The (geochemical) Hitchhikers’ Guide to Magmatic Ni-Cu Prospectivity in a Greenstone Belt
The (geochemical) Hitchhikers’ Guide to Magmatic Ni-Cu Prospectivity in a Greenstone Belt
Petri Peltonen1, Hannu Huhma2, Frank Santaguida1 and Steve Beresford1
1) First Quantum Minerals Exploration
2) Geological Survey of Finland Isotope Laboratory
Oxford dictionaries.com defines “hitch-hike”as travel by getting free lifts in passing vehicles.
Exploration geologists can travel quickly through greenstone belts using trace element and isotope geochemistry. While not exactly free, the amount of confidence gained through advanced geochemical analyses outweighs the costs of drilling in the wrong place looking for Ni-Cu-PGE deposits.
The Central Lapland Greenstone Belt in northern Finland developed over a 600 Ma period in which several episodes of rifting and extension are recorded by the widespread occurrence of mafic-ultramafic igneous complexes and dykes. Age dating of these intrusions yields an almost continuous spectrum of ages between 1.8 Ga and 2.6 Ga; however, 6 distinct magmatic episodes are evident. One in particular, at 2.05 Ga, seems to have been the most favourable for saturation of magmatic sulphides and formation of economic Ni-Cu-PGE deposits.
Trace element geochemistry of the 2.05 Ga mafic-ultramafic intrusions further discriminates barren versus productive magmatic centres. The Sm-Nd range for the Kevitsa deposit is unique (εNd = from -3.4 to -6.4) compared to the un-mineralised intrusions which give initial εNd values close to zero. Age data are not available from the host rocks of the Sakatti deposit, but apparent similarities with Kevitsa suggest that it may well belong to the same age group. The Sm-Nd range (εNd (2 Ga) from -3.4 to -6.4) is remarkably similar to Kevitsa implying a significantly enriched component in the magma.
The 2.05 Ga event represents a major metallogenic episode. In the Northern Fennoscandia Shield, crustal contamination was critical for magmas to reach sulphide saturation and produce magmatic Ni-Cu-PGE sulphides. Uncontaminated intrusions remain barren. Tracking this event using geochemical methods has been a useful guide in Finland for focussing advanced exploration. Globally, other circa 2.05 Ga igneous complexes hosting major Ni-Cu-PGE resources includes Bushveld, Molopo Farms, and Uitkomst in South Africa, as well as Voronezh (Russia) and the Booth River Complex (Canada).
Bio: Frank Santaguida, First Quantum
Frank Santaguida is a Principal Exploration Geologist for First Quantum Minerals Ltd. who operates metallic mines and development projects in Central America, South America, Europe, Africa, and Australia. The exploration group is active in greenfields to near-mine projects worldwide.
