Stillwater igneous complex

[3] The region had a quartz monzonite intrusion and underwent extensive metamorphism, faulting and folding during the Archean at about 2500 Mya.

The area was intruded by north trending mafic dikes before being unconformably covered by a middle-Cambrian sedimentary rock sequence.

[4] The intrusion forms a linear body stretching some 30 miles (48 km) and striking roughly N 60 °W and dipping from 50° to near 90° to the northeast.

The platinum group orebody is located in the lower part of the Banded series within a horizon referred to as the J-M Reef.

[1] In July 1972, the area was used by NASA to geologically train the Apollo Astronauts in recognizing a coarse grained igneous intrusion.

Stillwater igneous complex around Mouat chromite mine
Chromitite with bronzite phenocrysts from Stillwater Igneous Complex
Sulfidic serpentintite, platinum-palladium ore from the Stillwater Mine. This is an altered pegmatitic dunite very richly infused with intercumulate Pt/Pd-rich chalcopyrite & pyrrhotite (golden metallic minerals). In this sample, the blackish areas are serpentine masses (formerly large olivine crystals). Some magnetite is also mixed in with the serpentine. Ore grade is about 2.5 ounces of Pd-Pt per ton of rock, with a Pd-Pt ratio of about 3:1.