Hydraulic Sluicing at the Cobungra Mine
Published in The Argus, Monday 16th February 1885, page 9
By Our Special Reporter
Return to Part I: The Cobungra Diggings
No. II
The principal mine on the field is that in the possession of the Cobungra Company, and the sketch above shows the first of the three faces in the area upon which hydraulic sluicing is to be brought into active operation so soon as the unconstructed portions of the headrace are completed. The wash in the surrounding localities is in nearly every instance covered with basalt and only where the creeks and rivers cut through into the bed rock is it exposed to view. The face above shows the deposits to be a surface of basalt, then gravel interlaced by bands of lignite, or, more properly speaking, lignous clay with the heavier gravel or wash on the bed rock. Past experience has demonstrated the fact that these gravels are auriferous throughout, but from their great thickness averaging from 20ft. to 30ft., and the dissemination of gold throughout that thickness, the only possible method of working them to advantage and profit would be by hydraulic sluicing on a very extensive scale and by means of a greater supply of water than could be locally obtained. Private enterprise worked three faces, the last being the well known Italian’s claim to the south of the above face. Half a dozen of these foreigners were reported to have made £6 per man a week with the ordinary ground sluicing appliances, and a limited supply of water.
Information was conveyed to Melbourne by a stockdriver who had travelled cattle from Omeo through Cobungra of the success of a number of parties, and this led to the formation about two years ago of the Cobungra Company comprising a number of Melbourne and Ballarat capitalists. A survey of the locality disclosed the fact that a sufficient fall of water could be obtained from the head of the Cobungra River, a distance of eight miles to work the whole of the ground comprised in the company’s lease. All doubts as to the practicability of the proposed work having been set at rest, Mr T Hedley of Heathcote who had been appointed manager was despatched to Kiandra in New South Wales where similar appliances to those proposed to be used by the Cobungra Company were in active operation. The former company some time previously sent an expert to San Francisco, there to obtain the best information and latest improvements in the way of hydraulic sluicing. Authority was obtained from the Kiandra Company to allow the Mort’s Dock Company in Sydney who manufactured the original hydrant to make a similar one for the Cobungra Company. The pipes connecting the hydrant with the race are 1000ft. in length, and were made at Ballarat.
The race is seven miles five chains in length from the top of the spur shown on the sketch to the head of the west branch of the Cobungra River the depth is 2ft. 6in. with a width of 4ft. 6in. at the top, and 2ft. 6in. at the bottom. The fall averages 9ft. to the mile. The bottom end of the race connects with wrought iron pipes commencing at 22in. in diameter tapering down to 16in where the last length joins a V piece and two 16in. water valves. The hydrant has two separate motions, one vertical for reaching the more elevated positions of the face and the other horizontal. It also carries four adjustable nozzles ranging from 2½in to 5in. The weight of the water in the hydrant is counterbalanced by a loaded box so that the man directing the course of the stream has simply to steady and guide the hydrant. The race is constructed to convey 18 million gallons of water per day and the estimated pressure will be 78lb to the square inch. This tremendous force playing on the face undermines the wash just above the bedrock until the mass overhead crashes down towards the dump shaft, about 20ft. away. This shaft is 50 ft. in depth from the bedrock. The hydrant is then directed towards washing this mass down the shaft, where it is broken up by the fall on to vertical blocks below.
To the bottom of this dump shaft a tunnel has been driven from the side of the hill and in this tunnel the boxes are placed for a length of 328ft. The tunnel falls from the bottom of the shaft to the side of the hill at a grade of 8in. in 12ft. The boxes are 4ft in width, 2½in. deep and tongued and grooved with iron where the lengths join. Paving blocks are laid in these boxes and the interstices form the receptacles for the lodgment of the quicksilver and gold, it having been decided to amalgamate the latter. Whether this experiment will succeed in such a cold climate is open to much discussion. At Kiandra it is reported to have attained the object sought but if the Dark River experience goes for anything it will require a further trial before any decided opinion can be expressed. Often in the winter time the thermometer at Cobungra is below freezing point and the silver requires a great deal of “livening” by means of steam before it will amalgamate. The boxes will probably be carried a length of 600ft., with either one or two more dumps.
The race is one of the most extensive pieces of work in the mountains, and it would appear that a mistake has been made in constructing it in sections. Had the lower portion been made first there should have been water enough to commence washing with the autumn rains; as it is, work will have to be pushed on very rapidly to be ready in three months. In the seven miles there are over three miles of walling, reaching in some places as high as 18ft. The work, under the supervision of Mr Meikle has been of a heavy and trying character, the loose slips of basalt proving serious obstacles to construction.
No. 1 face that shown on the section above is about 300ft. across and with a consumption of 12 million gallons of water a day, it is estimated that 80 cube yards of dirt an hour will be put through the boxes. Here the wash averages 25ft. in height. The No 2, or western face is 80ft. in width by 80 yards long. The wash is 20ft. high on the western side where it dips into the hill south. At the Italian’s face, the height of the wash is 70ft. and the width 200ft. Here 40oz. of gold were washed from 6 ft. of dirt between a false bottom and the bed rock.
The company has spent something like £10,000 on the property, half of which has been devoted to the race. Opinions differ as to whether fluming instead of walling would not have been more economical in the end.
Such is a full description of the Cobungra Company’s mine, the pioneer of hydraulic sluicing in the Australian Alps. In two of the three faces I washed payable prospects. If the whole of the dirt is of equal quality and the supply of water insured, profitable results will be obtained. It will, however, never be what is known as a “market” claim. Shareholders may receive large or small dividends in return for their expenditure of capital, but the washing up will be at such lengthy intervals that opportunities for speculation in shares will be of rare occurrence.
To Mr. J. Ditchburn, the chairman of directors, and Mr. Hedley the manager, I am indebted for pilotage and succour in this inhospitable country.
Following a race south along the face of the spur we reach the Cobungra Tunnel mine. The lease which includes 12 acres adjoins the Cobungra Company a ground, and was originally applied for by Messrs Sharp and Gill. Owing to a dispute with their neighbours, the lease was not granted until 1884, when, after some court proceedings, five chains of their frontage to Brandy Creek was excised. The company was formed in July, but as the season was so far advanced, nothing could be done in the way of work until last spring. Prior to the formation of the company, the ground was prospected by means of shafts. The wash was found to carry gold almost from the edge of the basalt down to the lowest depths sunk. The bottom has never been reached, owing to the heavy flow of water. Last November a start was made with a tunnel from the side of the hill to drive for the lead, as it was quite apparent the steep declivity was only a slip from the main ratine On the day of my visit tilt tunnel was in 110ft. and measurements prove that it will be necessary to carry it on for another 60ft. or 70ft. before the bottom is reached. Driving is easy and inexpensive, owing to the favourable character of the ground. This wash now driven out will be put through the boxes as soon as they are ready.
Immediately to the south of this company Martin and party have driven a tunnel into a fair-looking wash at the side of the hill, but owing to a dispute among the partners work, has been suspended for several weeks.
Riding down Brandy Creek on the following day to the claims on the Cobungra River, the first we reach is that of the Cobungra Junction Compay. A tail race five chains in length, 3ft. wide in the clear, and 2ft. in depth has been cut to work a block about a mile long, with sluicing ground three chains wide. A shaft was sunk last winter at the end of the tail race, and prospects obtained of such a character as warranted the formation of the present company. The wash averages from 5ft. to 12ft. throughout the claim. In none of these river claims has the bottom been reached, owing to the appliances not being of a character to combat the water. Prospects of 7dwt. to the dish have been obtained higher up the creek.
Following the river in an upward direction, we reach the Murphy’s Creek Company’s mine, where work is progressing slowly. The races are almost completed, and by the time the autumn rains fall, everything should be ready for a steady continuance of sluicing operations. During the short stay we washed two dish prospects taken from the wash thrown up from the races and obtained in each instance about a gram to the dish.
Adjoining this company is the Cobungra Valley, where the races are almost ready to commence work. Here it is the intention to take out the first paddock without incurring the expense of a water-wheel. Similar prospects have been obtained to those on the other claims.
Returning by the same route, I proceeded down stream to the Cobungra River Company’s mine, the largest and most important of these bank sluicing claims. Unfortunately the manager was absent in Melbourne and the information to be obtained was meagre. However, I saw enough of the works to convince me that the success or otherwise of the mine will decide the future of all the others on the Cobungra River. A water-wheel, large enough to cope with the body of water that will undoubtedly have to be contended with, is on the ground and ready for erection. I was shown a fine sample of gold in Melbourne, washed some time ago at the claim. The work done up to the present consists principally of a wheel race to carry the water for motive and sluicing operations, and a wheel-pit that will return the water after being used to the tail race. Paddocking was in active progress, and shareholders ought not to be kept long in suspense as to the future of the river companies
Further down stream are the Mountain Stream and Cascade Companies, where the work of race-cutting is being carried on.
The gold in the river is of a coarser nature than that found in the terraces above, and as the prospected dirt appears to be pretty extensive, many of the claims with economical management may pay fair returns. Like those higher up in the hills, market operations in the stock will always be on a very limited scale.
About seven miles from the river claims, and six miles and a half from Cobungra township, is the mine of the Square Mountain Hydraulic Sluicing Company. Mount Tabletop is in the immediate vicinity, hence the name of the claim. Gold was first discovered by a miner named Box many years ago, who afterwards sold out his interest to Armour and Son. These men obtained 40oz. from a 12ft. paddock Then Valentine Perse, “the other Vagabond,” whom I met on the Nicholson River, last year worked the ground with fair success. Dunlop and Eccles afterwards obtained 10oz. per man a day, and four years ago J. Heritage (the present manager) and Petersen became owners.
The great drawback to operations then was the want of water. Last year portions of the interest were sold in Melbourne and the present company formed. Operations are suspended pending the disposal of 4,000 shares, which are now on the market. The average height of the wash from the bed rock to the basalt is about 30ft., and it dips rapidly into the hill. The best prospects obtained have been 4gr. to the dish, which, with an ample supply of water, would pay handsome dividends. The gold has been traced through the whole face of wash, and the success of the mine would appear to be a matter of either hard or soft ground. A tunnel has been started into the side of the hill, and will be carried on for 400ft. in order to obtain a dump of 30ft. The length of the main race is 4 miles up to a splendid dam of water, covering an area of 10 acres, and having an average depth of 14ft. The supply will be sufficient for sluicing the greater part of the year. The tail race runs into the Dargo River. There is timber in the vicinity for mining purposes for many years to come. A track to Cobungra is much required, as I have good cause to know by my 12 miles ride.
West of the Square Mountain and four miles south of Cobungra, is the Boiler Plains mine – ground that was surfaced 13 years ago. I am told that in those days wash averaging a pound weight of gold to the square foot was put through the boxes at the mine; but then I’m told a good deal in these mountains that I don’t believe. My informant was not in possession of statistics to enable him to state how many feet of this wonderful dirt had been blocked. The Government prospecting party some years ago drove the tunnel 66ft., when they were recalled owing to a change in the politics of the country placing another ruler in power at the Mines office. Later results reached in prospecting 5dwt. to the dish. In April a company was formed in 15,000 shares, and since then two drives were put into hard ground. Since my visit the survey of the upper portion of the race has disclosed the fact that sufficient fall cannot be obtained near the head. There is face of wash 45ft. in height ready for working.
Returning to Cobungra and changing horses, the same evening I started back for St Bernard. With a “Farewell, and get round Blowhard before night” from the little knot of diggers below, I make for the main divide But I was doomed to disappointment. A thick fog belched up from the ravines, and before reaching the Diamantina I was forced to grope my road along the narrow track. Twice I thought I knew more than my mountain horse, just rising up in time to discover I was on the edge of the precipice. At 9 o’clock the yelp of the mountain Cerberus brought us to a standstill before the welcome light of the Hospice could be discovered.
Next day, amid a heavy rain, I visited the Mammoth mine, four miles south-east of St. Bernard. Rounding the suggestive Mount Freeze-out by a well-defined track, and descending a steep gully leading to the Dargo, the claim, on the side of the hill, is reached. Years ago an attempt was made to float the company in England, but the British capitalist was of opinion that if there was any quantity of such stone as that exhibited, there was no necessity to seek foreign investors. The stone that has been crushed since at various times has yielded very handsome results. There are three tunnels in the side of the hill, the one at the highest level being in 300ft.; the second is 250ft. down the hill, and is in 570ft.; and the third 700ft. The reef in the top level is 10ft. in width; at No. 2, 15ft.; and in the bottom, 17ft. The same shoot of gold has been traced from the highest to the lowest, where we obtained prospects of about a grain of fine gold to the dish. At No. 2 level, a trial crushing of 80 tons gave 2oz. 12dwt. to the ton. The drawback to the development of the mine has been the want of a battery, the Evening Star, the only one in this part of the ranges, having been destroyed by fire. A few days before my visit a prospector named Wells obtained some splendid specimens from a reef close by the Mammoth. If capital was invested for the purpose of erecting a battery, a large reef, prospecting in the bottom 16dwt. to the ton, ought to pay handsome returns.
Down the Dargo the Happy Home Company have just completed their mill, and have 500 tons ready for crushing. The trail of 20 tons gave the satisfactory result of 3½oz. to the ton.
Round about Harrietville are several dividend paying mines, but all held in private hands. The Tiddle-de-Addlede (strange cognomen) are sinking on 7oz. stone, and has just paid the “Jackass” proprietors £500 for the right to drive their tunnel a distance of 800ft. to strike their first reef. During the last four years 20,000z. of gold have been taken from the first named mine at a depth of 1,200ft from the surface. There is a tramway a mile in length from the mine to the battery. Adjoining is the Mons Meg, worked by a party of three. A crushing of 100 tons was put through the mill a few days before my visit which returned 6210z. of gold. A battery is now in course of erection on the ground. They have driven 80ft. along the reef, which averages 3ft. in width for that distance. £3,000 was offered for one share, and refused.
In the township of Harrietville is the Harrietville Deep Leads, whose shaft is down 160ft. They had driven over the wash, and are now sinking 30ft. deeper, with a water-wheel and 12in lifts.
The recent discoveries have directed attention to the localities, and if prospecting is judiciously carried on, there is every possibility of further mining successes in the Australian Alps.
