LINKING GOLD MINERALIZATION TO TECTONOTHERMAL EVENTS USING IN SITU XENOTIME U–PB GEOCHRONOLOGY

Understanding the controls on gold mineralization requires linking the timing of mineralization to the tectonothermal framework. The Mount Olympus gold mine in the northern Capricorn Orogen of Western Australia, has been classified as an orogenic gold deposit despite having many characteristics of a Carlin-type deposit. A previously determined age of c. 1740 Ma for mineralization was thought to be associated with an Australia-wide orogenic event at 1750–1720 Ma [1]. However, more recent work shows that there is no evidence for accretionary or collisional orogenic events at this time, either in the Capricorn Orogen or across Australia.

We present new in situ U–Pb SHRIMP analyses of xenotime to date hydrothermal events and gold mineralization at the Mount Olympus mine. Xenotime intergrown with auriferous pyrite and ore-stage alteration minerals yields an age for mineralization of c. 1770 Ma. This is followed by hydrothermal xenotime growth at c. 1730 and 1670 Ma. The three ages of xenotime growth are linked to intracratonic reworking during which strike-slip reactivation of crustal-scale faults occurred during the final stages of the 1820–1770 Ma Capricorn Orogeny, early in the 1680–1620 Ma Mangaroon Orogeny, and during a more cryptic event at c. 1730 Ma, which is synchronous with monazite growth at the Paulsens mine situated 150 km to the northwest [2]. Our results demonstrate how precise in situ geochronology can be used to correlate the timing of hydrothermal events and gold mineralization with tectonothermal events of the surrounding region.

References

[1] Şener et al. (2005), Geology 33, 225–228.

[2] Fielding et al. (2017), Economic Geology 112, 1205–1230.