exploration

The Back Forty deposit, discovered in 2001, is located along the mineral-rich Penokean Volcanic Belt in Michigan’s Upper Peninsula.

Mineralization consists of massive, semi-massive, and stringer sulfide mineralization as well as precious metal zones with sparse sulfides. Geologic research shows it contains extensive deposits of four metals key to modern industry and everyday life: zinc, gold, copper, and silver.

The deposit is expected to produce 721 million pounds of zinc, 532 thousand ounces of gold, 74 million pounds of copper, 4.6 million ounces of silver, and 21 million pounds of lead. To maximize opportunities and leverage our investment in the community, we will continue to explore for additional resources during operations.

* 2014 Preliminary Economic Assessment

mine

The ore deposit will be accessed via open-pit mining, which is one of the most common methods used by miners. Open-pit mining is practical when orebodies are located closer to the surface. The open-pit will have stepped sides, called benches, to ensure the safety of the miners and a wide ramp where equipment can travel, allowing the product to be removed efficiently from the mine to the mill located three-quarters of a mile east of the open pit. A pattern of holes are drilled into the rock surface. Next, the holes are filled with explosives and then detonated in an engineered sequence to ensure the rock is safely broken into smaller fragments. The material with economic value is stockpiled on lined pads into two different processing groups in preparation for production of various concentrates.

From here the different ores are sent to their respective crushing circuits, where they are reduced to approximately ¼” in size and either sent to the mill for processing or stockpiled for refinement at a later date. The rock that has no economic value is called waste rock and will either be stored on multilayered Waste Rock Storage Facilities or utilized in the construction of the multilayered tailings storage facility. These facilities will ensure all water is captured and sent to the water treatment plant. Once treated, the water will be recycled back into the mining process or returned to the environment.

mine

The ore deposit will be accessed via open-pit mining, which is one of the most common methods used by miners. Open-pit mining is practical when orebodies are located closer to the surface. The open-pit will have stepped sides, called benches, to ensure the safety of the miners and a wide ramp where equipment can travel, allowing the product to be removed efficiently from the mine to the mill located three-quarters of a mile east of the open pit.

A pattern of holes are drilled into the rock surface. Next, the holes are filled with explosives and then detonated in an engineered sequence to ensure the rock is safely broken into smaller fragments. The material with economic value is stockpiled on lined pads into two different processing groups in preparation for production of various concentrates.  From here the different ores are sent to their respective crushing circuits, where they are reduced to approximately ¼” in size and either sent to the mill for processing or stockpiled for refinement at a later date.

The rock that has no economic value is called waste rock and will either be stored on multilayered Waste Rock Storage Facilities or utilized in the construction of the multilayered tailings storage facility. These facilities will ensure all water is captured and sent to the water treatment plant. Once treated, the water will be recycled back into the mining process or returned to the environment.

mill

At the processing plant, metals are extracted from the ore using conventional crush-grind-float technology and equipment. The zinc-copper-lead ore will be processed into a concentrate, while the gold-silver ore will be refined into semi-pure bars, called doré bars.

These products are then sent to our customers for further refining before they can be used in mobile phones, life support devices, computers, copper wiring, solar panels, power generation, water purification systems, and many other uses.

ball mill

Following the primary crusher, the ore is fed into the semi autogenous grinding (SAG) mill along with water and steel balls. The grinding process reduces the size of the ore particles, which is then sent to a ball mill to further break down the material. The ball mill is similar to the SAG mill, except it has a larger proportion of steel balls to assist in the grinding process. The grinding process reduces the ore to a fine grain size that is mixed with water to produce a slurry.

Next, the slurry (mixture of solids and liquids) goes into a multi-staged flotation circuit where the minerals are separated, or floated, from the non-economic material (waste rock). The non-economic material is thickened to remove as much liquid as possible and pumped to the tailings storage facility. The mineral bearing portion captured in the flotation process is thickened, filtered, and pressed into concentrate. Concentrate is similar to damp talcum powder.

We will produce separate zinc, copper, and lead concentrates. These products will be loaded into covered tractor trailers and transported to a transfer station before being placed in covered rail cars and transported to our customers.

The gold-silver ore is fed into a ball mill with water and steel balls, reducing the size of the material, which is then mixed with water to make a slurry mixture. The solids in the mixture are roughly the same consistency as fine beach sand. Such a fine particle size is required for the gold extraction process.

Next, the slurry is thickened to remove a majority of the water. The recovered water is reused in the grinding circuit, while the thickened slurry moves into the leaching circuit.

The circuit is comprised of series of tanks where a sodium cyanide solution is added. The tanks provide sufficient retention time to allow the gold and silver to be dissolved and later extracted. Oxygen is added to assist in this process.

While the leaching process continues in these tanks, the primary objective is to remove the gold and silver from the solution. This is accomplished by thickening the solution to separate the solids and the liquid. The barren slurry, now known as tailings, is pumped to the tailings storage facility for further treatment. The solids that contain gold and silver are collected and melted into doré bullion bars on site.

The bars will be transported to a mint, where they will be further refined to separate the gold and silver.

mill

At the processing plant, metals are extracted from the ore using conventional crush-grind-float technology and equipment. The zinc-copper-lead ore will be processed into a concentrate, while the gold-silver ore will be refined into semi-pure bars, called doré bars. These products are then sent to our customers for further refining before they can be used in mobile phones, life support devices, computers, copper wiring, solar panels, power generation, water purification systems, and many other uses.

Following the primary crusher, the ore is fed into the semi autogenous grinding (SAG) mill along with water and steel balls. The grinding process reduces the size of the ore particles, which is then sent to a ball mill to further break down the material. The ball mill is very similar to the SAG mill, except it has a larger proportion of steel balls to assist in the grinding process. The grinding process reduces the ore to a very fine grain size that is mixed with water to produce a slurry.

Next, the slurry (mixture of solids and liquids) goes into a multi-staged flotation circuit where the mineral bearing slurry is separated, or floated, from the non-economic material (waste rock). The non-economic material is thickened to remove as much liquid as possible and pumped to the tailings storage facility. The mineral bearing portion captured in the flotation process is thickened, filtered, and pressed into concentrate. Concentrate is similar to powder in that it is made up of minute, dry particles of semi-pure substance.

We will produce separate zinc, copper, and lead concentrates. These products will be loaded into covered tractor trailers and transported to a transfer station before being placed in covered rail cars and transported to our customers.

The gold-silver ore is fed into a ball mill with water and steel balls, reducing the size of the material, creating a slurry mixture. The solids in the mixture are roughly the same consistency as fine beach sand. Such a fine particle size is required for the gold extraction process.

Next, the slurry is thickened to remove a majority of the water. The recovered water is reused in the grinding circuit, while the thickened slurry moves into the leaching circuit.

The circuit is comprised of series of tanks where a sodium cyanide solution is added. The tanks provide sufficient retention time to allow the gold and silver to be dissolved and later extracted. Oxygen is added to assist in this process.

While the leaching process continues in these tanks, the primary objective is to remove the gold and silver from the solution. This is accomplished by thickening the solution to separate the solids and the liquid. The barren slurry, now known as tailings, is pumped to the tailings storage facility for further treatment. The solids that contain gold and silver are collected and melted into doré bullion bars on site.

The bars will be transported to a mint, where they will be further refined to separate the gold and silver.

site layout

The Back Forty Mine site will consist of an open-pit, mill, and support facilities. We will employ state-of-the-art mining and environmental protection technologies across the operation. Click the map to enlarge.