Heat, ventilation challenges and the disposal of waste rock within a working mine had to be overcome to arrive at this point.
In early June 2010, workers at Xstrata Copper’s Kidd Mine in Timmins, Ontario, broke through the last of the rock between the 9,500-foot and 9,600-foot levels, completing the deepest continual ramp from surface in the world. The ramp portal round was developed from the open pit in 1969, and the ramp, approximately 5.1 metres in width and height, now winds down from surface for approximately 20 kilometres at a grade of 15 per cent. The breakthrough is the latest in a series of development stages, the total cost of which is $148 million.
The majority of the ramp was driven down from the 8800 Level, starting in January 2007, and reached 150 metres past the 9500 Level in May 2010. In August 2008, development started from the 9600 shaft station up the ramp access to the ramp breakthrough location.
In addition to the challenges associated with working at such extreme depths — such as ventilation volumes and extreme temperatures — came the problem of removing the waste rock. The work crews developing a ramp and the five levels between 9,000 feet and 9,500 feet shared facilities with an operating mine producing 2.5 million tonnes per annum from 2,000 feet down to 8,800 feet. The down ramp development produces approximately 3,500 tonnes of waste a week, which is trucked either to the 8800 waste bin or directly to a waste stope between the 8300 and 8800 levels. The up ramp produces approximately 1,000 tonnes of waste a week, which has to be dumped onto a grizzly to load directly into the skip. Including vertical raising, the project produces, on average, 5,000 tonnes of waste per week, which must be handled along with the operating mine’s waste and ore.
For ventilation, the down ramp fresh air is supplied to 9000 Level through the No. 4 shaft and an internal fresh air raise, and then forced through three-metre-diameter fresh air raises to supply the required airflow to 9100 Level through to 9500 Level. The down ramp is currently exhausted through a 1.5-metre-diameter raise on 9100 Level and a six-metre-diameter raise on 9000 Level, with the permanent six-metre-diametre raise exhaust system from 9200 Level to 8300 Level expected to be complete this month. The up ramp is supplied with fresh air from the No. 4 shaft, and exhausted via ducting in the No. 4 shaft to 8800 Level. Prior to the ramp breakthrough, a ventilation curtain was constructed to maintain the same ventilation system. Now that breakthrough has occurred, ventilation tests are being carried out to optimize the air flow until the breakthrough of the new exhaust raise in August 2010.
Heat is also a major issue, and is especially a concern during the summer. Kidd uses a set of cold stopes (where ice is generated in the winter months) and a mechanical refrigeration plant to cool the air. However, in severe heat, Kidd implements a work/rest regime to minimize the risk of heat stress. As the project completes changes to the ventilation setup, the heat will become easier to manage.
Flooding also constrained development execution. Due to mine depth, the dewatering system is staged; consequently, if a higher pumping station requires maintenance, then the lower level will not pump, and when its sump overflows, it drains to the block below. In response, a temporary pumping station on 9200 Level was installed while developing the 9500 Level main sump.
To mitigate rock stress and protect the workers approaching breakthrough, the face was distressed within 12 metres of breakthrough. Eight-metre-reamed holes were drilled as part of the cut; as well, eight-metre perimeter holes were drilled at 45 degrees. These holes were charged with one stick of powder at the end of the holes and fired in sequence with a standard round to destress the area. To ensure the round was safe to drill, the face was screened and Swellexed.
With the breakthrough complete, the Stage II development team will continue the ramp down from the 9600 shaft station to a shaft breakthrough at approximately 9,800 feet. This will allow the mine to muck the shaft bottom and for the area to be used as over flow capacity for the main sump on 9500 Level. A new bin from the 9600 shaft station to 9200 rock breaker will also be completed by September. On 9500 Level, capital development will continue and some special projects, including a powder magazine and a fuel bay, will be completed. The stopes on 9400 Level, complete with exhaust and fresh air raises, are scheduled to be ready for operation in the first quarter of 2011 and on 9500 Level in the following quarter.
The three-year-long project included the contributions of Dumas Contracting for the down ramp, Redpath Mining for the up ramp, the mine services of Access Mining, Machines Roger for service hole and paste hole drilling, the electrical work of Monarch Automation Construction, diamond drilling from Orbit Garant, and mine and construction consultants Genivar. Despite over one million man hours worked, no lost time injuries occurred.
Ryan Roberts, C. Eng (U.K) works at Xstrata Copper and is the Stage II project engineer.