MINING 



operations, known as working in 

 the whole coal and working 

 brokens. Practice in bord-and- 

 pillar "working varies considerably 

 in different districts. A modifica- 

 tion of this system is often spoken 

 of as the Welsh stall method ; in 

 this, stalls 12 to 18 yds. wide are 

 driven, leaving ribs of coal 18 to 

 24 yds. between them ; when the 

 stall has been carried forward to 

 the full length as laid out, the 

 men in it turn round and work 

 backwards, each winning off half 

 the width of the rib. 



Under-cutting 



The actual operation of coal- 

 getting is usually performed by 

 kirving, or under-cutting the seam, 

 either in the coal itself, or in a band 

 of sufficiently soft material beneath 

 the seam, or occasionally in the 

 seam itself. The coal may then be 

 broken or wedged down, but more 

 often has to be brought down by 

 drilling shot-holes in the coal, 

 and blasting. The operation of 

 under-cutting is the most laborious 

 part of the collier's work, and this 

 is now, when conditions are suit- 

 able, performed by coal-cutting 

 machinery. In a few cases the whole 

 of the coal is got by scalloping, 

 that is, hewing down the whole of 

 the seam with the pick; but this 

 method is only applied to soft 

 coals, especially intended for 

 coking, where there is no advan- 

 tage in getting round coal. 



(6) Mineral veins are usually 

 opened up by means of a series of 

 levels, which may be from 50 to 

 200 ft. apart vertically ; these may 

 either be driven in as day drifts, or 

 more often are set off from a shaft 

 at corresponding depths. The level 

 is then carried along the vein, and 

 the vein -stuff between each pair of 

 levels is won off by stoping. This 

 is what is usually known as over- 

 hand stoping, where the stope is 

 carried upwards from the level. 

 The older method of under- hand 

 stoping, or carrying a stope below 

 the floor of the level, is sometimes 

 resorted to in special circumstances. 

 As a general rule only a portion of 

 the contents of a mineral vein are 

 worth further treatment, although 

 the entire vein has often to be 

 broken down in order to get the 

 valuable portion. Such of the 

 material as is not worth further 

 treatment, which is usually known 

 as deads, is left in the stopes. and 

 the workers in over-hand stoping 

 rise up on the pile of deads thus 

 formed. 



Passages known as shoots, pas- 

 ses, mill-holes, etc., are arranged at 

 intervals through the deads, and 

 through these the payable ore is 

 sent down to the levels, along 

 which it is trammed out to the 



5436 



day or to the shaft, as the case may 

 be. In some parts, notably in 

 West Australia, the method known 

 as rill-stoping is employed ; this is 

 a form of over-hand stoping in 

 which the back of the stope, 

 instead of being practically hori- 

 zontal, is carried at an angle of 45. 

 In contradistinction to rill-stoping, 

 ordinary over- hand stoping is some- 

 times designated flat -back stoping. 

 In relatively wide veins lying at not 

 too flat an angle, with good walls, 

 where the whole of the vein-stuff 

 is worth working, shrinkage stoping 

 or magazine mining may be used 

 with advantage. This is a system 

 of over-hand stoping in which the 

 broken-down ore is allowed to 

 accumulate in the stopes, the men 

 standing on it to do their work, 

 and only enough ore being drawn 

 off to leave room for working. 

 This operation is continued until 

 the stope has reached its full 

 height ; it then forms a magazine 

 of broken ore, which is drawn off 

 as may be required ; meanwhile, 

 of course, other magazine stopes 

 are being started. 



Vertical and Horizontal Slices 



(c) The method of working mas- 

 ses depends largely upon the form 

 of the mass and the nature of the 

 mineral, and is subject to numer- 

 ous modifications. Sometimes such 

 masses are worked by a succession 

 of vertical slices running the full 

 length between adjoining cross- 

 cuts, which are driven across a 

 deposit as may be required. Some- 

 times horizontal slices are carried 

 either longitudinally or trans- 

 versely across the deposit. The 

 method of top-slicing or caving is 

 used extensively, especially where 

 the mineral is comparatively soft 

 and where its value is not very 

 great, so that it is imperative to 

 adopt a cheap method of extrac- 

 tion, even though this may involve 

 the loss of a certain portion of the 

 mineral itself. It is quite largely 

 used in the red haematite deposits 

 of Cumberland and Lancashire. 

 Square set mining has been used 

 mainly in North America, and 

 consists of supporting the excava- 

 tions by a framework of strong 

 rectangular sets of timber ; it can 

 only be used where timber, is 

 plentiful and cheap, and where the 

 mineral to be extracted has a 

 comparatively high value. The 

 method of magazine mining 

 already referred to is quite often 

 used in the mining of masses. 



In modern mining practice the 

 use of rock drills and explosives is 

 universal ; piston drills, in which 

 the drill point is rigidly attached 

 to a piston caused to reciprocate 

 by the action of compressed air, 

 are generally used for sinking and 



MINING 



drifting as well as in large stopes 

 or other workings ; in a more con- 

 fined space, hammer drills, in which 

 the reciprocating piston strikes a 

 rapid succession of blows on the 

 end of a drill held by the machine, 

 are usually preferred. 



Open -cast mining is used in 

 exceptional cases where deposits 

 occur either outcropping to the 

 day, or under a relatively shallow 

 cover of barren overburden. 

 Mechanical excavators and steam 

 navvies are often used. 



Alluvial mining may be looked 

 upon as a separate branch of the 

 work, and is applied to the getting 

 of auriferous alluvials, tin-bearing 

 gravels, etc. These are got by 

 hydraulic mining, which consists 

 of disintegrating and washing down 

 the deposits by means of very 

 powerful jets of water under a 

 pressure of several hundred feet 

 of head directed against the face 

 of the rock by monitors or giants ; 

 or, when such deposits lie at low 

 levels, and especially when below 

 water level, they are generally won 

 by dredging. 



The mineral when obtained has to 

 be transported underground by suit- 

 able means to the mouth of the adit 

 or to the shaft, as the case may be. 

 In modern practice this is always 

 done in mine wagons, trams, or 

 tubs, consisting of rectangular 

 bodies carried on four wheels and 

 running on suitably laid rails. They 

 sometimes carry 5 tons, sometimes 

 only 2 or 3 cwt. For short dis- 

 tances such mine cars may be 

 pushed by men or lads, but for 

 longer distances horse haulage is 

 employed. In important mines, 

 where large quantities of mineral 

 have to be carried over quite con- 

 siderable distances, amounting 

 sometimes to several miles, mecha- 

 nical haulage is almost invariably 

 used. In mines working bedded 

 deposits, like coal and ironstone 

 mines, the methods usually adopted 

 are those of rope haulage. 



Underground Mechanical Transport 

 Other methods of underground 

 transport are electric locomotives, 

 compressed air locomotives, and 

 so-called fireless locomotives, in 

 which steam under reduced pres- 

 sure is employed. Ordinary steam 

 locomotives are not suitable for 

 underground work, except in a few 

 isolated instances, where large 

 main adits are available. The use 

 of electric locomotives is growing 

 rapidly, trolley locomotives being 

 used on the main roads, and 

 storage battery locomotives for 

 secondary haulage purposes. In 

 longwall mining face conveyors 

 of various types are coming into 

 extensive use. 



