Mine Development & Surveying

Classification & Ore Genesis

The processes that concentrate metals into mineable orebodies — magmatic, hydrothermal, sedimentary and placer — plus the grade/tenor arithmetic that decides if rock is ore.

PART 1

Topic Breakdown & Traps

The Engineering Principle

An ore is a rock from which a metal can be extracted at a profit — so an orebody is defined as much by economics as by geology. Ore genesis describes how ordinary crustal abundances are upgraded by a factor of tens to thousands into a mineable grade (tenor). Key processes: magmatic segregation (early dense sulphides/oxides settle in a cooling magma — e.g. chromite, Ni–Cu sulphides), hydrothermal (hot mineralising fluids deposit veins and disseminations along fractures — most base- and precious-metal lodes), sedimentary/residual (banded iron formations, bauxite from lateritic weathering), and placer (mechanical concentration of heavy, durable minerals — gold, cassiterite, diamond — in stream/beach sediments).

The Core Formula Matrix

Concentration factor:

C F = \frac{ore grade}{average crustal abundance}

Contained metal:

M = T \times g

(tonnage

T

× grade fraction

g

)

Recoverable metal:

M_{r ec} = T \times g \times R

(recovery

R

)

Grade conversion:

1% = 10, 000 ppm = 10 kg/t

; gold often quoted in g/t.

The ‘IIT Traps’

⚠
Grade is a fraction in the tonnage formula. A 2% Cu ore means $g = 0.02$ , not 2, when multiplying by tonnage.
⚠
ppm ↔ %. $1% = 10, 000 ppm$ . Mixing these by a factor of $1 0^{4}$ is the classic blunder.
⚠
Ore is economic, not just enriched. A high concentration factor does not make rock 'ore' unless extraction pays.
⚠
Placer ≠ hydrothermal. Placers concentrate by density/durability in sediments; they are not chemically precipitated from fluids.

PART 2

Progressive 3-Tier Question Suite

Q1BASIC1 Mark · MCQ

Alluvial gold and cassiterite are most characteristically concentrated by which ore-forming process?

Q2MEDIUM2 Marks · NAT

An orebody contains

5.0

million tonnes at an average grade of

1.2%

copper. If metallurgical recovery is

90%

, the recoverable copper metal is ______ tonnes. (Round to the nearest whole number.)

Q3HARD2 Marks · NAT

Copper has an average crustal abundance of about

55 ppm

. For a deposit to be mined at

0.55%

Cu, the concentration factor relative to crustal abundance is ______. (Round off to the nearest whole number.)