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Kuhmo - Hietaharju

The Hietaharju prospect is associated with a north-northeast trending talc-carbonate altered ultramafic cumulate body with associated multiple, discontinuous zones of chlorite-amphibole rocks. The ultramafic body is approximately one kilometre long and up to 100 metres thick, dipping between 70º east and vertical. The ultramafic is located within a sequence of near vertical to overturned quartzo-feldspathic schists in the east and pyritic schists within komatiitic basalts in the stratigraphic hangingwall in the west.




The deposit occurs as lenses of massive sulphide breccia and fine-grained disseminated sulphide hosted by a talc-carbonate rock and chlorite-amphibole rock unit within the footwall contact. Massive sulphides comprise pyrrhotite and pentlandite with some chalcopyrite. The southern part of the deposit usually occurs within chlorite-amphibole rock and close to the eastern (footwall) contact of the ultramafic unit. The northern part of the deposit is more commonly within talc-carbonate rock and further away from the interpreted footwall contact. The deposit is approximately 200 metres long and the thickness varies from less than 0.5 metre thick massive sulphide veins up to 10 metre thick units of disseminated talc-carbonate rock and massive sulphide veins. An aspect of the Hietaharju deposit that may be of significant economic value is the high platinum group element values reported in Vulcan’s drilling results. Diagrams on the Hietaharju assays indicative for the tenor of the deposit are presented in, Section 3.2.2. Nickel tenor is 2-5% and platinum+palladium is 0.5 – 5ppm. The Ni:Cu ratio of 2 is indicative of a more mafic host than a typical high MgO komatiite.

Previous Exploration

First exploration phase at Hietaharju area was initiated by prospector samples of massive nickel and copper bearing sulphides in the beginning of the 1960`s. Outokumpu completed an exploration program in 1961-63 covering the Kiannanniemi area. This programme led to the discoveries of the Hietaharju and Peura-aho nickel-copper deposits. At Hietaharju this phase of exploration included 22 drill holes totalling over 4000 metres of core.

Outokumpu carried out both a resource estimate in 1970. The conventional polygonal resource estimate on cross sections, quotes 238,000 tonnes at 0.86% nickel, 0.43% copper, 0.05% cobalt and 8.5% sulphur.