TWO NEW GEOCHEMICAL CERTIFIED REFERENCE MATERIALS (CRMS) REPRESENTATIVE OF NORITE AND ANORTHOSITE FROM THE STILLWATER COMPLEX, MT, USA

The Stillwater Igneous Complex in MT, USA, is one of the most notable mafic layered intrusions in the world, comparable to the Bushveld in S. Africa and a significant producer of PGE ore. Igneous petrologists have long debated the geochemical events that lead to the formation of complicated igneous layering, with particular interest to the ore-grade chromite and PGE layers in these intrusions. Representative anorthosite and norite reference materials are essential to properly calibrate instrumentation as well as quality control results; these are the first such widely available reference materials from the Stillwater Complex and will have a long-term availability (>200 kgs each produced).

Each rock type was processed internally using customized powder processing equipment and homogeneity was evaluated by WD-XRF for majors and minors and ICP-MS for traces. Certification was carried out by ten international laboratories that performed additional WD-XRF, ICP-OES, ICP-MS, and neutron-activation analyses. We present here final certification results for 40+ major, minor, and trace elements in each CRM at the certified and indicative levels, as well as associated uncertainties. Of particular interest are elevated concentrations of Al₂O₃, CaO, Ni and Cr.