The importance of the transport system in shaping the growth and form of kimberlite volcanoes

Transport of kimberlite magma from the mantle to the surface is a complex process that involves many, often sudden and dramatic, changes in transport style. The pace and magnitude of changes in the transport system acclerate as the magma nears the surface, culminating in eruptions during which multiple transport events take place simultaneously as well as single transport events that change significantly from their point of origin to final deposition. Understanding the range of transport styles recorded by kimberlite deposits is key to describing the type and style of eruptions, the growth of cones and craters, and the distribution, geometry and structure of the deposits that make up kimberlite volcanoes. In an economic context, building a clear picture of the processes that shape deposits is essential for selecting exploration targets and evaluating the grade and value of diamond-bearing kimberlites. Variations in diamond grade reflect differences in the diamond content of different magma parcels erupted during the lifetime of the kimberlite volcano, sorting during transport of eruption products, or re-working of diamonds during crater growth, cone collapse and erosion. Deep transport systems control delivery of magma and diamonds to eruption sites The initial stages of kimberlite transport involve rise of magma in narrow, interconnected networks of fluidfilled fractures. There is compelling evidence that kimberlite magmas are extracted from their source region and erupted without significant residence times in the crust. Many single kimberlite volcanoes have significant variations in diamond grade between different kimberlite phases, suggesting eruption of distinct (perhaps unrelated) magma parcels at the same site.