LINKING MULTIPLE GOLD MINERALIZING EVENTS TO REACTIVATION OF CRUSTAL-SCALE FAULTS

The distribution of gold deposits is often spatially associated with major mantle-tapping faults that act as pathways for mineralizing fluids during hydrothermal activity. However, the precise timing of gold mineralization is often poorly understood due to a lack of suitable geochronometers in hydrothermal ores and the ease with which many isotopic systems are reset during subsequent hydrothermal events. The Proterozoic Capricorn Orogen of Western Australia records the punctuated Proterozoic assembly of the Pilbara and Yilgarn Cratons, and over one billion years of subsequent intracratonic reworking. In the northern part of the Capricorn Orogen numerous gold deposits are spatially associated with mantle-tapping faults, such as the Nanjilgardy Fault. However, previously, the link between the timing of gold mineralization and fault (re)activation had not been established.

Here we present new in situ SHRIMP U–Th–Pb analysis of monazite and xenotime to date hydrothermal events associated with mineralization at gold deposits throughout the northern Capricorn Orogen. Our results indicate three discrete mineralizing events at c. 2400 Ma, 1770 Ma, and 1680 Ma, all of which can be linked to the well-established tectonothermal framework of the northern Capricorn Orogen. Orogenic gold dated at c. 2400 Ma is associated with monazite growth throughout the southern Pilbara region [1] and resetting of high-U zircons in tuffaceous mudstones of the Hamersley Group [2] between c. 2430 and 2400 Ma. Carlin-style gold mineralization dated at c. 1770 Ma and extensive gold remobilization at c. 1680 Ma are associated with movements along the Nanjilgardy Fault during intracratonic reworking during the final stages of the 1820–1770 Ma Capricorn Orogeny and early in the 1680–1620 Ma Mangaroon Orogeny. These results indicate that (re)activations of mantle-tapping faults and multiple gold mineralization events associated with hydrothermal fluid flow are linked to regional-scale orogenic activity.

References

[1] Rasmussen et al. (2005), Geology, 33, 773–776.

[2] Pickard (2002), Australian Journal of Earth Sciences, 49, 491–507.