| Popis: |
The Fox River Sill is a Paleoproterozoic intrusion that extends for most of the length of the >250 km long Fox River Belt in northeastern Manitoba, Canada. Previous exploration for platinum-group elements (PGE) mineralization in the sill delineated an interval several hundred meters thick of weakly and sporadically mineralized ultramafic and mafic rocks occurring in the upper part of the sill (Upper Central Layered Zone). We describe a second mineralized interval, the KO Zone, near the base of the sill (Marginal Zone). Maximum metal contents obtained to date from the KO Zone are 2.1% Cu, 0.9% Ni and 5.5 g/t combined Pd + Pt + Au. The Marginal Zone comprises the Basal Contact Unit, which is variably contaminated and contains gabbro, melagabbro and lherzolite, overlain by two cyclic units (Cyclic Unit 1, and Cyclic Unit 2) that grade from lherzolite at their base through melagabbro, gabbro, leucogabbro and, locally, anorthosite. The KO Zone occurs at the contact between Cyclic Units 1 and 2 and locally contains disseminated, Cu-, Ni- and PGE-rich sulfide mineralization. The KO Zone features a discontinuous, coarse-grained actinolite-bearing olivine websterite unit, and an overlying medium-grained lherzolite that locally hosts irregularly shaped varitextured gabbro pods. The basal contact of the KO Zone is undulatory and scalloped, with sulfides being concentrated in trough structures. The mineralization is interpreted to have formed in a two-stage process. (1) Early deposition of immiscible magmatic sulfides at the base of Cyclic Unit 2. (2) Upgrading of PGE tenors of the sulfides by interaction with upward migrating, PGE- and volatile-rich intercumulus melt derived from the underlying Cyclic Unit 1. |
