Geological resources
This domain tests classification of resources, ore-forming processes, reserve estimation and the environmental consequences of extraction. Andalusian deposits supply most of the examples.
Classification
- Renewable versus non-renewable resources; a resource is a concentration with potential value, a reserve is the economically and technically recoverable part.
- Energy resources include fossil fuels, nuclear fuel and renewables; Andalusia has limited hydrocarbons but strong solar, wind and biomass potential.
Ore deposits
- Magmatic: chromite, nickel-copper and platinum-group elements in mafic and ultramafic rocks, as in the Ronda peridotites.
- Hydrothermal: volcanogenic massive sulfides of the Iberian Pyrite Belt (Riotinto, Tharsis, Aznalcollar) carry copper, zinc, lead, gold and silver in Devonian-Carboniferous host rocks.
- Vein deposits: lead-zinc veins of Linares-La Carolina in the Variscan basement.
- Sedimentary and metamorphic: gypsum and halite, phosphorites, and Macael marble.
Water and soil
Aquifers are resources with recharge limits; overexploitation lowers water tables and can cause seawater intrusion or subsidence. Soil is a finite, slowly renewed resource.
Environmental impacts
Acid mine drainage results from pyrite oxidation, producing sulfuric acid, lowering pH and mobilising metals. Tailings dams can fail, as at Aznalcollar in 1998, when the Guadiamar valley was flooded with metal-rich sludge close to Donana.
Worked example
A deposit has volume 2 x 10^6 m3, density 2.8 t/m3, grade 1.5% Cu and recovery 90%. Mass = 2 x 10^6 x 2.8 = 5.6 x 10^6 t. Copper in situ = 5.6 x 10^6 x 0.015 = 84,000 t. Recoverable copper = 84,000 x 0.90 = 75,600 t. Convert volume to mass first, then apply grade and recovery.
Traps that cost marks
Resource versus reserve is a common slip. Grade units are confused: 1% equals 10,000 ppm. Recovery and dilution are forgotten. Volume is not tonnage without density. Acid drainage is a chemical process, not simply erosion.
Key points
- Reserves are the economic subset of resources.
- The Iberian Pyrite Belt is a VMS district.
- Ronda peridotites host magmatic chromite and PGE.
- Pyrite oxidation drives acid mine drainage.
- Grade calculations require mass, not volume.