The enigma of the Ni-Cu-PGE sulphide ores of the Sudbury Igneous Complex: what was the source of the metals?

Geochemical studies combined with U-Pb zircon age dating on the newly discovered Frood Intrusion and on the Sudbury Gabbro demonstrate that they are members of the 2.45 Ga Matachewan Large Igneous Province (LIP) and the 2.2 Ga Nipissing Diabase LIP, respectively. The Frood Intrusion has very similar extended spidergrams patterns and geochemistry to other members of the Matchewan LIP including the East Bull Lake and River Valley intrusions. The similarities in geochemistry between Sudbury Gabbro and the Nipissing Diabase demonstrate that the former is a more MgO-rich variant of the latter. Our 2421 +/- 3 Ma age of the Frood Intrusion is within error of ages for other EBL intrusions while our 2203 +/- 11 Ma and 2168 +/- 11 Ma ages for two of the Sudbury Gabbro sills are within error of published ages for the Nipissing Diabase. Mass balance considerations provide strong support for the concept that the metals in the Sudbury Ni-Cu-PGE sulphide deposits were sourced from protores associated with mafic intrusions in the country rocks that were incorporated into the melt sheet that was formed by the impact of the meteorite that formed the SIC.