ASBOG Economic Geology and Energy 2 — Questions and Answers
Question 1: Which ore deposit type forms when magmatic fluids cool and precipitate minerals into surrounding fractures, often at temperatures between 200–400°C?
- Skarn deposit
- Hydrothermal vein deposit (Correct answer)
- Placer deposit
- Residual deposit
Correct answer: Hydrothermal vein deposit
Hydrothermal vein deposits form as mineral-rich fluids cool and precipitate ore minerals into fractures and faults.
Question 2: The 'cut-off grade' in mining economics refers to:
- The deepest economically mineable level
- The minimum ore grade that covers all costs of mining and processing (Correct answer)
- The grade at which ore is blended with waste rock
- The maximum allowable ore dilution percentage
Correct answer: The minimum ore grade that covers all costs of mining and processing
Cut-off grade is the minimum grade at which ore can be mined and processed while still covering all associated costs.
Question 3: Unconventional natural gas trapped in fine-grained sedimentary rock and requiring hydraulic fracturing to produce is called:
- Coalbed methane
- Tight gas
- Shale gas (Correct answer)
- Geopressured gas
Correct answer: Shale gas
Shale gas is natural gas stored within shale formations and typically requires hydraulic fracturing ('fracking') for economic production.
Question 4: A porphyry copper deposit is characteristically associated with:
- Mafic intrusions in oceanic settings
- Felsic to intermediate intrusions at convergent plate margins (Correct answer)
- Sediment-hosted brines in rift basins
- Komatiitic volcanic sequences in Archean terranes
Correct answer: Felsic to intermediate intrusions at convergent plate margins
Porphyry copper deposits form from magmatic-hydrothermal fluids associated with felsic to intermediate intrusions at convergent plate margins.
Question 5: Which coal rank has the highest carbon content and is considered the best metallurgical coal?
- Lignite
- Sub-bituminous
- Bituminous
- Anthracite (Correct answer)
Correct answer: Anthracite
Anthracite has the highest carbon content (>86%) and lowest volatile matter among coal ranks, making it the highest-rank coal.
Question 6: The 'reserve-to-production ratio' (R/P ratio) for a mineral or energy resource represents:
- The ratio of ore reserves to waste rock removed during mining
- The estimated number of years reserves will last at current production rates (Correct answer)
- The economic feasibility index for a deposit
- The percentage of reserves recoverable by current technology
Correct answer: The estimated number of years reserves will last at current production rates
The R/P ratio divides total proven reserves by the current annual production rate, yielding estimated years of supply remaining.
Question 7: Volcanogenic massive sulfide (VMS) deposits are primarily enriched in which combination of metals?
- Cu, Pb, Zn, Au, Ag (Correct answer)
- Ti, V, Cr, Ni
- Mo, W, Sn, Li
- Al, Mn, Fe, Co
Correct answer: Cu, Pb, Zn, Au, Ag
VMS deposits are polymetallic, characteristically enriched in copper, lead, zinc, gold, and silver.
ASBOG Economic Geology and Energy 2
Which ore deposit type forms when magmatic fluids cool and precipitate minerals into surrounding fractures, often at temperatures between 200–400°C?