Economic minerals in Scotland

In this section the term ‘economic mineral' means a valuable rock or mineral other than sand, gravel, or building stone.

One of the most important economic minerals in the highlands today is the gold ore at Tyndrum. Although no gold has yet been produced, a substantial deposit of gold ore has been known there since the 1980s and the size of the deposit has been reconfirmed by recent investigations. On the basis of drilling to date the deposit is estimated to contain about 300,000 ounces of gold with a value of $US300 million. Preparations are currently underway to commence mining the ore within about 2 years.

plate 9

PLATE 9 ORE MINERALS
A, B and C. Gold ore from Cononish deposit, Tyndrum. The brassy metallic mineral is pyrite, the white rock is quartz.
There is no visible gold in these samples. D. Resinous-brown sphalerite from the Cononish deposit.
Sphalerite is the ore which provides zinc metal but it does not occur in economic quantities in the Cononish gold deposit.
E. Shiny black sphalerite from Tomnadashan, Loch Tay. Not known in economic quantities there F. Galena, the ore of lead.
Note how heavy it is. Source of sample unknown

 

The three samples 9A, 9B, 9C (Plate 9, samples A, B and C) are of gold ore from Tyndrum. The samples are mostly composed of quartz, as the gold occurs in a vertical quartz vein. These samples contain no visible gold (gold at Tyndrum generally occurs in microscopic particles) but there is abundant pyrite. Many people have been fooled into thinking that pyrite is gold, so pyrite is often called "fool's gold'. In this deposit, where there is abundant pyrite that means that significant gold is also present in the sample. A tonne of the type of rock shown here would probably yield about 10 grams of gold. Gold is important in international banking, and is also widely used in jewellery. A small amount of gold is used in electronics and dentistry.

gold mine

Horizontal tunnel at Cononish gold deposit extends for 1km into hillside.
The vertical bands above the gate are part of the quartz vein which contains the gold.

Also occurring within the Tyndrum gold deposit is sphalerite, the ore of zinc, but it does not occur in economic quantities at Tyndrum. Sphalerite, which is zinc sulphide, is sometimes colourless but it may be honey-coloured as shown in sample 9D. Notice the dull gray metallic material, which is galena, the ore of lead. This, too, only occurs in small quantities in the gold deposit at Tyndrum, although small lead-mining operations commenced in the Tyndrum area when lead was first discovered there in 1743.

Quartz vein

Cononish quartz vein (vertical shear) and two historic lead mines

Sphalerite can also be shiny and black, as in sample 9E from Tomnadashan on the southeastern shore of Loch Tay. Notice the abundant pyrite in this sample, and notice how heavy the rock is. This sample represents rich ore, but there is insufficient quantity known at Tomnadashan for a mining operation. One of the main uses of zinc is for the galvanising of iron to prevent it rusting.

Sample 9F is a small sample of galena, the ore of lead. Lead is a heavy, soft metal which is used in the production of car batteries. This small rock sample is discoloured except for the broken edge, but note the weight of the sample compared to its size. Galena, which is a sulphide of lead, has a characteristic blue-grey metallic sheen. The source of the sample is unknown. Also illustrated here is a small vein of galena from one of the historic lead mines at Tyndrum.

Lead

Vein of galena from historic lead mine at Tyndrum. Photo by Fritz Fitton.

Barite (sometimes referred to as baryte or barites) is barium sulphate, and it is a heavy rock - compare the weight of this sample of barite sample 10A (Plate 10, Sample A) with a similar sized lump of quartz. A large barite mining operation is currently under way near Aberfeldy, where there is a very large deposit of barite. The Aberfeldy barite is not used as a source of barium metal, but is used for heavy muds which are required in oil and gas drilling. This sample is sugary in texture. Sample 10B is a sample of barite from Glen Sannox on the island of Arran, and crystal faces are evident when the rock is turned to catch the light. Small mining operations took place there during the nineteenth century and between the World Wars but have since ceased.

plate 10

PLATE 10 OTHER ECONOMIC MINERALS
A. Sample of barite from the mine at Aberfeldy B. Sample of barite from Glen Sannox, Arran
C. Sample of coal as used domestically in Strachur

Coal is still one of Scotland's important economic minerals, although coal production in the UK as a whole has declined markedly from a peak of 300 million tonnes per year during World War I to 20 million tonnes in 2005. About half of the UK's coal comes from underground mines, the other half from open cast mines. The diagram below shows the distribution of open cast mines in Britain. Coal deposits do not occur naturally in the Strachur area, or in the highlands at all. Mostly they occur in the Midland Valley of Scotland, to the south of the Highland Boundary Fault.

Coal mining Britain

Coal is a black, lightweight combustible rock which occurs as seams within sedimentary rocks of the Carboniferous period which formed about 240 million years ago. It was formed by the compaction of carbonaceous matter, generally plant remains, and occasionally plant fossils can be recognised within lumps of domestic coal.

The sample of coal shown here (sample 10C) is typical of that burned domestically within the village of Strachur.

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