INDUSTRIES 



this there is a very small percentage of loss 

 in working out the pillars. The uniform 

 extension of the deposit over a large area is 

 also very marked. This deposit occurs in the 

 second limestone. 



IRREGULAR DEPOSITS (figs. 5, 6, 7, 8, 9, 

 10). The third form of ore deposit is that of 

 irregular and patchy masses in the limestone. 

 These deposits also occur in the vicinity of 

 ' faults.' They may be, and sometimes are, 

 connected with vein-like and bed-like deposits. 

 This kind of deposit cannot be worked in any 

 very systematic manner. The method usually 

 adopted is as follows : Assuming that the pit 

 has been sunk and a level driven out to the 

 ore, care must be taken not to drive the 

 workings too large until the nature of the 

 deposit is thoroughly understood. About 9 

 feet square is an average-sized working, but 

 this of course is altogether dependent on the 

 character of the ore. The first workings are 

 driven in the same way as in the bed-like 

 deposits, viz. by a series of working places 

 and pillars, until the enclosing stone is reached 

 on all sides and the horizontal extension of 

 the ore at that level is known. If ore has 

 been left in the roof, it is followed upwards 

 either at the junction of the ore with the 

 stone, or by plumb-rises in the ore at the most 

 suitable points with the view of ascertaining 

 the vertical extension in that direction ; and 

 if the height of the ore will permit, another 

 tier of workings is driven horizontally, leaving 

 a middling of sufficient thickness between the 

 sole of the upper and the roof of the first 

 working. If the full height of the pocket of 

 ore has been reached by the higher tier of 

 workings, any leads of ore into the surround- 

 ing stone are now followed up, and if the 

 royalty is a rich one other pockets of ore 

 may be opened out in this way. 



It may be that the connecting ore lead is 

 very small and not workable to profit ; but in 

 this kind of deposit better results are ob- 

 tained by following these than by drifting 

 through the solid stone, unless ore has been 

 proved by boring to lie at a convenient level 

 and at a short distance from some part of the 

 working. In such a case, should there be no 

 direct lead of ore, a stone drift is at once 

 driven in the direction of the bore-hole, ad- 

 vantage being taken of the existence of any 

 shale beds running in this direction, even 

 although it may be necessary to go a little 

 out of the direct course in doing so, the 

 difference in cost in driving through limestone 

 and shale being of material consideration. 



The stone surrounding these irregular de- 

 posits is often of a very hard and siliceous 

 character and full of loughs, rendering the 



operation of driving very slow and expensive. 

 It may be here stated that the cost of driving 

 a limestone drift varies greatly, and ranges 

 from 13*. to 405. per foot, while a shale drift 

 may be driven at a cost of from Js. to i6x. 

 per foot. As the development of the mine 

 goes on, the workings will consist of a num- 

 ber of ramifications through the limestone. 

 Sometimes the connection between one large 

 pocket of ore and another is by a gut of ore 

 of considerable size. These guts are usually 

 enclosed between two stone backs forming 

 the sides and by an irregular roof and sole. 

 If any ore is left in the bottom of the first 

 workings a downward or dip working is made, 

 and in the event of its continuance or further 

 development the shaft is deepened and another 

 level driven out. In this way it may be 

 found necessary to drive a series of levels, one 

 below the other, from the same shaft. In 

 the event of the ore, cut by the first level, 

 exhibiting a marked extension upwards and 

 necessitating the use of a number of hop- 

 pers or hurries before it can be conveyed to 

 the shaft, it is often found advisable to set off 

 an upper level from the same shaft, or, should 

 the distance be too great, to sink a new shaft 

 from the surface. 



Careful timbering is also required in the 

 working of this class of ore, more especially 

 if the pockets are of large dimensions. In 

 the working of some of the smaller pockets, 

 where the enclosing stone is of a hard nature, 

 no timber may be required. Small guts in 

 this kind of ground are worked as far as pos- 

 sible from the dip to the rise, and are subject 

 to similar nips and enlargements as those 

 accompanying other forms of deposits. The 

 guts usually run parallel to the main faults 

 nearest to them, and often continue for con- 

 siderable distances. The workings are first 

 carried to their farthest extension, and any 

 ore left in the roofs, soles or sides is stripped 

 off from the inside outwards. The taking 

 out of pillars and middlings left in the mine 

 after the ore-bearing area has been worked 

 over, is carried on in a similar manner to that 

 already described in dealing with bed-like de- 

 posits. 



The irregular masses of ore in the old and 

 new No. i pits and the No. 4 pit of the 

 Montreal mines may be mentioned as one of 

 the largest deposits of this kind in the district. 

 An immense quantity of haematite of good 

 quality has been raised from these mines dur- 

 ing the last thirty years, and although the 

 three forms of deposits are found in the 

 royalty, by far the largest proportion has been 

 obtained from the irregular deposit. Other 

 deposits, such as High House and Crossfield 



405 



