Lithium Resource Drilling and Comparison of Two Primary Methods

Mar 8, 2024 | Blog

BY: Andrew Smith (CEO) February 2024

Here at Imerys British Lithium, we are coming to the end of an extensive program of Resource drilling, the aim of which has been to further prove the size and grade of our lithium deposit, by obtaining representative samples of the granite beneath the surface here in mid-Cornwall.

The process of testing the lithium content, rock density, moisture content and identifying other impurities, and assessing rock strength is essential for our detailed mine planning and other work. A strategic pattern of holes have been drilled, allowing us to map the mineralisation in a three-dimensional environment using sophisticated software.

We have recently completed our fourth drilling campaign of 62 holes, aimed at increasing the confidence in our lithium deposit. Various contractors from across the UK and Ireland contributed to this significant effort.

Around 80 percent of our drilling utilises the reverse circulation (RC) drilling method with the remaining 20 per cent being diamond core drilling.

At our peak in 2023 we had six drilling rigs active in Greenslade pit, right next to our lithium pilot plant, near Roche in Cornwall. This programme is coming to an end next month. Whilst our average hole depth was 200 m, our deepest hole reached 720 m, revealing continuous mineralisation from the surface, showing the world-class scale of this deposit – an exciting discovery for us all! 

What is diamond core drilling?

Diamond core drilling involves a hollow diamond-faced drill bit on the end of a drill pipe, attached to a drilling rig, which rotates to bore through rock. As the drill advances, it creates a solid rock core, which is extracted for study.

During operation, water is supplied through the drill pipe to reduce heat from friction, but also to carry the drilling cuttings to the surface. Here at Imerys British Lithium we use triple tube drilling with an inner tube to maximise recovery of intact cores, even from variable strength ground.

The holes are just 4 ½ inches in diameter, so create little disturbance. They are all plugged upon completion, leaving little evidence of the activity behind.

What is Reverse Circulation (RC) drilling?

RC drilling is an advanced technique invented in Western Australia, commonplace in Australia, but less so in Europe. It uses a twin-walled drill pipe, fitted with an “air hammer” and tungsten drill bit. Compressed air  is blown down the “annulus”, being the space between the inner and outer pipe, powering an ‘air hammer’ to drive the rotating drill bit. This works like a household hammer-drill, to rapidly drill through solid rock.

Unlike diamond core drilling, which produces an intact rock core, RC drilling generates a pulverised sample including small rock chips. These cuttings are collected through the centre of the face-sampling bit, then blown up the inner tube and collected by a cyclone, metre by metre. This method provides an uncontaminated subsample of each metre drilled.

What happens next?

We begin by carefully capturing images of the diamond core using specialised techniques. Our skilled geologists then painstakingly record details such as lithography, petrology, structural dip, and grain size. To gain a comprehensive understanding of the deposit, we conduct measurements for moisture content, bulk density, and compressive strength.

We employ our automated saw to quarter the core length-wise. One of these quarters is dispatched to a laboratory for in-depth chemical analysis, while the remaining halves find their place in our “core library” for future reference and study.

Moving on to our RC samples, they undergo processing in our state-of-the-art sample preparation laboratory. Our geologists log a chip sample from each metre of drilling, preserving them in a chip tray library. The samples are carefully dried and split into representative sub-samples, which are then sent to an independent laboratory for chemical assay.

Ensuring the accuracy of our data is paramount, and our rigorous quality control process involves multiple independent checks. Once all the data is gathered, it is meticulously compiled into a comprehensive database. Our talented in-house geologists and mining engineers then employ sophisticated modelling techniques to map the continuity of the deposit. This includes crucial steps like “wireframing” and “domaining” to outline the zones containing minable material. Subsequently, we developed a detailed quarry design and a detailed mining schedule, over its anticipated 30-year lifespan.

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