Thermal history of an Early Paleozoic epithermal deposit: Constraints from 40Ar/39Ar and (U–Th)/He thermochronology at Zhengguang, eastern Central Asian Orogenic Belt

Abstract

The Zhengguang epithermal Au-Zn deposit, located in Heilongjiang Province, NE China, is an Early Paleozoic intermediate sulfidation epithermal deposit which is adjacent to the Duobaoshan and Tongshan porphyry Cu deposits in the Duobaoshan magmatic arc, eastern Central Asian Orogenic Belt (CAOB). Our new 40Ar/39Ar dating presents plateau ages of 276.9 ± 1.2 Ma (MSWD = 1.5) for adularia and 265.7 ± 1.2 Ma (MSWD = 3.5) for illite. These ages are clearly younger than the mineralization age of Zhengguang (~480 Ma) and therefore represent a post-ore event which reset the adularia and illite argon systems. The resetting event could be related to post-collision of Xing’an Block and Songliao-Xilinhot Block. The weighted mean of zircon (U–Th)/He ages (ZHe) and apatite (U–Th)/He ages (AHe) from the same dacite porphyry with illite dating sample are 192 ± 10 Ma (MSWD = 2.2) and 98.8 ± 5.3 Ma (MSWD = 2.1), respectively. The ZHe age (~190 Ma) indicates a tectonothermal resetting event, possibly related to the development of Tongshan fault whereas the AHe age (~100 Ma) likely reflects 3 km-deep burial at Zhengguang. The intra-sample variations of (U–Th)/He ages for zircon grains are mainly due to radiation damage, while those for apatite are unknown. We argue that the post-ore volcanic eruption and slow uplift and exhumation rate caused by rollback of the Paleo-Pacific plate could facilitate burial and preservation of the epithermal (and by inference porphyry) deposits in NE China. Considering the complex collisional and amalgamation history in this area, we believe that there is exploration potential for ancient porphyry and epithermal deposits within the eastern section of the CAOB.