ASBOG Economic Geology and Energy 4 — Questions and Answers
Question 1: In mining, 'stripping ratio' refers to:
- The ratio of ore grade to cut-off grade
- The volume or tonnage of waste rock removed per unit of ore mined (Correct answer)
- The percentage of mineral recovered in the processing plant
- The rate at which ore is removed from underground workings
Correct answer: The volume or tonnage of waste rock removed per unit of ore mined
Stripping ratio is the amount of overburden or waste rock that must be removed to access one unit of ore, critical for open-pit economics.
Question 2: Which type of uranium deposit is the world's highest-grade and forms at the unconformity between Proterozoic basement and overlying sandstone?
- Sandstone roll-front deposit
- Unconformity-related deposit (Correct answer)
- Calcrete (surficial) deposit
- Volcanic-related deposit
Correct answer: Unconformity-related deposit
Unconformity-related uranium deposits (e.g., Athabasca Basin, Canada) occur at redox interfaces at the unconformity and are the world's richest uranium ores.
Question 3: The 'oil window' in petroleum geology typically corresponds to what range of vitrinite reflectance values?
- 0.2–0.6% Ro
- 0.6–1.3% Ro (Correct answer)
- 1.3–2.0% Ro
- 2.0–4.0% Ro
Correct answer: 0.6–1.3% Ro
The oil window (peak oil generation) generally occurs between 0.6% and 1.3% Ro, with wet gas and condensate forming above ~1.0% Ro.
Question 4: Geothermal energy resources are BEST developed in areas characterized by:
- Thick sedimentary basins far from plate boundaries
- High heat flow, volcanic activity, or proximity to tectonic plate margins (Correct answer)
- Ancient crystalline shield rocks with low radioactive heat production
- Deep continental cratons with thick lithosphere
Correct answer: High heat flow, volcanic activity, or proximity to tectonic plate margins
Geothermal resources require elevated crustal heat flow, typically associated with volcanic arcs, rift zones, or hot spots.
Question 5: Which geologic formation is the primary source rock for the Permian Basin's prolific oil production?
- Wolfcamp Shale (Correct answer)
- Barnett Shale
- Marcellus Shale
- Eagle Ford Shale
Correct answer: Wolfcamp Shale
The Wolfcamp Shale (Permian) is the primary source and tight-oil reservoir in the Permian Basin, making it one of the most productive plays in the US.
Question 6: A 'roll-front' uranium deposit in sandstone forms due to:
- Magmatic fluids precipitating uraninite in fractures
- Redox interface where oxidizing uranium-bearing groundwater meets reducing conditions (Correct answer)
- Evaporite dissolution creating open-space voids
- Sedimentary exhalative processes on the seafloor
Correct answer: Redox interface where oxidizing uranium-bearing groundwater meets reducing conditions
Roll-front deposits form at the interface between oxidized (uranium-mobile) and reduced groundwater where uranium precipitates as uraninite.
Question 7: The 'proved reserves' category in petroleum resource classification requires that the deposit be:
- Geologically estimated to exist with at least 50% confidence
- Recoverable with reasonable certainty (≥90% probability) under existing economic and operating conditions (Correct answer)
- Identified by seismic data alone without drilling confirmation
- Economically mineable only under future technology improvements
Correct answer: Recoverable with reasonable certainty (≥90% probability) under existing economic and operating conditions
Proved reserves (1P) have at least 90% probability of recovery under current economic and technical conditions, typically requiring well control.
ASBOG Economic Geology and Energy 4
In mining, 'stripping ratio' refers to: