Geo skool




Drilling is the most common means of investigating what sort of mineralization exists beneath the ground surface.  There are several reasons to drill:

  • to determine the position or shape of underground formations

  • to ascertain the presence or absence of veins, ore bodies, or other type of mineral deposit

  • with more more, to estimate the tonnage and grade of an already discovered mineral deposit

Drilling requires a large amount of infrastructure and raises logistical and geological decisions: where to drill, the type of drill required, what road construction is required, and proximity to water.

Drill rigs in mineral exploration are smaller than those normally used in oil exploration, and can even be man-portable.

The aim of a drill program is to intersect the ore body as close to a 90 degree angle as possible.  If the drill intersects with the ore body, then the geologist cal estimate the width the vein at the intersection.  If multiple holes intersect the vein, the geologist can begin plotting the veins geometry from which the tonnage and the grade of the deposit can be developed.



Diamond drills:

Designed specifically for the resource exploration industry, diamond drilling is the most versatile of all drilling methods and the only method that generates core.  A core sample is a cylindrical section rock – usually 10 to 15 centimetres in diameter – and generates reliable samples for accurate geochemical assaying along the depth of the drill hole.

Diamond drilling consists of a ring-like bit studded with small, industrial grade diamonds mounted to the end of hallow doubled-walled shaft.  The bit rotates and cuts out a cylindrical core of rock, which is stored in the inner shaft of the drill rod, known as the core barrel. Water or mud is pumped down between the inner and outer rods to lubricate and cool the cutting surface, while sludge and rock chips comes up on the outside between the shaft and casing. 

In optimum conditions, drilling can advance at a rate of 10m per hour, but in exceptionally hard ground the rate is far slower. Costs vary with the length of the hole, but on average holes up to 300m cost approximately $50 - $80 US per meter.


Reverse Circulation (RC) Drilling:

Reverse circulation drilling uses a tungsten-studded button bit to bore a hole into the rock.  A pneumatic piston forces compressed air and water down the outer shell of a double-walled rod and drives the bit to cut and hammer the rock.  Air, water, and rock chips are then sucked back up the inner rod by the air differential.  At the top, the rock and water are separated by a cyclone, and the rock is deposited in a sample collection container. 

RC drilling is cheaper and faster than diamond drilling and has additional advantage that all the drilled rock is collected.  In contrast, diamond coring can be extremely slow in very hard rock. However, RC drilling only produces fragments and chips of broken rock, and so less geological information is available than would be obtained from core.

Collaring a Hole

Collaring a hole






Almaden Minerals