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anrt 7500 level Henderson development plans call fora 5 x S~ft slot raise to 6e driven to a height of 28 ft above the back in the center of each crosscut. As shown here. the crosscuts are designed so that the central 40 ft of the crosscut is driven perpendicular to the haul- agedrift. Each bell is drilled out on a fan pattern of seventy~two 3~in.-dia holes for a total of 2,270 tl. Burden between the fans is set at 6 ft, with each row blasted in sequence toward the free face pro vided by the slot. The completed bell resembles an inverted and truncated cone 14x40 }t long at the bottom and 4071 in diame~ ter at the top. The bell's function is to funnel caved ore to the drawpolnts, eliminating the need for the finger raises and Blusher drifts found m alder, conventional cavunl operations. Undercutting the ore for caving is done from 12 x 12.3~ft un~ dercut drifts located 55 ft above the main haula•le drifts. Under cut rings are drilled on 671 centers, each ring consisting of six- teen 3'/:~in.~dia holes drilled through an arc of :!44°. The 394 ft of drillhole per ring varies in length l0 34 ft deep Vertical boundary cutoff drilling and blasting-or induced fracturing along boundaries called "pre split"--must be done along hangingwalls and footwalls to facilitate caving, reduce the danger of arching and air-blasts, and limit diluti~rn of the ore. In general, management expects that an area of 1:30.000 sq ft will need to be undercut before good caving begins. ~ ~ ` ? eft 8,100 Level Production 8,050 Level Intake vent ~\ \ '~ \ 8,035 Level `~ \ '~ \ Exhaust vent 7,700 Level Future production 7,500 Level Haulage Ore passes and ventilation intake raises are located every 320 ft along each of Henden son's B,100~level haulage drifts. A Bubten ranean Model 009 raise bo ~er develops ore passes by drilling 12r/:~In.~c is pilot holes at 70° angles from the upper level to the 7,500 level and then bacl.reaming to an 8~tt~dia hole. Dump point: on the 8,100 level are concreted to a 4 z 6~ft opening without grizzly bars. Above each loading pocket on the 7,500 level there will be a surge load of 650-700 hens in the ore passes-enough for one complete train- load. The No. 3 shaft feeds irtake air to the 8,050~level ventilation laterals, driven per pendicular to the S.100~level production drifts. Air is directed from the 8,050 later- als through a series of intake air raises up to the 8,100 level. (The ~• x S~ft intake raises are developed by longholing.) From haulage drifts, fresh air is iirected to the work faces and used air is exhausted down ore passes under negative Irressure to the 8,035 exhaust ventilation I~teral and then up the exhaust ventilation shaft. Ventila~ lion laterals and drifts are 14 x 13.5 ft and 12 x 12.3 ft. respectively. Total Installed fan caF~acity for the main, No. I-No. 3 shaft ventilation circuit is 1.3 million cfm.