Exploration diamond drilling

Exploration Diamond Drilling

Technique of geological core drilling

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Exploration diamond drilling is a crucial method in the mining sector to examine known ore deposits and prospective sites. Utilizing a small-diameter core extracted from the orebody, geologists perform chemical assays and conduct petrological, structural, and mineralogical studies on the core sample. In geotechnical engineering, this technique is often employed in foundation testing alongside soil sampling methods. The procedure is named after the diamond-encrusted drill bit used in the process.

History

Rodolphe Leschot is frequently credited with inventing the first core bit in 1863. Early advancements in diamond drilling expanded mineral mining into previously inaccessible regions, spurring a surge in mineral exploration in remote areas. Prior to portable diamond drills, mineral prospecting was mainly restricted to surface outcrops and manual digging. In the late 1970s, General Electric introduced polycrystalline diamond compacts (PDCs) as a substitute for natural diamonds in drill bits.

Diamond Drilling

Exploration diamond drilling sets itself apart from other geological drilling methods, such as Reverse Circulation (RC) Drilling, by extracting a solid core for surface examination. The diamond drill's key component is its diamond bit, made from industrial diamonds set into a soft metallic matrix. As drilling progresses, the matrix gradually wears down, revealing more diamonds.

This diamond bit is attached to a core barrel and connected to a drill string, which is then connected to a rotary drill rig. Drilling mud is circulated through the drill pipe to clear rock cuttings and reduce heat from friction, thereby minimizing bit wear. Diamond bits are complex tools, often designed for specific rock types and featuring multiple channels for effective washing.

The drilling process yields a "core," which is photographed and split longitudinally. One half is assayed while the other half is stored permanently for possible future testing. Larger diameter cores are typically preferred but are also more costly. Standard wire line tube diameters are NQ (47.6mm) and HQ (63.5mm).

Core Extraction

During drilling, core extraction at depths around 300 meters requires an efficient method for retrieving the core. Constantly withdrawing the entire drill pipe is impractical; hence, wireline drilling methods are employed to retrieve the core within the barrel. This is crucial for applications that necessitate undisturbed cores in fractured rock formations.

The core is often extracted using a triple-tube wire-line system, which is capable of retrieving core even under the most challenging conditions, such as fault zones like the San Andreas Fault.

Tube Sizes

Several "wire line" tube sizes are available, each designed to balance the desired rock core diameter with the depth achievable by the drilling rig. Larger tubes yield larger rock cores but require more power to operate.

Standard "Q" wire line bit sizes:

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