Carver Industries
Diamond Exploration and Mining
Modern
exploration uses highly sophisticated technologies to determine the economic
viability of deposits. Examples include airborne surveys.
Geophysicists carry out the Ground Geophysical surveys, which are used as a
follow-up tool to detect and improve definition of anomalies associated with
kimberlite intrusions. Most exploration teams have one or more geophysicists
helping to manage the application of appropriate geophysical techniques and
interpretation of data. Frequently used geophysical methods include:
- Magnetics (both airborne and ground)
- Airborne multi-spectral analysis (AMS)
- Various suites of electro-magnetics
- Gravity
- Radiometric
- Seismic
Kimberlite, alluvial and marine mining use different techniques. Kimberlite mines are underground or open-pit. Alluvial stones may be mined commercially or on a small scale. Marine alluvial mining involves specialised ships. Diamonds are mined on all continents.
Once diamonds are detected, there are different types of mining operation used to extract them depending on the environment in which they are found. The majority of diamonds are extracted on an industrial scale by open pit mining and underground mining.
Open pit mining is excavation to reach diamonds on the surface of the ground. Underground mining is excavation up to and, in some instances, over 1km below ground.
Following extraction, the ore containing the rough diamonds goes through many stages of crushing and processing before it can be sorted and classified.
Diamonds are also extracted from alluvial deposits, where they are removed from sand, gravel and clay that has been naturally transported by water erosion and deposited along either the banks of a river, the shoreline or on the bed of the ocean. This process is called alluvial mining and is undertaken on an industrial scale by coastal and inland mining, which is removal of overburden, such as sand and soil, to find diamonds; and by marine mining, which is excavation of diamonds from the seabed.
Diamond mining on a non-industrial scale is undertaken involving individuals, families and communities and using the most basic equipment, such as sieves and pans – this is known as artisanal digging.
Rough diamonds are sorted based on characteristics such as shape, size, color, cuttability and quality. The Diamond Trade Company (the distribution arm of De Beers) sorts and distributes 45% of the world’s rough diamond supply. The balance is sorted and sold in centers such as Antwerp and more recently Mumbai. The DTC exclusively sells to 93 clients that are called “Sightholders”.
Once processed at the mine, rough diamonds are typically delivered to sorting experts to be sorted and valued into 12,000 different categories in preparation for sale.
These categories are dependent on size, shape, quality and color. The majority of diamonds fall within a range of standard colors from colorless to faint yellow or brown tints. Some very rare diamonds, known as ‘fancies’, are bright colors, such as pink, blue or green.
A perfectly transparent diamond with no color or hue is considered to be the purest, but all rough diamonds have some distinguishing marks, known as inclusions, which make each one unique. The Diamond Trading Company sorts, values and sells around half of the world’s rough diamonds – selling in excess of $6 billion worth of diamonds a year.
The best quality diamonds in terms of color and clarity are distributed to the gem market with an accompanying Kimberley Process certificate to prove that they are from conflict free sources. The remainder is ultimately used for industrial purposes, such as cutting and drilling.