Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

Songwe Hill, Chilwa Province, Malawi

The Chilwa Alkaline Province, in southern Malawi and adjacent areas of Mozambique is perhaps one of the most classic areas of carbonatite and alkaline magmatism. It comprises large alkaline intrusions ranging from Mulanje, which is a massif that covers approximately 640 km2 and rises some 3,000 m above the Phalombe Plain (750 m), to the Michese intrusion with a diameter of 8 km, to the smaller Machemba intrusions and minor plugs and dykes measuring only a few tens of metres in length. These intrusive centres, mainly early Jurassic, are remarkable for their diversity of rock types which include granites, quartz syenites, syenites and trachytes, nepheline syenites and phonolites, ijolites and nephelinites, and a plethora of dykes and carbonatites with associated fenites. The Province contains a number of major historically known rare earth and Nb deposits of which the Songwe Hill rare earth deposit is now the most advanced. Lancaster’s exploration activities at Songwe Hill have consisted of litho-geochemical sampling, soil sampling, channel sampling, geological mapping, ground magnetic, density and radiometric surveys, high-level petrographic and mineralogical analyses and two extensive diamond drilling campaigns. During the drilling campaigns, a total of 38 inclined and vertical diamond drill holes totalling 6,852.28 m were drilled in a series of fences spaced approximately 25 m apart in order to obtain different depth intersections of the mineralisation, and on which an NI 43-101 compliant mineral resource estimate was established, comprising an indicated and inferred component of 13.2 million tons (grading 1.62 % Total Rare Earth Oxide (TREO)) and 18.6 million tons (grading 1.38 % TREO) respectively, using a cut-off grade of 1 % TREOThis deposit thus represents an exceptionally well-characterised carbonatite system that represents an analogue for the intrusions at shallow depth beneath European occurrences such as Kaiserstuhl.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith