U-Th-He Geochronology of Pyrite from the Uzelga VMS Deposit (South Urals)—New Perspectives for Direct Dating of the Ore-Forming Processes

Abstract

We report on the application of the U-Th-He method for the direct dating of pyrite and provide an original methodological approach for measurement of U, Th and He in single grains without loss of parent nuclides during thermal extraction of He. The U-Th-He age of ten samples of high-crystalline stoichiometric pyrite from unoxidized massive ores of the Uzelga volcanogenic massive sulfide (VMS) deposit, South Urals, is 382 ± 12 Ma (2σ) (U concentrations ~1–5 ppm; 4He ~10−4 cm3 STP g−1). This age is consistent with independent (biostratigraphic) estimations of the age of ore formation (ca, 389–380 Ma) and is remarkably older than the probable age of the regional prehnite-pumpellyite facies metamorphism (~340–345 Ma). Our results indicate that the U-Th-He dating of ~1 mg weight pyrite sample is possible and open new perspectives for the dating of ore deposits. The relative simplicity of U-Th-He dating in comparison with other geochronological methods makes this approach interesting for further application.

Noble Metal Speciations in Hydrothermal Sulphides

“…In the Urals, about 25 million tons of VMS ores are processed per year, only 15-40% (for various plants) of the total gold is extracted and losses with pyrite concentrate and in the tailings of enrichment amount to 13-15 tonnes of Au per year [77].…”

“…1,5,6,9) and 420-640 m (body Nos. 2-4, 7, 8), with ~300 m between the levels [25,77]. Ore bodies are represented by thick lenses, sometimes by irregular ellipsoidal and isometric ones with obtuse terminations (ore body 4) or ballshaped ones (ore body 3).…”

“…Galena also occurs widely but in smaller quantities (up to 0.5 vol%). Pyrrhotite is abundant in the axial zone of the southern part of the largest ore body of the deposit (body 4, see [77]). Hessite, altaite, coloradoite and other Te minerals [25,78] are rare.…”

Editorial for Special Issue “Pyrite Varieties and LA-ICP-MS Geochemistry in Ore Genesis and Exploration”

“…In the final paper of the Special Issue [7], the application of the U-Th-He method for the direct dating of pyrite provides an original methodological approach for measurement of U, Th and He in single grains without loss of parent nuclides during the thermal extraction of He. It is important that the age of Uzelga VMS deposit (the Urals) formation is consistent with independent (biostratigraphic) estimations of the age of ore formation (ca, 389-380 Ma) and is remarkably older than the probable age of the regional prehnite-pumpellyite facies metamorphism (~340-345 Ma).…”

“…New complex technologies applied to hydrothermal pyrite allow new recommendations for the discovery of deeply located gold deposits [6]. This Special Issue finally investigates the provocative topic of employing an innovative U-Th-He method for the direct dating of pyrite [7]. This and other innovative methods to study pyrite are awaiting further development.…”