Vittoria Smith HBSc thesis abstract
The Anderson Lake Pegmatite is a N-S trending, S-type granitic pegmatite derived from the Hilma Lake Granite within the Quetico Basin of the Superior Province. It is composed of potassium feldspar – muscovite – quartz – beryl – and molybdenite with accessory ferrocolumbite, apatite and garnet. The pegmatite is crosscut by later vuggy quartz veins which occasionally host amethyst. The molybdenite within the pegmatite is syngenetic and occurs directly within quartz rich areas of the pegmatite, as well as within late stage dark gray quartz veins which crosscut the pegmatite, and in fractured surfaces of the pegmatite with ferrimolybdite.
The molybdenite occurs as coarse-grained euhedral florets, as well as pod-like aggregates within quartz rich pods of the pegmatite. There are three main trenches along the pegmatite and the molybdenite is most abundant in Trench A, with minor occurrences in Trench B and Trench C. Within Trench C, ferrimolybdite is present within fractures hosting molybdenite. The pegmatite is roughly N-S trending along the contact between the host metasedimentary rocks and the Hilma Lake Granite. The Anderson Lake pegmatite is classified as a molybdenite-bearing Nb-Be tabular pegmatite (beryl-ferrocolumbite). Re-Os dating of the molybdenite from the pegmatite produced an age of 2689 ± 12 Ma, which predates much of the plutonism, metamorphism and subsequent pegmatite injections within the Quetico Basin.
The associated Hilma Lake granite is classified within this study as an equigranular, coarse-grained monzogranite to syenogranite, containing plagioclase – potassium feldspar – quartz – biotite – muscovite – titanite – garnet – and apatite. The biotite is heavily altered to chlorite with magnetite inclusions between the sheets of the biotite. When plotted on a viii tectonic discrimination diagram (Rb vs. Y + Nb), the Hilma Lake Granite plots within the volcanic arc granite field. This would be expected had they formed during the subduction and transpression of the Wawa Terrane beneath the Wabigoon Terrane, when the Quetico was an accretionary complex composed of sediments derived from the volcanic arcs to the north and south.