Geochemistry and mineralization of the Archean Titan (Roaring River) intrusion, Thunder Bay, Ontario

Abstract

The 2690 ± 3.2 Ma Titan intrusion is an approximately 7 by 3 km, roughly ovoid, mafic-ultramafic intrusion, located just north of the inferred boundary between the Winnipeg River and Marmion terranes. Outcrop in the area is relatively sparse, largely due to cover from pervasive glacial till and Proterozoic diabase sills associated with the Midcontinent Rift. Titan consists of a variety of lithologies, including leucogabbros, melagabbros, gabbros, and pyroxenites, which are distributed throughout the intrusion. Both mafic and felsic dikes are observed in outcrop, as are felsic breccias. Titan consists of a single magma body, with one pulse of magma which has subsequently undergone fractional crystallization within a closed system. This is supported by smooth linear trends in the major element bivariate plots, with moderate amounts of scatter, and consistent, tight primitive mantle normalized REE trends. Titan samples have a range of (La/Sm)N from 0.7 to 3.8, a range of (Gd/Yb)N from 2.3 to 7.4, and a range of Nb/Nb* values from 0.02 to 0.47. [...]