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

Abstract. The Martabe gold deposits in Sumatra formed a shallow crustal epithermal environment associated with intermediate mafic intrusions adjacent to an active right-lateral wrench system. Gas/fluid temperatures reached 200–350 ∘C. structural geology suggests episodic switches stress orientations during Plio-Pleistocene seismotectonic evolution. Different mineralisation events may have been oscillations this earthquake cycle, so samples containing alunite were collected for 40Ar / 39Ar geochronology constrain the timing. diffusion experiments performed variation argon retentivity. age spectra produced by incremental step-heating heating times chosen similar percentages of gas release occurred as many steps possible. This ensured detail necessary analysis complex morphology these applying method asymptotes and limits, which enabled recognition different growth overprinting fluid systems. It was possible provide estimates frequency individual their duration. schedule also that Arrhenius data populated inverse temperature axis sufficient allow modelling. Activation energies between 370–660 kJ mol−1. Application Dodson's recursion determined closure range from 400–560 ∘C cooling rate 100 Ma−1. Such are higher than any be expected natural system, giving confidence ages represent timing periods movement alteration: hypothesis confirmed modelling using MacArgon program. We conclude Purnama pit resulted rock interactions very short episodes at ∼2.25 ∼2.00 Ma.