Original paper
Supergene iron phosphate minerals in Proterozoic ironstones from the Olary Block, South Australia
Ashley, Paul M.; Lottermoser, Bernd G.; Scott, Keith M.
Neues Jahrbuch für Mineralogie - Monatshefte Jg. 1997 Heft 7 (1997), p. 309 - 327
30 references
published: Sep 12, 1997
DOI: 10.1127/njmm/1997/1997/309
ArtNo. ESP156199707002, Price: 29.00 €
Abstract
Iron phosphate minerals have been found as apparent supergene alteration encrustations and cavity fillings in pyrite-bearing, magnetite-hematite-quartz ironstones of the Proterozoic Willyama Supergroup in the Olary Block, South Australia. The minerals are generally microcrystalline, with natrodufrenite and rockbridgeite being the most common. In places, they are accompanied by strengite and chalcosiderite, and are typically found in association with jarosite-type phases and goethite. Although crystallisation sequences may be reversed, there is an overall paragenesis of strengite altering to natrodufrenite, thence to rockbridgeite and goethite, implying increasing Fe3+ (+ Al)/PO43- as crystallisation of the phosphates proceeded. The surficial occurrence of the phosphates and their association with jarosite and goethite indicate oxidising, low-pH conditions for their formation. An origin for the phosphate minerals from the dissolution of pyrite in the ironstones and reaction of Fe-bearing, acid sulphate groundwaters with hypogene apatite, or with phosphatic guano deposits on the ironstone outcrops is favoured.
Keywords
Phosphate minerals • ironstones • supergene alteration • Olary Block • South Australia