Eduqas A-level Geology · G4

Earth materials and natural resources

50 exam-style questions with answers for G4 Earth materials and natural resources in Eduqas A-level Geology (spec A480QS). Practise with flashcards, a topic quiz, a random quiz across the course, 5 crosswords, or read every question and answer below.

All 50 questions and answers

Question 1 · Spec G4, Key Idea 1 · Ore deposits
Explain why a rock containing a metal is not necessarily an ore. [2 marks]
Answer:
An ore must contain enough metal (a high enough concentration) in a large enough deposit (1); to be extracted at a profit with current technology and prices (1).
Question 2 · Spec G4, Key Idea 1 · Magmatic segregation
Explain how magmatic segregation concentrates ore minerals. [2 marks]
Answer:
Dense ore minerals such as chromite crystallise early, or a sulfide liquid separates from the magma (1); and they sink and accumulate in layers at the base of the intrusion (1).
Question 3 · Spec G4, Key Idea 1 · Hydrothermal veins
Explain how hydrothermal mineral veins form. [2 marks]
Answer:
Hot fluids carry dissolved metals through fractures (1); minerals precipitate as the fluid cools or reacts with the wall rock (1).
Question 4 · Spec G4, Key Idea 1 · Placer deposits
Explain how placer deposits form. [2 marks]
Answer:
Dense, resistant minerals such as gold and cassiterite are released by weathering (1); and are concentrated where river flow slows, such as inside meander bends, while lighter grains are carried away (1).
Question 5 · Spec G4, Key Idea 1 · Residual deposits
Explain how residual deposits such as bauxite form. [2 marks]
Answer:
Intense chemical weathering removes soluble elements (1); leaving insoluble material such as aluminium oxides concentrated in the residue (1).
Question 6 · Spec G4, Key Idea 1 · Evaporites
Explain how evaporite deposits form a mineral resource. [2 marks]
Answer:
Evaporation concentrates dissolved ions in seawater or lakes (1); until minerals such as halite and gypsum precipitate in thick beds (1).
Question 7 · Spec G4, Key Idea 1 · China clay
Describe how china clay forms from granite. [2 marks]
Answer:
Feldspar in the granite is altered to kaolinite (1); by hydrothermal fluids and weathering (kaolinisation) (1).
Question 8 · Spec G4, Key Idea 1 · Aggregates
State three factors other than thickness that affect the value of a sand and gravel deposit. [3 marks]
Answer:
Any three from: grain size and grading (1); durability of clasts (1); thickness of overburden (1); contamination, e.g. clay (1); access to transport and markets (1).
Question 9 · Spec G4, Key Idea 2 · Hydrocarbons
State two features of a good hydrocarbon source rock. [2 marks]
Answer:
A high content of organic matter, e.g. a black shale (1); buried to the right temperature for long enough to mature (1).
Question 10 · Spec G4, Key Idea 2 · Hydrocarbons
Explain why both temperature and time affect hydrocarbon generation. [2 marks]
Answer:
The reactions that turn organic matter into hydrocarbons depend on temperature (1); and take time, so a lower temperature over a longer time can give the same result (1).
Question 11 · Spec G4, Key Idea 2 · Hydrocarbons
Explain why oil turns to gas with excessive heating. [2 marks]
Answer:
Above about 150 °C large hydrocarbon molecules are broken down (cracked) (1); into smaller gas molecules such as methane (1).
Question 12 · Spec G4, Key Idea 1 · Coal
Place peat, lignite, bituminous coal and anthracite in order of increasing rank and state how carbon content changes. [2 marks]
Answer:
Peat → lignite → bituminous coal → anthracite (1); carbon content increases and volatile content decreases (1).
Question 13 · Spec G4, Key Idea 1 · Coal
State the evidence that coal formed from vegetation growing in place. [1 mark]
Answer:
A seat earth with fossil roots below the coal seam.
Question 14 · Spec G4, Key Idea 1 · Reserves
A deposit is 500 m long, 200 m wide and 4 m thick. Calculate its volume. [1 mark]
Answer:
500 × 200 × 4 = 400 000 m³.
Question 15 · Spec G4, Key Idea 1 · Reserves
The 400 000 m³ deposit has a density of 2.0 t/m³. Calculate its mass. [1 mark]
Answer:
400 000 × 2.0 = 800 000 tonnes.
Question 16 · Spec G4, Key Idea 1 · Reserves
Only 80% of the 800 000 t deposit can be recovered. Calculate the recoverable reserve. [1 mark]
Answer:
0.80 × 800 000 = 640 000 tonnes.
Question 17 · Spec G4, Key Idea 2 · Porosity and permeability
Distinguish between porosity and permeability. [2 marks]
Answer:
Porosity is the percentage of the rock's volume that is pore space (1); permeability is the ability of a rock to allow fluids to flow through it (1).
Question 18 · Spec G4, Key Idea 2 · Porosity
A rock has a bulk volume of 200 cm³ and a pore volume of 40 cm³. Calculate its porosity. [2 marks]
Answer:
40 ÷ 200 × 100 (1); = 20% (1).
Question 19 · Spec G4, Key Idea 2 · Porosity
Define primary porosity. [1 mark]
Answer:
Pore space between grains that formed when the sediment was deposited.
Question 20 · Spec G4, Key Idea 2 · Porosity
State two ways secondary porosity forms. [2 marks]
Answer:
Fracturing (1); dissolution of grains or cement (1).
Question 21 · Spec G4, Key Idea 2 · Permeability
Explain why clay can have high porosity but low permeability. [2 marks]
Answer:
Clay has many pores (1); but the pores and connections between them are very small, so fluids cannot flow easily (1).
Question 22 · Spec G4, Key Idea 2 · Reservoir quality
Explain how cementation reduces the quality of a reservoir rock. [2 marks]
Answer:
Cement fills the pore spaces, reducing porosity (1); and blocks the pore throats, reducing permeability (1).
Question 23 · Spec G4, Key Idea 2 · Darcy's Law
State Darcy's Law. [1 mark]
Answer:
Q = KA(Δh ÷ L), where Q is discharge, K is hydraulic conductivity, A is area and Δh ÷ L is the hydraulic gradient.
Question 24 · Spec G4, Key Idea 2 · Darcy's Law
Calculate Q when K = 2 × 10⁻⁵ m/s, A = 50 m², Δh = 6 m and L = 100 m. [2 marks]
Answer:
Q = 2 × 10⁻⁵ × 50 × (6 ÷ 100) (1); = 6 × 10⁻⁵ m³/s (1).
Question 25 · Spec G4, Key Idea 2 · Hydraulic gradient
Head falls from 120 m to 105 m over 300 m. Calculate the hydraulic gradient and state the flow direction. [2 marks]
Answer:
(120 − 105) ÷ 300 = 0.05 (1); water flows from high head to low head (1).
Question 26 · Spec G4, Key Idea 2 · Darcy's Law
Q = 1 × 10⁻⁴ m³/s, A = 100 m² and the hydraulic gradient is 0.02. Calculate K. [2 marks]
Answer:
K = Q ÷ (A × gradient) = 1 × 10⁻⁴ ÷ (100 × 0.02) (1); = 5 × 10⁻⁵ m/s (1).
Question 27 · Spec G4, Key Idea 2 · Darcy's Law
State what happens to discharge if the cross-sectional area doubles. [1 mark]
Answer:
Discharge doubles, as Q is directly proportional to A.
Question 28 · Spec G4, Key Idea 2 · Migration
Explain why oil and gas migrate upwards. [2 marks]
Answer:
They are less dense than the water in the pore spaces (1); so they rise by buoyancy through permeable rocks (1).
Question 29 · Spec G4, Key Idea 2 · Traps
State the three conditions needed for a hydrocarbon accumulation. [3 marks]
Answer:
A porous and permeable reservoir rock (1); an impermeable cap rock (seal) (1); a trap structure (1).
Question 30 · Spec G4, Key Idea 2 · Traps
Describe the arrangement of fluids in an anticlinal trap. [2 marks]
Answer:
Gas collects at the crest beneath the cap rock, with oil below it (1); and water below the oil, because of their densities (1).
Question 31 · Spec G4, Key Idea 2 · Traps
Explain how a sandstone pinch-out forms a stratigraphic trap. [2 marks]
Answer:
The permeable sandstone thins out and ends within impermeable mudrock (1); so hydrocarbons migrating up-dip are trapped (1).
Question 32 · Spec G4, Key Idea 2 · Traps
Explain why a fault can trap hydrocarbons or let them escape. [2 marks]
Answer:
A fault can trap hydrocarbons if it places the reservoir against impermeable rock or has a clay-rich gouge (1); but open fractures in the fault zone can let them escape (1).
Question 33 · Spec G4, Key Idea 2 · Traps
Explain how a salt dome forms hydrocarbon traps. [2 marks]
Answer:
Low-density salt rises and bends the overlying beds upwards (1); and the impermeable salt seals reservoir beds against its sides (1).
Question 34 · Spec G4, Key Idea 2 · Groundwater
Distinguish between an aquifer, an aquitard and an aquiclude. [3 marks]
Answer:
An aquifer stores and transmits water easily (1); an aquitard transmits water slowly (1); an aquiclude is impermeable (1).
Question 35 · Spec G4, Key Idea 2 · Groundwater
Distinguish between a confined and an unconfined aquifer. [2 marks]
Answer:
A confined aquifer lies between impermeable layers, so the water is under pressure (1); an unconfined aquifer has the water table as its upper surface (1).
Question 36 · Spec G4, Key Idea 2 · Groundwater
Define the water table. [1 mark]
Answer:
The upper surface of the saturated zone in an unconfined aquifer.
Question 37 · Spec G4, Key Idea 2 · Artesian water
Explain why water rises in a borehole into a confined aquifer. [2 marks]
Answer:
The water is under hydrostatic pressure from the higher recharge area (1); so it rises to the level of the potentiometric surface (1).
Question 38 · Spec G4, Key Idea 2 · Artesian water
State the condition needed for an artesian well to flow at the surface. [1 mark]
Answer:
The potentiometric surface must be above ground level at the well.
Question 39 · Spec G4, Key Idea 2 · Groundwater
Explain how a cone of depression forms. [2 marks]
Answer:
Pumping removes water faster than it can flow back (1); so the water table is lowered around the well in a cone shape (1).
Question 40 · Spec G4, Key Idea 2 · Groundwater
Explain why the recharge area of an aquifer must be protected. [2 marks]
Answer:
Rainwater entering there replenishes the aquifer (1); pollutants entering there can travel through the aquifer to wells (1).
Question 41 · Spec G4, Key Idea 2 · Groundwater quality
Explain why groundwater chemistry changes with residence time. [1 mark]
Answer:
The longer water is in contact with the rock, the more minerals dissolve in it.
Question 42 · Spec G4, Key Idea 3 · Gravity surveys
State a geophysical method to locate a dense ore body and one limitation. [2 marks]
Answer:
A gravity survey detects a positive anomaly (1); but different combinations of depth, shape and density can give the same anomaly (1).
Question 43 · Spec G4, Key Idea 3 · Magnetic surveys
Explain why magnetic surveys are useful for finding magnetite ore. [2 marks]
Answer:
Magnetite is strongly magnetic (1); so it produces a large anomaly compared with the surrounding rock (1).
Question 44 · Spec G4, Key Idea 3 · Resistivity surveys
Explain why a low resistivity anomaly is not always caused by a metal ore. [2 marks]
Answer:
Clay or saline groundwater also have low resistivity (1); so other evidence is needed to identify the cause (1).
Question 45 · Spec G4, Key Idea 3 · Seismic reflection
Explain why seismic reflection surveys are used in oil exploration. [2 marks]
Answer:
Seismic waves reflect from boundaries between rock layers (1); producing an image of folds, faults and possible traps underground (1).
Question 46 · Spec G4, Key Idea 3 · Seismic reflection
A reflection has a two-way travel time of 1.2 s. The velocity is 2500 m/s. Calculate the depth. [2 marks]
Answer:
Depth = velocity × time ÷ 2 = 2500 × 1.2 ÷ 2 (1); = 1500 m (1).
Question 47 · Spec G4, Key Idea 3 · Geochemical prospecting
Explain why stream sediment samples should be interpreted using the drainage network. [2 marks]
Answer:
Sediment in a stream comes from the whole catchment upstream (1); so the source of an anomaly lies upstream of the sample point (1).
Question 48 · Spec G4, Key Idea 3 · Geochemical prospecting
Explain why anomalous metal values are compared with local background values. [2 marks]
Answer:
Some rocks naturally contain more metal than others (1); so comparing with background shows whether there is a true anomaly (1).
Question 49 · Spec G4, Key Idea 3 · Micropalaeontology
Explain how microfossils from boreholes help oil exploration. [2 marks]
Answer:
They can be recovered from small drill cuttings (1); and are used to date and correlate rock units between boreholes (1).
Question 50 · Spec G4, Key Idea 3 · Exploration
Explain why several prospecting methods are combined in an exploration programme. [2 marks]
Answer:
Each method measures different properties and has limitations (1); combining them reduces risk before expensive drilling tests the target (1).

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