ALLUVIAL

 DIAMONDS

Regional erosion of areas containing kimberlite intrusions results in different levels of preservation.For example, the largest economically important kimberlite in the world are Mwuadui in Tanzania (146 ha),Orapa(106 ha) and  Jwaneng (51 ha) in Botwana ,and Udachnaya (52 ha) in Siberia.These Kimberlite have suffered very little erosion and their crater facies were stillpreserved prior to mining. The processes  that led to the deposition and the concentration of diamond in rivers sediments are obviously of direct ;economic importance in the formation of mineable alluvial diamonds deposits.They also carry a secondary significance in concentrating associated minerals ('indicator minerals'),such as garnet and ilmernite which can guide prospecters to the primary sources.