Lake Johnston Operation

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Mine TypeUnderground
StatusCare and Maintenance
  • Nickel
Mining Method
  • Longhole open stoping
  • Sub-level caving
  • Longhole stoping
Backfill type ... Lock
-Emily Ann - 1.5Mt @ 3.5% Ni mined / processed between 2001-2007
-Maggie Hays – initial Resource of 12.3Mt @ 1.5%Ni, mined and processed between 2008-2013
-Maggie Hays - 3.5Mt @ 1.5% Ni for 52kt Ni
-1.5Mtpa process plant (on C&M)
-GR Engineering plant refurb estimate of $31M2 and opex of $36/t2
- NewExco exploration targeting completed, 1st phase drilling program of 15,000m POW approved, planned for CY2023
- Update mining study on Maggie Hays
- Undertake BFS
Related Asset


Poseidon Nickel Ltd. 100 % Direct

Deposit type

  • VMS


The surface geology at Emily Ann is totally obscured by transported sediments and a thick saprolite profile extends down to about 80 m below the surface.

The deposit occurs in a complex geological setting, consisting dominantly of felsic volcaniclastics hosting subordinate discontinuous lenses of mineralised and barren ultramafics, which dip at between 40° and 60° to the east in the vicinity of the deposit. The ultramafics and associated nickel-sulphide mineralisation do not extend to the bedrock surface and are therefore totally blind. The deposit has been subdivided into two main mineralised structural domains, termed the upper mineralised horizon (UMH) and lower mineralised horizon (LMH).

The UMH has a strike extent of about 520 m and down-dip extent of up to 150 m. The mineralisation is highly variable and consists dominantly of disseminated to matrix pyrrhotitepentlandite and lesser stringer and massive sulphides. The proportion of massive sulphides increases downwards towards the boundary mylonite. The mineralisation in the LMH is of greater economic significance and consists of lenses of high tenor (8-14% Ni) massive nickel sulphides (pyrrhotite-pentlandite) distributed over a strike length of about 520 m and with a down-dip extent of about 270 m.

The Maggie Hays deposit is blind, with the top of the main disseminated sulphide zone commencing at a depth of about 200 m beneath the surface and the massive sulphides at a depth of about 350 m beneath the surface, as shown in the cross section along 82700N.

The main zone of the deposit is located at the base of the CUU in association with olivine orthocumulate and mesocumulate lithologies that have subvertical dips to the east and west. Structurally, the zone occurs at a local pinch out in the CUU against stratigraphically overlying BIF (to the west) and underlying felsic volcanics (to the east). The structural termination is controlled by an early thrust, which dips at about 50° to the east and plunges at about 45° to the south, thereby terminating the main zone of the deposit at depth. A second lower grade portion of the deposit, known as the southern zone, occurs several hundred metres to the south. The Maggie Hays North zone of the deposit is controlled by the same thrust, with the mineralisation totally hosted.

Main Zone:
• Located at the base of the CUU with the bulk of the deposit located between 200 and 500 vertical metres beneath the surface and over a strike extent of 600 m.
• Basal massive sulphide zone of 4-6% Ni, located towards the lower (down-dip) margin of the disseminated zone and the northern structural termination of the ultramafic.

Northern Zone:
• Hosted entirely by felsic volcanics with the mineralisation controlled by an early thrust fault. The zone dips at about 50° to the east and has a strike extent of about 800 m.
• Massive, stringers and breccia sulphides. The sulphides form as a matrix to felsic clasts.

Southern Zone:
• Located several hundreds of metres to the south of the main deposit in high-magnesium ultramafics.
• Up to 10% disseminated sulphides, similar to the main disseminated zone.



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Mining Methods


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Crushers and Mills

Milling equipment has not been reported.



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Operational metrics

Annual processing capacity 1.5 Mt

Production Costs

Commodity production costs have not been reported.

Heavy Mobile Equipment

Fleet data has not been reported.


Mine Management

Job TitleNameProfileRef. Date
....................... Subscription required ....................... Subscription required Subscription required Mar 19, 2024

Aerial view:


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