Exercises: Geological resources: exploitation and responsible use

State four minerals or rocks in everyday use (for example, gypsum, salt, quartz, or limestone), indicate one application for each, and explain what type of deposit or quarrying/mining operation they are obtained from.

Define ore and gangue in a metallic deposit and explain what determines whether a deposit is profitable to mine, considering the metal price and the proportion of ore.

Reason why geological resources are considered non-renewable on a human scale and what two strategies make it possible to extend their availability — recycling and substitution with other materials —, providing an example of each.

Classify these geological resources as metallic, non-metallic (industrial) and energy resources: copper, gypsum, coal, silica sand, oil and iron, and give one application of each.

Explain the difference between an open-pit quarry and an underground mine, what type of resources is extracted in each, and give a Spanish example of each type of operation.

What is the grade of an ore? Explain why the average grade of mined deposits falls over time and what consequences this has for profitability and for future mining (could deposits discarded today be exploited?).

Name three building materials obtained from geological resources (sand, gravel, gypsum, ornamental stone) and explain their use and where they are extracted in your nearest surroundings.

Explain why coal, oil and natural gas are called fossil fuels and what the expression "fossil sunlight" means applied to the energy they release when burned.

Describe two environmental impacts of open-cast mining (on the landscape, water, or atmosphere) and explain what the subsequent restoration of a site consists of, citing a specific land recovery measure.

Lithium, cobalt, and rare earths are considered strategic resources. Explain for which technologies they are essential, what external dependency problem they pose for Europe, and what alternatives are being explored.

Observe the characteristics of the six numbered mineral samples:

1. Brass-yellow cubic crystals with a metallic luster.

2. Colorless and transparent cubic crystals, with a vitreous luster.

3. Colorless hexagonal prisms terminated in a pyramid, with a vitreous luster.

4. Translucent rhombohedral crystals with very distinct cleavage.

5. Whitish mineral mass, very soft (can be scratched with a fingernail).

6. Lead-gray cubic crystals, metallic luster, and high density.

1. a) Identify each one by its appearance (luster, color, crystal shape). b) State a daily or industrial use for each mineral. c) Point out which ones are non-metallic and explain the difference between a metallic and a non-metallic mineral resource.

Sand is, after water, the most extracted resource on the planet. Explain what it is used for (concrete, glass), what impacts its extraction has on rivers and beaches (deepening of riverbeds, coastal retreat) and why not all sand is suitable (what problem does desert sand have?).

Almadén (Ciudad Real) hosted the largest mercury mine in the world. Explain its historical importance (the silver of America and amalgamation), why it closed and what persistent environmental problems it left (mercury in soils and fish), as well as its present value as heritage.

When the extraction from an aquifer exceeds its recharge, we speak of "water mining". Explain what this expression means, why it is literal in fossil aquifers (almost zero recharge), and give an example of the tension it generates between irrigation and conservation (Tablas de Daimiel, Doñana).

Describe the phases of the life cycle of a mining operation (prospecting, extraction, ore concentration, closure and restoration) and discuss why the closure plan must be approved and funded before digging begins.

Compare obtaining one tonne of copper from a mine with recovering it from electronic scrap: energy consumption, $\text{CO}_2$ emissions, waste generated and employment created. Conclude what role recycling can play in the future supply of the metal.

A mining company submits a project to reopen an open-pit polymetallic sulfide (copper and zinc) mine 3 km from the boundary of a Natural Park located on a karst massif with protected aquifers. The company defends its environmental viability by claiming that the pit is situated at a topographic elevation 80 m lower than the park's springs and that it will create 350 direct jobs in a demographically declining region.

1. a) Refute the company's hydrogeological argument: justify why the topographic difference does not guarantee hydrogeological safety in karst terrain if continuous dewatering in the pit alters the regional water table.
2. b) Predict the hydrochemical and hydrodynamic consequences for the Natural Park's springs of forming a cone of depression that reverses the hydraulic gradient.
3. c) As an environmental officer, design three non-negotiable technical conditions (related to piezometric monitoring, tailings confinement, and the post-closure restoration bond) that you would demand in order not to issue an unfavorable Environmental Impact Statement.

An open-pit gold mine exploits an ore with an average grade of 1,5 g of Au per ton of displaced rock, with a carbon footprint of 14.000 kg of CO₂ eq per kilogram of refined metal obtained. In contrast, printed circuit boards from discarded mobile phones have average concentrations of 300 g of Au and 120 kg of Cu per ton of waste.

1. a) Calculate how many tons of mineralized rock must be extracted and crushed in the primary mine to obtain the same amount of gold contained in 2 t of mobile phone circuit boards. Interpret the comparative geomorphological impact of both sources.
2. b) If the metal concentration is so much higher in electronic waste, justify why primary mining still provides more than 80 % of the world's gold: analyze two thermodynamic or technological limitations linked to material dispersion (complex alloys, solders, miniaturization) and one logistical collection barrier.
3. c) Predict what environmental impact on soils and groundwater would be caused by recovering these metals through artisanal or informal acid leaching, comparing it to closed-loop industrial hydrometallurgy.

Analyse the following simplified Life Cycle Assessment (LCA) data for the production of 1 t of aluminium:

• Primary aluminium (from bauxite): energy consumption = 170 GJ; emissions = 12 t CO₂ eq; solid waste = 1,8 t of caustic red mud containing heavy metals.

• Secondary aluminium (scrap recycling): energy consumption = 15 GJ; emissions = 0,6 t CO₂ eq; solid waste = 0,1 t of salt slag.

1. a) Interpret the data and calculate the percentage of energy savings and GHG emission reductions achieved by the circular economy for this metal compared to the linear extractive route.
2. b) In the automotive industry, different aluminium alloys are blended with magnesium, zinc, or silicon. Justify why "downcycling" (recycling with a loss of purity and mechanical properties) poses a bottleneck to closing the loop and how ecodesign can prevent it.
3. c) A manufacturer claims: "Replacing aluminium with carbon-fibre-reinforced polymers in vehicles reduces the overall ecological footprint because it avoids bauxite mining." Refute or qualify this statement by analysing the full life cycle of the substitute (petrochemical origin and difficulty of end-of-life recycling).

The International Energy Agency estimates that manufacturing an electric vehicle requires an average of about 205 kg of critical minerals (copper, lithium, nickel, manganese, cobalt, and rare earths), compared to the 35 kg needed for a conventional internal combustion vehicle.

1. a) Analyse the environmental paradox: if the rollout of electric vehicles aims to decarbonise transport to curb climate change, predict which local geomorphological, hydrological, and geochemical pressures will shift to mining areas if the global vehicle fleet (1.400 million cars) is replaced at a 1:1 ratio.
2. b) A corporate report forecasts that by the year 2032, 100% of the critical metals in its batteries will come from recycling its own vehicles. Using the concept of residence time and the growth rate of the vehicle fleet, demonstrate why this goal is mathematically impossible in the medium term.
3. c) Justify how substituting battery technologies (for example, sodium-ion cells instead of lithium-ion, or lithium iron phosphate cathodes free of cobalt and nickel) reduces the geological risk of supply shortages, taking into account the crustal abundance of each element.

Hydrochemical analysis of the leachate emerging from the base of an abandoned mine waste dump rich in pyrite ($FeS_2$) yields the following values: pH = 2,4; $[SO_4^{2-}] = 3.800\text{ mg/L}$; $[Fe^{total}] = 750\text{ mg/L}$; cadmium and arsenic concentrations 50 times above the environmental quality standard. At 1,5 km downstream, this stream joins a hardwater river whose bed runs over limestone ($CaCO_3$).

1. a) Write the overall oxidation reaction of pyrite in the presence of water and atmospheric oxygen. Justify why the metabolic activity of chemolithotrophic bacteria (such as Acidithiobacillus ferrooxidans) exponentially accelerates this process and turns the drainage into a self-sustaining phenomenon for decades after the mine's closure.
2. b) Predict in detail the chemical processes that will occur in the mixing zone with the limestone river: changes in pH, formation of the ochre precipitate of ferric hydroxides (schwertmannite/goethite), and the resulting alteration of light penetration and the benthic community.
3. c) Design a passive treatment system for this effluent combining a preliminary anoxic limestone drain with an organic-compost subsurface flow anaerobic wetland. Justify the role of sulphate-reducing bacteria in immobilising dissolved heavy metals.

In 1998, the Aznalcóllar tailings dam collapsed due to basal shearing, releasing more than 5 million m³ of acidic water and pyritic sludge rich in zinc, lead, arsenic, and cadmium into the Guadiamar River towards Doñana.

1. a) Following the accidental spill, one of the first emergency measures was to mechanically remove the sludge before the autumn rainy season using mechanical diggers, also scraping away the first few centimetres of the underlying soil. Geochemically justify why it was critical to prevent the sludge from drying in the sun and oxidising in situ on the alluvial soil.
2. b) During the restoration phase ("Guadiamar Green Corridor"), limestone amendments and compost were applied to the remaining soil, and grazing and agricultural cultivation were prohibited in favour of phytostabilisation with white poplars (Populus alba) and tamarisk (Tamarix africana). Justify the edaphic and ecotoxicological rationale behind this decision as opposed to allowing agricultural use or resorting to phytoextraction.
3. c) Many historical tailings dams were raised using the "upstream" method (placing successive dykes directly on top of previously settled tailings). Justify why this geotechnical design carries a high risk of failure due to seismic liquefaction or pore water overpressure, and compare it with the modern alternative of dry stacking.

Nearly 70% of the refined cobalt used in global electronics and the automotive industry is mined in the copperbelt of the Democratic Republic of the Congo, where industrial operations coexist with informal artisanal mining lacking occupational health controls and toxic runoff treatment.

1. a) Apply the concepts of "extraterritorial ecological footprint" and "externalised costs" to explain why the market price of a product containing these metals does not reflect its true environmental or human replacement cost.
2. b) A European supply chain due diligence directive requires multinationals to certify that their minerals are free from human rights abuses and river basin contamination. Predict two technical and mineralogical traceability difficulties that arise when auditing the origin of the ore once it passes through intermediary smelters that blend batches from diverse sources.
3. c) Critically assess whether individual "responsible consumption" campaigns are sufficient to resolve the environmental injustice associated with global mining extraction, or whether structural transformations in device replacement rates and international resource governance treaties are required.

A city of 120.000 inhabitants generates approximately 18 t of waste electronic circuit boards and discarded mobile phones each year. However, municipal recycling drop-off centres only manage to collect 15% of this material; the rest remains kept in homes ("hoarding effect") or is improperly mixed with residual household waste.

1. a) If the collected waste contains 280 g of gold per tonne and the metallurgical recovery process has an efficiency of 85%, calculate how many grams of pure gold are lost annually in the city due to the 85% of waste that does not enter the recycling loop.
2. b) Compare two treatment routes for shredded circuit boards: pyrometallurgy (smelting in a high-temperature furnace) versus bacterial bioleaching with Acidithiobacillus. Analyse the advantages and disadvantages of each in terms of energy consumption, atmospheric emissions, and processing time.
3. c) Design a comprehensive municipal plan to raise the collection rate of this waste above 70%: propose two economic incentive or domestic reverse logistics measures and one change in citizen habits, justifying why merely increasing the number of on-street containers is ineffective.

Unit Challenge. Imagine you are advising the Ministry for the Ecological Transition on the sustainable management of a lithium deposit in peninsular granitic massifs. Your mission is to write a reasoned technical proposal ($1,5$ pages) that integrates Earth and biosphere dynamics following these phases:

1. Real data collection: Access the IGME cartographic viewer (igme.es) and locate a Spanish igneous body. Note down its main lithology (e.g., granite or basalt) and the associated economic and rock-forming minerals.

2. Geodynamic and biological connection: Justify how continental drift and plate tectonics generated this landform through intrusive or effusive magmatic processes. Describe how the weathering of these rocks releases mineral salts that support local vegetation through root nutrition structures.

3. Management and responsible use plan: Design a table that assesses two environmental impacts derived from the extraction of this geological resource, and propose three viable measures for soil restoration and the promotion of a circular economy.

Assessment criteria:

• Coherence in explaining the genesis of the landform and deposit from plate tectonics and magmatism.

• Rigor in linking geosphere minerals to plant nutrition structures.

• Quality of the data from the IGME and ethical and environmental feasibility of the proposed corrective measures.