Si-P impure Al-Goethite Mineralization on the island of Dugi Otok (Central Adriatic, Croatia)

• Published in: Geologia Croatica 2008-07, Vol.61 (1), p.19-26
• Main Authors: Šegvić, Branimir, Lugović, Boško, Tadej, Neven, Bermanec, Vladimir, Panjkota, Lovro
• Format: Article
• Language: English
• ISSN: 1330-030X; 1333-4875
• DOI: 10.4154/gc.2008.04

At the western seaward coast of the island of Dugi Otok, unusual goethite mineralization occurs as the infilling of a system of thin crevices in the Upper Cretaceous limestones of the Adriatic carbonate platform. Goethite is exceptionally well ordered and shows a variety of chemical compositions ranging from almost pure FeO·OH to Al-substituted composition accompanied by high Si and P impurity. The most characteristic textural type assemblages are goethite and coarse grained calcite in composite aggregates. These aggregates contain Al-substituted goethite with metamorphic silicate minerals embedded in the core, (black goethite) armoured by the XRD-pure, almost stoichiometric goethite (brown goethite). The geochemical and mineralogical features of the mineralization suggest an ascending solution from a hidden metamorphic source. We speculate that the source could have been activated by the thermal influx linked to the Pliocene intraplate magmatism in the eastern segment of Adria.