Geochemical patterns of the Akdagmadeni (Yozgat, Central Turkey) fluorite deposits and implications

Abstract

Fluorite and fluorite-bearing Pb–Zn–Ag (Cu) deposits are quite common in granitoids and associated skarn formations that are products of Late Cretaceous–Early Paleocene magmatic intrusions into Paleozoic metamorphic rocks of the so called Central Anatolian massif. This study investigates the geochemical features, mainly REE distributions, of fluorites from the Akdagmadeni fluorite and fluorite bearing Pb–Zn–Ag (Cu) deposits. These include the vein type Tad Dere, epidote-skarn hosted Büyükçal Tepe and the skarn and granite hosted Akçakisla deposits. The REE contents of these deposits are 20.6–48.5 ( x=36.0), 61.3–149.3 ( x=113.0) and 279.2–4222.4 ( x=1280.0) ppm for the Tad D., Büyükçal T. and Akçakisla, respectively. In general, the REE contents are intermediate to high and decrease in abundance with increasing distance from the granitic bodies. The LREE contents are dominantly higher than HREE contents and REE normalized patterns indicate decreasing abundances with increasing atomic number. These indicate that all the fluorites are early stage mineralizations. However, Tb/Ca–Tb/La ratios show distinct differences in the nature of the mineralizing fluids. The high ratios of Akçakisla fluorites are evidence of mineralizing fluids rich in late-stage differentiates from a felsic magma, while intermediate to high ratios of the Büyükçal T. fluorites are products of late-stage differentiates from hydrothermal fluids. Tad D. fluorites were mineralized under hydrothermal conditions. Decreasing ΣREE contents in the order of Akçakisla, Büyükçal T., and Tad D., and Sc/Eu vs Sr distribution (Sr increases with increasing distance from the magmatic rocks) also supports this order of formation. Each of the three types of fluorite deposits plot in well-defined areas in the Sc/Eu vs Sr diagram. Eu and Ce anomalies give a mixed pattern; the Tad D. fluorites have strong negative Eu anomalies indicating low T and low fo 2 mineralizing fluids. Strong positive Eu anomalies for the Akçakisla fluorites are probably due to high fo 2. The Ce anomalies are strongly negative for the Akçakisla, negative for the Büyükçal T. and weakly negative for the Tad D. fluorites. These indicate high fo 2 conditions for the Akçakisla, intermediate for the Büyükçal T. and low for the Tad D. fluorites. Because of distinguishable differences in REE patterns, the fluorite deposits plot in well-defined areas in Sc/Eu vs Sr, (La/Yb) n –(Eu/Eu ∗) n , Sr–(Eu/Eu ∗) n , Sc–ΣREE, (Tb/Yb) n –(La/Yb) n , Tb/Ca–Tb/La diagrams, and indicate different origins and depositional histories. 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, 390 to 430 °C with the corresponding salinities 8 and 12 wt% NaCl for the Akçakisla and Büyükçal Tere ores. Consequently, the field, fluid inclusion data and REE geochemistry indicate that the composition of mineralizing fluids, the locations of ore formations relative to the plutons, the mineralizing mechanisms and the prevailing physicochemical conditions of the depositional environments for the fluorite deposits of Akdagmadeni, were different.