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.