First undercut rings fired at the Oyu Tolgoi underground mine in Mongolia marking the start of underground production
Posted by Paul Moore on February 14, 2022
Following a new long-term agreement between Rio Tinto, Turquoise Hill Resources (TRQ) and the Government of Mongolia, underground production has officially started at Oyu Tolgoi. In a major advance, and after the excavation of more than 90 km of tunnels over 11 years, the first undercut rings have recently been fired at Oyu Tolgoi underground boulder cave
The first undercut blast created a vertical void from apex to undercut level (UCL) and involved 114 holes loaded with 6 tons of explosives. Once the charge was complete, blasting was initiated remotely using an electronic blasting system. The Hugo-Dummett deposit will be mined in a series of extractions, the first stage being Hugo North Lift 1 (500 Mt) which will use the caving mining technique. The Elevator 1 mining levels are approximately 1,300m below the surface. Six distinct levels have been developed to operate Elevator 1. The Apex level is 17m above the undercut level, which in turn is 17m above the extraction level (floor to floor ). The rolling level is 44 m below the extraction level. In the footprint area, the exhaust ventilation level is between the extraction and transport levels.
The undercut blasting extends 18m (one bell spacing) from the center of pull in each production drive to ensure the propagation of troughs for the bells along the edge of the cave. Perimeter Undercut and Apex Level Drives are located at least 32.5m outside of the undercut blast area to protect against the stresses of the cave abutment. After blasting an undercut ring, approximately 60% of the blasted tonnage (swell) in the ring will be cleared from the undercut level. At the extraction level, an El Teniente style drawpoint layout is offered for the entire footprint with drawpoints angled at 60⁰ to the extraction drives.
Access to the mine and ventilation of the workings is provided by a series of five shafts as well as access to the C2S conveyor. Shaft 1 (6.7 m in diameter) and Shaft 2 (10 m in diameter) are multipurpose service, production and intake ventilation shafts sunk to a depth of 1,385 m and 1,284 m respectively. Shaft 3 is a concrete-lined intake shaft 10 m in diameter and 1,148 m deep. Shaft 4 is a concrete-lined extraction shaft 11 m in diameter and 1,209 m deep. Shaft 5 is a concrete-lined extraction shaft 6.7 m in diameter, with two underground ventilation stations and a depth of 1,178 m. The Surface Conveyor System (C2S) comprises three identical 2,202m long and 1.6m wide steel cable conveyors operating at 6m/s and capable of carrying the planned production rate of 32 Mtpa. The conveyors were installed in a conveyor ramp 6 m wide by 5.4 m high.