Every diamond drilling program starts with a decision about core size, and that decision follows the core all the way to the core shed. BQ, NQ, HQ and PQ are not just drilling codes: they determine how much rock you recover per metre, how heavy each run is, and what kind of tray the core needs to sit in. Choosing a tray that does not match the core diameter leads to cramped channels, damaged core and a lot of wasted handling time, so it pays to understand the sizes before ordering anything.
What BQ, NQ, HQ and PQ Mean
These are the standard wireline core sizes, listed from smallest to largest. Each code corresponds to a drill hole diameter and to the diameter of the core that comes out of it:
- BQ: about 36.4 mm core from a hole of roughly 59.9 mm. Often used in shallow or tight-budget exploration and underground drilling.
- NQ: about 47.6 mm core from a hole of roughly 75.7 mm. The most common exploration size, and the one that offers the best balance between depth capacity and sample volume.
- HQ: about 63.5 mm core from a hole of roughly 96 mm. Typical for resource definition and for ground where better recovery is needed.
- PQ: about 85 mm core from a hole of roughly 122.6 mm. Used for large-diameter, metallurgical or geotechnical samples, and in broken or unconsolidated ground.
Variants such as NQ2 and HQ3 use different inner tubes or bit profiles to improve recovery or adjust core size, so it is worth confirming the actual core diameter with the drilling contractor before ordering trays.
Why Core Size Matters Beyond the Drill Rig
Larger core gives more sample per metre, better recovery in broken ground and more material for metallurgical testing, but it costs more and drills more slowly. It is also much heavier: an HQ core metre weighs noticeably more than an NQ one, and larger drill strings place greater demands on the rig. As a result, most standard exploration rigs are far more comfortable with NQ at depth than with PQ.
Many programs use a telescoping strategy to manage this. The hole is started in a larger size through weak surface ground, then reduced to a smaller size as the rock becomes more competent. A single hole can therefore produce more than one core size, which means the sample chain has to handle more than one tray format.
How Core Size Determines Tray Size
A core tray is organized into channels, and each channel has to be slightly wider than the core it holds so the core can be laid in and removed without forcing it. That is why tray sizes follow the drilling codes: you choose an NQ tray for NQ core, an HQ tray for HQ core, and a PQ tray for PQ core.
Three tray characteristics matter most when matching:
- Channel diameter: it should be a few millimetres wider than the core. For example, Coreplast’s Model 2 HQ4 tray has a 69.5 mm channel for HQ core of about 63.5 mm, and its NQ5 tray has a 53 mm channel for NQ core of about 47.6 mm.
- Number of channels: thicker core means fewer, wider channels per tray. An HQ tray typically has four or five channels, while a PQ tray has only two.
- Linear capacity: the total metres of core the tray holds. Capacity is what lets you work out how many trays a hole will need.
Matching Coreplast Trays to Each Core Size
Coreplast’s range of core trays covers the most common sizes across three models, so teams can choose by core diameter and by how they plan to transport and store the trays:
- Model 1: available in HQ4, NQ5 and PQ2 formats, with matching separators and lids.
- Model 2: described as the lightest tray in the range, in HQ4 (4 linear metres of capacity) and NQ5 (5 linear metres) formats. It features drainage holes, built-in handles, measurement marks, stacking capability and nesting that saves around 40% of space during transport.
- Model 3: a half-metre format in HQ5 and NQ5, each with 3 linear metres of capacity, extra ribbing for strength, embossed measurement marks and nesting that saves around 80% of space during transport.
All trays are made from non-toxic polypropylene, and the nesting capability matters in practice: empty trays that nest take up a fraction of the volume when they are sent back to a drill site, which reduces freight costs.
How Many Trays Does a Hole Need?
Once the core size and the tray model are chosen, the number of trays is a simple calculation: divide the planned hole depth by the linear capacity of the tray, then add a margin for broken core, rubble intervals and the partially filled tray at the end of every hole. As an example, for a 500 m hole:
- Model 2 HQ4 (4 m per tray): 125 trays before margin.
- Model 2 NQ5 (5 m per tray): 100 trays before margin.
- Model 3 HQ5 or NQ5 (3 m per tray): about 167 trays before margin.
It is always better to order a few more trays than the math suggests, since broken ground and partial trays use more space than the nominal capacity implies.
Common Mistakes When Choosing Tray Size
- Ordering by nominal size without checking the actual core diameter. Variants like NQ2 or HQ3 can change the core diameter slightly.
- Forgetting about telescoped holes. A hole that starts in PQ and finishes in NQ needs trays for both sizes.
- Ignoring tray weight and format. A full tray has to be lifted, stacked and carried by people, so a lighter model or a half-metre format may suit certain sites better.
- Underestimating quantity. Not allowing for broken core and partial trays leads to last-minute shortages in the field.
Frequently Asked Questions
What is the difference between BQ, NQ, HQ and PQ core?
They are standard wireline core sizes with approximate core diameters of 36.4 mm (BQ), 47.6 mm (NQ), 63.5 mm (HQ) and 85 mm (PQ). Larger sizes provide more sample per metre and better recovery in broken ground, but they cost more and drill more slowly.
Can I store NQ core in an HQ tray?
It is not recommended. Trays are designed with channels that match a specific core diameter, so smaller core will move around in a larger channel and can be damaged or disordered during transport. It is better to use the tray size that corresponds to each core size.
How do I calculate how many core trays I need for a drill hole?
Divide the planned hole depth in metres by the linear capacity of the tray you are using, then add a margin for broken core and the partial tray at the end of the hole. For example, a 500 m hole in a tray that holds 4 m of core needs 125 trays before margin.
