Where are diamonds found?
Diamonds were probably formed millions of years ago in molten lava. As the lava flowed to the Earth’s surface through vents known as pipes, it cooled and solidified into kimberlite, a blue rock. Kimberlite contains the diamonds and is known to diamond miners as blue ground. Diamonds have been found on all continents. India was once a chief source. About 600 AD diamonds were found in Borneo and are still mined there. The rich fields of Brazil was discovered in the 1700s. In the 19th century even richer diamond fields were found in South Africa. Most of the world’s diamonds are mined in African countries. Zaire produces mostly industrial diamonds. South Africa is the major source of gem-quality diamonds. Congo, Ghana, Namibia (South West Africa) and Angola are other major suppliers. Russia has diamond-mining operations in northeastern Siberia and since the late 1970s many diamond finds have been made in Australia. About 20 percent of the world’s output is used for industrial purposes, wi
Diamonds are usually found in association with igneous rocks that are derive directly from mantle rocks (kimberlites and lamproites). These rocks rose from the mantle and intruded into the crust in relatively narrow bodies called pipes. These are usually found only in old crust. The problem with locating these pipes is that they don’t seem to be related to crustal geology. So, it is difficult to predict where we will find them. Most such pipe were discovered because someone stumbled across diamonds in sediments derived from them and followed the diamonds back to the pipes. As for just where diamonds are known to exist and are being mined today, take a look at http://www.amnh.org/exhibitions/diamonds/world.html and you will find a map and a graph showing diamond production by country from 1860 to 1995. You will also find much more info on diamonds at that site.
Geologists use many methods to explore for kimberlites, including satellite remote sensing, geophysics and reconnaissance sampling, before drilling the kimberlites themselves to establish whether or not they contains economic quantities of diamonds. The first step is generally to investigate areas with a history of diamond recovery, and then to follow up with stream or deflation sampling for evidence of kimberlite indicators such as garnets. Thereafter, the use of geophysics to search for magnetic anomalies is applied. Sampling and drilling are then used to confirm whether the anomalies are indeed kimberlites. Once an anomaly has been confirmed as a kimberlite, heavy mineral analysis (HMA) sampling of representative material is carried out as a quick and efficient method of assessing whether the kimberlite has the potential to be diamondiferous. Micro-diamond and mini-bulk sampling are then used to establish if there is the potential for those kimberlites prioritised by HMA sampling to
