Mount Brussilof (Baymag) Mine

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Mine TypeOpen Pit
  • Magnesium
Mining Method
  • Truck & Shovel / Loader
Production Start... Lock
SnapshotBaymag Inc. produces magnesite at the Mount Brussilof mine from Cambrian limestones in which magnesium has replaced calcium.


Baymag Inc. (operator) 100 % Indirect

Deposit type

  • Sediment-hosted
  • Hydrothermal


The genesis of the deposit is thought to be mineralogical replacement or molecular substitution. As such, the process occurred when a fine-grained dolomite CaMg(CO3)2 was substituted by a coarse-crystalline magnesite MgCO3. The replacement, when taking place in geological past, likely included several phases of progressive influx of magnesium (Mg) rich fluids into existed dolomite sediment.

On the molecular basis, the incursion resulted in a near complete removal of Ca+2 from chemical structure of the sediment and a fill up of available vacancies with Mg+2. The above chemical process was accompanied by a textural transformation, where original fine-grained layout of dolomite molecules was transposed into coarsecrystalline texture of newly formed magnesite.

When viewed on a large scale the deposit is a relatively homogenous, high-grade orebody. Its appearance is well defined by a white to light-grey colour and remarkably evident crystalline texture of the magnesite rock. Closer examination, predominantly by chemical analysis, have identified that broad irregular zones of contaminants occur through such forms as veining, in-filling of fractures and within the magnesite matrix itself. The value of these contaminants and the form in which they occur play a key role in determining whether the material is considered as ore or waste.

The components of vein material are generally fine-grained pyrite and/or aphanitic white dolomite. Veins occur as irregularly oriented structures with individual veins swelling to thickness of 10 cm and pinching out to nothing. Some veins, especially pyrite, tend to form in swarms covering areas tens of meters wide.

In-filling of fractures occurs in thickness up to 5 cm and generally occurs as a light brown silty clay material, aphanitic white dolomite or as pyrite. Minor occurrences of palygorskite can sometimes be seen coating fracture walls. The fractures are generally narrow elongated curvy-planar structures with local deviations of strike and dip. An invisible chemical halo often brackets the more visible fracture. These halos pinch and swell in a similar manner as veining but on a larger scale.

The interstitial or in-matrix contaminants are comprised of thin coatings of calcite or dolomite between magnesite crystals or as a simple Ca ion exchange within the crystal lattice itself. This form of contamination is the broadest form, covering areas as wide as 100 meters. With sufficient drilling, these areas can now be generally classified in the complimentary and marginal ore types, as contaminant values are usually less than occur in the other forms of contamination.

The competitive market and specific end uses of magnesite, place a great importance on the chemical
specification of the product. Somewhat unique to industrial minerals and magnesite in particular, as opposed to metal mining, is the requirement of continually meeting a set grade specification without receiving any bonus for surpassing it. Material under spec on the other hand, has a very sharp value cut-off and is essentially valueless mere tenths of a percent below spec.



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Mining Methods


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Crushers and Mills

Milling equipment has not been reported.



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CommodityUnits2022 *2021 *2020 *2017 *2016 *2015
Magnesite kt  ....  Subscribe  ....  Subscribe  ....  Subscribe230230220
All production numbers are expressed as ore. * Average annual production reported in 2016

Operational metrics

Ore tonnes mined 220 kt

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 Apr 8, 2023
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Aerial view:


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