Testing ore deposit models using in situ U-Pb geochronology of hydrothermal monazite: Paleoproterozoic gold mineralization in northern Australia

Abstract

The inability to establish absolute ages for gold deposition in the Pine Creek orogen of northern Australia has led to conflicting ore deposit models, ranging from intrusion related, which predict that gold mineralization was synchronous with granite magmatism (ca. 1835-1820 Ma), to orogenic, which place ore deposition nearly 100 m.y. later. Here we present ion microprobe U-Pb geochronology for a mineralized quartz reef from Tom's Gully mine, Mount Bundey, Northern Territory, Australia, and nearby granitic rocks and associated contact aureoles. Isotopic dating of zircon and monazite indicates that intrusion and contact metamorphism occurred ca. 1825 Ma, whereas hydrothermal monazite from the auriferous quartz reef gives a mean 207 Pb/ 206 Pb age of 1780 ؎ 10 Ma, interpreted as the time of gold mineralization. Mineralization therefore postdated intrusion by ϳ45 m.y. and preceded a postulated ca. 1740-1730 Ma cratonwide orogenic gold event by ϳ50 m.y. Hence, neither the intrusion-related model nor the recently proposed orogenic model is applicable. Combined with a reevaluation of age data from the nearby Goodall gold deposit, our data suggest that mineralization coincides with, and may be related to, an episode of regional low-grade metamorphism, deformation, and fluid circulation (Shoobridge event). Our results demonstrate the importance of high-precision in situ geochronology and detailed petrography for deciphering age relationships in ore deposits, and of testing the veracity of models for ore formation.

Timing of Gold Mineralization in the Hutti Gold Deposit, Dharwar Craton, South India

“…Brown et al, 2002, Salier et al, 2004, the Pine Creek inlier (Rasmussen et al, 2006), and for Brazilian Cu-Au deposits (e.g., Tallarico et al, 2004). Direct dating of REE phosphates associated with ore minerals has been carried out at several gold deposits in the Yilgarn craton, Western Australia (e.g.…”

Bushveld-aged fluid flow, peak metamorphism, and gold mobilization in the Witwatersrand basin, South Africa: Constraints from in situ SHRIMP U-Pb dating of monazite and xenotime

“…The growth of authigenic monazite and xenotime during contact metamorphism, very low and low-grade regional metamorphism, and hydrothermal alteration requires the movement of heated fl uids (Rasmussen et al, 2005(Rasmussen et al, , 2006. In the Witwatersrand basin, the presence of 2.06-2.03 Ga monazite and xenotime provides strong evidence for signifi cant movement of heat and fl uids during the Bushveld magmatic event.…”

Indirect Associations Between Lamprophyres and Gold-Copper Deposits

“…Although the gold mineralization at Tom's Gully is bracketed in time by the lamprophyre dykes, the lamprophyres do not have intrinsically high Au contents and no direct genetic association is evident (Sheppard 1992). More recent work (Rasmussen et al 2006) dates the gold mineralization at Tom's Gully at 1780 ± 10 Ma and thus postdating the Mount Bundey pluton by about 45 m.y. Hence, the shoshonite-gold association at Tom's Gully is interpreted to be indirect, representing only similar structural controls on both dyke intrusion and mineralization, as at Goodall in the same terrane.…”

“…The lamprophyres are dated via conventional U-Pb in zircon methods at 1831 ± 6 Ma (Sheppard 1992(Sheppard , 1995. The Mount Bundey pluton is dated at 1825 Ma (Rasmussen et al 2006). …”