Reply to Discussion: The timing of gold mineralization across the eastern Yilgarn Craton using U–Pb geochronology of hydrothermal phosphate minerals

This is a reply to the discussion article doi: 10.​1007/​s00126-015-0609-

Tellurides from Sunrise Dam gold deposit, Yilgarn Craton, Western Australia: A new occurrence of nagyagite

© Springer The original publication can be found at www.springerlink.comThe complex Pb-Sb-Au tellurosulfide nagyágite is found together with eight tellurides (hessite, petzite, calaverite, altaite, tellurantimony (and Bi-bearing tellurantimony), melonite, tetradymite and an unnamed Au(Ag)-As-telluride) in sulfide-sulfosalt assemblages from late, high-grade veins (D4) and post-D4 veinlets in the world-class orogenic gold deposit at Sunrise Dam, Eastern Goldfields Province of the Archaean Yilgarn Craton, Western Australia. The composition of nagyágite at Sunrise Dam conforms to ideal stoichiometry, with negligible As content and Au/(Au+Te) ratio of 0.325 [i.e., (Pb4.84Sb1.10 As0.05)5.99S5.99(Au0.98 Te2.03)3.01]. The diverse mineralogy of the post-D4 veinlets, relative to the host veins, is attributed to small-scale reaction fronts established along zones of replacement at the polished section scale. The association of telluride assemblages and native gold is interpreted in terms of remobilization of ore components (including Ag, Sb, Te and Au) from the pre-existing assemblages, and their redeposition during subsequent tectonic events. The presence of nagyágite and Au-Ag tellurides in veins, in quantities that may be significant in economic terms, as well as the character of their breakdown products, have implications for ore processing and gold recovery, as well as for the genetic interpretation of the deposit. The strong structural control upon formation of the telluride-bearing assemblages at Sunrise Dam and the ability of these minerals to reflect changes in the local environment, contradicts the current view that these tellurides have a magmatic affiliation.Y.-H. Sung, C. L. Ciobanu, A. Pring, J. Brügger, W. Skinner, N. J. Cook and M. Nugu

Zirconolite and xenotime U-Pb age constraints on the emplacement of the Golden Mile Dolerite silland gold mineralization at the Mt Charlotte mine, Eastern Goldfields Province, Yilgarn Craton, Western Australia.

In situ SHRIMP U-Pb dating of magmatic zirconolite (CaZrTi2O7) in the Golden Mile Dolerite from the Mt Charlotte gold deposit (Yilgarn Craton, Australia) has yielded the first robust emplacement age (2,680 9 Ma) for the principle host-rock of gold mineralization in the Kalgoorlie district. In contrast, comagmatic zircon gave ages from approx 2.68 Ga to approx 2.17 Ga, reflecting isotopic resetting of high-U and -Th crystals. In situ SHRIMP analysis of hydrothermal xenotime (YPO4), which co-exists with gold in alteration pyrite, provided a Pb/Pb isochron age of 2,655 13 Ma. This date indicates that the youngest deposit in the Kalgoorlie district (Mt Charlotte) formed at approx 2.65 Ga, and provides a new minimum age for the structurally older Golden Mile deposit. Our results indicate that gold mineralization at Mt Charlotte is approx 50 million years older than indicated by recent 40Ar/39Ar dating and places new constraints on the timing of late-stage regional faulting (D4) in the province

The timing of gold mineralization across the eastern Yilgarn craton using U–Pb geochronology of hydrothermal phosphate minerals

The highly mineralized Eastern Goldfields of the eastern Yilgarn craton is an amalgamation of dominantly Neoarchaean granitoid-greenstone terranes and domains that record a history of early rifting, followed by westward directed collision with initial arc formation, collision and clastic basin formation, and final accretion to the western Yilgarn proto-craton between 2.66 and 2.60 billion years ago. The gold deposits that define this region as a world-class gold province are the product of orogenic processes that operated during accretion late in the tectonic history, after initial compressional deformation (D1–D2) and the majority of granitoid magmatism. Minor gold was also deposited throughout the entire tectonic history in magmatic-hydrothermal-related systems. However, such mineralization (mostly < 0.3 g/t gold) is nowhere economic unless it overprints, or is overprinted by, much higher-grade orogenic gold lodes.Robust SHRIMP U–Pb geochronology of gold-related hydrothermal xenotime and monazite supports structural studies that gold mineralization occurred during late transpressional events (D3–D4), shortly before cratonization. However, westward migration of collision and accretion produced a complementary diachroneity in the timing of gold mineralization of 5 to 20 m.y. between c. 2.65 Ma in the east (including Laverton District, Kurnalpi Terrane) to c. 2.63 Ma in the west (including Kalgoorlie Terrane) across the eastern part of the craton. The robust geochronology refutes previous suggestions that significant gold mineralization events extended from DE to D4 in the evolution of the orogen and that the Kalgoorlie gold deposits formed over a period of 45 m.y. The crustal continuum model is applicable within terranes where orogenic gold depositional events were penecontemporaneous, but must be modified to account for diachroneity of orogenic events and gold mineralization across the Eastern Goldfields