Definitions and Basic Geology Flashcards
Chemical Elements
Chemical elements are a pure substance consisting of one type of atom. They are the building blocks of matter.
Compounds
Elements combine to form compounds. A compound contains at least two different elements.
Molecule
A molecule is formed when two or more atoms join together chemically. Compounds form when two or more different atoms join together. All compounds are molecules but not all molecules are compounds. Molecular hydrogen (H2), molecular oxygen (O2) and molecular nitrogen (N2) are not compounds because each is composed of a single element. Water (H2O), carbon dioxide (CO2) and methane (CH4) are compounds because each is made from more than one element.
Mineral
A mineral is a solid, naturally-occurring, inorganic compound having a definite chemical composition that may vary within limits.
Hematite (Fe2O3) is an oxide commonly called rust.
Pyrite (FeS2) is an iron sulfide. If pyrite such as that shown on the left of Figure 2 (below) is exposed to air and water it begins to look like gold, shown on the right of Figure 2. Hence pyrite is also called “fool’s gold.” However, the cubic crystals give it away.
Chalcopyrite (CuFeS2) is a common copper sulfide.
Galena (PbS) is lead sulfide. A sample is shown in Figure 3 (below).
Rock vs. Soil
A rock is a solid assemblage of minerals. A soil is also an assemblage of minerals but it is not solid. Soils are produced by weathering of rock.
Ore Deposit
An ore deposit is a solid, naturally occurring, mineral concentration usable as mined or from which one or more valuable constituents may be economically recovered.
The implications are that current technology and economic conditions make economic recovery possible. However, time is an important consideration. It can take some time for technology to develop into a practical form. Also it is long term economic conditions that govern whether a mine goes into operation and stays in operation. Short term economic disruptions, such as the crisis in 2008, do not have much effect on mining operations.
This is not a legal definition of ore. The legal definition of ore involves the issue of having the technical and legal ability to extract something of value from it.
Base Metal
A base metal is a metal basic to industry and society such as iron, copper, lead, zinc, and aluminum.
Precious Metal
A precious metal is a rare, naturally occurring metallic element of high economic value such as gold and silver and the platinum group metals.
Ore Grade
Ore grade is the concentration of economic mineral or metal in an ore deposit.
The fundamental unit used in defining grade
tonnage:
There is the US ton (~2,000 lb) and the metric tonne (1000 kg or ~2,200 lb).
1 tonne = 1.1 ton
The grade of a base metal deposit is expressed as?
a mass percentage.
For example: copper grade at Highland Valley mine, BC ~0.43%
- 0043 × 1000 kg = 4.3 kg/tonne (4.3 kg ~ 9.5 lb)
- 0043 × 2000 lb = 8.6 lb/ton
The grade of a precious metal deposit is expressed as?
The grade of a precious metal deposit is expressed in grams/tonne or oz/ton. Note that the ounces are troy ounces where 1 troy ounce = 1.097 oz = 31.1 grams
For example: gold grade at Eskay Creek mine, BC ~0.96 oz/ton
This is very rich ore—more typical is 0.2 oz/ton or less (6.84 grams/tonne)
Since there are 1000 kg in a tonne and 1000 grams in a kilogram, there are 1 million grams in a tonne. If gold grade is given in g/t, then it is in parts per million, e.g. 6 g/t is 6 ppm.
To convert a weight percentage to ppm, multiply the percentage by 10 000. Thus 0.4% is 0.004 × 1 000 000 gm = 4000 gm in 1 million grams, i.e. 4000 ppm or 0.4 × 10 000.
For diamonds, 1 carat = 0.2 g so that 4 cpt = 4 × 0.2 = 0.8 g/t or 0.8 ppm.
Troy ounces
The origin of the word troy comes from the city of Troyes in France, an important trading city in the Middle Ages. A troy ounce is about 10% larger than the avoirdupois ounce sometimes used to measure the weight of things like the weight of the human body or food items. If you consider your body precious and measure its weight in troy ounces, you can fool yourself into thinking that dieting is unnecessary.
How big is one tonne of rock?
One cubic meter of solid rock weighs between 2.5 and 3 tonnes. This is the density of rock. Assume the density is 2.6 tonnes per cubic meter or 2.6 t/m3. Invert this to get 1/2.6 = 0.385 m3/t. This means that one tonne of rock occupies a volume of 0.385 cubic meters. This volume could be any shape. If it’s a cube, then one side of the cube is 0.3851/3 = 0.73 m or 73 centimeters. Such a cube is shown at right.
If the volume is a sphere, then because the volume of a sphere of radius r is given by 4πr3/3, we can compute the radius of the sphere as (3×0.385/4π)1/3 = 0.45 m or 45 centimeters. Its diameter is 90 centimeters. Such a sphere is shown in Figure 5 (left).
When you can, extend a measuring tape to these dimensions to get an idea of how big these volumes are.
The Structure of the Earth
The Earth is composed of three concentric shells. The crust is the outer shell, 30–50 km thick under the continents, 5–10 km under the oceans. It is underlain by the mantle which extends from the crust to the interface between the mantle and the Earth’s core at a depth of 2900 km. The Earth’s core, which has a radius of about 3400 km, consists of an outer liquid core and an inner solid core. The radius of the Earth is about 6371 km (see Figure 6, right).
