vats to be treated with solution by the percolation. method. This process was a great failure, and metallurgists were at a loss to understand why this was so for some time, until the chemical reactions during roasting and cyaniding were fully understood. In roasting, the lime and magensia in the ore are converted into sulphates, and this, on being wetted by the solution in the vats, set hard, so that in several instances the half treated ore was removed from the vats by picks and bars. The ore was under treatment for periods up to a month with low extraction and high consumption of cyanide.

This treatment would not do, so grinding pans were installed on the Gt. Boulder Main Reef, the idea being to slime all the ore. The process was to dry crush, roast, mix the ore with salt water, grind and amalgamate in pans, the slime forced into presses and the water filtered out, the slime being then mixed with cyanide solution and pressed again. This was probably the first time the press was used on roasted ore. The Lake View Consols and Associated companies remodelled their plants on these lines, their system being to break the ore in Gates crushers and Rodger rolls, crush in Krupp mills, roast in Brown and Ropp furnaces, mix with cyanide, agitate and then treat in the presses. The Kalgurli had a Ropp, the roasted product being separated, the slime being air agitated and pressed, while the sand was treated in vats for some weeks with cyanide solution circulated by means of small air-lifts. At the Associated mill and possibly some of the others Wilfley tables were being worked to catch the unroasted pyrite that came from the furnaces, this in itself showing what sort of work the furnaces were doing. (It may be mentioned here that the rabble carriages in these roasters used to carry raw ore from the feed to the discharge end and drop it there to mix with the roasted ore. This went on for some time.) The Kalgurli had Halley percussion tables for the same purpose, the concentrate being afterwards ground in a pan.

The Gt. Boulder Perseverance had in the meantime erected a large dry crushing plant, using Griffin mills and the Holtoff-Wethey furnace. This type was also a poor roaster. The Koneman desulphurising process was tried on the Gt. Boulder. Roughly, it consisted of roasting the ore in lump form in a furnace of three compartments, the ore falling into an increasing heat to be thoroughly oxidised. The roasted ore was to be crushed in a machine patented by Mr. Koneman. The process was not a success.

In the dry crushing mills it was very apparent that something must be done to improve the roasting and subsequent treatment. In the case of the Lake View Consols, the plant was shut down, and the treatment of the ore was continued in the stamp battery, to be discussed later on in this review. About this time the Edwards-and later on the Mertonfurnace from Victoria was introduced, and the seven hearth at the Main Reef, the Brown at the South Kalgurli, the Ropps on the Kalgurli and Associated were thrown out, and these newest types of mechanical furnaces were erected on all these mines, and also the Gt. Boulder, the Perseverance later on converting the Holtoff- Wetheys into the Edwards type. From this time onward, the roasting was good. This problem being settled, the treatment of the roasted ore was the next question, and with few differences the treatment on the Associated, Associated Northern, Gt. Boulder, Kalgurli, Main Reef, Perseverance, and South Kalgurli settled down to the following:

Breaking the ore in Gates or Blake crushers.
Milling in Krupp or Griffin mills.

Roasting in Edwards or Merton furnaces.

Cooling or not the roasted ore.

Mixing with weak cyanide solution.

Classification, the sand being ground in pans and the coarse gold amalgamated.

The slime from all sources being thickened, run into agitators.

Treated with cyanide from 2 to 12 hours, and Finally filter-pressed, the residue being disposed of in various ways.

Before adopting the above, the South Kalgurli installed the Reicken process. Its principle was as follows:

The roasted ore from the Brown furnace was cooled, mixed with cyanide and agitated. It was then run into the Reicken vats, which had sloping sides and a curved bottom, a horizontal shaft with arms attached keeping the pulp in motion. The sides of the vat were lined with copper plates, which served as the cathode, and iron bars suspended in the vat acted as the anode. An electric current of low voltage was used. A constant stream of mercury was made to flow over the copper plates, thus keeping them bright. The gold from the cyanide solution was precipitated on the plates as amalgam, as was also the coarse free gold in the pulp. When it had been treated for 12 hours, it was discharged into agitators and filter-pressed. This process was also used by the Gt. Boulder No. I Co. for a time, but it was a failure at both mills, its weak points being very prominent.

In the wet crushing mills the necessity of close concentration was early noticed, to separate the pyrite from the ore. All kinds of concentrators were tried, but the Wilfley table did the best work, and is installed in all the wet mills now. Canvas strakes were also put in to recover the fine mineral, but still some got away with the pulp. It was found that the Wilfley tables did better work if given a certain feed, so the preliminary separation of the stamp pulp into certain grades was decided upon, these going to different tables. In the treatment of the concentrate it was tried to cyanide this product direct in vats, with poor results. Then it was shipped to smelters, but this was too expensive. Lastly, the roasting of the concentrate in Edwards or Merton furnaces, fine grinding and amalgamating in pans, agitation with cyanide and filter-pressing was experimented with, and is the treatment to this day. The pulp from the Wilfley tables was at first pumped up to collecting vats. Here, the sand settled, and was given a short cyanide treatment, then dropped into other vats for a few days' more treatment. The slime overflowing from the collecting vats was thickened, agitated with cyanide and filter-pressed.

This process was greatly in advance of previous efforts, but extraction was still only fair. Something was wanting. Very fine concentrate and telluride escaped with the pulp. The finer grinding of the pulp from the tables was then tried at the Hannan's Star in a tube mill, this being the first tube mill used in the world in grinding gold-bearing ores. At the same time bromo-cyanide was tried. In this chemical, tellurides are soluble, not being so in plain cyanide; and there is no doubt that the tellurides escaping were partly responsible for the low results in the earlier treatment with cyanide. At the Hannan's Star, where bromo-cyanide was first used in 1899-1900, the plant had ball mills, the dry crushed ore being mixed with water or solution previous to rough classification and fine grinding.

The Lake View Consols followed in 1901 in using bromo-cyanide in its mill, after all the pulp had been ground fine, the agitated slime being filter-pressed. About the same time the Brown Hill followed with the same treatment. These were the first instances of all sliming in wet mills. Later on the Golden Horseshoe and the Ivanhoe went in for finer grinding. In the new mill of the former it was all sliming with tube mills, and at the latter partly sliming in pans, and treatment of sand and slime still continues. At the

At

Hainault also the latter system is in vogue. present the Lake View Consols uses the tube mills alone, and the Oroya-Brown Hill and Golden Horseshoe use pans and tube mills in series with subsequent treatment of the slime with bromo-cyanide. The Ivanhoe uses bromo on its slime only.

FILTER-PRESS IMPROVEMENTS.

Improvements in the filter-press were rapid until 1899, and the press used now is practically as it was in that year. These were hand-screwed, the hydraulic closing type being worked later at the Gt. Boulder, Ivanhoe and Brown Hill. The first little press experimented with is still at the Lake View. This should be preserved, and so that it could be shown to interested mining men and visitors as the forerunner of the machine that has done so much for the treatment of our ores. The presses were first charged by pressure tanks; but pumps were afterwards tried, and are now universally used. The vacuum process of treating slime became fashionable in America some five years ago and was tried here experimentally. The only serious competitor of the press up to 1908 was the mechanical vacuum plant on the Gt. Boulder, but in 1908 and 1909 vacuum plants were erected on the Lake View Consols and Oroya-Brown Hill to retreat the residue on those mines. The vacuum plant is cheaper in first cost than the filter-press plant, but its efficiency has not been proved superior. Experiments are now underway with the press, the idea being the discharge of the slime by sluicing without opening up. It will be interesting to note the improvements effected in these two types of filters, and the survival of the fittest.

DISPOSAL OF RESIDUE.

The disposal of residue has been an interesting subject from the start of milling on a big scale. The various systems may be put down as: Hand and horse trucking, electric locomotives, belt conveyors, elevators and swinging booms, and, lastly, the sluicing away to dams. The difference in the cost of each method is not very much, and in this windy place high dumps. have been a curse to the engineers, workers and inhabitants of the belt. Of course, where the residue needed retreatment it had to be stacked near the mills.

In the recovery of the gold from the cyanide. solutions there has been a certain amount of trouble at times, but on the whole the precipitation on zinc shavings has been good. In the clean-up the lead-lined press for filtering the sludge from the acid tank was

first used here, as was also the tilting turnace for the smelting of the roasted sludge with the usual fluxes. THE WATER QUESTION.

One thing not to be forgotten in this review is the water supply for the mills. Until 1903 the supply consisted of salt water procured from some of the mines. This was not good for general work, and it was very destructive to machinery. The Coolgardie Goldfields Water Scheme was completed in 1903, and we have an abundant supply. There is no doubt that, if the mines had to depend upon the salt water and rain water conserved in dams, mining and treatment would not have been on half the scale it is now. This is no place to go into details of cost of treatment, but it may be said that in the days of shipments of ores to smelters the cost was as high as £6 per ton, whereas the present cost, Ios. 6d. per ton, may be considered a fair average for wet and dry crushing mills. It is probable that costs are on bedrock.

Extraction varies, but may be averaged at 91 per cent. in both wet and dry mills. The following questions are still debatable on this field :

Breaking the ore in Gates or Blake crushers.
Milling in Krupp or Griffin mills.

Roasting in Edwards or Merton furnaces.
Fine grinding in pans or tube mills.

Agitating in air, A.Z., or ordinary agitators.
Filtering the solutions from the pulp in presses

or vacuum plants.

Disposal of residue by belts or sluicing; and, finally one that has lately been suggested, namely:

The efficiency and economical working of the Krupp mill-wet crushing-as against the modern heavy stamp.

CONCLUSION.

In the above review, necessarily somewhat incomplete, I had the assistance of Mr. C. M. Harris, manager of the Hannan's Proprietary, Ltd., and local secretary of the Australasian Institute of Mining Engineers, who furnished the history of ore treatment from 1893 to 1897, and revised this article. My own observations and experience date from thence onwards, especially in the latter part of 1899 and in 1900, when there were fireworks outputs, construction of big mills, and other work which was extremely interesting and of great value to the future of the mines of the "Golden Mile" of Kalgoorlie.

The discovery of telluride ore on Block 45 in 1896 and a little later on in the Lake View Consols mine, set the metallurgist experimenting as to the most suitable method that could be economically adopted for the treatment on a large scale. Various methods were tried, with varying amounts of success, until Mr. J. W. Sutherland, metallurgist of the Lake View Consols, tried roasting in the ordinary assay muffle furnace. After such roasting the ore was readily treated by amalgamation and cyanide and induced him to make the experiments on a large scale, and in 1897 the first roasting furnace on the Golden Mile was erected on the Lake View mine. The furnace was after the style of the old hand rabbled reverberatory of Victoria, the length being 15 ft. and width II ft. As it was necessary to dry crush the ore before roasting, the Lake View loaned one of the ball mills on the Associated mine and crushed the ore through an mesh screen. The results from roast

ing larger quantities were equally successful, and it is on these results that the foundation of the present roasting plants is based It being decided in 1898 by Mr. Callahan, manager of the Lake View Consols, to instal a properly equipped roasting plant, instructions were given to Mr. Pratt, the engineer, to proceed to the Eastern States and inspect and report on the roasting plants then in use. While he was making his report the Lake View Consols office was in communication with Europe and when the whole of the information was available a Brown straight line furnace was ordered, and in 1899 the two furnaces started roasting on a large scale, and were it not for the Swansea people supplying rope in place of chain for the rabbles the obtaining of a sweet roast would not have been so seriously delayed. It is not intended to go into the technicalities but nearly every one is conversant with the varying results obtained, sometimes necessitating the blasting out of the sands in the

leaching vats. While Mr. Pratt was away the Gt. Boulder Main Reef decided on a roasting plant and sent Mr. Marriner, the metallurgist, to the Eastern States to inspect and report, and it was on his report that the Mt. Morgans shaft furnace was installed on the Main Reef in 1899. In connection with this furnace, one of our goldfields papers went so far as to say that the Gt. Boulder Main Reef was the first mine on the fields to pay a dividend on sulphide ore and the extractions were given out at 96 per cent. of the gold contents, although later investigations qualified these reports to a certain extent. While these two mines were roasting and completing the roasting plants, the Associated and the Kalgurli mines were erecting the Ropp furnaces, the Perseverance the Holtoff-Wethey, and the South Kalgurli the Brown straight line. It was during 1900 that these plants were put into operation. The Gt. Boulder had pinned its faith to the Kooneman process and under Mr. Kooneman's superintendence were erecting a gas-fired vertical column furnace somewhat similar to the Stetefeldt furnace. This furnace was designed for roasting the ore in particles as large as nuts and to do away with the fine grinding which was necessary with all the other plants. Unfortunately, this plant was rapidly proved a failure and in 1900 the management chose Mr. Lilburne, the metallurgist, to take a parcel of the Gt. Boulder sulphide ore to Ballarat to be roasted at the Edwards pyrites works at Ballarat. The trials were very successful and on his return the erection of a set of Edwards furnaces was put in hand. A feature of these furnaces was to be the gas firing and in conjunction with the roaste.s a gas plant was installed, but the economy of gas fuel was not the success anticipated for it, and after a lot of hard work the officials had to reluctantly revert to the wood firing.

In 1901, with all the different types of furnaces roasting, the metallurgists were busily engaged in obtaining the very best results from the furnaces, and in comparing results with the adjacent mines. The mines were rapidly developing large sulphide ore bodies and an increase of roasting plant was becoming an urgent necessity, and the managements were anxious that the additional furnaces should be of the best of the different types, so naturally the roaster was the most prominent metallurgical topic amongst the mines. The Kalgurli mine was the first to admit that the Ropp was not suitable for the work, and in making additions to the plant discarded this type entirely and erected in its place the Edwards furnace, with a single line of rabbles, and raising and lowering gear to alter the furnace hearth to any level which was thought necessary and nine of these furnaces started work early in 1901.

At about this time the Ivanhoe, who had been running a small tower furnace with a capacity of three tons a day, since February, 1900, and the Brownhill, where the stamp mill and wet crushing with concentration was in use, decided that the concentrates that were being produced could be more profitably treated by roasting on the mine than shipping to the customs. works, and placed the order for the furnaces with Edwards. The Ivanhoe installed three single rabble and the Brown hill two single rabble Edwards furnaces. The results obtained from this change proved eminently satisfactory, the furnaces at the Ivanhoe being still in use. A fourth furnace was added in 1902 and a fifth in 1906, making a total of five Edward's Simplex furnlaces as in use at the present day. The Gt. Bouder management at this time was also anxious to increase the monthly tonnage of ore treated, and not being altogether satisfied that the Edwards furnace was the best, instructed Mr. G. M. Roberts to investigate and report on the Merton furnace, and it was on his recommendation that the company decided that the additional furnaces should

be of the Merton type. These furnaces were duly installed and were working in 1903. The Associated company was now being thoroughly convinced that the Ropp furnace could be improved upon and were making enquiries as to what they should instal. All the furnaces were getting fairly good results and in making the choice they, helped by Mr. G. M. Roberts, who pronounced strongly in favor of the Merton, prevailed upon the manager, Mr. Gliesberg, to erect ten of this type. These were complete and running in 1904. The Kalgurli had decided to again increase the monthly tonnage and the South Kalgurli to overhaul their mill and make it up-to-date, and the question of the best type of roaster was exercising the minds of Mr. F. A. Moss on the Kalgurli and Mr. J. Morgan on the South Kalgurli. The Kalgurli decided on installing the Edwards furnace with a bricked in hearth in place of the tilting furnace. The South Kalgurli replaced the Brown straight line with the Merton. These alterations and additions were completed in 1905. The Golden Horseshoe, who were using the stamp mill and concentration, had decided to follow the lead of the Ivanhoe and Brownhill and roast the concentrates from the Wilfleys on the mine, and the management approved of Edwards in regard to the workings of his furnace with two lines of rabbles, in place of the single line as used on the Kalgu li and other mines. After going into the plans with the maker, Mr. J. W. Sutherland placed an order and

constructed the first duplex furnace for roasting concentrates on the Golden Horseshoe in 1905. The results of this furnace were so excellent that the Perseverance seeing the improvement that was possible with the double line of rabbles made drawings for the replacing of the rabble of Holtoff-Wethey by the Edwards duplex and the using of the lower hearth as a conveyor and cooling surface. This alteration was successfully carried out by Mr. G. C. Klug in 1905, this being the first duplex furnace on roasting sulphide ore on the Golden Mile.

The Associated was putting in another Merton. The Associated Northern decided in favor of the Merton, whilst the Oroya-Brownhill replaced their Edwards by the Meiton. The furnace practice had now fined itself down to the two types, with the exception that Mr. Dagger, of the Associated, had designed and erected a two hearth furnace, practically a combination of the Merton and Edwards, and called it the Associated furnace, each finding strong support with masses of figures of costs and extraction to bear out their contentions and it then looked as if the two types would have equal support for all time, but Mr. Hamilton, of the Gt Boulder, wishing to increase the tonnage and having both types of furnace in use, deciding on erecting a duplex Edwards, and Mr. Roberts, of the Associated, the strong supporter of the