Mineralogical, petrological, and geochemical characteristics of Şenkaya Chrysoprase, Turkey

Abstract

Şenkaya chrysoprase is a gemstone and can be found near the Turnalı village located in the west-northwest of Şenkaya (Erzurum) county in the uplifted Kırdağ of Northeast Anatolia of Turkey. Chrysoprase only found in Şenkaya County and known with the same name commercially in Turkey is a light-dark green and cryptocrystalline structure gemstone encountered in the Örükyayla Mélange. Samples were collected from the field for defining mineralogical-petrographical, XRD, XRF, ICP-MS, optical cathodoluminescence microscopy (OCLM), FTIR-Raman and stable isotopic properties of Şenkaya chrysoprase. According to mineralogical and petrographic examination, Şenkaya chrysoprase has generally heterogeneous color distribution in macroscale and has 5 Mohs mineral hardness. Microquartz filling (10%–15%) was seen in the microexamination with serpentine as main component with partly massive opal type silica. The XRF analyses indicate that many samples had high SiO2 values (91.45–94.38 wt%). As a result of trace elements, rare earth elements, Au-Pt group analyses using ICP-MS, Ni (167–387 ppm) and Co (12.57–74.78 ppm) values are quite remarkable. In the OCLM studies, few metallic minerals which could produce CL and could spread CL in different colors due to some trace activator elements were observed. Oxygen isotopic (δ18OV-SMOW) values obtained from three chrysoprase samples are 24.8‰, 27.7‰ and 30.63‰, respectively and mean formation temperature is 96–99 o C.