Technical note: Pyrite (U,Th)-He geochronology using scanning fiber-laser He extraction: analytical workflow and case studies from two orogenic gold systems in the Russian Far East

Abstract. This study presents a new analytical approach to (U,Th)-He dating of individual pyrite grains. We demonstrate that a widely available commercial fiber-laser marking system operated in scanning mode can efficiently extract radiogenic He from pyrite encapsulated in quartz ampoules. The ampoules retain the thermal decomposition products and associated parent nuclides, allowing U and Th to be subsequently determined in the same material from which He was extracted. The proposed extraction technique was validated using pyrite from two gold-bearing sites in the Russian Far East: the Pavlik orogenic gold deposit in the Magadan Region and the Upryamoe gold occurrence, Chukotka. The resulting pyrite (U,Th)-He ages are 139.3 ± 1.7 Ma (MSWD = 2.5; n = 7) and 125.4 ± 2.1 Ma (MSWD = 0.87; n = 5), respectively. Compared with the previously developed high-vacuum furnace procedure, the scanning fiber-laser approach increases the analytical throughput of pyrite (U,Th)-He dating by approximately an order of magnitude, allowing up to eight samples to be analysed per day. By making individual-grain age determinations faster and operationally simpler, the method enables larger datasets to be acquired and thereby improves the statistical characterization of pyrite ages from a range of geological settings.