Extensive metallurgical testwork has been historically performed at Tonopah by a number of Company’s including Rio Algom, Kennecott Minerals, Newmont Gold, Midway Gold and most recently Viva. Work programs have included gold recovery testing methods including: cyanide soluble assay, shake flask; bottle roll leach; column leach; carbon-in-leach (CIL); gravity; and flotation test work. All tests have demonstrated that Tonopah gold mineralization is well oxidized and that gold may be recoverable by all methods with prior crushing or grinding for liberation of contained gold content. A clear particle size versus gold recovery relationship exists at Tonopah where a high gold recovery is dependent on particle size reduction for liberation. Please see Viva’s 2022 PEA study for greater detail.
Recent metallurgical testwork by Kappes Cassiday Associates of Reno Nevada has demonstrated low-grade (<1.0 grams per tonne (g/t)) heap-leach gold recoveries averaging around 65% to 70% using a conventional three-stage crush, cement agglomeration, heap-leach circuit is possible.
2022 PEA resource modeling demonstrated that roughly 20% of the mineralized tonnes at Tonopah carries 50% of the contained gold ounces above a 1.0 g/t cutoff grade. This originates primary from structurally related gold mineralized zones. Per testwork by KCA, this higher-grade mineralization sees only 50%-70% gold recovery in conventional heap leach due to free gold content and or possible silica encapsulation. This same material, with an additional grind step to a 75 microns (200 mesh) particle size, achieves test recoveries in CIL leach of 93-94%. Higher-grade mineralization is found in sufficiently large blocks in the resource model that it will conceivably support selective mining with a well-managed ore control program. This process represents a potential economic upside if proven feasible.
With these process dynamics, the concept of pulp-agglomeration leach was examined by KCA in 2023. This process is not believed to be feasible due to cement application rates and costs. We believe that this is due to the sedimentary argillite content, which produces excessive fines in crushing.
Separate low-grade heap leach (~80% of tonnes) and high-grade mill circuits (~20% of tonnes) are options to optimize gold recovery. Both circuits would be fed from the same crushing plant and dry-stack tails from the small-scale CIL mill would be stored in cells on the leach pad, avoiding the need for a tailings dam. Initial review indicates that higher gold recovery may potentially offset the additional operating cost of the CIL circuit while giving an accretive return on capital invested. Conversely, if a lower average gold recovery can be feasible, then a heap-leach only scenario may be contemplated. These varying flow sheets require additional metallurgical testwork and feasibility study analysis to further validate.
Environmental and Permitting
Viva has the permits and authorizations necessary to conduct mineral exploration activities on both public and private land. Authorizations include:
- Decision Record (DR) and Findings of No Significant Impact (FONSI) issued by the United States for a Plan of Operations to disturb up to 75 acres during exploration.
- Department of the Interior Bureau of Land Management (BLM) Casefile NVN-076629, and Reclamation Permit 0210 issued by the Nevada Division of Environmental Protection (NDEP) Bureau of Mining Regulation and Reclamation (BMRR).
Studies by a prior operator on the project were undertaken to support a potential small-scale underground mining operation. The studies identified and evaluated baseline hydrogeologic conditions, groundwater quality, storm water controls, mine dewatering requirements, ore and waste rock geochemistry, and surplus water management options including re-infiltration and underground water injection.
A Baseline Needs Consultation Meetings was held between the BLM, Nevada Department of Environment (NVDEP) and Viva Gold in March 2021. As a result of that meeting a BLM project manager was appointed and a Baseline Needs Assessment Form (BNAF) has been completed for Tonopah. This form outlines 36 different Baseline environmental or technical studies that require completion before initiating a construction permitting process. Of that total roughly half of the tasks were deemed not required or to be addressed in the final permitting process. The following studies have subsequently been completed by the Company:
- All wildlife, bird, soil and vegetative studies were submitted to the BLM in September 2022 (8 total from checklist)
- Approximately 50% of an updated Class III Cultural Resource Inventory update was completed in 2021.
- Acid based accounting and humidity cell testwork was completed in 2023 demonstrating benign geochemical characteristics for waste and mineralized materials.
- Two additional upstream water monitoring wells were drilled and completed in 2022
- Seeps and Springs water studies completed for 10-mile radii in 2022
- Baseline water sampling and characterization testwork completed quarterly over three-year period by the end of 2023. Quarterly sampling work is planned for 2024
- Pump down hydrologic test work completed in late 2022 and initial hydrographic water modelling completed in 2023
Work Plan
As a result of its 2022 PEA study work and subsequent analysis, Viva believes that Tonopah has a strong potential of becoming viable gold mining project. As a result, all work on the project is targeted towards demonstrating this point and in removing risk from future project development. Viva’s 2024 gold for Tonopah include:
- Additional drilling to further delineate and validate the near surface, high-grade zones of mineralization discovered in the eastern half of the main pit as a result of our 2022/23 drill programs
- Sequential complete tasks from the 2021 BNAF list to be ready to commence project permitting on completion of a Plan of Operations as part of project Feasibility Study
- Advance the project to pre-feasibility/ Feasibility level study
- Complete a Plan of Operations as part of Feasibility study work to initiate the Environmental Impact Study process.
