Text 4. Kherti and kolihan mines
The strike length of the deposits worked by the Kherti mine is about 3,6 km the workings being divided into North, Central and South blocks. The Kolihan workings are located on three lodes and extend over a total length of 600 m. The distance between the shaft systems of the two mines is about 7,6 km. All levels in both mines are denoted by their lights relative to mean sea level.
The uppermost level of Kherti mine, 421 m is served by adits and has been worked by trackless equipment (1,58 m3 LED’s and 10t shuttle cars feeding a surface crusher). The ore reserves on this level are now practically worked out.
The next level, 350 m is a tracked level served by inclines from surface. Ore is loaded by rocker shovels to Gramby cars, trains of which are hauled by battery locomotives to a main ore pass, which connects to the “shaft mine” ore pass system.
All working below 350 m belong to the “shaft mine”, access to which is through two vertical shaft sunk from surface to serve the 0,0 m horizon, together with an incline which descends as far as the 180 m level. Details of the shafts and the incline are given in table 1.
Mine levels are at 60 m intervals, on the 300 m, 240 m 180 m, 120m, 60 m and 0,0 m horizons.
The Kolihan mine, similarly, has an adit section (the 424 m level); a Decline section, in which a 1 in 9 decline 5,5 m x 3,25 m in cross-section, serves the 364 m and 306 m levels; and the Shaft section, for which access is via a shaft sunk from the 424 m level. In this section, development has been carried out on the 306 m, 246 m and 184 m horizons.
The methods of exploration, development and stoping are similar in both mines.
Main exploratory levels are driven at 3,5 m x 3 m section, 30 m away from the ore either in the hanging wall or foot wall, depending on whether the drilling to define the ore is to be made downwards or upwards. These levels are later utilized as the main tramming drives during stoping operations.
The driving of headlings is a three shift operation, using Silver 3 jackhammers and air-leg equipment. A typical round comprises 53 holes of 33 mm diameter, using a Burn cut. Blasting is by special gelatin 80% explosive with half-second electrical delay detonators.
On tracked levels, mucking is done by rocker shovel to Granby cars, trains of which are hauled by electric trolley-wire or battery locomotives. On trackless levels the loading is under-taken by LHD-low profile dump track combinations.
Timber props steel sets are employed for roadway support wherever needed, and in bad ground conditions lagging may also be used.
Raises were previously put up using drifters and Alimak raise climbers, but a long-hole drop raising technique has been perfected whereby 60 m raises are put in using a pattern of five parallel 152 mm holes, crater-blasted sequentially Drilling of large diameter long holes is carried out using either an imported MissionMegadrill or an Indian-made WDS-400 drilling rig.
The principal stoping method used hitherto has been sub-level open stoping using ring drilling. Each stope is developed from a slot raise and a service raise, with 3,0 m x 3,0 m sub-levels being driven at 18 m vertical intervals, plus a through drive. Ring drilling comprises 54 mm diameter holes up to 18 m long. The toe spacing is 2,2 m and rings are 1,5 m apart in the trough, 1,8 m apart when drilling from sub-levels. (fig. 46, 47).
