A brief history of gold extraction methods

Gold panning

The oldest method of gold extraction is gold panning, exploiting the higher density of gold to separate it from the lighter accompanying materials. It is necessary to agitate the gold-bearing material so that gold can settle on the bottom of the pan or concentrating table. The simplest gold extraction method uses pans. A more advanced technique uses concentrating tables – troughs in which the pulverized gold-bearing material is gradually floated and particles of gold are caught on various obstacles on the bottom (indentations, sheepskin, cloth). If the content of gold in the material is relatively low these methods require much physical work.

The oldest archaeological finds of the remnants of such tables date from the 2nd – 3rd century BC (Modlesovice in the Strakonice district). In addition, gold-panning has left behind some relatively large superficies of the so-called placers.

The placers are mounds of extracted gravel. Their length is from 5 – 8 metres and their height is from several decimetres to 5 metres. They are separated by artificial cavities made when the silt was gradually removed until an auriferous vein was found. Hundreds of them are found in Modlesovice. The oldest placers date from the Celtic period and the most recent ones from the 12th – 14th century. The total area of the historical placer grounds was estimated at 75 square kilometres in 1895. The placer sites are classified as technological monuments and archaeological sites today.

Mining for gold

The first mining ventures were perhaps undertaken during the Celtic period. According to legend, it was in the year 942 that Prince Boleslav sent miners to the mountains in the vicinity of Boubin near Cizova to mine there for gold. Archaeological finds from the 13th century are documented at the oldest extant gold mine – the Havirka near Pisek – in the Sumava region. The tunnels were hand-driven in the Middle Ages. The main tools were the cutter and the sledge. During a six-hour shift the miners extracted on average a cubic metre of rock (and in so doing blunted 20 – 30 cutters).

The ore was carried out in wooden hods, leather bags or baskets, later by two-wheeled trolleys and hand-barrows and in the early modern period by mine cars. If the miners were to be successful it was essential for them to have good lighting because they had only their eyes to distinguish the lighter auriferous quartz from the darker parent rock. The mine lighting fixtures developed from tallow lamps made of clay with a hole for the miner's finger (from the 13th century) and later petroleum, carbide and electric mine lamps.

There were two basic extraction methods. The first one, apparently more frequent, involved the sinking of a vertical shaft on relatively flat ground where the auriferous quartz was found at the surface and following the gold veins at a depth of 4 – 6 metres. This method has left behind some typical remnants in the form of craters.

The other method was used on hillsides with protruding ore mineralization where the miners excavated shafts or entire galleries with pillars 30 – 50 metres deep. The waste rock was dumped by the shaft openings. In the region of the Ore Mountains there were thousands of shafts of both types.

Today there are some remnants of the modern history of mining in Roudny near Vlasim where mining took place in 1893 – 1930. In the pit heaps there is gold content of 2 grams per ton so that extracting gold from them can be again considered.

Processing gold ore

It should be borne in mind that extracting the ore is only the first step. Several methods of gold extraction were gradually developed. The oldest procedures used water streams and the principle of different precipitation of the lighter and heavier particles – gold panning (Turkey, 6th century BC). The technical principle of treatment of gold ore in the mining districts of Southern Bohemia in the Middle Ages consisted in heat separation (the ore was first heated and then immediately cooled by water), mechanical crushing and subsequent separation or amalgamation. The principle of amalgamation is extraction of gold from the pulverized ore by mercury. The ore dust was rubbed with mercury which amalgamated with the gold. The amalgam thus produced was an alloy of mercury and gold. Gold was separated from the mercury either by filtering it through leather or by distillation. As the mercury could be reused, its consumption was not great. When we compare these methods with the treatment of gold ore in modern times we only see that more mechanization is used and instead of amalgamation, the more effective cyanidation method.