Where gold exists in nugget form it can be mined directly, or even picked up on the ground. Smaller particles are often washed out of the ground and picked up by panning in streams.
However when the gold is mixed up with other ores in solid rock, it has to be removed by chemical processes. Such was the case at Rodalquilar. The problem with chemical processes is that it relies on dangerous procedures both during and after production. At Rodalquilar two processes were used, mercury and cyanide, both highly toxic.
Gold will form an amalgam with mercury so the finely crushed ore is passed over this. The gold is then removed from the mercury by distillation or filtering through leather. Unfortunately mercury vapour is highly toxic - remember the mad hatter in Alice in wonderland? This was because mercury was used in the hatmaking process and hatmakers frequently became mentally disturbed because of the vapour. Ideas were developed to alleviate this problem but I suspect they were too late for the early mines that used mercury.
It hardly needs saying that cyanide is a deadly poison. At one time it was a big favorite with crime writers such as Agatha Christy. Not only is it lethal on its own, the by products of gold production are also hazardous. Sunlight, of which there is plenty in Almeria can produce vapours and other delightful stuff such as arsenic and mercury. On top of all that, the remaining slurry is a biohazard. Today it is treated, then they just dumped it in a pit.
I was surprised to discover that most of the cyanide produced today is used for other products, including, surprisingly, cosmetics and food processing. Other areas include plastics, adhesives, fire retardants, pharmaceuticals, and as an anti-caking additive for table and road salts. Only about 15% is now used in gold production.
The ore is first crushed finely. This may well free some gold, which can be filtered out. The ore is then mixed with cyanide. Air is fed into the mixture to aid oxidation. Oxygen may also be used for better results, and was possibly used here. The metal is recovered from the solution with zinc dust, as here, or by adsorption onto activated carbon. The gold is then precipitated (zinc) or washed out (carbon) and smelted to produce a high level of purity. The two pictures below are from a chart on the wall of the exhibition hall with my translation overlaid
The history of mining in the Cabo de Gata area goes back thousands of years. Copper, Alum, Lead, Silver and Zinc were just some of the minerals mined1.
However, it wasn’t until the late 1800s that gold was discovered. Many small mines were opened up but it was 1925 before the first serious attempt was made. This was by the Rodalquilar Gold Mines Company. They used mercury to dissolve the gold as did a later company, the Exploitation of Rodalquilar Gold Mines. Both mines failed to make a profit and closed down.
In 1931 a new company started, the Rodalquilar Mines Ltd, using the cyanisation method. This was known as the Durr Mill. This company, which used British experts was quite successful and carried on until 1936 when the civil war forced its closure. They extracted close to two tons of gold.
After the war, the mines were nationalised and in 1942, the company called ENADIMSA was formed. This mouthful meant in English, the Adaro National Enterprise for Mining Ltd. New mines were opened and a new large smelter called the Denver Smelter was installed. By the end of the 1950s, mining reached its peak and the village of Rodalquilar grew to 1400 with facilities such as doctors and schools normally only found in large towns.
The expert’s estimation of the gold reserves proved to be wildly optimistic2 and in 1967 the mines closed. The population of the village dropped to less than 100.
There was one more effort to extract ore. In the 1980s an American enterprise called St Joe, which was a subsidiary of the multinational company Cluff Resources and Antofagasta Holdings tried. It wasn’t to be however and in 1990 the mines closed permanently.
Today the mines can be visited (with great care!) as can a new and wonderful exhibition hall next to the mines. The hall gives information about the mines, geology and terrain over the whole of Andalusia, but has a room dedicated to Rodalquilar, with a wealth of information.
The following three pictures are of the model in the exhibition hall. I have left them full size for clarity but this has meant putting them in separately. Press the back button or Alt-left arrow to return to this page.
Front view1In 1953 various Roman tombs were found in a necropolis. They were of stone and had been robbed out in antiquity. The only object found was the mouth of a glass vase. However, in the hills nearby, Roman ceramics have been found. This necropolis has to belong to a Roman mining village of a late era (after the 2nd century), remote from the normal Roman routes.
2A geographical study of the time said, “The mineral zone is much more extensive than might be thought. For example the area north-east of Rodalquilar, in El Madroñel parish there are deposits yielding an extraordinary 150 to 200 grams per tonne. It seems then that this area will give many benefits to the country. Spain will have gold deposits of which to date it has had little.”
The pictures show, from L to R;
The pictures show, from L to R;
©Copyright Don Gaunt
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