Rochester Resources

Technology

An operating problem, solved.

Rochester is a mining operator, not a technology company. The recovery process came from working on a specific problem at Mina Real: manganese in the mineralized material.

  1. 01 · Problem

    Manganese interferes with recovery.

    Mina Real’s mineralized material carries a naturally high manganese content. Manganese occludes silver and interferes with conventional cyanide leaching, which historically limited recovery.

    Why conventional leaching fell shortIllustrative schematic. Silver grains are enclosed by manganese. Under conventional cyanidation about 4 in 10 grains are reached by the cyanide solution, in line with the historical silver recovery baseline near 43%. With the pretreatment ahead of cyanidation, about 6 in 10 are reached, in line with industrial pilot recoveries of 62% and 56%.Conventional cyanidationHistorical baseline near 43%With pretreatmentIndustrial pilot: 62% and 56%ManganeseSilver reachedSilver not reachedCyanide solution
    Illustrative only, not to scale. Proportions reflect the historical baseline (~43%) and industrial pilot results (62% mine mineralized material, 56% tailings). How the pretreatment works is not shown.
  2. 02 · Research

    A laboratory testing program.

    In 2024, a laboratory testing program evaluated mine mineralized material, tailings, and blends of both.

  3. 03 · Solution

    Pretreat, then leach.

    The program identified a pretreatment combining ammonia bisulfite and sulphuric acid, applied ahead of conventional cyanidation. The pretreatment adds a step in front of the leaching process; it does not replace it.

Conceptual process flowTailings (500 tons per day design; processing plan being finalized) and fresh mineralized material (160 tons per day design) feed a pretreatment stage using ammonia bisulfite and sulphuric acid, followed by conventional cyanidation and recovery of silver and gold. Water and cyanide are recovered for reuse. Tailings are filtered and dry-stacked.Tailings500 tpd design · plan in progressMineralized material160 tpd · design capacityNEW STAGEPretreatmentAmmonia bisulfite + sulphuric acidConventionalcyanidationRecoverySilver & goldWater + cyanideRecovered for reuse · decanterFiltered tailingsDry-stacked, not wetReusedFeed
  1. Tailings500 tpd design · planned
    Mineralized material160 tpd design
  2. New stagePretreatmentAmmonia bisulfite + sulphuric acid
  3. Conventional cyanidation↺ Water + cyanide recovered for reuse
  4. RecoverySilver & gold
    Filtered tailingsDry-stacked
Conceptual illustration · confirmed relationships onlyNot an engineering process flow diagram
  1. 04 · Validation

    Lab first. Then a three-month industrial pilot.

    Laboratory results were positive, with substantial improvements in recoveries. A follow-up three-month industrial pilot at the plant confirmed the lab work.

Silver recovery at the plant

Historical baseline, industrial pilot and reported fiscal-year results

Historical baselineSilver recovery before the new process~43%
Industrial pilot: mine mineralized materialThree months at the plant62%
Industrial pilot: tailingsThree months at the plant56%
Fiscal 2025Reported, year ended May 31, 202552.98%
Fiscal 2026Reported, year ended May 31, 202666.70%

Fiscal-year figures are reported plant results from the MD&A for the year ended May 31, 2026. Gold recovery was 99.60% in fiscal 2026 (fiscal 2025: 96.76%). Pilot figures are from a three-month industrial pilot.

  1. 05 · Implementation

    A full-scale circuit.

    A conceptual engineering study defined a full-scale circuit. Engineering, permitting, procurement and construction followed, with plant modifications beginning in October 2024, and the new circuit commenced operations on March 21, 2025.

    Design capacity
    500 tpd
    Tailings, tons per day
    Design capacity of the full-scale circuit
    Design capacity
    160 tpd
    Fresh mineralized material, tons per day
    Design capacity of the full-scale circuit
    Estimate
    ~US$4M
    Estimated capital cost
    Conceptual engineering study estimate
  2. 06 · Result

    Improved recoveries.

    The results have been positive, with improvements in both silver and gold recoveries. Improved cash flow followed, also aided in large part by improvement in commodity prices. A larger pretreatment tank is being added to increase capacity through the mill.

    Historical
    ~43%
    Historical silver recovery baseline
    Expected
    Oct 2026
    Larger pretreatment tank: expected completion
    Mid to late October 2026. Expected to allow increased capacity through the mill