Pahtavaara – Geology & Exploration
In mid-2018 the company completed a re-appraisal of the regional geological setting of the Pahtavaara project and highlighted the prospectivity for hosting further orogenic gold deposits beyond the Pahtavaara mine. A detailed ground gravity survey over 200km2 of the licence, a new magnetic survey, detailed mapping, logging of historic drilling and over 15,000m of reconnaissance drilling resulted in the discovery of six new gold occurrences in Area 1, 25km southwest of the Pahtavaara mill.
Highlights from recent geological studies
- Rupert Resources’ revised 2018 geological interpretation of the existing mine identified Pahtavaara as possessing a significantly larger footprint (up to 1,500m strike and 500m width) than previously considered. The regional setting was also shown to be comparable with deposits hosted in other greenstone belts including the Abitibi in Canada and Norseman-Wiluna in Western Australia. The Abitibi and Norseman Wiluna belts have each hosted over 100Moz of gold.
- Identification of distinct geological domains within Savaukoski Group i.e. Pahtavaara Domain ultramafics in the east forming two distinct volcanic centres and, the Rajala Domain mafic-intermediate volcanics, coarse sediments and fine turbidites in the west that demonstrate more similarities to the Kittila group, to the north west.
- The 2018 structural studies also identified a 25km structural corridor between four distinct domains which likely acted as a regional fluid conduit, and has potential to host mineralisation, as demonstrated by the discoveries in Area 1.
- The definition of the main phase of gold mineralisation, associated with the second D2 structural deformation phase during convergence and basin formation around an Archean dome. A later D3 east-west compression phase potentially re-activates deep seated structures.
Area 1 geology
Regional exploration has focused on gold mineralisation associated with predominantly sedimentary host rocks, including ultramafic-derived sedimentary units, in the western part of the Pahtavaara exploration licences (Area 1). Here, late brittle fracture in albite-altered siltstones hosts gold mineralisation associated with either pyrite-tourmaline veinlets e.g. Island and Saitta prospects, or elsewhere, pyrrhotite-chalcopyrite assemblages e.g. Heinä Central prospect. At the Ikkari discovery (first reported in May 2020), gold mineralisation is associated with strong pyrite-silica alteration envelope and albite-sericite-pyrite zones of high-grade gold.
The current interpretation suggests that late gold-bearing fluids have been introduced along pre-existing pathways, including remobilised faults and earlier metamorphic quartz-siderite veins.
Reconnaissance base of till sampling is employed to generate new targets with follow up drill targeting based on base of till anomalies coincident with structural interpretation from detailed geophysics.
Pahtavaara mine geology
Pahtavaara gold mine is hosted by the predominantly pyroclastic, voluminous ultramafic volcanics of the Sattasvaara komatiite complex, part of the 2.05Ga Savukoski group (Mutanen, 1997). Least altered komatiites consist of a talc-chlorite assemblage resulting from regional greenschist facies metamorphism. Extrusive ultramafics, including pillow lavas and hyaloclastites are intercalated with minor sedimentary lenses, comprising predominantly carbonaceous shales and coarse, crystalline actinolite-tremolite assemblages believed to be the alteration product of a more pyroxenitic volcanic phase.
At Pahtavaara Mine the coarse-grained amphibole dominated lithologies, dip and plunge subvertically to the west-southwest within the larger, more diffuse, amphibole porphyroblast alteration domain which overprints the talc schists. Mineralisation is hosted predominantly by:
- coarse-grained and non-schistose amphibole rocks hosting brittle dolomite ± quartz (± barite) veins, representing a relatively early, brittle phase of gold mineralisation and thus limited to the amphibolite rocks and synchronous the with the D2 folding of the wider komatiite sequence.
- biotite-talc (± chlorite) dominated schists with talc-carbonate ± pyrite ± magnetite veins, which have been interpreted to represent a relatively late ductile phase of gold mineralisation related to failure at the contact between the amphibolite rocks and the talc-chlorite schists.
Gold mineralisation is identified in two phases: early fine grained and a later, more coarse-grained phase. Both are ‘free’ gold and the deposit exhibits predominantly non-refractory metallurgical characteristics.
Gold at Pahtavaara was previously mined from two main zones Samurai and DB with the Karoliina and Lansi zones discovered towards the end of the last period of ownership in 2013. Recent work by Rupert has generated three new targets at Harpoon, NFE and T-Zone.
In April 2018, Rupert reported an Inferred mineral resource at a 1.5 g/t Au cut off grade of 4.6 Mt at a grade of 3.2 g/t Au (474 koz). A link to the full National Instrument 43-101 report can be found below
Potential to increase yield above historical 2000 oz/vertical metre
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