AGE OF MONAZITE FROM THE ICHETJU OCCURRENCE,THE MIDDLE TIMAN (CHIME AND LA-ICP-MS METHODS)
The study of morphology, composition, and age (by CHIME and LA-ICP-MS methods) of monazite from the Ichetju ore occurrence, located in the Middle Timan, has revealed some principal differences in typomorphic features and genesis of its two varieties. The common yellow monazite from this occurrence is represented by monazite-(Ce), in which the La content is higher than the Nd content. The time of its crystallization (recrystallization) is estimated by the CHIME method as 518 ± 40 Ma. The time of formation of kularite (grayish-brown oolitic shape variety of monazite in which the Nd content is higher than the La content) is defined as 978 ± 31 Ma. Some of kularite grains show the age of 520 ± 27 Ma, which may be interpreted as the age of a hydrothermal event that led to the simultaneous recrystallization of both monazite and kularite. However, these two varieties of monazites were formed in two completely different sources, and were then combined in the mineral parasteresis of the Ichetju occurrence. Estimated by CHIME ages of monazite from Ichetju occurrence, as related to two intervals (500–600 and 960–1000 Ma), are close or coincide with values of the isotopic age determined by LA-ICP-MS method in the same monazite grains.