Updated Preliminary Economic Assessment (effective date July 23, 2024; report dated January 6, 2025) proposes a three-stage crushing and valley-heap-leach operation with carbon adsorption for the Spurr, Varga, Sphinx and East Ridge deposits. The study is a proposed design, not a constructed plant; no on-site doré production is claimed.
Report context
This technical report presents an updated preliminary economic assessment for the Bell Mountain project in Churchill County, Nevada. The processing section draws on metallurgical testwork conducted by McClelland Laboratories Inc. (MLI) in 2013–2015, using 447 boxes of PQ and HQ drill core from the Varga, Sphinx and Spurr deposits. No metallurgical testing data was available for the East Ridge deposit; similarities with other deposits were used to estimate recovery for that smaller deposit. The qualified persons caution that the term "ore" in referenced earlier reports does not imply current mineral reserves.
Processing route
Comminution and crushing
Blasted material is fed to a primary jaw crusher that reduces maximum particle size to 4 inches. Secondary crushing uses a standard cone crusher, with a ¾-inch screen recycling oversize material. The target product is 80% passing ¾ inch. The crusher work index determined by FL Smidth in late 2015 was 13.8 kWh/ton, classified as "soft-medium" ore hardness and considered amenable to crushing. Sample density reported by FL Smidth was 2.6, presumed representative of the denser material on site.
Heap leach design: valley leaching with multiple lifts
Crushed mineralized material is placed on a permanent pad in 20-foot lifts using trucks. A dozer rips the travelled surface before leach solution is applied. The design proposes valley leaching, where successive lifts are stacked on top of previously leached lifts. Pregnant leach solution from the upper lift percolates through the lower lift, extending the effective leach cycle for lower lifts beyond the nominal single-lift period.
Hydraulic conductivity tests on compacted ore columns showed equivalent permeability at 40-foot heap lift height and at over 220 feet, supporting the potential for tall stacked heaps. The report states that based on these results, Bell Mountain ores could be stacked over 200 feet high and still maintain good solution percolation.
Solution management and metals recovery
PLS from the collection system at the pad base reports to a Pregnant Solution Storage Tank. It is then pumped through a series of activated carbon columns that adsorb gold and silver cyanide complexes. Once loaded, the carbon is collected, drained and shipped to a toll refiner for metal extraction. Fresh carbon is added to the final column, and carbon is advanced countercurrently through the tanks. Barren solution from the carbon columns goes to a Barren Solution Storage Tank; make-up sodium cyanide maintains constant cyanide concentration, and solution is recycled to the heap.
The report recommends carbon adsorption over Merrill-Crowe because of the combination of relatively high gold recovery (approximately 80%) and very low silver recovery (below 15%), despite a silver-to-gold ratio of about 25:1 in some materials.
Reagent consumption and testwork limitations
Bottle-roll tests (96-hour duration, 80% passing 10 mesh, 40% solids) on Spurr, Varga and Sphinx composites showed:
- Sodium cyanide consumption: <0.14 lb NaCN/ton ore
- Lime consumption: 2.6–3.3 lb/ton
Column leach tests used standard solution at 2 lb NaCN/ton solution applied at 0.005 gpm/ft², running for at least 152 days (125 days for Sphinx). For Spurr and Varga, both -¾-inch and -⅜-inch crush sizes were tested; Sphinx was tested only at -⅜-inch. No leaching tests were reported for East Ridge.
The report notes that column leach recovery curves for Spurr and Varga were still rising after 152 days, supporting the valley-leach strategy where lower lifts experience longer total leach times. MLI reported no significant difference in final tails assays between -¾-inch and -⅜-inch columns for Spurr and Varga, though they concluded that finer crushing would yield significantly better recoveries based on bottle-roll results. The report authors defend that similar recovery would be achieved for -¾-inch rock over extended multiple-lift leaching.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Primary crush product | 80% passing ¾ inch | Proposed design |
| Crusher work index | 13.8 kWh/ton | FL Smidth testwork (2015) |
| Heap lift height | 20 ft | Proposed design |
| Maximum stackable heap height | >200 ft | Hydraulic conductivity testing |
| NaCN consumption | <0.14 lb/ton | 96-hour bottle-roll testwork |
| Lime consumption | 2.6–3.3 lb/ton | 96-hour bottle-roll testwork |
| Au recovery, Spurr (-¾ inch, 152 days) | 83.7% | Column leach testwork |
| Au recovery, Spurr (-⅜ inch, 152 days) | 85.7% | Column leach testwork |
| Au recovery, Varga (-¾ inch, 152 days) | 68.6% | Column leach testwork |
| Au recovery, Varga (-⅜ inch, 152 days) | 76.5% | Column leach testwork |
| Au recovery, Sphinx (-⅜ inch, 125 days) | 85.2% | Column leach testwork |
| Au recovery, East Ridge (assumed, -¾ inch) | 80% | Estimated by analogy; no testwork |
| Ag recovery, Spurr (-¾ inch, 152 days) | 29.6% | Column leach testwork |
| Ag recovery, Spurr (-⅜ inch, 152 days) | 33.3% | Column leach testwork |
| Ag recovery, Varga (-¾ inch, 152 days) | 12.8% | Column leach testwork |
| Ag recovery, Varga (-⅜ inch, 152 days) | 14.4% | Column leach testwork |
| Ag recovery, Sphinx (-⅜ inch, 125 days) | 11.3% | Column leach testwork |
Project website: https://www.lincolnmining.com/news-media/news-releases/lincoln-announces-acquisition-of-bell-mountain-gold-project-nevada
Technical qualifications
The processing route described is a proposed design supported by metallurgical testwork on three of four deposits; it does not describe an operating plant. No on-site doré production is claimed; loaded carbon is sent to a toll refiner. The East Ridge recovery estimate (80%) is an assumption without supporting column or bottle-roll testwork. The report explicitly recommends further metallurgical testing on -¾-inch Sphinx material and on East Ridge material. All recoveries are from column leach tests at specified crush sizes and leach durations; overall project recovery will depend on the valley-leach strategy and total leach time per lift.
Source: Sections 13.0 (Mineral Processing and Metallurgical Testing) and 17.0 (Recovery Methods) of the referenced report.
