Kimberlite discoveries in NW Liberia: Tropical exploration & preliminary results

Abstract

This report is brief in context and rich in unexpected discovery. With >2km of erosion, kimberlite models predict the near-complete removal of pipes with exposures to the pipe-root-zones of dikes. Exploration in NW Liberia has, indeed, uncovered eight kimberlite dikes (~10m wide) but also an en echelon pipe, comparable in size to the Kimberley pipe and De Beers' pipe in South Africa. Discoveries are in a narrow 200–300m wide valley of extraordinary thick bush, undergrowth, and organic overburden. Ilmenite and co-existing leucoxene were used as diagnostic tracers for detecting hard rock kimberlite in this tropical terrane. Micro-diamonds show that the redox state of ilmenite is a potentially useful proxy as an index for macro-diamond preservation. The tectonic control of kimberlites is complex, with diverse lithologies. Discoveries include a well-defined regional trend for kimberlite dikes along paleo-fracture zones, Precambrian in age (Liberia Trend), coupled with kimberlite dikes on the craton that are traced to Mesozoic oceanic transform faults (the Sierra Leone Trend). Although long predicted, this is the first report of kimberlite dike-trends in Liberia that are similar in orientation to those in Sierra Leone. An explosive blow on a Liberia-Trend dike demonstrates a similarity to the dynamics attendant in rich (50–500cpht) diamond-bearing dikes in Sierra Leone, and in South Africa of comparable age. The potentially high grade dikes, along with the pipe (~500×50m), now more reasonably accounts for the enormous number of alluvial diamonds (blood and non-conflict), recovered over more than seven decades, downstream from the discovery cluster.A neglected region since the classic work by Bardet (1974), and with few contributions on Liberia since then, an update is considered timely, particularly in the context of discoveries of diamond-bearing kimberlite.