The geology and petrology of the Marble Delta

Otto, J. D. T. (1973-02)

Thesis (MSc) -- Stellenbosch University, 1973.


The Marble Delta is an area of approximately 40 sq. km in Natal (30°22' Long., 30°40' Lat.), occupied by Precambrian marble and associated granites. The deeply dissected country was geologically mapped on a scale of I : 6 000. A new lithostratigraphic classification of the metasediments is proposed. The base of the lowermost Le Joncguet Formation (composed of dolomitic marble and siliceous beds) is not exposed. This is followed by the predominantly ca.lcitic Oribi Formation with interbedded dolomite and graphitic layers. The marble is unconformably overlain by the Cherrywillingham Formation which comprises mainly amphibolite and granulite. The .three formations together constitute the Marble Delta Group. The main petrological units are calc-silicate marble, metaquartzite, dolomite marble, cluster serpen~ine marble and ce,lcite marble. Graphite layers are considered to have originated in situ from organic remains; there is occasional evidence of ionic transfer of carbon from this graphite by magmatic fluids. The common mineral assemblages are diopside + calcite + dolomite, tremolite + calcite + diopside + quartz, calcite + quartz + dolomite, forsterite + calcite + dolomite, plagioclase + cordierite + garnet + quartz, amphibole + clinopyroxene + plagioclase, hornblende + clinopyroxene + calcite, wollastor~te + calcite + diopside. Other minerals are graphite, antigorite, chrysotile, sphene, spinel, clinohumite, chondrodite, zoisite, clinozoisite, hedenbergite, phlogopite, ilmenite, hercynite, dravite, cummingtonite, talc, apatite, microcline, saponite. The mineral assemblages resulted from regional metamorphism and polyphase contact metamorphism.

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