Two occurrences of ultramafic hornfels in the Biggenden Beds,southeastern Queensland |
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| Authors: | P M Ashley E P Ambler R H Flood |
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| Institution: | 1. Minerals Department , Esso Australia Ltd , G.P.O. Box 4047, Sydney, N.S.W., 2001;2. Hooker Industrial Sands , Hooker House, 175 Pitt Street, Sydney, N.S.W., 2000;3. School of Earth Sciences , Macquarie University , North Ryde, N.S.W., 2113 |
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| Abstract: | Ultramafic hornfelses containing the assemblages hornblende + olivine + spinel + magnetite, and clinopyroxene + olivine + spinel + magnetite, are reported from two localities in the Biggenden Beds in southeastern Queensland. They are associated with mafic hornfelses in the contact metamorphic aureoles of the Mungore Adamellite and the Wateranga Gabbro. Chemical composition and minerology of the olivine + amphibole + spinel + magnetite hornfelses suggest that they represent metamorphosed picritic rocks, or possibly, altered serpentinites (blackwall rocks), whereas the clinopyroxene + olivine + spinel + magnetite hornfelses are interpreted as metamorphosed altered clinopyroxene‐rich picritic rocks. Cr‐Fe spinel relations in the hornfelses indicate partial homogenisation of primary chromian spinel with secondary magnetite ± ferrichromite during contact metamorphism. |
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