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Vol. X L V . No.
1. L O N D O N , J U L Y ,
1 93 1. C O N T E N T S
PRICE ONE SHILLING
Ed i t o r i a l
Notes ... 2
Lectures on T ropical H ygiene ; O pening of th e B enguela R ailw ay ; In te rn a tio n a l Congress on th e H isto ry of Science an d T e c h n o lo g y ; I n s titu te of M etals’ S u m m e r M eeting ; P roposed N ew T erm in M etallurgy.
Geophysical P r o sp ectin g ... 2
The re p o rt of th e Im p e rial G eophysical E x p e rim en tal Survey is review ed.
Non-Ferrous Metals R esea rch ... 3
The w ork of th e B ritish N o n -F erro u s M etals R esearch A ssociation is ex am in ed ap ro p o s th e opening of new h e a d q u arte rs.
The Bickford Centenary ... 5
The celebration of th e c e n te n a ry of th e in v e n tio n of safe ty fuse is recorded. R ies . _ , E n g i n e e r i n g Geology
15 18
Re v i e w o f Mi n i n g... Ar t i c l e sThe Treatment of Oxidized Zinc T a ilin g s ... B . W . Holman
A tten tio n is d irected to th e W aelz v o latilizatio n process as in use a t Vieille M ontagne.Ratio of Concentration and Recovery F o rm u la e...Eldred A . K n a p p
W ith th e aid of tw o c h a rts th e a u th o r offers a g raphical so lu tio n of these ore-dressing form ulae.The Magnesite Deposits of Mytilem
V. Jerome A kyla s T h e a u th o r describes th e m agnesite d ep o sits on th is island in th e G recian Archipelago.Ore Reserve Calculations at the Bawdwin Mine
A llan B . Lolquhoun 23 (■Concluded fro m the J u n e issue, p . 333.) Le t t e r t o t h e Ed i t o r T h eD utv of a Mine Management
W . G. G. Cooper 26 Bo o k Re v i e w s L a h e e ’ s " F ie ld Geology ” Dr. M u rra y Stu a rt an d W a ts o n ’s " E le m e n ts of 26 D r. M u rra y S tu a rt 27 jsfjjw s Le t t e r sJohannesburg ...
« r t h e r n Free S ta te ; P rospecting in R hodesia ; K im b e rle y Reef P ro s p e c ts ; R hodesian B anket F i e l d s ; Pongola Valley Gold ; Iceland S p ar ; Three A s b e s t o s Mines Closed.27 V ancouver... 29
M ining durin g 1930 ; Bridge R iver ; T he K ootenays ; P o rtla n d CanaL
Toronto ... 31
S ud b u ry ; Porcupine ; K irkland Lake ; R ouyn.
B risb a n e... 33
P ro d u ctio n a t M ount I s a ; A ustralian Gold M in in g ; A nother M ount Morgan Move ; Oil P ro sp e c tin g ; B endigo an d B a lla r a t; B ism uth in Tasm ania.
Camborne ... 35
R elieved A nxiety ; S o u th C rofty ; E a st Pool and A gar ; G eevor ; W heal K itty ; Mine D evelopm ent Scheme. P e r s o n a l ...
36
T r a d e P a r a g r a p h s ...
36
L o b n itz D r e d g e ... 37
H o lm an S crap er H au lag es . 40 M e t a l M a r k e t s ...
41
S t a t i s t i c s o f P r o d u c t i o n ...
43
P r i c e s o f C h e m i c a l s ...
45
S h a r e Q u o t a t i o n s ...
46
Mi n i n g Di g e s t L ead B la s t-F u rn a c e O p e ratio n s a t B roken H ill ... O. H . Woodward 47 T h e S u lta n a G old M ine, O n tario J . G. Cross 51 P recio u s M etals in T ra n s v a a l P la tin u m O res H . R . A d a m and R . J . Westwood 53 F la sh R o a stin g of S u lphide Ores H . Freeman 55 T h e M ig ra tio n of G old . . . . F . W . Freise 56 S crap er M ucking a t F lin F lon M . A . Roche 58 O p e n -P it M ining ... H . A . Thorne 60 B u lk F lo ta tio n of Gold . . . . L . A . Grant 61 Q uicksilver R eco v ery a t C learlake, C alifornia W. Bradley 61 S h o r t N o t i c e s ...
61
Re c e n t Pa t e n t s Pu b l i s h e d . Ne w Bo o k s, Pa m p h l e t s, e t c. Co m p a n y Re p o r t s ...
. . . . 62
. . . . 62 63
A ram ayo Mines ; B angrin Tin ; E speranza Copper an d S ulphur ; Geevor Tin ; G reat B oulder P ro p rietary ; K aduna Prospectors ; K ad u n a Syndicate ; L a h at Mines ; Libiola Copper ; Poderosa ; San Finx Tin ; Siamese Tin ; Talerng Tin ; T ransvaal Gold Mining E s ta te s ; W aihi G rand J u n ctio n .
Di v i d e n d s De c l a r e d...
Ne w Co m p a n i e s Re g i s t e r e d...
64 64
U J i , .
E D IT O R IA L
A COURSE which should prove of interest to those going to a warm climate for the first time is to be given by the British Red Cross Society, this comprising nine lectures and demonstrations on tropical hygiene, the first being on Monday, September 28. Particulars of the course may be obtained from the County Secretary, 9, Chesham Street, S.W. 1.
T H E extension of the Benguelaline from the Angola border to Tenke was opened officially at the beginning of this month and it is now possible to make the complete journey across Africa by rail. The first shipment of Union Minière copper has already been made by the new route, a prelude to the extensive use this company will make of the service to Lobito Bay.
T HE International Congress of the History of Science and Technology was opened by the President of the Board of Education in the Great Hall of the Royal Geographical Society on June 29. This meeting, the second of the triennial congresses arranged by the Comité International d ’Histoire des Sciences, in co-operation with other interested societies, lasted five days and was attended by representatives from 24 countries.
T HE annual meeting of the Institute of Metals will be held in Zürich from September 13 to September 15 by invitation of the Schweizerische Verband für Material- prüfung and a local reception committee has been formed. Prior to the m eeting the first congress of the new International Association for Testing Materials will be held in the same place and afterwards it will be possible to visit the International Foundry Exhibition at Milan, or to take part in certain optional tours which have been arranged.
The programme of the meeting will include visits to many important works as well as the presentation and discussion of papers.
F REQUENT attempts have been made to coin a word which would suitably describe that branch of metallurgy covering the science of the properties and treatment of metals and alloys, as distinct from the
processes by which they are extracted from their ores, the subject having been referred to in these columns as Metallurgy II. The most recent suggestion is that made by Dr.
Rosenhain, who, having several years ago introduced the expression “ physical metallurgy,” now proposes the use of the single word “ metallics ” as being a term sufficiently vague and broad to cover a wide subject. The main objection to the term suggested seems to lie in the fact that it already has a specific meaning for assayers and prospectors and might possibly lead to ambiguity.
G e o p h y s ic a l P r o s p e c tin g
The present blight which has settled on world affairs in general and which has had such a serious effect on all com m odity prices is particularly evident in the state of the metal market, so that it is hardly surprising that all prospecting is at a discount, except, perhaps, in so far as it concerns gold. At the moment, unfortunately, efforts are largely concentrated on the restriction rather than on the expansion of mining enterprises and yet it is imperative that the existing depression should be regarded as temporary only, for any feeling of inevitability can only succeed in mortgaging the future.
This is a period when steps must be so well planned that much of the misery of unemployment must disappear, as far as is possible in such an increasingly efficient world. Looking ahead, therefore, it is the opinion of many people that prospecting activity should soon be revived and from this point of view it is possible to extend additional welcome to the publication of the Report of the Imperial Geophysical Experimental Survey 1 which concluded its work “ down under ” last year.
It will be recalled that the work of the I.G.E.S. was carried out under the joint auspices of the British Empire Marketing Board and the Commonwealth Government, each sponsor contributing the sum of ¿16,000 towards the cost. Its object was not to
1 T he P rin c ip le s a n d P ra c tic e of G eo p h y sical P ro s p ec tin g , b e in g th e R e p o rt of th e I m p e r ia l G eophysical E x p e rim e n ta l S u rv ey . E d ite d b y A. B. B ro u g h to n E d g e a n d T . H . L a b y . C a m b rid g e U n iv e rs ity P ress. P ric e 15s.
JULY, 1931 3 prospect for minerals, but to test the
applicability of several standard geophysical methods to those Australian conditions which might be considered as characteristic of considerable portions of the Empire.
The procedure adopted by the Survey was developed along the broad outlines suggested by the Geophysical Sub-Committee of the Committee of Civil Research, the report of which was published in 1927, and its field parties worked in selected, widely-separated areas in the six Australian States. While the work was in progress a serious setback occurred, owing to the death of Dr. E. S. Bieler, the Deputy Director, this unfortunate loss particularly affecting the electro-magnetic part of the work, in which Dr. Bieler was a recognized authority. In this emergency Professor T. H. Laby, of the University of Melbourne, was asked by the Australian Committee to come to the help of the Survey and he readily placed his services as consulting physicist at its disposal. In many other respects the undertaking is indebted to the Australian authorities, the State Depart
ment of Mines having carried out con
firmatory shaft and drilling work and, indeed, all those interested have helped to carry the Survey to a successful conclusion.
The report itself is divided into two parts, Part I covering the field investigations, together with elementary accounts of the methods employed, while Part II gives more detailed explanations of field procedure, design of apparatus, interpretation of results, and additional theoretical matter. Much of the information regarding electrical instruments is here given for the first time and this feature is intended to provide material assistance to those who contemplate the use of such methods of prospecting.
In this respect the report carries a stage further the wishes of the Sub-Committee of the Committee of Civil Research, which was of the opinion that a full disclosure of the scientific facts governing electrical methods would tend to stimulate this method of exploration by placing it on a scientific footing, this branch of geophysics having previously been in the nature of a jealously-guarded trade secret.
The work of the Survey showed that the outstanding applications for geophysical work in Australia would be : (1) Electrical surveys for base-metal ores where salinity of the surface and underground waters does not interfere; (2) electrical surveys
in saline-water districts to determine the distribution and character of underground water supplies ; (3) gravimetric surveys over brown coal fields ; (4) magnetic surveys over sub-basaltic tin and gold deep-leads, and (5) both gravimetric and seismic surveys in sub-alluvial gold and tin deep-lead work. Other uses to which the various methods might be applied are also set out in the report. It is true that most of the Survey’s work was carried out on long-established mining fields ; nevertheless, a satisfactory proportion of valuable results was obtained and in several instances important mineral discoveries were made, although it was known that in certain cases the chances of obtaining definite results would be rather remote, as, for example, in districts where saline waters were prevalent. In addition it is justly claimed that some of the negative results which occurred may have meant the absence of mineral. The amount of work carried out by the Director of the Survey, Mr. A. B.
Broughton Edge, and those associated with him is evidenced by the thoroughly practical information contained in the report and the claim of those responsible for its publication that it should lead to a more accurate estimation of the present possibilities of applied geophysics and that there is ample scope for the combined work of physicists and geologists in the search for ore-bodies and in the interpretation of doubtful geological structures may be held to be thoroughly justified.
N o n -F e r r o u s M e ta ls R e se a r c h
The progress achieved by the British
Non-Ferrous Metals Research Association
has frequently been noticed in these columns
and last month we were able to record the
opening of new central laboratories by
Lord Rutherford. The work of the
association lies entirely within that branch
of the profession well described as secondary
metallurgy, or, as it has been called here,
Metallurgy II, but the introduction of new
metals or alloys to industry is of such
fundamental importance that no excuse is
needed for making more extended reference
to the work of this industro-scientific
organization. The new headquarters near
Euston Station have been installed in a
building admirably suiting the needs of
the association and they permit of much
of its work being undertaken under one roof,
4 THE MINING MAGAZINE which enables the Director to feel that he
is working with a team which is at once stim ulated by any results obtained in a particular problem. The occasion of the recent opening was marked by the publication of a pamphlet entitled “ Ten Years of Research for the Metal Industries,” and this admirably sums up the activities of this band of workers and thé results which have been achieved.
Before approaching those"items of research which have been successfully tackled it may be as well to recall something of the history of the association. It was incor
porated in 1920, under the auspices of the Department of Scientific and Industrial Research, and had as its object the provision of a co-operative research organization for the British metal industries, the war having revealed the necessity for a closer association between science and industry. From the time of incorporation it was intended that the new body should serve a dual purpose.
It was to be an intelligence bureau for the industry and also to be the means by which researches could be undertaken which required prolonged investigations, work which did not lend itself readily to execution by individual firms. Among such investigations mention might be made of those on atmos
pheric corrosion and tarnishing of metals, carried out at the Royal School of Mines, and the study of the effect of impurities in copper, which has been in progress at the National Physical Laboratory for the last nine years. Most of the work, however, has been directed toward the solution of distinct industrial problems, such as the explanation of causes of breakdown or defects in constructional materials, and this has included detailed studies of technical processes in order to improve existing deficiencies. The following summary of some of the tangible results achieved by the association will give an indication of the wide range of the problems which have been studied. The introduction of ternary lead alloys, consisting of lead, cadmium, and tin, or of lead, cadmium, and antimony, for cable sheathing and water- pipe manufacture has been already noticed in the
M a g a z i n e ,but the fact that it is possible to use ternary alloy pipes of much less weight and of equal strength to the heavier lead pipes, which they replace, and which are often of foreign origin, should be emphasized. Investigations into condenser-tube corrosion and the intro
duction of aluminium-brass for the manufacture of such tubes have had important results in the industries affected, while the examination of tin solders has immensely clarified the knowledge of the uses to which various solder specifications are applicable. Another research of far- reaching importance is that into the break
down of locom otive fire-boxes and stays, results proving without question that such breakdowns have been due in the past to lack of elasticity in the metal used, a defect found to be imm ediately remedied by the presence of minute quantities of silver, amounting to 0'05 per cent., in the copper used for the purpose. Perhaps one more investigation deserves specific mention, this being that into alloys for high-temperature service. When this piece of research was commenced no alloy was known which had a greater creep-strength than 1'9 ton per square inch at a temperature of 800° C., but it has now been possible to prepare nickel-chrome alloys which have a strength exceeding 5 tons per square inch at the same temperature. Other work includes investigations into copper welding, annealing furnace practice, electro-deposition of metals, the effects of gases in metals, spectroscopic analysis for industrial purposes, and the casting and working of brass, aluminium, zinc, and nickel. Finally mention should be made of the intelligence service of the association, which demands intensive study of all published relevant work for the purposes of record and information, the most important item s being communicated to members in the Bulletin, which it is hoped will soon become a m onthly publication.
It has been pointed out by the Director that one of the most important achievem ents of the past ten years has been the accumula
tion of experience on how to afford service
to the industry. Efforts are being made to
bridge the gap which undoubtedly exists
between the solution of a problem in the
laboratory and its general application. It is
emphasized that, although the interest of
a particular industry m ay be aroused bv the
issue of a laboratory report, there is still an
appreciable time-lag before the result has
actual influence on practice, so much so
that disappointment must often be felt by
those anxious for the promotion of industrial
research. The personal efforts of Dr. H utton
to reduce this interval to a minimum are
very evident and his endeavour to foster the
work of his intelligence staff and to spread
JULY, 1931 5 the knowledge of technical advances is
worthy of every commendation.
T h e B ic k fo r d C e n te n a r y
Mining would still perhaps be classed by many people as a dangerous occupation, but the realization of how much greater would be the hazards of underground work without such devices as the safety lamp or safety fuse forcibly reminds us how much advances in mining practice have been due to these two great inventions.
To the first is due the enormous growth of our coal industry, while the advances in hard rock mining could not have been made without the help of a safety device for igniting blasting charges. This fact was brought home to us last March by the notice that the firm of Bickford, Smith, and Co. had chosen on June 25 and 26 to commemorate the invention, a hundred years ago, of the safety fuse by William Bickford, the founder of the firm. The celebrations took place at Tuckingmill, in Cornwall, and they were attended by representatives of associated companies overseas and of Imperial Chemical Industries.
Mining is a calling of great age in Cornwall and it is hardly surprising that many inventions which have been calculated to assist the industry should have emanated from the county, perhaps the most striking being the application of steam to mine pupiping. The frequency of blasting accidents in Cornwall at the beginning of last century led William Bickford, then a leatherseller, to consider whether some method of firing blasting charges could not be found which would be safer than those then in vogue. At that time miners used squibs or touch paper for the purpose, although the most common method lay in the use of goose quills. These were inserted one in the other, telescope fashion, until a tube the length of the blasting hole had been made. This was then filled with powder and the hole tamped, touch paper being applied to the top of the quill before the miners escaped. Misfires and premature explosions were all too common, as might be anticipated, resulting in many serious accidents. Bickford had already had ideas for making cartridge or parch
ment bags to hold powder charges, but had found this too expensive, and it is related that the principle of the present
fuse came to him somewhat by accident.
He is said to have been visiting a friend, a ropemaker, in Tuckingmill and that he walked up and down with him while, with hemp around his waist, he spun the yarn for making rope. It struck Bickford that if a funnel of gunpowder could be so fixed as to pour a stream of powder into the rope as it was spun and afterwards bound securely it would provide the desired means for safely transmitting fire to the charge. The idea grew and the first patent for his invention was granted on September 6, 1831, the first fuse being manufactured and sold in the same year. The new device was soon adopted in the principal Cornish mines, although like most new inventions it was subject to considerable opposition, mostly interested, one of the chief opponents of the device naturally being the goose- quill vendor. The principle of the fuse having been established, attention was next directed to blasting conditions and fuse coatings for damp and wet ground were soon adopted, one of gutta percha being found suitable for submarine work.
Naturally vast improvements have been made in the manufacture of the fuse during the past hundred years, both in the rate of output and in its reliability and efficiency, as well as in the manufacture of gutta percha compositions for fuse coverings. It was found that the invention of electric firing did not seriously compete with the safety fuse, the scope of which has been much extended by other inventions, the chief being the discovery of instantaneous fuse by D avey at Rouen and of cordeau-detonant, a lead piping filled with T.N.T., so that it is not surprising to find that the demand for the products of the firm has continued to grow, the output of Bickford fuse being at the present day larger than ever.
From its inception in Cornwall in 1831 the firm of Bickford Smith has continued to expand. In 1836 the manufacture of its products began in the United States, to be followed in 1843 at Rouen. A factory at Meissen, in Saxony, was opened in 1844 and in 1849 another was started at Wiener- Neustadt in Austria, to be followed twenty years later by an installation in Hungary.
At the present day manufacture is carried
on in Canada and Australia, in addition
to the countries already mentioned, the
company in 1917 becoming merged into
what is now known as Imperial Chemical
Industries.
R E V IE W O F M IN IN G
In tro d u ctio n .—The most important event of the past month has been the proposal of President Hoover that a year’s suspension of war debt paym ents should be accepted b y those interested. After a period of doubt over the French attitude, the proposal has now been accepted in principle. Although the first effect of the scheme was an improvement in general conditions, the view seems to be held in well-informed quarters that something more than a year’s holiday will be needed to set the world on its feet again. The position with regard to tin has been strengthened by the announcement that Siam has agreed to adopt the international quota scheme. This will bring 92 per cent, of the world’s tin out
put under control.
T ran svaal.—The output of gold on the Rand for June was 855,073 oz. and in outside districts 42,677 oz., making a total of 897,750 oz., as compared with 910,279 oz.
in May. The number of natives employed in the gold mines at the end of the month totalled 207,209, as compared with 207,109 at the end of May.
The accompanying table gives the dividend declared by the Rand gold mining companies on account of the past half- year. For the purpose of comparison the figures for the preceding three half-years are given and from these it will be seen that the Durban Roodepoort Deep is the only company to show an increase. There are, however, several reductions, which seem to indicate that the improved labour situation is not having the important
effect considered likely in many quarters.
2nd half, 1929.
1st half, 1930.
2 nd half, 1930.
1st half, 1931.
s. d . s. d. s. d. s. d.
B ra k p a n ... 0 0 4 3 4 6 4 0
C onsolidated M ain R eef. . 1 1) (1 9 1 3 1 3
Crown ... 3 8 3 3 3 6 3 6
D u rb an R o o d ep o o rt D eep 0 3 U Ö 0 9
G eduld ... 8 3 8 3 3 3 3 3
G eld en h u is D eep ... 0 6 0 9 1 0 1 0
G o v ern m en t A r e a s ... 2 3 2 8 2 3 2 3 L a n g laag te E s ta te ... 1 Ö 2 0 0 0 2 0
M odd erfo n tein B ... 2 0 2 0 2 U 1 0
M odd erfo n tein D e e p . . . . 3 « 3 3 3 3 3 u
M odd erfo n tein E a s t . . . . 2 0 2 0 2 0 2 1)
N ew M odderfontein . . . . 7 (1
fi
9 6 6 e 0N ew S ta te A reas . . . . 1 0 1 6 2 0 2 0
N ourse M ines ... (1 « 0 (i 0 9 U 9
R ob in so n D eep (A Is.) . 1 6 1 e 1 6 1 6
R obinson D eep ( B ) ...
S p rin g s M in es... 3 9 3 6 4 Vi
0 3
4*
9 S u b N i g e l ... 2 U 2 u 3 0 3 0 V an R y n ... U Ü* 0 6* 0 e* U Ö*
V an R y n D e e p ... 3 6 3 0 3 0 2 6 W e st S p r in g s ... 1 0 1 0 1 0 U 9
W itw a te rs ra n d Gold . . . 0 Ö 1 0 1 0 0 Ö
* F ree cf ta x .
It was announced last month that in sinking operations at No. 2 north shaft of Randfontein Estates the Randfontein leader was struck at a depth of 4,328 ft., the ore having a value of 6'75 dwt. over a width of 42 in. and a dip of 15°.
At a meeting of shareholders of Lydenburg Estates, to be held this month, a resolution will be considered which proposes to capitalize £10,000 standing to the credit of various reserves. This will be done by paying in full for a corresponding amount of second debenture stock which will be distributed at the rate of £1 for every 100 shares held. If the resolution is carried meetings of debenture holders will be called to approve an agreement to sell the company’s assets to a new undertaking, in which they will receive identical holdings.
The accounts of Henderson’s Transvaal E states for the year ended March 31 last show a profit of £36,335, which, with the sum of £10,538 brought in, made available
£46,873. Dividends equalling 5% were paid for the year, leaving £18,345 to be carried forward.
Towards the middle of last month a fire occurred in the W est Rand Consolidated west shaft, all electric plant being burnt out and operations at the shaft suspended.
The accident was expected to interfere with the working of the mine for about six weeks, but it has been stated that the damage and loss of profits are covered by insurance.
The board of the Anglo American Corporation of South Africa decided last month to defer the paym ent of the half- yearly dividend on the cumulative preferred stock, considering it advisable to conserve its cash resources.
D ia m o n d s.—The continued depression is
having serious effects on the South African
diamond industry. The De Beers company
has closed down the Du Toits Pan mine,
but is continuing to work the Bulfontein
and Wesselton deposits in such a manner
as to give short-time employment to the
white staff. At the Premier mine work
has been reduced to one eight-hour shift
in alternate weeks, while at Jagersfontein
and on the properties of the Consolidated
Diamond Mines of South-W est Africa
operations are only being continued on
a very small scale. Meanwhile both the
De Beers and Premier companies have
6JULY, 1931 7 passed the preference dividends usually
declared at this time of the year.
C ape P r o v in c e .— During 1930 the Namaqua Copper Company suffered a loss of £31,033, the accounts showing a debit balance of £19,752. The output of blister and precipitate was estimated to contain 1,086 tons of copper, while the concentrates produced contained 697 tons of the metal.
Smelting operations were suspended in July, 1930, but mining on a small scale was continued for a time, the mine closing down last month.
S ou th ern R h od esia.—The output of gold from Southern Rhodesia during May was 43,731 oz., as compared with 43,776 oz.
for the previous month and 47,645 oz.
for May, 1930. Other outputs for May were : Silver, 5,730 oz. ; copper, 166 tons ; coal, 51,278 tons ; chrome ore, 6,326 tons ; asbestos, 3,410 tons ; mica, 36 tons.
Shareholders of Southern Rhodesia Base Metals Corporation have been informed that developments of the sulphide ore- bodies on the Alaska mine have not come up to expectations and this, together with the fall in copper prices, has made it necessary to close down the plant.
The accounts of Falcon Mines for the year ended September 30 last show an adverse balance of £629, which increases the deficiency brought in to £174,752.
Arrangements have been made for a clean
up of the mill site at the Falcon mine and tribute operations on the Athens mine are expected to start next month.
N orth ern R h od esia.—The report of Rhodesian Anglo American, Ltd., for the year ended March 31 last shows a profit of £83,554, which, added to the sum of
£323,603 brought in, makes an available total of £407,157. After making various allowances and transferring £158,362 to reserve, the balance of £124,008 was carried forward. As part of the arrangements made when the Rhokana fusion was carried out, the company transferred its engineering staff to the Rhokana Corporation and its geological staff to the British South Africa Company.
The second unit of the Roan Antelope mill was completed towards the end of last month, starting work on June 25.
Meanwhile the tonnage of ore treated by the first unit has already exceeded its designed capacity, the output for June being 2,225 tons of 53'57% concentrates from 39,175 tons of 3'81% ore.
In a circular to the shareholders of Luiri Gold Areas it is stated that on the recommendation of Mr. P. K. Horner, who has visited the mine, it has been decided to suspend treatment of Matala Hill ore for the present and only ore from the Dunrobin deposit will be dealt with during the next three months.
G old C oast.— Shareholders of Ashanti Goldfields have been informed of favourable developments during June. At No. 18 level cross-cut No. 8 S.W. shows a width of 19 ft. of reef assaying 38'4 dwt., while cross-cut No. 15 N .E. on No. 25 level has cut 5 ft. of reef assaying 2’8 dwt. and cross-cut No. 16 N.E. on the same level 10 ft. of reef assaying 50'8 dwt. On No. 26 level cross-cut No. 7 N.E. has now cut 45 ft. of reef assaying 23‘7 dwt.
During the year ended March 31 last Taquah and Abosso Mines added con
siderably to its ore reserves, which were increased to 284,290 tons, averaging 33s. Id.
per ton, while decreased working costs bring an additional 42,330 tons within the payable lim it. During the year 118,589 tons of ore was treated, yielding £191,023 of gold, the profit being £28,878. Dividends paid absorb
£18,201, a balance of £10,945 being carried forward.
A u stralia.—The mill at Mount Isa started work in May and during June 26,630 tons of ore was treated, producing 783 tons of lead bullion. The first shipment of 453 tons of lead was made on June 25 from Townsville.
The accounts of the Zinc Corporation for 1930 show a loss on mine account of
£41,874, against a profit of £137,156 in the previous year. Interest, dividends, etc.
were £113,787, against £124,830, the net profit being £68,381, as compared with
£246,050 in 1929. The total sum available for distribution was £179,429 and, after allowing for the payment of preference dividends and plant expenditure, there remained a balance of £26,585 to be carried forward. During the year under review 337,041 tons of ore was mined and 67,950 tons of lead concentrates and 53,105 tons of zinc concentrates produced, the recoveries being lead 94'5%, silver 90'6%, and zinc 80'3%. Working costs have fallen from 35s. Id. per ton in 1927 to 29s. 8d. in 1930.
The ore reserves at the end of the year
were estimated to be 2,880,000 tons in
the lead lode and 249,000 tons in the
zinc lode.
8 JULY, 1931 During the year ended March 31 last South Kalgurli Consolidated treated 97,576 tons of ore for £176,620 and made a profit of £32,955. Dividends equal to 2s. 6d.
a share absorbed £31,251, the balance carried forward being increased to £4,610.
The ore reserves at the end of the period under review were estimated to be 214,000 tons blocked out, of an average value of 8'5 dwt. per ton, and 112,000 tons of
“ probable ore,” of an average value of 6J dwt. per ton. Operations are now being conducted on the Croesus lease, approxi
m ately 2,600 tons of ore m onthly coming from this source.
A circular to shareholders of Wiluna Gold Corporation indicates that the treat
ment plant is now running more smoothly, the power plant operating in a much improved manner. During May 22,086 tons of ore was treated, yielding bullion valued at £23,486. It is considered that the mine should be treating a larger tonnage and average grade by next month.
A strike of firewood cutters in Western Australia which took place last month threatened to affect the gold mining companies, which were ready to import coal from Collie, if necessary. B y the action of the Arbitration Court, however, the men have been forced to resume work pending inquiries.
In d ia.—The fire at the Nundydroog mine continued to burn throughout June, seriously affecting operations. Cabled advice at July 6 intimated that conditions had much improved and justified the assumption that the fire was out. Steps are being taken to clear the mine of poisonous gases and to recommence stoping and development.
B u r m a .—At an extraordinary meeting of Mawchi Mines held last month a proposal to reduce the capital to £161,347 4s. by cancelling 16s. on each ordinary share issued, to divide the 126,684 unissued ordinary shares into 4s. shares, and to restore the capitalization to £300,000 by the creation of 693,264 new ordinary 4s.
shares was approved.
M alaya.—The reports for 1930 of the companies in the Tronoh group were issued this month. During the year Tronoh Mines recovered 1,447 tons of tin concentrates which realized £130,991, as compared with 1,863 tons worth £236,632 in 1929, the decrease being mainly due to restriction.
The profit was £36,881, which increased the sum available to £93,733. Dividends
equal to 12J% absorbed £37,500 and the balance of £56,233 was carried forward.
The output of Sungei Besi Mines was 499 tons, against 554 tons in 1929, the amount realized being £49,868, equal to £99 19s. 2d.
per ton, as compared with £132 9s. 6d.
for the preceding year. The profit was
£5,155, increasing the sum available to
£35,752, of which £3,700 was distributed as dividend, equal to 2J%, and the balance of £32,052 carried forward. Southern Tronoh’s output for the 10 m onths worked was 567 tons of tin ore, which realized
£51,031, the working profit being £14,338.
The debit balance brought in was thus wiped out and a dividend equal to 2|%
was paid, absorbing £5,000, a balance of
£174 being carried forward.
M exico.—In spite of the effects of the recent fire at the Don Carlos mine and the low price of silver, the board of the Santa Gertrudis Company has found it possible to declare a dividend of 9d. per share, making 11J% for the year. Camp Bird, Ltd., however, has been compelled to defer the payment of the usual half-yearly dividend on the preference shares, it being stated that the state of the m etal markets has severely curtailed the com pany’s revenue.
C orn w all.—The report of W heal K itty Tin for the year ended January 31, 1931, states that up to September 27 last, when the mine was closed down, 22,450 tons of ore was milled yielding 322 tons of tin concentrates. The accounts show a deficit of £5,389, which added to the debit balance brought in and the expenses of closing the mine increases the debit balance to £17,673.
The mine and plant have been left in a condition which will enable a speedy re-opening when conditions improve.
A n g lo -O rien ta l M in in g.—The accounts of the Anglo-Oriental Mining Corporation for the year ended February 28 last show a profit of £34,379. Dividends paid absorbed
£12,916, while £10,000 has been appropriated for taxation account and £15,000 for invest
ment reserve, the sum carried forward being £84,859, as compared w ith the
£82,043 brought in. At an extraordinary m eeting held last month a resolution converting the 200,000 unissued preference shares into 800,000 ordinary shares of 5s. each was approved.
B r itish -A m e r ic a n T in .—The accounts
of the British-American Tin Corporation
for 1930 show a profit of £1,285, which was
carried forward.
T H E T R E A T M E N T OF OXIDIZED ZINC TAILINGS
By B E R N A R D W . H O L M A N , A .R .S .M ., M.I.Chem.E.
In th is a r tic le th e a u th o r , w h o is A s s is ta n t P r o f e s s o r o f M in in g a t th e R o y a l S c h o o l o f M in e s , p a y s p a r tic u la r a tte n tio n to th e ‘‘ W a e l z ” v o la tiliz a tio n p ro c e s s as in u s e a t th e V ie ille M o n ta g n e M in e s , B e lg iu m
One of the most interesting visits of the m any arranged in connexion with the Inter
national Mining Congress held in Liege last summer was that to the Vieille Mpntagne company's lead-zinc mines in Malmedy.
The mines are connected by aerial rope
way to a central dressing plant where the daily output is dealt with. A particularly elaborate system of hand-picking is followed b y jigs and tables of standard types.
JThe special feature of the surface equip
ment is the new plant for the treatment of
way. Moreover, owing to its extreme fineness and its sticky condition, it is not possible to wash it or to treat it with percolating solutions, and to mix it with coke or other solid fuel is extremely difficult.
It is a material well calculated to defy alike the art of the ore-dresser and the science of the metallurgist, yet a successful metallurgical process has been evolved, a process about which the management appeared to be not only satisfied, but enthusiastic.
Fi g. 1 .— Ge n e r a l Vi e w o f Wa e l z Pl a n ta t Vi e i l l e Mo n t a g n e.
the accumulated slimes produced many years ago when a more oxidized ore was mined. These accumulated slimes, called locally “ calamine slim e,” resemble in appearance a thick yellow clay. The material is thoroughly oxidized, extremely fine, and appears uniform in composition ; generally no separate particles of valuable mineral can be detected with a hand lens.
Its average composition as delivered for treatment is : —Zinc, 11-0%; lead, 0‘7% ; iron, 5-5% ; sulphur, 0'4% ; silica, 46'0% ; alumina, 15'0% ; and lime, 1‘0%. In situ it contains about 30% of water both in summer and w in ter; it is, therefore, impossible to store the material in the usual
This process, which has been named the
“ Waelz ” process from the German word
“ waelzen,” which means a trundling motion, not a waltz, is a volatilization process and was originally developed for the treatment of similar material in Upper Silesia during the years 1923-25. Since then plant of an annual capacity of over one and a quarter million tons has been installed in various parts of the world under the direction of Messrs. Krupp’s technical staff at the Magdeberg Works in Germany.
The Waelz process is carried out in a
long rotary kiln and its success depends
essentially on the reduction of the zinc
oxide in the charge by carbon, in such
10 THE MINING MAGAZINE a way that the zinc vapour and carbon
monoxide evolved are burnt im mediately above the charge, in order to maintain its temperature. The heat expended during the reduction of the zinc oxide to zinc is thus regenerated by the burning of the zinc to zinc oxide, and of the carbon monoxide produced to carbon dioxide. The reaction in the first case proceeds according to the two simple equations :—-
ZnO + C = Zn -j- CO — 57,000 calories Z n -t-C O + O , = ZnO + C 0 2 + 57,000 calories
The main objective in cem ent work is the calcination and sintering of the charge ; this action is accomplished by the action of the flame. In the W aelz process at Vieille Montagne, calcination is unnecessary and sintering must actually be avoided, the main objective is the volatilization of the zinc in the charge ; this action is accom
plished by pre-mixing fuel with the charge.
Actually an oil burner is used also, but this is employed to assist in the pre-heating of the air entering the furnace, and to give
Fi g. 2 . — Ki l n- Fe e d i n g Eq u i p m e n ta t Vi e i l l e Mo n t a g n e.
There are, of course, many minor reactions involved in practice, but they are not essential to the principle of the process.
A ctually some additional fuel must be added to make good the loss of heat by radiation and the loss of heat in the flue gases ; much of the latter can be recovered in various ways.
In appearance the kilns used for the Waelz process are extrem ely like those used for the manufacture of cement. They are long inclined rotary kilns fed at the upper end, and discharged at the lower. The heated gases in each case pass through the kiln in the opposite direction to the charge.
N evertheless the mode of operation is very different.
accurate control of the temperature of the kiln, not to effect the reduction and volatilization.
The temperature employed for zinc
volatilization at Vieille Montagne is about
1,200° C., a good deal higher than that
required for the calcination of cement,
which is about 1,000° C., but the actual
amount of heat required in the Waelz
kiln is much less. This is because of the
extra heat required to sinter the cement
and because the zinc vapour and the carbon
monoxide produced in the kiln are burnt
in the kiln itself, directly above the reducing
charge. The heat given to the walls of the
kiln by this combustion is transmitted back,
not only by radiation, but also by conduc
JULY, 1931 11 tion, as the heated surface is passed beneath
the charge by the rotation of the kiln.
This is one of the most remarkable advantages of the process.
The passage of air into the kiln is readily controllable, and the combustible materials, the zinc vapour and the carbon monoxide, rise freely from the surface of the charge, so that no large excess of air is needed as with, for example, the combustion of coal in a boiler plant. The heat carried away in the flue gases is, therefore, a minimum and of this minimum not all is lost, some is used for pre-heating the air entering the kiln and some for drying the charge before it enters. The flue gases under normal working conditions contain up to 2% of carbon monoxide and up to 28% of carbon dioxide, the free oxygen being under 1%.
The efficiency of operation depends on the free and uniform evolution of zinc vapour and carbon monoxide in order to blanket the surface of the charge from the oxidizing atmosphere of the kiln. This is obtained by close chemical control of the composition of the charge so as to avoid the formation of fusible compounds at the temperatures employed and by control of the amount and continuity of combustion within the kiln.
Fusible constituents cause a pasty condi
tion of the charge which prevents evolution of the zinc vapour and causes the formation of concretions, which are liable to adhere to the walls of the kiln and make the passage of the charge down the kiln uneven. In
sufficient amount and continuity of combustion reduce the capacity of the kiln and may also cause the oxidizing atmos
phere of the kiln to come into contact with the charge. W ith proper control, the pre
heating of the charge in the kiln may only require 20% of the length of the kiln, reduction taking place throughout the remainder. In cement work, 60% of the length of the kiln is occupied in merely pre-heating the charge. The greater the quantity charged into a kiln of given diameter, the greater the length of the kiln.
Increased capacity can be obtained from a kiln of given diameter and length by increasing the speed of rotation, but the fuel and air used per unit of zinc produced are then increased. There is, therefore, an optimum diameter and length for a given output.
At the works at Vieille Montagne, one kiln 40 metres long and 2'25 metres in
diameter is used for a daily through-put of 100 to 120 tons of “ calamine slime.”
Elsewhere kilns with a through-put of up to 250 tons per day have been installed.
(See Fig. 7.)
The plant at Vieille Montagne is of particular interest because of the difficulty of handling and mixing the moist, adhesive, extremely fine material already described.
Coke breeze is used as the reducing reagent because it is readily obtained locally. With
Fi g. 3 . — Mi x i n g a n d Cr u s h i n g Pl a n t a t Vi e i l l e Mo n t a g n e.
regard to the mixing, an insufficient distribu
tion of the coke will cause the charge to form into lumps in the kiln and give an unsatisfactory extraction of the zinc. This tendency to form into lumps could be reduced by the addition of limestone to the charge; but the addition of limestone would reduce the capacity of the kiln and also use up fuel unproductively and, in this case, is not necessary to prevent actual fluxing of the charge. The low price of coke here renders it more economical to refrain from adding limestone, but to mix a certain surplus of coke with the charge. The coke in the charge thus reduces the zinc com
pounds in the charge, assists the charge to
crumble when it is fed into the kiln, and
provides, by combustion, the extra heat
necessary to maintain the temperature of
12 THE MINING MAGAZINE the kiln. The total quantity of coke added
varies from 33% to 36% of the charge.
Special mixers have been installed (Fig. 3), and the product from these is fed into an edge runner. In this machine a further grinding of the coke takes place, as well as a still more thorough mixing of the charge. The edge runner is so designed that the finished product is pressed through the runner bed in the shape of small ovals. It was found that even these small ovals would sometimes stick together on the conveyor belt, agglomerate in thé feed channel,
of fusion, make for even working conditions, and result in but little attack of the kiln lining. The process is almost automatic, charging and discharging are, of course, mechanical, and the recovery obtained is well over 90% owing to the infusible nature of the material. In plants treating a fusible material the recovery m ay be no more than 80%.
The zinc oxide produced is recovered by a Cottrell plant ; the flue dust, equal to about 3% by weight of the charge and containing about 35% of zinc, is returned
Fi g. 4 . — Wa e l z Ki l n a x Vi e i l l e Mo n t a g n e s e e n f r o m Di s c h a r g e En d.
and subsequently form large lumps in the kiln due to the burning together of the lumps, not to fluxing of the charge. This has been successfully overcome by arranging for the ovals to discharge from the edge runner on to two travelling steel bands (Fig. 2) carrying a thin layer of crude zinc oxide.
This crude oxide, which is returned to the kiln, suffices to prevent the adhesion of the ovals in the feed channel.
The special difficulties due to the physical nature of the material at Vieille Montagne appear now to have been perfectly solved.
The chemical nature of the material gives no special difficulties. On the contrary its high silica content, low iron content, and uniform composition give an absence
to the kiln. W ith the electrical precipitation, no fumes were noticeable and vegetation in the neighbourhood did not appear to have suffered much from the new plant. Also the brightly tiled mine offices were as clean and smart as ever.
The passage of the zinc oxide and the flue gases through the furnace is controlled by an exhaust fan behind the dust collector, hence the pressure in the plant circuit is slightly below that of the atmosphere.
This prevents acrid fumes from issuing from every crack and joint in the brickwork as they once did in some old Swansea retort houses.
The material takes about two hours to
pass through the kiln, which compares
JULY, 1931 13
Fi g. 5 . — Ki l n Di s c h a r g e, Vi e i l l e Mo n t a g n e.
favourably with the claim of 2J to 3 | hours temperature in the reaction zone is about made for the Coley process, but the 1,200° C. in the Waelz process as compared
Fi g. 6 . — Sl a g Tr a n s p o r t t o Du m p a t Vi e i l l e Mo n t a g n e.
