MININli 



3435 



MINING 



i washing," an unfurl unite 



(nil, l lenders necessary 



of the further phrase dr\ 



eleiming of coal," when such 



Is are employed. 



l'i ill mining operations the 

 methods adopted depend essen- 

 tially upon the nature of the 

 1 1 deposits which it is in 

 tended to work. For this purpose 

 ! il>- posits may be classified 

 as (a) Symphytie deposits, that is, 

 deposit" \\hieli form an essential 

 part of a geological formation, and 

 are therefore stratified and form 

 more or less continuous beds ; as 

 examples of these may be quoted 

 coal seams, beds of iron -stone, 

 beds of rock salt, the auriferous 

 "reefs" of the Witwatersrand, the 

 cupriferous schists of Mansfeld, 

 etc. ; (6) Epactic deposits, or de- 

 which do not form members 

 of a jreological formation ; these 

 ib-divided into : 



(1) Veins, like the lead veins of 

 Al-ti'ii, the tin veins of Cornwall, 

 the auriferous quartz veins of Cali- 

 fornia, etc. (2) Irregular deposits or 

 masses which may assume many 

 different forms ; amongst these 

 are included such deposits as the 

 red haematites of Cumberland, the 

 lenticular deposits of cupriferous 

 pyrites in the Huelva district, the 

 immense masses of magnetite of 

 Kiinmavaara, etc., in Northern 

 Sweden, the nickel and copper- 

 bearing pyrites deposits of Sudbury, 

 Canada, the porphyry deposits of 

 the Western States of America, 

 consisting of masses of monzonite, 

 portions of which are sufficiently 

 rich in disseminated copper ores 

 to constitute them an ore of that 

 metal, etc. It is obvious that the 

 methods of searching for, opening 

 up, and working these deposits must 

 be conditioned essentially by the 

 nature of the deposits themselves 

 and by their mode of occurrence. 

 Scope of Prospecting 



Prospecting operations include 

 various methods of searching, 

 trenching, etc., on the surface, 

 and more particularly deep boring 

 operations for the discovery of 

 deep-seated mineral deposits. It 

 is obvious that these can be applied 

 with much advantage in the case 

 of the bedded deposits referred 

 to under a above ; they are also 

 frequently used for deposits of the 

 6(2) type, when these are known 

 or supposed to be of reasonably 

 large dimensions ; they are, how- 

 ever, practically useless for veins, 

 for since these latter lie approxi- 

 mately vertical and carrying 

 generally their values in relatively 

 restricted areas, a borehole put 

 down from the surface would in all 

 probability miss the deposits 

 altogether, or even if it penetrated 



them it uuiild IM- purely a matter 

 of accident whether it happened 

 to strike a rich or a poor j> 

 Very deep boreholes have been 

 put down in searching for coal, oil, 

 and the auriferous reefs of the 

 Witwatersrand, the deepest bore- 

 hole in the world being at Zcu- 

 chow, Rybnik, in Upper Silesia, 

 which has reached a depth of 7,350 

 ft. ; another one at Virginia, 

 U.S.A., is 7,310 ft. deep. 



Mineral deposits are opened up 

 either by means of tunnels driven 

 in from the surface, usually spoken 

 of as adits or day drifts, or 

 else by means of shafts. The first 

 named method is only applicable 

 in mountainous or broken ground, 

 where considerable portions of the 

 deposit lie at a higher point than 

 some readily accessible portion of 

 the surface, as for example in the 

 bottom of a valley. Relatively few 

 mineral deposits are situated so 

 advantageously as to admit of this 

 method of attack, which is natur- 

 ally always employed whenever 

 possible. In most cases where an 

 important deep adit is driven, it is 

 arranged to serve as a drainage 

 adit, as a means of access to the 

 deposit, and as a travelling road, 

 by means of which the minerals 

 wrought in the mine are trans- 

 ported to the surface. 



Types ol Shafts 



By far the greater number of 

 mineral deposits are opened up by 

 means of shafts, this being natur- 

 ally the usual method when deal- 

 ing with bedded deposits. There 

 are a number of very deep shafts 

 in various parts of the world ; 

 probably the deepest at the present 

 moment is the shaft at Morro 

 Velho in Brazil, which has reached 

 a depth of 5,826 ft. Shafts as a 

 general rule are vertical, but in- 

 clined shafts are sometimes used, 

 either to follow down a steeply 

 pitching deposit, or to get past 

 some obstacle. Ordinary shafts 

 are either rectangular in cross sec- 

 tion or circular, local custom 

 being often the sole guide as to 

 which should be employed. 



Thus, the majority of colliery 

 shafts in the S. of Scotland are 

 rectangular, while similar shafts 

 sunk under similar conditions S. 

 of the Tweed are almost without 

 exception circular. The cost of 

 sinking a shaft and the methods 

 employed in sinking it necessarily 

 depend upon the nature of the 

 strata to be passed through, par- 

 ticularly as to whether they are 

 water-bearing or not ; shafts 

 through strata carrying only a 

 moderate amount of water are 

 generally sunk by blasting. A 

 small amount of water may be 

 hoisted by buckets, but it is more 



usual t<> employ pumps ; the lining 

 of such shaft* depends mainly upon 

 their form. Rectangular shaft* are 

 generally timbered, circular shaft* 

 are lined with brick work. The 

 cost of sinking increase* rapidly if 

 water is met with, anything more 

 than 100 gallons per minute adding 

 greatly to the outlay and to the 

 time required for the operation. 

 Shafts for Deep Sinkings 



At Horden, co. Durham, shafts 

 were sunk to a depth of 1 ,260 ft. by 

 ordinary methods, using pumps, 

 against a flow of 9,000 gallons per 

 minute, but this is by far the largest 

 amount that has ever been success- 

 fully dealt with in this way. Under 

 ordinary conditions, especially in 

 the case of deep sinkings, a flow of 

 2,000 to 3,000 gallons per minute 

 necessitates the use of special 

 methods, and even much smaller 

 quantities of water than these may 

 render ordinary methods prohibi- 

 tive, if layers of quicksand of any 

 thickness have to be passed through. 

 Shafts in wet ground, however 

 sunk, are usually lined watertight, 

 either by the use of cast iron tub- 

 ing (quite exceptionally steel), 

 concrete, or in recent times more 

 often ferro-concrete. 



The subject of exploitation, or 

 the getting of minerals, involves 

 not only the actual severance of 

 the mineral from its deposit, but 

 the entire subject of laying out the 

 mine to best advantage, and the 

 special methods used for attacking 

 the face of the mineral. 



(a) Bedded deposits, like coal 

 seams or beds of ironstone, usually 

 lie at very flat angles, and the 

 methods usually described as bed 

 mining are applicable to them, 

 as to all other deposits lying 

 more or less horizontally and of 

 moderate thickness, as is typi- 

 cally the case with the majority of 

 coal seams in this country. There 

 are two main methods employed, 

 usually classified as Longwall and 

 Bord-and-Pillar, both described 

 under their respective headings. 



There are several varieties of 

 longwall, that known generally 

 as advancing longwall being the 

 most usual ; in what is known as 

 retreating longwall the roads are 

 driven to the boundary and the 

 longwall face is brought back 

 towards the shaft, leaving the goaf 

 on the in-bye side of the coal, 

 thus avoiding the necessity for the 

 maintenance of goaf roads. This is 

 the safest and, as regards actual 

 working, the cheapest form of long- 

 wall, but is not applicable except 

 in the case of comparatively small 

 royalties. 



Bord-and-pillar working differs 

 from longwall essentially in that 

 the coal is gotten in two distinct 



