Epigenetic gold occurrence in a Paleoproterozoic meta-evaporitic sequence in the Rompas-Rajapalot Au system, Peräpohja belt, northern Finland

Ranta, Jukka-Pekka; Molnár, Ferenc; Hanski, Eero; Cook, Nick

doi:10.17741/bgsf/90.1.004

Cited by 18 publications

(30 citation statements)

References 64 publications

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“…2; Ranta et al, 2018). This is in good agreement with the extensive pre-orogenic albitization event, which is widespread in the PB and typically initiated during sedimentation and diagenetic processes in evaporitic environments (Eilu et al, 2003;Ranta et al, 2018). This pre-orogenic Na-metasomatism mechanically prepared the rocks for the Co-rich mineralization within the Co-Only zones.…”

Section: Sources and Precipitation Of Cobalt And Goldsupporting

confidence: 77%

“…Considering the intratectonic basinal setting at Rajapalot, the source rocks for the Co-transporting high-salinity fluids, could have been the evaporitic Petäjäskoski Formation (see Fig. 2; Ranta et al, 2018). This is in good agreement with the extensive pre-orogenic albitization event, which is widespread in the PB and typically initiated during sedimentation and diagenetic processes in evaporitic environments (Eilu et al, 2003;Ranta et al, 2018).…”

Section: Sources and Precipitation Of Cobalt And Goldsupporting

confidence: 52%

“…1c). This age was also confirmed by Ranta et al (2017Ranta et al ( , 2018, who conducted a trace element, boron isotope and fluid inclusion study on tourmaline from quartz-tourmaline-sulfide-native gold veins at Rajapalot (Palokas prospect). By using tourmaline, the authors could evaluate the physico-chemical characteristics of the mineralizing fluid, which provide a genetic link to the 1.78 Ga granitoid magmatism and the fracture-related gold mineralization (Ranta et.…”

Section: Geology Stratigraphy and Mineralization Of The Rajapalot Au-co Projectmentioning

confidence: 57%

“…The area of the Rajapalot Au-Co project hosts an epigenetic hydrothermal Au-Co-system that has properties comparable to an orogenic gold deposit with atypical metal association. Considering that the supracrustal sequences of the PB formed in an old intracratonic basin, multiple hydrothermal events could have invoked metal precipitation during pre-, syn-and post-orogenic processes (Lahtinen et al, 2012;Eilu, 2015;Molnár et al, 2016Molnár et al, , 2017Ranta et al, 2018). There is even the possibility that prior to regional metamorphism the episodic intrusion of felsic and mafic magmas locally altered the supracrustal sequences https://doi.org/10.5194/se-2021-119 Preprint.…”

Section: Relationship Between Alteration and Concentration Of Elements In The Host Rocksmentioning

confidence: 99%

“…However, the supracrustal metamorphic model is not in favor of genetically linking the post-tectonic intrusions with fracture-related gold. In association with the tectonic evolution of the PB, three emplacement periods of granitic intrusions are distinguished: (i) pre-orogenic Kierovaara granite (1.99 Ga; Ranta et al, 2018),…”

Section: Sources and Precipitation Of Cobalt And Goldmentioning

confidence: 99%

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Application of lithogeochemical and pyrite trace element data for the determination of vectors to ore in the Raja Au-Co prospect, northern Finland

Raič

Molnár

Cook

et al. 2021

Preprint

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Abstract. Discovering ore deposits is becoming increasingly difficult, and this is particularly true in areas of glaciated terrains. As a new exploration tool for such terrains, we test the vectoring capacities of trace element and sulfur isotope characteristics of pyrite, combined with quantitative tools for whole-rock geochemical datasets. Our target is the Rajapalot gold-cobalt project in northern Finland, where metamorphosed Paleoproterozoic volcanic and-sedimentary rocks of the Peräpohja belt host recently discovered gold prospects, which also have significant cobalt enrichment. The focus is particularly put on a single gold-cobalt prospect, known as Raja, an excellent example of this unusual cobalt-enriched gold deposit, common in the metamorphosed terranes of northern Finland. The major lithologies at Rajapalot comprise variously altered and deformed calcsilicate rocks that alternate with albitized metasedimentary units, mafic volcanic rocks, mica schist and quartzite. Mineralization at Rajapalot prospects is characterized by an older Co-mineralizing event and a younger high-grade Au-mineralization with re-mobilization and re-deposition of Co. Detailed in situ laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a powerful technique that produces the robust trace element and sulfur isotope databases from paragenetically and texturally well-characterized pyrite from the Raja prospect. The results are treated with appropriate log-ratio transformations and used for multivariate statistical data analysis, such as the computation of principal components. Application of these methods revealed that elements such as Co, Ni, Cu, Au, As, Ag, Mo, Bi, Te, Se, Sn, U, Tl and W have high vectoring capacities to discriminate between Co-only and Au-Co zones, as well as between mineralization stages. The systematic pyrite study suggests that homogenous sulfur isotopic characteristics (1.3 ‰ to +5.9 ‰.) and positive loadings of Co, Se, As, Te, Bi and Au onto PC1 are reflective of an early stage of Co-mineralization, while the opposing negative loadings of Mo, Ni, W, Tl, Cu and Ag along PC1 are associated with the Au-mineralizing event. The sulfur isotopic signature of the latter pyrite type is between −1.2 ‰ and +7.4 ‰. Subtle patterns recognized from the whole-rock geochemistry favor an As-Au-Se-Te-W-U signature along the positive axis of PC1 for the localization of high-grade Au-Co-zones, whereas the element group Ni, Cu, Co, Te, Se and As, which has negative loadings onto PC2, will predict Co-only zones. This study shows the efficiency of trace element geochemistry in mineral exploration targeting, which has the capacity to define future targets by characterizing the metallogenic potential of a host rock, as well as distinguishing various stages of mineralization.

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Section: Sources and Precipitation Of Cobalt And Goldsupporting

confidence: 77%

Section: Sources and Precipitation Of Cobalt And Goldsupporting

confidence: 52%

Section: Geology Stratigraphy and Mineralization Of The Rajapalot Au-co Projectmentioning

confidence: 57%

Section: Relationship Between Alteration and Concentration Of Elements In The Host Rocksmentioning

confidence: 99%

Section: Sources and Precipitation Of Cobalt And Goldmentioning

confidence: 99%

See 3 more Smart Citations

Application of lithogeochemical and pyrite trace element data for the determination of vectors to ore in the Raja Au-Co prospect, northern Finland

Raič

Molnár

Cook

et al. 2021

Preprint

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Silver isotope analysis and systematics of native gold from the Rajapalot Co-enriched gold deposit, Finnish Lapland

Tepsell,

Lahaye,

Molnár

et al. 2023

Miner Deposita

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Silver is probably the closest isotopic proxy to track monoisotopic gold and has been shown to have great potential to yield new information on the origin and enrichment processes of gold. This study describes the development of a tailored analytical protocol for accurate analysis of Ag isotopes and provides the first Ag isotope data for the Paleoproterozoic Rajapalot Au-Co deposit, Finnish Lapland. Six native Au samples yield ε109Ag values (relative to NIST SRM 978a) from −6.8 to +2.1 and are within the range of Ag isotopic compositions reported for native Au samples. The mean of the analyzed Au samples is ε109Ag = −3.8 ± 1.7 (2SD) with most of the samples with negative ε109Ag values (−6.7 to −2.0); one sample has a positive ε109Ag value of +2.1 ± 0.5. Silver isotope fractionation in the Rajapalot Au deposit was likely associated with physicochemical processes related to deposition and/or re-mobilization of the ore rather than with source region inheritance. It is suggested that redox reactions involving Ag+ ↔ Ag0 phase change primarily account for the isotopic differences within the deposit. Our results also suggest that the Rajapalot Au-Co deposit was formed via multistage ore-forming processes and/or that the primary ore was re-mobilized, which caused isotope fractionation along fluid pathways. Silver isotope variation within a deposit may mark a fractional crystallization trend with the lightest isotopic composition representing the earliest precipitate. Hence, Ag isotopes show potential as an isotopic vectoring tool in search of Au-enriched domains.

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Cobalt Prospectivity Using a Conceptual Fuzzy Logic Overlay Method Enhanced with the Mineral Systems Approach

Nykänen,

Törmänen,

Niiranen

2023

Nat Resour Res

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This paper describes mineral prospectivity research conducted in Finland to predict favorable areas for cobalt exploration using the “fuzzy logic overlay” method in a GIS platform and public geodata of the Geological Survey of Finland. Cobalt occurs infrequently as a core product in mineral deposits. Therefore, we decided to construct separate conceptual mineral prospectivity models within the Northern Fennoscandian Shield, Finland, for four deposit types: (1) “Orthomagmatic Ni–Cu–Co sulfide deposits,” (2) “Outokumpu-type mantle peridotite-associated volcanogenic massive sulfide (VMS)-style Cu–Co–Zn–Ni–Ag–Au deposits,” (3) “Talvivaara black shale-hosted Ni–Zn–Cu–Co-type deposits” and (4) “Kuusamo-type (orogenic gold with atypical metal association) Au–Co–Cu–U–LREE deposits”. In addition, we created a model combining till geochemical data with data derived from bedrock drilling and mineral indications, including boulders and outcrops. The mineral prospectivity models were statistically tested with the “receiver operating characteristics” method using exploration drilling data from known mineral deposits as validation sites. In addition, the predictive performance of the models was evaluated by using success rate curves, where the number of previously identified deposits was compared with the area coverage of the predicted highly favorable areas. These results indicate that the knowledge-driven mineral prospectivity method using parameters derived from mineral systems models is effective in defining favorable exploration target areas at the regional scale. This study's innovation lies in its comprehension of the process of evaluating mineral prospectivity when the commodity of interest is not the primary commodity within the mineral system.

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Epigenetic gold occurrence in a Paleoproterozoic meta-evaporitic sequence in the Rompas-Rajapalot Au system, Peräpohja belt, northern Finland

Cited by 18 publications

References 64 publications

Application of lithogeochemical and pyrite trace element data for the determination of vectors to ore in the Raja Au-Co prospect, northern Finland

Application of lithogeochemical and pyrite trace element data for the determination of vectors to ore in the Raja Au-Co prospect, northern Finland

Silver isotope analysis and systematics of native gold from the Rajapalot Co-enriched gold deposit, Finnish Lapland

Cobalt Prospectivity Using a Conceptual Fuzzy Logic Overlay Method Enhanced with the Mineral Systems Approach

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