I came across this article while searching for information on the history of Rodalquilar Gold Mine. It is very detailed and my translation is only a small part of it, nor does it include the many diagrams, charts and pictures. For a really in depth look at the mines, go to Sr. Ortiz' site at the location below. It is worth a look even if you do not read Spanish as there are some interesting pictures.
THE GOLD MINE OF RODALQUILARThe article starts here
During times past, mines have operated during certain periods of time, while at others they have been inactive. If the mineral mined at a particular location is the same we have to ask the question; why is mining profitable at some times but not at others? This article addresses this question at a particular mine: that of the gold deposits of Rodalquilar in the Cabo de Gata park (Almería).
In the geographical centre of the Sierra del Cabo de Gata, one finds located the mineral deposits of Rodalquilar, where mineral has been exploited by man for centuries (Hernández Ortiz, F, 2002).
The geological mark of the Sierra is that of the Neocene chalcoalkaline vulcanism of southeast Spain (López Ruiz, J. & Rodríguez Badiola E. 1980). The Rodalquilar deposit has its origin in the processes related to the formation of the complexes of collapsed calderas of Rodalquilar and La Lomilla which have dimensions of 8km in an E-W direction and 4km in a N-S direction. The typology of the deposit is epithermal and contains mineralised veins of low sulphurisation with Pb-Zn(Cu-Ag-Au) and of high sulphurisation with Au(Cu-Te-Sn) (Arribas Moreno, A. 1998). The substances exploited commercially have been fundamentally gold, alum, silver, lead and Kaolin, not forgetting paving stones (Hernández Ortiz, F. 2002).
In general terms one can say that a collapsed caldera is the result of the collapsing of the magma chamber and the expulsion of great quantities of igneous material that can be measured in cubic kilometres. Continuing with general considerations a caldera is defined as a volcanic collapsed structure that, as a result of that collapse, has emitted at least 1km3 of igneous material. Throughout history (more than 4000 million years) records remain of collapsed calderas that have expelled more than 1000 km3 of material and many that exceed 100 km3. In the case of Rodalquilar the amount has been calculated as a little over 1 km3. This geological date holds a direct implication for the economic mining history of Rodalquilar such that the means of production and the management structure had to be appropriate to this type and size of deposit.
Today we know with reasonable certainty that Rodalquilar is the type of caldera mentioned above and that the geology model shows the extent of the deposits (Arribas Rosado, A. et al. 1995). However, in the past, such knowledge was unavailable, resulting on more than one occasion in incorrect technical and economic planning, giving rise to the failure of these ventures (Hernández Ortiz, F. 2002).
Parallel to the advance of science and technology were the advances made in production methods. Without going deeply into the different economic, empresarial or political factors that helped or hindered the various methods of production available in the market, I will try to describe technically the historic evolution of the means of production available at the end of the 19th century and throughout the 20th. To attempt to reach this objective we consider four sections.
The means of extraction used at Rodalquilar at the beginning of the 20th century was by explosives, although they were used in small quantities due to two factors:
The first was the limited economic capacity of the mine owners and the second was the limited capacity of work that existed, the drills for piercing the rock were operated manually, using hammers and hand drills. The silica rock there was especially hard and abrasive. This resulted in the small amounts of extracted mineral recorded.
A document produced in the middle of 1916 detailed some mineral extraction dates during the first auriferous operations in the vicinity of the cortijo known as “El Estanquillo” that today is the site of Rodalquilar village. These dates refer to the mines “Las Niñas”, “Ronda y el Resto” and “Consulta”. In the 1910s some 2,500 tonnes annually were extracted with a yield of between 12 an 25 grams per tonne. By the beginning of WW1 production tailed off.
It was in 1930 when a change in the available technology occurred. It was the new company “Minas de Rodalquilar SA” that took advantage of this. This company had enough capital to purchase the amount of explosives needed. Also, they possessed compressed air driven drills which vastly increased output. A downside was the increase in silicosis in the workers from the silicon dust in the galleries.
Although the new drills were not in themselves an extraction tool, they contributed greatly to the speed of drilling and blasting. The company had 9 drills. Each one weighed 15 kilos and operated at a pressure of 6 kg per cm2. To generate the compressed air, there were two compressors, one of 70hp serving 6 drills and one of 30hp serving the other 3. The drills used were of hexagonal hollow steel, made in a diesel operated forge and two grinders, also operated by compressed air (Rubio de la Torre, J. 1935).
The new technology considered also a change in the energy requirements of the workers. Up to 1930 it just required the manpower to operate the hammers and drills but along with the arrival of compressed air came electricity. The electricity used by the company was supplied by “Fuerzas Motrices del Valle de Lecrín”, a company with English Capital. The 25KV supplied was transformed down to 220V. As a back-up there was a reserve supply from 2 x 110hp diesel alternators (Hernández Ortiz, F. 2002).
During the Civil War, production slowed and virtually stopped (Hernández Ortiz, F. 2002).
After the war, the state seized the mines and the state company Adaro arrived in 1943. It began a new qualitative and quantitative change in working methods. There were changes both inside and outside the mines. Drilling methods were improved by the introduction of water into the compressed air drills, significantly reducing silicosis (Estadística Minera y Metalúrgica de España).
In the open-cast mines much greater quantities of explosive were used, generally with Sabulitao? in the blasting. Generally about 5,000 tonnes was extracted for each blast (Puig, I. 1961). This raised the quantity of ore produced to an historic maximum. Compare this with previous efforts which only produced 2,500 tonnes per annum, half of that in just one explosion. This open-cast method was a first and was a key in the success of the operations of Adaro (Hernández Ortiz, F. 2004c).
According to the testimony of those who worked there Adaro introduced 30 Ingersol-Rand compressed air hammers (three times that of “Minas de Rodalquilar SA”). Each had a potential of 9 kilos pressure 30% better than before. At the end of the 1940s, these were replaced by 40 Gesa-17 units with air and water, with the benefits mentioned above. In 1950, these units were changed to Gesa-24, like the 17s but more powerful.
From 1956, there was also a “Wagon-drill” (a drill mounted on a wagon!) which worked at the open-cast mines in the Cerro del Cinto. This could drill 10 meters deeper and larger diameters than the air drills (Puig, I. 1961). Workers at the mine also remembered that the compressors for the wagon-drill and the compressed air hammers were as follows.
Motor house No1 in the Cerro del Cinto had 1 compressor Ingersol-Rand of 70hp and 2 compressors Atlas of 40hp each.
Motor house No2 next to the Cerro del Cinto next to the Cortijo del Fraile had 2 compressors Ingersol-Rand of 25hp.
Motor House No3 in the Cerro del Cinto had 3 compressors of 150hp each plus the reserve power plant this was the one used by “Minas de Rodalquilar S. A.”
Finally, there was the American enterprise “St Joe” that represented the final period of operations at the mine. It operated exclusively open cast work using large quantities of explosives (I.T.G.E. 1991).
These may be split into two categories: a) those used inside the mines and b) those used to carry the ore from the mines to the mine installations.
At the beginning of the 20th century the methods used in the 19th continued (carts pulled by animals as well as pack donkeys). These took the produce to the loading bay at Playazo beach (about 4km - DG). From here, boats took the ore to foundries at Puerto de Mazarrón (Sant Elisa Foundry) and Cartagena (Estadística Minera y Metalúrgica de España).
Inside the mines they continued to use human muscle power with “gavias” - groups of miners with esparto containers on their shoulders.
All of this meant that the extraction rate was very low as was the rate of transport.
Things changed when the company “Minas de Rodalquilar S.A.” took over between 1930 and 1936. This British concern built tracks (probably Decauville – DG) along the main routes although manpower was still used in the narrow sections (Rubio De La Torre, J. 1935). Each wagon could carry a cubic metre of ore. Another innovation was the use of a “Somua” lorry with massive wheels to carry the ore from San Diego to the “Dorr” plant. This may well have been the first time that a combustion engine was used at Rodalquilar to carry ore by road.
When Adaro took charge in 1943, they used the same means of transport as before, abandoning finally the use of muscle power. They increased the use of mechanical methods (Hernández Ortiz, F. 2002).
According to the testimony of workers, regarding the transport used, between 1943 and 1949 there was a Ford 4 truck of 1 tonne capacity and a 3HC truck called “the Russian” of under 3 tonnes capacity. Neither truck was a tipper and the ore was carried in esparto baskets for ease of loading and unloading.
In about 1950, three GMC lorries of 10 wheels arrived. Each could carry 5 tonnes. They had petrol engines and were used then by the US army. They were tipping lorries and emptied their load into the hoppers for the Dorr plant by gravity. Shortly after, 3 new lorries were purchased, this time 8 tonne Pegasus vehicles with right-hand drive and side tippers. These continued to load the hoppers by gravity.
Around 1956, with the introduction of the Denver plant, all 6 lorries were replaced by new 8 tonne Pegasus vehicles with left-hand drive and rear tippers.
The big improvement of the day was the introduction of two O&K shovels operated by cables. (Was this Orenstein and Koppel? If so, I guess they were steam operated– DG.) These were used to load the lorries at the quarry, although at the plant, hoppers were still used.
In 1966 the mines closed and all of the machinery was sent elsewhere or sold.
When the mines were re-opened as St Joe, a new fleet of 25 tonne lorries and shovels were brought in. However, these were not bought but subcontracted, showing a different way of working. The lorries carried the material from the quarries at Cinto to the nearby installation situated next to the Cortijo del Fraile (I.T.G.E,1991).
When in 1864, the first intimations of gold at Rodalquilar appeared, the principal method of production was by amalgamation, a process that had been used for many years. However, the process, which used mercury, required the gold to be in a free state. Here it was situated in quartz with veins of other metals, notably lead and silver. These technical problems prevented commercial exploitation of the deposits. Companies such as “Stolberg & Westfalia” from Germany knew of the gold but were unable to extract it. Only small local concerns took the trouble to send, by boat, small quantities of ore to Mazarrón, as mentioned above. At the foundry they obtained lead, which was analysed and the value of the gold contained was given to the miners, less 25% for transport costs (Anonymous, 1916). The gold/lead was then sent to Antwerp where it was separated out (Pérez de Perceval, M. A. 1989). This unusual profit method was typical of the peculiar spirit of the owners of the mines at the time and their lack of empresorial approach.
The breakthrough came on 19th October 1887 when the cyanisation method was patented. The first installation to use this method was the “Crown” mine in New Zealand. A second was built in South Africa and a third in the USA. This signalled a great advance in metallurgy of precious metals such that now there was no need for high percentages of recuperation, even in complex mines where the yellow metal was mixed with others. The new technology now made profitable those gold deposits that were previously of low value using amalgamation.
The cyanisation method depended on the mobility of precious metal in the presence of alkaline cyanide when in the presence of oxygen or other oxidant according to Elsner’s equation (Hernández Ortiz, F. 2002): 2 Au + 4 CNK + O + H2O = 2 (CN)2AuK + 2 KOH. (A search on Google produces a number of hits to “Elsner”, many of which contradict this equation. I am not a chemist so am unable to comment – maybe some reader will enlighten me – DG)
However, although the first cyanisation plant was working by 1889 the Rodalquilar mines did not use this because of insufficient capital combined with its general speculation character mentioned above. In May 1915 gold was discovered in free form in the mine “Maria Josefa”. This prompted the installation of a proper mining complex although still only of the amalgamation type.
The first costing analysis was undertaken in 1919. The cost of extracting 1 tonne of ore was set at 13 ptas plus another 3 ptas to bring it to the surface. The cost of milling was given as 11-12 ptas/tonne. General costs were 10% of the total, i.e. 3 ptas. The total came to 27 ptas/tonne. (At the exchange rate of the time, this equated to approx £1/tonne – DG.) Considering a price of 3 ptas/gram for gold, they established a minimum standard by which exploitation would be profitable as 9 grams/tonne of mineral treated (this minimum standard was well exceeded by "María Josefa"). Finally an important factor had to be taken into account, the storage of water necessary for the mine, something that was scarce in the region and had to be considered as an extra cost (Hernández Ortiz, F. 2002).
In 1925 the "María Josefa" amalgamation installation was opened. This was able to treat 20 tonnes of ore/day (Estadística Minera y Metalúrgica de España). It consisted of:
But the mean character of the miners would influence in a decisive way the failure of the enterprise. The heating of the mineral before crushing meant that deposits covered the surfaces of the ore, making it impossible for the mercury to penetrate and amalgamate with the gold. The result was that the attempt to save a few pesetas by heating meant that little gold was recovered. The company suffered a grave reverse in its fortunes (Hernández Ortiz, F. 2002).
Despite the failure of “Minas Auríferas de Rodalquilar”, in 1929 “Explotaciones y Minas Auríferas de Rodalquilar” began operating. This new company was built and installed by the German firm "Krupp Grusonwerk” in the grounds of the “California” mine, next to the village of Rodalquilar. It had the capacity to treat by amalgamation 20 tonnes/day of gold ore.
It consisted of (Hernández Ortiz, F. 2004a):
Scarcely a year after starting, in 1930 the installation closed due to technical and economic problems. (Hernández Ortiz, F. 2004a). That same year, a company, controlled by the British, “Minas de Rodalquilar S.A.”, was found constructing next to Rodalquilar village, a cyanisation plant for gold production. In 1931 the first production dates appeared and in 1933 the whole world recognised the technical and economic success of the company. The key to the success was the investment in up to date technology and the investment planning needed to acquire said technology. The process consisted of (Hernández Ortiz, F. 2002):
In 1934 each tonne of material treated cost the company 45 ptas and the purity of the ore obtained was 622 thousandths, the rest being silver and some copper (Hernández Ortiz, F. 2002). Up to 1936, everything went well but at the outbreak of the civil war the installations were seized by the sindicalists (trade unionists – DG) (Mining and metallurgic statistics of Spain).
At the end of the war the installations and mines were seized by the state. INI (The National Industrial Institute) by means of its subsidiary Adaro took charge of the “Dorr” plant, property of the Minas de Rodalquilar SA and continued using it up to 1956. Then it was enhanced by a new installation the “Denver” plant. This was similar to Dorr but with ten times the capacity. Between 1943 and 1966 the Dorr and Denver plants continued with success. From the Denver plant, the purity reached 998 thousandths.
It is worth mentioning that when Franco inaugurated the Denver plant in May 1956, it was the largest gold mine of its type in Western Europe. This large size, together with other factors would be that which provoked the closure of the mine in 1966 (Hernández Ortiz, F. 2002).
In 1989 would open the last gold extraction plant at Rodalquilar. It used the latest technology which was the method of leaching in piles (I.T.G.E., 1991). It permitted the treatment of large quantities of ore at low cost due to the small amount of crushing and milling required. The capacity of the installation was 200,000 tonnes per annum. It was designed and constructed by the Dutch firm CYMET. Production was estimated at 280kg of gold per annum. For the precipitation of the gold they used for the first time in Spain, columns of active carbon, followed by chemical refining then smelting. This was an improved and successful method of extraction, however, a fall in the price of gold forced the closure of operations in 1990.
The success of the gold mines at Rodalquilar during the 20th century was not linked to the richness or not of the deposits but to the way that the various enterprises undertook their operations.
Although it might seem obvious, to achieve a successful mine, the volume of production has to be sufficient to achieve a profit. This profit must take into account both planning and exploration. These will assure the future of operations.
In the first third of the 20th century, the volume of production was around 2000 tonnes per annum. This was insufficient to cover future needs, only day to day operations. This resulted in eventual failure.
This all changed in the period 1930-1936 when Minas de Rodalquilar SA commenced. This company extracted around 20,000 tonnes per annum i.e. ten times that previously obtained. This yield was sufficient to achieve the objectives mentioned above. If it had not been for the civil war, this company would have probably been viable for many more years.
In the period 1943-1956, the volume of production was maintained, however, this was a state concern and the only client was the state, which controlled prices. Thus there was no free market. INI (due to political and social factors) handled things badly, including the seizure of assets by dubious legal means. The net result was that the mines were not profitable.
Between 1956 and 1966 the state continued to run things. It invested in the new plant and increased extraction another ten times to 200,000 tonnes per annum. Although this was good for profit, the amount of ore available could not withstand this onslaught and the mine was exhausted, closing in 1966.
New attempts were made between 1989 and 1990. These were able to extract gold as low as 1 gram per tonne as opposed to a requirement of 4 grams per tonne. This meant that ore untreated in 1966 could now be recycled. The plans were for a tonnage the same as before i.e. 200,000 tonnes per annum. However the money situation was now different. The gold standard had finished in the 70s. Now a mine had to survive the fluctuations in the price of gold. Rodalquilar was not well suited to this due to its relatively small output. For example the Yanacocha mine in Peru had an extraction rate of 350,000 tonnes per day. So although the mine was technically competent, the scale of operations was too small and the mine closed definitively in 1990.
Will the mines ever open again? It seems unlikely.
End of document
©Copyright Don Gaunt
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