GEOLOGY AND OXIDE MINERALIZATION OF THE PIPESTONE LAKE ANORTHOSITE COMPLEX, MANITOBA

The late Archean Pipestone Lake anorthosite complex (PLAC) is a 0.9 x 17 km sill-like layered intrusion that is part of a suite of coeval me gacrystic anorthosite bodies in the Cross Lake region, northwestern Su perior Province. Exploration for Ti-V-Fe oxide mineralization and conc urrent geological investigations have contributed to a greater underst anding of the lithostratigraphy of the PLAC and its oxide mineralizati on. Mapping and drill core studies have established a laterally contin uous igneous stratigraphy comprising six leucogabbro/anorthosite zones and three melagabbro/gabbro zones. Field evidence, including disrupte d blocks of layered units, scour contacts, and size-graded and modally -graded layering, suggests younging towards both the northern and the central parts of the complex. A decrease in the anorthite content of t he feldspars from An(75) in the south to An(30), in the north suggests that the magmas become more evolved to the north. Macrothythmic layer ing and gross morphological features suggest that the PLAC crystallize d from four major influxes of geochemically similar basaltic magmas. T he paucity of magmatic erosional features in the PLAC indicates that l ayering developed in a relatively static magma chamber, so that in-sit u crystallization processes are required to account for the observed p etrologic diversity. Drilling has confirmed that a significant Ti-V-Fe resource is contained in two of the four discrete mineralized subzone s in the PLAC. Textural evidence and the stratiform nature of the oxid e-enriched subzones are consistent with a magmatic origin for the oxid e mineralization. (C) 1997 Canadian Institute of Mining, Metallurgy an d Petroleum.