Geology and metallogenic potential of the northwesternmost Norrbotten Province around Altevatn in Troms, northern Norway

Slagstad, Trond; Willemoes-Wissing, Bjørn; Coint, Nolwenn; Stampolidis, Alexandros; Ganerød, Morgan; Ofstad, Frode

doi:10.17850/njg95-3-07

Cited by 3 publications

(6 citation statements)

References 36 publications

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“…At present, we therefore favor the hypothesis by Schärer et al (1996) that the zircons most likely grew from small amounts of evolved melt trapped between high-Al orthopyroxene megacryst aggregates. Although this evolved, residual melt would initially have been homogeneously distributed in the crystallizing anorthosite mush, the presence of the rigid high-Al orthopyroxene megacrysts might have created local low-pressure sites into which the residual melt migrated and concentrated, as has been observed in some migmatites (e.g., Slagstad et al, 2015). We therefore interpret the zircons to have grown from the last vestiges of melt in the anorthosite.…”

Section: Anorthosite Emplacement Related To Doming In An Extending Comentioning

confidence: 70%

Magma-driven, high-grade metamorphism in the Sveconorwegian Province, southwest Norway, during the terminal stages of Fennoscandian Shield evolution

et al. 2018

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Recently it has been argued that the Sveconorwegian orogeny in southwest Fennoscandia comprised a series of accretionary events between 1140 and 920 Ma, behind a long-lived, active continental margin characterized by voluminous magmatism and high-grade metamorphism. Voluminous magnesian granitic magmatism is recorded between 1070 and 1010 Ma (Sirdal Magmatic Belt, SMB), with an apparent drop in activity ca. 1010-1000 Ma. Granitic magmatism resumed ca. 1000-990 Ma, but with more ferroan (A type) compositions (hornblende-biotite granites). This ferroan granitic magmatism was continuous until 920 Ma, and included emplacement of an AMCG (anorthosite-mangerite-charnockite-granite) complex (Rogaland Igneous Complex). Mafic rocks with ages corresponding to the spatially associated granites suggest that heat from underplated mafic magma was the main driving force for lower crustal melting and long-lived granitic magmatism. The change from magnesian to ferroan compositions may reflect an increasingly depleted and dehydrated lower crustal source. High-grade metamorphic rocks more than ~20 km away from the Rogaland Igneous Complex yield meta morphic ages of 1070-1015 Ma, corresponding to SMB magmatism, whereas similar rocks closer to the Rogaland Igneous Complex yield ages between 1100 and 920 Ma, with an apparent age peak ca. 1000 Ma. Ti-in-zircon temperatures from these rocks increase from ~760 to 820 °C ca. 970 Ma, well before the inferred emplacement age of the Rogaland Igneous Complex (930 Ma), suggesting that long-lived, high-grade metamorphism was not directly linked to the emplacement of the latter, but rather to the same mafic underplating that was driving lower crustal melting. Structural data suggest that the present-day regional distribution of high-and low-grade rocks reflects late-stage orogenic doming.

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Section: Anorthosite Emplacement Related To Doming In An Extending Comentioning

confidence: 70%

Magma-driven, high-grade metamorphism in the Sveconorwegian Province, southwest Norway, during the terminal stages of Fennoscandian Shield evolution

et al. 2018

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“…Pleitavino et al (2021) utilized the concentrations of U, Th and K as well as the radiogenic heat production to divide genetic types of granites according to I‐S‐A‐M types. Given that the large ion lithophile elements (LILEs), incompatible elements (e.g., Li, Rb), and U, Th, and K elements preferentially enter melt during magma crystallization differentiation, the highly fractionated granites thus have high potential to form high heat production granite (Pleitavino et al, 2021; Slagstad, 2008; Xue, 2017). In addition, some of S‐type granites also might form high heat production granites, resulting from crustal re‐melting when LILEs get to be concentrated within granites (Zhou et al, 2020).…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, these plutons, including Nannihu, Daping, Shibaogou, Lengshui, Shangfang, Yuku, and Huoshenmiao plutons, were formed under post‐collision settings during the Late Mesozoic (Yang et al, 2019), whereas the coeval Huangbeiling pluton was generated under syn‐collision settings (Qian et al, 2022). In general, the collision‐related tectonic settings and high degree of fractionation of mantle‐derived melts would be favourable for the formation of high‐degree fractionation of granitic magmas, which will result in the high concentrations of incompatible elements (e.g., U, Th) and the formation of high heat production granites (Slagstad, 2008).…”

Section: Discussionmentioning

confidence: 99%

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High heat production of the Late Mesozoic Luanchuan granites from East Qinling Orogen, China: Implications for petrogenesis and mineral exploration

et al. 2023

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Some of the high heat production granites in the continental crust have been suggested to be linked with I‐, A‐, and partly S‐type granitoids which aided in the formation of associated polymetallic deposits. Here, we investigate the Shibaogou and Laojunshan plutons in the Luanchuan region, East Qinling Orogen, China, and integrate these with published geochemical information to compute the rate of heat production per unit rock mass (RHP value, unit μW/m3). In addition, we also present RHP contour maps of all the Late Mesozoic granitic plutons in the Luanchuan region, with a view to evaluate the link among the high heat production granites, their petrogenesis and mineralization. The RHP values of granitoids in the Luanchuan region vary from 1.7 to 14.44, with the Nannihu pluton showing the highest RHP peak value of 6.04, whereas the Huoshenmiao pluton has the lowest RHP peak value of 2.59. The RHP values have a positive correlation with the degree of magma differentiation, as suggested that the Nannihu pluton is a highly fractionated I‐type granite and the Huoshenmiao pluton is a quartz diorite. This is also consistent with U, Th and K which are incompatible elements that tend to enter the melt during magma evolution. Furthermore, the higher RHP value intrusions (e.g., Nannihu, Daping) show close genetic links with high economic deposits, whilst the plutons with lower RHP values are generally related to small ore deposits. We envisage that the high heat production granites underwent protracted cooling process, which promote the convection and circulation of hydrothermal fluids, so that ore‐forming materials (e.g., Mo, W) can sufficiently accumulate and precipitate as economic mineralization. This also indicates that these granitoids with relatively higher RHP values have a greater metallogenic potential. The RHP contour mapping results show high RHP value domains ranging from 2.68 to 4.82 in the southeast and northeast segments of the Shibaogou pluton, whereas the RHP values of other regions in this pluton vary from 2.14 to 2.68. In contrast, the high RHP value regions mostly occur within the western and eastern parts of the Laojunshan pluton, and range from 4.91 to 6.21. Other regions in the Laojunshan pluton have low RHP values in the range of 2.69–4.91. A few Mo‐W deposits are mostly hosted in the southeastern part of the Shibaogou pluton, implying that these regions with high RHP values might have higher metallogenic potential. The contour mapping of RHP maximum, minimum, average and peak values of all the Mesozoic granitic plutons in the Luanchuan region also show high value zones within and/or at peripheral regions of the Nannihu ore fields and these segments between the Nannihu and Yuku ore fields, which suggest that these zones likely have high potential for Mo‐W exploration.

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“…The Målselva Group mainly shows a very low magnetic response, and this low-magnetic anomaly seems to continue towards the northwest, under the Caledonian nappes, to the outer Malangen area between eastwards into the Altevatn area. Furthermore, supracrustal units with low metamorphic grade are not known from the Altevatn basement area (Stølen, 1997;Slagstad et al, 2015). The diffuse magnetic signals are partly due to the lower quality of the data, but probably also due to thicker Caledonian nappes.…”

Section: Regional Correlationsmentioning

confidence: 99%

Geology and gold mineralisation in the Mauken Precambrian basement window, Målselv, Troms, northern Norway

Bjerkgård¹,

Slagstad²,

Henderson³

et al. 2016

NJG

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The Mauken Precambrian basement window in southern Troms is situated approximately midway between the West Troms Basement Complex (WTBC) and Altevatn-Dividalen basement areas. Work in the Mauken window is part of a NGU project focusing on the basement areas with the main goal to work out a structural-tectonic-metallogenic model and interpretation for the whole region. The window comprises a central unit of metavolcanic and metasedimentary rocks -the Målselva Group, bounded by mainly felsic intrusive rocks to the west,.the Andsfjell-Kampen intrusions, and a very diverse suite of intrusive rocks in the east,.the Øverbygd intrusions. Ages obtained (U-Pb on zircons) on the intrusions range from Neoarchaean to Palaeoproterozoic (2836-1892 Ma). Geochemistry of the greenstone unit in the Myrefjell formation of the Målselva Group indicates an arc/back-arc affinity. The upper part of the Målselva Group, the Aurevatn formation, consists of clastic sedimentary rocks such as siltstone and sandstone, partly forming turbiditic units. On this basis, the Målselva Group must have been formed close to a continent. A granodiorite intruding the greenstone was dated to 2108 Ma, meaning that the lower part of the Målselva Group is Palaeoproterozoic or older in age. Regional magnetic data indicate that the most likely continuation of the Mauken window under the Caledonian nappes is to the area between Senja and Kvaløya of the WTBC, and the Astridal and Torsnes belts of supracrustal rocks. The only significant gold mineralisation found in the Mauken window is the so-called 'Main Zone', which is localised in a sand-/siltstone unit close to the contact to underlying greenstone. Gold is associated with and strongly correlated with arsenic. One possible source of the gold and arsenic in this setting is carbonaceous sediments, which are known to concentrate different metals in early formed, diagenetic iron sulphides. A possible formation model for the deposit is that gold, arsenic and sulphur were released from the diagenetic sulphides because of recrystallisation during metamorphism, and that the resulting fluids followed structural pathways, e.g., along or close to the greenstone-sediment contact, and deposited the metals higher up in the sequence. With the size and gold grades of the mineralised zone known today, the mineralisation is not economic. In the RombakTectonic Window of northern Nordland there are some Au-As mineralisations which are associated with metagreywacke and metasiltstone. Those mineralisations have been suggested to be of orogenic type, related to shear zones and structures formed during the Palaeoproterozoic, but they also show many similarities with the Mauken mineralisation, suggesting that these too could have formed in the same way.

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Geology and metallogenic potential of the northwesternmost Norrbotten Province around Altevatn in Troms, northern Norway

Cited by 3 publications

References 36 publications

Magma-driven, high-grade metamorphism in the Sveconorwegian Province, southwest Norway, during the terminal stages of Fennoscandian Shield evolution

Magma-driven, high-grade metamorphism in the Sveconorwegian Province, southwest Norway, during the terminal stages of Fennoscandian Shield evolution

High heat production of the Late Mesozoic Luanchuan granites from East Qinling Orogen, China: Implications for petrogenesis and mineral exploration

Geology and gold mineralisation in the Mauken Precambrian basement window, Målselv, Troms, northern Norway

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