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sand and gravel or gravels containing gold, tin, diamonds, platinum, titanium, or coal. Hydraulic king utilizes a high-pressure stream of water that is directed against the mineral deposit (normal]) but not always a placer) undercutIing it, and causing its removal by the erosive actions of the water. Dredging performed from floating vessels, accomplishes the extraction of the minerals mechanically or hydraulically. Solution mining includes both horehole mining, such as the methods used to extract sodium chloride or sulfur, and leaching, either through drillholes or in heaps on the surface. Placer and solution mining are among the most economical of all mining methods but can only be applied to limited categories of mineral deposits.
1. Introduction
An open pit mine is an excavation or cut made at the surface of the ground for the purpose of extracting ore and which is open to the surface for the duration of the mine's life. To expose and mine the ore, it is generally necessary to excavate and relocate large quantities of waste rock. The main objective in any commercial mining operation is the exploitation of the mineral deposit at the lowest possible cost with a view of maximizing profits. The selection of physical design parameters and the scheduling of the ore and waste extraction program are complex engineering decisions of enormous economic significance. The planning of an open pit mine is, therefore, basically an exercise in economics, constrained by certain geologic and mining engineering aspects.
Several factors are significant indicators of economic and technological trends in surface mining. Among these are increasing production, a shift in emphasis from underground to surface mining, a decline in ore grade and quality of some crude materials, and, with few exceptions, an increase in productivity of labor. Increasing production is the result of a growing demand for more mineral commodities, induced by an increase in population and per capita consumption.
Paradoxically, productivity has increased even with declining grade and quality, which is indicative of the rapid technological improvement taking place in open pit mining techniques. This pattern of change has permitted production from many formerly uneconomic mineral resources occurring near the surface at a time when higher-grade ores are inadequate to meet increasing demand.
It is generally conceded that surface mining is more advantageous than underground mining in terms of recovery, grade control, economy, flexibility of operation, safety, and the working environment. There are, however, many deposits P19
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clarity are essential attributes of a good calculation book.
5. Maps and Sections
Formerly all mine maps were hand-drawn. Now, however, with the ever- increasing use of computer graphics, many maps are produced by plotters. Even so, there is continual need for updating maps manually.
Great care should always be taken in laying out the original grids to make sure that the horizontal and vertical lines are exactly perpendicular and that the lines are exactly spared. Only if this is correctly done can the subsequent work be plotted properly.
Each map should be numbered and the master tracing indexed and filed for easy reference and recovery. Storage should be in a fireproof vault. Very important maps should also be microfilmed and the films stored in a different location for greater security. Working copies are easily reproduced or copied as needed. surveying [ ss'veiiq] n. llieodolite [ 0ifodalait] n. plani meter [ plae'niraitd] n. contouring [ ksn'tugrig ] n. Vocabulary 测量 经纬仪 测面器，求积计 作等值线，作悝值线（法〉； 外型修整 测量鉴定人 方向的 不同种类的，多种多样的； 三角测量，分成三角形 三边测量（术） 导线测量 视距，视距仪器 空气的，空中的 照明；强度；彩灯，灯饰 十字准线，交叉丝?，瞄准器 周围的，包围着的 子午圈，子午线 垂直的；成直角的 纬度 surveyor [ &a'veia] n. directional [ di'rekjanal] adj. miscellaneous [ imisi'leinps] adj. Iriangiilation [ traijaerj^jii'leiJon] n. frilateration [ txaijl^to'reijon n. travelling [ .trsevasin」n. stadia [丨steidjd] n. aerial [ 'eari^l, adj. iilimiination [ ijjuimi'neij'an j n. crosshairs [ knjslicaz] n. meridianLma'ridian ] ri. peipendirular [ tp3：pQn'dikjulo] adj. latitude [ ?lastitjuid] n. ambient [ 'a^mbiant _ adj. P18
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elevations will be positive.
A level surface is considered to be a plane, and the meridians are considered to be parallel and
perpendicular to the lines of latitude. These simplifying assumptions are entirely satisfactory for
compact mining operations, but may not be adequate for distances exceeding several miles. In such cases，the principles of geodesy must be invoked. 3 underground traversing
The traverse is of paramount impottance in inderground surveying. Since mine
workings provide the only access to a given point, all lines must be carried through them. If these workings are narrow and tortuous, the traversing will be difficult and less accurate. However, modern mechanized mining commonly requires more space, making surveying operations easier. Even so, traversing is the only practical means of carrying line and grade to the headings.
Stations Underground traverse stations should bo located in the back or on the roof，behind the working faces wherever possible. This prevents their being disturbed or destroyed by current mining operations. The positions of these stations should be selected with care so as to afford convenience in setting up under them and good lines of sight in all directions.
Station identification Each station should be identified by a permanent marker. This can be of metal, usually brass or plastic. If of metal, the tag should not be in contact with the spad, particularly in wet or damp locations, as galvanic auction can cause accelerated corrosion that will destroy the station. A wide variety of tags in different sizes, shapes, and compositions is available. 4. Calculations
The mine surveyor should develop the habit of making all his calculations in a bound workbook, except for those that are required in loose-leaf form for convenient filing. As these books become filled, they should be indexed and filed for easy back reference.
If the work involves computer printouts or calculator tapes, it is wise to attach these in appropriate fashion. The goal is to facilitate the work, to be meticulously accurate, and to leave a record so complete that subsequent readers will have no difficulty in understanding what was done and in checking the work. Neatness and P6
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Area selection is also influenced by the commodity being sought，exploring for gold occurs in a different manner and within different rocks and areas to exploration for oil or natural gas or iron ore. Areas which are prospective for gold may not be prospective for other metals and commodities.
Area selection may also be influenced by previous finds, a practice affectionately named nearology, and may also be determined in part by financial and taxation incentives and tariff systems of individual nations. The role of infrastructure may also be crucial in area selection t because the ore must be brought to market and infrastructure costs may render isolated ore uneconomic.
The ultimate result of an area selection process is the pegging or notification of exploration licenses，known as tenements. (14) Target Generation
The target generation phase involves investigations of the geology via mapping, geophysics and conducting geochemical or intensive geophysical testing of the surface and subsurface geology. In some cases, for instance in areas covered by soil, alluvium and platform cover, drilling may be performed directly as a mechanism for generating targets,
(15) Geophysical Methods
Geophysical instruments play a large role in gathering geological data which is used in mineral exploration. Instruments are used in geophysical surveys to check for variations in gravity, magnetism electromagnetism (resistvity of rocks) and a number of different other variables in a certain area.The most effective and widespread method of gathering geophysical data is via flying airborne geophysics.
Airborne magnetometers are used to search for magnetic anomalies in the Earth's magnetic field. The anomalies are an indication of concentrations of magnetic minerals such as magnetite, pyrrhotite and ilmenite in the Earth's crust. It is often the case that such magnetic anomalies are caused by mineralization events and associated metals.
Ground-based geophysical prospecting in the target selection stage is more limited, due to the time and cost. The most widespread use of ground-based geophysics is electromagnetic geophysics which detects conductive minerals such as minerals within more resistive host rocks.
Ultraviolet lamps may cause certain minerals to fluoresce, and is a key tool in