A three-dimensional view of mineralization in the Stillwater J-M Reef

Understanding Mineral Deposits

“…The sulfides generally occur as blebs or as an interstitial network in the lower part of the Reef, and as fine disseminations toward the top. In general agreement with many previous workers (e.g., Upper zone <:::c====~~ Todd et al 1982, Raedeke and Vian (1986) proposed a model involving mixing of magmas oftwo distinct compositions for the formation of the OB-I cumulate layer and its sulfide-PGE zones. In some cases, cuspate sulfides are entirely enclosed in oikocrystic bronzite, which also contains remnants of resorbed olivine, indicating that the resorption occurred after the sulfide liquid bOO solidified.…”

“…Raedeke and Vian (1986) described PGE-sulfide mineralization at four stratigraphic levels ("zones") within the J-M Reef in the Minneapolis adit area, where the Stillwater Mining Company's active mine is located. The sulfides generally occur as blebs or as an interstitial network in the lower part of the Reef, and as fine disseminations toward the top.…”

Metal Deposits in Relation to Plate Tectonics

“…6.13). Sketch illustrating the zones of PGE mineralization associated with the J-M Reef, Stillwater Igneous Complex (After Raedeke and Vian 1986) Platinum group metal mineralization seems to be related in some manner, as in the case of the Merensky Reef, to the presence of a chloride-rich aqueous phase (Boudreau 1988), but in both Complexes the extent to which transport of PGE occurred through the agency of volatiles is unclear (see Naldrett et al 1987). For example, in both Reefs the PGE occur in sulfides that lie at or near the base of a cyclic unit marked by the appearance of high-temperature cumulus phases and reversals of mineral composition trends.…”

Magmatic ore deposits in layered intrusions - Descriptive model for reef-type PGE and contact-type Cu-Ni-PGE deposits

“…By selectively mining approximately 30 to 40 percent of the volume of the reef, 80 percent of the contained metal was recovered (R.W. Vian, oral commun., 1989; see also Raedeke and Vian, 1986). Lateral variations in PGE grade are also characteristic of the Merensky Reef and the UG2 chromitite in the Bushveld Complex.…”