MINING. 



MINING. 



078 



do not appear worth exploring. We will suppose, however, that a 

 continuous body of ore is met with in one of the upper levels, and that 

 winzes have been regularly carried down to the level below it. Similar 

 operations will then be required here, and winzes will be sunk from it 

 to the next deeper one in the same manner, but they will generally be 

 situated about mid-way between the former, so that each may explore 

 the ground under the middle of the rectangle formed by the two upper 

 winzes and the levels between which they are placed, so as effectually 

 to explore the vein with the smallest number of excavations. The 

 system of works by which a vein is thus laid open, although by no 

 means so regular, is not unlike the seams formed by courses of masonry, 

 the horizontal joints of which may be supposed to represent the levels, 

 and the vertical one the winzes. In cases where the ore extends above 

 the upper level in the mine, this part of the vein may be laid open by 

 perpendicular excavations similar to winzes, but formed in the reverse 

 manner, or by " rising " upwards instead of " sinking " downwards, as 



in the former cases, the height to which these " rises " are carried 

 depending on the extent of the ore in that direction. 



Should the vein be found to contain ore of good quality and in 

 sufficient quantity, both laterally and in depth, the various operations 

 which have now been described may proceed indefinitely. The shaft 

 will continue to be sunk, cross-cuts driven to the vein at every ten 

 fathoms or thereabouts, levels extended in both directions from them 

 (the upper level being always of course considerably more advanced 

 than the lower, from having been longer in progress), and the ground 

 between them subdivided by winzes as before described. The excava- 

 tions mil now have assumed a regular form, and become what is 

 properly termed a mine, the objects for which they were undertaken 

 having been accomplished, or the contents of the vein thoroughly 

 explored, and its produce, where of sufficient value, rendered capable of 

 being economically and expeditiously extracted. In the accompanying 

 sketch, Fig. I, the state of the works is shown, the shaded portion repre- 



Fig. I . Longitudinal Section, showing the manner in which the vein is laid open by the level and winzes. 



senting the parts of the mine whence the ore has been extracted as 

 described below. Fig. 2 gives a cross section of the mine, and with the 

 former will completely illustrate the foregoing description. 



Fig. 2. Cross Section, shotting the progress of a shaft after cutting the vein. 



Railing of Ore. The operation last named, or the extraction of the 



ill not however have waited the advanced state of the works 



which we are now contemplating : a certain quantity will have been 



produced by driving the) upper levels and sinking winzes below 



them, although not forming the primary object of these works ; and 



wherever orey ground was seen in the " back " or upper part of the level 



first driven, it will early have been pursued upwards towards the 



i', and will yield the first returns of the mine. When by the 



further progress of the works the vein has been divided into the solid 



rectangular masses before described, the mine will have been brought 



into an effective state of working, and parties of men will be set to raise 



ores from all the most productive points. Where the vein is not very 



hard, the ore maybe broken down with the " pick " only, but it is 



lly necessary to blast it with powder, by which process large 



ities are detached from the vein by every shot. In raising ores 



the men generally work upwards from the " back " or upper part of 



one level towards the " bottom " of another, and the excavations are so 



arranged that the ore may readily fall down to the level below them, 



whence it is carried in tram-waggons to the shaft, and thence raised to 



the surface. As in all large and well-regulated mines it is desirable to 



keep the quantity of ore raised as nearly as possible to a uniform 

 standard, the process of " opening ground," as above described, will 

 generally either keep pace with or even exceed the rate of exhaustion, 

 so that a portion of the ore thus laid open may always be held as a 

 reserve to keep up the returns of the mine during periods of temporary 

 depression, when only poor and unproductive ground may be presented 

 by the works of discovery. This judicious mode of proceeding is 

 justly regarded as one of the greatest modern improvements in the 

 economy of mining : it provides a compensation for those great 

 irregularities and fluctuations to which all mineral deposits are con- 

 tinually subject; it keeps up the returns of the mine during temporary 

 intervals of poverty, and enables those trials to be effected which may 

 again place it in a productive state. 



Extension of the Worts. As the workings of a mine become more 

 extended, they gradually lose the simplicity which we have been sup- 

 posing, and, from the multiplication of shafts and other excavations, 

 become highly complex, a result to which the irregularity of mineral 

 deposits greatly contributes. The nature of these ulterior operations 

 will now be briefly described, still considering the mine as a mere 

 system of excavations, and reserving till hereafter the subject of 

 drainage, support, &c. When the levels have been extended to a con- 

 siderable distance from the shaft, the ventilation will again become 

 defective, notwithstanding their communication by winzes ; the current 

 of air, from the greater distance it is carried, becomes more and more 

 feeble; and this evil is still further augmented by the increasing 

 number of men now employed in the works, the number of candles, 

 and the frequent process of blasting. The expense of the transport of 

 ore and masses of rock and rubbish to the shaft also becomes con- 

 siderable ; and if the prospects of the mine continue such as to warrant 

 the expense, a new shaft must now be sunk on one or both sides of 

 the former. Whether one or two shafts will be necessary will depend 

 on the direction in which the ore is found to extend, and the indica- 

 tions exhibited by the vein ; and they will be so placed as to command 

 that portion of it which, for reasons before stated, is without the reach 

 of the former one, which by this time also may have become inade- 

 quate for the various purposes of extraction, drainage, and descent, to 

 which it is applied. 



In order to avoid the expense and delay of unnecessary cross-cuts, 

 the new shaft will be so placed as to intersect the vein much deeper 

 than the former, and this point will be so arranged as to correspond 

 either with one of the deepest levels, or some proposed level deeper 

 still. The new shaft may have been commenced in anticipation, while 

 the levels were yet distant from the point whore it is sunk ; and in 

 this case its communication with the mine will have been accelerated 

 by driving levels to meet those which are proceeding from thence 

 towards it. When this communication has been effected, its benefits 

 will be immediately felt, both in the thorough ventilation of the mine 

 and the increased facilities afforded for the extraction of ore and stuff. 



As the process of sinking a shaft is often extremely slow, from the 



