Wireline Drilling

    Most of the drilling which is done nowadays is done by using the wireline method, this method was introduced in the 1960s. By using this method, an inner tube containing the core is detached from the core barrel assembly when the core barrel is full or a blockage happens. The tube and core contained in it are pulled up to the surface by a wire which is dropped down the string of drill rods. An overshot assembly which snaps on to the top of the inner tube or latch is used for this specific purpose, the inner tube is then quickly hoisted to the surface within the string of drill rods.

    After the removing of the core, the inner tube is dropped down into the outer core barrel and the drilling continues. This way, the core is removed without the necessity of having to pull out all of the rods.

    Cores of up to 100 mm in diameter have been recovered by large drills from depths of more than 15,000 feet (4,500 meters).

    The core is carefully placed in sequential order in trays or boxes and are taken to an office for examination by geologists or to a geological field camp. Sections which are interesting are split along their length by a splitter of cores, with half of the section being put back in its place in the core box and the other half is sent to an assayer for careful analysis. The boxes or trays are most of the time stored on racks in a core shack.

    It is sometimes desirable to get a second intersection of a particular ore zone or geological structure from a single hole. This action is done by placing a wedge at some point above the intersection to deflect the bit in another direction. This procedure of wedging is frequently used in deeper holes, where it can save money and time considerably.