Terry J. Sinclair HBSc thesis abstact

Thesis Title: 
A Petrologic Study of Two Trenched Gold Showings on the Maki Prospect, Vincent Township, Northwestern Ontario
Terry J.

The study area lies within the Beardmore-Geraldton Greenstone Belt, a portion of the Wabigoon Subprovince.  This belt hosts one of the most famous gold camps in the Canadian Shield where production was realized from eighteen mines.  Gold mines and occurrences within the belt have been subdivided on the basis of location and host rock lithology.  The three sub-belts include: the southern mafic volcanic dominated belt, the southern sedimentary dominated belt, and the northern felsic volcanic dominated belt.

This study is concerned with mineralization in the Maki prospect which lies within the southern mafic volcanic dominated belt.  It is underlain by massive, pillowed, and tuffaceous intermediate to mafic metavolcanics.  Oxide-silicate-carbonate iron formation of regional extent as well as quartz-carbonate veins occur within the mafic to intermediate metavolcanic assemblage.  Gold, although erratic, is associated with sulphides within iron formation and quartz-carbonate veins.

The petrology of two trenched gold showings on the Maki prospect was examined.  This study entailed extensive use of thin sections and X-Ray diffraction techniques to determine mineralogy as well as relative timing of metamorphism and hydrothermal alteration.

It was determined from mineral crosscutting relationships that the hydrothermal alteration responsible for gold deposition, pre-dated greenschist to epidote-amphibolite facies metamorphism.

Extensive carbonate alteration of host rocks suggests that the fluid responsible for gold deposition were rich in CO2.  Such fluids could be produced from dehydration and decarbonation of a deeply buried mafic volcanic sequence during upper amphibolite to granulite facies metamorphism.  Fluid access to the above rocks was probably provided by fracture zones and other conduits.  Gold deposition within vein systems is thought to be a result of fluid-wallrock interaction at temperatures and pressures of greenschist to lower amphibolite facies metamorphism.  Since metamorphism post dated infiltration of hydrothermal fluids within the Maki prospect, it is believed that the required temperature range of the metamorphic front had not yet reached the study area at the time of hydrothermal flooding.  If this fluid once carried significant amounts of gold, then most of it was probably deposited at greater temperatures and depths.  It is possible that small amounts of gold which did not precipitate as the preferred temperatures may have continued upward, forming low grad auriferous deposits within the study area.

The iron formations lack suitable structurally prepared sites, (i.e. minor folding) and thus, even if temperature conditions had been favourable, it is debatable whether viable gold deposition would have occurred.