A New Life for Moss Mine

Northern Vertex Mining Corp. Bullhead City, Arizona, USA
Through design-build delivery, CDM Smith helped Northern Vertex Mining Corp. reactivate the idle Moss Mine in Arizona, USA, a Civil War-era gold excavation site.

Trans­form­ing a Historic Site into a Productive Model of Mining
Moss Mine, a historic gold property in the Oatman District of Bullhead City, Arizona, dates back to the Civil War, when burros and black powder were used to mine high-grade ore near the surface. To help Northern Vertex Mining Corp. reactivate the idle mine, CDM Smith implemented a design-build programme that allowed Northern Vertex to dig deeper and transform the historic site into a productive model of mining.

Planning for Success
CDM Smith provided turnkey “life-of-mine” services, including preliminary engineering and environmental permitting at the beginning of the project. “For mining projects, the very first phase is ore discovery, and companies cannot get permits or begin design until this phase is complete," explained Bob Vince, PG, CDM Smith associate and metals and mining client service leader. "These projects are made or broken by engineers’ planning and cost projections.” CDM Smith leveraged its regulatory and environmental expertise to secure and expedite the appropriate permits, taking advantage of regulatory provisions that allowed for immediate production.

The project also involved significant environmental controls, including managing runoff from the region’s frequent monsoon rains, keeping fine powder and soil in place, and using liners and leachate detection to prevent processing fluids and chemicals from being released into the environment. All of these measures were installed to protect the soil, water and air. Before implementing the site's new heap leach mining system, the project team employed best practices in scientific exploration to help define the limits of the mineralisation.

A 3D Pot of Gold
CDM Smith implemented the project’s new heap leach mining system, where excavated raw ore is crushed and reduced into fine pellets, stacked on a liner or leach pad, and then irrigated with sodium cyanide to separate the gold from solids. The gold-laden solution drains to a pond and is then pumped to a processing plant to recover the gold. “It is the most economical way to recover gold, and we worked with Northern Vertex's seasoned mining executives to design the solution,” stated Vince. Roughly 5,000 tons of gold ore are processed at the site daily, with an estimated gold and silver equivalent of 27 kg.

The extent of the deposit has grown through the use of modern scientific exploration tools.
Joe Bardswich, Northern Vertex Project Manager

To optimise mining efforts on the highest-grade reserves, advanced modelling software converts raw exploration data, such as gold assays from core samples, into 3D models of the subsurface ore. “The extent of the deposit has grown through the use of modern scientific exploration tools, and we continue to define the limits of the mineralisation using the best science available,” stated Joe Bardswich, Northern Vertex project manager. “We strive to do this as a socially responsible corporate citizen, with occupational and environmental safety as a guiding principle.”

Safety and Sustainability
The 3D model also delineates hidden hazards such as historic underground workings. Using old mining maps and topographic laser scans results in better above- and below-ground condition analysis for site safety. Safety is so important in mining that the industry is regulated by its own government agency, the Mining Safety and Health Administration—a sister agency to the Occupational Safety and Health Administration. Ken Meyer, CDM Smith principal health and safety manager and Mining Safety and Health Administration-certified trainer, developed the mine’s health and safety plans. “An effective health and safety culture is paramount for mining clients. Unless you have worked on a mine, you might not recognise the potential for hazards, like heavy-duty crushing equipment, large trucks and undetonated explosives.”

To improve public safety around the mine, adits—openings in the ground—and other mining hazards were closed. “These are fragile environments, so we had to ensure that what we’re leaving behind is stable and safe. We wanted to orient operations and develop land use toward productive post-mining, such as natural habitats and off-road recreation,” said Vince. “Often, mine hazard closures are funded by taxpayers. Northern Vertex and CDM Smith worked with state mine inspectors to safely close and reclaim the abandoned mines and historic workings at no taxpayer cost.”

Beyond local economic benefits, the mine’s success may serve as a model for other sites. Vince also believes that today’s approach to mining has longer-term benefits. “The return to these historic properties, which were developed prior to environmental awareness, allows today’s mining companies to address past impacts with solutions that preserve the industry and environment.” For Bardswich, the ultimate measures of success are fundamental, “Zero accidents, minimal disturbance, proper reclamation and profitable operations. Very few exploration projects progress to production; the success of this project gives us a good chance at being a profitable mining operation."

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