Diamond Core Drill Rig

Overview

A diamond core drill rig is the standard machine of mineral exploration. Rather than breaking the rock into chips, it grinds a thin circular kerf with a diamond bit and leaves a solid cylinder of rock in the center, which it recovers intact as core. That core is the most valuable data in exploration: it shows the rock fabric, the grade, the structure, and the contacts exactly as they sit underground. The rig turns a diamond-set bit on a string of hollow rods while pushing it down with controlled thrust, circulates fluid to cool the bit and clear cuttings, and uses a wireline system to pull each core run up the inside of the rods without tripping the whole string.

The major systems work together on every run. The Mast and Feed sets the hole angle and feeds the bit, the Rotation Head turns the rods, the Power Pack pack and Hydraulic System supply the energy, the Drill String and Bit does the cutting, the Drilling Fluid System system circulates mud, the Wireline Retrieval retrieves the core, and the driller runs it all from the Operator Controls console on the Carrier Chassis carrier.

Rotation and feed

Coring needs steady rotation and carefully metered thrust. The Rotation Head carries two Head Hydraulic Motor piston motors driving through a Gearbox Housing and Helical Gear Pair gears, which gives the operator a low-speed high-torque range for hard ground and a high-speed range for fast cutting. A Drill Chuck grips the rod, the Drive Spindle passes fluid through while it turns on Ball Bearing bearings sealed by Oil Seal seals, and a Water Swivel feeds mud into the spinning string. Thrust comes from the Mast and Feed: a pair of Feed Cylinder cylinders work through a Feed Chain so the head can travel a full rod length, and the Angle Pivot sets any hole angle from vertical to flat. Getting feed pressure right is the heart of the driller's skill: too little and the bit polishes, too much and it wears or jams.

The drill string and bit

The Drill String and Bit is what actually cuts. A Diamond Core Bit set with industrial diamonds in a metal matrix grinds the annular kerf, while a Reaming Shell just above it keeps the hole to gauge. The cut cylinder passes up into the Core Barrel, a double tube whose Outer Tube rotates with the string while the Inner Tube stays still on bearings in the Barrel Head, so the core is not twisted as it forms. When the run is full, a Core Lifter grips and snaps the core off so it can be brought up. The rods, dozens of Drill Rod lengths threaded end to end, carry both the torque and the drilling fluid down to the bit.

Wireline core retrieval

The wireline system is why diamond drilling is efficient at depth. Instead of pulling every rod out of the hole to empty a core barrel, the Wireline Retrieval drops a Overshot on a thin Wireline Cable down the inside of the hollow rods, latches the loaded inner tube, and the Wireline Winch hauls it to surface over the Mast Sheave. An empty inner tube is then dropped back down and pumped to bottom. Only when the bit wears out does the whole string come out, so a deep hole is drilled with very little rod tripping, which is the main saving in time.

Power, hydraulics, and fluid

A turbocharged Diesel Engine diesel drives the rig through a Pump Drive Gearbox gearbox into the Hydraulic System system, where two Main Pump piston pumps feed a Valve Bank that the operator controls. Oil draws from the Hydraulic Tank, passes a Oil Cooler and Return Filter filters, and runs everything from rotation to feed to winch. The Drilling Fluid System system is separate: a Triplex Mud Pump triplex pump pushes water mixed with polymer and bentonite from a Mixing Hopper down the rods to cool the diamonds, carry rock flour out, and hold the hole open. Without circulation the bit overheats and the core is lost.

Carrier, controls, and operation

The whole rig rides on a Carrier Chassis carrier, usually a tracked Track Frame that walks into remote sites, with Leveling Jack jacks to anchor and level it at the collar. The driller works from the Operator Controls console, reading a Gauge Cluster cluster and an LCD Panel for feed and rotation pressure, with a Rotation Guard around the turning rods and Emergency Stop stops within reach. A run cycle is drill ahead one core length, wireline the inner tube up, empty and log the core, drop the tube back, and repeat.

Core sizes, depth, and use

Rigs are sized by the core diameter they cut, from slim BQ for deep holes through NQ and HQ to large-diameter PQ for metallurgical samples, and the same rig often drills several sizes by changing the string and reducing as the hole gets deep. Depth capacity ranges from a few hundred metres on a light rig to well over a kilometre on a heavy one. Diamond coring is the method of choice when the geologist needs intact rock for grade, structure, and geotechnical work; where only chip samples and speed matter, a Reverse Circulation Drill Rig is faster and cheaper. The oriented structural data a diamond hole provides is often recorded with a Drill Core Orientation Tool run in the same string.