Lake Johnston

  • 1.5Mtpa processing plant
  • Maggie Hays Ni 52kt Ni* (grade - 1.5%)
  • Abi Rose Ni discovery confirms prospectivity
  • Intrusive and Extrusive models to be tested


  • Emily Ann - 1.5Mt @ 3.5% Ni mined and processed b/n 2001-2007 
  • Maggie Hays - 10Mt @ 0.6%Ni mined and processed b/n 2008-2014

Recent exploration activities at Lake Johnston focussed on the collation of geological data and verification of geology models and targets previously generated. The work was completed by NewExco with final report, delivered during September 2021, indicating the tenements remain prospective for further nickel sulphide discoveries and prioritising targets requiring drill testing. Poseidon and NewExco have designed an exploration program to test the upper surface of the Western Ultramafic looking for Kambalda-style nickel deposits (see figure below).

The Lake Johnston project is considered highly prospective for further nickel discoveries. Future exploration works will focus on building resources to facilitate a recommencement of mining and processing operations, leveraging off the 1.5Mtpa processing plant and associated infrastructure located on site.

Magnetics map of the Lake Johnston area highlighting project areas.

Future Operations & Processing Plant Refurbishment

While the Company is focused on restarting the Black Swan Project, Lake Johnston could be restarted once Black Swan is in operation. By developing a second processing hub the Company can expand its nickel production and achieve its strategic production target of at least 15k tonnes per annum nickel in concentrate.

Exploration activities are planned to grow Lake Johnston’s mineral resource and reserve, supporting a recommencement of operations. GR Engineering Services Limited (“GRES”) was engaged to provide Poseidon with capital and operating cost estimates for the refurbishment and operation of the ore treatment circuit and associated infrastructure at Lake Johnston (to a +/- 20% level of accuracy).

Lake Johnston Primary Mill

In January 2022 GRES estimated the capital expenditure to refurbish the plant and associated infrastructure to be approximately $31 million with an estimated refurbishment schedule of seven months, assuming power supply can be supplied and installed within this period.

GRES estimate of operating costs was $36.04 per tonne at a processing capacity of 0.9 million tonnes per annum. Ore will be treated through the existing crushing, grinding and flotation circuit of the Lake Johnston plant to produce a nickel concentrate.


In 2022, the Program of Work (PoW) lodged with the Department of Mines, Industry Regulation and Safety (DMIRS) was approved for an exploration program targeting the high priority Western Ultramafic unit. The program will consist of up to 250 holes on 43 lines, drilling up to 15,000 metres. The Company is yet to commence this program.

Current resources & infrastructure

  • Maggie Hay - 3.5Mt @ 1.5% Ni* for 52kt Ni
  • 1.5Mtpa process plant (on C&M)
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