Mining and Mineral Prospecting

In everyday life we depend on copper for electrical wiring, iron for the various steel objects we use, aluminium for wrapping and a range of other metals. All of these have to be mined - and we need to know where to look for them.


What the Syllabus Says - and the Details

You need to be able to interpret geochemical and magnetic prospecting data to identify possible metalliferous mineral resources.

Geochemical Surveying

Metals form compounds with other elements as they react over time - and geological time gives them plenty of opportunity. Many of these compounds will dissolve and so small amounts of them can be carried away by rivers and water flowing through the ground. Geochemists try to find deposits of these chemicals in the sediments at the bottom of rivers and in the soil where water has flowed through. 

If they can find traces of the metals in fairly large amounts, that suggests that there is an ore deposit (an accumulation of a useful metallic mineral in the ground) nearby. The key is to look for anomalies - places where the amount of metal content is higher than in the surroundings. The anomaly map below shows accumulations of lead around Denver State in the USA - the interesting bits are the red areas.

The survey won't be cheap to do. You'll only want to look where the geology suggests that there could be ore deposits. Around the edges of plutons is often a good place. The maps below show the results of looking for gold (Au) and tin (Sn) around the southern edge of Dartmoor.

Are you more interested in buying the purple areas or the land which is 'uphill' from them?

Magnetic Surveying

Magnetic surveying only works if you're looking for a magnetic metal; iron, nickel or cobalt. Iron is generally found in beds of iron-rich sandstone, nickel and cobalt in basalt dyke structures or in gabbro plutons.  It is common to do the survey from the air, as shown here.

Notice how the magnetometer picks up an increase in the magnetic field strength when it is over the deposit and also detects a fall off in magnetic field to below background levels to either side of the deposit. This happens because the magnetic metal effectively focuses the Earth's magnetic field through it leaving less to go through each side.

The map below shows a magnetic field strength survey of most of Afghanistan. The bits with the highest anomalies are likely to contain the most magnetic metal ore. Of course - you may 

have some difficulty as a western world mining company trying to extract what you find!