Koidu Limited


Diamonds Doing Good

One of our objectives is to demonstrate that through responsible development of diamond projects, the good that flows into the local communities, the economy and the country.  Through perseverance and by investing back into the Company and Community this has provided the community with access to clean drinking water, promotes education and training, provides free healthcare and develops infrastructure, all with a long term view that what we do well today, will enable others to prosper tomorrow.

Diamond Deposits FAQs

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.
Kimberlite magmas form by melting of the Earth’s mantle at great depths, between 200 and 670 kilometers below surface. As the kimberlite magma ascends towards the surface, it interacts with and incorporates large amounts of upper mantle material. Ascending kimberlite magma can either solidify below the surface as dykes (vertical sheets), sills (horizontal sheets) and plugs (small pipe-shaped intrusions) or erupt at surface to form pipe-like bodies and / or craters filled with volcanic kimberlite.
Diamond is a very high pressure mineral that can only form and be preserved in significant quantities at depths of > 120 km within the Earth’s mantle below the thick stable parts of continents. It forms locally within mantle rock types such as peridotite and eclogite, most likely as a result of the influx of carbon-rich fluid. Most gem diamonds are apparently very old, having formed between approximately 1 and 3.6 billion years ago.
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.
Diamond deposits are termed primary when diamonds are found in the host igneous or volcanic rocks. The host rock types in which significant quantities of diamond can occur include kimberlite and, more rarely, orangeite and lamproite, igneous rocks with similar characteristics to kimberlite. Primary diamond deposits occur as intrusions (dykes, sills, plugs) and volcanic pipes.
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.
Some kimberlites are emplaced as steeply-dipping sheet-like bodies known as dykes. These can form complex systems of multiple dykes that extend for many kilometers and may be exposed at surface. The dykes consist of coherent kimberlite (i.e. that formed by direct cooling and crystallisation from a magma) and can vary in width from less than a centimeter to more than a meter. Small pipe-like features known as blows are occasionally formed along such dyke systems. These can be cylindrical to irregular in shape and may consist of coherent kimberlite and volcaniclastic kimberlite (i.e. kimberlite formed following explosive fragmentation of the magma by volcanic processes).
Some kimberlites occur as steep-sided pipe-like bodies that are the erosional remnants of kimberlite volcanoes. These generally occur as clusters of two or more pipes. Kimberlite pipes are commonly filled with volcaniclastic kimberlite, a mixture of fragmented kimberlite and country rock material. Kimberlite pipes are sometimes associated with previously-formed kimberlite dykes and the pipes themselves may be cross-cut by later kimberlite dykes. The surrounding host rock is commonly brecciated and altered as a result of pipe formation.

Types of Diamond Deposits

The Kimberley Process

Sierra Leone and the Kimberley Process Certification Scheme

With the burden of being the birthplace of the concept of “conflict diamonds”, The Republic of Sierra Leone carries the tremendous responsibility to its citizens and the international community to ensure that diamonds recovered from the alluvial river gravel deposits mined by the many artisanal mining licence holders, as well as those liberated from the hard rock kimberlite pipes and dykes by large-scale commercial, mechanised mining operations like Koidu Limited, are not used to fund armed conflict anywhere in the world.

The Kimberley Process Certification Scheme (KPCS) was established in May 2000 to find a solution to the international problem of the trade in conflict diamonds, “which can be directly linked to the fuelling of armed conflict, the activities of rebel movements aimed at undermining or overthrowing legitimate governments, and the illicit traffic in, and proliferation of, armaments, especially small arms and light weapons”.  The KPCS is an international certification scheme for rough diamonds, based on national laws and practices and meeting internationally agreed minimum standards.

The KPCS imposes extensive requirements on its members to enable them to certify shipments of rough diamonds as “conflict-free” and prevent conflict diamonds from entering the legitimate trade.  Under the terms of the KPCS, participating States must meet ‘minimum requirements’ and must put in place national legislation and institutions; export, import and internal controls; and also commit to transparency and the exchange of statistical data.  Participants can only legally trade with other participants who have also met the minimum requirements of the scheme, and international shipments of rough diamonds must be accompanied by a KP certificate guaranteeing that they are conflict-free. As a participant in the Kimberley Process Certification Scheme, the Government of Sierra Leone has undertaken to implement the principles and internal controls recommended. The recommendation for control over diamond mines calls for participants “to ensure that prospecting and mining companies maintain effective security standards to ensure that conflict diamonds do not contaminate legitimate production”.  All diamond mines around the world are required to have very strict access control.  Koidu Limited, with the support of the Government of Sierra Leone, are taking steps to continuously improve our compliance with the Kimberley Process. These include having an extremely well controlled Chain of Custody, following the movement of our diamonds from each ore source through the mining, processing and export processes.

Diamonds of Sierra Leone

Famous Diamonds of Sierra Leone

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.

The Star of Sierra Leone

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.

Koidu Diamonds