GEOLOGY FOR MINING ENGINEERS. Prof.Dr.Kadir DİRİK Lecture Notes 2014

Transcription

1 GEOLOGY FOR MINING ENGINEERS Prof.Dr.Kadir DİRİK Lecture Notes 2014

2 THE SCIENCE OF GEOLOGY GEOLOGY is the study of the Earth, including the materials that it is made of, the physical and chemical changes that occur on its surface and in its interior, and the history of the planet and its life forms. Most of the Earth is solid rock, surrounded by the hydrosphere, the biosphere, and the atmosphere. Prof.Dr.Kadir Dirik LectureNotes

3 Most of the Earth is composed of rocks. Rocks, in turn, are composed of minerals Prof.Dr.Kadir Dirik LectureNotes

4 Most of the Earth is solid rock, surrounded by the hydrosphere, the biosphere, and the atmosphere. Although more than 3500 different minerals exist, fewer than a dozen are common. We study the origins, properties, and compositions of both rocks and minerals. There are two processes acting on the earth namely internal and external processes INTERNAL PROCESSES Processes that originate deep in the Earth s interior are called internal processes. These are the driving forces that raise mountains, cause earthquakes, and produce volcanic eruptions. SURFACE PROCESSES Surface processes are all of those processes that sculpt the Earth s surface. Most surface processes are driven by water, although wind, ice, and gravity are also significant. The hydrosphere includes water in streams, wetlands, lakes, and oceans; in the atmosphere; and frozen in glaciers. It also includes ground water present in soil and rock to a depth of at least 2 kilometers. Prof.Dr.Kadir Dirik LectureNotes

5 THE ATMOSPHERE The atmosphere is a mixture of gases, mostly nitrogen and oxygen. It is held to the Earth by gravity and thins rapidly with altitude. Ninety nine percent is concentrated within 30 kilometers of the Earth s surface, but a few traces remain even 10,000 kilometers above the surface. THE BIOSPHERE The biosphere is the thin zone near the Earth s surface that is inhabited by life. It includes the uppermost solid Earth, the hydrosphere, and the lower parts of the atmosphere. Land plants grow on the Earth s surface, with roots penetrating at most a few meters into soil. Animals live on the surface, fly a kilometer or two above it, or burrow a few meters underground. Sea life also concentrates near the ocean surface, where sunlight is available. Some aquatic communities live on the deep sea floor, bacteria live in rock to depths of a few kilometers, and a few windblown microorganisms are found at heights of 10 kilometers or more. But even at these extremes, the biosphere is a very thin layer at the Earth s surface. Prof.Dr.Kadir Dirik LectureNotes

6 UNIFORMITARIANISM AND CATASTROPHISM James Hutton was a gentleman farmer who lived in Scotland in the late 1700s. Although trained as a physician, he never practiced medicine and, instead, turned to geology. Hutton observed that a certain type of rock, called sandstone, is composed of sand grains cemented together. He also noted that rocks slowly decompose into sand, and that streams carry sand into the lowlands. He inferred that sandstone is composed of sand grains that originated by the erosion of ancient cliffs and mountains. Hutton tried to deduce how much time was required to form a thick bed of sandstone. He studied sand grains slowly breaking away from rock outcrops. He watched sand bouncing down streambeds. Finally he traveled to beaches and river deltas where sand was accumulating. Hutton concluded that the sequence of steps that he had observed must take a long time. He wrote that on us who saw these phenomena for the first time, the impression will not easily be forgotten.... We felt ourselves necessarily carried back to the time... when the sandstone before us was only beginning to be deposited, in the shape of sand and mud, from the waters of an ancient ocean.... The mind seemed to grow giddy by looking so far into the abyss of time. Prof.Dr.Kadir Dirik LectureNotes

7 Hutton s conclusions led him to formulate a principle now known as uniformitarianism. The principle states that geologic change occurs over long periods of time, by a sequence of almost imperceptible events. Hutton surmised that geologic processes operating today also operated in the past. Thus, scientists can explain events that occurred in the past by observing changes occurring today. Sometimes this idea is summarized in the statement The present is the key to the past. Prof.Dr.Kadir Dirik LectureNotes

8 William Whewell, another early geologist, agreed that the Earth is very old, but he argued that geologic change was sometimes rapid. He wrote that the geologic past may have consisted of epochs of paroxysmal and catastrophic action, interposed between periods of comparative tranquility. Whewell was unable to give examples of such catastrophes. He argued that they happen so infrequently that none had occurred within human history. Today, we know that both Hutton s uniformitarianism and Whewell s catastrophism are correct. Thus, over the great expanses of geologic time, slow, uniform processes are significant, but improbable, catastrophic events radically modify the path of slow change. Gradual Change in Earth History Within the past few decades, geologists have learned that continents creep across the Earth s surface at a rate of a few centimeters every year. Catastrophic Change in Earth History Chances are small that the river flowing through your city will flood this spring, but if you lived to be 100 years old, you would probably see a catastrophic flood. When we study the 4.6 billion years of Earth history, they find abundant evidence of catastrophic events that are highly improbable in a human lifetime or even in human history. For example, giant meteorites have smashed into our planet, vaporizing enormous volumes of rock and spreading dense dust clouds over the sky. Similarly, huge volcanic eruptions have changed conditions for life across the globe. Geologists have suggested that these catastrophic events have driven millions of species into extinction. Prof.Dr.Kadir Dirik LectureNotes

9 Prof.Dr.Kadir Dirik LectureNotes

10 THE GEOLOGIC TIME SCALE Geologists have divided Earth history into units displayed in the geologic time scale. The units are called eons, eras, periods, and epochs and are identified primarily by the types of life that existed at the various times. Prof.Dr.Kadir Dirik LectureNotes

11 The Origin of the Solar System and the Differentiation of the Early Earth The currently accepted theory for the origin of our solar system involves: (a) a huge nebula condensing under its own gravitational attraction, then (b) contracting, rotating, and (c) flattening into a disk, with the Sun forming in the center and eddies gathering up material to form planets. As the sun contracted and began to visibly shine, (d) intense solar radiation blew away unaccreted gas and dust until finally, (e) the Sun began burning hydrogen and the planets completed their formation. Prof.Dr.Kadir Dirik LectureNotes

12 Heat from the Sun boiled most of the hydrogen, helium, and other light elements away from the inner Solar System. As a result, the four planets closest to the Sun Mercury, Venus, Earth, and Mars are now mainly rocky with metallic centers. These four are called the terrestrial planets because they are Earthlike. In contrast, the four outer planets Jupiter, Saturn, Uranus, and Neptune are called the Jovian planets and are composed primarily of liquids and gases with small rocky and metallic cores. (a) Mercury is a small planet close to the Sun. Consequently, most of the lighter elements have long since been boiled off into space, and today the surface is solid and rocky. (b) Prof.Dr.Kadir Dirik of Lecture Notes Jupiter, on the other hand, is composed mainly gases and liquids, with a small solid core.

13 (a) The early Earth was probably of uniform Composition and density throughout, (b) Heating of the early Earth reached the melting point of iron and nickel, which, being denser than silicate minerals, settled to the Earh s center. At the same time, the lighter silicates flowed upward to form the mantle and the crust. (c) In this way, a differentiated Earth formed, consisting of a dense iron nickel core, an iron rich silicate mantle, and a silicate crust with continents and ocean basin Prof.Dr.Kadir Dirik LectureNotes

14 A schematic view of the interior of the Earth Jumps in density between Earth s major layers caused by changes in their chemical composition Prof.Dr.Kadir Dirik LectureNotes

15 Continents float high because they are made of rocks with lower densities than rocks of the mantle or oceanic crust Prof.Dr.Kadir Dirik LectureNotes

16 Prof.Dr.Kadir Dirik LectureNotes

17 Axial ridge Givergent boundary Transform Subduction zone Convergent boundary Extensional zone in the continents Uncertain plate boundary Prof.Dr.Kadir Dirik LectureNotes

18 Convection carries heat upward by the motion of matter Continental lithosphere Trench Mid oceanic ridge Ocean Subduction Oceanic lithosphere Prof.Dr.Kadir Dirik Lecture Notes (Monroe&Wicander, 2005) 18

19 Mid oceanic ridge Transform plate boundary Divergent plate boundary Continental Continental convergent plate boundary Continental Oceanic convergent plate boundary Trench Divergent plate boundary Oceanic Oceanic convergent plate boundary Upwelling Asthenosphere Lithosphere Upwelling (Monroe&Wicander, 2005) An idealized cross section illustrating the relationship between lithosphere and underlying asthenosphere and the three principal types of boundaries convergent (yaklaşan), divergent (uzaklaşan) and transform (transform). Prof.Dr.Kadir Dirik Lecture Notes 19

20 Prof.Dr.Kadir Dirik Lecture Notes

21 Prof.Dr.Kadir Dirik Lecture Notes

22 Prof.Dr.Kadir Dirik Lecture Notes

23 Prof.Dr.Kadir Dirik Lecture Notes

24 A schematic view of the interior of the Earth Jumps in density between Earth s major layers caused by changes in their chemical composition Prof.Dr.Kadir Dirik LectureNotes

25 Most of the Earth is composed of rocks. Rocks, in turn, are composed of minerals Prof.Dr.Kadir Dirik LectureNotes

26 MİNERALS AND ROCKS Minerals are the building blocks of rocks. A few rocks, such as limestone, contain only a single mineral (calcite). Other rocks, such as granite, are made of several different minerals. Mineral is defined as a naturally occuring, solid crystalline substance, generally inorganic with a specific chemical composition. Minerals are homogenous; they cannot be divided mechanically into smaller components. Prof.Dr.Kadir Dirik Lecture Notes

27 Matter and its Composition Anything that has mass and occupies space is matter. The atmosphere, water, plants and animals, and minerals and rocks are all composed of matter. Matter occurs in one of three states or phase all of which are important in geology: solids, liquids and gases. In this course we are concerned chiefly with solids, because all minerals are solids. Elements and Atoms All matter is made up of chemical elements, each of which composed of incredibly small particles called atoms. Atoms are the smallest units of matter that retain the characteristics of an element. The Structure of Atoms At the center of every atom is a dense nucleus containing two particles: protons and neutrons. A proton has a positive electric charge of +1. A neutron is electrically neutral that is, uncharged. Atoms of the same chemical element may have Different number of neutrons but the number of Protons are same. These atoms are named as isotopes. Prof.Dr.Kadir Dirik Lecture Notes

28 Electron structure of the carbon atom (carbon 12). The electrons, each whith a charge of 1, are represented as a negatively charged cloud surrounding the nucleus, which contains six protons, each with a charge of +1, and six neutrons, each with zero charge. The size of the nucleus is greatly exaggerated Prof.Dr.Kadir Dirik Lecture Notes

29 Schematic representation of the isotopes of carbon. Carbon has atomic number (number of protons) of 6 and atomic mass number (sum of the proton and neutron)of 12,13 or 14 depending on the number of neutrons (n) in its nucleus Chemical Reactions The structure of an atom determines its chemical reactions with other atoms. Chemical reactions are interactions of the atoms of two or more chemical elements in certain fixed proportions that produce chemical compounds. For example two H atoms combine one O atom forming new chemical compound, water H 2 O. The properties of of a chemical compound may be entirely different from those of constituent elements. Na sodium (metal) combines with Cl chlorine (a noxious gas) forming Sodium chlorid (NaCl), known as table salt. Prof.Dr.Kadir Dirik Lecture Notes

30 CHEMICAL BOUNDS Chemical compounds, such as minerals, are formed either by electron sharing between the reacting atoms (covalent bond) or by electron transfer between the reacting atoms (ionic bond). Atoms of metallic elements, which have strong tendencies to lose electrons, pack together as cations and the freely mobile electrons are shared and dispersed among ions. This free electron sharing result in metallic bounding. covalent bond Prof.Dr.Kadir Dirik Lecture Notes

31 Some atoms transfer electrons, forming ionic bonds. Prof.Dr.Kadir Dirik Lecture Notes

32 Carbon forms two polymorphs, graphite and diamond, that are alternative structure of a single chemical compound Prof.Dr.Kadir Dirik Lecture Notes

33 Physical Properties of Minerals Hardness, cleavage, fracture, luster, color, streak, density, crystal habit are most important physical characteristics of minerals. Hardness is a mineral s resistance to abrasion and is controlled mostly by internal structure. For example graphite (1 2) and diamond (10). Prof.Dr.Kadir Dirik Lecture Notes

34 Cleavage is a smooth plane or planes of weakness determined by the strength of bonds within a mineral structure along which it tends to split or break. Fracture is a mineral breakage along irregular surfaces. Any mineral can be fractured if enough force is applied, but fracture surfaces are commonly uneven or conchoidal (curved) rather than smooth. Cleavage of mica. The diagram shows the cleavage planes in the mineral structure, oriented perpendicular to the plane of the page. The photograph shows thin sheets seperating along the cleavage planes. Prof.Dr.Kadir Dirik Lecture Notes

35 Cleavage in one direction Cleavage in three directions, not at right angles Cleavage in two directions at right angles Cleavage in four directions Cleavage in three directions at right angles Cleavage in six directions Several types of mineral cleavage Prof.Dr.Kadir Dirik Lecture Notes

36 Luster is the quality and intensity of light reflected from surface of mineral. Two common types: metallic and nonmetallic. Types of nometallic luster are: glassy or Vitrous (quartz), dull or earthy, waxy, greasy, and brilliant (diamond) Prof.Dr.Kadir Dirik Lecture Notes

37 Streak refers to the color of the fine deposit of mineral dust left on an abrasive surface, such as a tile of un glazed porcelain, when a mineral is scraped across it. Hematite may be black, red or brown, but it always leave a reddish brown streak when strached along a ceramic plate. Mineral s crystal habit is the shape in which its individual crystals of aggregates of crystal grow. Prof.Dr.Kadir Dirik Lecture Notes

38 Important physical property of calcite: it will react vigrously with the dilute hydrochloric acid and release carbondioxide which causes the acid to bubble or effervesce Prof.Dr.Kadir Dirik Lecture Notes

39 Some Chemical Classes of Minerals Prof.Dr.Kadir Dirik Lecture Notes