Th-, U- AND LREE-BEARING GROSSULAR, CHROMIAN FERRIALLANITE-(Ce) AND CHROMIAN CERITE-(Ce) IN SKARN XENOLITHS EJECTED FROM THE GOLCUK MAAR CRATER, ISPARTA, ANATOLIA, TURKEY

Abstract

Thorium-, U- and LREE-bearing skarn xenoliths have been found in the volcaniclastic products of the Golcuk explosive maar crater, Isparta, southwestern Turkey. The samples predominantly consist of clinopyroxene, garnet, plagioclase, wollastonite, esseneite, olivine, calcite and dolomite, with accessory ferriallanite-(Ce), phlogopite, amphibole, quartz, apatite, spinel, cerite-(Ce) and monazite. We report the whole-rock geochemistry and electron-microprobe data for related Th-, U- and LREE-bearing garnet, ferriallanite-(Ce) and cerite-(Ce). Extreme enrichments in the LREE (1600–9400 ppm La, 2200–13500 ppm Ce, 270–900 ppm Pr, 400–2000 ppm Nd), and in Th (200–300 ppm), U (20–400 ppm), Y (50–150 ppm), Be (13–108 ppm), Cu (14–1600 ppm), Zn (50–600 ppm) and Au (up to 9.5 ppb) are observed. A strong correlation between U + Th abundance and ∑REE (5900–26000 ppm) exists in whole-rock samples. Among the minerals, grossular (Th + U: 0.10–3.97 wt.%, ∑LREE: 4.40–7.80 wt.%), chromian ferriallanite-(Ce) (Th + U: 0.02–0.20 wt.%, ∑LREE: 19.30–24.50 wt.%) and a chromian variety of cerite-(Ce) recorded here for the first time (Th + U: 0.97–1.35 wt.%, ∑LREE: 56.83–60.64 wt.%) are the principal hosts of the Th, U and the LREE. The fluids responsible for the geochemically enriched zones are most likely of contact-metasomatic origin, affecting the interface between a shallow magma-chamber and a carbonate wallrock. High concentrations of gold (up to 4.2 ppb) in the magmatic rocks of the Golcuk district demonstrate an important economic potential.