Economic & Ore Geology

Ore Minerals, Deposit Types & Grade

Principal ore minerals, the magmatic-to-hydrothermal spectrum of deposits, and basic grade–tonnage arithmetic.

PART 1

Topic Breakdown & Traps

The Engineering Principle

Economic geology studies how metals concentrate into mineable ore deposits. Key ore minerals: galena (Pb), sphalerite (Zn), chalcopyrite (Cu), cassiterite (Sn), chromite (Cr), hematite/magnetite (Fe), bauxite (Al). Deposits span magmatic segregation (chromite, PGE in layered intrusions), hydrothermal (porphyry Cu, vein gold, MVT Pb–Zn), sedimentary/chemical (banded iron formation) and residual weathering (laterite/bauxite). Resource value is set by grade (metal %) above a cut-off, times tonnage and recovery.

The Core Formula Matrix

Contained metal: tonnage × grade.

Weighted average grade:

\frac{\sum g _{i} t _{i}}{\sum t _{i}}

.

Recoverable metal: tonnage × grade × recovery.

Cut-off ratio: average grade ÷ cut-off grade.

The ‘IIT Traps’

⚠
Chalcopyrite ≠ lead. Galena is Pb; chalcopyrite is Cu; sphalerite is Zn.
⚠
BIF is sedimentary, not hydrothermal. Banded iron formations are chemical sediments.
⚠
Grade × tonnage units. Watch %, g/t and tonnes — convert consistently.

📚 Standard references

Economic Mineral Deposits — Jensen & Bateman
Ore Geology and Industrial Minerals — Anthony M. Evans

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

The principal ore mineral of lead is

Q2MEDIUM2 Marks · NAT

An ore body of

5

million tonnes assays

2%

Cu. The contained copper is _____ tonnes.

Q3HARD2 Marks · NAT

Two ore blocks:

20

kt at

2%

and

10

kt at

5%

. The combined average grade is _____ %.