Читать книгу The History of Mining - Michael Coulson - Страница 20

It is in the nature of great empires to expand at least partly because of their need to acquire natural resources to fuel this expansion; one might say that expansion begets expansion, and such wealth as results from this becomes critical to the health of the imperial power. The Roman Republic (510 BC to 44 BC), which saw Rome begin to expand from its primarily central Italian base, and the Roman Empire (44 BC to 476 AD), which continued the expansion, were no exceptions to this. An important economic part of Roman conquests was the acquisition of sources of essential raw materials, in particular metals and minerals. The main areas providing the Empire with key metals were Spain, Britain, France (Gaul), central Europe along the Danube, Greece and Asia Minor. The metals produced included gold, copper, iron, tin and lead.

The gold mines of Spain were particularly important in providing finance for the Roman Empire as it continued the expansion begun by the Republic. In 31 BC Augustus became Emperor and after military success in subduing Egypt he turned to Spain. Here Rome was already strong in the south and was already exploiting the gold and base metal deposits in the region which had been developed by the Carthaginians before they were ejected by the Romans from southern Spain at the end of the 2nd century BC.

The Greek geographer, Strabo, in his magnum opus, Geographica, describes in detail the mines of the region that is now Andalucia. The mines in the region produced gold, silver, copper, lead and iron ore, all of which were of course of material value to the Romans. Strabo is particularly interesting on the issue of treatment of the ores, where on occasion furnaces became overheated leading to a loss of metal due to vaporisation. He also describes the necessity for chimneys over silver smelters due to the poisonous nature of the furnace fumes, probably caused by the lead often associated with silver ore. The area was also a source of very high grade ores with pure gold nuggets commonly found on the surface. Copper ore mined was also of a high grade, as much as 25%, but such figures are obviously difficult to authenticate. It is thought that Strabo never visited Spain, his own travels being confined to the eastern end of the Mediterranean, so he relied on third-party sources for his information.

In the northwest in Galicia, according to Pliny the Elder, the Roman philosopher, naturalist and military commander (see below), gold mining output reached an aggregate figure of over 200,000 ozs. A diversity of mining methods were used, including the traditional alluvial mining techniques along the Spanish run of the Tagus and Douro rivers, and in Galicia larger operations incorporated both underground shaft and gallery mining methods. In the case of the Galician underground operations Pliny records that shafts were sunk through the soft surface earth which was supported by wooden props. The shafts were aimed to intersect gold channels or reefs which were hacked out and the ore was taken to the surface where it went through the familiar process of crushing, washing and burning in a furnace to produce a powder. This powder was then crushed further and heated again in the furnace, which Pliny describes as made of a white material like potter’s clay, whereupon gold was finally released. Where large rocks – often of flint – were brought down in the tunnelling process they were broken up with large 150 pound iron rams and wedges, and carried to the surface in baskets.

The most spectacular mining method used was where galleries were driven into mountains or hillsides using a chain mining system; miners worked from deep inside the mountain passing out the mined rock. Left behind was a pillar-supported gallery and the pillars were then part cut to weaken them. The mine was evacuated when a spotter on a nearby hill, who watched for the outside signs that the gallery was on the point of collapse, signalled the workers to leave. When the mountain finally collapsed huge quantities of loose, broken material could then be treated in an attempt to extract any gold trapped in the material. This was a somewhat hit-or-miss operation as gold could not be guaranteed at the end of the process – the Romans would have had some idea of the prospectivity of the mountain or hill for gold, but their geology was rudimentary.

The secret of the treatment process used was being able to bring large quantities of water to the site and then store it in a reservoir so that a strong but controlled stream of water could be brought to bear on the broken material. A complex patchwork of channels and wooden sluices were also constructed to carry water and slag away, and trap any released gold. The system and scale of the operation puts one in mind of the gold workings in California in the mid-19th century where hydraulic mining was pioneered. Certainly historians think tens of millions of tonnes of ore were mined by the Romans in the region.

The technologies the Romans used in their Spanish mines were also sophisticated, as they had to be when shafts were sometimes sunk several hundred feet in pursuit of rich ore. Because of the sometimes large quantities of water at depth, de-watering was often an insurmountable problem, but a screw pump was uncovered at the ancient Centenillo mine near Linares in Andalucia. The pump was designed by Archimedes based on a system he had observed being used on the Nile to raise water. The machine consisted of a screw within a wooden cylinder, which was turned by hand and foot, with the feet working peddles which turned the screw. The turning of the screw enabled water to rise slowly up the cylinder and when it reached the top the water was then directed away from the workings.

The gold mined for the Romans was used in two ways. The primary aim was to provide money in the form of coinage to lubricate the Roman economy and importantly to pay for Rome’s imperial ambitions as well as the empire itself. There is much evidence that the second main use of gold was as gold ornaments for the upper layers of society – gold plate and jewellery has been unearthed over the centuries by archaeologists.

Indeed, it is postulated that before the reign of Constantine there was a period when gold supplies being used for coin were under pressure because a rising percentage of gold was being diverted into fabrication for personal use. There is also a view that after Spain the only new sources of gold for the Empire came from mines in Dacia in the Carpathian region of the North Balkans, conquered by Trajan in the 2nd century AD. Over the next two centuries there appears to have been little in the way of additional gold found in the Empire and gold prices, having previously fallen, then strengthened a little. This encouraged the inflationary practice of debasing the coinage by clipping coins in circulation enabling additional coins to be minted without the imperial treasury having to purchase new (and more expensive gold) for the coins.