- •Gold mining
- •Text 1. Some facts from the history of gold mining
- •Diamond Placer
- •Text 3. La paz placers
- •Text 2. Placer mining вy excavating machinery
- •Fig.1. Ruston-Bycyrus dragline excavator
- •Fig. 2. Dragline making first cut
- •Fig.5. General arrangement of property for dragline mining
- •Text 3. Power shovels
- •Cableways
- •Text 4. Excavating equipment in тнe mid 80s
- •Electric mining shovels
- •Hydraulic excavators
- •Fig. 13. Ransomes and Rapier w2000 walking dragline stripping overburden at phosphate mine in Jordan
- •Fig. 14. Shows the rh120c introduced in 1933 as an intermediate size between the rh75 and rh300, incorporating “Tripower" geometry
- •Text 2. Dredging in the north
- •Stripping
- •Dredging
- •Vocabulary
- •Text 3. Thawing
- •Other operating problems
- •Nodules
- •20° Angle Gave Best Results
- •Fig. 17. Nodule dredge configuration shown was chosen after a series of increasingly complex dredge designs
- •Larger Dredge Lines Cause Problems
- •Dredge Vessel Specifications
- •Ship Positioning By Dead Reckoning
- •10 Tpd Average
- •Fig. 18. Stages in mining diamondiferous gravel
- •Transport
- •Milling
- •Effects
- •What is Cyanide?
- •Prevention/Solution
- •Text 2. Sluicing
- •Sluice Boxes
- •Water Required
- •Tailings
- •Text 3. Excavation and treatment of gravel
- •Fig. 29. Sluicing by direct loading method
- •Fig. 30. Method of working with ample water supply and steep valley
- •Text.2 working of terrace and alluvial deposits
- •Fig. 33. Method of working river terrace and eluvial deposits
- •Fig. 34. Example of exploitation plan
- •Text 2. Hydraulic mining
- •Fig. 35. Sketch of giant or monitor
- •Text 3. Hydraulic elevators
- •Fig. 41. Hendy hydraulic gravel elevator
- •Fig. 42. Section of elevator pit (Joshua Hendy Iron Works)
- •Text 4. Sluice boxes for hydraulicking
- •Text 2. Miscellaneous methods of mining
- •Text 3. Khetri copper complex
- •Text 4. Kherti and kolihan mines
- •Fig. 46. Longituainal section of Kherti mine, showing principal shafts, main levels and stoping areas
- •In Kolihan mine, small footwall ore-shoots are worked by a sub-level top-slicing method using jackhammers and remote controlled Cavo loaders.
- •Shafts at the Kherti and Kolihan mines
- •Fig. 48. The service shaft, Khetri mine
- •Central services
- •Personnel and housing
Dredging
After a season's stripping, and as soon as thawing is well under way, plans can be made for the erection of the dredge. For this purpose a dredge pit is first excavated and a construction yard leveled off beside it. Lumber and machinery are brought in from "outside", the hull is built and floated and the dredge is completed at the point where it will first commence to dig.
There have been no radical changes in dredge design during the past twenty years or more.
The bucket or dredging line of the floating gold dredges consists of some 65 to 67 manganese steel buckets varying in capacity from 5 to 16cu.ft. These buckets move up the line at a normal speed of 22 per min, and dump into a large cylindrical trommel screen which revolves at an angle in the body of the dredge. The screen is fitted with perforated manganese steel plates, and material which is too large to pass through these perforations finds its way down by gravity to the outlet: of the screen from whence it passes on to an endless rubber belt up the stacker, or conveyor, to be dumped on the tailing piles behind the dredge. Fine material including all gold dust passes through the perforations on the screen plates, and is flushed down over gold saving "tables". These consist of a series of sluice boxes in which the flow of water is obstructed by riffles and also by cocoanut matting placed at the heads of the first six or eight lines of sluices below the screen. A high proportion of the gold is caught on the cocoanut mats.
Every two or three days, the mats are taken up and washed and the contents sent to the gold room for further concentration. Once a month, the rifles in all the sluices are taken up and a "general clean-up" made.
Gold dust can be melted directly into gold bricks. For the more effective cleaning of black sand, and other material recovered by the dredge, a grinding barrel and mercury are used.
Dredging areas can be worked either up or down stream, or in the wider valleys, from side to side. Prom the point of view of the dredge the most effective course is usually to dredge upstream against the flow of the creek. In this way it is easier to handle problems of grade and to maintain, by tailing dams, the level of the dredge pond in raising ground. However, it is often more important to consider questions of water supply and stripping and thawing operations. When it is necessary to keep the stripping run-off water separate from the thawing plants it is more practicable to dredge down stream.
The water supply available for the dredges depends on the spring run-offs and the amount of rainfall during the operating season. A long dry spell may have serious effects on the dredges operating in narrow creek valleys or near the heads of the creeks. In such cases, stripping and thawing may have to be seriously curtailed, and there may even be difficulty in maintaining the level of the dredge ponds. A long rainy spell on the other hand, may have a disastrous effect on the roads and transportation service.
COMPREHENSION CHECK
Exercise 8. Complete the sentences using the information from text 2:
There have been three main ... for the development of the dredging industry during recent years.
It was necessary to develop a successful method of "stripping" or flushing off the thick layer of barren frozen ... which overlays the gold-bearing...
The dredge limits of payable values must be determined and the width and course of the dredge ... decided upon.
The creek gravels are almost invariably frozen to … except beneath the running water of the creek itself.
Stripping of the muck is effected by the use of ... under pressure in very much the same way as in the case of hydraulic mining.
The bucket of the floating gold dredges consist of some 63 to 67 ... buckets varying in … from 5 to 16 cu.ft.
Exercise 9. Find the English equivalents of the words and word combinations in the text:
грохот; водоем; барабан; понтон; устье реки; оттайка; драгирование; очистить; перегородки; плавучий; гидромонитор; замерзший; налегающий пласт (россыпь); подстилающий пласт; глубина; покрывающая порода; смывать.
LANGUAGE REVIEW
Exercise 10. Write sentences in another way, beginning as in the example:
Example: It is possible to distinguish flecks of gold within gold-bearing ore bodies. - Flecks of gold are possible to distinguish within gold-bearing ore bodies.
It is not safe to generate solid waste in various phases of mining operations. – Solid waste is not safe __________
It is expensive to maintain the equipment. – The equipment is _______
It is difficult to work hill and bench gravels. Hill and bench gravels are ____
It is not easy to change the working order. The working order is _______
Exercise 11. Complete the sentences with the correct linker:
because but so
It is a difficult time for the industry _but__ the company is still growing.
The out of the enterprise is now increasing _____ we bout some new machines.
The best option is to but new machinery ______ the old machines are always breaking down.
The number of accidents is increasing ______ management does not seem very worried about it.
There is steady growth of mineral output _____ we are planning to raise the wages.
SPEAKING
Exercise 12. Answer the questions based on the information of text 2 and on your own experience.
What are the reasons for the development of dredging in the North?
What preliminary work is done before the dredging operation?
What gravels are the most suitable for dredging?
How is muck cleared up?
What equipment is necessary for dredging operations?
How does a dredge work?
When is it more practicable to dredge: upstream or downstream?
What does the water supply for the dredges depend on?
Exercise 13. Complete the sentences based on the information in the text:
There have been three main reasons for the development dredging industry in the North ...
The gold content is determined by ...
When the ground has been surveyed and the dredging area determined, it is necessary to make …
The overburden consists primarily of ...
Stripping or the removal of the muck is effected by ...
The bucket or digging line of the floating gold dredges consist of …
The screen is fitted with ...
Gold saving tables consist of ...
Every two or three days the mats are taken up and ...
From the point of view of the dredge the most effective course is ...