Nimbus Project

Click for more information



Mine TypeOpen Pit
StatusCare and Maintenance
  • Silver
  • Gold
  • Zinc
Mining Method
  • Truck & Shovel / Loader
ShapshotNimbus silver mine operated from 2003 to 2007, producing 3.6 million ounces of silver at an average grade of 352g/t silver (11.7 oz/t). The old milling circuit has since been removed and the area rehabilitated.

During 2023 year, activities focussed on initial discussions with potential equity and JV partners that have shown significant interest in the project.


Horizon Minerals Ltd. 100 % Indirect
Horizon Minerals Limited owns the Nimbus silver-zinc project 100%.

Deposit type

  • VMS
  • Epithermal


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).

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-iron sphalerite, galena, pyrargyrite, marrite, boulangerite, arsenopyrite, chalcopyrite, Ag-bearing tetrahedrite) associated with the autoclastic facies of thick units of dacite; and
2. Stringer and disseminated sulfides (dominated by pyrite and sphalerite) in coherent pseudobrecciated dacite at depth. Hydrothermal alteration is characterised by intense and pervasive quartz-sericite-carbonate±Cr-V mica, with chlorite predominantly associated with mafic units.

Hydrothermal alteration is characterised by extensive and pervasive quartz-sericite-carbonate which becomes more intense towards mineralisation. Compared to other VHMS 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 rocks, ocean-plateau like low-Th basalts), mineralogy (e.g. low Cu-Au through most of the deposit, abundance of Ag and Sb sulphosalts) and alteration assemblages (e.g. lack of chlorite, presence of kaolinite at depth, fuchsite).

Nimbus primary sulfide resources occur as a series of stacked plunging lenses, overlying mined supergene and oxide mineralisation. The mineralogy is complex and includes the presence of mercury in the oxide and transition zones.

Three main zones of mineralisation have been defined, Western, Discovery and Eastern. Only the Discovery zone (oxide and transition mineralisation) and Eastern zone (oxide mineralisation) have been mined.

Other zones of mineralisation have been intersected but the data available makes interpretation of these somewhat difficult. The intersections themselves are significant nevertheless with thin zones of semi-massive sphalerite occurring along with high silver grades in excess of 500g/t.



- subscription is required.

Mining Methods


- subscription is required.


Crushers and Mills

Milling equipment has not been reported.


The Company has successfully completed the first phase of its processing study for the Nimbus Silver-Zinc Project, assessing flotation models to produce a saleable zinc concentrate followed by a Merrill-Crowe leach. It is now examining options to leach silver from the zinc concentrate to potentially produce higher value, separate silver dore, and zinc concentrate product streams. This analysis involves undertaking further metallurgical test work on samples of ore from the Nimbus Ag-Zn deposit. The next stage of test work has commenced at ALS Metallurgy. Assessment of a caustic boil after concentrate re-grind has significantly improved silver recovery from zinc concentrate to 78.8% silver extraction, against the cyanide-only leach result of 45.1%. However, this work was performed at a concentrate re-grind size of P80-38 microns. Follow up testwork in December-January will analyse results from a finer regrind of P80-10 microns. It is expected that the finer grind will further increase silver recovery from a shorter duration leach, this work was not finalised during the quarter.



- subscription is required.


Production Costs

Commodity production costs have not been reported.

Heavy Mobile Equipment

Fleet data has not been reported.


Mine Management

Source Source
Job TitleNameEmailProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Nov 7, 2023
....................... Subscription required ....................... Subscription required ........... Subscription required Mar 29, 2022

Aerial view:


- subscription is required.