NORSE

GRAVITY · MERCURY · CYANIDE

THREE VERY DIFFERENT WAYS TO RECOVER GOLD.

Gravity separates. Mercury binds. Cyanide dissolves. The important question is not which method sounds best — it is what the ore actually requires.

THE BASIC DIFFERENCE

PHYSICS AND CHEMISTRY DO DIFFERENT JOBS.

Gold recovery methods are often discussed as if they were interchangeable. They are not. Each works through a different mechanism and each has different technical limits.

PHYSICAL SEPARATION

Gravity

Uses the density difference between gold and surrounding minerals.

  • No mercury or cyanide is added.
  • Works best when gold is physically liberated from the host rock.
  • Performance depends strongly on particle size, liberation and circuit design.
  • Modern centrifugal equipment can recover finer liberated particles than traditional gravity equipment.
AMALGAMATION

Mercury

Mercury forms an amalgam with gold that is later heated to separate the metals.

  • Simple and portable, which explains its continued use in parts of ASGM.
  • Creates serious worker-health and environmental risks when mercury is handled or released.
  • The Minamata Convention requires Parties with relevant ASGM to reduce and, where feasible, eliminate mercury use.
  • NORSE does not use mercury in its clean processing route.
CHEMICAL LEACHING

Cyanide

Dissolves suitable gold into solution so that it can be recovered downstream.

  • Highly effective for many gold ores when correctly designed and operated.
  • Can recover gold that gravity may leave behind when the gold is sufficiently exposed to leaching.
  • Requires controlled storage, handling, process-water management, tailings management and emergency systems.
  • Cyanide processing is not presented as a current NORSE capability.

WHY GRAVITY IS CHANGING

GRAVITY IS OLD. MODERN GRAVITY IS NOT.

Panning and sluicing are ancient. The development of enhanced-gravity equipment, better ore characterisation and better process control has changed what physical separation can do.

01

From natural gravity to enhanced gravity

Centrifugal concentrators apply much higher effective acceleration than conventional gravity equipment. This improves the separation kinetics of small, dense particles and has expanded the useful range of gravity recovery.

02

Better liberation

The challenge is not simply to grind finer. It is to liberate the gold without creating unnecessary ultrafines. Crushing, grinding and classification therefore have to be designed together with the recovery step.

03

Staged circuits

Modern gravity recovery is rarely one machine and one pass. Concentrate, middlings and tails can be treated differently, and material can be recirculated until the process reaches a practical balance between recovery and operating simplicity.

04

Testwork and data

Gravity-recoverable-gold testing and controlled experiments make it possible to compare ore response, grind size and operating variables before a full process line is selected.

THE NORSE POSITION

GRAVITY FIRST DOES NOT MEAN GRAVITY ONLY.

Gravity First means testing how much of the gold can be recovered physically before a chemical route is considered. If the ore responds well, physical recovery may remove the need for mercury and can reduce the amount of material that would otherwise require chemical treatment.

If the gold is too fine, insufficiently liberated or locked in minerals that gravity cannot separate effectively, the test result should say so. The correct answer may then be another properly controlled technology.

The ore determines the process — not the other way around.
IMPORTANT LIMIT

Gravity cannot recover gold it cannot physically separate.

There is no responsible basis for claiming that gravity replaces cyanide for every ore. In industrial gold processing, gravity is often used alongside flotation or cyanidation. NORSE is deliberately testing where a physical route can do more — and where it cannot.

See the NORSE Process

AN EMERGING CYANIDE-FREE ROUTE

THIOSULFATE + SELECTIVE METAL SEPARATION.

Gravity is the first physical route NORSE wants to test wherever the ore allows it. But some ores will still require leaching. One development we are following closely is Chromafora's thiosulfate-based gold-leaching process combined with its SELMEXT™ selective metal separation technology.

Thiosulfate leaching itself is not new. The challenge has been to make the chemistry and downstream metal recovery technically and economically practical. Chromafora has developed the route further and, together with project partners, demonstrated the Thiosulfate–SELMEXT technology at pilot scale.

NORSE sees strong potential in this type of development as a future complement when gravity alone is not enough — and as a possible alternative to conventional cyanide leaching where the ore and testwork support it.

Gravity where possible. A safer leaching route where necessary. Always let the ore and the test results decide.
CURRENT STATUS

Pilot demonstrated — not presented as a current NORSE process.

Vinnova records the Chromafora-led project as completed and states that the Thiosulfate–SELMEXT technology was demonstrated at pilot scale and that the objective of showing its economic potential was achieved.

Chromafora is therefore presented here as a technology development NORSE is following and believes may become important. Chromafora is not presented as a formal NORSE partner, and this is not presented as an existing NORSE operating capability.

WHY THIS MATTERS FOR SMALL-SCALE MINING

THE BEST ALTERNATIVE HAS TO WORK IN PRACTICE.

UNEP and the Minamata Convention identify mercury reduction and mercury-free processing as a major priority for artisanal and small-scale gold mining. A replacement only succeeds when it is technically suitable, affordable, understandable and workable for the miner.

Health

Removing mercury from the recovery step eliminates a major source of direct toxic exposure associated with amalgamation and burning.

Measurement

A controlled physical process can be sampled, weighed and reconciled, making the result easier to review with the miner.

Economics

A cleaner route has to recover enough gold, consistently enough, to make economic sense. Environmental benefit alone will not create adoption.

SOURCES & FURTHER READING

BUILT ON CURRENT TECHNICAL AND POLICY SOURCES.

Minamata Convention on MercuryArtisanal and small-scale gold mining UNEP Global Mercury PartnershipIllustrated Guide to Mercury-Free Artisanal and Small-Scale Gold Mining Frigger et al., Minerals Engineering (2024)Operational variables and recovery/grade in a Knelson concentrator Minerals (2024)Gravity Recoverable Gold testing on contrasting gold ores International Cyanide Management CodeBest-practice framework for cyanide use in gold and silver miningChromafora (2025)Thiosulfate gold leaching + SELMEXT™ pilot resultsVinnovaCompleted pilot-scale Thiosulfate–SELMEXT project

Start with the ore.

Characterise it, test it and let the result determine the route.

Test Your Ore