Typomorphism and bedrock sources of placer-forming minerals of the Umyt’ya rare metal–titanium placer (Khanty-Mansi Autonomous District)

Abstract

The paper reports the results of study of the main placer-forming minerals (ilmenite and zircon) from the Umyt’ya coastal–marine placer in the western part of the Khanty-Mansi Autonomous District, Yugra. Microprobe study of 1450 zircon grains taken from the upper and lower ore bodies of the Umyt’ya placer (29 samples) and their comparison with zircon in magmatic rocks from the adjacent folded framing of the North and Nether-Polar Urals (40 analyses) allowed us to recognize five geochemical types of the mineral: Aurbakh (prevailing in the Umyt’ya placer), Severorudnichnyi, Tagil-Kytlym, Shemur, and unknown source. Crystallomorphological characteristics of the identified geochemical types of zircon are given. According to the microprobe data (300 analyses), ilmenite is subdivided into six groups. Comparison of these groups with the composition of ilmenite from magmatic complexes of the North and Nether-Polar Urals showed that they correspond to the same complexes as zircon. Based on peculiarities of the geological structure of the eastern slope of the North and Nether-Polar Urals, four separate areas were identified, each comprising spatially close magmatic complexes regarded as possible sources for ore minerals of the placers: Shchekur’ya–Khorasyur, Yalpigner–Chistop, Vizhai–Ivdel, and Denezhkin Kamen. Based on additional criteria, the Yalpigner–Chistop area was the main source for the Umyt’ya placer.