Show windfall wi windfall M mine ine and cyanide M mill i 11 eureka neva nevada da BRAYTON P CAMPBELL IN EUREKA SENTINEL the following interesting description of the windfall mine and cyanide mill located near eureka nevada and owned by the windfall mining company was written for the eureka sentinel by brayton P campbell mill superintendent for the company the windfall mine is situated about four miles south of ruby hill and four and one half miles southwest of eureka nevada on the east flank of prospect mountain which is the axis of an anticline striking north and south the rocks of the district are of the precambrian pre cambrian and cambrian age and consist principally of lime stones and lying conformably quartzite forms the lowest member of the series and above this thia occurs in regular order shale prospect handled by pick and shovel the quartz ledge has an average width of six feet and runs north and south and approximately parallel the contact in many places it is apparently made up of fragments of quartzite firmly cemented together the hamburg limestone is a hard limestone which readily breaks with a snap when fed to the crushers the shale has a thin laminated structure but is quite firm at the contact with the limestone it has undergone decomposition and has given rise to a heavy clay gouge the mine is in charge of T M dark clark to whom is due the credit for the low cost of mining of which details are given elsewhere the usual system of timbering with finished product bin after passing the rolls no further scree screening nin is attempted the crushed material is so porous that the solutions have no difficulty in penetrating to every part of the mass the following is a screen analysis of the milled ore retained on a 20 mesh sieve per cent retained on a 40 mesh sieve per cent retained on a 80 mesh sieve 1625 per percent cent retained on a mesh sieve 2680 per cent I 1 passed a mesh sieve per cent total per cent the only treatment to which the ore is subjected is that of cyaniding cyan iding amalgamation and concentration are entirely unnecessary the ore is an ideal one for cyaniding cyan iding and the extraction is extremely satisfactory k f 7 LX 7 copyright tj ly C H amman got man windfall cyanide mill capacity tons per day mountain limestone secret canyon shale hamburg limestone and hamburg shale the droppings crop pings of the different formations extend north and south parallel to the axis of the uplift the mine is situated in the hamburg limestone near the contact with the hamburg shale the ore body consists of a quartz ledge which is accompanied by irregular masses of sand through which course numerous small seams of iron oxide this sand carries high values and consists principally of calcium carbonate it contains only 15 per cent of silica the values were probably deposited in the sand by solutions without doubt the same ones that deposited the iron it is worthy of note that the iron seams carry much higher values than the surrounding sand the sand Js is slightly cemented together but is quite soft and can be readily broken down and square stes is employed during the month of july tons of wet milling ore or tons dry weight were hoisted from the mine this ore coming from the first second and third levels after the ore leaves the mine it is delivered over to me for treatment the wet ore is first dumped on a grizzly with the bars set four inches apart that which passes through is delivered to a foot revolving covered with one quarter inch mesh screen set directly over the finah ed product bin into which the screened material falls the rejected material together with that which has failed to pass through the grizzly amounting in all to about five per cent of the whole is then fed to a gates crusher set at five eighths inch prom from here it goes to a set of inch allis ailis chalmers chalmer i s style B rolls set at 3 9 16 inch and drops into the As the ore is practically nothing but limestone acidity is entirely absent the cyanide plant contains the following equipment six deachin leaching 9 tanks twenty two ft by six ft deep one water tank tons capacity one strong gold tank twenty eight tons capacity one weak gold tank twenty eight tons capacity one strong sump seventy eight tons capacity one weak sump seventh devent eight tons capacity one stock solution storage tank seventy eight tons capacity cape city one standard solution storage tank forty tons capacity six seven compartment zinc bozes one three inch centrifugal solution pump A forty horsepower horse power fairbanks morse gasoline engine supplies the power for the entire mill the tanks and zinc boxes are made from no 10 steel the filter bottoms in the leac leaching ahing tanks consist of pine strips three fourths b by y one mch laid at right angles 11 on top of inch supports this grating bein being covered with cocoa matting and burlap the leaching tanks are arranged in a straight line and are filled by means of a 14 inch robbins bobbins belt conveyor to which is attached an antOn automatic self propelling and reversing distri distributing distribution butin g tripper the sand is shoveled through 12 1 2 inch discharge 11 doors and falls onto a 14 inch belt conveyor which carries it off to the dump As soon as sufficient ore has been delivered to a tank to cover the bottom a 25 pound cyanide solution is turned in under the filter bottom and is allowed to rise slowly at a rate which does not permit it to show above the ore until some little time after the tank has become filled with ore this does not occur until four hours from the time the ore is first turned into the tank i after filling the charge is allowed to poun pounds ds and of zinc pounds for the month of july the average extraction was per cent in cleaning up the zinc boxes the cyanide solution is first displaced by fresh water which run through from the head compartment the slimes are then put through a 12 mesh screen and the short zinc thoroughly washed and the screenings transfer transferred to the acid tank which is filled about one quarter full of water this tank is fitted with a mechanically driven agitator and a two inch pipe connection below the teem of the agitator through which sulphur dioxide is led in from a sulphur burner the sulphur burner is enclosed enclose d and derives its supply of oxygen for the combustion of the sulphur from a small air compressor the pressure produced inside of the burner is sufficient to force the sulphur fumes through the water in the acid tank the treatment of the slime by sulphurous acid is very on the dry we weight the tons of wet ore equivalent to tons of dry weight the cost sheet is as follows mining per ton department amount wet ight mining 2263 76 g 1 60 2820 timbering track laying and air air lines power 1493 surface work assaying office expense general expense interest and exchange 1003 total less ft of development at per foot 1894 cost tons mill or mining 1124 per ton milling per ton dry ight crushing charging tanks leaching 1463 discharging tanks 1207 u ZVI 4 V it J it A A y N 4 A copyright j by C H gorman carman windfall mine in october i gog 1908 in sacks on the dump soak for four hours longer when percolation is started As soon as the strong solution disappear a two pound solution is run tn ill on top and this is in turn followed by the water wash after which the tank is discharged the following is the cycle of operations with the amount of time required hours pilling 2 soaking finishing Ini shing saturation 2 abashing AV draining asi fa with t P pound iid 0 solution o 36 4 ashing 24 2 discharge Dis scharling chargi ng 4 complete cycle 72 2 with six leaching tanks the plant has a daily capacity of tons dry ore the average rate of percolation is one and three quarters barters tons solution per hour each tak ank the average consumption of iura DI cyanide per ton of dry oe is satisfactory and is vastly cheaper than by sulphuric acid the cost of sulphur for a cleanup was only 40 cents after the slime is given an acid treatment it is washed by decantation several times and finally collected on a vacuum filter it is then dried roasted in a muffle and finally melted down in a coke furnace through the courtesy of our general manager mr C M dull I 1 am permitted to publish our cost sheet for last july if no not t actually the lowest recorded cost of mining and milling in the world for a mine of this size it is certainly very close to the record and we take a justifiable pride in presenting it the cost of mining is based on the weight of ore hoisted and this includes the moisture while the cost of milling is based precipitation and refining ning 89 power 14 1806 assaying 50 water 00 surface work 1225 12 25 total milling per ton the total cost of mining and milling per ton |