Mark, Geordie, and Pollard, Peter J. (2003) Contrasting composition of metasomatic and metamorphic scapolite in the Eastern Fold Belt, Northwest Queensland, Australia. In: Proceedings of the 7th Biennial SGA Meeting. pp. 1083-1086. From: Mineral Exploration and Sustainable Development, 24-28 August 2003, Athens, Greece.

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Abstract

The Proterozoic Eastern Fold Belt (EFB) of the Mount Isa Inlier, Australia, preserves one of the largest areas of scapolite-rich rock in the world, and is comparable to several other districts of similar age and metallogenic affinity. The close temporal and spatial association between Cl-rich scapolite and Cu-Au miner-alization in the EFB implies that scapolite could be a useful indicator of mineralized systems. The occurrence of metamorphic scapolite and multiple generations of metasomatic scapolite apparently unrelated to Cu-Au mineralization complicate this relationship. However, we propose that scapolite of various generations can be differentiated on textural, chemical and mineralogical grounds, where metamorphic scapolite (marialite; Mas. so) typically contains less Cl and Na and more Ca, Al and C than those derived via metasomatism (Maso.95). Among the metasomatic scapolites, those associated with Cu-(Au) mineralization have higher Cl and Na (Ma>7o). Texturally, metasomatic scapolite fonns as irregular rounded growths, or as subhedral to euhedral vein-fill, as opposed to metamorphic scapolite that typically fanned cauliflower-shaped porphyroblasts. A primary rock control is also evident \Vhere metamorphic scapolite is restricted to calc-silicate rocks (c. 1.7 Ga) as opposed to metasomatic scapolite that is hosted in a range of rock types of various age (c. 1.7-1.5 Ga).

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