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

• Published in: Solid Earth
• Main Authors: S. Raič, F. Molnár, N. Cook, H. O'Brien, Y. Lahaye
• Format: Article in Journal/Newspaper
• Language: English
• Published: Copernicus Publications 2022
• Subjects: Geology; QE1-996.5; Stratigraphy; QE640-699; Northern Finland
• Online Access: https://doi.org/10.5194/se-13-271-2022; https://doaj.org/article/17a875bdbc34454a9d4880c8208e6834

Discovering ore deposits is becoming increasingly difficult, and this is particularly true in areas of glaciated terrains. As a potential exploration tool for such terrains, we test the vectoring capacities of trace element and sulfur isotope characteristics of pyrite, combined with quantitative statistical methods of 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 amphibolite facies metamorphosed and polydeformed calcsilicate rocks that alternate with albitic 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 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 ...