ASBOG - Association of State Boards of Geology Economic Geology and Energy Questions and Answers

Question 1

An exploration geologist discovers a large, stratabound ore body hosted within a Paleozoic dolomite reef complex. The primary ore minerals are sphalerite and galena, with minor fluorite and barite. Fluid inclusion studies indicate formation temperatures of 100-150°C from highly saline fluids. This ore deposit is best classified as which of the following types?

Accepted Answer

Mississippi Valley Type (MVT)

Answer

Mississippi Valley Type (MVT) deposits are characterized by their epigenetic, carbonate-hosted (limestone/dolomite) nature. They are typically dominated by lead (galena) and zinc (sphalerite) and form at relatively low temperatures (typically 90-200°C) from migrating basinal brines, far from any igneous activity. The features described in the scenario perfectly match the MVT model.

Question 2

Which of the following lists the five essential elements required for the formation and preservation of a conventional hydrocarbon accumulation?

Accepted Answer

Source rock, Reservoir rock, Seal, Trap, and Migration

Answer

A viable petroleum system requires all five components: a source rock with sufficient organic matter, a migration pathway for hydrocarbons to move, a reservoir rock with porosity and permeability to store them, a seal or cap rock to prevent their escape, and a trap to concentrate them. The other options list related concepts or examples, but not the complete set of five fundamental elements.

Question 3

A geologist is logging core from a porphyry copper system and observes a central zone rich in secondary biotite and K-feldspar. This is immediately surrounded by an extensive zone of quartz-sericite-pyrite alteration. What are the correct names for these two alteration zones, from the core outwards?

Accepted Answer

Potassic, Phyllic

Answer

Porphyry copper deposits have characteristic, large-scale alteration zoning. The core is typically the highest temperature potassic zone, characterized by secondary K-feldspar and biotite. This is commonly surrounded and overprinted by the phyllic (or quartz-sericite-pyrite) zone. Further out are the argillic and propylitic zones.

Question 4

A seismic survey reveals a potential hydrocarbon accumulation where a porous sandstone reservoir pinches out updip, becoming encased in impermeable marine shale. There is no evidence of faulting or folding in the immediate area. What type of trapping mechanism does this describe?

Accepted Answer

Stratigraphic trap

Answer

This scenario describes a stratigraphic trap. These traps are formed by changes in lithology or depositional features, such as a reservoir rock terminating, or 'pinching out', against a sealing rock. This is distinct from structural traps, which are formed by deformation like folding (anticlines) or faulting.

Question 5

Which of the following correctly lists the ranks of coal in order of increasing heat content, carbon content, and metamorphic grade?

Accepted Answer

Lignite, Sub-bituminous, Bituminous, Anthracite

Answer

Coalification is the process where peat is converted into coal through burial, increased pressure, and temperature. The sequence represents increasing metamorphic grade, carbon content, and energy content. It begins with Lignite (lowest rank), then Sub-bituminous, then Bituminous, and finally Anthracite (highest rank).

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Practice Test

ASBOG - Association of State Boards of Geology Economic Geology and Energy Questions and Answers