Diamond Mining

Insight into diamond mining in Sierra Leone and the workings of a fully operational diamond mining site


Campbell Coyle Gems Ltd ventures into Sierra Leone, the birth place of the famous “The Star of Sierra Leone” diamond which is featured further down on this Page.

Campbell Coyle Gems Ltd looks forward to the future of progressive diamond mining in Sierra Leone where we will be able to source “from pit to polish” diamonds for the investment market.

Read more about diamond deposits, the Kimberley Process as well as diamonds of Sierra Leone. For all enquiries related to diamond investments, please feel free to visit our contact page to retrieve all necessary contact details.


Two of the world’s ten largest and most famous rough diamonds were discovered in the gravels of the Woyie River flowing through the town of Koidu. Tributaries of the Woyie River have drained the areas surrounding the Koidu kimberlite pipes and dykes over millions of years, concentrating diamonds and other heavy minerals derived from the kimberlite into rich alluvial diamond deposits.

The first large diamond to be recovered from the Woyie River in March 1943 weighed 249.25 carats, followed by an even larger 532 carat stone in June of the same year. The Woyie River Diamond, weighing 770 carats, was found in January 1945 and, at that time, was the largest alluvial diamond known. After a hiatus of almost 27 years, the fourth and largest diamond to be recovered from the Woyie River presented itself on the picking table of the Diminco recovery plant. The Star of Sierra Leone, as it became known, weighed 968.9 carats and is currently ranked the third largest rough diamond in the world, with the Woyie River Diamond in sixth place.

Although being of the finest colour, both the Star of Sierra Leone and the Woyie River Diamond contained flaws and impurities which dictated the number and shape of the polished stones finally separated from the original rough diamond. The Star of Sierra Leone was first cut into an emerald shaped stone weighing 143.2 carats but was later re-cut due to an internal flaw into seventeen smaller stones. Six of the stones, including the largest which weighed 53.96 carats, were incorporated into the Star of Sierra Leone Brooch. The Woyie River Diamond was cut into 30 gem stones, the largest of which was an emerald cut weighing 31.35 carats and became known as the Victory diamond.


Kimberlite is a special type of igneous rock that sometimes contains diamond. It is named after the town of Kimberley in South Africa, where kimberlite was first recognized (in the late eighteen hundreds) as a primary source of diamond. Kimberlites are relatively rare and occur in continental areas as small intrusions (dykes, sills and plugs) and as volcanic pipes.

They range in age from about 45 million to in excess of 2 billion years. Depending on their mode of formation, kimberlites can be highly variable in appearance and mineral content. However, they are usually dark rocks that contain high concentrations of olivine and an unusual suite of minerals that are very important for their exploration and evaluation.


Because kimberlites are generated at great depths below continents and interact with mantle material, they sometimes incorporate pre-existing diamond-bearing rocks. These can be retained within the magma during its ascent through the Earth’s upper mantle and crust, resulting in trace quantities of diamonds in the final kimberlite rocks preserved at surface.

Diamonds may occur as inclusions contained within fragments of mantle rocks in the kimberlite or, more commonly, are liberated from their original host rock and dispersed within the kimberlite. About one in 100 kimberlite pipes contain gem-quality diamonds and only a very small proportion of these contain sufficient quantities of diamond to support economic extraction.

Other rock types can be diamondiferous, but kimberlites are by far the most important source for economic concentrations of diamonds. 


Alluvial diamond deposits are formed as a result of surface weathering and erosion of primary diamond deposits over millions of years. The diamonds are transported by rivers, and deposited and concentrated in a new environment such as certain portions of the river bed, a shoreline or an ocean floor.

Diamond, being the hardest known natural mineral, survives weathering, erosion and transport. Alluvial diamond mining is the process by which diamonds are recovered from such deposits. Around 10% of the world’s rough diamonds are sourced through industrial alluvial mining and 14% through artisanal or small-scale informal alluvial diamond digging.


When starting a diamond operation it is imperative to have the best earth moving machinery backing up your production.

Always make sure to speak to a qualified consultant in the earth moving machinery Industry to find out which machines will best suit your operation and given how big or small your operation is, an expert  earth moving machinery consultant may advise as to the sizing of machinery which is best suited to your mining operation without breaking the bank. 

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