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Margarite from the Olary Province of South Australia

Published online by Cambridge University Press:  05 July 2018

Graham S. Teale
Graham S. Teale*
Affiliation:
Department of Geology and Mineralogy, University of Adelaide, Adelaide, South Australia 5000
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Synopsis

In Lower Proterozoic rocks of the Olary Province of South Australia margarite occurs in conjunction with sodic muscovite, pseudomorphing chiastolitic andalusite in graphite-rich schist, and as a pseudomorphic phase in rocks consisting of coarse muscovite together with lesser amounts of chloritoid, sillimanite, staurolite, and corundum. In the latter occurrence the assemblage (muscovite-sillimanite - chloritoid ± staurolite ± corundum) replaces massive andalusite. The margarite and sodic muscovite within the pseudomorphs lack a preferred orientation which suggests that their development was associated with the waning stages of the Palaeozoic Delamerian Orogeny (cf. Glen et al., 1977) which was the last major tectonothermal event in the region.

Within the chiastolitic andalusite pseudo-morphs, equal proportions of margarite and sodic muscovite are separated from the rock matrix by a rim of coarser-grained muscovite, which has developed at the pseudomorph margins. A suggested reaction for the development of margarite is 10Al2SiO5+1.7Ca2++1.2K++Na++10H2O⇄(Ca1.6Na0.4)Al4(Si4Al4O20)(OH)3.6+(K1.2Na0.6Ca0.1)Al4(Si6Al20O20)(OH)4+6Al3++12.4OH−.

The excess aluminium and hydroxyl ions from the above reaction leave the pseudomorph system but probably react with free quartz and more K+ ions to produce the muscovite fringe. 6SiO2+2K++6Al3++12OH−⇄K2Al4(Si6Al2O20)(OH)4+8H+.

The above reactions are pertinent only for margarite and sodic muscovite produced by the pseudomorphism of chiastolitic andalusite.

Margarite and sodic muscovite in the muscovite- chloritoid - sillimanite ± staurolite ± corundum rocks replace coarser-grained (up to 1 mm) muscovite, sillimanite, corundum, and chloritoid; staurolite is unaffected. The coarse muscovite of the earlier pseudomorphic assemblage contains 7–16 mole % paragonite in solid solution whereas the sodic muscovite assocated with margarite contains 22–33 mole% paragonite in solid solution. Margarite contains negligible muscovite but substantial (17–26 mole%) paragonite in solid solution. The phases plagioclase and paragonite were not detected in any of the investigated samples. Staurolite has an Mg/(Mg+Fe) value of 0.21 and associated chloritoid a value of 0.20.

It is possible that much of the previously described sericitic alteration of andalusite (cf. D'arcy, 1977) within schists of the north-eastern Willyama Complex (north of Broken Hill) involves the production of margarite.

Type
Research Article
Information
Mineralogical Magazine , Volume 43 , Issue 327 , September 1979 , pp. 433 - 435
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1979

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References

References

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Vernon, (R.H.), 1969. J. Geol. Soc. Aust. 16, 20-55.Google Scholar
Bence, (A.E.) and Albee, (A.L.), 1968. J. Geol. 76, 382-403.CrossRefGoogle Scholar
Berry, (R.F.), Flint, (R.B.) and Grady, (A.E.), 1978. Trans. Re,y. Soc. S. Aust. 102, 43-54Google Scholar
Binns, (R.A.), 1964. J. Geol. Soc. Aust. 11, 283-330.CrossRefGoogle Scholar
Chinner, (G.A.), 1974. Geol. Mag. 111, 75-78.CrossRefGoogle Scholar
D'arcy, (W.F.), 1977. Abst. Geol. Soc. Aust. 2nd Conv. 53.Google Scholar
Frey, (M.) and Niggli, (E.), 1972. Naturwiss. 59, 214-216.CrossRefGoogle Scholar
Glen, (R.A.), Laing, (W.P.), Parker, (A.J.) and Rutland, (R.W.R.), 1977. J. Geol. Soc. Aust. 24, 125-150.CrossRefGoogle Scholar
Griffen, (D.T.) and Ribbe, (P.H.), 1973. Am. J. Sci. 273-A, 479-495.Google Scholar
Guidotti, (C.V.) and Cheney, (d.T.), 1976. Am. Mineral. 61, 431-434.Google Scholar
Hock, (V.), 1974. Contrib. Mineral. Petrol. 43, 262-273.CrossRefGoogle Scholar
Jan, (M.Q.), Kempe, (D.R.C.) and Tahirkheli, (R.A.K.), 1971. Mineral. Mag. 38, 106-109.CrossRefGoogle Scholar
Lanphere, (M.A.) and Albee, (A.L.), 1974. Am. J. Sci. 274, 545-555.CrossRefGoogle Scholar
Reed, (S.J.B.) and Ware, (N.G.), 1975. J. Petrol. 16, 499-519.CrossRefGoogle Scholar
Velde, (B.), 1971. Mineral. Mag. 38, 317-323.CrossRefGoogle Scholar
Vernon, (R.H.), 1969. J. Geol. Soc. Aust. 16, 20-55.Google Scholar