Fig. 30. Method of working with ample water supply and steep valley

The long tom is set up alongside the paddock, where the gravel is to be excavated, and a few yards upstream from the long tom a small dam is constructed to hold up the available water; a launder is then fixed in the dam for supplying water to the head of the long tom, as and when required. A few yards below the long tom, another small dam is constructed to bank up the water discharged from the long tom. Gravel is loaded into the tom, by shovel, water is allowed to enter until the gravel is thoroughly washed when the water supply is stopped, and a new charge of gravel thrown in, and the procedure repeated until the water in the dam is finished, when this occurs the water collected by the dam below the long tom is run back into the upper dam, by means of a launder, and sluicing continued.

Fig. 31. Method of working small deposit by long tom

Fig. 32. Method of working small deposit by long tom when water is a scarce

When water is very scarce, the following method may be used, employing a long tom, for the treatment of gravel. The water that is available is dipped up by pans or buckets, and emptied into the long tom for washing the gravel; to commence with, this water when discharged from the tom is bald up by means of a small embankment of earth, but as the tailings bank up they gradually force the water back into the excavated cut, into which the overburden from the next cut or paddock has been thrown. As gravel from paddock 1 is excavated, so the overburden from paddock 2 is thrown into it, and the long tom moved backwards, in the direction of the arrow; as the tailings again bank up in this new position, so the water is forced forward into paddock 1 where it is dipped up and used for wash water. This procedure is repeated until the area is worked out.

COMPREHENSION CHECK

Exercise 16. Complete the sentences using the information from the text.

1. Excavation … gravel is usually done … a series … trenches or paddocks.

2. The overburden excavated is thrown … … the finished cuts.

3. The gravel is loaded directly … shovel … the iron or wooden launders.

4. The water that is available is dipped … … pans or buckets, and emptied … the long tom for washing the gravel.

Exercise 17. Look through the text and find the words below. Use five of them to make sentences.

канава; долина; желоб; траншея; выгон; промывать песок; погрузка; глубина; узкий; крутой; промышленный участок; избегать (делать что то); количество воды; воды реки; разрушать; строить; требовать; повторять.

SPEAKING

Exercise 18. Render in English

1. Количество воды для промывки зависит от свойств песка.

2. Если количество воды, требуемое для промывки песка, недостаточно, то необходимо построить ряд небольших запруд для накопления достаточного количества воды для промывки на шлюзах.

3. Песок загружают в перемычку лопатой и подают воду до тех пор, пока песок не будет тщательно промыт, затем поступление воды прекращается, поступает новая порция песка и процесс повторяется.

4. Если россыпное месторождение находится у истока реки, где нет достаточного количества воды для промывки на шлюзах, то в таком случае для промывки песка используют длинную перемычку, которую строят рядом с выгоном, где будет происходить экскавация песка.

Exercise 19. Answer the questions.

1. How is gravel excavation performed?

2. How are sluice boxes placed in the case when the river valleys are narrow and have steep sides?

3. What is built across the valley when the quantity of water for washing is Inadequate?

4. In what case is a long torn employed for treating the gravel?

5. Where is the long torn set up?

6. What method for the treating of gravel may be employed when water is very scarce?

UNIT 6

ALLUVIAL DEPOSITS

PRE-READING

Exercise 1.

1. Gold plays an important part in modern life? Can you prove it?

2. What are the hazards of gold mining?

Exercise 2. Match the words and their synonyms:

remove pollution affect poisons unsuitable

improper influence extract toxic contamination

READING

Exercise 3. Read the text and learn about the problems for the environment

Text 1. Hazards of Gold Mining

Gold has become an essential part of our life. We use it in jewelry, medicine and electronics, but the mining of it causes a lot of problems for the environment. The production of one gold ring leaves behind 20 tons of waste, and the mining process and waste pose significant hazards for our air, water, soil and forests.

There are many hazards in gold mining, and a lot of them are fatal.

Once gold is mined, it is converted into bars in a device called a smelter. The smelter heats the ore to a temperature at which the metal melts, and these smelters release huge amounts of lead, as well as nitrogen oxide and sulfur dioxide, which are returned to the earth in the form of acid rain. Another problem results from driving to and from the mine site. All of this driving generates large amounts of dust, which adds pollution to the air.

After ore is gathered from mines, it has to be extracted. This can be done in a variety of ways, but a common technique is leaching. This is a inexpensive method of removing the ore from the waste. To do this, workers pile up low-grade gold ore into an outdoor heap and then put a cyanide solution on it. The cyanide dissolves the gold, which then runs down a slope into reservoirs before it is collected. The problem with this is that these materials can then make their way into water supplies like lakes, rivers and streams. When this happens, aquatic life and animals are affected, and so are humans as the poisons enter the tap water systems.

Mining requires the clearing of large areas of land around the mining site. This is especially the case when using open-pit mining techniques, as roads need to be constructed to open remote areas and forests to the miners. An example of this can be seen in Indonesia, where the No Dirty Gold campaign projects that 230 square kilometers will be cleared in 30 years.

When gold is mined, large amounts of land are upturned, and after the gold is extracted, a lot of waste is left behind. Piles of waste are created, which can cause heavy metals and other poisons to soak into the soil, poisoning animals and creating high levels of toxins in plants. Animals that eat the plants can then become diseased, and plant life can be completely destroyed as heavy metals and toxins can remain in soil for decades, making the area unsuitable for human living. (http://www.ehow.com/info_8075896_hazards-gold-mining.html)

COMPREHENSION CHECK

Exercise 4. Are the statements true or false? Correct the false statement using the facts from text1.

1. A smelter is a device which heats the ore and melts the metal.

2. The method of removing the ore from the waste is very expensive.

3. Mining requires small areas of land around the mining site.

4. Heavy metals and toxins can remain in soil for years.

VOCABULARY

swamp (marsh) – болото

reed – камыш, тростник

river terrace – насыпь реки

disintegrate – разрушать

dumping ground – участок для отвала

pick – работать киркой

loose – взрыхлять

recede – спадать (о паводке)

hoe – мотыга, кирка

cave – обрушать

sluice race – путь, желоб

tail race – желоб

drop – падение, спад

huahing – размыв выхода жилы водой

booming – стрела, вылет

release – освобождать, выпускать

tracing – прослеживание

Exercise 5. Find the meaning of the word combinations in the dictionary and try to remember them:

drain; flume; setting; discharge; tailings; paddocks; trestle; rig up; fork; tailings launder; sluice; sluicing; sluice race; tail race; loose; dumping; ground; cave; treatment plant; shallow; cheap; repeat; flow; wash; sluice box; permit; yardage; avoid; grade.

READING

Exercise 7. Read the text below looking for the main ideas concerning methods of working alluvial deposits.