Preprints
https://doi.org/10.5194/gchron-2020-41
https://doi.org/10.5194/gchron-2020-41

  21 Dec 2020

21 Dec 2020

Review status: this preprint was under review for the journal GChron. A final paper is not foreseen.

Direct dating of overprinting fluid systems in the Martabe epithermal gold deposit using highly retentive alunite

Jack Muston1, Marnie Forster1, Conrad Alderton2, Shawn Crispin2, and Gordon Lister1 Jack Muston et al.
  • 1Structure Tectonics Team, Research School of Earth Sciences, Australian National University, Canberra, 2601 Australia
  • 2PT Agincourt Resources, Martabe Mine, Sumatra, Indonesia

Abstract. The Martabe deposits in Sumatra, Indonesia formed in a shallow crustal epithermal environment (200–350 °C) associated with mafic intrusions, usually recognised in domes, adjacent to an active right-lateral wrench system. Ten samples containing alunite were collected for high-resolution 40Ar/39Ar geochronology, to determine if overprinting fluid systems could be recognised. At the same time, ultra-high-vacuum (UHV) furnace step-heating 39Ar diffusion experiments were conducted, to determine the argon retentivity of the mineral grains being analysed. The heating schedule chosen to ensure Arrhenius data uniformly populated the inverse temperature axis, with sufficient detail to allow the application of the Fundamental Asymmetry Principle (FAP) during data analysis. The heating time for each step was chosen to ensure reasonable uniformity in terms of incremental percentage gas release during each step. Results show activation energies between 360–500 kJ/mol, with normalised frequency factor between 1.89e14s−1 and 8.62e18s−1. Closure temperatures range from 390–519 °C for a cooling rates of 20 °C/Ma, giving confidence that the ages represent growth during periods of active fluid movement and alteration. The Martabe deposit formed at temperatures < 200 °C at a depth of < 2 km. Five distinct alunite growth events can be recognised: (A) 3.48–3.46 Ma; (B) 3.24–3.22 Ma; (C) 2.51–2.12 Ma; (D) 2.08–1.90 Ma; and (E) 1.70–1.40 Ma. Gold in the Purnama pit is the result of fluid rock interactions in periods C and D.

This preprint has been withdrawn.

Jack Muston et al.

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Interactive discussion

Status: closed
Status: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version Supplement - Supplement

Jack Muston et al.

Jack Muston et al.

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This preprint has been withdrawn.

Short summary
The timing and duration of fluid activity within a gold deposit enables a greater understanding of how the deposit evolved and thus help future mineral exploration. This research uses high resolution dating methods to unravel the overprinting fluid activity at the Martabe gold field in Sumatra. Methods outline in this report can be applied to deposits globally.