Scapolite-Bearing Marbles and Calc-Silicate Rocks from Tungkillo and Milendella, South Australia

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Abstract
On the eastern side of the Mount Lofty Ranges of South Australia, impure marbles and calc-silicate rocks characterized by assemblages rich in scapolite and pyroxene have been formed on a regional scale by high grade metamorphism of limestones and calcareous shales. It is suggested that this metamorphism is essentially iso-chemical and that even chlorine in the scapolite (Me 55[60) could have been derived from the original sediments.A secondary paragenesis consisting of epidote, actinolite, and calcite at Tungkillo and epidote, actinolite, calcite, and garnet at Milendella, is the result of late metasomatism and reaction associated with the formation of granites, migmatites, and veined gneisses. At Tungkillo, outside the sphere of granite activity, the secondary, retrograde assemblage is due to limited metasomatism chiefly involving the introduction of water, whereas at Milendella where marbles and calc-silicate rocks are intimately associated with granitic rocks, reaction and metasomatism giving rise to the secondary minerals has been more intense. Here garnet of the andradite-grossularite series has developed.

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