Text 4. Sluice boxes for hydraulicking
It has already been stated that success of all hydraulic mining work will depend largely upon the proper construction of the sluice boxes, and their grade, and therefore it is of vital importance to see that the highest possible efficiency is obtained from the sluice system installed, which means that special attention should be paid to design. The main factors to be considered in the design and installation of sluice boxes for hydraulic mining, in their order of importance, may be enumerated as follows:
(a) Width. The width of sluice boxes for hydraulics depends on the average quantity of water available for treatment purposes, the size of the large gravel and boulders in the wash, as the naturally affects the duty of water, and the grade of the sluice line. It will readily be understood that if the sluice box is insufficient width the gravel capacity will be reduced, and, conversely, if the sluice box is too wide, the duty of water will be lessened. Assuming the duty of water to be such that 1 cubic foot of water per minute will treat 2 cubic yards of gravel per 24 hours, and that the grade of the sluice line is from 5 to 7 inches per box of 12 feet Nowman gives the figure shown in Table for calculating the widths of sluices. It is stated that these figures are based on actual practice on hydraulic mines in the USA and have proved to be sufficiently accurate for all practical purposes:
Quantity of Water available, cubic feet per minute |
Width of Sluice Box, in inches |
300-400 600 900 1500 2250-3000 4500 |
24 30 36 40 48 60 |
(b) Length. The length of a line of sluice boxes should be sufficient to ensure the disintegration of the gravel and the release of the mineral contents, and the general practice is to increase the length of the sluice line, so long as the recovery from the tail sluices pays for the cost of their installation and maintenance. If the line of sluice boxes can be rigged up at such a grade as to admit of one or more drops being provided in the line, then the length of the sluice line can be reduced, as a series of drops tends thoroughly to disintegrate the gravel - in other words, short sluice lines with drops are more efficient than long sluice lines without drops.
(c) Grade. The grade to be given to a sluice box depends on the character of the wash and on the general topography of the country; if the latter is such that an unlimited fall is available, then the character of the gravel will determine the grade. Where the water supply is adequate and the gravel is "free wash", a light grade would be suitable, whereas if the water supply is limited and the wash is heavy, a steep grade would be required. Generally speaking, a grade of from 5 to 7 inches per 12-foot box is adopted, although there have been cases where the grade has been as light as 3 inches and others where a grade of 9 inches per box has been found necessary.
Bottom and side boards for sluices vary from 1 1/2 to 2 inches in thickness and should be as free of knots as possible, tongue and groove joints between the bottom boards should be employed to make the box absolutely watertight. Posts and sills vary from 4 inches by 6 inches to 6 inches by 6 inches, and are placed from 3 to 4 feet apart.
Bedrock cuts. The bedrock cuts, which convey the excavated gravel from the working faces to sluices, should have a minimum grade of 4 to 5 %. If the necessary grade is lacking, booster giant may have to be utilized to speed up the movement to the sluice boxes, as has been described.
Sluice boxes for hydraulic elevators. The width of sluice boxes to be employed in conjunction with hydraulic elevators has already been given, and these should be adhered to аs closely as possible. The line of sluice boxes is usually short, as the gravel has already been thoroughly disintegrated during its passage up the upraise pipe of the elevator.
Bedrock ditches. The bedrock ditches or sluices, which feed the excavated material to the elevator sump or ground section, should have a grade of 8 to 15%, a 10 to 12% grade being common.
Tailings disposal. Tailings are transported to the dump by means of a tailings race or sluiceway, and as the rapid discharge of the tailings is necessary the grade of the race should be at least 4%. Where bedrock grade is lacking a tailings stacker may be employed; this may be described as an inclined sluice, up which the tailings are driven by means of giants and washed over the upper end of it and discharged on to the tailings pile. The disposal of tailings is a serious problem, as in most countries mines are restrained by law from polluting rivers and streams by the washing down of large quantities of material into them, and means have therefore to be devised of impounding the tailings, which in many places is both difficult and expensive.
In alluvial mining, tailings are usually held back by means of impounding dams, constructed as cheaply as possible of brushwood or log cribbing, and not made watertight, as the idea of the impounding dam is to hold back only the sand and silt, allowing the water to escape. The storage area behind the dam should be sufficiently large to produce a sheet of still water, where the sand and silt will have a chance of settling, and not going over with the escaping water.
Brushwood dams are constructed by depositing bundles of brushwood, tied together, in layers on the chosen site, and weighing them down with large boulders, the butt ends of the bundles facing downstream; a cheap and efficient impounding dam is this obtained.
Log cribbing dams, as their name implies, are constructed of timber cribs; in some cases the cribs are filled up with stones, boulders, and earth, so that the escaping water, instead of flowing out between the spaces of the cribbing, is forced to flow over the top of the dam, which thus acts as a spillway for its entire length. In both types of dams the sand and silt are held and allowed to settle whilst the water is permitted to escape.
COMPREHENSION CHECK
Exercise 23. Fill in the missing prepositions.
The success or non-success ... all hydraulic mining work will depend very greatly ... the proper construction … the sluice boxes, and their grade.
It is stated that these figures are based ... actual practice ... hydraulic mines ... the USA.
The author has found that a grade ... 5... 6 inches ... box … 12 feet ... the entire sluice line works equally as well when an average wash is being treated.
... alluvial mining, tailings are usually held back ... means … impounding dams.
... some cases the cribs are filled ... ... stones, boulders and earth, so that the escaping water, instead ... flowing ... ... the spaces ... the cribbing, is forced to flow ... the top ... dam, which thus acts as a spilling ... its entire length.
Exercise 24. Complete the sentences based on the information from the text.
The width of sluice boxes for hydraulics depends on … …
The length of a line of sluice boxes should be sufficient to ensure ...
The grade of a sluice box depends on ...
Bottom and side boards for sluices vary from ...
The bedrock ditches or sluices, which feed the excavated material to the elevate sump should have a grade of ...
In alluvial mining, tailings are usually held back by means of ... ...
Where bedrock grade is lacking a tailings stacker ...
SPEAKING
Exercise 25. Render in English
Успех гидродобычи значительно зависит от правильно установленных шлюзов.
Основными факторами, которые следует рассматривать при строительстве и установке шлюза, являются ширина, длина, наклон шлюза.
Доски для дна и боков шлюза могут быть толщиной от 1,2 до 2 дюймов и должны быть без сучков насколько это возможно.
Ширина шлюза зависит от среднего количества воды, нужной для промывки песка.
Наклон шлюза представляет большую важность и зависит от крупности песка.
Exercise 26. Discuss the questions with the partner.
What main factors should be considered in design and installation of sluice boxes?
What does the width of sluice boxes for hydraulic mining depend on?
What does the grade of a sluice box depend on?
What is the minimum grade of the bedrock cuts which convey the excavated gravel from the working faces to the sluice?
Where are tailings transported?
What material are log cribbing dams constructed of?
UNIT 8
UNDERGROUND MINING
PRE-READING
Exercise 1.
Gold is produced in many countries around the world. Do you know what it is produced for?
Do you agree that gold mining damages the environment?
Exercise 2. Match the words and their meanings:
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READING
Exercise 3. Read the text and learn more about the effects of gold mining .
Text 1. The Effects of Gold Mining
Mines around the world produce gold for jewelry, bullion and industrial use. Like all mines, gold mines disrupt the environment surrounding them. The processes used to extract gold from surrounding rocks also produces chemical and solid waste. The No Dirty Gold organization estimates that production of one gold ring leaves behind 20 tons of various types of waste.
Deforestation
Mining operations require the clearing of an area around the mine for extraction operations in addition to the space required for the mine itself. No Dirty Gold gives an example of one mine in Indonesia that is projected to clear 230 square km of forest over 30 years. The impacts are high because three quarters of operating mines and explorations for new mine sites are in areas that have a high conservation value, according to No Dirty Gold.
Water Contamination
Gold ore is removed from the earth and crushed. Then miners begin gold extraction processes. Substances are added to the ore that react with gold but not with surrounding rocks. A process called amalgamation uses mercury to draw out the gold. Mercury is mixed with the ore, and the gold forms an alloy, called an amalgam, with the mercury. This substance is collected. Then the mercury is removed from the amalgam. Heating can evaporate the mercury, or the amalgam can be dissolved in nitric acid to separate the mercury from the gold.
Another extraction process is the leach-heap method. Miners collect ore in piles and pour cyanide over these heaps. The cyanide filters through the ore, dissolving gold along the way. Charcoal absorbs the gold from the gold-cyanide solution, and the leftover cyanide flows into holding pools until the next leaching process.
The containment ponds and the pipes that contain mercury or cyanide can spill because of ruptures or overflow. The toxic materials enter surface and ground water, where they kill aquatic life and animals that drink the polluted water. They can enter tap water systems and poison people in surrounding areas.
The disruption of the landscape around a gold mine can cause toxic runoff indirectly. In some places, like the surroundings of the Zortman-Landusky mine in Montana, the rocks contain sulfides. Normally, these rocks are underground. After gold mining brings them to the surface, the sulfides react with rain to create acidic runoff.
Air Pollution
Gold is formed into bars as it is heated in a device called a smelter. This process releases toxic gases, like nitrous oxide and sulfur dioxide, into the air. These pollutants can harm people and animals living downwind of the smelter. They are also components in acid rain.
Solid Waste
Gold extraction leaves the surrounding rocks behind as waste. Heaps of crushed rocks surround the mine site. Toxic materials left over from extraction, like cyanide and mercury, taint the piles and make them hazardous sites. They can contaminate rain and contribute to toxic runoff problems. (http://www.ehow.com/list_7307546_effects-gold-mining.html)
COMPREHENSION CHECK
Exercise 4. Are the statements true or false? Correct the false statement using the facts from text1.
All mines disrupt the environment surrounding them.
The process of amalgamation uses copper to draw out the gold.
Charcoal is used to absorb gold from gold-cyanide solution.
Toxic materials can enter ground water because of ruptures or overflow.
VOCABULARY
miscellaneous - смешанный
drift mining- подземная разработка россыпей шурфами и штольнями
entry, - вход, доступ
hoisting - подъем
tram out - откатывать
branch pay streak - прожилок
raise - восстающая выработка
tin - бункер
tip - выгружать, опрокидывать
headroom - высота выработки
capping - покров, вскрыша
feed - подача, питание, приток
flush - струя, приток
hose - шланг
waste dump - отвал пустой породы
ridge - гребень, хребет, сводчатая кровля
hard - твердый
soft - мягкий
planking - обшивка досками
wear - износ
displacement - смещение
breaking - отбойка
mouth - устье, начало
subsidence - оседание, осадка
longwall mining - выемка длинным забоем
room and pillar mining - камерно-столбовой метод
blasting - взрывание
spiling - скрепление сваями
tunnel - туннель
bottom - дно
drift - штрек
Exercise 5. Find the meaning of the word combinations in the dictionary and try to remember them:
buried placer gravel; thickness; drainage; blasting; require; dump; bin; bedrock; incline; sink; install; waste dump; shaft; deep; expose; connect; soft; timber; frame timber; displacement; mouth; strip; preliminary work; driven; cause.
Exercise 6. Fill in the blanks with a preposition
Drift mining is the method employed ... working ... alluvial deposits ... underground methods.
Mining methods vary but consist ... a form ... longwall or room and pillar mining.
The blasted-down gravel is flushed ... a section ... the sluice leading … the V-shaped flume ... a 3-in. hose connection ... the pipe-line.
The tunnel is usually driven a little … one side … the main vertical shaft and a short cross-cut is made to connect the bottom ... the shaft ... the tunnel.
The shaft is then lined ... top ... bottom ... heavy planking placed inside ... the frame timbers.
READING
Exercise 7. Read the text below looking for the main ideas concerning methods of underground mining.