Overview
The Hasbrouck Mtn (Mountain) gold and silver project, located in the heart of Esmeralda County, Nevada, stands as a premier example of modern heap leach engineering within the prolific Walker Lane structural trend. Situated just five miles south of the historic mining hub of Tonopah, the project represents a strategic development by Augusta Gold (formerly West Kirkland Mining). The project is uniquely designed as a dual-deposit operation, split into the Three Hills Mine and the Hasbrouck Mountain Mine. This phased development approach allows for a staggered capital expenditure while maximizing the economic life of the regional infrastructure. Nevada, consistently ranked as one of the world’s most attractive mining jurisdictions, provides a stable regulatory environment and a rich history of gold production, making the Hasbrouck Project a significant contributor to the local economy and the broader domestic gold supply.
The technical significance of Hasbrouck Mtn lies in its optimized metallurgical approach to varying ore types across its two main deposits. While Three Hills is characterized by its simplicity—utilizing a Run-of-Mine (ROM) heap leach—Hasbrouck Mountain requires more sophisticated mineral processing due to its geological complexity. The project utilizes conventional, proven technologies including three-stage crushing, cyanide heap leaching, and a centralized Adsorption-Desorption-Recovery (ADR) circuit. With gold prices analyzed at a base case of approximately $1,790 per ounce and silver at $22.50 per ounce in recent feasibility studies, the project demonstrates robust economics. The strategic location near Highway 361 and existing power infrastructure further enhances its viability, positioning it as a low-cost, mid-tier gold producer in a top-tier global district.
Key Process Stages
The mineral processing circuit for the Hasbrouck Project is divided into two distinct operating philosophies based on the phase of the mine life. Below is a detailed breakdown of the technical stages involved in gold and silver recovery:
- Phase 1: Three Hills ROM Leaching – Ore from the Three Hills deposit is mined via conventional open-pit methods and delivered directly to the heap leach pad (Run-of-Mine). Because the ore is highly porous and amenable to leaching without size reduction, this phase bypasses the crushing circuit, significantly reducing initial capital costs.
- Phase 2: Hasbrouck Mtn Crushing – As operations transition to the Hasbrouck Mtn deposit, a dedicated crushing plant is commissioned. This involves a three-stage circuit:
- Primary Crushing: A jaw crusher reduces the run-of-mine ore to a manageable size.
- Secondary/Tertiary Crushing: Cone crushers operating in closed circuit with screens achieve a target product size (P80) of approximately 3/8 inch (9.5mm) to 3/4 inch (19mm) to maximize solution-to-mineral contact.
- Agglomeration and Stacking: For the crushed Hasbrouck ore, Portland Type II cement (approx. 5 lb/ton) is added to the ore during the conveyor transport. This process, known as agglomeration, binds fine particles to larger fragments, ensuring high permeability within the heap and preventing “blinding” or solution channeling.
- Heap Leaching: Ore is stacked on high-density polyethylene (HDPE) lined pads. A dilute cyanide solution is applied via drip emitters. As the solution percolates through the ore, it dissolves the gold and silver, forming a “pregnant” solution.
- ADR Circuit (Adsorption-Desorption-Recovery):
- Adsorption: The pregnant solution is pumped through a series of carbon columns where the gold is adsorbed onto activated carbon.
- Desorption (Stripping): The loaded carbon is treated in a pressurized vessel to strip the gold back into a concentrated solution.
- Recovery/Electrowinning: The concentrated solution undergoes electrowinning to plate the gold onto cathodes, which are then smelted into doré bars.
Critical Data
The following table summarizes the key technical and operational parameters for the Hasbrouck Mtn project based on pre-feasibility analysis.
| Parameter | Value | Unit |
|---|---|---|
| Three Hills Throughput | 15,000 | Tons Per Day (TPD) |
| Hasbrouck Mtn Throughput | 17,500 | Tons Per Day (TPD) |
| Gold Recovery (Three Hills ROM) | 79 – 82 | Percentage (%) |
| Gold Recovery (Hasbrouck Crushed) | 74 – 76 | Percentage (%) |
| Silver Recovery (Hasbrouck) | 11 – 15 | Percentage (%) |
| Crush Size (Hasbrouck Phase) | 3/8 to 3/4 | Inches (P80) |
| Cyanide Consumption | 0.75 | lb/ton of ore |
| Cement for Agglomeration | 5.0 | lb/ton of ore |
| Carbon Consumption | 30 | Tons per year |
| Projected Mine Life | 8 – 10 | Years |
Technical Details and Sustainability
The engineering design of the Hasbrouck Mtn project reflects a deep understanding of the metallurgical challenges inherent in Great Basin volcanic-hosted gold deposits. One of the most critical technical evaluations involved the comparison between conventional crushing and High-Pressure Grinding Rolls (HPGR). Metallurgical testing, including column leach tests performed by Kappes, Cassiday & Associates (KCA) and McPartland (2012), demonstrated a clear correlation between particle size reduction and gold recovery. While HPGR was considered for its potential to create micro-fractures in the ore and enhance recovery, the final flowsheet opted for a robust three-stage conventional crushing circuit to balance capital efficiency with reliable performance. The choice of a P80 3/8-inch crush for the Hasbrouck phase is vital; it ensures that the relatively lower-grade ore meets the recovery targets necessary for project profitability.
Environmental sustainability and water management are at the forefront of the project’s design. Located in a high-desert environment, the Hasbrouck project utilizes a closed-loop solution management system. All leaching occurs on engineered composite liners consisting of clay and HDPE geomembranes, ensuring zero discharge to the environment. Water is recycled through the ADR plant and returned to the heap, minimizing the need for fresh groundwater makeup. Furthermore, the project’s power requirements are met through efficient grid connections, reducing the carbon footprint compared to remote sites reliant on diesel generation. The use of scale inhibitors (antiscale agents) at a rate of 6 ppm ensures the longevity of the piping and pumping infrastructure, preventing the buildup of mineral salts that could compromise flow rates and recovery efficiency.
From a reclamation perspective, the project is designed for concurrent reclamation where possible. Once leaching is complete, the heap leach pads will be rinsed to neutralize residual cyanide and then re-contoured and seeded with native vegetation to restore the landscape. The phased approach—starting with the lower-elevation Three Hills deposit—provides a unique “buffer” that allows the company to establish cash flow and operational stability before tackling the more capital-intensive Hasbrouck Mtn phase. This strategic sequencing, combined with the technical rigor of the ADR circuit and the focus on heap permeability through cement agglomeration, makes the Hasbrouck Mtn project a blueprint for modern, responsible gold mining in Nevada.
Source: Hasbrouck Mtn
Source: NI 43-101 Technical Report
This article provides an overview of mineral processing developments based on publicly available technical reports and industry analysis.
