Also pentlandite and pyrrhotite predominate, but chalcopyrite is present in appreciable amounts. Largely a matter of speculation. They would appear to be associated with episodes of continental rifting, similar to that responsible for the Columbia River Plateau. Thus, ores are of primary mantle origin much as those of oceanic alpine peridotite deposits. Localization of ores at the base of the sill-like intrusion strongly suggests immiscible liquid segregation and gravitative settling of sulfides.
Some disturbing questions remain.
Flood Basalt Ni-Cu Deposits Host rock is an undifferentiated gabbro, overlain by basalts. Ore bodies occur as tabular layers at the base of the gabbroic sills. Ores and host rock formed in linear, fault-bounded troughs. Intrusives are both younger and smaller than the related LMIs. Dominant ore phases are pentlandite and pyrrhotite.