Phosphate mineralogy of the Hålsjöberg and Hökensås kyanite deposits

Abstract

Phosphates present at Hålsjöberg, Värmland, and at Hökensås, Västergötland, Sweden, represent at least two different stages of rock formation, as shown by their spatial relationships. At Hålsjöberg a chemical separation into an early F-rich and a later Al-rich assemblage is indicated. The former comprise wagnerite, F-apatite and wyllieite and the latter is represented by lazulite-scorzalite, trolleite, augelite, gatumbaite, berlinite, burangaite, a ‘wicksite-like’ phase and ferro-wyllieite. At Hökensås Mn-apatite, lazulite-scorzalite, trolleite, augelite, woodhouseite, crandallite and florencite-Ce occur. For the ‘wicksite-like’ phase and wyllieite Mössbauer spectroscopy data are presented. At Hålsjöberg, peak metamorphic conditions are estimated at P>2kb and 520°C<T<575°C. The intimate association of banded kyanite and early phosphates at Hålsjöberg suggests a simultaneous formation due to a common mechanism. A genetic model, proposed by Wise & Loh is adopted, whereby kyanite and early phosphates formed by hydrolyzing solutions acting upon Al-rich rocks. During retrograde metamorphism, at T<475°C, the Al-dominant phosphates crystallized together with secondary kyanite along fractures caused by tectonic movements.

Key Words:

• Protogine Zone
• hydrothemal alteration
• kyanite
• augelite
• berlinite
• burangaite
• gatumbaite
• florencite-Ce
• souzalite
• wyllieite
• trolleite
• ‘wicksite-like’
• Hålsjöberg. Hökensås