Francisco de Mendoza expedition from Madrid, 1556
On the orders of newly crowned King Felipe II in 1556, Francisco de Mendoza, a member of the Council of Finance, travelled to Rio Tinto to inspect and report on a number of Roman mines found around Seville between 1551 and 1555 (including Guadalcanal) and also to search for others.
This was a direct response to the Crown's need for money, despite an inflow of funds from the New World. His father, Carlos I of Spain, and also Carlos V in his capacity as Holy Roman Emperor, had taken on ruinous loans to fund intrigues and wars. Weary of fighting wars and the struggle to raise money to repay German and Genoese bankers, Charles I abdicated.
In June 1556 Mendoza visited a number of shafts in Aracena and Valverde del Camino and noted them for further investigation. They heard tales of abandoned shafts and galleries near Zalamea la Real, to the south.
"They cleared a ridge and saw ahead of them a network of valleys in which great mounds of slag stood in dark contrast to the green shrub-covered hillsides. As they rode on they recognised with mounting excitement the signs of ancient Roman occupation: carved columns, the dressed stone of tumbling walls and immense drainage adits emerging from the hill-face. They had rediscovered some of the greatest mines of the ancient world." (Avery P.22)
Mendoza retuned to Madrid to deliver a preliminary report, and perhaps escape the heat and discomfort, leaving two subordinates: a Madrid priest called Diego Delgado and a gentleman from Castro Nuño, Pedro de Aguilar.
Diego and Aguilar obtained accommodation in the village of Zamala La Real and explored an unnamed hill (now Cerro Colorado) where they were shown a great cave "like a church". They descended shafts by rope to 90 feet (30 metres), found evidence of buildings and furnaces, and sent back samples of rock to Mendoza.
"The priest developed a great interest in the river and spent much time talking about it to villagers who explained to him that it was devoid of fish and undrinkable, though useful medicinally if applied sparingly to some diseases of the eyes and body such as hydatid cysts and herpes. Their claims that iron would disappear if placed in the water he tested for himself and found it to be true. The water had another property that he would not entrust to paper but he declared that he would report it personally.
He had perhaps noticed that iron not only disappeared in the river water but was converted to copper.
He reported, too, on the thick red deposit of silt that was continuously accumulating on the river banks. This was copperas, rich in iron sulphate, which every August and September had to be collected by the people of the neighbourhood for delivery to the archbishop of Seville as a customary tribute. This commodity was used in dyeing, tanning and ink making." (Avery P.25)
At the end of August Diego returned to Madrid, presented his report to Francisco de Mendoza and within a month the report was in front of the King, who ordered that Diego's samples should be immediately assayed and he should return to collect more. Mendoza was dispatched to Flanders on a political mission.
"Back at Rio Tinto Diego collected his samples and sent them for testing and then waited. As the months went by he sent a series of letters to the council praising the potential of the mines. His last letter was sent from Rio Tinto on 10th June 1557 and complained of the way in which his earlier letters had been ignored. To encourage the council to reply he included three small pieces of silver that he had produced by his own efforts. But again he met with no response. He decided to make the journey to travel to Valladolid where the King was in residence. But within a few days of his arrival in August he died there with nothing accomplished.
In the margin of Delgado's last letter the King notes, 'He is dead. This to be sent to don Francisco (de Mendoza) for him to look into the matter and advise me whether the place and the mine are as stated'." (Avery P.26)
Mendoza did as instructed and returned again to Rio Tinto but no records survive and the Council of Finance appear to have let the matter slip.
Over the next 170 years a number of concessions were granted for Rio Tinto mining by the then established Council of Mines, all coming to nothing. Failure was understandable, due to the remoteness of Rio Tinto and the capital needed to start production on any scale. Spanish 17th century entrepreneurs were aroused to enthusiasm by dreams of vast riches, but lacked the scientific know how.
Thanks to David Avery and RTZ for their 1974 book Not on Queen Victoria's Birthday, which is the definitive history of the Rio Tinto Mines. Thanks to William Giles Nash for his 1910 book The Rio Tinto Mine: Its History And Romance, from which much of this information was sourced. You can buy a second-hand copy of Avery's book, and a scanned on demand reprint of Nash's book, from Amazon. (Click on books in right hand margin of this page)