Skip to content
UNITED STATES
DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health

Report of Investigation

Underground Metal Mine
(Copper)

Fatal Fall of Ground Accident

January 31, 2000

Mission Mine
ASARCO, Incorporated
Sahuarita, Pima County, Arizona
ID No. 02-02626

Accident Investigators

Larry O. Weberg
Supervisory Mine Safety and Health Inspector

Robert V. Montoya
Mine Safety and Health Inspector

Joseph A. Cybulski, P.E.
Supervisory Mining Engineer

Michael A. Evanto, P.G.
Geologist

Thomas E. Lobb
and
Michael J. Getto
Physical Scientists Explosives & Blasting

Originating Office
Mine Safety and Health Administration
Rocky Mountain District
P.O. Box 25367, DFC, Denver, CO 80225-0367
Claude N. Narramore, District Manager


OVERVIEW

Jose Villanueva, miner, age 59, was killed and Joseph A. Olson, Jr., miner, age 52, and Javier Vargas, operator, age 44, were seriously injured on January 31, 2000, when a slab fell from the back of a stope where they were loading blastholes.

The accident occurred because ground support had not been installed after a series of first back-lifts had been taken out. An examination and test for loose ground had not been conducted prior to work commencing.

Villanueva had a total of 37 years experience as an underground miner. He had worked at this operation for 14 months. All three miners had received training in accordance with 30 CFR Part 48.

GENERAL INFORMATION

The Mission Mine, a multi-level underground copper mine, owned and operated by ASARCO, Incorporated, was located near Sahuarita, Pima County, Arizona. The principal operating official was John D. Low, general manager. The mine was normally operated three, 8-hour shifts a day, 7 days a week. A total of 85 persons was employed; of this number 64 worked underground.

The ore body rested within a block of paleozoic-era, carbonate rocks which had been altered to skarns, locally known as tactites. These mineralized rocks were faulted into contact with unmineralized mesozoic-era argillite. Copper-bearing ore was drilled and blasted from stopes at various levels in the mine. Broken material was transported to the surface on trucks where it was dumped near the mine opening. The material was then loaded onto surface haulage trucks and transported to the mill for crushing, grinding and processing.

The last regular inspection at this operation was completed on November 23, 1999. Another inspection was conducted in conjunction with this investigation.

DESCRIPTION OF THE ACCIDENT

On the day of the accident, Jose Villanueva (victim) reported for work at 4:00 p.m., his normal starting time for the afternoon shift. He, Joseph Olson, Jr. and Javier Vargas were assigned to load blastholes in the 215-north stope, which had been drilled during the previous shift. Approximately 85 holes were to be loaded with ANFO prill blasting agent. A Getman series 2-500 ANFO loading boom truck was brought into the stope, but the back was too high, so a JLG 600S telescopic boom lift was brought in to reach the top holes. The Getman truck contained the ANFO loading equipment which included two, 1,000 pound capacity stainless steel lined ANFO pots, a vibrator and 50 feet of delivery hose.

The crew worked without unusual incident until about 8:00 p.m., when the slab fell from the back of the stope. The slab measured approximately 9-1/2 feet by 11-1/2 feet by 1-1/2 feet and weighed an estimated nine tons. It struck the boom of the JLG manlift. Villanueva and Olson were loading holes from the man basket and were jostled out. They fell approximately 20 feet to the floor. Vargas was operating the Getman prill dispenser and was injured when the slab rolled off the boom and struck him.

Louis Marrujo, shift supervisor, came to the area moments after the accident occurred. Mechanics from the surface shop and miners from other working places came to assist. Emergency medical technicians and an ambulance crew assisted the victims and prepared them for transportation. Olson was airlifted and Vargas was taken by ambulance to a hospital in Tucson, Arizona. Villanueva was pronounced dead at the scene by the County Coroner. Death was attributed to crushing injury to the torso.

INVESTIGATION OF THE ACCIDENT

MSHA was notified at 9:30 p.m., on the day of the accident by a telephone call to Ronald Renowden, safety and health specialist, from Robert Jordan, safety administrator for the mining company. An investigation was started the next day. MSHA's investigation team traveled to the mine and made a physical inspection of the accident site, interviewed a number of persons, and reviewed documents relative to the job being performed by the victim, his co-workers and their training records. An order was issued pursuant to Section 103(k) of the Mine Act to ensure the safety of miners. The miners' representative participated in the investigation.

DISCUSSION

The accident occurred in the 215-north stope at the intersection of the L and 9 drifts. Initial development of this stope began in 1996. It had not been worked for about two years until two weeks prior to the accident. Drifts were mined typically 20 to 25 feet wide and approximately 25 feet high. Artificial ground support consisted of 8-foot long split-set friction rock stabilizers, installed in conjunction with 6-inch by 6-inch bearing plates, and 8-foot long steel mats. The split-sets were installed on roughly 4-foot by 4-foot centers with the steel mats typically oriented longitudinally down a drift. At the time of the accident, portions of the 215-north were being back stoped. This mining method involves taking two additional lifts from the back in a previously developed stope, each about 10 to 12 feet high, leaving a final stope height of 40 to 44 feet. A series of first back-lifts was completed east of the K access drift and included the 9, 10, and L drifts, including the accident site.

The ore being mined in the 215-north stope generally consisted of hanging-wall garnet skarn bounded by footwall argillite waste rock. The rock composing the back and ribs consisted of the hanging wall high-grade garnet skarn, footwall waste argillite, an intrusive igneous dike, and a lens of waste wollastonite skarn.

Total overburden above the underground mine varied from 300 feet to 1,500 feet, depending upon location in the ore body relative to the pit wall. Overburden at the accident site was estimated to be 430 feet.

Over-mining had taken place in the 221 stope directly above the accident site. After one back-lift had been taken, sill thickness was estimated to be 36 feet at the time of the accident. Reportedly, the designed minimum sill thickness after completion of the second back-lift was 20 feet. The closest undermining to the accident site was in the 213 stope and was located below drift 10 on the 215 stope.

Prior to mining the first series of back-lifts in the 215 stope, a mechanical scaler was used to remove the steel mats from the back. Reportedly, during this process some of the split sets were also brought down. The first series of back-lifts then brought down the remaining split-sets. No split-sets were installed after the back-lifts had been taken. Stope height, measured at several locations in this area, ranged from 29 to 34 feet. At the time of the accident, about 85 blastholes were being loaded with explosives. The holes were 1-1/2 inches in diameter and drilled to a depth of ten feet. These holes were to be the completion of the first series of back-lifts and the start of the second back-lift. Two holes for the second back-lift had been drilled through the slab that fell.

The failed slab was composed of wollastonite skarn. Maximum dimensions of the fallen slab were approximately 11-1/2 feet by 9-1/2 feet and 1-1/2 feet in thickness. The fall cavity in the back was bounded on the southeastern side by a joint striking approximately north 20 degrees to 30 degrees east and dipping approximately 70 degrees southeast. This southeastern side was the thick side (18-inches) of the failed rock. The northern and western edges of the fall cavity were feathered and did not follow any observed geological discontinuity. The northern edge appeared to coincide with the lateral extent of the wollastonite skarn. The distance that the rock broke into the back was within the wollastonite lens and did not follow any observed geological discontinuity, suggesting that the top failure surface was likely created by previous blasting of the back.

A visual inspection revealed explosives scattered throughout the accident scene and additional explosives loaded in the back. No potential source for detonation was observed and it was determined that the first step in the recovery operation was to remove the explosives that had not been loaded. Thirty holes had been loaded, primed and tied together with detonating cord. It was determined that the loaded explosives did not pose a hazard once the detonation cord was cut.

Removal of the scattered explosives from the accident scene and their return to the magazine, along with the severing of the detonating cord from the roll and the flushing of the ANFO pots, effectively remediated the potential explosives hazards that existed at the scene.

CONCLUSION

The accident was caused by previous blasting of the back that probably loosened the slab of rock. A thorough examination and test of ground conditions had not been done prior to work activities commencing in the stope. Ground support, which had been installed during the development phase of the stope, had not been replaced in the back after being blasted out during the back-lift mining cycle. Failure to wear safety belts while working from the elevated basket likely contributed to the severity of the accident.

ENFORCEMENT ACTIONS

Order No. 7934317 was issued on January 31, 2000, under the provisions of Section 103(k) of the Mine Act:
A serious accident resulting in a fatality to one miner and serious injuries to two others occurred at this operation on January 31, 2000, when a fall of ground occurred. This order is issued to assure the safety of persons at this operation until the mine or affected areas can be returned to normal operations as determined by an authorized representative of the Secretary. The mine operator shall obtain approval from an authorized representative for all actions to recover persons, equipment, and/or return affected area of the mine to normal operations.
This order was terminated on February 4, 2000, after it was determined that the mine could safely resume normal operations.

Citation No. 7904504 was issued on February 2, 2000, under the provisions of Section 104(d)(1) of the Mine Act for violation of 30 CFR 57.3200:
One miner was fatally injured and two others were seriously injured at this operation on January 31, 2000, when a slab of rock fell from the back while they were working in the 215-north stope. The loose ground that created the hazard had not been taken down or supported. Failure to scale or support hazardous ground is a serious lack of reasonable care constituting more than ordinary negligence and is an unwarrantable failure to comply with a mandatory safety standard.
This citation was terminated on April 24, 2000. The 215-north stope was abandoned and the area was barricaded and posted to prevent entry.

Order No. 7904505 was issued on February 2, 2000, under the provisions of Section 104(d)(1) of the Mine Act for violation of 30 CFR 57.3401:
One miner was fatally injured and two others were seriously injured at this operation on January 31, 2000, when a slab of rock fell from the back while they were working in the 215-north stope. Examination and testing for loose ground had not been conducted prior to commencement of work. Failure to examine and test ground is a serious lack of reasonable care constituting more than ordinary negligence and is an unwarrantable failure to comply with a mandatory safety standard.
This order was terminated on April 24, 2000. The 215-north stope was abandoned and the area was barricaded and posted to prevent entry.

Order No. 7904506 was issued on February 2, 2000, under the provisions of Section 104(d)(1) of the Mine Act for violation of 30 CFR 57.3360:
One miner was fatally injured and two others were seriously injured at this operation on January 31, 2000, when a slab of rock fell from the back in the 215-north stope. Ground support had not been installed and maintained to control the ground. Failure to support ground where persons work or travel is a serious lack of reasonable care constituting more than ordinary negligence and is an unwarrantable failure to comply with a mandatory safety standard.
This order was terminated on April 24, 2000. The 215-north stope has been abandoned and the area was barricaded and posted to prevent entry.

Order No. 7904507 was issued on February 3, 2000, under the provisions of Section 104(d)(1) of the Mine Act for violation of 30 CFR 57.15005:
One miner was fatally injured and two others were seriously injured at this operation on January 31, 2000, when a slab of rock fell from the back while they were loading blastholes in the 215-north stope. Two of the miners were working from an elevated work basket and fell to the floor when the slab struck the boom. Safety belts and lines were not being worn. Failure to assure the use of safety belts and lines is a serious lack of reasonable care constituting more than ordinary negligence and is an unwarrantable failure to comply with a mandatory safety standard.
This order was terminated on April 24, 2000. The mine operator has reinforced the requirements of this standard through safety meetings and training.

Related Fatal Alert Bulletin:
Fatal Alert Bulletin Icon FAB2000M05

APPENDIX A

Persons participating in the investigation

ASARCO, Incorporated

Peter Graham, general mine supervisor (underground)
Gary Torres, mine supervisor (underground)
Tomm Heyn, corporate safety director (Tucson)
Robert Jordan, safety administrator
George Zugel, safety engineer (underground)
Gary Byers, miners' representative, International Union of Operating Engineers
Patton Boggs LLP
Mark Savit, counsel
BLM Engineering of Canada
Dave West, consultant
State of Arizona
David Hamm, chief deputy state mine inspector
Tim Evans, deputy mine inspector
Phillip Howard, assistant mine inspector
Mine Safety and Health Administration
Larry O. Weberg, supervisory mine safety and health inspector
Robert V. Montoya, mine safety and health inspector
Joseph A. Cybulski, P.E., supervisory mining engineer
Michael A. Evanto, geologist
Thomas E. Lobb, physical scientist
Michael J. Getto, physical scientist
APPENDIX B

Persons Interviewed

ASARCO, Incorporated
Peter Graham, general mine supervisor (underground)
Gary Torres, mine supervisor (underground)
George Zugel, safety engineer (underground)
Louis Marrujo, supervisor (underground)
Ralph Bejarno, miner
Joey Miller, miner
Raymond Barragan, shift mechanic
Joseph Olson, Jr., miner
Javier Vargas, operator
International Union of Operating Engineers
Gary Byers, miners' representative