Nimbus is a shallow-water and low-temperature VHMS deposit with epithermal characteristics (i.e. a hybrid bimodal felsic deposit), which is consistent with its position near the margin of the Kalgoorlie Terrane.
The local stratigraphy comprises a NW-trending and steeply dipping bimodal-felsic package of volcanic rocks (i.e. quartz-feldspar porphyritic dacite and lesser basalt, plus their autoclastic equivalents) with subordinate carbonaceous mudstone, tuff, polymict conglomerates and volcanic breccias. Komatiite flows, volcanic sandstones/siltstones, carbonaceous mudstone, basalt and dolerite were intersected in a distal drill hole (Hollis 2016).
Economic VHMS mineralisation in the Archaean Yilgarn Craton of Western Australia is largely restricted to two main zones of juvenile crust as revealed through regional (Nd, Pb) isotope variations. One of these zones runs north- south through the central Eastern Goldfields Superterrane and is associated with the high-grade Teutonic Bore, Jaguar and Bentley deposits, plus subeconomic VHMS mineralisation further south at Anaconda and Erayinia (Hollis 2016).
Mineralisation
Nimbus primary sulfide resources occur as a series of stacked plunging lenses, overlying mined supergene and oxide mineralisation.
In the primary sulfide zone, early well-developed massive pyrite is underlain by:
1. Semi-massive, stringer and breccia-type Ag-Zn±Pb(Cu-Au) sulfides (including: pyrite, lowand high-ir ........
