Topic 1: Types of ore Bodies and Mine Processes

• Extraction– Open Pit– Strip Mining– Underground

• Crushing– Initial – Autogenous Circuit

• Beneficiation– Physical– Chemical– Electrochemical

• Smelting

Types of Ore• Massive: base metal

Cu, Ni, Zn

• Disseminated: gold,

• Diamonds Snow Lake

0.16 oz Au / tonne

INCO Thompson Ni ore

Ekati, NWT, Diamonds

Bissett Au

Bedded Ore bodies

Potash, SaskatchewanSyncrude, Oil sands, Fort McMurray

Black Thunder Coal MineWyoming, USA

Extraction process depend on shape, position and

value of ore body• Open Pit

• Strip Mining

• Underground Mine

• Dissolution: potash, uranium,

• In situ mobilization: oil shale

• Heap Leach

What are the major environmental issues related to each form of extraction?

Open Pit

Bingham Canyon Cu Mine

Ekati Diamond Mine

Note: The amount of waste rock to be removed to provide reasonable gradient for trucks.Only efficient for large ore bodies close to the surfaceCan be useful for dumping mine waste at closure

Strip Mining

Very efficient for high level flat lying ore bodies. Overburden and top soil can be replaced minimizing environmental damage

Underground

Dissolution: potash, uranium In situ mobilization: sulfur, oil shale

NaCl or KCl dissolved in water

Acid in situ leach of metallic ore

Hot water or steam used to mobilize sulfur or oil

Heap Leach

Landusky, Montana, CN Heap Leach Gold Mine 1979-1996

Crushing• Ore bearing and non ore-bearing rock will be separated as soon as

possibleWhat happens to non-ore-bearing rock?• Ore-bearing rock will be crushed to the size necessary to liberate

the required mineral• Heap leach requires only very coarse crushing• Much finer crushing for gold and PGE as they are enclosed within other mineral grains• Initial crushing underground • In mill, crushing in autogenous circuit withfeedback of large particles• Final crushing in rod or ball mills

Beneficiation (Extraction of metal from rock/mineral)

• Physical techniques– Gravity

• Gold from quartz• Diamonds• Tantalum

– Flotation• Sulphides from silicates• Cu and Ni sulphides• NaCl from KCl

• Chemical Techniques– CN leaching– Roaster oxidizes sulphide to SO2

• Smelting• Electrochemical Refining of pure metal

Consider the waste generated at each stage

Gravity Separation

Whiffle tableSeparator

Fine grained waste goes to tailings pond. What does it contain?

Flotation Cells

Ore becomes attached to air bubbles, float, and are collected.Gangue sinks to the bottom of the flotation cells and piped to tailings pond

Chemicals added include:Frothers: pine oils & alcohols promote the formation and stability of bubbles. Collectors promote adherence of air bubbles to the mineral. Conditioners: make the surface of the mineral particle either more or less susceptible to concentration. Activators e.g. copper sulfate, lead nitrate, lead acetateDepressants e.g. sodium cyanide, zinc sulfate

Chemical Separation

• Cyanide leaching for gold– at pH 11– gold retrieved by Merrill

Crowe (precipitation on zinc dust) or Carbon in Pulp (CIP) process

• Roaster oxidizes sulphide to SO2

– Releases metal for refining and SO2 to the atmosphere unless scrubbers are in place

Smelting

• Separates remaining silicates from metals

• Slag (molten silicates) pored off

• Metal pores into bars or sent for final electochemical refining