Diamond Drilling Underground vs Surface: Costs per Metre

Whether it is diamond drilling underground from a mine drive or from a pad on the surface, the method is the same: a hollow bit set with industrial diamonds grinds an annulus of rock and leaves a solid cylinder, the core, inside the barrel. Nothing else in exploration gives you the rock intact. That is why diamond core sits at the centre of resource drilling, structural studies and metallurgical sampling, and why its cost per metre deserves close attention.

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The original version of this page focused on diamond drilling costs and discovery in Africa. That topic is still here, in its own section, but costs only make sense once you know what each method delivers. So we start with the methods, then the numbers, then the specific pressures on programs in African countries. For how diamond core fits among the other rig types, see our guide to exploration drilling methods and costs.

“Diamond core costs several times more per metre than aircore or RC, but it is the only method that returns the rock intact.”

How exploration diamond drilling works

In exploration diamond drilling, the rig rotates a string of hollow rods with a diamond-impregnated bit at the end. Water, often with drilling additives, is pumped down to cool the bit and flush cuttings. As the bit advances, core slides into an inner tube. Modern rigs use wireline systems: at the end of each run an overshot is lowered on a cable to retrieve the inner tube, so the rods stay in the hole. Ontario’s permit guide describes the finished core being stored in marked boxes, logged by a geologist and then cut in half, one half to the lab and one kept.

Core sizes and triple tube

Core size follows the wireline bit series. Geodrill’s core drilling page, for one West African contractor’s example, lists seven diameters: PQ 85.0 mm, PQ3 83.0 mm, HQ 63.5 mm, HQ3 61.1 mm, NQ2 50.5 mm, NQ 47.6 mm and BQ 34.4 mm. The “3” sizes are triple-tube versions, where a split inner liner protects broken or soft core as it comes out, at the price of a slightly thinner core.

Published figures for the same nominal size vary a little between manufacturers; a common reference lists BQ core at 36.5 mm, where Geodrill quotes 34.4 mm. Always check the exact bit specification in the contract, because core volume, and so sample mass, depends on it.

Surface diamond drilling

Surface diamond drilling covers most exploration diamond work: rigs on skids, tracks or trucks, set up on a pad and angled toward the target. Ontario’s guide notes that diamond drilling is the most common type in that province and that holes range from a few metres to several thousand metres. Surface rigs can reach deep targets and start holes anywhere there is access, but every new site needs a pad, water and a way in.

Directional diamond drilling

Directional diamond drilling steers a hole with downhole motors or wedges so it curves toward a target, or branches daughter holes off a parent hole. One deep parent with several daughters can give multiple pierce points through an orebody without re-drilling hundreds of metres of barren rock each time. It needs specialised tools and crews, so check what each bidder owns.

Diamond drilling underground: when and why

Diamond drilling underground uses compact, often electric-hydraulic rigs set up in mine drives or purpose-cut drill cuddies. From one station a rig can drill a fan of holes up, down and sideways into the orebody. Diamond drilling underground is how mines extend known lodes at depth, define the next stopes and test parallel structures without drilling from surface through hundreds of metres of cover.

What changes underground

• Shorter holes, better angles: the rig starts close to the target, so holes can cut veins nearer to true width.
• Less mobilisation per hole: moves are between stations, not across country.
• Tight space: rig size, ventilation, power and water supply set limits.
• Survey discipline: fans of holes from one set-up need accurate collar and deviation surveys to avoid overlapping pierce points.
• Integration with mining: drilling has to fit around development, blasting and haulage.

A review of underground gold grade control by Dominy and co-authors in the journal Minerals notes that diamond core and RC drilling have become important in the grade control process in many mines, alongside traditional chip and channel sampling. In other words, diamond drilling underground is not only for exploration; it feeds day-to-day mining decisions too.

Diamond drilling in mining versus exploration

Diamond drilling in mining (resource definition, grade control, geotechnical holes for stope design) tends to be closer-spaced and repetitive. Exploration diamond drilling is sparser and more speculative, and each hole carries more decision weight. The same contractor may do both, but the scope, the reporting and the pace are different, and so is the right price structure.

Planning an underground drill station

Good diamond drilling underground starts with the station. The geologist picks a position in a drive or cuddy from which a fan of holes can cut the target at useful angles, then checks that the site has room for the rig, rods and core trays, plus power, water, compressed air and ventilation. Mine surveyors mark the collar and the line of each hole. Because several holes start within a few metres of each other, small errors in set-up angle can make pierce points bunch together or leave gaps, so each set-up should be checked and recorded before drilling.

Fans also create a geometry problem on paper. Holes drilled steeply up or down from one point cut the orebody at different angles, so apparent widths vary from hole to hole. Logging the angle of each vein to the core axis, as the CIM guidelines ask, is what lets the geologist convert intercepts to true widths later.

Surface versus diamond drilling underground: where to drill from

For a deep extension below an operating mine, the choice between surface and diamond drilling underground usually comes down to three questions. How far is the target from existing development? How much barren rock would a surface hole pass through? And can the mine spare the space, power and time for a rig underground? Surface holes to great depth are long, slow and prone to deviation. Diamond drilling underground from a nearby drive can reach the same target with a fraction of the metres, but it competes with production for access.

• Favour surface when there is no nearby development, when the target lies outside the mine footprint, or when the mine cannot host a rig.
• Favour underground when drives already run close to the target and the holes would be much shorter.
• Consider both for large programs: surface for wide-spaced step-outs, underground for infill close to development.

Core handling and safety below ground

Core from diamond drilling underground has to travel to surface for logging, often in stacked trays on a shift vehicle or cage. Trays should be lidded, labelled and secured so pieces do not shift, because a disordered tray loses the depth control that makes core valuable. Underground rigs work in confined space near moving equipment, so crews follow the mine’s own traffic, ventilation and ground-support rules as well as their own drilling procedures. Ask any contractor bidding for diamond drilling underground how many underground rigs and crews it runs and what mine safety inductions its drillers already hold.

Aircore drilling and RC: the cheaper alternatives

Not every question needs core. Novo Resources’ drilling glossary describes aircore drilling as a three-blade bit on dual-tube rods, with compressed air returning samples through the inner tube to limit cross-contamination. It only cuts unconsolidated or weathered material, which makes it the tool of choice for sampling the base of transported cover and the weathered top of bedrock over large areas. Quoted base rate: $18–30 per metre.

Reverse circulation uses a hammer bit driven by compressed air, with chips returning through the inner tube. It cuts fresh rock quickly and, per the same glossary, generally gives cleaner samples than RAB or aircore, at $30–55 per metre. RC is how most programs test and outline a zone before deciding where core is justified.

RC precollars with diamond tails

A common compromise is to drill the barren upper part of a hole with RC, then switch to diamond for the target zone. The JORC Code’s Table 1 explicitly asks reports to state the “depth of diamond tails”, and Western Australia’s co-funded drilling program allows its deep diamond holes to include an RC precollar. The calculator below compares the two approaches using your own rates.

Diamond drilling costs and cost per metre

Diamond drilling costs are quoted per metre, but the invoice is built from many lines. Novo’s glossary gives diamond base rates of $110–250 per metre and warns that consumables, poor penetration, standby, mobilisation and water cartage often bring the all-inclusive figure to double the base rate. That doubling applies to every method, which is why the gap between chips and core stays wide on an all-in basis.

A public all-in benchmark

For a government reference point, Newfoundland and Labrador’s maximum allowable cost schedule caps diamond drilling at $200 per metre for its incentive rebates, all-in including standby, moves and consumables, with downhole geophysics at $25 per metre extra. Rebates are paid on actual verified costs, so the cap is a ceiling, not a price. The schedule carries no date on its face; check the current version before using it.

What pushes diamond drilling cost per meter up

• Depth: rates usually rise in depth bands because tripping rods takes longer.
• Core size: PQ and HQ cost more than NQ in bits, rods and time.
• Ground: broken, clay-rich or very hard rock slows penetration and wears bits.
• Access: helicopter support, long water lines and poor roads add moves and standby.
• Orientation and surveys: oriented core and frequent downhole surveys add time per run.
• 📊 Program size: fixed mobilisation spread over more metres lowers the average cost per metre.

What a diamond drilling schedule of rates contains

A contractor’s schedule of rates splits the diamond drilling cost into lines, so the metre rate is only part of the bill. When you compare bids, line them up item by item.

• Mobilisation and demobilisation: a lump sum to bring the rig, crew and camp to site and take them away.
• Metre rates: usually priced by core size and depth band, rising with depth.
• Moves and set-ups: a charge per hole or per pad move.
• Standby and hourly work: waiting on access, weather or the client, plus reaming, casing and cementing.
• Consumables: bits, reaming shells, mud and additives, often at cost plus a margin.
• Water supply and cartage: a separate line on dry sites.
• Surveys and orientation: downhole surveys and oriented core runs.
• Core trays, camp and meals: sometimes included, sometimes charged.

Core size also sets the downstream cost, because it fixes the sample mass per metre. Dominy and co-authors (Minerals, 2018) give about 3 kg per metre for BQ core, 8.7 kg for HQ and 15 kg for PQ. More mass means more cutting, preparation and assay cost for every metre sampled. Ask each bidder to price the same hole design so the totals are comparable.

How costs differ for diamond drilling underground

The cost per metre of diamond drilling underground is not automatically lower than on surface. Holes are shorter, so the depth-band premium matters less, and moves between stations are short. Against that, underground rigs share the mine’s infrastructure and schedule, and time lost waiting for access, ventilation or blasting shows up as standby. Contracts for diamond drilling underground often price shifts or rig-days as well as metres for that reason. When comparing surface and underground options, compare the total cost to reach each pierce point, not the metre rate alone.

With the defaults (five 400 m holes, 200 m RC precollars, midpoint rates, doubled for extras), the mixed approach costs about 38% less than drilling every metre in core. The saving shrinks as the precollar gets shorter, and disappears if the target turns out to start inside it.

Diamond drilling costs and discovery in Africa

The costs listed above apply everywhere, but some weigh more heavily in many African programs. Remote sites raise mobilisation and camp costs. Long dry seasons and scarce surface water push up water cartage, one of the extras Novo lists. Wet seasons can close roads and create standby. Consumables and spare parts may need to be imported, so a broken rig part can stop drilling for days.

Contractors and registration

Local presence matters. Geodrill, for example, lists bases in Kumasi (Ghana), Bouaké (Côte d’Ivoire), Sukari (Egypt) and Dakar (Senegal). In Ghana, drilling firms register as mine support service providers, and the Minerals Commission’s support service register lists companies such as Geodrill Ghana Limited and Orbit Garant Drilling Ghana Limited with Class A support service permits. Ask any contractor for its current registration in the country where you will drill. Our guide to picking a precision exploration drilling contractor covers the rest of the checks.

Where discovery really comes from

Drilling confirms discoveries; it rarely makes them on its own. In large, under-explored African belts, the cost that matters most is often the cost of drilling the wrong target. Tightening the target list before the rig arrives (through mapping, geochemistry, geophysics and satellite screening) usually saves more than negotiating a few dollars off the metre rate. Our geophysics hub and mineral exploration guide cover those earlier steps, and our guide to soil and stream-sediment sampling covers the geochemistry.

Diamond core drilling in mineral exploration: getting value from each metre

Diamond core drilling in mineral exploration pays off only when the core is treated as the asset it is. The CIM Mineral Exploration Best Practice Guidelines ask for core to be logged by trained staff, photographed before splitting, oriented where structure controls mineralisation, and retained for future reference. Each of those steps costs little compared with the metre rate.

1. Choose core size for the mineralisation, larger for coarse gold or broken ground.
2. Orient the core when veins or shears control grade.
3. Photograph every tray wet and dry before cutting.
4. Sample to geology, with barren shoulders on both sides of each zone.
5. Insert QA/QC samples and report them, as JORC and CIM expect.
6. Store the retained half where it will survive and can be found.

Core recovery: the number that decides what a metre is worth

A metre of core that comes back as rubble, or does not come back at all, is a metre you paid full price for and cannot fully use. JORC Table 1 asks every public report to explain how core recoveries were recorded, what was done to maximise them, and whether recovery and grade are related. That last question matters most in gold and in soft, clay-altered zones, where the lost material is often the mineralised part.

Recovery is measured run by run: the length of core recovered divided by the length drilled. Drillers can improve it by shortening runs in broken ground, reducing feed pressure, changing mud mixes or switching to triple tube. Geologists can help by warning the crew before the hole reaches a fault or a vein zone that is known to be fragile. Put a recovery target in the contract and review it weekly; it is the clearest single measure of whether you are getting value from each metre.

Choosing core size with cost in mind

Larger core costs more per metre, but it can be cheaper per useful result. In coarse gold, where a few particles carry the grade, a larger diameter gives each sample more mass and a better chance of representing the rock. In fine, evenly spread copper or base-metal mineralisation, NQ often gives assays as reliable as HQ for less money (our comparison of XRF, fusion and assay methods explains the lab side). Many programs start holes in a larger size through weak ground near surface and reduce to a smaller size at depth, which saves money on the deepest and slowest metres. Agree the size-reduction rules with the contractor before drilling, because each change costs time.

Where satellite targeting fits

Our satellite-based mineral detection screens your licence before any core is cut. We analyse multispectral and hyperspectral imagery to flag alteration halos, faults and fractures and deposit-associated patterns, with no ground disturbance, and deliver in 5 to 20 business days from coordinates, a KML/KMZ file or a polygon. The Premium+ report adds TargetMax™ Drilling Intelligence: drilling-angle recommendations aimed at higher ore-intersection probability, and 3D subsurface models of vein structures. Early exploration moves from months to days at up to 80–85% lower early-exploration cost. We have scanned 100,000+ hectares for 20+ mineral types in 25+ countries.

Targets from orbit are exploration targets, not resources; diamond drilling confirms them. See a sample of satellite-driven 3D mineral prospectivity mapping, draw your licence on mining.farmonaut.com: Map Your Mining Site, or get pricing on the mining query form.

“In many underground mines, diamond core and RC drilling now sit alongside chip and channel sampling in grade control.”

Diamond drilling cost: published figures in one table

Most published benchmarks put a diamond drilling base rate between $110 and $250 per metre, and the all-in cost can be about double that once extras are added. The figures below are public reference points, not quotes. None of the sources gives a price date, so treat them as a starting check and get current bids.

On the Novo midpoints, a diamond metre costs about four times an RC metre. That ratio, more than any single rate, is why most programs drill chips first and save core for the best zones.

Frequently asked questions

Reviewed September 2026 against the JORC Code (2012) Table 1, the CIM Mineral Exploration Best Practice Guidelines (2018), Ontario’s Early Exploration Permit Activity Information guide, Newfoundland and Labrador’s maximum allowable cost schedule, Novo Resources’ drilling techniques and costs glossary, Geodrill’s core drilling page, the Ghana Minerals Commission support service register and Dominy et al. (2018) in Minerals.

Rates and caps are published benchmarks, not quotes, and change over time; confirm with contractors before budgeting. Satellite targets are exploration targets, not mineral resources.