DEPARTMENT OF LABOR
MINE SAFETY AND HEALTH ADMINISTRATION
Metal and Nonmetal Mine Safety and Health
Report of Investigation
Underground Metal Mine
Double Fatal Fall of Ground Accident
October 12, 1999
Getchell Turquoise Ridge Mine
Getchell Gold Corporation
Goldconda, Humbolt County, Nevada
I.D. No. 26-02286
John R. Widows
Supervisory Mine Safety and Health Inspector
Collin R. Galloway
Supervisory Mine Safety and Health Inspector
George J. Karabin
Supervisory Civil Engineer
Michael A. Evanto
Originating Office - Mine Safety and Health Administration
2060 Peabody Rd., Suite 610
Vacaville, CA 95687
James M. Salois, District Manager
On October 12, 1999, Ronald F. Spry, lead miner, age 58, and Raymond E. Vaughn, miner, age 49, were fatally injured by a fall of ground while installing ground support at the face of an underground access drift. Spry and Vaughn had drilled and blasted an eight-foot round from the face of the drift earlier that day. After scaling and mucking the round, the two miners were beginning to install 6-foot Split Set stabilizers and wire mesh in the back when the ground fall occurred. The fall of ground was estimated to be 8 feet to 10 feet wide, 12 feet long, up to 8 feet thick and consisted of approximately 48 tons of rock.
The accident occurred because the method of ground support used did not adequately support the back of the drift in an area of locally weak and geologically unstable rock.
Ronald Spry had a total of 29 years mining experience, with one year and 15 days at this mine. Raymond Vaughn had 30 years mining experience, with eight months at this mine. Both miners had received training in accordance with 30 CFR Part 48.
The Getchell Turquoise Ridge Mine, an underground gold mine, owned and operated by Getchell Gold Corporation, a wholly owned subsidiary of the Placer Dome Group, was located 28 miles northeast of Golconda, Humbolt County, Nevada. The principal operating officials were Michael D. Winship, general manager, William L. Hocevar, production superintendent, and William A. Crouch, safety and training coordinator.
The mine normally operated two, 11-hour shifts, seven days a week. Total employment was 190 persons. Ninety-six of these employees worked in the underground portion of the mine with the remainder working at the surface milling operation. Daily production was 1000 tons.
The Getchell Turquoise Ridge mine was a multi-level, underground gold mine utilizing two shafts for access. Gold-bearing ore was drilled and blasted in open stopes. Broken material was transported from the stopes on haulage trucks to ore chutes, then crushed and hoisted to the surface. Depending on grade, the ore was either milled, or hauled to a cyanide leach pad for processing. The milled or leached product was sent to the plant refinery for removal of impurities and pouring into dor� bars. The bars were transported to refineries off site for final processing prior to being sold to customers.
The last regular inspection of this operation was completed on May 24, 1999. Another inspection was conducted at the conclusion of this investigation.
DESCRIPTION OF ACCIDENT
On the day of the accident, Ronald Spry and Raymond Vaughn (victims) reported to work at 7:30 a.m., their normal starting time. They were assigned their normal underground work duties which consisted of advancing the Powder Hill access drift. After Spry and Vaughn drilled and blasted an eight-foot round in the drift, Kory F. Black, miner, arrived at about 11:00 a.m., with a six-yard load-haul-dump (LHD) unit and sloped the muck pile in preparation for supporting the back. When Black finished his task, the three men loaded the drills, associated equipment, and ground support materials into the bucket of the LHD and traveled to the face.
Vaughn scaled the back while Spry and Black unloaded the materials from the bucket of the LHD. The three miners proceeded to install ground support until shortly before noon when Black's jackleg drill broke. The three miners then installed wire mesh for ground support. David A. Stovall, shift foreman, and Wayne D. Tucker, miner, arrived and all discussed how the roof bolting was proceeding and the competency of the back. There was some general concern over the competency of the ground on the left side of the drift, but the consensus was that the back was solid. Drilling had been hard and the Split Set stabilizers had been driving in tight. Stovall and Tucker gave Black a ride out of the drift to the shop to pick up parts for his broken drill. Black walked back to the Powder Hill access drift, arriving between 12:00 and 12:15 p.m. Black saw that a fall of ground had occurred at the face. He called out for Spry and Vaughn and when they failed to answer he traveled to the No. 2 shaft station and summoned help.
Nearby crew members responded to this request along with the mine rescue team. Recovery efforts were immediately started. Spry and Vaughn were recovered several hours later that same day. The victims were transferred to a local hospital where they were pronounced dead. Death was attributed to blunt force trauma for both victims.
INVESTIGATION OF THE ACCIDENT
John Widows, acting supervisor of the Elko, Nevada, MSHA office, was notified at 1:15 p.m. on the day of the accident by a telephone call from Timothy Kilbreath, surface safety coordinator, Getchell Gold Corporation.
An investigation was started the same day. An order was issued pursuant to Section 103(k) of the Mine Act to ensure the safety of miners. MSHA conducted an inspection of the accident site with the assistance of mine management, miners, and the Nevada Department of Business and Industry, Mine Safety and Training Section. The miners did not request nor have representation during the investigation.
1. Since opening in 1997, the Getchell Turquoise Ridge Mine had reported eight falls of ground to MSHA, five of which, including the fatal accident, are known to have been significant. In addition, the mine has reported sixteen incidents where either their miners or contractors had been injured by falling ground. Reportedly, all of the major falls were related to localized geologic structure such as slips, gouge zones, dikes or the presence of water.
2. In April 1999, the Roof Control Division of MSHA's Pittsburgh Safety and Health Technology Center was asked by the MSHA Western District office to conduct an investigation to evaluate ground stability and control measures used at the mine, subsequent to three significant falls of ground and two serious injuries which had been attributed to falling rock. That investigation concluded that supporting intersections, which were the location of the major ground failures, with 12-foot long tensioned resin anchored bolts in addition to 6-foot long Split Set stabilizers should be continued. The report further recommended that the use of tensioned resin anchored bolts be considered in long-life drifts and that geological features (such as slips, dikes and water) be identified and that appropriate action , such as effective scaling and/or supplemental bolting and shotcreting, be taken to assure ground stability.
3. The mine was associated with the Getchell trend, a series of gold deposits in north central Nevada. The ore zones are located beneath Ordovician age, Valmy formation basalt and are located in the Comus and Preble formations. The Preble formation is Cambrian in age and is composed of metamorphosed black carbonaceous shales and grey limestones. The Comus formation of Ordovician age is predominately composed of grey to brown shales and minor grey limestone. Geologic features and discontinuities including; faults with and without clay gouge and/or calcite, joints with and without calcite filling, intrusive igneous dikes, and bedding ranging from centimeters to meters is prevalent throughout the mine.
4. The mine had four levels, 900, 1250, 1550, and 1715, all of which were accessed through two vertical shafts. The bottom three levels, 1250, 1550, and 1715, were also interconnected by spiral declines. Mining methods used included blind benching, underhand drift-and-fill, breasting up and down, and longhole stoping. At the time of the accident, ore was not being extracted and the only mining activity consisted of development mining in waste rock.
5. Drifts were conventionally mined, arched in shape, and ranged from 12 to 20 feet wide and 14 feet to 20+ feet high. Ground support of the drifts generally consisted of 6-foot long Split Set stabilizers (1 �-inch outside diameter in 1 3/8-inch boreholes) placed on approximately 3-foot centers with 6-inch by 6-inch bearing plates in conjunction with chain link mesh. The Split Set/mesh support was usually installed across the back and down the ribs to within five to seven feet of the drift floor. Sections of steel mats (9 1/4-inch by 17 3/4-inch) were used to control sloughing at some locations. Additional support was added as conditions warranted in the form of up to 12-foot long tensioned resin anchored bolts (No. 7 or No. 8) with enough resin to grout the top five feet of the bolt and/or 2 to 4 inches of shotcrete. The 12-foot long tensioned resin anchored bolts had primarily been used in intersections to supplement the Split Set support.
6. Test data provided by the company indicated that the Split Set stabilizers developed anchorage levels of about 1 ton/foot and the tensioned resin anchored bolts (4-foot to 5-foot resin length) exceeded 16 tons of total anchorage.
7. The 6-foot long Split Set stabilizers were installed with hand held jackleg drills or by a Tamrock (Secoma) jumbo drill machine equipped with a canopy (falling object protection). All longer supports (Split Set stabilizers or tensioned resin anchored bolts) were installed by hand held jackleg drills. Decisions regarding the selection and installation of ground support were left up to the mining crew based on their evaluation of ground conditions at a specific location.
8. The accident occurred at the face of the advancing Powder Hill access drift on the 1250 level (1250 feet below the surface). The initial 60 feet of development had been completed in October 1998, and the drift was subsequently used as a muck bay. Mining was re-initiated on October 10, 1999, and the face had advanced approximately 44 feet in six lifts. Each lift consisted of up to an eight-foot round that was drilled, blasted, scaled, supported, and mucked in an 11-hour shift. No other mining had taken place within a 180-foot radius above or below the Powder Hill access drift.
9. The Powder Hill access drift was located in waste rock and was advancing toward a projected ore zone. The rock was locally known as a brown hornfel greater than marble (BNHF>MBL), which was a fine grained and medium to thin bedded nonschistose black to dark green metamorphic rock. The ground was highly jointed and often contained fractures that were commonly filled with calcite or gouge material.
10. Drift dimensions ranged from approximately 15 to 21 feet in width, with an average of 18.2 feet wide, and from 16 feet to 20 feet high, with an average of 17.8 feet in height in the portion of the drift developed in 1998. Because of continuing ground instability in the accident area, investigators did not go into the fall area to collect precise dimensions of the face and caved section. However, it was estimated that the drift width in that area varied from 16� to 19� feet based on a survey conducted by the mine operator using a remote cavity profiling system. The pre-fall height ranged from 16 feet to 20 feet.
11. Ground support in the drift consisted of 6-foot long Split Set stabilizers, installed with 6-inch by 6-inch bearing plates and/or 9 1/4-inch by 17 3/4-inch by 3/32-inch thick mats, and chain link mesh throughout the drift. The Split Set stabilizers were placed on 2 to 3 foot centers along the back and walls to within 7 feet of the mine floor. The first 66 feet of the drift had also been lined with two to four inches of shotcrete, reportedly to prevent damage to the split set/mesh support by haulage equipment.
12. Several geologic features were identified by mine geologists in the face and back of the Powder Hill access drift when mining was reactivated. These included a gray clay gouge zone, 1 � feet thick, striking N10ºE and dipping 40º to the southeast, noted in the face on October 10; a gray clay gouge zone, 2 feet thick, striking N30ºE and dipping 20º to the northwest and a steeply dipping joint striking approximately N15ºE and dipping 85º to the northwest, both identified in the face on October 11, 1999; and a zone of calcite filled joints, striking N10ºE and dipping 55º to the southeast, was observed in the face on October 12, prior to blasting the final round. Each of these features was noted on shot cards prepared by the geologist and subsequently transferred to the geologic map of the area. However, according to mine personnel, the geologic map was not routinely used to evaluate ground conditions nor was it used to aid in the selection and placement of appropriate ground support. Also, geologic information on the map was not generally communicated to miners working in the drift.
13. Reportedly, two rows of holes had been drilled in the back and ribs of the newly exposed ground and Split Set/mesh support had been installed on the left side of the drift. The victims were installing Split Set stabilizers and chain link mesh on the right side of the drift when the fall of ground occurred. Two Midwestern Model-83 jackleg drills were used to drill the holes and insert the Split Set stabilizers.
14. The ground fall that resulted in fatal injuries to the victims reportedly came in mass, encompassed the right side of the drift, and extended from a point six or seven feet northwest to a point approximately 19 feet northwest of the face. Mine personnel indicated that the initial fall varied from eight to ten feet in width, was 12 feet long, and weighed approximately 48 tons. Reportedly, it was wedge shaped and varied in thickness from a foot or two at the sides to roughly eight feet at its apex, and tapered from front to back. The bulk of the fall occurred in supported ground and the ends of a number of Split Set stabilizers were observed protruding from portions of the slab during recovery operations.
15. Material continued to fall from the cavity after the initial ground collapse. By the morning of October 14, the caved area had increased to roughly 15 feet (at its widest point) by 23 feet in length. Mine personnel estimated the total weight of fallen rock at that time to be 110 tons based on the amount of material remotely loaded out of the area. The front right of the cave appeared to be bounded by the high angle joint (striking N15ºE and dipping 85º to the northwest) noted on the geologic map in Appendix E. The left side of the cave appeared to occur along a steep joint set (striking sub parallel to the drift at about N17ºW and dipping at roughly 75º to the east-northeast) that was evident in the face and along the back. Two Split Set stabilizers were observed, free of rock and protruding three to five feet, anchored in the back within the left one-third of the cavity and two Split Set stabilizers remained suspended (free of rock) in the chain link mesh along the front right of the cave.
By November 9, the fall area further expanded to a point about 33 feet from the face. The remote cavity profiling survey conducted by the Operator indicated that the total height of the drift ranged from 23 to 26 feet in the vicinity of the accident (seven to ten-foot fall thickness) and 18 to 25 feet high as it propagated forward, and confirmed the structural features forming the cavity. Six additional Split Set stabilizers (free of rock and generally pristine) were observed hanging in wire mesh along the left front side of the cave at that time.
16. Examination of a portion of the fallen material that had been loaded out of the cave indicated it to be composed of brown Hornfel (black to dark green) that was highly fractured. Calcite was noted on many fracture faces. Clay and mud gouge was prevalent throughout the examined material. The fact that eleven Split Set stabilizers observed anchored in the cavity or hanging in the chain link mesh around the perimeter of the fall were free of rock and generally free of damage further illustrates the weak nature of the ground which crumbled away from the supports. Fourteen Split Set stabilizers and bearing plates recovered from the fall were examined and showed no signs of excessive stress (plate deformation). This lack of damage corroborated that the initial fall occurred in mass near the top of the Split Set stabilizers.
17. Water was observed flowing in two places from the left rib of the drift, approximately 46 feet northwest of the face and standing water was observed at this location. The face of the drift appeared relatively dry and water did not appear to have a role in the fall of ground.
The root cause of the accident was the failure to properly support the weak ground in the back where intersecting geologic discontinuities formed an unstable wedge-shaped mass of rock. Managements failure to adequately communicate the geologic features to the miners working in the drift was a contributing factor.
Order No. 7967043 was issued on October 12, 1999, under provisions of Section 103(k) of the Mine Act.
Two miners were fatally injured in a fall of ground accident at the 1250 level of the Powder Hill access drift. 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 person, equipment, and/or return affected areas of the mine to normal operations.The order was terminated on January 20, 2000. Conditions that contributed to the accident have been corrected and normal mining operations can resume.
Citation No. 4375715 was issued on January 21, 2000, under the provisions of Section 104(a) of the Mine Act for violation of 30CFR 57.3360.
Two miners were fatally injured in a fall of ground in the Powder Hill access drift on the 1250 level of this mine on October 12, 1999. The miners were installing 6-foot Split Set stabilizers in the back when the fall occurred. Appropriate ground support was not used where ground conditions, or mining experience in similar ground conditions in this mine, indicated it was necessary. Additionally, the support that was installed did not maintain or control the ground in places where the miners worked or traveled in performing their assigned tasks.The citation was terminated on January 22, 2000. The operator submitted a ground support plan to MSHA which will ensure that appropriate and adequate ground support will be used where necessary.
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