Geological setting and SHRIMP U-Pb geochronological evidence for ca. 2680-2660 Ma lode-gold mineralization at Jundee-Nimary in the Yilgarn Craton, Western Australia

The 7 million oz. Jundee-Nimary lode-gold deposit occurs in the northern po rtion of the Yandal greenstone belt in the northeastern part of the Archean Yilgarn Craton of Western Australia. Gold mineralization at Jundee-Nimary is similar in structural style, mineralogy, geochemistry and relative timin g with respect to deformation and metamorphism, to other Western Australian Archean greenstone-hosted gold deposits, but is unusual in the fact that m ineralized structures are crosscut by structurally late intermediate to fel sic dykes. Within the Deakin South open cut, gold mineralization is hosted in brittle-ductile shear zones primarily developed within the dacitic Mitch ell Porphyry. The Moore Porphyry, a broad dyke of porphyritic granodiorite, intrudes the Mitchell Porphyry, crosscutting and post-dating gold minerali zation. Analytically indistinguishable SHRIMP U-Pb zircon ages of 2678 +/- 5 Ma for the Mitchell Porphyry and 2669 +/- 7 Ma for the Moore Porphyry req uire that gold mineralization at Jundee-Nimary occurred at ca. 2680-2660 Ma , approximately 40 million years earlier than the majority of published rob ust ages for gold mineralization in the Yilgarn Craton, which mostly overla p at ca. 2640-2630 Ma. The close spatial and temporal relationship between gold mineralization and felsic to intermediate magmatism at Jundee-Nimary a lso raises the possibility of a genetic link between hydrothermal and igneo us activity. However, additional work is required to establish a firm conne ction. Current research on lode-gold mineralization in Archean, Paleozoic a nd Phanerozoic terranes suggests a model which postulates that these deposi ts formed during transpressional to compressional deformation in accretiona ry and collisional orogens and that their formation is intimately related t o orogenic processes. Consequently, mineralization and regional metamorphis m are expected to be diachronous, as terranes are. accreted and the front o f orogenesis migrates. Consideration of the new data presented in this pape r in conjunction with previously published dates supports the hypothesis th at gold mineralization, along with regional metamorphism, was generally dia chronous from northeast to southwest across the Yilgarn Craton, over a peri od of approximately 40 million years from ca. 2680-2660 Ma to ca. 2640-2630 Ma. This is directly analogous to the accepted model for the timing of oro genic lode-gold mineralization in other provinces and therefore provides fu rther support for a unified model for this style of deposit through geologi cal time.