Proposed Crandon Mine Information
Economic deposits of valuable metallic minerals are rare in occurrence and depend on the geological history of a region. Several areas of economic mineralization have been identified in Northern Wisconsin. Exxon Coal and Minerals Company discovered a deposit located in Forest County during the mid-1970's through geophysical reconnaissance and an extensive exploration drilling program. Nicolet Minerals Company is proposing to develop the ore body and is currently engaged in the mine permitting process.
Project History and Ownership
In 1976 Exxon Coal and Minerals Company announced the discovery of a zinc-copper ore body located in northeastern Wisconsin near the city of Crandon. During the early 1980's, Exxon submitted the necessary permit applications and environmental studies necessary to characterize the environment surrounding the project site. In November 1986 the Wisconsin Department of Natural Resources published a Final Environmental Impact Statement, which described the proposed project, the affected environment including natural and cultural resources, environmental impacts of the proposed project, and alternatives to the proposed project and their impacts. An environmental impact statement was produced to inform the project's decision-maker and the public of the mine's effect on the environment. In December 1986 Exxon withdrew their permit application, citing depressed minerals prices, and a formal permitting decision and evaluation on adequacy of the environmental impact statement was never determined.
|This thumbnail image links to a
larger version of a map of the Crandon Project location in PDF format.
Beginning in February 1994, interest in mining the Crandon Deposit was renewed when Crandon Mining Company (which at the time was a partnership between Exxon and Rio Algom, Ltd.) formally submitted a Notice of Intent to collect data to support a mining permit application for the proposed Crandon Mine. This initiated an informational hearing and opportunity for public comment.
In January 1998, Rio Algom announced that it had purchased Exxon's interest in the Crandon Project and renamed the mining permit applicant to Nicolet Minerals Company (NMC). Also, in 1998 the applicant proposed the following three significant alterations to the project design, primarily related to waste management, mine operation, and wastewater treatment and discharge:
- pyrite would be separated during the mineral concentration process, mixed with cement, and placed underground as a cemented paste backfill (due to the pyrite separation the waste disposal facility was reduced in size to about 75% of the originally proposed 345 acres);
- a grout blanket would be installed over the ore body in order to reduce water inflow into the mine from the overlying glacial sediments, and therefore would result in a reduction of groundwater and surface water drawdown and mitigation requirements;
- wastewater would be treated via reverse osmosis and evaporation-condensation, to meet numeric standards for groundwater quality, and discharged on-site through a system of groundwater seepage cells (the original proposal to discharge treated wastewater into the Wisconsin River via a 38.3 mile pipeline is no longer applicable).
During November of 2000, Billiton, Plc. announced that it had acquired ownership of Rio Algom. Then in July 2001 Billiton merged with BHP (Broken Hill Proprietary) to form BHP Billiton, with headquarters in Australia. BHP Billiton is the current owner of the Crandon Project.
In September 2002, BHP Billiton announced that it was putting the mining project up for sale and closing the NMC office and the project information center in Crandon.
Then in April 2003, Nicolet Minerals Company was purchased by Northern Wisconsin Resource Group, a Limited Liability Company. The new owner of NMC has indicated that it will not withdraw the permit applications.
|This thumbnail image links to a
larger version of a map of the Crandon Project Area and Surface
Facilities in PDF format.
Nicolet Minerals Company is proposing to develop the Crandon Project, which would entail the construction, operation, and reclamation of an underground zinc-copper-lead mine, mill, and waste management disposal facilities located about five miles south of the city of Crandon, Wisconsin. The company proposes to develop the project as an underground mine and remove 55 million tons of ore from the sulfide mineral deposit, which is approximately 4,900 feet long, 2,200 feet deep, and 100 feet wide. The total surface area that would be disturbed during mine development is approximately 550 acres, all located in Forest County. The expected project life is 34 years, assuming 1 to 3 years for initial construction/mine development, 28 years for operation, and 3 years for reclamation.
Ore is expected to be mined at a rate of 5,500 tons per day. The ore body consists of two distinct types of mineralization containing zinc-, copper-, and lead-bearing minerals with minor amounts of gold and silver. At Crandon, ore would be blasted, crushed, hoisted to the surface, and directed to the mill for concentrating using a selective flotation process.
Finely ground ore would be pumped as a slurry into a series of flotation tanks. Air and reagents would be added to create a froth, and additional reagents would be added to selectively promote the flotation of the desired mineral and depress the flotation of the other minerals. The desired minerals adhere to the froth and are skimmed from the surface. As the slurry proceeds through the mill circuit, reagents are adjusted to produce zinc, copper, and lead concentrates. Metal concentrates would be shipped by rail to out-of-state smelting facilities. In addition, pyrite concentrate would also be recovered and used as backfill material during operation of the underground mine. The remaining material, called tailings, would be transported hydraulically to the tailings management area for permanent disposal.
Typically, metallic mining projects generate large volumes of waste materials (rock and tailings) and require the construction of engineered facilities for permanent disposal of waste products. Tailings and waste rock from sulfide mineral deposits have the potential to oxidize and release contaminants (metals, sulfate, and acidity) into the environment. In order to address this concern, NMC has committed to maintaining a net-neutral waste disposal facility to minimize the potential release of contaminants from the facility.
Nicolet Minerals Company has proposed to construct an engineered surface disposal facility or tailings management area (TMA) to contain the tailings. The TMA would have a disturbance footprint of roughly 282 acres, and is similar in design to a modern solid waste landfill. At Crandon, the expected ore production of 55 million tons would result in roughly 45 million tons of tailings and waste rock that would require disposal. Approximately 40% of the tailings would be disposed of at the TMA and 60% would be used as backfill for the underground mine. Tailings would be transported to the disposal facility as a slurry, and water would be decanted and reused in the mill or eventually transported to the wastewater treatment plant and ultimately discharged at the on-site groundwater seepage cells. Tailings disposal would occur in stages during the life of the project. The average tailings depth in the TMA is expected to be about 90 feet.
Mining waste disposal facilities must comply with stringent groundwater quality standards at the design management zone (DMZ), established at a distance of 1,200 feet from the outside edge of this facility. In addition, operators must take action if standards are exceeded at an intermediate intervention boundary set at 150 feet. As part of the permitting process, an applicant is required to demonstrate through predictive modeling that groundwater standards will not be violated at the DMZ. There is also a similar compliance standard for the underground mine (or reflooded mine) once mining activities have ceased.
Nicolet Minerals Company has proposed to separate potentially acid-generating pyrite during the ore-concentration process, from the mine tailings. As a result, the pyrite concentrate would be mixed with cement and placed (backfilled) underground as a paste. Following reclamation, and once the groundwater table recovers to near pre-mining conditions, the pyritic paste backfill would be submerged in the reflooded mine.
Copies of Nicolet Mineral Company's Environmental Impact Report are available for public review at several locations. The Department has been leading the State review of this project since 1994 and has committed to publishing a Draft Environmental Impact Statement approximately four months after all of the necessary information is received from the applicant and verified by the Department. It is expected that a DEIS will be published during the summer of 2003. An overview of the metallic mining permitting process (leaves Crandon Web site) is discussed at the Bureau of Waste Management's site, process flow diagrams are also available there.