Economic Minerals – minerals that can be extracted, processed, and marketed at a profit.

Factors: -interest in the mineral, -size of the deposit, -mineral

concentration, -mineral depth below the surface

-market value.

An ore is a natural material with a high concentration of economically valuable minerals that can be mined for a profit

1) Magmatic Deposits accumulations of metals associated with magma that forms igneous rocks

Certain metals are enriched in certain magmas and further concentrated during cooling of the magma

Magmatic Deposits: A) Layered Gravitational Settling

heavy minerals that crystallize early, settle and concentrate on the bottom of the magma chamber this results in a layered deposit.

High-density minerals sink to the bottom of the magma chamber.

Magmatic Deposits: B) Disseminated Deposits in which the metal is evenly

distributed in generally low concentrations throughout large masses of igneous rock. Ex: porphyry copper deposit

(e.g. Sudbury, Ontario and Voisey’s Bay, Newfoundland and Labrador)

A sample of nickel-bearing rock from Sudbury.

Diamonds Most diamonds are found in unique

ultramafic igneous rocks called kimberlites

Magma generated by partial melting of asthenosphere below 150 kilometres and then rises quickly to the surface, picking up diamonds from solid lithospheric mantle

2) Hydrothermal Deposits any concentration of metallic minerals

formed by the precipitation of solids from hot mineral-rich water (hydrothermal solution).

hot water dissolves and transport minerals, interconnected openings in the rock allows the solutions to move, and chemical reaction result in deposition. Deposition can be caused by boiling, by a drop in temperature, by mixing with a cooler solution, or by chemical reactions between the solution and a reactive rock. produce vein deposits.

Hydrothermal Deposits Can occur as disseminated deposits,

which are distributed throughout the rock body, rather than concentrated in veins; called porphyry deposits = (low grade; large volume)

3) Sedimentation Secondary enrichment A class of residual deposits formed by both

the removal of valueless material in solution and the solution and redeposition of valuable ore minerals.

Because solution and redeposition occurs the process is known as a secondary enrichment.

Weathering Secondary enrichment Bauxite

Principal ore of aluminum Forms in rainy tropical climates from

chemical weathering and the removal of undesirable elements by leaching

Stratiform Deposits Copper-bearing brines moving through

coarse-grained sedimentary rock are forced upward through oxygen-poor, sulphide-rich mud, which promotes precipitation of minerals

Sedimentary Deposits Banded Iron Formations

Conditions during the early Precambrian resulted in large quantities of ferrous iron in solution

At some point, photosynthesizing bacteria generated sufficient oxygen to precipitate iron oxide minerals. Ex: Bell Island Deposit

4) Placer deposits – formed when heavy metals are mechanically concentrated by currents

Examples: Gold, Platinum, Diamonds

5) Metamorphic Deposits Many of the most important metamorphic ore deposits are produced by contact metamorphism. Sphalerite (zinc) Galena (lead) Chalcopyrite (copper)