Stockton Mine 2002 to 2009, West Coast, South Island
August 2, 2010
Coal mining and earthmoving at Stockton Mine for Solid Energy NZ dominated the attention of Doug Hood Mining (DHML) for 7½ years
At Stockton Mine since 2002 building the Mt Augustus road & completing the Mt Fred sidecast contract, DHML, in November 2003, won the Stockton Mine 5 year contract for overburden removal, coal winning and associated work. In November 2008 a 1 year extension was awarded. The Stockton Mine contract ended on 2nd October 2009.
Scope
Mining was on a 24/7 operational basis utilising up to 3 x 180 tonne excavators (4 on site) as the main digging tools. Coal was predominantly mined with 2 x 100 tonne excavators.
A fleet of up to 29 x 85-100 tonne 777′s, 4 x 50 tonne 773′s and 24 x 35-40 tonne articulating dump trucks were used for both coal and overburden mining. D8, D9 & D11 tractors were utilised in pits and on tip heads.
Rehabilitation and auxiliary civil works were undertaken on a continuous basis utilising the large fleet of smaller excavators and articulating dump trucks.
Overburden removal
Overburden stripping and coal winning were from multiple pits on an ongoing basis. Mining includes extensive previous (historic) underground workings.
Overburden consisted mainly of competent granites and some mudstones. Overburden removal increased 100% from tender to up to 500,000 m3 per month with 24.5 million m3 moved on contract rates over the 6 year contract period.
Coal mining
Stockton coal varies in quality and seam thickness and is selectively mined accordingly. Coal winning was also characterised by complex blending of multiple coal face & stockpile sources, with up to 10 or more mixed on a shift.
With coal winning requiring a minimum of 8,000 tonne of coal per 24 hours, approximately 9.1 million tonnes of coal was handled to ROM or stockpile with a peak production of 2.1 million tonnes per annum.
Mangatini Sump
In 2007 DHML tendered for and won the contract to construct the Mangatini Sump, a key component of the Stockton water management programme, within the Stockton Mine site, and completed this in 2009. The sump required the drill, blast, excavate and dump of 1M m3 of solid rock.
Weather conditions
Difficult stripping of previous workings provided challenges to drill & blast and coal winning while severe weather (including fog-outs) conditions were a constant challenging factor with all site and mining activities. Site mobility was greatly reduced by the impact of water on haul roads and pit access due to the site receiving up to 7 metres of rain per annum.
People
Employee numbers associated with this contract increased from 100 at contract commencement to a peak of 450 employees.
Plant
The tendered plant fleet increased four-fold to achieve required production increases. Fleet size at the end of the Stockton contract was 128 items of heavy plant.
