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Seleine Mines Iles de la Madeleine EarthCache

Hidden : 01/22/2014
1.5 out of 5
1.5 out of 5

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Geocache Description:

Welcome to Grosse-Ile, a small village on Iles de la Madeleine known for the Seleine Mine and salt. The mine sits on top of a salt deposit measuring several kilometres thick. This salt deposit is a significant geological resource to Quebec, Atlantic Canada and the Eastern seaboard of the United States. The listed coordinates for this earthcache put you at the Seleine Mine's Interpretation Centre (Figure 1) ("Salt Essentials" exhibit), with an excellent view of the Canadian Salt Company's Iles de la Madeleine mine (Figure 2). If you're lucky enough, the visitor's centre may be open to explore and learn more about the mine and salt [open June 7-September 30, 2014; Sunday-Friday 1000-1800 hours, Saturday 1200-1800 hours].

Common salt (visit link) sodium chloride or NaCl, is a mineral essential to life and health. The importance of salt in the human diet cannot be over emphasised. Sodium is one of the primary electrolytes in the body. Salt contains many vital minerals needed for proper bodily function. Too much or too little salt in the diet can lead to muscle cramps, dizziness, or electrolyte disturbance, which can cause neurological problems, or indeed be fatal. Drinking too much water and consuming too little salt, puts a person at risk of water intoxication. However salt is also dangerous if excessive salt is consumed in the long term. It is associated with increased risk of stroke, heart problems and cardiovascular disease.

Salt is also a fundamental material in our industrial society. In regions with cold climates, such as Quebec and Atlantic Canada, large quantities of rock salt are used to help clear our highways of ice and snow during the winter (visit link)

Common salt, or halite (visit link) (Figure 3), is typically found in one of three forms:

(1) Underground in undisturbed bedded deposits;
(2) In underground salt domes; and
(3) In the ocean as natural brines.

Creation of the Islands

Some 320 million years ago, before the continental drift began to separate the land masses, Les Îles de la Madeleine were located close to the Equator in a basin situated below sea level and where the average ambient temperature was 38 °C (100 °F). Seawater flowed often into this basin and its evaporation caused layers of salt to accumulate on its floor. Over time, this layer of accumulated salt grew to a depth of 5 km.

Meanwhile, Les Îles de la Madeleine started their long migration towards the north, eventually ending up in their current location in the heart of the Gulf of Saint Lawrence. Geological activity subsequently covered the salt with another 4 km of rock and lava.

Two to five million years ago, the pressure of the rocky layer overlaying the salt raised its temperature to nearly 300°C (572°F). The salt, more fluid and malleable than the rocky layer tended to rise towards the surface. Pressure from rising salt lifted the overlaying rock, creating the famous salt domes supporting Les Îles de la Madeleine.

Iles de la Madeleine's large underground salt deposits are found in a rock unit called the Windsor group. These deposits were formed 335 to 350 million years ago during the early Carboniferous Period. At that time, most of the Maritime Basin was covered by a body of water called the Windsor Sea (Figure 4). The hot, dry climate of the Carboniferous Period caused evaporation of water in the sea, making it extremely "salty". As the water evaporated, salt and other minerals precipitated from the water and were deposited on the sea bed. The sea level rose and fell periodically during the 15 million years the Windsor Sea existed, leaving behind layer after layer of mineral deposits. The Windsor groups is approximately a kilometre thick and is a major source of industrial minerals and base metals.

Salt Dome. Just as a cork released at the bottom of a swimming pool will float up through water, wet salt can float up through denser, freshly deposited sediments. A salt dome begins to form when a small part of a wet salt layer rises. Other salt in the layer then flows horizontally and up into a rising plume. If the salt is thick and saturated with water, friction offers little resistance, and salt will continue to feed into the rising plume. The upturned (or bowl-shaped) layers next to the salt dome can become traps in which oil collects, so understanding salt domes has great economic value. Note: If all the sediments in and above the salt layer had not been loose, freshly deposited, and nearly frictionless (saturated with water), there would be no salt dome.

Over time, the salt deposits of the Windsor group were covered with sediment and became buried. Since the density of salt is generally less than that of its surrounding material, it has a tendency to move upward toward the surface, forming large bulbous domes (Figure 5) as it rises. This explains why salt deposits, like this one in Grosse-Ile, tend to be found in a "dome" shape and why the salt can sometimes be found quite close to the surface (30 metres in the case of the Seleine Mine).

Opened in 1982, the salt mine and plant is located in Grosse-Ile and extracts salt from an underground mine 30 metres below Grande-Entree Lagoon, produces 1 million tonnes of rock salt yearly, and employs 160 to 200 people.

Rock salt is the mineral form of sodium chloride, otherwise known as table salt. It's sometimes referred to as “halite,” especially when it is used industrially.

The primary difference between rock and table salt is the size. Rock salt forms in very large, chunky crystals, as opposed to the small crystals seen in table salt. Like table salt, it also has an assortment of trace minerals that can have an impact on how it looks and behaves chemically. Because of the large crystal size, rock salt is not usually used directly in cooking, since it takes a long time to dissolve.

This form of salt is mined from deposits that form underground. In contrast, table salt comes almost exclusively from evaporation ponds that remove salt from seawater.

In 2002, total world production (of sodium chloride in general, not just table salt) was estimated at 210 million tonnes, the top five producers being the United States (40.3 million tonnes), China (32.9), Germany (17.7), India (14.5) and Canada (12.3) [thus Iles de la Madeleine's Seleine Mine accounts for just under 10% of Canada's production]. During the period 2003 to 2008, global production of salt increased by 12% per year, and China took over as the largest producing nation as its chemical industry expanded. Food grade salt accounts for only a small part of salt production in industrialized countries (7% in Europe), although worldwide, food uses account for 17.5% of salt production.

To log this earthcache, e-mail me the answers to the following questions.

1. How many grams/litre of salt is the concentration of water before salt starts to crystallize out of solution?

2. Road salting takes advantage of freezing point depression. What is the maximum depression of the freezing point before it's ineffective?

3. Put a small amount of salt (NaCl) in a flame -- what colour do you get and what is responsible for this colour?

4. What shape is a salt (sodium chloride) crystal?

Additional Hints (No hints available.)