Methods of Mining and Factors for Mineral Exploitation – Mining in Africa (Senior 3 Geography) | Ganzaa

Mining in Africa

Lessons

Senior 3 · Geography

Mining in Africa

4 lessons

Lesson 2 of 4

Methods of Mining and Factors for Mineral Exploitation

30 min

Let's begin

At Jwaneng in Botswana, diamond-bearing rock is dug from a vast open pit, terrace by terrace, by shovels and dump trucks. Near Johannesburg, gold miners travel kilometres down vertical shafts to reach a thin reef of gold-bearing rock. In the river gravels of Kono District, Sierra Leone, a man with a sieve washes mud in search of a single diamond. All three are mining, yet the methods could hardly be more different. What decides how, and whether, a mineral is mined?

Methods of mining

Figure 2 shows the main methods side by side. The choice depends mostly on how deep the mineral lies and what form it takes: a wide body near the surface, a thin sloping vein deep underground, loose grains in river gravel, or a liquid trapped in rock.

Method	How it works	Used where	African examples
Open-cast (open-pit) mining	The overburden is removed; the ore is blasted and dug out in benches by shovels and trucks	Large ore bodies near the surface	Copper at Nchanga, Zambia; diamonds at Jwaneng, Botswana; coal on South Africa's Highveld
Underground (shaft) mining	A vertical shaft is sunk; horizontal levels lead to the ore, which is broken and hoisted up	Deep ores and thin veins or reefs	Gold on the Witwatersrand, South Africa; copper at Mufulira, Zambia
Adit (drift) mining	A horizontal tunnel is driven into a hillside to reach a seam or vein	Minerals exposed on a valley side	Coal at Enugu, Nigeria; many small tin and coltan mines in hilly areas
Alluvial (placer) mining	River sand and gravel are dug, then washed by panning, sluicing or dredging to separate heavy grains	Minerals eroded and dropped by rivers	Diamonds in Sierra Leone; gold in Ghana
Drilling	Wells are drilled into rocks holding oil or gas, on land or from offshore platforms	Liquid and gas fuels	Oil in the Niger Delta, Libya and offshore Angola
Dredging	Ships or floating dredges suck up gravel from the sea bed or river bed	Minerals under water	Diamonds from the sea bed off Namibia

Definition

Overburden: the soil and rock lying above an ore body, removed before open-cast mining. Shaft: a vertical tunnel from the surface down to the ore. Adit: a horizontal tunnel driven into a hillside. Reef or vein: a thin layer or sheet of ore within other rock. Alluvial deposit: minerals mixed in sand and gravel laid down by a river. Artisanal mining: small-scale mining by individuals or small groups using simple tools.

Factors that favour mineral exploitation

Factor	Why it matters	Example
Grade (quality) of the ore	Rich ore gives more metal per tonne dug, so profits are higher	High-grade copper ores of Katanga
Size of the deposit	A large deposit repays the cost of machines, roads and towns for many years	The Witwatersrand gold reefs, mined since 1886
Depth and accessibility	Shallow deposits can be mined cheaply by open-cast methods	Open pits at Jwaneng and Nchanga
Capital	Exploration, machines, shafts and processing plants cost a great deal	Large mining companies and foreign investors
Technology and skilled labour	Needed to find, extract and process ore safely	Deep-level gold mining in South Africa
Transport	Heavy ore and metal must reach ports cheaply	The TAZARA railway from Zambia's Copperbelt to Dar es Salaam
Power and water supply	Smelters, pumps and processing plants use large amounts	Hydroelectric power from Kariba for the Copperbelt
Market demand and prices	High world prices make poorer or deeper ores worth mining	Rising demand for coltan for electronics
Government policy and stability	Fair laws, licences and peace attract investment	Botswana's stable partnership with its diamond miners

Worked example

Worked example 1: ore grade (illustrative figures). Mine A digs ore containing 2% copper; mine B digs ore containing 0.5% copper. How much copper does each obtain from 10,000 t of ore?

Mine A: 2% × 10,000 t = 0.02 × 10,000 = 200 t of copper.
Mine B: 0.5% × 10,000 t = 0.005 × 10,000 = 50 t of copper.
Conclusion: for the same digging cost, mine A produces four times as much metal, so a rich ore can be worked even where transport is expensive.

Worked example

Worked example 2: the stripping ratio (illustrative figures). To reach 3 million tonnes of ore in an open pit, a company must remove 12 million tonnes of overburden. What is the stripping ratio, and what does it tell us?

Stripping ratio = waste ÷ ore = 12 ÷ 3 = 4, written 4 : 1.
Four tonnes of waste are moved for every tonne of ore. The higher the ratio, the more expensive the ore; at some depth, an underground mine becomes cheaper than a deeper pit.

Warning

Do not confuse an adit with a shaft. A shaft goes straight down from the surface; an adit goes into a hillside horizontally. Both are underground methods, but an adit needs no hoist to lift the ore.

Tip

For a "describe a method" question, follow the order of work: find the ore → reach it (remove overburden, sink a shaft, drive an adit or drill) → extract it → transport it to the surface → process it. Add a named example at the end.

Mining for Zambia: a short visual journey through the stages of copper production in Zambia. Note each stage between the open pit and the finished copper.

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Practice

Define overburden and alluvial deposit.
Describe how open-cast mining is carried out.
Why is gold on the Witwatersrand mined underground rather than by open-cast methods?
Give one African example each of alluvial mining, drilling and adit mining.
Explain how transport and power supply have helped copper mining on Zambia's Copperbelt.
Ore containing 1.5% copper is mined. How many tonnes of copper are in 40,000 t of this ore?
A pit must remove 15 million tonnes of overburden to reach 5 million tonnes of ore. Calculate the stripping ratio.
"The grade of the ore is the most important factor in deciding whether a mine opens." Discuss.

Show answersHide answers

Overburden: the soil and rock lying above an ore body. Alluvial deposit: minerals mixed in sand and gravel laid down by a river.
Vegetation and overburden are removed; the ore is drilled, blasted and dug out in steps (benches) by shovels; dump trucks carry it up haul roads to the processing plant; the pit deepens step by step.
The gold lies in thin reefs that dip steeply deep underground, so digging a pit down to them would mean moving far too much waste rock.
Alluvial: diamonds in Sierra Leone or gold in Ghana. Drilling: oil in the Niger Delta, Libya or offshore Angola. Adit: coal at Enugu, Nigeria.
Railways such as TAZARA carry heavy copper to the ports of Dar es Salaam (and others) for export; hydroelectric power from Kariba runs the mines, pumps and smelters.
1.5% × 40,000 = 0.015 × 40,000 = 600 t.
15 ÷ 5 = 3, so 3 : 1.
Grade matters because it decides how much metal each tonne yields, but size of deposit, depth, prices, transport, capital, power and government policy can outweigh it: a rich ore in a remote, unstable area may stay unworked, while a low-grade ore near a railway with high prices can be profitable.

Sources and credits

Open-pit mining, Shaft mining, Placer mining, Jwaneng diamond mine and TAZARA Railway: Wikipedia contributors, Wikipedia, CC BY-SA 4.0, adapted by Ganzaa.
Photo: Jwaneng Open Mine, Cretep, Wikimedia Commons, public domain.
Photo: Alluvial diamond miner Sierra Leone 2005, Laura Lartigue, USAID, Wikimedia Commons, public domain.
Video: How Copper is Produced, Mining for Zambia, embedded from YouTube.
Figure 2, tables, worked examples and exercises: written by Ganzaa.

This lesson adapts CC BY-SA material and is shared under CC BY-SA 4.0.

1Methods of mining

2Factors that favour mineral exploitation

Methods of mining

Factors that favour mineral exploitation