Exploration drilling
Exploration drilling with core recovery to prospect for minerals and groundwater.
Exploration holes are drilled to study the subsurface and establish whether a mineral or water is present, at what depth and in what volume. Before a deposit is developed or a major investment is committed, only these holes give reliable data about the ground.
Where it is used
- Ore exploration — tracing the extent, thickness and grade of orebodies.
- Construction materials — proving reserves for limestone, clay, sand-and-gravel and dimension-stone quarries.
- Groundwater prospecting — locating aquifers ahead of large water-supply projects.
- Infill drilling at existing deposits — refining reserves and the mine plan.
Wireline core drilling
The main exploration method is core drilling. A diamond bit cuts an annulus of rock, and the cylinder left in the middle, the core, passes into the core barrel. With wireline, the inner tube is hoisted on a cable through the rod string without pulling the rods, which saves a great deal of time in deep holes.
Core quality is measured as core recovery: the share of each drilled metre that comes up as core. The higher the recovery, the more reliable the logging and assays, so drilling parameters, fluid and tooling are matched to the rock.
Choosing a size
| Size | Hole diameter | Core diameter | Typical use |
|---|---|---|---|
| PQ | 122.6 mm | 85.0 mm | soft and broken ground, large sample volume |
| HQ | 96.0 mm | 63.5 mm | early-stage exploration, fractured rock |
| NQ | 75.7 mm | 47.6 mm | the most common size, balancing depth and sample |
| BQ | 60.0 mm | 36.5 mm | deep holes, faster and cheaper drilling |
In difficult ground a hole is collared in a larger size and then reduced. The larger rods are left in place as casing.
Handling the core
- As soon as it is brought up, core is laid in boxes in depth order.
- The start and end of every run are marked with core blocks.
- Recovery is measured and entered in the log.
- Boxes are labelled and photographed.
- After geological logging, samples are selected and packed for the laboratory.
Work sequence
- Agreeing the programme: hole locations, depths and size.
- Preparing the pad, arranging water and access.
- Drilling, boxing core and daily reporting.
- Abandoning the hole or keeping it for monitoring, cleaning up the site.
- Handing over drill logs, photographs and core boxes.
When you get in touch, tell us the area, the number and depth of holes, the core size you need and the rock you expect. If there is no geological data yet, say so and we will help you choose the size and tooling.