Geological resources: extraction and responsible use
The salt in the kitchen, the gypsum in the walls, the copper in the wiring, and the metals in a cell phone all come from the geosphere. They are not renewed on a human timescale. Extracting them transforms the land, and that is why it requires planning, restoration, and a way of consuming that does not assume there will always be more.
Types of geological resources
A computer cable contains copper, a window is made from fused quartz sand, and a good part of our electricity comes from burning natural gas. How do we classify geological materials with such different uses?
Nonmetallic materials are obtained in different ways. Limestone for cement and gravel come from open-pit quarries. Salt comes from salt works, where seawater evaporates in ponds, as in Guerrero Negro, Baja California Sur. Veins of silver or lead are followed with underground mines, like those in Zacatecas or Chihuahua.
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…
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.
Ore, gangue, and the profitability of a deposit
To obtain barely 2 g of gold, you have to crush and process about a ton of rock. What do we call the small usable part, as opposed to the mountain of rock that gets discarded?
Profitability depends on three things: the grade, the price of the metal on the market, and the cost of extracting and processing the rock.
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.
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.
Recognizing everyday minerals
Minerals are recognized by their appearance: luster, color, crystal shape, hardness, and cleavage. With these clues you can identify a sample and know what it is used for.
| Mineral | Appearance | Use | Origin |
|---|---|---|---|
| Pyrite (FeS₂) | brass-yellow cubes, metallic luster | obtaining sulfur and sulfuric acid | hydrothermal vein |
| Halite (NaCl) | colorless cubes, glassy luster | table salt, food preservation | evaporation in salt works |
| Quartz (SiO₂) | colorless hexagonal prisms with a point | glass, electronics | veins and sands |
| Calcite (CaCO₃) | rhombohedra, pronounced cleavage | cement, lime | limestone quarry |
| Gypsum (CaSO₄·2H₂O) | very soft white mass (scratched by a fingernail) | drywall, construction plaster | quarry or evaporite |
| Galena (PbS) | lead-gray cubes, metallic luster, very dense | lead for batteries | underground mine |
Observe the numbered mineral samples in the image. a) Identify each one by its appearance (luster, color, crystal shape). b) State an everyday or industrial use for each…
Observe the numbered mineral samples in the image. a) Identify each one by its appearance (luster, color, crystal shape). b) State an everyday 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.
Environmental impacts of mining
Open-pit mining transforms the landscape on a large scale, generates dust, and can alter or contaminate water. A very specific risk is acid mine drainage.
After extraction comes restoration: grading the slopes (smoothing the steep sides), covering the ground with soil, revegetating with native species, and monitoring water quality. It does not bring back the original landscape, but it recovers an ecological function and avoids an environmental liability.
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…
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.
Evaluating a mining project: the karst case
In a karst, the limestone rock is dissolved by water and crossed by cracks and conduits. Water moves through them quickly and almost without being filtered; examples are the cenotes of the Yucatán Peninsula. In such rocks, the elevation of the terrain does not tell you where the water goes.
Evaluating a project means weighing the benefits (jobs, income) against the environmental costs. The mine's jobs are temporary, while aquifers are permanent and shared. In Mexico, this is reviewed through the Environmental Impact Statement (Manifestación de Impacto Ambiental, MIA) submitted to SEMARNAT, with consultation of the communities. Some alternatives are another site, another method, recycling, or a closure plan with a financial guarantee.
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…
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.
- 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.
- b) Predict the hydrochemical and hydrodynamic consequences for the Natural Park's springs of forming a cone of depression that reverses the hydraulic gradient.
- 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.
Strategic resources and the energy transition
About 65% of the world's cobalt is mined in a single country (the Democratic Republic of the Congo), and about 90% of rare earths are processed in China. Why does the natural distribution of the crust turn certain elements into key pieces of the energy transition?
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Lithium: batteries for cell phones and electric cars. In Mexico there are deposits in Sonora, and since 2022 lithium has been declared of public utility, under State control.
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Cobalt: battery cathodes.
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Rare earths: magnets for wind turbines and motors, screens.
Alternatives include recycling, batteries with less cobalt (such as lithium iron phosphate batteries), sodium batteries, more efficient designs, and diversified suppliers.
Lithium, cobalt, and rare earths are considered strategic resources. Explain for which technologies they are essential, what external dependency problem they pose for…
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.
Responsible use: recycling, urban mining, and restoration
Geological resources are nonrenewable on a human timescale: they formed over millions of years and we consume them in decades. There are two strategies to extend their availability:
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Recycling: returning already-used metals to the cycle (aluminum cans, copper scrap).
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Substitution: using another, more abundant material for the same function (glass optical fiber instead of copper cables).
The obstacles to urban mining are technical and social. Devices mix many materials that are hard to separate, and the amounts of metal per device are small. There are almost no collection systems, and informal recycling can burn plastics and expose people to toxins. Also, many people keep their old cell phones in a drawer instead of turning them in.
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…
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.
"Urban mining" recovers metals from electronic waste. Explain what it consists of, why the proportion of valuable metal in a cell phone exceeds that of many natural…
"Urban mining" recovers metals from electronic waste. Explain what it consists of, why the proportion of valuable metal in a cell phone exceeds that of many natural ores, and what technical and social obstacles are hindering its take-off.
External agents: where surface material comes from
Many useful deposits (sands, gravels, fertile soils, gold placers) form at the surface through the action of external agents.
Analyse the following simplified Life Cycle Assessment (LCA) data for the production of 1 t of aluminum: Primary aluminum (from bauxite): energy consumption = 170 GJ;…
Analyse the following simplified Life Cycle Assessment (LCA) data for the production of 1 t of aluminum:
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Primary aluminum (from bauxite): energy consumption = 170 GJ; emissions = 12 t CO₂ eq; solid waste = 1.8 t of caustic red mud containing heavy metals.
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Secondary aluminum (scrap recycling): energy consumption = 15 GJ; emissions = 0.6 t CO₂ eq; solid waste = 0.1 t of salt slag.
- 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.
- b) In the automotive industry, different aluminum 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.
- c) A manufacturer claims: "Replacing aluminum with carbon-fiber-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).
Summary
Back to the beginning: the 2 g of gold per ton are the ore versus the gangue, and whether that rock gets mined or not depends on the grade, the price of the metal, and the environmental cost.