| Show N MC I 1 ti 01 01 aw A A W tl C A air A at act mono A A the ou alaska juneau log gold p mining property is Y situated about two om and one half miles irva east of fo the ati city of fo juneau nox v aj aan of fo vil its location ut in a picturesque setting caving system of JO mining low grade ores as 99 practiced at 19 janeau alaska xa by J f A WILLIAMS chief engineer alaska juneau gold plo mining co 03 ut in the dupont magazine for january ul in the alaska V juneau mine on november 26 1926 a od powder ilip ft blast using pounds of jo powder I 1 was responsible oj for i aj caving buiar of JO tons SUOI of jo ore alo this aliw mine daily send to 01 sal s mill between pur and tons SUOI of jo mol low 12 grade aar apr PIOS gold ore ajo staining nta ining not IOU over 90 06 cents in ul gold piol ad per ton ul in order japo to oj Y this large tonnage IV at mol low cost ISO wholesale mining has been adopted the method briefly consists of jo cutting out 7 feet dia high Q 01 ur an area p t about inozu feet by feet with the necessary holes ul n 1 11 1 IV at the same time driving in ul the ground to ol be caved five or six raises sesel to 01 the level above then when the undercutting is S completed the back of jo the alp st is blasted down by lalu su jo f large charges of jo powder placed ut in od powder JOPA slip drifts driven bially from the raises these drifts are an four feet by agaj ul in section and vary from thirty to ol sixty feet ul in 11 length ne burden on them st is generally about thirty five feet depend sul ing on the nature of jo the ground and the size azis of jo the aej open aado slope ados below after a has started palms to ol produce ou no one enters it 1 powder drifts are driven pur and blasted sr as needed pur and the rock pw ST is ap drawn uma out ino jr at the bottom abak where aj secondary iq breaking louiva 1 takes place ut in the bulldozing 1 1 chambers where the ore aio si is usually not IOU I 1 in u the south half of jo the mine ever jaaj feet deep it 11 st is customary X to oi bring i the a through pur and then blast ut in the walls possible sr as to on the surface su as of p the open pit lid with powder drifts the large blast mentioned took nom place ut in the south q half clr of jo atil mine abw see aas figure 1 I 1 it II was SUM located ut in the middle of jo a which separated pair N no 0 2 pillar eighty feet wide pur and feet long judas and P support to ol it I 1 IV at one allo pua end pit lid from ON no 3 adois ur gave open the other pua end of jo the alp of jo A fault nearly vertical made up a part while strike formed its SI however laAM ul in spite of jo a ladois pur and the great area of jo III the boundaries these weaknesses along qi the 51 pe feet feat by feet no large amount of natural caving took tock place due to the strength and toughness of the meta gabbro and slate in which the ore occurs prior to the pillar blast tons of rock had been broken by twenty five blasts of powder in drifts driven a total length of 2060 feet T these h e s e operations greatly contributed to the final result when the pillar was destroyed for this final blast a powder drift see figure 2 was driven sixty five feet each way f from rom the top of a raise forty feet above no I 1 level south the powder iritts were driven about parallel with the axis of the pillar so that the burden aver GROUND WHICH 71 WHICH CAVED AS rea Z voa PIT OF I 1 CAVED AS RESULT I 1 noa STORE aa eno e no 2 LEVEL EN 0 V ae W VIEW F fig i g 1 I these sketches prepared from drawings made by the author show left to right longitudinal and end views of the ore body before the blast aged forty feet six piles of powder containing an average of pounds of 40 per cent du pont red cross extra dyna dynamite mite were used one charge was placed in each face while the others occupied 10 foot spurs spaced equidistant along the drifts the dynamite in I 1 ya 4 inch by 8 inch cartridges was tramm ed cd to the bottom of the raise where it was transferred to canvas sacks and carried to the top of the raise by means of a portable hoist it was then dragged into the powder drifts and the cart safety fuse immediately after the blast which took place in the going off shift certain doors were closed to prevent the gases from penetrating the rest of the mine where operations continued the T h e ventilation system worked so successfully that the doors were opened with safety within eight hours after the shot was set of off f the blast actually broke out tons this proved to be the key holding over tons which sub subsided sided within 0 few hours for the total production from no 3 the powder consumption for primary breaking will be less than pounds of powder per ton of ore broken while the secondary brea breaking kingi it is estimated will probably not require more than 22 pounds per ton of ore which is the average for the alaska juneau mine no 3 5 CORDEAU 3 TamIN 11 no 8 CA soo I 1 bevel 4 5 FEET 0 10 20 30 40 i va p pa r fig 2 how the charges were placed pla cedor for the final blast which broke tons of ore and caused the caving of tons metal mines in texas in 1927 produced ounces of sold I 1 ounces of silver and pounds of lead according to charles W henderson united states bureau of mines 1 I he greater part of the production came from the presidio mine at shafter Sli after presidio county operated by the american metal company this mine has been a consistent producer since 1885 the total production of texas from 1885 to 1927 inclusive mostly from this mine is ounces ridges packed tightly against the solid rock the charges were connected in duplicate by double countered d cordeau fuse and then carefully tamped camped for about 15 feet with fine rock stemming the cordeau was detonated by no 8 blasting caps and two 30 36 foot lengths of in 1927 the homestake Home Horne stake mine the largest pf af producing pro ducin 0 P old mine in the united states produced approximately 6 in gold and ounces of silver states charles W V hender of the united states bureau of mines I 1 in n 1926 the hc g and several small gold mines in south dakota produced in gold and ounces of silver the ore of the hoole M ia stake mine averages about 4 in gold and is treated by ama mation followed b by of the sands and 51 slimes inies |
