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1. Natural waters contain many dissolved substances that can act … solvents. 2. Thermal stress weathering results … expansion and contraction of rock. 3. It is caused … the approximately 10% expansion of ice. 4. Chemical and physical weathering often go hand … hand. 5. Physical weathering can occur due … temperature, pressure, frost. 6. Organisms and plants also take part … rock disintegration. 7. These intrusive rocks are exposed and the pressure … them is released. 8. It should not be confused … erosion, which involves the movement of rocks and minerals by agents. 9. Intrusive igneous rocks are formed deep … the Earth's surface. 10. Roots penetrate … fissures and develop the lateral pressure.

14. Fill in the articles if necessary:

1. Intrusive igneous rocks (e.g. granite) are formed deep beneath … Earth's surface. 2. Physical weathering can occur due to temperature, … pressure, frost. 3. The process of peeling off is also called … exfoliation. 4. Frost weathering is the collective name for … several processes where ice is present. 5. All rocks exposed on the surface are decomposed to … some degree. 6. It is caused by the approximately …10% expansion of ice. 7. Thus, … water causes complex and varied changes. 8. In general, chemical weathering is an acid attack on the rocks, in particular on … most abundant minerals. 9. … most commonly observed is the oxidation of Fe2+ (iron). 10. Natural waters contain … many dissolved substances that can act as solvents.

 

14. A three-minute talk. Discuss these questions with your group mates:

a) the difference between the two types of weathering;

B) oxidation of iron.

Complete a project: “The Earth’s Crust”.

 


SUPPLEMENTARY READING

Basic Aspects of Geology for Underground Mining

Importance of Geology

A thorough understanding of the geology of a mineral deposit is fundamental to its successful exploitation, and this is especially important for underground workings. Once a mining method is chosen, a major variance in the geology may make it difficult to change the approach to mining, compared to more flexible opencast work.

Let us review some of the important basic aspects of geology that may affect decisions about mining methods

The Earth's Crust

 

Tne earth's crust consists of a variety of rocks, formed under different circumstances, and with a wide variety of properties. Rocks usually consist of one or more minerals, ranging from single chemical elements to complex compounds. There are known to be more than 3,000 different minerals.

Of the 155 known elements, some of which do not occur naturally, oxygen is by far the most common, making up about 50% of the earth's crust by weight. Silicon forms about 25%, and the other common elements, such as aluminium, iron, calcium, sodium, potassium, magnesium and titanium, build up the total to 99% of the earth's crust.

Silicon, aluminium and oxygen occur in the commonest minerals such as. quartz, feldspar and mica, which form part of a large group known as silicates, being compounds of silicic acid and other elements. Amphiboles and pyroxenes contain aluminium, potassium and iron. Some of the Earth's commonest rocks, granite and gneiss, are composed of silicates.



Oxygen also occurs commonly in combination with metallic elements, which are often important sources for mining purposes. These compounds can form part of oxidic ores, such as the iron ores magnetite and hematite.

Sulphur also readily combines with metallic elements to form sulphide ores, including galena, sphalerite, molybdenite and arsenopyrite.

Other large mineral groups important in mining include: halogenides, such as fluorite and halite; carbonates, such as calcite, dolomite and malachite; sulphates, such as barite; tungstates, such as scheelite; and phosphates, such as apatite.

Rarely, some elements can occur naturally without combination. The important ones are the metals gold, silver and copper, plus carbon as diamonds and graphite.

 

Minerals

In some circumstances, the properties of individual minerals can be important to the means of mining, and will certainly be important for the means of extraction of the required materials to be exploited. More often, however, minerals will be mixed with others to form the various types of rocks, and the properties will be combined to form both homogenous and heterogeneous structures.

Feldspar accounts for almost 50% of the mineral composition of the Earth's crust. Next come the pyroxene and amphibole minerals, closely followed by quartz and mica. These min­erals all make up about 90% of the composition of the Earth's crust.

Minerals have a wide variety of properties that can be important in their usefulness to Man, to the best way to mine or tunnel through them, or both. Some of these important characteristics, which are also important for correct mineral identification in the field before chemical analysis, are hardness, density, colour, streak, lustre, fracture, cleavage and crystalline form. The particle size, and the extent to which the mineral is hydrated or otherwise mixed with water, can be very important to the behaviour of the rock structure when excavated.

Mineral hardness is commonly graded according to the Moh 10-point scale shown in the table below.

The density of light-coloured minerals is usually below 3.0. Exceptions are barite or heavy spar (barium sulphate - BaSO4 - density 4.5), scheelite (calcium tungstate -CaWO4 - density 6.0) and cerussite (lead carbonate - PbCO4 - density 6.5).

Dark coloured minerals with some iron and silicate have densities between 3.0 and 4.0. Metallic ore minerals have densities over 4.0. Gold has a very high density of 19.3. Minerals with tungsten, osmium and iridium are normally even denser.

Streak is the colour of the mineral powder produced when a mineral is scratched or rubbed against unglazed, white porcelain, and may be different from the colour of the mineral mass. Fracture is the surface characteristic produced by breaking of a piece of the mineral, but not following a crystallographically defined plane. Fracture is usually uneven in one direction or another.

Cleavage denotes the properties of a crystal whereby it allows itself to be split along flat surfaces parallel with certain formed, or otherwise crystallographically defined, surfaces. Both fracture and cleavage can be important to the structure of rocks containing substantial amounts of the minerals concerned

 


Date: 2015-12-24; view: 804


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