MB GeoTour 38 – Jim’s Favourite Spot in MB, Pelican Harbour, Lake Winnipeg 2014
Archean rock is exposed on the shore of Lake Winnipeg, at Pelican Harbour (13-36-25-8E1, NTS 62P1NW; NAD 83, Zone 14U, 683391E, 5673192N).
Archean rock is exposed in a flat lying outcrop on the shore of Pelican Harbour, south of Seymourville, in the south basin of Lake Winnipeg. The outcrop is tonalite gneiss intruded by veins of granite and pegmatite. It is situated across a narrow strait of water from Black Island. Louis-Joseph Gaultier de La Vérendrye visited an ochre deposit at Red Cliff on the south shore of the Island in 1739; and a train car wheel was cast from the deposit in 1885. This believed to be the site of the first mining and processing of Precambrian rock in Manitoba. A former Ordovician silica sand quarry can also be seen across the strait. Jim feels that the entire geological column of Manitoba and deposition and erosion that occurred during the Phanerozoic can be visualized at this site, which is why it is his favourite spot in Manitoba.
This video shows Jim’s favourite geological spot in Manitoba, an “unassuming” flat-lying shoreline Archean tonalite gneiss, intruded by veins of granite and pegmatite. The outcrop is situated at Pelican Harbour (south of Seymourville) in the south basin of Lake Winnipeg. It was mapped as quartz diorite by Davies (1951); and as tonalite by Bailes and Percival (2005).
Jim begins by describing early mineral exploration in the immediate vicinity that was carried out in 1739 on a deposit of ochre at Red Cliff, on the south shore of Black Island (shown on Map 50-2 of Davies, 1951). The work was done by Louis-Joseph Gaultier de La Vérendrye (the youngest son of the famous explorer). Black Island can be seen in the background, across a narrow strait of water. Next, he describes the extraction of hematite (or iron ore) from Red Cliff, where a dock was built and from which 5.4 tonnes of hematite were shipped by sailboat to Winnipeg. The ore was then transported by rail to Chicago, where a train car wheel was cast in 1885. Although, this marked the first mining and processing of Precambrian rock in Manitoba; it should be noted that Phanerozoic commodity use (including the recovery of salt from brine springs) had been done much earlier.
Also located on the south shore of Black Island is the former Ordovician silica sand quarry (also shown on Map 50-2 of Davies, 1951). The quarry (described in GeoTours 35 and 37; and by Watson (1985, p. 21, 22)) can be seen in the video, behind Jim, across the narrow strait of water.
Jim calls this outcrop setting “his Rosetta Stone” and he visualizes an ancient marine shoreline that was present at this locality 550 million years ago, during the Ordovician. At that time, the central portion of the continent of North America (known as the Western Canada Sedimentary Basin) was below sea level and extended from Alberta to Manitoba. During that time, Winnipeg Formation silica sand was being deposited on the 2-4 billion year old Precambrian shoreline (where he was sitting). Jim pictures that during the succeeding Silurian, Devonian, and possibly even the Mississippian period that carbonate sediment was being deposited above his head in the Basin. This was then followed by shale and sand deposition during the Mesozoic; and finally by the uppermost Paleocene Turtle Mountain Formation (GeoTour 21). All of these Phanerozoic overlying beds were then eroded away during numerous erosional events caused by falling sea levels or by continental uplift, including 80 million years of weathering at the end of Paleocene time. This set the stage for multiple glaciations during the Pleistocene, shown by glacial till and glacial striations (or stria) on the Precambrian rock surface. This was followed by melting of the last continental ice sheet; deposition of lacustrine clay at the bottom of Glacial Lake Agassiz; and dewatering of the area, as most of the permanent ice melted from the Hudson Bay area.
Bailes, A.H. and Percival, J.A. 2005: Geology of the Black Island area, Lake Winnipeg, Manitoba (parts of NTS 62P1, 7 and 8); Manitoba Industry, Economic Development and Mines, Manitoba Geological Survey, Geoscientific Report GR2005-2, 33 p.
Davies, J.F. 1951: Geology of the Manigotagan-Rice River area; Manitoba Mines and Natural Resources, Mines Branch, Publication 50-2, 16 p.
Watson, D.M. 1985: Silica in Manitoba; Manitoba Energy and Mines; Mineral Resources Division, Economic Geology Report ER84-2, 35 p.