Economic Geology and Energy Resources
What to know
Ore deposits are grouped by process: magmatic segregation (chromite, Ni–Cu, PGE), porphyry Cu–Mo–Au, skarn, volcanogenic massive sulfide, SEDEX, Mississippi Valley-type Pb–Zn, epithermal Au–Ag, orogenic gold, banded iron formation, laterite (Ni, bauxite), carbonatite REE, pegmatite (Li, Ta, Be), and placer deposits. A genetic model requires a source, a transporting fluid (chloride and bisulfide complexes carry metals), and a trap (boiling, cooling, mixing, pH change, reduction).
Resource classification matters: a resource is a concentration with reasonable prospects; a reserve is the economically recoverable part, demonstrated by technical study. Contained metal = tonnage × grade.
The petroleum system has six elements: source rock (organic richness, kerogen type, thermal maturity), migration, reservoir (porosity plus permeability), seal, trap, and timing. The oil window is roughly 60–120 °C (vitrinite reflectance ~0.6–1.3%), with gas at higher maturity. Coal rank runs peat → lignite → sub-bituminous → bituminous → anthracite, measured by vitrinite reflectance and volatile matter. Unconventional resources include shale oil/gas, tight gas, coalbed methane, and gas hydrates.
Traps
Confusing reserves with resources; equating coal rank with geologic age; assuming porosity guarantees production (permeability matters); forgetting the seal or timing element in a petroleum play; confusing grade units (%, g/t, ppm).
Rule of thumb
1% Cu over 10 million tonnes = 100,000 t contained copper. Always multiply before comparing deposits.