Text 2. Miscellaneous methods of mining

Drift mining. This is a method employed for working alluvial deposits by underground methods, and is generally confined to the exploitation of high-grade buried placer gravels of moderate thickness. The mode of entry is the same as for other underground workings, but it should always be a matter of consideration so to choose the method of opening that drainage and hoisting will be reduced to a minimum or altogether eliminated.

Mining methods consist of a form of longwall or room and pillar mining, the ground being broken by picks, although in some cases blasting is required, transport of ground being by barrow or truck; the ground may require support and in some cases spilling is necessary.

In the mode of entry by a tunnel or adit, the gravel is usually trammed out and dumped into a bin, where it is fed into the sluice boxes. In the mode of entry by a shart, the gravel is hoisted up to surface and tipped into bins, which are sufficiently high to allow of headroom for the sluice boxes and tailings disposal.

Here follows the description of a particular drift mining practice in detail. The pay lead of auriferous gravels rests on a slate bedrock and is in turn overlain by a capping of lava, 500 feet thick, the gold, which is fairly course, being mostly found near bedrock. An adit, 2700 feet long, was driven into the side of the hill, under an ancient river bed, which contained the auriferous gravel, and later, an upper adit, 400 feet long, was driven into the well, which intersected a branch pay streak; an incline was commenced with the idea of following this branch pay streak down, but had to be abandoned, so subsequently a raise was commenced from the bottom adit for a height at which point a drift was started along the bedrock, to connect with the incline sunk from the upper adit. Water was damned off in the upper workings and a 4-inch pipe-line was installed down incline, being fitted with valves at numerous points, to provide water for a V-shaped flume, which was also installed down the incline, resting on bedrock.

Mining of the gravel was on the room and pillar system, the room being 10 feet wide and the pillars 20 feet wide; the gravel requires blasting with powder, and stands well if mined only up to a height of 10 feet at a time. The blasted-down gravel is flushed into a section of the sluice leading to the V-shaped flume by a 3-in. hose connection to the pipe-line, and the flume in turn carries the washed gravel to the raised chute, whence it is drawn off and trammed to the waste dump.

Sluice boxes are made from 12-inch boards and are fitted with iron riffles. Boulders of more than 3 to 4 inches in diameter, encountered in the gravel, are used for packing and filling in stoped-out areas. (fig.43)

Fig. 43. Lay-out or working for drift mining

When gravels are to be opened up by means of a bedrock tunnel, it should have a grade of 4 to 5%, and it is generally best to bottom the gravel deposit with a deep shaft before commencing to drive the tunnel, so as to be able to carry the necessary surveys over the intervening ridge and thereby locate the proper level at which to commence the mouth of the tunnel, due allowance being made for grade and distance, to avoid all danger of the tunnel being driven at too high an elevation and coming out in the gravel above the bedrock. Under the above conditions of mining deep gravels, where natural drainage can be obtained by means of a tunnel, it is very often a serious problem how to commence the actual washing of the banks, as it commonly happens that there is no section of bedrock conveniently exposed which will communicate with the tunnel and where mining operations may be begun.

The tunnel is usually driven a little to one side of the main vertical shaft and a short cross-cut is made to connect the bottom of the shaft with the tunnel. The base of the tunnel is then heavily and securely timbered, and, if the bedrock is soft, a pit is excavated and floored with timber, and filled up to the tunnel level with boulders of hart stone or quarts. The shaft is then lined from top to bottom with heavy planking placed inside of the frame timbers, so as to protect them from wear and displacement. If the tunnel is located in rock sufficiently hard to resist erosion, this is used as a natural race otherwise the tunnel is securely timbered and the flume is built inside and communicates with the bottom of the shaft.

Mining operations may now be commenced at the mouth of the shaft, and the frame timbers and lining may be removed step by step from the surface downwards, as benches of gravel can be conveniently worked back from the mouth. The gravel as it is broken down, is piped directly into the shaft radius all around the shaft, another set of timbers may be removed and a second bench commenced. It is not advisable to attempt to crowd this preliminary work or to strip too many timbers, and commence too deep a bench at one operation, as a "jam" is likely to occur in the neck of the shaft, which would be found costly and difficult to remove. Operations have been successfully carried on as outlined, through vertical shafts having a depth as great as 200 ft. Attempts have been made to drive inclined upraises from the and of the tunnel, but it has been found that the seepage waters get underneath, the timbers, causing frequent subsidence and other troubles, and the consensus of opinion seems to favor vertical shafts.

COMPREHENSION CHECK

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

1. Sluice boxes are made from 12-inch boards and ore fitted...

2. Where deep gravels are to be opened up by means of a bedrock tunnel, it is customary … …

3. The shaft is then lined from top to bottom with,

4. The gravel as it is broken down, is piped …

5. The ground may require support and in some cases …

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

смешанный; штрек; штольня; шахтный ствол; проходить выработку; изменяться; камерно-столбовая система разработки; бункер; отвал пустой породы; устье выработки; подготовительная работа; мощность; глубокий; мягкий; твердый; крепежный лес; крепление; наклонная выработка.

SPEAKING

Exercise 10. Make questions to the sentences and ask them the partner.

1. Water was damned off in the upper workings and a 4-inch pipe-line was installed down the incline, being fitted with valves at numerous points.

2. Boulders of more than 3 to 4 inches in diam., encountered in the gravel, are used for packing and filling stopped out areas.

3. The base of the tunnel is then heavily and securely timbered, and, if the bedrock is soft, a pit is excavated and floored with timber and filled up to the tunnel level with boulders of hard stone or quartz.

4. Mining operations may be commenced at the mouth of the shaft.

Exercise 11. Answer the questions about drift mining.

1. Where is drift mining employed?

2. What can you say about the mode of entry with this method?

3. What system is used for the mining of the gravel?

4. Where is the blasted-down gravel flushed to?

5. What are sluice-boxes made of?

6. What are the boulders of more than 3 to 4 Inches in dia used for?

7. What is the grade of the tunnel where deep gravels are to be opened up?

8. Where is tunnel usually driven?

9. At what place may mining operations be commenced?

10. In what case have the operations been successfully carried on?

LANGUAGE REVIEW

Exercise 12. Read the text about how computers help geologists . In most of the lines 1-10 there is one extra word, some lines are correct. Tick (√) if the line is correct or write an extra word in the space:

The type of software geologists use very depends on their focus. Some may use programs focused specifically on map analysis and representation. One program may focus on maps that they show fault lines. Another may give a view of mineral deposits layers. Some these programs compare multiple kinds of information in one map. Other geologists use 3D programs to test the strain on rocks in specific shapes. Some use simple diagnostic programs that show the geometric qualities of minerals and maps.

__very___ ___√____ ________ ________ ________ ________ ________ ________ ________ ________

Exercise 13. Render in English

1. Подземные способы очень разнообразны, но в основном состоят из форм разработки сплошным забоем или камерно-столбовой системы.

2. Там, где способ вскрытия месторождения осуществлен туннелем или штольней, песок обычно откатывают и сливают в бункер, откуда его затем подают на шлюзы.

3. Штольня длиной 2700 футов проводилась под руслом древней реки, которая содержала золотоносный песок, а затем верхняя штольня, 400 футов длиной, проводилась в горе, которая пересекала ...

4. Разработка песка проводилась камерно-столбовой системой, причем камеры были шириной 10 футов, а целики – 20 футов шириной.

5. Шлюзы делаются из 12-дюймовых досок и оборудованы железными трафаретами.

6. Валуны более чем 3-4 дюйма в диаметре, которые встречаются в песках, используются для закладки отработанного пространства.

VOCABULARY

smelter – плавильный завод

refinery – очистительный завод

refer – относиться к, ссылаться на

royalty - пошлина

to function - действовать, функционировать

cease - прерывать

hand over - передать кому-либо

feasibility - возможность, вероятность

remain - оставаться

gap - брешь, разрыв

proceed - продолжать

transfer - переводить

come on stream - начать действовать

by-product - побочный продукт

shortage - нехватка, недостаток

occur - встречаться, случаться

deposit - месторождение

working - выработка

strike - простирание

level - уровень

Exercise 13. Find the meaning of the words, try to remember them.

super-group; sub-divided; predominantly; sediments; transition; strike; give rise to; lode; shear zone; ensure; encounter; investigation.

READING

Exercise 14. Read the text below looking for the main ideas concerning one of the copper complexes in India.