Composition Characteristic of Turquoise from Mongolia

Abstract

The turquoise from Mongolia is rich in colour, ranging from blue to green. To enrich the study on the composition of turquoise from Mongolia, this study determined the contents of main components, trace elements, and rare earth elements(REE) by electron probe microanalysis (EPMA) and laser ablation plasma mass spectrometer (LA-ICP-MS). The content of Al2O3, P2O5, CuO and TFeO were 35.22%-36.73%, 34.34%-35.84%, 8.27%-9.24% and 2.20%-3.76% respectively. The TFeO / CuO ratio of the sample increased with the colour change from blue to green. As the increase of Fe3+ content, the green hue of the sample increases. The content of As was as high as 1 453.9-1 760.3 mg/kg. The EDS scanning showed that As was uniform distributed in the sample substrate. The contents of Sr, Ba, and Pb in the samples were higher than those in Anhui, Shaanxi, and Hubei provinces. The U content was similar to that in turquoise samples from Ma'anshan and Ankang of Anhui Province, and lower than that in Yunyang district and Zhushan area of Hubei Province. There were two different patterns of REE distribution, one was right inclined, and the heavy and light rare earth were differentiated, and Eu loss was not obvious; the other was rich in medium rare earth, and the difference between light and heavy rare earth was relatively insignificant, and Eu showed positive anomaly. According to the difference of distribution curves, it was inferred that there were two stages of mineralization of turquoise, low temperature hydrothermal metasomatism and weathering leaching. The rare earth content of the former was higher than that of the latter, and the light rare earth was enriched, while the latter was lost, but the contents of medium rare earth and heavy rare earth were consistent with the former. The author studied and determined the composition characteristics of turquoise in this area and infers the genesis of turquoise and provided the basis for distinguishing the origin of turquoise from Mongolia.