KHETRI AND KOLIHAN MINES
Two underground mines are in operation at Khetri Copper Complex. Khetri mine was designed to produce 5000 tonnes per day considering four levels under production. Maximum production done from the mine was over 1 million tones in the years 1990 to 1993 (1.00 million t in 1990-91, 1.06 million t in 1991-92 and 1.05 million t in 1992-93) when four levels were active. Until 1.4.2006 cumulative extraction from Khetri mine is over 20.9 million tones of ore containing more than 1,69,022 t copper.
Kolihan mine was designed to produce 2500 tonnes per day considering three levels under production. Maximum production done from the mine was 0.63 million tones in the years 1987-88 when three levels were active. Until 1.4.2006, cumulative extraction from Kolihan mine is over 15.5 million tones of ore containing more than 2,32,543 t copper.
KHETRI MINE Mine workings extend over a strike length of about 3.6 km. It is the largest underground metal mine in the country. The mine is divided into main levels at 60m interval. The top level is 421meter level (ML) and the lowest level is 0 ML coinciding with mean sea level. The other levels are 350 ML, 300 ML, 240 ML, 180 ML, 120 ML and 60 ML. Ore from upper four levels viz. 421 ML, 350ML, 300ML and 240 ML is completely mined out and present production is contributed by 180 ML, and 120 ML levels. The mine is developed on track system of transportation except 421 ML and 300 ML, which were developed on trackless system.
Two major openings are constructed from surface in the central part of mine. These are service shaft and production shaft. The shafts are sunk to a depth of 392 meters and 475 meters respectively from surface. The production shaft is designed to hoist ore from 0 ML. Similarly, service shaft also serves to the levels upto 0 ML. A third shaft is sunk in the north close to Banwas deposit for ventilation purpose. This shaft is 300 m deep from surface. The levels connected to service shaft are 300 ML, 240 ML, 180 ML, 120 ML, 60 ML and 0 ML. Besides, there are three inclines in hanging wall, which were actively used at the upper levels, when the levels were in operation.
Service shaft is used for man and material winding & ventilation application, it works as intake of fresh air. A 1600 KW double drum winder is installed for the winding purpose. Production shaft is used for ore hoisting. It also acts as a return airway for ventilation. A 2870 KW tower mounted friction Koepe winder is used for ore hoisting. An axial flow fan of 175 KW, capable of delivering 8400 cum per minute of air, is installed at the top of the shaft. For northern side of Khetri Mine a ventilation shaft is in use having an axial flow fan of 125 KW, capable of delivering 5000 cum per minute of air.
KOLIHAN MINE Kolihan mine is a compact mine extending over a strike length of 600 meters only. This is the first mine in India which was developed on trackless and ramp system of mining. The mine is divided into main levels at 60 meter interval. The top level is 424 ML and the lowest level is 0 ML. The other levels are 364 , 306, 246, 184, 124 and 64 MLs. Ore from upper three levels viz. 424 ML, 364 ML and 306ML is completely mined out and present production is contributed by 246 ML, and 184 ML.
SERVICE OPENINGSThe access to the orebody is through an adit (5.5 m x 3.5 m ) and an underground shaft of 5.9 m diameter. The single shaft serves the purpose of ore production and man winding. 520 m deep shaft located at 424 ML is connected to 306 ML, 246 ML, 184 ML, 124ML, 64 ML and 0 ML. 400 KW winder has been installed for cage and counter weight for man-winding and waste rock/material handling. 800 HP Koepe winder has been installed for ore hoisting.
The mine is developed on ramp system where a decline is driven from surface to 105 ML at 1 in 9 gradient. The decline serves as second outlet and return air way. It was used for production of ore from 364 ML. There are three more adits at 486 ML, 475 ML and 460 ML.
METHOD OF WORKING AT THE MINES
The method of exploration, development and stoping are similar in both the mines. A footwall drive is developed based on surface drill hole intersections and definition drilling is carried out from these drives to delineate the geometry of orebody, with the help of underground diamond drill machine. Mine development is done with the help of jackhammers. The removal of blasted rock in sub levels is done by auto-loaders. At main levels, trackless load-haul dump (LHD) and Low Profile Dump Trucks(LPDT) are used.
Principal stoping method is sub level open stoping for narrower ore bodies (preferably less than 15m) and large diameter blast hole stoping for wider ore bodies. In sub level stoping, stope drilling is done in ring fashion by pneumatic drifter either BBC 120 or M-110 C. The hole diameter is 57 mm and maximum hole length is 25 meter. In blast hole stoping method, large diameter holes are mostly parallel to the general dip of the orebody. The hole diameter is 165 mm and the length is about 50 m. The machines in use are Down The Hole (DTH) drilling machine like Mission Megametic .
The mine is highly mechanised. For transportation of mineral from underground to the surface, Granby Cars of 10 t capacity in combination with trolley wire locomotive, are used.
ORE HOISTING. Ore hoisting at both mines is centralized. Ore from different levels is transferred to a central ore pass. It is than directed to a crusher located below 0 ML of the mine. Ore is crushed to minus 150 mm and hoisted to surface in skips. At Khetri mine, it is directly fed to plant stockpile whereas at Kolihan mine it is discharged at surface stockpile then it is transported to the plant stockpile by 7.5 km long bicable aerial ropeway.