This company tried the Minerals Separation process in 1907, after abandoning the Potter process. The Minerals Separation process was rejected in turn, and the Elmore process installed, which latter process was used successfully for two years, when the Minerals Separation process was again adopted at the beginning of 1911. The Minerals Separation process had shortly before this time been considerably improved as regards its mechanical operation, and had demonstrated its adaptability to the slimiest material.

In all the company owns 27 dumps, most of which are either of a refractory nature, or are slime dumps ; and, seeing that all have to be removed by a given time, it is necessary to take a certain amount from each.

The cheapest and easiest way of removing these dumps is an important problem. At first sight a mechanical means of handling the tailing suggests itself, but as only a small portion of the daily tonnage treated is taken from each dump, it would never pay to incur a heavy capital expenditure on a mechanism which would be worked considerably under its capacity. As these dumps are scattered over a large area, extending from the north to the south end of the Broken Hill district, the material is hauled (with the exception of the South mine tailing- dumps, which have been equipped with an aerial tram) by the Silverton Tramway Company in its railway trucks. A tram-track is laid into each of the dumps, and at a height a little above the top of the truck a loading gantry or staging is erected ; this staging is hinged on the dump side of the track, and can be lifted by means of a small block and tackle to allow the locomotive to pass. The trucks supplied by the Silverton Tramway Company are strong iron cars of the box type, 15-ton capacity, i5ft. by jit. 6in., with doors at each side opening in the centre about half the length of the side, leaving a quarter standing vertical at each end. These trucks are certainly not the most suitable type, and entail much labour to empty, all of which has to be done by shovelling. A gang of men (the transport gang) are kept constantly employed at this class of work ; and, in addition, they unload all coal, mine stores, etc. As the dumps are so scattered, the company is compelled to lay quite a quantity of tracks both to the dumps and at the works, which at the present time amounts to 22,oooft. The tramway company has set (subject to approval) a time-table each week, stating the number of trucks required from each dump, and the time suitable to both parties, namely, the contractor loading and the tranrway company sending the empty trucks to each dump to be filled. The trucks, on arrival at the works, pass over a Pooley weighbridge, capable of weighing 40 tons, and after being weighed and then sampled for assay and moisture, the tailing is emptied into two storage-bins, having a total storage capacity of 1,888 tons (No. i, 666 tons ; No. 2, 1,222 tons). These bins are excavated out of the ground and made of concrete. At the bottom of the bins are openings, which deliver to 16 Challenge feeders (size of table, 2ft. 6in. diam., 15 r.p.m.). No. I bin has 10 feeders ; No. 2, 6 feeders. By means of the Challenge feeders the millman is able, to some extent, to mix the material from the various dumps. The Challenge feeders deliver to a conveyorbelt, one to each bin parallel to it, and these again deliver to another conveyor-belt at right angles to the bin conveyors, which conveys the tailing up the hill, first to a rubbish trommel (8ft. 6in. by 4ft. by 2ft. 6in., 21 r.p.m.) clothed with a punched plate, having 2in. holes ; this trommel is for the purpose of removing any stones, large chips, and lumps of slime or any large size material that would interfere with the feeding arrangements from the mill bins, or which would be too coarse to enter the tube-mill feed-pipes, and so cause serious chokage. The product through the trommel passes to another conveyor, No. 4, 24in. wide, troughed 6in., running 363^. per minute, and then to another conveyor running at right angles to these over the top of the bins. This belt is fitted with an automatic Robins distributor or take-off, which distributes the material evenly over the bins, and is of great assistance in mixing the material.

The discharge from the tube-mills (size of mill approximately 10 to 15ft., line with ribbed liners, running at 24 r.p.m), together with the material from the pans, runs to a Callow settler 8ft. diam. by 9ft. deep, fitted with annular overflow, for thickening; the overflow from this settler runs to four more 8ft. Callow settlers for de-watering, the clear water returning into circuit, while the thickened slimy product runs through a small spigot, and unites with the thickened pulp coming from the single settler first mentioned ; then to an elevator (size i6in., 8-ply, 30oft. per min.), which delivers to the mixer-box for flotation.

The mixer-box is divided into 16 compartments, eight of which are for mixing and eight for flotation ; the mixing is done in each of the compartments (3ft. square) by means of an impeller or paddle, 2ft. diam., working horizontally on a vertical shaft, having a speed of 306 r.p.m. From the mixer-box to the flotationbox there is an opening, 14 by 4in. and I2jin. from the bottom of the box, as an outlet from the mixer-box to the flotation compartment. At No. i mixer-box the acid solution, the eucalyptus oil, and the steam for heating are added. The feed running into No. i mixer-box receives a certain amount of agitation by means of the horizontal impeller before it passes into No. i flotation compartment.

The feed, being mixed with the acid and oil, becomes emulsified, and causes immediate flotation of a fair proportion of the sulphide particles, which flow over the lip of the flotation compartment into a launder. The rest of the material which has not been lifted falls to the bottom of the flotation compartment, and from there it is drawn by means of No. 2 impeller into No. 2 mixer-box through a 5in. pipe, and after receiving a certain amount of agitation and aeration it is forced into No. 2 flotation compartment, and a further amount of sulphides is floated off into the launder. This zig-zag track is continued through the length of the mixer-box until it reaches the last flotation compartment, and by that time all the free sulphides should be removed ; there only remains the residue, which is removed by opening a valve at the bottom of the last flotation compartment. This valve regulates the whole of the flow through the boxes, and has to be adjusted according to the proportion of water to feed, which is 3.5 of water to i of tailing by weight.

No. i compartment contained a high percentage of lead, and also of insoluble matter, and it was found that 7 and 8 also contained such a high percentage of insoluble matter that it was necessary to return these to No. i mixer-box again for re-flotation, with beneficial results. If was found, however, that, in spite of all the precautions, a high percentage of insoluble matter came over with the float, with certain ores, particularly those containing granular garnet. It is difficult to obtain a high-grade final zinc concentrate from these ores, although they are easily floated, requiring very little acid and oil. With the object of further raising the grade, it was decided to re-float the whole of the concentrate obtained from the first two units of the plant by passing it into a third flotation unit. The results obtained by re-floating the whole of the flotation concentrate from the two units have been very satisfactory, and can easily account for about a 2% rise in the zinc content of the ultimate flotation concentrate. At the time of writing the results obtained from a 14.8% zinc feed are approximately 42% zinc flotation, 44% re-flotation, and 46.5% finished zinc from the de-leading plant.

No. i compartment contained a high percentage of lead, and also of insoluble matter, and it was found that 7 and 8 also contained such a high percentage of insoluble matter that it was necessary to return these to No. i mixer-box again for re-flotation, with beneficial results. If was found, however, that, in spite of all the precautions, a high percentage of insoluble matter came over with the float, with certain ores, particularly those containing granular garnet. It is difficult to obtain a high-grade final zinc concentrate from these ores, although they are easily floated, requiring very little acid and oil. With the object of further raising the grade, it was decided to re-float the whole of the concentrate obtained from the first two units of the plant by passing it into a third flotation unit. The results obtained by re-floating the whole of the flotation concentrate from the two units have been very satisfactory, and can easily account for about a 2% rise in the zinc content of the ultimate flotation concentrate. At the time of writing the results obtained from a 14.8% zinc feed are approximately 42% zinc flotation, 44% re-flotation, and 46.5% finished zinc from the de-leading plant.

The over-size from the revolving screens runs to a revolving distributor, then to 7 of the first row of Wilfleys (running at 310 r.p.m.) for treatment. The under-size runs to a distributor, then to 12 of the second and third rows of Wilfleys (running at 310 r.p.m.), six in each row. These tables make a lead and a zinc concentrate, a middling, and slime. The zinc and the lead concentrates each run to their respective elevators, and are delivered into separate tanks for settling and draining. The middling from the first row of Wilfleys is returned by means of an elevator (i6in. by 8-ply, 28oft. per min.) to three Wilfleys on the same row, and re-treated, making a zinc and a lead concentrate and a small portion of middling, which is returned. From the second and third row of Wilfley tables come a zinc and a lead concentrate, also a middling and slime.

The middling from the second and third rows of Wilfleys is returned by two elevators (i6in. by 8-ply, 28oft. per min.) to eight of the tables in the second and third row, four in each row, and re-treated for a zinc and a lead concentrate, a small portion of middling being made, which is returned.

The slime from the .three rows of Wilfleys is run to two 9 by i8in. 3-throw plunger-pumps, running at 32 r.p.m., and pumped to six Callow settlers ; the thickened product is run to 12 Weir- Meredith vanners, which make a lead and a zinc concentrate, a middling, and slime. The middling is returned to two Callow settlers, then to five vanners again, and the slime made on all the vanners is pumped to the dam on the flat for future sale or treatment. This slime, although high enough in zinc to go with the zinc concentrate, is so difficult to drain that it was found advisable to store it rather than include it with the coarser concentrate. If it was included with the zinc concentrate, the moisture in the shipping concentrate would be excessive, involving a penalty on all excess moisture over 6%. This zinc slime, which is high in silver and lead (see analysis of zinc slime), is a saleable product by itself, and some has already been sold.

The overflow water from both the zinc and lead concentrate settling-tanks runs to five Callow settlers ; the thickened product from these runs to the slime-pumps, and is re-treated on the vanners. The overflow runs to two large settling-tanks, 6oft. in diam. and 4ft. deep, having an annular overflow. These tanks are built of concrete, and have sufficient area to thoroughly clarify the slimewater. The clarified overflow water runs to two 3-throw 9 by i8in. plunger-pumps, and is pumped to the de-leading section supply-tanks, of which there are two, having a capacity of 10,000 gal. each ; it is from these tanks that the wash- water for the screens, Wilfley tables, and vanners is supplied. The residue-sand coming from the No. 8 compartment of the flotation section runs direct to two Callow settlers, 8 by 9ft., having an annular overflow, the material passing over going to the elevator carrying the feed to the mixer, while the thickened product is drawn from the bottom, and runs to a 36in. conveyor draining-belt working in an iron trough ; the overflow from the iron trough is pumped by means of a 4-in. Robinson centrifugal pump to four round tanks, and the residue-slime allowed to settle. These residue-slime tanks (i8ft. diam. and 4ft. 6in. deep) are fitted with annular launders, the overflow going to two 9 by i8in. three-throw plunger pumps, which pump the water into the three supply-tanks (16 by 8ft., 10,000 gal.), each elevated sufficiently high to supply the whole plant by gravitation. The residue-slime from these tanks is pumped out by means of a 6 by I2in. three-throw plunger-pump on to the flat, and forms a dam and bank around the main residue-dump.

The sand-residue is conveyed by two 36in. conveyors running slowly, i8ft. per min., to allow sufficient draining, and is dropped upon an i8in. by 5-ply conveyor-belt (rubber), travelling 2ioft. per min., and conveyed for a considerable distance to a boomstacker, which is building the sand dump to a great height.

Owing to the sloppy nature of the residue and the difficulty experienced in conveying it, also to the essential oil being a solvent of rubber, which quickly causes the belts to deteriorate, it has been decided to install a combination sluicing and conveying plant. By this scheme the residue will run direct to large draining-tanks, as far as the natural fall of the ground will allow, and then the residue, which will by this time have its moisture reduced to about 8%, will be conveyed the rest of the distance. By this scheme the conveying will be reduced by more than half and there should be less loss by evaporation, thereby effecting a saving in both belting and water.

The finished lead and zinc concentrates (see analysis) from the de-leading section, after leaving the Wilfleys, are elevated into draining-tanks (18 for the zinc concentrate and three for the lead concentrate). These tanks, which are fitted with filter bottoms by means of battens, cocoanut matting, and hessian, are emptied through a circular discharge at the bottom on to a conveyor (one conveyor to each three vats), which conveys the concentrate to another conveyor running at right angles to it, and is discharged into the shipping bins.

The capacity of each zinc-tank is 85 tons, of each lead-tank 125 tons, and the total capacity of the zinc and shipping bins 3,200 tons, making a total holding capacity of finished zinc concentrate 4,730 tons and of lead concentrate 575 tons. The shipping bins are built of stone, fitted with doors and chutes on both sides of the line for filling the shipping trucks ; the extreme south end of the bin is partitioned off for the lead concentrate, and the same conveyor is used for conveying the zinc and lead concentrates alternately. After being filled into the Silverton Tramway trucks and sampled, the Zinc Corporation operations are finished.

The Minerals Separation plants and their capacity now in use are as follows: Sulphide Corporation, 700 tons; Zinc Corporation, 1,000 ; Kyloe Copper Mines, 60 ; Junction North, 600 ; Silver Peak, 80 ; Wallaroo and Moonta, 400 ; Etheridge, 80 ; Great Fitzroy, 250 ; Pinnicles, 160 ; Great Cobar, 400 ; Chillagoe, 200 ; Bradin, 1200 ; Cuba Copper Co., 150 ; Saxbergets, 150.