Water Required

The water required for sluicing varies greatly according to the characteristics of the gravel to be treated, and the nature of the mineral to be recovered, and no calculation can be made, as sufficient data is not available to enable any particular formula to be used. For such flow of water, all the gravel is carried over the riffles.

Peele gives the following data on the moving power of water in streams, where there are no riffles:

0,25 feet per sec - begins to wear away fine clay;

0,50 feet per sec - just lifts fine sand;

0,66 feet per sec - carries fine sand;

1,00 feet per sec - moves fine gravel;

2,00 feet per sec - moves pebbles of 1-inch diameter;

3,00 feet per sec - moves pebbles of egg size;

5,33 feet per sec - moves stones; 3- to 4-inch diameter;

6,66 feet per sec - moves stones, 6-to 8-inch diameter;

10,00 feet per sec - moves stones 12 to 18-inch diameter.

The duty of water also varies greatly according to conditions. It varies from 2.37 yard cubic yard to 7 cubic yard per hour per cubic foot of water per second, whereas Longridge states that, in New Zealand, the average duty of water is 7,2 cubic yard per hour per cubic foot of water per second. No hard and fast rules can be given, as a stiff clayey gravel reduces the duty of water, while with a free wash gravel, the duty of water may be considerably increased.

Length of Sluices

The length of a sluice line depends entirely on condition, in general extra boxes should be added as long as gold is going over in the tailings discharge; however, this is limited by the gold lost and installation of extra boxes required.

Starting Sluices

New sluices are usually run for a couple of days with a very small head of water, so as to stop any cracks and leaks that may exist in the boxes; light gravel is then run through, until the riffles are well packed, after which sluicing proper may commence.

Clean Up

The flow of water is first discontinued, on­ly such water being allowed to flow down the boxes as is necessary for the clean up; false bottoms, screens, or gratings etc., are removed and washed carefully, and then, starting at the head of the sluice box, the first three or four sets of riffles are removed, and the heavy concentrates collected behind them are washed down the box, until they are held up by the next set of riffles; here the heavy concentrates are scooped up into pans or buckets, after which the next three or four sets of riffles are removed and the procedure repeated, till the whole length of sluice has been cleaned up. At the finish it is good practice to scrub the sides and bottom of the box thoroughly with a stiff wire brush, to ensure a complete clean up of the concentrates being made. The concentrates so collected in the clean up are then washed and panned for the recovery of the mineral contents.

Tailings

Sluice boxes should not be moved and rigged up frequently, as this results in a loss of both time and production; they should be worked until the lead from the working face becomes excessive or until the pilling up of tailings necessitates a new set-up; to avoid frequent moves sluice boxes should be kept at a certain height above the alluvial flat being worked, but where this Is not possible or where the thickness of gravel is great and the river flat wide, the tailings collecting at the discharge end of the boxes may mount up to such an extent as seriously to Interfere with and obstruct operations. In this case it may be possible to discharge the tailings farther away from the sluices by means of tailings launders and turn-off, as shown in fig. 25. These are placed in position below the tailings discharge end of the line of sluice boxes.

Fig. 25. Turn-offs for disposal of tailings

In many countries the fouling of rivers and streams, by the washing down of large quantities of tailings, is strictly prohibited by law, and therefore, to overcome this difficulty, it may be necessary to dam back or impound the tailings produced by sluicing operations. For this purpose a brushwood or log cribbing dam is sufficient, built as cheaply as possible and not made watertight, as the whole idea of the dam is to hold up the sand and sit, causing it to settle, and to permit the water to escape. Farther details of impounding dams will be given in the next chapter (fig. 26, 27).

Fig. 26. Sluicing equipment for catching fine gold. Uganda

Fig. 27. Details or sluicing equipment used in Congo

(http://www.hecklerfabrication.com/files/sluice-build-partIII-2.pdf)

COMPREHENSION CHECK

Exercise 8. Complete the sentences using the information from text 2:

1. Alluvial mining consists of ...

2. Sluice boxes are made ...

3. Timber sluices have ...

4. The grade of a sluice box is usually expressed in …

5. The water required for sluices varies ...

Exercise 9. Find the English equivalents of the words and word combinations in the text:

промыв наносов; разгружать; осаждение; проволочная щетка; оборудовать; осушать; дренаж; загрязнение; желоб; получать; запрещать законом; плотина; отходы; хвосты; шлюзы; лоток.

LANGUAGE REVIEW

Exercise 10. Complete the sentences with correct prepositions:

1. You must report __about__ the progress __to __ the manager every month.

2. Ore mining procedures depend _____ the specific operations.

3. Surface mining occurs _____ an open pit.

4. High temperature and high pressure thrust liquid gold up _____Earth's crust.

5. As the industrial population of the world has grown the demand _____ gold has steadily increased.

Exercise 11. Read the economic profile of a country. In most of the lines 1-11 there is one extra word, some lines are correct. Tick (√) if the line is correct or write an extra word in the space:

The country has become a completely modern market economy. It is characterized by high-tech agriculture, the up-to-date industry, and an extensive government welfare measures. Other features include good living and standards, as well as dependence on foreign trade. It exports energy, gas and timber. The government has so reduced high unemployment rate and maintained low inflation and stable currency. It has also raised environmental with taxes. In order to deal with long-term demographic changes which could reduce the labor force, the government it has introduced a number of labor market reforms.

___√___ ___the__ ________ ________ ________ ________ ________ ________ ________ 10) ________ 11) ________

SPEAKING

Exercise 12. Render in English

1. Разработка россыпных месторождений состоит из следующих этапов: очистка участка от кустарника, леса; уборка торфов и экскавация песков; транспортировка песков на обогатительную фабрику; промывка песков на обогатительной фабрике; извлечение металла.

2. Для разработки неглубоких россыпных месторождений, промывка наносов на шлюзах является самым простым и дешевым методом.

3. Шлюзы могут устанавливаться прямо на поверхности земли или быть подняты на опорах.

4. Деревянные шлюзы служат недолго, но они дешевы.

5. Наклон шлюза зависит от количества имеющейся в наличии воды для промывки, а также от песка, который обрабатывается.

6. Во многих странах загрязнение рек и проточных вод от промывки большого количества хвостов строго запрещено законом.

7. Не всегда возможно разрабатывать наносы русла реки и другие месторождения этого класса гидравлическим способом, в таких случаях следует применять обычную промывку на шлюзах.

8. Метод промывки наносов на шлюзах состоит из проходки неглубокой траншеи по одну сторону разрабатываемого месторождения, в которую направляется поток воды до тех пор, пока траншея не углубится до плотика и полученный таким образом песок не вымоется потоком воды в шлюзы для промывки.

Exercise 13. Answer the questions to the text, discuss them with the partner.

1. Is sluicing the simplest and cheapest method used in alluvial mining?

2. What can you say about the size of a sluice box?

3. What material are sluice boxes made of?

4. What can you say about the grade of a sluice box?

5. How is the grade of a sluice box usually expressed?

6. What data on the moving power of water do you know?

7. Where may it be possible to discharge the tailings?

8. Is the fouling of rivers and streams in many countries strictly prohibited by law?

VOCABULARY

gravel– песок

trenche – траншея

paddocks – выгон, околоствольная площадка

valley – долина

pan – лоток

wheel barrow – тележка

yardage – длина в ярдах

treat – промывать (песок)

edge – край

cut – канава

wash down – промывать

payable ground – промышленный участок

silt – ил, тина

bank up – окружать валом, делать насыпь

dip up – падать, залегать вниз

steep – крутой

river head – исток реки

dam – загрузка, перемычка

employ – применять, использовать

Exercise 14. Find the meaning of the word combinations and make up sentences with five of them:

trenches, paddocks, right angles, payable, narrow, avoid, can be treated, loading, rig up, overburden, impounding, wooden launders, supply of water, available, washing purposes, quantity, large scale, repeat, bank up.

READING

Exercise 15. Read the text below looking for the main ideas concerning excavation of gravel