72 | MINING Waikaia Gold Mine remediation at the forefront Karen Phelps The mine worked across four highly productive, dry stock sheep and beef farms and mining access agreements with the landowners required Waikaia Gold to restore the land back to its original contour. Approximately 85 per cent of the land affected by Waikaia Gold Limited’s alluvial gold mine operations on the floodplain of the Waikaia River near Freshford, Southland, has been fully remediated and the land returned to farmers. Remediation of the balance of the land has been effectively completed with monitoring and any remedial works continuing over the next 18 months. According to Waikaia Gold managing director Warren Batt remediation was at the forefront, before mining even commenced back in 2013, and Waikaia Gold is proud that first class farms have been returned to the landowners. The project was a finalist in the 2020 New Zealand Minerals Sector Awards in the environmental management category. “Farm planning was integrated with rehabilitation plans from the onset of mining and successful outcomes have been dependent on extensive consultation with landowners throughout operations. “The restoration programme demonstrates the temporary nature and positive impacts of the use of land for alluvial mining with virtually no evidence of the passage of the mine where rehabilitation has been completed,” he says. Over the life of the mine 15.3 million bcm of overburden and 4.3 million bcm of wash were mined. The mine worked across four highly productive, dry stock sheep and beef farms and mining access agreements with the landowners required Waikaia Gold to restore the land back to its original contour and return the productive capacity of the land to the same, if not better, than that pre-mining. The project comprised three stages: progressive return of mined areas to post-mining contours including spreading of soils; seasonal levelling, cultivation and sowing of pasture and replacement of farm infrastructure after allowing time for any settlement and remedial drainage During the mine development phase Warren says that top-soils from the starter pit area, designated gravel and silt stockpile areas, haul roads and settling pond areas were removed and stockpiled to a maximum height of two metres. Approximately 500,000 bcm of gravel and silts from the starter pit and initial advance were stockpiled until the mine had advanced sufficiently to be able to move pre-stripped gravels directly to the backfill over mine tailings. Gravel backfill was built to a design surface approximately 0.5 metres below the planned final rehabilitation surface and ripped to break up any pan, which may have developed as a result of trafficking, by dump trucks operating on the tip-head. Silts mixed with gravel to aid traffic-ability were then dumped and levelled to form a sub-soil base. Once gravels and silts were in place, topsoils pre-stripped ahead of mining were hauled and dumped directly onto backfill in windrows before spreading to a depth of 0.2 metres as ground conditions allowed, to build backfill to final rehabilitation surface. Where disturbed ground was over old tailings and there was a deficit of topsoil, silts were used as a substitute for soils. He says that the pre-mining stratigraphy of topsoil-silt-gravel was replicated as best as possible. The Mataura Silt underlying the top-soils is important on the Waikaia floodplain as it allows moisture to drain while retaining sufficient moisture to slow the rate at which the soil dries out, he says. An example of how wildlife was preserved includes the fact that historic dredge ponds in the mine path were surveyed before disturbance and ponds with populations of native fish, including giant kokopu, eels and perch, were fished and the captured populations released to suitable ponds outside the mine path. “The major benefits of good environmental and rehabilitation practice has been socio-economic benefits over and above fiscal returns from gold production,” says Warren. Benefits include a 30–35 hectare increase in arable land, 90% replacement of fences, improved farm layout, establishment of reticulated stock water to replace reliance on natural water sources, increased riparian bank protection and creation of new ponds. Waikaia Gold Limited is a private company founded by Buzz and Sam March and Warren Batt in 2009 to acquire Mining Permit 41602 at Waikaia, Southland from Eureka Mining Limited. The company’s new project is an upcoming alluvial gold mining operation at Waikaka. Waipounamu Contracting Ltd A G R I C U L T U R A L , S I L A G E , B A L I N G & T O T A L F A R M S E R V I C E S Waipounamu Contracting specialise in all aspects of Haymaking, Baleage and Silage, Agricultural Services, Earthmoving and Drainage, General Cartage o ice@sansonag.co.nz 03 202 5737 “The major benefits of good environmental and rehabilitation practice has been socio-economic benefits over and above fiscal returns from gold production.”
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