EARTHSCI LESSON 6

Mineral Occurrence

Concentration of a mineral that is of scientific or technical interest.

Mineral Deposit

Mineral occurrence of sufficient size and grade or concentration to enable extraction under the most favorable conditions.

Ore Deposit

Mineral deposit that has been tested and known to be economically profitable to mine.

Aggregate

Rock or mineral material used as filler in cement, asphalt, plastic, etc; generally used to describe nonmetallic deposits.

Ore

Naturally-occurring material from which a mineral or minerals of economic value can be extracted.

Economic Minerals

Minerals that can be extracted, processed, and marketed at a profit. Factors: interest in mineral, deposit size, concentration, depth, market value.

Geologic Processes

Rock cycle and plate tectonics play major roles in accumulation and concentration of valuable minerals.

Origin of Mineral Deposits

A mineral deposit is a volume of rock enriched in one or more minerals. Mineral deposits classified by the mechanism responsible for concentration.

Metallic Mineral Deposits

Magmatic Deposits

Minerals crystallize from a magma body; heavy minerals may sink to bottom or form along chamber sides.

Magmatic Deposits: Layered

Heavy minerals crystallize early and settle, concentrating at chamber bottom.

Magmatic Deposits: Disseminated

Metal evenly distributed in low concentrations throughout large masses of igneous rock. Examples: copper, nickel.

Magmatic Deposits: Pegmatites

Late-stage crystallization forms pegmatites; residual elements concentrated.

Hydrothermal Deposits

Minerals concentrated by hot fluids in fractures/pore spaces; groundwater heats near magma or deep circulation, dissolves minerals, then cools and precipitates them. Includes black smokers, vein deposits.

Placer Deposits

Heavy metals concentrated by flowing water; deposited where current velocity is low. Examples: gold, platinum, diamonds, magnetite.

Secondary Enrichment

Chemical weathering in warm, wet climates leaches soluble materials, leaving residues. Produces limonite, bauxite.

Bauxite

World’s primary aluminum source; forms in tropical climates via chemical weathering.

Residual Deposits

Formed by chemical weathering; soluble minerals leached, leaving insoluble residues.

Laterites

Leached soils mined for iron and sometimes nickel.

Banded Iron Formations

Contain more than 90% of world’s iron.

Evaporite Deposits

Minerals (gypsum, halite, anhydrite) deposited by evaporation/precipitation.

Metamorphic Deposits

Produced by contact metamorphism.

Skarns

Metal-rich deposits in carbonate rocks altered by contact metamorphism; ores of tungsten, zinc, iron.

Non-Metallic Mineral Deposits

Diamonds

Found in ultramafic igneous rocks called kimberlites; magma from asthenosphere (>150 km depth) rises quickly, carrying diamonds from lithospheric mantle to surface.