Details

Autor(en) / Beteiligte

• Skublov, S. G.
• Makeyev, A. B.
• Krasotkina, A. O.
• Borisovskiy, S. E.
• Li, X.-H.
• Li, Q.-L.

Titel

Isotopic and Geochemical Features of Zircon from the Pizhemskoye Titanium Deposit (Middle Timan) as a Reflection of Hydrothermal Processes

Ist Teil von

• Geochemistry international, 2022-09, Vol.60 (9), p.809-829

Ort / Verlag

Moscow: Pleiades Publishing

Erscheinungsjahr

2022

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• A comprehensive isotope-geochemical study of zircon (oxygen isotopic composition, trace element composition, and U-Pb SIMS dating) from two samples (50 points) of ore-bearing red-colored and gray-colored sandstones of the Pizhemskoye deposit (Middle Timan) made it possible to establish that peak values in the age spectrum are at around 1200 and 1500 Ma. Zircon from the red-colored sandstones shows three less intense age peaks at 1400, 1800, and 2220 Ma. Zircon from the gray-colored sandstones reveals two less intense peaks at about 1270 and 1050 Ma. In both samples, zircon younger than 1000 Ma was not found. This indicates that the Ti-bearing Malorucheiskaya Formation is no older than 1000 Ma, while the age of the deposit itself can be established from other minerals-geochronometers. No less than 25% of all zircon grains have an elevated contents of non-formula trace elements, which are confined to the CL-dark domains and rims. Their total REE content can exceed 23000 ppm. The REE distribution patterns are flat due to an increase in the LREE content with reduced positive Ce and negative Eu anomalies. The total content of trace elements, including REE, can exceed 6.5 wt %. The Y content reaches an extremely high value of 30850 ppm. The elevated P, Ca, as well as Ti contents make it impossible to use titanium for estimating the crystallization temperature of zircon. In the discrimination diagrams (La–Sm N /La N and U–Ca), zircon with elevated contents of trace elements falls in the field of hydrothermal zircon or zircon reworked by fluid. The rest of the zircon has the geochemical characteristics of unaltered zircon of magmatic origin. In a sample of the ore-bearing red-colored sandstones, 6 of 25 zircon points have a δ 18 O value lower than the “mantle signature” (from 2.2 to 5.1‰). Such significant decrease in δ 18 O can only be explained by the impact of high-temperature hydrothermal processes. The isotope-geochemical study of the zircon argued for the hydrothermal–metamorphic (rather than sedimentary–placer) genesis of the Pizhemskoye titanium deposit.