Zircon and apatite fission track analyses on mineralization ages and tectonic activities of Tuwu-Yandong porphyry copper deposit in northern Xinjiang, China

Abstract

The mineralization ages reported in the past in the Tuwu-Yandong copper district not only are different, but also fall into the Hercynian epoch. This study has achieved 9 zircon and 7 apatite fission track analysis results. The zircon fission track ages range from 158 Ma to 289 Ma and the apatite ages are between 64 Ma and 140 Ma. The mineralization accords with the regional tectonics in the copper district. We consider that the zircon fission track age could reveal the mineralization age based on annealing zone temperature of 140–300°C and retention temperature of ∼250°C for zircon fission track, and metallogenetic temperature of 120–350°C in this ore district. Total three mineralization epochs have been identified, i.e., 289–276 Ma, 232–200 Ma and 165–158 Ma, and indicate occurrence of the mineralization in the Indosinian and Yanshan epochs. Corresponding to apatite fission track ages, the three tectonic-mineralizing epochs are 140–132 Ma, 109–97 Ma and 64 Ma, which means age at about 100°C after the mineralization. The three epochs lasted 146 Ma, 108 Ma and about 100 Ma from ∼250°C to ∼100°C and trend decrease from early to late. It is shown by the fission track modeling that this district underwent three stages of geological thermal histories, stable in Cretaceous and cooling both before Cretaceous and after 20 Ma.