and operated under an agreement between the research councils of Denmark, Norway and Sweden, the Geological Survey of Finland and the Swedish Museum of Natural History. This is Nordsim contribution no. 448. The staff of the Nordsim laboratory, Martin Whitehouse, Kerstin Lindén and Lev Ilyinsky, and the staff of the Isotope laboratory of the Geological Survey of Finland, Hugh O'Brien, Yann Lahaye and Leena Järvinen, are thanked for the sample preparation and technical assistance. Tom Andersen is acknowledged for providing program to handle the LAMC-ICPMS data. Comments from reviewers Stefan Claesson and Mike Fowler and editorial work by Victoria Pease are highly appreciated.
Mineralogy and Petrology, 1990
Teilen von Megazyklus III entwickelt sein. PGE Anreicherungen sind entweder an Sulfide (haupts/ic... more Teilen von Megazyklus III entwickelt sein. PGE Anreicherungen sind entweder an Sulfide (haupts/ichlich Pyrit-Kupferkies-Pentlandit) oder an disseminierten Chromit gekniipft. Der letztere Vererzungstyp ist durch h6here Gehalte gekennzeichnet. Wfihrend der Intrusion der Magmen des Megazyklus IV kam es zu einer Magmenmischung zwischen diesen und/ilteren Magmen. Es kann angenommen werden, dab dieses "Magma-mixing" fiir die Ausfgllung und Anreicherung der PGE's in den Sulfiden, die in den tieferen Anteilen der Olivin-Kumulate auftreten, verantwortlich zu machen ist und der Grund fiir diese disseminierte an Sulfide gebundene Vererzung ist. Das Eindringen mfichtiger neuer Magmensch~be und die Ausbreitung dieses Magmas fiber die obersten, bereits konsolidierten Gabbro-Kumulate des Megazyklus III, verursachten eine lokal intensive Erosion in diesen obersten bereits kristaltisierten Lagen. L~ingliche Spaltensysteme und/oder Einsenkungen,/ihnlich wie bei St6rungen, wurden angelegt. In diesen Spaltensystemen und Einsenkungen sammelte sich filtere Schmelze, die an Elementen der Platingruppe angereichert war. Sie bildete die an disseminierten Chromit gebundene Vererzung im SJ Reef.
Journal of Geological Society of India, 1996
Electron Microprobe studies on BIF from Kudremukh area have indicated the presence of Ag-Bi- and ... more Electron Microprobe studies on BIF from Kudremukh area have indicated the presence of Ag-Bi- and Pb-Tellurides in association with other sulphides
The 2444 Ma Penikat layered ultramafic-mafic intrusion in northern Finland contains at least six ... more The 2444 Ma Penikat layered ultramafic-mafic intrusion in northern Finland contains at least six platinumgroup element (PGE) enriched horizons, including the SJ, AP and PV reefs, each with 4 to >10 ppm Pt+Pd over a width of between 10 m. The mineralisation formed by orthomagmatic processes as indicated by strong positive correlations between Pt and Ir contents. Subdued stratigraphic variation in incompatible trace element ratios and Nd isotope ratios indicates that mixing of magmas of distinct lineage, or in situ contamination with country rocks, was not required to form the PGE reefs. There is also no evidence for addition of external sulphur to the magma, based on S/Se ratios at, or below, primitive mantle levels. Instead, sulphide melt saturation was likely reached in response to silicate fractionation of a siliceous highmagnesium basalt. We propose that the SJ reef formed through hydrodynamic sorting of crystal mushes, hereas the AP and PV reefs formed through tectonically in...
The Fennoscandian School of Ore Genesis in Layered Intrusions. Online Workshop 2, 2022
The Penikat layered intrusion is located in southwest Lapland, Northern Finland. The intrusion co... more The Penikat layered intrusion is located in southwest Lapland, Northern Finland. The intrusion contains two main units: the marginal series and layered series, the layered series being further divided into five megacyclic units (MCUs). The intrusion contains three major PGE-enriched zones. The middle one, termed Ala-Penikka PGE reef contains a large PGE enriched pothole structure.
Bulletin of the Geological Survey of Finland
The structure of the Archaean Kuhmo greenstone belt, which forms the central portion of the Tipas... more The structure of the Archaean Kuhmo greenstone belt, which forms the central portion of the Tipasjärvi-Kuhmo-Suomussalmi (TKS) greenstone complex in eastern Finland, is essentially a regional scale, northerly trending synclinorium. It was deformed and metamorphosed during several phases of deformation, youngest of which was dated as Proterozoic. Migmatized banded amphibolites, originally Fetholeiitic in composition, and intermediate and felsic volcanic rocks are interpreted as the oldest preserved supracrustal rock units, and are between 3100-2900 Ma in age. They are transected by and occur as enclaves within felsic and intermediate tonalite-trondhjemite-granodiorite (TTG) intrusions, which were deformed and metamorphosed during the D 2/M 2 event at 2843±18 Ma, when the U-Pb isotope systematics of the TTG complex were homogenized. The lowermost stratigraphic unit of the TKS greenstone complex proper is composed of felsic to intermediate volcanic rocks, which have yielded zircon ages...
Undiscovered resources of copper, zinc, lead, gold and silver in volcanogenic massive sulphide (V... more Undiscovered resources of copper, zinc, lead, gold and silver in volcanogenic massive sulphide (VMS) deposits, undiscovered resources of copper, molybdenum, gold and silver in porphyry copper deposits, and undiscovered resources of copper, zinc, nickel and cobalt in Outokumpu-type deposits were estimated down to the depth of one kilometre in the bedrock of Finland using the threepart quantitative assessment method. Grade-tonnage models were constructed for felsic, bimodal-mafic and mafic VMS deposits using data from known Fennoscandian deposits. A grade-tonnage model for porphyry copper deposits was constructed using global data from Precambrian deposits. For the Outokumpu-type deposits, a grade-tonnage model was developed using data from wellknown deposits within the Outokumpu area. Thirty-one permissive tracts were delineated for VMS deposits, 10 for porphyry copper deposits, and one for Outokumpu- type deposits. The VMS tracts cover an area of 41,600 km2, the porphyry copper trac...
Mineralogy and Petrology, 1990
Bulletin of the Geological Society of Finland, 2016
We document a new and unusual occurrence of patterns of protruding spheroidal weathering develope... more We document a new and unusual occurrence of patterns of protruding spheroidal weathering developed in a dunitic rock of the Pados-Tundra mafic-ultramafic complex of Early Proterozoic age, Kola Peninsula, Russia. It provides an example similar to that reported recently from a mineralized harzburgite in the Monchepluton layered complex in the same region. These patterns are genetically different from common results of "normal spheroidal weathering" sensu stricto. The spheroidally weathered dunite at Pados-Tundra consists of a high-Fo olivine, Ol (Fo 87.5), which is, in fact, not altered. Accessory grains of aluminous chromite are present. Relief spheroids (1.5 to 4 cm in diameter; up to ~5 vol. %) are distributed sparsely and heterogeneously. They are hosted by the olivine matrix and composed of talc, Tlc, and tremolite, Tr, (Mg# = 95-96) formed presumably at the expense of orthopyroxene, Opx, (i.e., pre-existing oikocrysts) during a deuteric (autometasomatic) alteration. In contrast, oikocrystic Opx (En 86.0) is quite fresh in related spheroids at Monchepluton, in which only minor deuteric alteration (Tlc + Tr) are observed. We infer that (1) the ball-shaped morphology of the weathered surface is a reflection of the presence of oikocrysts of Opx, which crystallized after Ol at the magmatic stage; they were entirely replaced by the deuterically induced Tlc + Tr at Pados-Tundra. (2) Differential rates of weathering are implied for rock-forming minerals in these ultramafic rocks, with a higher resistance of Opx vs. Fo-rich Ol, and Tlc + Tr vs. Fo-rich Ol. (3) The ball-like shape of the large spheroids, produced by magmatic processes, may likely represent an additional factor of their higher stability to weathering in the superficial environment. Similar patterns can be expected in other mafic-ultramafic complexes, especially in layered intrusions.
The Canadian Mineralogist, 2002
is a new parkerite-type sulfide discovered in the Penikat layered complex, Finland. It occurs in ... more is a new parkerite-type sulfide discovered in the Penikat layered complex, Finland. It occurs in altered pyroxenite in the Kirakkajuppura deposit in association with actinolite and clinochlore, accessory chromite, various platinum-group minerals [vysotskite, zvyagintsevite, cuprorhodsite-(ferrorhodsite)-malanite, laurite-erlichmanite, irarsite, keithconnite, unusual Pb-(Pd)-rich thiospinels of Cu, Fe, Rh and Ir, unnamed Pd 9 PbO 10 and Rh(Ni,Fe,Cu) 2 S 3 ], Pd-rich gold, and minor base-metal sulfides (chalcopyrite, bornite and millerite). Laflammeite occurs as individual subhedral to euhedral crystals up to 0.3 mm in size, and in intergrowths with Pt-Ni-poor vysotskite. Laflammeite is opaque and cream-colored with a brownish tint in reflected light in air. The anisotropy is weak, from brownish gray to grayish brown. The bireflectance is weak; pleochroism was not observed. Reflectance percentages in air (and in oil) are,
The Palaeoproterozoic Penikat layered intrusion in northern Finland contains at least six platinu... more The Palaeoproterozoic Penikat layered intrusion in northern Finland contains at least six platinum-group element (PGE) enriched horizons exposed along >20 km of strike, amongst them the SJ reef, with 3-7 ppm Pt+Pd over a width of 1-2 m. Important PGE enrichments also occur in the PV reef (avg. 2.6 ppm Pd, 4 ppm Pt over 1.1 m) and AP1 reef (avg. 6.2 ppm Pd, 1.7 ppm Pt over 0.7 m0. The PGE reefs formed by predominantly orthomagmatic processes. Late-magmatic fluids played no significant role in concentrating PGE. Subdued stratigraphic variation in incompatible trace element ratios (Ce/Sm mostly 5-10) and Nd isotope compositions (eNd -3 to -1) indicate that mixing of distinct magmas, or in situ contamination with country rocks, was not required to form the reefs. There is also no evidence for addition of external sulphur, based on S/Se ratios at, or below, primitive mantle levels. Instead, we propose that sulphide melt saturation was reached in response to magma fractionation, and th...
The Kirakkajuppura platinum-group-element (PGE) deposit, in the Penikat layered complex, Finland,... more The Kirakkajuppura platinum-group-element (PGE) deposit, in the Penikat layered complex, Finland, is associated with the low-sulfide Sompujiirvi PGE reef, located near the contact between ultramafic and gabbroic cumulates, close to the country rocks. The deposit is unique among PGE deposits in layered intrusions as it displays, on a relatively small scale, very high bulkrock concentrations of PGE (up to >0 5 kg/t total PGE) aLong with a low content of S and Cr, e.g.,\fcn 224 ppm. 108 ppm S and 0.8 wt.% Cr; (Pd + Pt)/(Os + Ir + Ru) = 93.9 and Pd/ft = 3.0 (mean of four whole-rock analyses). The platinum-group minerals (PGM), predominantly Pt-Ni-poor vysotskite-braggite, zvyagintsevite and a Pd-Pb oxide, mainly occur in altered pyroxenite, among grains of Mg-rich actinolite and clinochlore, as unusually large veinlerlike or chain-like aggregates up to -1 cm in length. In agreement with the whole-rock data, the PGM do not show a close relationship with base-metal sulfides (8M,9) and ...
Mineralogy and Petrology, 2020
Several mafic-ultramafic layered intrusions were emplaced in the Fennoscandian Shield during wide... more Several mafic-ultramafic layered intrusions were emplaced in the Fennoscandian Shield during wide-spread mantle-sourced magmatism at 2.5–2.4 Ga. The Näränkävaara intrusion (surface area 5 × 30 km 2 ), northeastern Finland, contains a 1.5–2 km thick basal dunite (not dated), and a 1.5 km thick layered series (2436 ± 5 Ma). A newly discovered marginal series between the basal dunite and the layered series indicates that the basal dunite is older, and highlights the need for further study on their relationship. Along its southern basement contact, the basal dunite contains a 200–300 m thick zone of olivine ortho- and mesocumulates, but the bulk of it is composed of olivine adcumulates and lesser olivine-orthopyroxene heteradcumulates. Based on whole-rock geochemistry, the basal dunite is divided into a low-Fe zone (average FeO t 10.2 wt% and Ni 2250 ppm) and a high-Fe zone (average FeO t 12.5 wt% and Ni 1700 ppm). Both zones have high MgO (32–47 wt%) and varying Cr (830–5160 ppm) and A...