GEOCHEMICAL ASSESSMENT OF THE METALLOGENIC POTENTIAL OF PROTEROZOIC LIPS OF CANADA

The association between mafic-ultramafic Large Igneous Provinces (LIPs) and magmatic Ni-Cu-PGE mineralisation is well established; however, the Precambrian LIP record is poorly understood in terms of the processes that operate during LIP formation, the potential for LIPs to host hitherto unknown Ni-Cu-PGE mineralisation, and the lithogeochemical techniques and signatures that can differentiate between barren and prospective LIPs.

Four key factors need to be determined before the Ni-Cu-PGE prospectivity of a LIP can be identified: (1) are the magmas that formed the LIP fertile; (2) what processes control the formation of Ni-Cu-PGE mineralisation in LIPs and what geochemical signatures do these processes have; (3) when and where does sulphur saturation occur in an individual LIP and how can this be identified and (4) what techniques are effective in discriminating between barren and prospective LIPs and between different segments of a LIP. To address these points, here we present initial interpretations of whole-rock geochemistry from eight LIPs within Canada, using the database of Ernst and Buchan (2010; GSC Open File 6016); the 1.14 Ga Abitibi, 1.87 Ga Chukotat, 0.72 Ga Franklin, 0.59 Ga Grenville, 1.27 Ga Mackenzie, 2.49-2.45 Ga Matachewan, ~1.25 Ga Seal Lake and 1.24 Ga Sudbury LIPs.

A number of the LIPs studied, for example the Matachewan, Mackenzie and Chukotat events, have both chalcophile element depleted and undepleted samples; the most contaminated samples from these events are amongst the most chalcophile element depleted, suggesting that these LIPs underwent S-saturation due to assimilation of crustal material. This caused the segregation of magmatic sulfides, potentially linking to the Raglan and Muskox mineralization associated with the Chukotat and Mackenzie events. Samples from the Abibiti and Seal Lake events are only weakly crustally contaminated and are uniformly depleted in chalcophile elements, suggesting that the primary magmas that formed these LIPs did not sequester significant amounts of chalcophile elements during mantle melting and may not be fertile. In addition, the geochemistry of the Grenville and the majority of the Franklin LIP is suggestive of only small amounts of crustal contamination and does not indicate S-saturation, signifying that these LIPs may be unprospective.