Abstract
Economic volcanogenic massive sulphide (VMS) deposits of the Archaean Yilgarn Craton, Western Australia, are restricted to zones of juvenile crust, as revealed through regional Nd, Pb and Hf isotopic variations and the geochemistry of felsic volcanic rocks. Interpreted as Archaean palaeo-rift zones, one such zone runs N-S through the Eastern Goldfields Superterrane (broadly coincident with the Kurnalpi Terrane) and is associated with the high grade ca. 2690 Ma Teutonic Bore, Jaguar and Bentley deposits, plus sub-economic VMS mineralisation further south. Only small historic resources and barren pyritic lenses have been recognised in the older plume-dominated lower stratigraphy of the Eastern Goldfields.
The Nimbus Ag-Zn-(Au) deposit (12.1 Mt at 52 g/t Ag, 0.9% Zn and 0.2 g/t Au) is located approximately 10 km east of Kalgoorlie, near the margin of the Kurnalpi rift zone. Its origin has been contentious for a number of years, with previous models favouring seafloor/sub-seafloor VMS mineralisation or a high sulphidation fault-hosted system. Compared to other VMS occurrences in the Yilgarn Craton, the Nimbus deposit is unusual in terms of its tectono-stratigraphic position, the geochemistry of its host sequence (i.e. FI-affinity felsic volcanic rocks, ocean-plateau like low-Th basalts), ore mineralogy (e.g. abundance of Ag-Sb-Pb-As bearing sulphosalts, high Hg, low Cu) and carbonate-sericite dominated alteration assemblages. Classification of Nimbus as a shallow water and low temperature VMS deposit with epithermal characteristics (i.e. a hybrid bimodal-felsic deposit) is consistent with these features and its position near the margin of this palaeo-rift zone and juvenile Pb isotope values. The recognition that the Nimbus deposit is associated with 2.7 Ga plume magmatism (SHRIMP U-Pb: 2703 ± 5 Ma and 2702 ± 4 Ma) opens up new areas for VMS exploration in the Eastern Goldfields Superterrane, over a strike length exceeding 500 km. Activity associated with the Palinuro Volcanic Complex of the northern Aeolian arc, Tyrrhenian Sea, Italy, represents a comparable modern shallow marine hydrothermal system.
The Nimbus Ag-Zn-(Au) deposit (12.1 Mt at 52 g/t Ag, 0.9% Zn and 0.2 g/t Au) is located approximately 10 km east of Kalgoorlie, near the margin of the Kurnalpi rift zone. Its origin has been contentious for a number of years, with previous models favouring seafloor/sub-seafloor VMS mineralisation or a high sulphidation fault-hosted system. Compared to other VMS occurrences in the Yilgarn Craton, the Nimbus deposit is unusual in terms of its tectono-stratigraphic position, the geochemistry of its host sequence (i.e. FI-affinity felsic volcanic rocks, ocean-plateau like low-Th basalts), ore mineralogy (e.g. abundance of Ag-Sb-Pb-As bearing sulphosalts, high Hg, low Cu) and carbonate-sericite dominated alteration assemblages. Classification of Nimbus as a shallow water and low temperature VMS deposit with epithermal characteristics (i.e. a hybrid bimodal-felsic deposit) is consistent with these features and its position near the margin of this palaeo-rift zone and juvenile Pb isotope values. The recognition that the Nimbus deposit is associated with 2.7 Ga plume magmatism (SHRIMP U-Pb: 2703 ± 5 Ma and 2702 ± 4 Ma) opens up new areas for VMS exploration in the Eastern Goldfields Superterrane, over a strike length exceeding 500 km. Activity associated with the Palinuro Volcanic Complex of the northern Aeolian arc, Tyrrhenian Sea, Italy, represents a comparable modern shallow marine hydrothermal system.
| Original language | English |
|---|---|
| Pages (from-to) | 84-85 |
| Journal | Applied Earth Science |
| Volume | 125 |
| Issue number | 2 |
| DOIs | |
| Publication status | Published - 13 Apr 2016 |