Cornwall contract provides fresh challenge for Meridian Drilling

Working in extreme weather conditions is par for the course for Meridian Drilling, but when it came to starting a contract closer to home, the UK-headquartered company had to overcome a brand new set of environmental challenges.

Meridian Drilling’s latest project is working with Treliver Minerals on a project near St Columb, Cornwall to explore for tin.

The contract will see Meridian complete 3,500 metres of diamond core drilling, some 16 years after the last Cornish tin mine – South Crofty – closed.

While Cornwall doesn’t have the extreme climate of Ethiopia or the Republic of Congo – where Meridian has had its longest running contracts – starting work during one of the wettest UK winters on record provided a serious test for the drilling team.

Meridian Drilling MD and Cornishman Jeremy Moore said: “Initially the climate presented almost as many difficulties as working in the Danakil Depression.

“Clay becomes a problem when it comes into contact with freshwater, because its small particle size has a tendency to swell.

“The project was initially set for RC but this was quickly changed to diamond coring due to the high water table and the adverse effect it could have on pastureland.”

The drilling team also found that the ground at site can change dramatically between each borehole, so the drilling fluid needed to change regularly to suit the ground.

To deal with this, Meridian has been working closely with  mud consultants to achieve the right drilling fluid mix to ensure good quality core recovery.

The switch to diamond drilling also improved meterage and core recovery.

For the diamond drilling, Meridian started using a track mounted, Coretech Maxi 10C diamond rig with a 12 tonne pull back, drilling in PQ to 50 metres before reducing to HQ to a target hole depth of 120m.

Mark Thompson, CEO of Treliver Minerals said: “We have developed a really good working relationship with Meridian. Their guys have been tremendous – working from dawn to dusk on one of the wettest outcrops in the British Isles, during the wettest winter in living memory.

“I take my hat off to them, they have really worked hard to keep the project moving ahead.”

The site geology at the Treliver Minerals project in St Columb is divided into two sections with an average depth of 120 metres.

It has a top section of clay and mudstones, with some very hard quartz sections and coarse gravel layers up to a depth of 80 metres and below the hard and solid rock section.

In the early 1980s Billiton Exploration UK conducted a greenfield and brownfield exploration programme in the area at an estimated cost of circa £1.5m. The first hole drilled at Treliver returned 63 metres of near continuous mineralization from 23 metres.

However Billiton’s exploration programme was cancelled in 1985 following the collapse of the International Tin Council and a significant drop in tin prices.

If successful the project could mean a new beginning for Cornwall’s 2,000 year association with tin, creating jobs for up to 600 people, mining an estimated $1bn worth of the base metal.

The exploration work has followed increasing demand for tin in the electronics market, where its use as solder has seen its price rise to $23,000 per tonne, with analysts expecting further increases to come.

Cornishman Bill Pullen, who is supervising the project for Meridian Drilling, is optimistic about the possibility of tin mining returning to Cornwall. Having started his career as a driller in a tin mine in Redruth, Bill has since worked in countries as far afield as Ghana and Saudi Arabia.

He said: “After South Crofty closed, I expected that to be the end of mining in Cornwall. But with this new project there is the real possibility that we could see a mine here again, and a tin mine too. It gives me real hope for local jobs.”