Pahtavaara – Geology & Exploration
In mid 2018 the company announced its first re-appraisal of the regional geological setting of the Pahtavaara project and prospectivity for hosting further orogenic gold deposits beyond the Pahtavaara mine. A detailed ground gravity survey over 200km2 of the licence, detailed mapping, logging of historic drilling and importantly the recent drilling in the south western extents at “Area 1” have all contributed.
• 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.
• 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 similarites to the Kittila group to the north west.
• The 25km structural corridor that acts as a boundary between the domains, likely acted as a regional fluid conduit, and has potential to host mineralisation, as demonstrated by the previous discoveries in Area 1 and gold occurrences at Koppelokangas and Kutuvuoma.
Rupert Resources’ revised geological interpretation of the existing mine identifies Pahtavaara as possessing a significantly larger footprint (up to 1,500m strike and 500m width) than previously considered with a mineralisation style 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.
Pahtavaara is hosted by ultramafic rocks (described as komatiites to high magnesian basalts). Gold mineralisation is structurally controlled and associated with: low sulphidation; quartz-carbonate polyphase veining resulting in a complex vein overprinting history with multiple deformation stages varying from brittle to ductile and back to brittle; intense alteration related to both prograde and retrograde metamorphism.
Pahtavaara’s complex alteration sequence exhibits multiple phases of overprinting, governed by changes in fluid chemistry and their reaction with host rocks with differing mineralogy. Unusual aspects of Pahtavaara include: Ni-Cu-Co geochemical ‘signature’ – most probably due to the ultramafic host rocks and massive sulphide lenses formed during prograde metamorphic and ductile conditions.
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
New drilling and reinterpretation expanding mineralised zones
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