Show stratton s independence I 1 ri L i adelen d ence mi e I 1 I 1 BY PROF PHILIP ARGALL in experimenting with cripple creek ores toward the close of 1893 the writer tried removing the bs bj b S simple concentration and in the following year published the advantages to be derived by removing the tell urides in this way before subjecting the fulp to the state of the arts of concentration and at that early date did not justify the application of concentrating cyaniding cyan iding methods to the higher grades of tell urides of the early nineties but thirteen years later when called upon by the directors of Strat tons independence limited to advise them with regard to the treatment of 3 to 4 telluride ores these old tests formed the starting point in the elaboration of the milling methods put into successful operation with the starting of Strat tons independence mill in march 1908 the mill was built primarily to treat the dump of the mine which was known to contain about tons of refuse that was thought would average about 4 or 5 per ton but it is also treating the low grade ore as it comes from the mine after the most careful experiments and a minute working out of details the writer advised the directors that a mill of tons capacity per month could treat the dump for per ton the fact that tons of this dump since milled have shown ei a total value of but 3 per ton has in no way aff affected acted the returns promised as the fiscal year just passed showed an extraction of 50 60 per cent of the contained value at a cost of per ton it is important to remember that the costs also include the cost of dump mining which is 11 cents per ton leaving the true milling costs at per ton the ore from the dump and the low grade ore f from rom the mine after passing through breaker plants by which it is broken to pass a one and one half inch ring is then sent to respective spec tive sets of inch rolls which reduce it to three eighths inch it is then delivered direct to the chilian mill bins fine crushing this plant consists of akron chilian mills of six feet diameter three of which easily give the required tons per month while the fourth is held in reserve until needed to replace one of the others these mills with inch screen aperture at thirty three revolutions per minute give a fairly steady output of tons each in twenty f four our hours Tell urides are friable and while the fine is richer than the coarse in most cases yet the ores of cripple creek afford the greatest contrast in this respect from the lumps that will pass through a two inch grizzly to the dust caught in the rafters of the mill the finer pieces and particles are invariably the richer advantage was taken of this fact and extensive experiments conducted to determine the best method of crushing and the most economical size of reduction experiments were made with rolls stamps pans and chilian mills the latter giving the best results then followed experiments with size crushing on a full working scale made through screens varying to inch aperture the best average results were obtained around screen aperture which on ore gives us a sand tailing averaging after concentration tra tion about 80 cents per ton and a slime running from to 2 per ton after concentration c cent ent 1 ration both products being subjected to further cyanide treatment the guide chosen after months of experimenting peri is not to allow the sand tailing from the table to exceed 1 per ton when this limit is approached a finer screen is used on the mills comparatively coarse crushing and eliminating 40 to 50 per cent of the ore as sand with as poor a tailing as we can obtain from the slime is one of the nice points in our practice not generally seen or at least understood by either the casual observer or the critic here the physical character of the ore is utilized to obtain 1 A coarse sand from which a high grade concentrate and an almost worthless tailing are obtained in one operation 2 an enriched slime from which a high grade concentrate can also be obtained leaving but 50 to 60 per cent of the original ore for special treatment such as air agitation oxidizing chemicals and fil filtration 1 concentrating I 1 the discharge from the chilian mills is run to two ovoca classifiers where the sand is separated from the slime the sand passes to a distributor which feeds twenty card concentrating tables or cr any less number as the distributor is automatic and so arranged that any table being plugged off the pulp immediately arranges itself to suit the smaller number of tables the slime passes to thickeners the thickened slime from these to a similar distributor which supplies the deister slime tables and the four banners van ners or any less number from card and deister tables alike there are obtained a 4 to 5 ounce first grade concentrate running 8 to 10 per cent silica and 35 to 43 per cent iron and a middling product which is returned to tube mill ground and concentrated re giving a two ounce product with 14 per cent silica and 30 per cent iron the card table sand tailing usually assays essays 04 ounce while the deister and vanner slime tailing averages 10 ounce both iloth sand and slime tailing is s pumped from the concentrator building to the cyanide building by four inch centrifugal pumps while the concentrate is collected drained and shipped to the smelters shelters sm elters after concentration the various tailing products are pumped to the cyanide plant and again passed through 0 ovoca oca classifiers to be separated into clean sand and slime these classifiers give a sand practically free from slime and carrying from 15 to 25 per cent moisture as desired they consequently perform a double service slime separation and sand de watering bromo will break up gold telluride provided the ore is reduced to pass a screen of mesh to the lineal inch hence the importance of having the slime practically free from sand particles to clean sand at the head of the classifiers is added as much barren solution as will pass through the tanks during filling the mixture of sand and barren solution being conveyed to the desired tank by means of a reciprocating conveyor leaching thus continues throughout the filling process and is continued until the value is extracted when after water washes the sand is sluiced to the tailing ponds the slime is collected in cone bottomed steel collecting tanks and charges of thickened slime are drawn from these every twelve hours to a similar shaped treatment tank fitted with a pneumatic agitator the air lift tube ends about ten feet below the surface of the charge where a small reverse cone disperses the ascending stream in this way the upper portion of the charge is kept in brisk agitation by a surprisingly small amount of air sana if present sinks and is deflected toward the side of the vat by the lower cone rapidly settling to the suction of the lift it jasses asses up again and in this way is kept in active agitation in the pneumatic type of agitator where the air lift discharges above the surface of the charge the compressed air escapes into the atmosphere before it is fully expanded while in the method here described the expanding airas air is dispersed and keeps the whole charge above the reverse cone in brisk agitation instead of that small portion of the charge within the central cental tube as in the old style of pneumatic agitator the slime is worked in charges of about eighty tons agitated in cyanide solution of varying strength and as required given a final treatment with bromo the solutions are precipitated on zinc shaving the dried precipitate being ground to impalpable powder in a special tube mill and sold to the refineries the clear solution overflowing from the slime settlers in this department returns to the chilian mills flows 0 over ver the t tables a bles nd returns to this department with more eilind slime thus forming a closed circuit suf solution is withdrawn and precipitated from the circulation each day to keep the gold content down to less ss than a dollar per ton conclusion the points to be especially noted in this brief description are the following a this is the first mill anywhere in the world to successfully treat 3 sulphide telluride ores b concentration in cyanide solution c the closed circuit i 1 e the solution is constantly in circulation from the chilian mills over the tables through the tanks over the zinc boxes and back to the I 1 chilian mills T d the use of bromo ya on the most rebellious ores milling costs coarse crushing and sorting fine crushing concentrating and treating concentrate cyaniding Cyan iding and special chemicals miscellaneous expense working cost tons mining dump ore total working cost exclusive of amortization of milling plant delayed for a time through financial reasons the mill started work in april 1909 and has been in continuous and successful operation from the first and is earning more than 15 per cent per annum on the capital stock of the company the costs of the process undoubtedly set a record for the treatment of low grade rebellious ores especially for those of the cripple creek district where the lowest open rate when the erection of Strat tons independence mill was begun amounted to per ton since reduced to per ton there are no secrets the methods being simply a combination of already well known processes adapted to meet the conditions and the methods so worked out in this mill have since become the standard method in use in the successful telluride mills of the district |