Orebodies
The chromium orebodies are restricted to the peridotite member of the ultramafic zone. The platinum group orebodies are located in the lower part of the banded zone within a horizon referred to as the J-M reef.
The J-M Reef is similar to the Merensky Reef of the Bushveld complex of South Africa. It is a continuous layer near the base of the banded zone. It consists of one to three meter thick pegmatitic peridotite and troctolite with disseminated sulfide minerals. Common sulfides include pyrrhotite, pentlandite (containing up to 5% Pd), and chalcopyrite along with lesser amounts of moncheite ((Pt,Pd)(Te,Bi)2), cooperite ((Pt,Pd,Ni)S), braggite ((Pt,Pd,Ni)S), kotulskite (Pd(Te,Bi)1-2) and platinum-iron alloys. Overall the reef contains an average of 20-25 ppm platinum plus palladium in an average two meter thicknesss. It has a Pd/Pt ratio of about 3.6.
Read more about this topic: Stillwater Igneous Complex