Geology
From IntFX
A mineral is a natural, homogeneous material which is expressible by a chemical formula (e.g. Calcite CaCO3). An ore mineral is one with valuable constituents.
A rock is an aggregate of minerals. The three major classes of rocks are Igneous rocks, Sedimentary rocks and Metamorphic rocks.
Igneous rocks are those that have solidified from molten rock known as magma, which is a complex silicate. Magma from a volcano is called lava. Igneous rocks are usually in areas where there is tectonic activity. Granite and basalt are commonly found examples.
Sedimentary rocks are formed from the breakdown of pre-existing rocks and can be deposited on both land and water. Alternately they can form via accumulation of organic matter (e.g. oil shale and coal seams) or from chemical precipitation (e.g. dolomites and cherts). Sedimentary rocks are found usually in huge basins.
Metamorphic rocks result from modification of pre-existing Igneous rocks or Sedimentary rocks under physical processes (e.g. temperature, pressure, water action). Examples of such include Marble, gneiss and slate.
They usually occur in layers known as beds or strata.
The formation of mineral deposits depending on three important factors:
- There must be a source of metals,
- A means of transporting them,
- Finally suitable sites and conditions for deposition and concentration.
Primary deposits are those which relate to the chemistry of the rocks:
- Primary segregations
- Hydrothermal deposits
- Sedimentary exhalative deposits
- Contact metamorphic deposits
- Sedimentary deposits
Secondary deposits relate to processes in the surface environment:
- Alluvial deposits
- Residual deposits
- Gossans and Secondary enrichment
The Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (the JORC Code) outlines the minimum standards by which public companies must comply in their public reporting.
