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Home » Atlas » Cyclic Unit 1 and Lower Mafic Succession,Darwendale Subchamber

Cyclic Unit 1 and Lower Mafic Succession,Darwendale Subchamber

Grid Ref (WGS84 Lat/Long in decimal degrees)

-17.979580, 30.435100
Map: Harare 1:250,000 Sheet SE-36-5, Makwiro River,west side
Great Dyke - Ultramfic, ‘Picrite’

This is located on the marginal facies of the harzburgite of Cyclic Unit approx. 250m below the base of the Mafic Sequence.This rock is remarkably fresh with < 30% of the olivine altered to serpentinite.This rock type is a phlogopite-bearing plagioclase harzburgite.It comprises zones of medium-to coarse-grained olivine crystals together with large oikocrysts of orthopyroxene enclosing fine-grained and highly rounded olivine.Small amounts of very fine-rained chromite are present throughout the rock and are mainly located at the boundaries of the olivine crystals and within the orthopyroxene oikocrysts.Approx. 100m downstream towards the west is an outcrop of highly-weathered olivine pyroxenite to pyroxenite underlain by phlogopite-bearing plagioclase harzburgite.Approx. 20m downstream from the bridge is a narrow granite dyke intruding the harzburgite.The dyke contains variable amouts of chromium.

Further Reading: 
Book:”The Great Dyke of Zimbabwe:”Platinum –Genesis to Beneficiation