Constraints on the timing of lode-gold mineralisation in the Wiluna greenstone belt, Yilgarn craton, western Australia

40Ar/39Ar ages of hydrothermal muscovites constrain the age of gold mineralisation in the Wiluna greenstone belt, Western Australia. A single muscovite sample from the Matilda M1 deposit, hosted in the,greenschist-amphibolite facies Matilda domain, has a 40Ar/39Ar plateau-like segment corresponding to an age of 2623 +/- 12 Ma (2 sigma). This is interpreted as the probable age of mineralisation and is similar to radiometric ages of mineralisation from other parts of the craton. Two muscovite samples from an altered microdiorite dyke from the East Lode deposit, located within the prehnite-pumpellyite facies Wiluna domain have 40Ar/39Ar plateau-like segment ages of 2565 +/- 12 Ma and 2563 +/- 12 Ma. A third sample, consisting of muscovite from an altered high-MgO basalt, has an enigmatic spectrum with no obvious plateau-like segment and the highest temperature steps have apparent ages of ca 2600 Ma. Two alternative interpretations are considered for the data from the East Lode deposit: (i) mineralisation in the Wiluna and Matilda domains occurred during a craton-wide gold-mineralisation event at ca 2630 Ma and the younger 40Ar/39Ar ages for muscovites from the Wiluna East Lode deposit have been isotopically reset; and (ii) mineralisation at the East Lode deposit occurred significantly after that at Matilda and elsewhere in the Yilgarn Craton, and represents a discrete hydrothermal episode that occurred some 90 million years after the ca 2630 Ma mineralising event. If the latter is the case then this is further evidence that discrete episodes of gold mineralisation occurred within the Yilgarn Craton after the widespread ca 2630 Ma event. A 2749 +/- 7 Ma (95% confidence limits) U-Pb zircon date from a pre-mineralisation porphyritic microdiorite dyke in the Wiluna domain is a minimum age for the formation of the komatiite-bearing stratigraphic sequence and maximum age for subsequent gold mineralisation in the Wiluna domain.