New 40Ar/39Ar and (U-Th)/He dating for the Zhunuo porphyry Cu deposit, Gangdese belt, southern Tibet: implications for pulsed magmatic-hydrothermal processes and ore exhumation and preservation

Abstract

Understanding the magmatic-hydrothermal cooling and exhumation history is fundamental for investigating porphyry deposit formation and preservation. In the Zhunuo porphyry copper deposit of southern Tibet, hydrothermal biotite related to early potassic alteration likely formed from 14.7 ± 0.3 Ma (zircon U-Pb age) to 14.23 ± 0.13 Ma (molybdenite Re-Os age) and cooled below the closure temperature for 40 Ar/ 39 Ar system at 13.91 ± 0.05 Ma (hydrothermal biotite 40 Ar/ 39 Ar plateau age). The 40 Ar/ 39 Ar spectra of another hydrothermal biotite sample that was selectively replaced by chlorite record the timing of late phyllic alteration at 13.53 ± 0.08 Ma. Zhunuo hydrothermal alteration and mineralization likely ceased at 13.09 ± 0.07 Ma based on the 40 Ar/ 39 Ar plateau age of the fresh magmatic biotite crystals. The biotite 40 Ar/ 39 Ar systematics have not been reset by~12.0 Ma post-mineralization granite porphyry within ore district, which is likely due to rapid cooling and/or absence of fluid exsolution for the granite porphyry. In combination with previous zircon U-Pb and molybdenite Re-Os data, two-pulses of magmatic-hydrothermal activity from 14.78 ± 0.11 to 14.44 ± 0.05 Ma and from 14.23 ± 0.13 to 13.53 ± 0.08 Ma can be recognized at Zhunuo. (U-Th)/He thermochronological data on zircon and apatite from the inter-mineralization monzogranite porphyry suggest three cooling events characterized by first-stage magmatic cooling at a rate of~1850°C/m.y., and two later phases of uplift and exhumation at~70°C/m.y. and~10°C/m.y. Approximately 1.4-km thickness of materials have been removed from the Zhunuo Miocene monzogranite porphyry during uplift and erosion, including a large volume of ore.

Thermal History of the Naruo Porphyry Deposit in the Duolong Ore District, Western Tibet: Evidence from U‐Pb, 40Ar/39Ar and (U‐Th)/He Thermochronology

“…The Paleozoic or Precambrian porphyry deposits are much less than their Mesozoic or Cenozoic counterparts on account of their tendency to be eroded in rapidly uplifting arcs (Kesler and Wilkinson, 2006;Wilkinson and Kesler, 2007). The studies of the duration of magmatic-hydrothermal processes (McInnes et al, 2005a, b;Sillitoe, 2010;Chiaradia et al, 2013;Lang et al, 2013;Buret et al, 2016;Sun et al, 2021) and postmineralization processes that control the exhumation and preservation of porphyry deposits (McInnes et al, 1999;Kesler and Wilkinson, 2008;Zhou et al, 2020Zhou et al, , 2022Gong et al, 2021) are critical to mineral resource exploration.…”

“…U-Pb, Re-Os, 40 Ar/ 39 Ar and (U-Th)/He dating which are broadly applied to reveal timing and duration of mineralization process, rate of exhumation and erosion of intrusive ore deposits and comparative preservation potential (McInnes et al, 2005a;Harris et al, 2008;Bineli et al, 2012;Braxton et al, 2012;Evans et al, 2013;Zhao et al, 2016;Leng et al, 2018;Yang et al, 2019Yang et al, , 2020Yang et al, , 2021Sun et al, 2021) are applied to the Naruo porphyry-cryptoexplosive breccia copper (gold) deposit. The objectives of the present work are to investigate the magmatic-hydrothermal cooling and postmineralization process at Naruo deposit and provide some insights into the mineral exploration in the Duolong ore district.…”