The ratio of Zn:Ni and Zn:Cu in basaltic rocks is not consistent with these ratios in Ni-pyrrhotite ores considered to be of immiscible segregation (magmatic) origin, in view of the fact that sphalerite occurs as a minor constituent associated with chalcopyrite and pyrrhotite in basaltic rocks and norites. If the magmatic origin is to be accepted for the so-called magmatic Ni-pyrrhotite ores, the low Zn:Ni and Zn:Cu ratios of these ores must be explained. Likewise, any other mode of origin for these ores must explain their relatively low Zn concentrations.

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