The Akdagmadeni (Yozgat, Central Turkey) fluorite deposits and their REE geochemistry

摘要

This paper provides evidences from two fluorite deposits, respectively the Tad Dere and the Bueyuekcal Tepe, located in SE and NE of Akdagmadeni, Yozgat, central Turkey. The alkali-granite-hosted Tad Dere deposit occurs as veins and lenses in E-W, and NW-SE-striking fault zones in micaschists. The Bueyuekcal Tepe deposit is emplaced in epidote-bearing skarns along the granitoid-marble contacts. Fluorite mineralization from the Tad Dere area exhibit intermediate REE contents, ranging from 20.6 to 48.5 ppm (mean REE = 36.0 ppm), whereas the fluorite from Bueyuekal Tepe shows higher REE contents with concentrations ranging from 61.3 to 149.3 ppm (mean REE = 113.0 ppm). Both fluorites are marked by the enrichment in light REE. The Tad Dere ores have positive, but the Bueyuekcal Tepe ores have negative Ce anomalies. This implies that low fo_2 and high fo_2 were dominant at the source of hydrotermal solutions during the deposition of, respectively the Tad Dere and the Bueyuekcal Tepe fluorites. Similarly, negative Eu anomalies for the Tad Dere and positive Eu anomalies for the Bueyuekcal Tepe can be interpreted as the former ores have had high Eu~(+2) compared to later ones. Positive Eu anomalies may be due to feldspar alteration and thus, the oxidation state of Eu~(+2) to Eu~(+3) may arise from Ca in fluorite. The fluorites from both areas display low Tb/La and Tb/Ca values. This profile indicates an early stage crystallization of fluorite from a fraction of fluid. The chondrite-normalized patterns also point out the hydrothermal origin for the Tad Dere fluorite, and pegmatitic to hydrothermal origin for the Bueyuekcal Tepe fluorite. The homogenization temperatures (T_h) range from 156°to 185°C with the corresponding salinities between 12 and 23 wt% NaCl for the Tad Dere ores. Consequently, the field, fluid inclusion data, and REE geochemistry support these findings.