Show mi mine ne and milling miling plant of the elko ko prince BY J V N DORR B S AND L D B S the elko prince mine is in the gold circle district nevada about one and one half miles from the town of midas fifty five miles west of battle mountain and fifty miles northeast of golconda Go leonda the district is described by emmons in U S geological survey bulletin 1910 little was said of the elko prince however as only a small amount of work had then been completed the geological structure of the region is simple the oldest exposed formation covering most of the area is rhyolite which has a light colored devi devitrified trifled g groundmass r 0 u n d enclosing phe of feldspar quartz and magnetite it has been somewhat weathered and partially stained with oxide of iron there are several outcrops of andesite which cut the rhyolite the ore deposits occur as fissure veins replacement veins and sheeted zones the elko prince vein is of the first firs t type the rhyolite near the veins is stained with oxide of iron and at s some ome localities cali ties replaced by ore or is so permeated by metals as to be classed as ore the vein filling consists chiefly of quartz and the values consist entirely of gold and silver part of the gold exists as the native metal and part is associated with pyrite silver occurs tree free and as argenite in banded streaks through the vein these veins trend in a northwesterly direction with dips dip s varying from 65 degree to vertical development of the elko prince gold was discovered in the district in the fall of 1907 and a characteristic rush followed the town of midas was laid out and shortly had 2000 inhabitants several paper presented at september meeting 1918 of am ins M E F small mills were built one of which the rex ran several years after the first excitement cit ement the people drifted away rapidly and at present only about remain the elko prince claims were located in 1907 by paul ehlers a prospector and ten claims were patented in 1913 after considerable sid erable development work had been done the property was purchased in 1908 by the elko prince mining co L L savage president and was extensively developed between 1911 and 1915 the outcrop of the prince vein is is in pig fig 8 view of the elko prince property significant only a narrow seam of 0 low grade quartz or an obscure fissure containing no quartz or metals the first work on the property was a 60 foot shaft sunk on the cropping A narrow seam of mineralized quartz was followed but nothing of importance was found then a foot drift on the vein gave similar results later a foot crosscut reached the vein feet below surface and cut an ore shoot almost in the center subsequent work developed a vein ha having an average width of 14 to 15 inches 4 a total tonnage of and a gross value of 0 approximately the limits of the ore body being quite well defined in june 1915 the elko prince mining co made an agreement with the dorr company whereby the latter was to design finance and build a cyanide mill of at least forty tons daily capacity furnish additional mine equipment and operate the property until certain financial results had been attained milling was begun in november 1915 and the original terms were completed in june 1917 but the dorr company operating through the elko prince leasing company has continued in charge of the lo 10 g IN 1 ar 1 at A s as ewt A i TN N iii aa 4 A t r 1 f 4 A toe S alwa i x sa 4 ow ra property to the present time the prince vein the prince vein has a uniform north west southeast strike and a dip varying from vertical to 85 degrees to the northeast one horizontal fault of a few feet feel occurs in the 1400 feet of dev development loument lop ment on the property and a second 0 of f much greater extent probably occurs just beyond the south end line the vein filling is hard but brittle quartz with a very small amount of sul nhi alp partial dation extends from the surface to the deepest openings manganese in oxidized f form orm is found in i spots no enrichments enrich ments due to leaching and have been observed except as to a small portion of the silver the gold is mainly free but very fine about 50 per cent can be amalgamated ga mated thin flakes of native silver are found in the toot wall and penetrate its seams in places to a depth of an inch the silver exists chiefly as argentite and giving the quartz the characteristic banded appearance that usually accompanies the presence of these minerals A characteristic analysis of the ore is per cent ia aloa ajo 20 fe 30 cao 40 s a 01 As 01 ab g b 01 7 mn 0 trace ignition loss 20 cu 00 au oz per ton 07 ag oz per ton being to mine the east wall as narrow as possible use it for filling break the ore away from the west wall and run it all out the vein however was too brittle in many places to permit this all of the quartz in the gouge would have been lost as well as much of the vein proper the advantages of this method the small amount of high grade ore to be milled and the smaller plant to be erected were more than offset by the greater cost of mining and the inevitable losses the ore with some waste as little as possible required a va n n T C 47 pm em wea lo 10 TA 14 av v ml J 4 ir X AV A P X A at 11 J t fig 3 an ore are chute elko prince mine A second vein the june bell is parallel to the prince and lies a short distance to the west it is of the same type but much smaller and gives promise of producing but little metal the development of the prince vein at the time milling began is shown in fig 1 the dotted lines indicating the extent of ore estimated as profitable above the foot or main level mining has confirmed the accuracy of the estimate below the foot level the ore body has been pro proved ved to extend slightly further to the north considerably sider ably further to the south and some little ore has been found below the foot level minin i practice sloping the following conditions influence the method of mining the vein is almost vertical its average width is 15 inches seldom less than 12 or more than 24 inches thick the west wall is smooth hard and firm with quartz sometimes frozen to it the least east wall is less well defined decomposition having extended into it to a depth of a few inches to two or three feet a sliding movement has occurred in the east side of the vein and at some points a considerable amount of gouge is found containing pieces of vein matter when planning a method of mining stripping was considered the idea plant of 25 to 50 per cent greater capacity and involved a small increase in power a and nd supplies consumed but this method permitted the recovery of all of the ore and it I 1 was thought that the increased milling expenses would be less than the loss by any selective method of mining overhead was adopted enough daily from every shoot and the tha broken ore was not permitted to remain at rest for a whole day it would remain loose enough to run f reely freely predictions as to the most efficient stop to ing width ranged from 30 inches to aa 4 inches it has been found possible and practicable to maintain an average width of 32 inches throughout the mine above the foot level the average was 28 inches in many places the miners broke only 20 inches but the ore would not draw freely through such narrow fig 2 shows a typical with good walls at the north end of the shoot where the ground was quite dry the was carried from the right through to the level at the south end where rather wet an intermediate ter mediate level at was found advisable drilling five 16 V waughs baughs supplied with 1 inch cruciform steel are used in drifting and sinking are done with ith waugh clipper drills using 78 inch hollow steil steel A pressure of 85 pounds of air is maintained at the drills contract mining was first done on straight days pay but within a few months a bonus system was adopted whereby a premium increasing with each 5 feet was paid on all footage drilled in excess of 50 feet per day before initiating that system a ca careful reful record was kept of the work of each man for two months in order to secure a basis for a just bonus it was understood that no change in unit prices would be made thene thereafter after regardless of the amount that might be e UP ed it is most important for the successor af pf any bonus system that the men shall recognize that the whole saving as compared with days labor is to be divided with them and that the system is not to be designed for the purpose se of reducing them to the standard wages of the damme twy r i ero r 1 7 fa f af pf rt 55 NIL fig 9 diagrammatic drawing of dorr closed type tray thickener patented ore being drawn daily to maintain proper working room above the broken ore no sorting was attempted in the in spite of the fact that the were almost vertical and that one wall was hard and smooth the ore would occasionally hang and cause trouble after a time it was found that if a little ore was drawn camp it was found that some men on ground aroun tract would break twice as much I 1 was vas some so as when on days pay there if 1 tendency to place holes too close t together ht the ground was easy for drilling contracting was finally adopt adopted edt based 0 the t the square foot of vein area broken beep the wa walls contractors are obliged to keep free groin from ore and maintain the within limits designated by the foremen the company furnishes the powder and the men do the shooting the usual price in such contracts is from 12 to 15 cents per square foot at which rate the men make from 25 to 75 per cent more than days pay loading and the chutes on each level are spaced about 27 feet apart and are equipped with the gate shown in fig 3 by having the gate boards extend across the end of the chute they can be knocked open at either side without binding the mine cars are 30 cubic feet truax side dump cars weighing 1100 pounds one man and a horse readily handle sixty tons a day with an average haul of 1100 feet in using a five car train from the foot drift to the mill bins hand is done on the lower levels two men handling the full tonnage R aas W goodr ra cc I 1 L ena r a orr fig I of the elko prince vein hoisting the selection of hoisting equipment was determined by the following considerations 1 the shaft followed the changing dip of the vein making rapid hoisting dangerous 2 it was expected that with the size of engine available for the power plant this would be fully loaded making a high load factor imperative 3 with the small tonnage the saving of a single man meant a large cut in the cost per ton A denver engineering works double drum electric hoist with counterweight was selected it is driven by a 10 horse power volt direct current motor and has a hoisting speed of feet per minute the complete cycle takes 5 minutes from the foot to the foot level the self dumping skip weighs 1200 pounds and has a capacity of 35 cubic feet the tram train mers dump their cars directly into the skip through a chute timbering when the mill started the need of ore required drawing faster than shrinkage allowed and the miners were obliged to work on trench jacks were found advantageous for this purpose as they could be removed before shooting and put back into place much quicker than the main timbering now consists of chutes man ways and in the as the ore is drawn the wet sticky nature of the ore in the narrow causes the ore to pull nearly vertical over the chutes and thus requires close st but light pieces such as 3 by as or 4 by as are sufficient in most places very little timbering is required in the drifts cost of mining mining costs for 1917 are given in table 1 covering a total of tons ions or tons per day the costs do not include prospecting for additional ore bodies table 1 mining costs coats per ier ton for 1917 timbering and chutes blacksmith I 1 sloping I hoisting air powder caps and fuses repairs drill steel miscellaneous total note miscellaneous includes local supervision v assaying insurance taxes and sundry miscellaneous items milling practice general design the financial arrangements allowed the mill to be designed so that when the ore body already developed had been worked out and the plant scrapped the greatest net profit would have been made the treatment of fifty tons of sorted ore daily promised a life of about three and one half years with the chance of an extension by finding other ore bodies or obtaining custom ore labor was scarce in the district and although there was no labor union the tonopah scale of 4 minimum for eight hours had been paid redhouse on the western pacific the nearest freight station is thirty four miles away and hauling by wagon costs from 1350 to 15 per ton the road from redhouse to midas is a good desert road with a large increase in grade in the last five miles the chance of heavy snow at the upper end in winter and the certainty of very heavy hauling in spring make it essential to stock up by december to run until may hauling by team has proved more satisfactory than by motor truck oil storage of gallons was provided at the mill no electric power was available although the ore is a hard quartz a variable quantity of very slow settling gouge occurs with it so that it was necessary to provide a large settling area per ton the treatment shown in fig 4 and 5 follows the standardized lines of ball mill crushing and fine grinding with count countercurrent ercument decantation and zinc dust precipitation As this pulp cannot be thickened to less than 60 to 95 5 per cent moisture a de watering filter is used to enable the tailings to be conveniently handled and to reduce mechanical ch anical losses of cyanide and metal fig 6 shows a plan of the mill with many of the details omitted but with flooring and runway elevations indicated fig 7 shows one elevation it will be noted that the working floors are nearly at one level and that the machines requiring close attention such as the diesel engine the filter etc are grouped near the center of the main building where they can be under observation from any point where the operator must work this arrangement feasible only in a small plant enables one man to keep general watch over the whole operation of fine grinding and cyaniding cyan iding as well as the power plant for mine and mill so that while two men are used on the two night shifts as a matter of precaution the mill man frequently sends his helper to the crusher room for a few hours when short of ore when not so required the shift men do a good deal of repa repairing ring and pre prepare pare the samples for the assayer the relative elevations of the fine grinding and cyaniding cyan iding departments are of interest if the objection frequently urged to the elevation of pulp had been considered and a gravity flow from the classifier to the first thickener had been attempted the cost of the excavations and the building I 1 would have been much greater the convenience veni ence of operating diminished and additional dit ional pumping of clear solution would have been needed we consider awell a well de signed wet elevator to be at least as efficient as a pump except this one elevation of combined ore and solution it will be noted that in all elevations some other necessary purpose is accomplished as well for instance the diaphragm pumps transferring the thick pulp also serve to regulate its discharge and the clarifying filter and precipitation press pumps serve to elevate the solution no 3 thickener serves as a mill solution supply tank and the barren solution flows directly to no 4 thickener there should be however a sump or reserve tank large enough to take the contents of a thickener to avoid possible loss of solution in case of an accident such a tank could be outside the mill coarse crushing two 10 by 12 foot receiving bins with 3 3 tj T lot Q j ie AA ott 72 76 ILL rap A WIN 00 1 machiros MACH Iroc U tj icil ai 6 0 0 8 7 0 fig 6 plan of the mill listing the elevations to |