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 here. The resource was updated in November 2022 as part of the PEA study for Ikkari.
November 2022 Mineral Resource Estimate at various cut-offs for the Pahtavaara mine
The independent and qualified person for the Mineral Resource Estimate as defined by NI43-101 is Brian Wolfe, Principal Consultant, International Resource Solutions Pty Ltd. These are mineral resources not mineral reserves as they do not have demonstrated economic viability. Results are presented in situ. Ounce (troy) = metric tonnes x grade / 31.103475. Calculations used metric units (meters, tonnes, g/t). Any discrepancies in the totals are due to rounding effects. The effective date of the 2022 Mineral Resource Estimate for Pahtavaara is 28 November 2022 and the Mineral Resource Estimate at Pahtavaara is calculated using the multiple indicator kriging (MIK) method. The Mineral Resource Estimate is reported both within a designed open pit and as a potential underground operation outside that The Mineral Resource Estimate at Pahtavaara is reported using a cutoff grade of 0.5g/t Au for mineralisation potentially mineable by open pit methods and 1.5g/t Au for mineralisation potentially extractable by underground methods. The potential open pit mine and cut off-grades are calculated using a gold price at $1650 per ounce, 20% mining dilution, 89% Au recovery, and a mining cost at $2.6/t. process cost at $10.2/t (concentration at Pahtavaara and transport to Ikkari), other costs (includes TSF costs and closure) at $1/t and G&A including royalties and refining at $3.1/t. The calculated cutoff grade is rounded up to 0.5g/t for reporting. The underground cutoff grade is calculated at underground mining cost $49.6/t and underground mining dilution at 10% based on long hole open stoping. The calculated underground cutoff grade is 1.5g/t.
High voltage electrical power is transmitted directly via the main line located 5 km south of the mine. Mine access is by road.
Surface infrastructure at the Pahtavaara mine incudes a heavy vehicle workshop, administration building, two core sheds and a processing plant.
In the first five years of operation over 2 million tonnes of ore was mined from three open pits but from 2006 to 2014 mining was from underground with ramp access.
There has been some 35km of underground 5m x 5m tunnelling developed since operations commenced. Mining was previously undertaken by contractor using long hole stoping methods
Pahtavaara has a working mill with capacity of over 1400tpd. It has a track record of extremely low processing costs due to low power costs and a simple flow sheet comprising a primary crusher, autogenous mill, cyclones, shaking tables, spirals and flash flotation. There is a permitted tailings facility with multiple years of existing capacity and potential to be expanded.