Group voices concern over mine safety
MARQUETTE — As an Upper Peninsula environmental group raises concerns over a partial cave-in incident last year at the Eagle Mine in northern Marquette County, the Michigan Department of Environmental Quality prepares to host a public meeting Thursday to gather input on the company’s permit request to expand its operation and begin mining the untapped Eagle East deposit.
The DEQ will hold the public meeting from 6 to 9 p.m. in the Westwood High School auditorium, at 300 Westwood Drive, Ishpeming. The DEQ will also accept written public comment until 5 p.m. July 6. Comments may be addressed to DEQ Eagle East Permit Amendment, Office of Oil, Gas and Minerals, 1504 W. Washington St., Marquette, MI 49855. Emailed comments can be sent to DEQ-Mining-Comments@michigan.gov, and should include “Eagle East Permit Amendment” as the subject.
The Eagle Mine requested permission from the DEQ to finish an underground access tunnel and begin extraction of the Eagle East deposit in March, about seven months after an underground vertical column of ore, also called a stope, gave way and fell unexpectedly while routine blasting occurred at another part of the mine.
Mining company officials said employees are not permitted underground when blasts occur, and there were no injuries resulting from the Aug. 5 incident.
Matt Johnson, Eagle Mine’s external relations manager, said the incident — which industry terms identify as a “fall of ground” — was partly due to a horizontal fault in the stope.
“A fall of ground is an unplanned rock fall that occurs in a localized area and is an inherent risk in any mine around the world,” he said.
Johnson said Eagle Mine employees discovered the incident during the post-blast inspection and shortly later notified the federal Mine Safety and Health Administration. MSHA conducted an investigation and, according to its report, estimated the fall of ground to be between 30 and 40 feet high.
Requests for comment from the MSHA’s local office in Marquette were directed to regional headquarters in Duluth, Minnesota, though no response was received by press time today.
However, federal inspectors, in their report, stated the discontinuity in the ore deposit and vibrations from blasts elsewhere in the mine likely contributed to the fall of ground, as well as a lack of support beneath the stope. To address that, MSHA suggested Eagle Mine change its mining method so that natural rock support structures, also known as “rib pillars,” be left in place at the bottom of stopes until the column is mined, according to the inspection report.
The incident caught the attention of environmental advocates with the Mining Action Group, a grassroots volunteer organization formerly known as Save the Wild U.P., and an affiliate of the Upper Peninsula Environmental Coalition.
Following the submission of a Freedom of Information Act request earlier this year for the MSHA report, the group in a press release issued late last month accused Eagle Mine of concealing the incident and neglecting to address it during recent community forums.
“Eagle Mine’s failure to disclose a serious underground collapse is outrageous, in light of their request for more permits to expand mining into the new Eagle East orebody. Permitting hinges on public accountability,” Kathleen Heideman, member of the Mining Action Group and UPEC, said in the release.
Johnson described the incident as an internal production and safety issue and said officials didn’t consider it noteworthy to share unless asked.
“The information was included as back up slides in the presentation if there was interest; however, we had very low attendance at the forums and conversations focused on other operational areas,” he said. “We did, however, have two communications with UPEC last year and they were well aware of the fall of ground and chose not to attend the community forums or didn’t ask for an update if they did, until this spring.”
Johnson said the change in procedure suggested by MSHA is being implemented and will still allow Eagle Mine to collect the same amount of ore and won’t impact the economics of the operation.
Through Eagle Mine’s extraction method, ore deposits are separated into alternating primary and secondary stopes, or columns. Access tunnels are cut horizontally above and below a segment of stope to be mined, which vertically is about 80 feet. Ore from the primary stopes is removed first by drilling downward from the top of the segment, Johnson explained. The ore then falls to the lower level where it is removed. The space is backfilled with a cement-rock material, and the same process is repeated afterward for secondary stopes.
“Had the ore block in the secondary stope … been uniform and massive, it is unlikely that failure would have occurred,” the MSHA report states. “Not only would the full height of the ore block been in contact with (cement-rock backfill) in both neighboring primary stopes, but the front and rear of the block would still have been connected to country rock. Although the unanticipated presence of the … discontinuity might be considered the primary cause of the block failure, perhaps in combination with blast vibration from the blasts on August 5, the effect of removing the rib pillars cannot be discounted.”
By removing the two rib pillars, expected to be about 9 feet wide each, the width of the lower level access tunnel was widened from 15 to 33 feet, leaving the additional unsupported weight of the partial ore column to be placed on the cable bolts that are installed to support stopes, according the MSHA report.
Since the horizontal fault was “unanticipated, and the failure block was too large to support with a reasonable bolting system, it must be assumed that similar discontinuities could be encountered at any time,” the MSHA report states.
MSHA inspectors stated secondary stopes face greater chances of experiencing fall of ground incidents due to being flanked on either side by the backfill of primary stopes, and suggested the rib pillars be left in place for secondary stopes to “provide physical, standing support to any unanticipated, potential detached block.”
The environmental group also questioned the integrity of Eagle Mine’s “crown pillar,” which essentially is the roof of bedrock at the top of the underground mine. The group claims experts have debated the crown pillar issue for more than a decade.
“Several mining engineers, after examining drill cores and rock quality data, have concluded that Eagle Mine’s design is fundamentally unstable, based upon flawed or falsified stability data,” the release states, and that a crown pillar less than 300 feet thick would likely collapse.
Johnson said Eagle Mine is following the original mine plan and permit regulations, which allow for a crown pillar 95 feet thick but required the company to submit additional geotechnical data demonstrating the upper levels of the mine, are safe to extract. He said external consultants have validated the data and supported the crown pillar design.
“In September 2016 Eagle received regulatory approval to mine one of the two levels,” Johnson said. “There is no change in the crown pillar design, which is supported by three years of hydrological, geotechnical modeling and continuous subsidence monitoring.”
The Eagle East deposit is about one-third the size of the ore body currently being mined.
Johnson said he expects final permit decisions to be determined by the end of this year, and, if approved, mining of the new deposit could begin in 2020, extending the life of the mine into 2023.
“The development of Eagle East is a $100 million investment that not only creates additional jobs in the community but extends existing jobs into 2023,” he said.
Ryan Jarvi can be reached at 906-228-2500, ext. 270. His email address is email@example.com.