Magmatic Deposits

Minerals begin to crystallize as a body of molten rock cools, they sink to the base of a magma chamber or they accrete to the sides of it. Htese are most of the time the ordinary minerals which form rocks, but at times they are useful minerals like base metal sulphides or the oxides of chromium, titanium or iron. Mafic or ultramafic igneous rocks can have concentrations of these minerals that have the sufficient amounts to be minable.

A large proportion of the world’s copper and cobalt and a lot of its nickel come from deposits of sulphide of this kind in mafic igneous rocks, like the copper-nickel deposits found in Sudbury, Ontario.

Palladium, platinum and a few other precious metals are most of the time recovered as a byproduct in sulphide-nickel deposits. The sulphides can be disseminated or massive through the silicate rock. Chalcopyrite and pyrrhotite, plus one or more nickel sulphides, are the minerals which are considered the common ones. The mineralized bodies most of the time have tabular or a shape similar to lens.

Chromium and titanium oxides, either disseminated or massive, can also form magmatic deposits. The mineralized bodies can even have the appearance of being in layers similar to sedimentary beds, even though their origin is definitely not sedimentary.