The 23rd IAGS pre-symposium field trip was a 4-day tour (10-13 June) of mines and cultural sites that travelled across Spain, from Madrid to Oviedo, via Seville and Salamanca. The tour group was led by Jorge Loredo (University of Oviedo), assisted by Alejandro Bel-Lan (Institutio Geológico y Minero de Espana: IGME) and Juan Locutura Rupérez (IGME). The participants consisted of 23 geologists/geochemists and two accompanying persons, representing eight countries. We met early on Sunday morning at the IGME in Madrid and were given a thick tour guide and two large rolled maps of the geology of Spain as we boarded our 50 seater bus.

After leaving Madrid, we had a quick comfort stop in the small town of Puerto Lápice (Ciudad Real), famous for an association with Don Quixote, and then travelled on to Almaden for lunch at the Hotel Restaurante La Plaza attached to a hexagonal bull ring (Fig. 1). Many photos were taken of tour participants acting as pseudo-bulls in the ring. Our introduction to field trip food was a series of courses of ham and fish with Rijoa red wine. When we thought we had finished, the main course was served – a large pork steak – the most magnificent pork I have ever tasted. Apparently, the secret ingredient is that the pigs eat acorns dropped from green oak trees. Off to the Almaden mercury mine at the other end of town feeling a little sluggish but more than satisfied.

Mercury (cinnabar) mining at Almaden commenced in Roman times (Fig. 2) and from 1499 produced about 275,000 t of mercury, one third of the global resource. The mine ceased production in 2002 and has since been developed as a tourist attraction. We descended a shaft to the 50 m level at the base of the hill. Our guide, a former metallurgist in the mill, led us through various tunnels, many lined with brick, to view a sequence of exhibits illustrating changing mining techniques from ancient to modern, as well as sections of slate and volcanic country rock, and quartzite ore with occasional splashes of red cinnabar and droplets of native mercury, originally deposited from sea floor volcanic exhalations. We didn’t see the magnificent expanses of cinnabar impregnated quartzite illustrated in our guidebook and exposed in levels 200 m or more below us. The total depth of the mine is 500 m. A mine train ride from the shaft took us out the side of the hill to a walk by the derelict mill, followed by a quick visit to the museum housing many magnificent specimens of the Silurian to Upper Devonian country rock and ores, as well as models of the mine and mill.

A three and a half hour bus drive took us to our home for two nights, the Al-Andalusia Palace Hotel in Sevilla near the south coast of Spain. We dined at the Tablao El Patio Andaluz Sevillano restaurant while watching an exhibition of flamenco dancing and then went for a walk around floodlit buildings in the old part of the city and down by the river.

Day two (Monday) started in the Iberian Pyrite Belt (IPB) with a visit to Rio Tinto, an Early Carboniferous volcanogenic massive sulphide (VMS) deposit mined from about 5000 years ago and the birthplace of the Rio Tinto company in the late 1800s. The mine closed about five years ago although there is still some exploration in the immediate mine area. While viewing the vista of Corta Atalaya open pit (San Dionisio VMS lens) (Fig. 3), the geology of Rio Tinto was described by Carmen Conde (IGME). Pre-mine resources in eight massive sulphide lenses were about 500 Mt at 0.9% Cu, 2.1% Zn, 0.8% Pb, 0.5 ppm Au and 26 ppm Ag.

Our second stop was Cerro Colorado open pit, followed by a tourist train ride down the Red River valley for about 12 km to its terminus (Fig. 4). From the train we saw vast tailings and waste areas and black slag left over from smelting and the heavily polluted Red River (Fig. 5). Talk of rehabilitation seemed pointless when the moonscape landscape is an A1 tourist site. Lunch was at a restaurant in Minas de Riotinto village followed by a visit to another VMS deposit in the IPB, the Las Cruces mine, operated by Cobre Las Cruces SA. We were given a lecture on the deposit by Mike Doyle, the mine manager who was previously chief of exploration and responsible for discovering the blind deposit by drill testing a gravity anomaly. The open pit is working down through 100 m of Tertiary cover rocks and is expected to start producing ore in March 2008 with a 16 year life expectancy. The pyrite-chalcocite ore is localized at the apex and contact of an anticline of shale over volcanic rock. Weathering and development of a gossan occurred in the Jurassic. Mike described the unusual occurrence of galena as a secondary mineral in the gossan, which caused great debate amongst the tour participants. A late dinner, including paella, was at Hosteria del Laurel, Plaza de los Venerables in Sevilla, followed by more late night walking around the old city (Fig. 6).

Day three (Tuesday) started at the Aguablanca (white water) Ni-Cu-PGM mine north of the IPB and operated by Rio Narcea (Fig. 7). Francisco Bellón and Cesar Martinez Chaparro presented lectures on the mine and its geology and were followed by an overview of the pit, and a scramble around a stockpile of boulders of country rock and pyrrhotite-pentlandite-chalcopyrite mineralisation.

Two steeply dipping orebodies are hosted by a breccia pipe within a gabbro-diorite pluton (Aguablanca Stock ca 10 km2) all of Carboniferous age. The pluton represents a ‘staging magma chamber’ emplaced at shallow level (<2 km) into Cambrian limestones (with associated skarns) and other sedimentary rocks. The ore grades 0.66% Ni, 0.45% Cu, 1.5 – 2 g/t Pt, 1.5 g/t Pd, 100 g/t Co. The open pit is expected to finish in 2013, but work has already started on developing an underground mine which will start producing ore in 2008 and continue beyond the life of the open pit. The mine is almost totally surrounded by National Parks and operates under strict environmental regulations requiring zero water discharge. Sewage water is used for processing. About 4000 trees had to be relocated during mine development.

Lunch was hosted by Rio Narcea in the nearby very picturesque Real de la Jara village at the foot of a hill caped with a 1500s Moorish castle. After a two hour drive north, we stopped in Cáceras city for a quick tour of the old city, then another two and a half hours drive to Salamanca to the Hotel Rona Dalba. Dinner was at Restaurante Pata Negra celebrating Russia Day with toasts of vodka supplied by our Russian comrades on the tour.

Day four (Wednesday) started with a guided walking tour in the old part of Salamanca, including the University and new Cathedral. Late in the morning we hit the road to Ponferrada and lunch at a Bavarian/Swiss style restaurant/winery Restaurante Palacio de Canedo en Canedo, Prada a Tope. Our bus ride was marked by an extreme contrast in scenery as we left the arid plain of central and southern Spain and drove into some hilly landscape where the country was lush with dense tree cover. The transition was also marked by a change from towns of almost totally apartment dwellings to houses plus a few apartments.

After lunch, we visited the World Heritage Site Las Médulas Roman placer mine museum and walked the 3 km track through the excavated gullies. This was the largest of the Roman gold mines in Spain and was worked for 200 years in the 1st and 2nd century AD by up to 4,000 miners, producing about 5,000 kg or 160,000 oz of gold, exported to Rome and used mainly for the manufacture of coins. The Miocene red fanglomerates and alluvial conglomerates (Fig. 8) consist of a 5 m thick basal layer grading 60-300 mg/m3, overlain by 25 m grading 20-100 mg/m3 and up to 100 m grading 10-20 mg/m3. An estimated 100 M m3 of gravel were excavated by hydraulic mining with water channelled in from up to 80 km away. One novel technique of mining was to release large volumes of water into previously excavated galleries and wells to undermine the rock mass by collapse and in some cases blow out the side of the hill.

On leaving Las Médulas we had a three hour drive to Oviedo through spectacular scenery of forested high hills, then over a plain covered with some sparse trees, followed by mountainous country with rocky outcrops and peaks, grassy valleys and some lakes. As we neared Oviedo, we passed through coal country as evidenced by a very large coal fired power station.

In addition to the mine geology, I am left with many lasting memories of the tour including great company, very large and very late lunches and dinners, wine that got better and better during the trip (or was I getting the taste for Tempranillo), late nights that were completely out of balance with early morning starts, and a fridge on the bus from which we helped ourselves to bottles of water, and cans of coke and beer, with some care because of the infrequent comfort stops. Many thanks to the organisers and our host companies and mine staff for an informative and wonderfully enjoyable tour.

Tony Christie
GNS Science
1 Fairway Drive
Avalon, PO Box 30-368
Lower Hutt, 5040
New Zealand
Email: t.christie@gns.cri.nz