Mill Building for Golden Eagle Gold Mine
Ada County, Idaho

Leavitt & Associates Engineers, Inc. completes a new gold ore processing plant for the Golden Eagle Mine owned and operated by Greyhound Mining & Milling, Inc. The Golden Eagle Mine is located on Blacks Creek Road east of Interstate 84 in Ada County, Idaho. Leavitt’s scope included civil engineering of the mine site design, structural engineering for the mill building and plant facilities, geotechnical engineering for the soils and foundations, environmental engineering and permitting, building permit acquisition and material testing and special inspection of construction.

The Golden Eagle Mine is an underground operation which was originally patented in 1914. Dan Yanke and his sons have owned and operated the mine since 1984.

The new processing plant includes an outside crushing and screening circuit and an indoor mill grinding, classification, concentration and products circuit. The facility is scheduled to begin operations in the spring of 2010. The mill will operate 24 hours each day, Monday through Friday. The mill will be shut down during the winter months. Approximately 50 tons of ore will be processed per day and 10,000 tons per year yielding approximately 1,000 ounces of gold per year.

The existing mine site was revised to add the new mill building and material handling equipment. The mine site plan was updated to show the existing facilities and the new site additions. New site access, mine roads and parking areas were added. A new crusher was added to reduce the size of the ore to be processed. Material handling receiving hoppers, belt conveyors, screens and transfers were added to carry the material through the outdoor crusher circuit and deliver the ore to the processing plant. A new 250 KW diesel generator with a 2,000 gallon diesel tank was added to provide crusher circuit power. A new tailings pond and mine dewater and storm retention pond was added. The storm water retention plan was developed and designed to manage on site storm drainage and runoff.

The processing plant uses the gravity separation and the froth flotation process which is an old and proven technology. The mine uses no cyanide or mercury in the ore processing. The mill building is constructed on a slope to aid the gravity separation and flotation process. This arrangement reduces the requirements for pumps and the power required to run them.

The mill building is a 3,128 square feet and 30 feet high engineered metal building. The plant processing equipment is founded on heavy concrete foundations designed to resist the heavy equipment processing loads and vibrations. The mill building houses a 70 ton fine ore bin, a 7’ Diameter by 4’ Conical Ball Mill, a 6’ Diameter by 4’ Round Ball Mill, Roche spiral concentrator(s), a Gemini shaker table, a 6-cell Denver Flotation Machine and the control room.

Leavitt coordinated response to Ada County Development Services’ questions and requests for additional information for the Master Site Plan and Accessory Use Permit application.

Leavitt designed the mill building, and equipment access and foundations.
Building permits and plan review approvals were coordinated and obtained by Leavitt & Associates from Ada County Development Services, Ada County Engineer, Ada County Highway District, the Idaho State Fire Marshal, Central District Health Department, DEQ, and EPA.

Environmental engineering and permitting included development of the Emergency Response Plan and Spill Prevention Countermeasures and Contingency (SPCC Plan) Plan. The SPCC Plan is designed in accordance with good engineering practice to implement the Environmental Protection Agency (EPA) rules to manage delivery and storage of diesel fuel.

The Golden Eagle Mine Dust Prevention and Control Plan was designed with progressive control strategies to manage fugitive dust emissions in accordance with DEQ rules. Procedures, control strategies, and control strategy limit triggers were developed to operate the facility per IDAPA 58.01. A Daily Inspection Checklist, monitoring and recordkeeping procedures were developed. An Odor Management Plan was waived by DEQ based on the findings and recommendation of Leavitt & Associates.

Water sampling and testing of the mine well drinking water and mine dewatering pond water was completed to verify and satisfy Department of Environmental Quality (DEQ) and EPA water quality standards. Water samples were tested for Nitrates, Nitrites, Arsenic and coli forms.

Leavitt prepared and submitted the application and submittal documents to DEQ for Permit to Construct – Exemption (PTC-Exemption). The diesel generator emission calculations demonstrated compliance with the requirements for a PTC-Exemption and showed that the facility emissions were below regulatory concern.

The Storm Water Pollution Prevention Plan (SWPPP) was designed to implement Best Management Practices (BMPs) for erosion and sediment control, site stabilization, good housekeeping and the Construction Site Inspection Checklist to manage storm water runoff and control during construction.

Leavitt & Associates Engineers, Inc. has a mining engineer on staff and provides plant facilities, mine design and engineering solutions and services throughout the western states.