1. The District of Algoma is a gateway from southern Ontario to a region of ancient rocks, known as the Superior province of the Canadian Shield. The Agawa Canyon railway tour from Sault Ste. Marie is a great way to visit Algoma.
Visiting the Agawa Canyon?
2. Hemlo was once a little halt on the railway line to the West, but a major discovery of gold next to the Trans-Canada Highway opened an exciting new era for the area: the Hemlo gold deposit soon boasted three gold mines. Fifteen years later, Hemlo still produces more gold than any other district in Canada.
Did you know that Winnie the Pooh came from White River, just east of Hemlo?
3. The Coldwell area west of Marathon is hilly and rocky. The landscape is built of rocks such as this, which cooled from hot magma more than a billion years ago. Rocks which form in this way are called igneous; they may erupt at the surface of the Earth as volcanic rocks or remain underground as intrusive rocks, which may be exposed after millions of years of erosion.
4. The Beardmore-Geraldton Area on the Northern Route of the Trans-Canada Highway was the scene of extensive gold mining more than 50 years ago. This old headframe structure housed equipment which lowered the miners down a vertical shaft deep below surface.
5. Banded Iron Formation is a type of sediment formed under the sea, found in many areas of ancient, Archean rocks (more than 2.5 billion years old). Such rocks may enclose deposits of iron, as at Wawa, or of gold, as here at Geraldton.
6. Shore of Lake Superior at the Neyes Park. The variety of hard rocks along the northern shores of Lake Superior have generated beautiful scenery that can be explored in several national and provincial parks.
7. The Keweenawan. Westwards from Terrace Bay, the coastal route of the Trans-Canada Highway (Hwy. 17) winds up and down impressive hills, with views of deep valleys and glimpses of the lake below. Here we see red sandy sediments cut by sill of dark magma which crystallized as a sheet below an ancient surface upon which lavas erupted, much like Hawaii or Iceland today. The rocks seen at many aparts around western Lake Superior are named Keweenawan, after the Keweenaw peninsula of north Michigan. These rocks are of Proterozoic age, around 1.1 billion years old, the same age as the Coldwell rocks, but much younger than the rocks we saw near Hemlo and Geraldton.
8. The Sibley Peninsula. Looking out to the lake from the Thunder Bay area, we often glimpse the long, low outline of the distant Sleeping Giant, a mass of igneous rock of Keweenawan age.
9. Silver Islet is a little island (now actually an underwater reef) located off the southeast shore of the Sibley peninsula, just out of sight of the village of the same name. It is famous for a rich "bonanza" silver deposit, mined for a short time in the late 19th century. This is a photograph taken with a microscope, showing white silver metal with grey lead sulphide and other minerals. This view is about 3 mm (1/10 inch) wide.
10. The Lac des Iles area, north of the city of Thunder Bay, is reached via the highway which runs north to the railway town of Armstrong. Some of the rocks are enriched in rare metals such as palladium and platinum.
11. The Lac des Iles mine was developed on the rare-metal mineralization. The most important product of the mine is palladium, accompanied by platinum and other metals. The metals are used in jewellery, dentistry and other trades, and to help clean the exhaust fumes from cars and trucks.
12. The Lac des Iles deposit contains a number of different minerals. The ore (valuable rock) includes sulphide minerals, which include the yellow one shown here, a copper-rich mineral called chalcopyrite. The field of view is again 3 mm.
13. Belts of Archean rocks north of Thunder Bay, west and southwest of Lake Nipigon, underlie the younger Keweenawan layers. In recent years the area around Lac des Iles has been explored for more deposits of the platinum-group metals. This photo shows a vein of pale granite intruding older rock.
14. Archean bedrock and a younger "visitor" display contrasting colours. The bedrock types are similar to the previous image. A red boulder of sandstone sits on top: it is an erratic, a block of Keweenawan sediment carried southwards by a sheet of ice and deposited here at the end of the Ice Age when the ice melted.
15. Sand-sized mineral grains such as this garnet have an important role in detective stories which play out as geologists try to find signs of nearby mineral deposits. Sand and soil may form locally, or be brought long distances by water, wind and ice. Some minerals may indicate a valuable deposit hidden nearby. This is an unusual garnet grain about 1 mm long, found in a granitic rock, like the veins seen in Photos 13-14. Garnet sand from local streams matches the properties of this grain, revealing the rock from which it was formed.
16. The city of Thunder Bay is an important regional centre, a transportation link by road and rail, air and water. The impressive dockside structure shown here was used to load large vessels ("lakers") with iron ores from the Steep Rock mine at Atikokan. Trains would be shunted into the upper level of the building, and a series of hoppers would funnel the crushed iron ore from railway cars to the holds of the waiting laker below.
17. Iron Formation at Kakabeka Falls. The rock here, although less brightly-coloured, has some similarities to the rocks at Geraldton shown in Photo 5. The rock at Kakabeka Falls is known as the Gunflint Formation, and is famous for the preservation of tiny fossils, microscopic traces of early life.
18. A Gravel Pit in the Shebandowan area, west of Thunder Bay, shows bold structures in the sand and gravel which are thought to have formed during the Ice Age by deposition of sediments into a lake. This lake, known as Lake Kaministikwia, vanished when the ice sheet retreated with the coming of warmer climate, and the waters of the lake found new outlets to the sea.
Highway 61 runs southwest towards Duluth, crossing the International Border from Canada to the U.S.A. at the Pigeon River near Pigeon Point.
19. The Duluth Igneous Complex in northeast Minnesota underlies a large region at the western end of Lake Superior. The magmas of the complex crystallized under a cover of lavas during the opening of the Midcontinent Rift, a regional splitting-apart of the what would become the North American continent, depositing the Keweenawan rocks some 1.1 billion years ago. This photograph of an outcrop in the Duluth city area shows a block of an older, darker rock (gabbro) which has been engulfed by a younger, pale granitic magma.
20. A "local" mineral known around the world is pigeonite, named for Pigeon Point, Minnesota. Pigeonite is a special form of the dark greenish or brownish silicate mineral family known as the pyroxenes. It is found in some some coarse granular dark igneous rocks known as gabbro. The colourful microscope photo, field of view 3 mm, shows two minerals - bright pigeonite and grey feldspar, in a rock from the Duluth area.
21. Dresser Trap Rock Quarries, Wisconsin. The opening of the Midcontinent Rift resulted in the eruption of enormous volumes of lava in a geologically-short period. This large quarry extracts and crushes basalt lavas to be used as aggregate for road construction. The lava flows have been used in this way since 1855.
22. The White Pine copper mine, which closed recently, mined sediments which contained copper as both copper sulphide minerals and also natural copper metal (referred to as native copper). This microscope view shows bright native copper in between rounded grains of quartz and feldspar in the host sediment. The field of view is 1.4 mm.
23. The Minesota copper mine is one of many old mines in the Keweenaw district, centred on Houghton. The mine was developed in the 1840s, and was famous for large masses of native copper. Some of the largest were as big as a car, or even a bus! Miners emigrated to American mines from many other countries. Some were from the famous old mining district of Cornwall in England. The legacy of the Cornish miners can be enjoyed in the region to this day, in the form of pastry-covered meat-and-potato pies known as pasties!
24. Giant masses of native copper such as this exhibit on the Keweenaw peninsula were encountered in underground mining, or found on surface as large ice-transported "float" boulders, and some were used by native Americans thousands of years ago to construct a range of weapons, tools and ornaments, such as arrow points, axes and beads.
Visit the Seaman Mineral Museum in Houghton!
25. Nuggets of Native Copper. Copper and a number of other chemical elements occur in the "native" or uncombined state, including sulphur, carbon (as graphite and diamond), silver and gold. Samples of native copper are popular with rockhounds. These 6-cm examples are from the Houghton district.
26. Archaeological Artefact made of Native Copper. Native peoples used the locally abundant copper to make useful and decorative articles. later, after contact with Europeans, they also used copper traded to them as copper kettles. This copper was not found in metallic form, but was smelted from copper ores in Europe. A simple trick with a microscope can distinguish the native copper from the smelted copper. This sample of copper is from a site in Ontario. It is very pure metal, cut by a thin vein of copper oxide. The view is 0.7 mm in width.
27. Archaeological Artefact made of Smelted Copper. There are both chemical and visual (microscopic) ways of distinguishing the native from the smelted copper. Here is another sample from Ontario, in which tiny rounded specks of a copper oxide slag are dispersed through the metal. This slag tells us that the copper used was smelted, and so from a European source.
Sherlock Holmes might have enjoyed being a geologist, or an archaeologist! The scale (width) of the photo is again 0.7 mm.
28. The Lake Ellen Kimberlite is not a very impressive rock to look at: it is a rather crumbly, pale greenish material in its small outcrop in northern Michigan. The interest in kimberlite, a rock named for a town in South Africa, is due largely to the tiny proportions of diamond that it sometimes contains!
29. Heavy Minerals in Kimberlite include some unusual types, with unusual chemistry, and the geological sleuth uses them to hunt for kimberlites which might contain diamonds. In this pan we can see grains red and orange garnets amongst more common, dull green minerals. The garnets can tell an expert much about the rock they came from, even if the little grains have travelled far from their source, carried by a river or a glacier.
30. Cliffs of the "U.P." (Upper Peninsula) of Michigan east of the Keweenaw peninsula are mostly low, sandy affairs, compared with the high, rocky northern shores. The area does have the colourful cliffs of Pictured Rocks National Lakeshore, and other attractions such as the Hiawatha National Forest and Seney National Wildlife Refuge. This stretch of shoreline displays the erosion of soft, sandy sediments that can be seen at many places around the Great Lakes.