exploration

Products manufactured from minerals are all around us, and we rely on them daily. They shape our way of life, our health, and the global economy. However, mineral deposits are not as common as you may think and we cannot choose where they exist. The world has 200 million square miles of land, which makes locating large quantities (i.e., deposits) a difficult task. Knowing where future mineral resources will come from is vital for sustaining demand.

Today, geologists discover most mineral deposits by aerial exploration. Equipment attached to planes, helicopters, and even drones detect anomalies in the earth’s crust from the air. Only 1 in 100,000 anomalies detected from the sky contains potentially mineable quantities of minerals.

So, what about the Back Forty deposit? Zinc and copper minerals were discovered in 2001 when a local landowner had a new water well installed. Additional drilling took place in 2002, resulting in the discovery of the deposit, which sits along the mineral-rich Penokean Volcanic Belt in Michigan’s Upper Peninsula.

The deposit is expected to produce 512 million pounds of zinc, 468 thousand ounces of gold, 51 million pounds of copper, 4.5 million ounces of silver, and 24 million pounds of lead. To maximize opportunities and leverage our investment in the community, we will continue to explore for additional resources during operations.

Yet, the story of the Back Forty deposit can be traced 1.8 billion years ago to the formation of a hydrothermal vent on the seafloor. High concentrations of dissolved metals from the vent surged up and mixed with frigid seawater. The change in temperature and chemistry caused the metallic elements including zinc, gold, and copper to bind with other minerals and settle onto the seabed as metal-bearing minerals. Over the course of time, this accumulation became the Back Forty deposit we know today.

We plan to continue exploration during operations while providing the minerals society depends upon today.

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 we’ll refine the gold-silver ore into semi-pure bars, called doré bars.

During an average year, we’ll produce 71,160 tonnes of zinc concentrate, 23,120 tonnes of copper concentrate, and 5,600 tonnes of lead concentrate. Also, we’ll provide an average of 67,000 oz of gold.

These products will then be sent to our customers for refining before use in mobile phones, life support devices, computers, copper wiring, solar panels, power generation, water purification systems, and many other applications.

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.

Click to enlarge

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 to enlarge