Allen Wywrot Honours Thesis Abstract

A lamproitic igneous occurrence was recently discovered by a prospector working in the area to the north of Marathon, Ontario.  It occurs near a large number of features related to the 1.1 Ga Midcontinent Rift such as the Coldwell Complex and the Trans-Superior Tectonic Zone, but no radiometric dating has been completed on this particular unit of rock.

At outcrop level, the unit appears as a collection of metre-scale mafic sills within granitic country rock.  These sills appear on all sides of a large lake, marking the lake as the likely location of the main body of the lamproitic rock.

The rock is composed of a variety of minerals, including forsteritic olivine, diopside pyroxene, sanidine feldspar, and a variety of spinels. Later periods of magmatism contributed secondary apatite and phlogopite.  At the same time, the volatile-rich fluids produced by the magma created a variety of alterations, such as serpentine, chlorite, and carbonate, and heavily disrupted the primary minerals in the rock.

This rock retains a classification as a paralamproite, with a mineral assemblage that cannot fulfill the defined composition of lamproite due to geochemical differences between definition and observed samples.