Pechenga and Raglan - Comparison of these northern nickel camps helps in understanding their ore forming processes

Both the Pechenga and Raglan nickel camps are major producers of sulphide nickel. Their remote northern locations have prevented the scope of visits and studies normally seen in more accessible areas. Few geologists get to visit Raglan unless they worked there. Likewise even after the breakup of the Soviet Union, access to Pechenga is relatively difficult. This may explain why the impressive similarities between the two camps have not been described in the literature.

Both Raglan and Pechenga are interpreted to be located in an intercontinental rift. At Raglan the underlying stratigraphy dips consistently northwards and consists of a succession of MORB like mafic volcanites, some alkaline volcanites and related sedimentary rocks. Pechenga is underlain by a very thick sequence of continental alkaline volcanites and evaporitic sediments, followed by more MORB like volcanites and black shales. The ore hosts at Raglan are contaminated komatiitic ultramafic magmas with an estimated MgO content of the parent magma being 18%. The ore hosts at Pechenga are highly contaminated ferropicritic ultramafic magmas with an estimated MgO content of the parent magma of 15%. The best age estimate for each location is between 1950 and 2000 MA. In each case the known ore deposits occur along an east-west belt of hosts rocks about 50 km long and a number of significant deposits occur in each place. Ores occur as a sequence of massive to net textured to disseminated nickel-copper sulphides at the base of peridotite-gabbro (Raglan) or gabbro-wehrlite (Pechenga) bodies of similar size at each camp. The bodies have been variously interpreted as intrusive and extrusive in each case. Later metamorphism is relatively minor, but a series of structural deformation events have modified the original ore depositional sites in both cases. Comparisons of metal ratios, precious metal contents, and sulphur isotopes are also very interesting and will be reviewed in this talk. In both instances the sulphur isotopes and S/Se ratios are consistent with assimilation of sulphur from local sedimentary rocks.

Of particular interest to ore genesis models are the comparison of the ore hosts - their petrology, the timing of contamination, their interpreted mode of emplacement (intrusive, extrusive) and the location of the richest ores.