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A Wagner STS LHD works on a Henderson development heading. When operations reach 30,000 tpd, the mine will employ twenty- two 5-yd LHDs in production. Development mucking so far has been done with 10 Wagner ST5s, seven Eimco 915 LHDs, a Cat 966 front end loader, and four Eimco 980 dump trucks. Manage ment has made all reasonable attempts to keep maximum LHD not begun. However, a positive factor that will contribute to caving the Henderson is the 3,000 to 4,000 ft of rock mass lying above the first undercut level. Large boulders should be readily accessible to drilling and blasting within the 40-ft-dia bells, which were designed to overcome large boulder hangup problems. Precaving development will include a substantial amount of vertical boundary cutoff-drilling and blasting a minimum 5-ft-wide fractured zone along two adjacent sides o(the caving zone. Access will be provided into the orebody at various lev- els to allow stations for any longhole drilling-blasting needed for destruction of stable arch formations. Dan- gerous arch formations will be shot down before they can develop a potential for serious airblasts. In panel caving the Henderson, the orebody will be di- vided into a series of panels that are defined by the pro- duction drifts; each panel is 80 R wide and of varying length. There are no pillars left between the panels, which will be caved in a sequential manner, progressing in two directions simultaneously, either along the panels or across them. The caved face will advance progressively, with a new area brought into production as an old one is ex- hausted. The first production level, the 8,100, is 2,350 ft below the collar o(the access shaft. The second production level, the 7,700, to be opened in later years, is 200 ft above the per- manent main railroad haulage level. When the mine reaches a 30,000-tpd production rate, the active production area will have horizontal dimensions of some 700 x 700 R, and will require 370 available draw- points. A 5-yd LHD will service some eight drawpoints un- der normal conditions. Although Henderson operations are designed to be highly mechanized, about 900 employ- ees will be engaged in underground operations, service, and general and administrative work. The mill will em- ploy an additional 200 workers. Mine water sumps are located at both the No. I and No. 2 shafts. The No. I shaft sump, with a 70,000-gal settler ca- damming distances to less than 1,500 ft, with trucks used over the longer hauls. During production, LHDs will always be oper~ sting within 160 ft of an ore pass. During ttie development phase, muck is being hoisted from the No. 1 shaft in two 6~ton skips at 1,200 tpd and from the No. 2 shaft by one counterbal~ anted 16~ton skip at 900 tpd. pacify, is serviced by 350-hp, 2,500-gpm. 420-R-TDH Haz- leton pumps that lift the water 380 ft between shaft pump stations. The No. 2 shaft sump has an 83,000-gal settler sump on the 7,500 main haulage level. On the 8,100 level, there is a combined 134,000-gal settler sump and 125,000-gal clear well sump. Eight Worthington 500-hp, 2,Sq)-gpm pumps lift water in two stages from the 7,500 to the 8,100 level. From the 8,100 level, three Byron Jackson I,-l50-hp, 1,660- gpm, 2,720-ft-TDH pumps lift mine water to the surface. The Public Service Co. of Colorado supplies power to the Henderson complex through aclosed-loop system be- tween two sources. The system provides insurance against a power inlertuption from either source. Power at 115 kv is transmi«ed by the PSC to its substa- tion loop system. From the mine substation, the 13.8-kv two-source loop transmits power underground to three substations and one rectifier station, which in turn provide 4,160-, 480-, 220-,and 1 10-v power within the mine. Control of coring data during exploration phase During exploration of the Henderson, 45 diamond drill- holes averaging 3,400 ft were drilled at inclinations from -90° to -37° Crom the surface oC Red Mounuun and from underground sites of the Urad mine. Rugged terrain and the limited number of underground headin;;s precluded use of a formal grid pattern. Normally, BX b is were used and core recovery averaged better than 905. Stabilized core Bartels and wedges were used to limit drillhole de- flection to generally less than 0.5° in inclination per 100 (t. During drilling, a bottom survey was taken every 300 ft with an Eastman single-shot survey instrument. The in- strument is atimer-actuated camera that photographs an enclosed, gimbal-mounted compass and inclinometer. In holes without caving problems, the ins«ument was lowered to the bottom with the drill wire line. When cav- ing presented problems, the instrument was lowered either on drill rods (with a minimum 17 ft of nonmal,netic spacer