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Vol. X L IX . No. 2. L O N D O N , A U G U S T , 1933. P R I C E O N E S H I L L I N G
C O N T E N T S
Ed it o r ia l
N o te s .. .
Lectures on T ro p ic al H ygiene ; In s titu te of M etals . Silver Jubilee M eeting ; D evelopm ent of N orthern A u stralia ; The M etallurgist again Assists the Archaeologist ; N ativ e W elfare on the R and Com pared w ith th a t on the Gold C o a s t; T he G overn
m e n t’s Scheme to Aid th e Oil-from-Coal In dustry.
S ilic o sis...
T he im p o rtan t results of recen t research on silicotic lungs are revealed.
The Economic C o n feren ce...
D ecisions reached a t th e conference affecting silver and tin producers are discussed.
The Petroleum Conference . ...
A brief survey of th e conference held in London last m o n th .
Re v i e w o f Mi n i n g...
6(1
67
68
69
70 Ar t ic l e s
Sm elting Practice a t th e Roan A n te lo p e ...A . Russell M erz 73
Following on th e article on th e R oan c o n c en trato r th a t appeared in th e J u ly issue of th e Ma g a z i n e the a u th o r com pletes th e account of metallurgical p ractice a t this N o rth ern Rhodesian copper p roducer.
Alluvial G old... H. L . Holloway 82
T he au th o r discusses th e deposition of alluvial gold and shows how an exam ination of practical considerations m ay be of help in assessing th e p o ten tial value of a placer deposit.
Prim itive Mining in th e Philippines Laurence L. Wilson 85
A description of th e gold and copper m ining m ethods adopted b y th e Ig o ro t in Luzon, Philippine Islands, an d an acco u n t of som e of th e religious beliefs b y w hich th e ir w ork is influenced.
E a rth M o v e m e n ts.. . .C. P. Stromeyer 91
[Concluded from the J u ly issue, p . 30.) Bo o k Re v i e w s
Mead's “ H ydraulic Machinery ”
Humphrey M . Morgans 95 Emmons, Thiel, Stauffer, and Allison's
“ Geology " ...T. H . Whitehead 95 Geological Survey of Uganda Memoir
No. I l l — “ The Volcanic Area of Bufumbira, South-W est Uganda ”
Dr. A . W. Groves 96 Ne w s Le t t e r s
B r is b a n e ... 97
P A G E 98 M ount Isa ; In d u stria l C ourt Decisions ; M ount Coolon ; M ount W andoo ; Oil Shales ; Gold in P apua. V ancouver... Coast ; Bridge River ; Lillooet ; Cariboo ; 'Clinton ; Nelson ; Boundary ; East Kootenay. T o ro n to... 100
Gold Production ; Sudbury ; Porcupine ; Kirkland Lake; North-Western Ontario; North-Western Quebec ; Manitoba ; Great Bear Lake. J o h a n n e sb u rg... 103
West Witwatersrand Areas ; Western Reefs Exploration ; Middle Witwatersrand (Western Areas) Company; Klerksdorp; Proposed New Company; Witpoort No. 14 : Welgedacht; Northern Transvaal Copper ; Gold Law Amendment Bill; Government Geologist. Pe r s o n a l... 105
Tr a d e Pa r a g r a p h s... 105
Ransom es and Rapier E x c a v a to r s... 106
Climax D rifters and Prospecting Drills . . . 106
Me t a l Ma r k e t s... 107
St a t is t ic s o f Pr o d u c t io n ... 109
Pr ic e s o f Ch e m i c a l s... I l l Sh a r e Qu o t a t i o n s... 112
Mi n i n g Dig e s t The World Petroleum Congress... 113
Mine Timber Preservation. .B . M . Winegar 115 Diam ond Drilling at Mount Isa R. P itm an Hooper 116 Minerals in Silicotic Lungs D r. W. R. Jones 121 Itabira Iron O r e s ...B. H . Sanders 123 The Scottish Aluminium Industry George Boex 124 {Continued from the J u ly issue, p. 51.) Void Content of Close-Packed Powders R. N . Traxler, L. A . H. Baum , and C. U. P ittm an 125 Sh o r t No t i c e s... 125
Re c e n t Pa t e n t s Pu b l i s h e d... 126
Ne w Bo o k s, Pa m p h l e t s, e t c... 126
Co m p a n y Re p o r t s... 127
Angola Diamond : Aramayo Mines ; Juga Valley Tin ; Kamra Tin ; Kent (F.M.S.) Tin Dredging ; Kramat Pulai; Malaysiam Tin ; North Kalgurli (1912) ; Poderosa Mining; Rhodesia Broken Hill; Tanganyika Concessions; Tin Properties ; Zambesia Exploring. Di v i d e n d s De c l a r e d... 128
Ne w Co m p a n i e s Re g i s t e r e d... 128
2—2 65
E D IT O R IA L
A
COURSE of seven lectures on tropical hygiene, arranged b y th e B ritish Red Cross Society, will commence a t th e London b ran ch office, 9, Chesham Street, Belgrave Square, S.W. 1, on Septem ber 22. The fee for th e course for non-m em bers is 7s. 6d.S
IL V E R jubilee celebrations will m ark this y e a r’s m eeting of th e In stitu te of M etals, which is to take place a t B irm ingham from Septem ber 18 to Septem ber 22.
The au tu m n lecture, which is to be given b y Mr. W. R. B arclay, will be devoted to a review of 25 y e ars’ progress in m etallurgical plant.
P
LANS were p u t forw ard last m onth by the A ustralian G overnm ent th a t have in view th e developm ent of N orthern A ustralia as a “ w hite m a n ’s co u n try .” I t is proposed to g ra n t chartered rig h ts to two approved com panies prepared to u ndertake th e opening up of these v ast territories, m uch of w hich is com paratively unexplored and m ay well be rich in m ineral w ealth. The Com m onwealth G overnm ent will u ndertake to obtain the co-operation of th e B ritish and W estern A ustralian G overnm ents in order to give effect to its policy.R
E A D E R S of th e M a g a z i n e are fam iliar w ith th e contributions m ade by m etallurgists to th e elucidation of the problem s confronting th e archaeologist and h istorian, as witness th e valuable w ork of Sir H arold C arpenter and his collaborators.A nother link in th e chain has been forged as th e resu lt of investigations b y Dr. C. H . Desch, of the N ational Physical L aboratory, who has been able to show th a t th e fragm ent of a dagger recovered from th e excavations a t Tell Asm ar, near B aghdad, is of nickel- free iron, and therefore n o t of m eteoric origin. T his significant discovery places m an-m ade iron in an earlier age th a n has h ith e rto been claim ed for it.
A
N article in The Tim es last m o n th by Mr. W. M. Macmillan, of the U niversity of th e W itw atersrand, was loud in its praise of th e efficient organization of gold- m ining on th e R and and of copper m iningin N orthern R hodesia an d the Belgian Congo, b u t was inclined to be critical of the w ork being done for th e n ativ es in other A frican goldfields, p a rtic u la rly those on the Gold Coast. This view was com bated by Mrs. Malcolm M aclaren, who, speaking from personal experience of th e R an d an d the Gold Coast, was em p h atically of th e opinion th a t th e n ativ es on th e la tte r are th e stronger, h ealthier, an d h ap p ier com m unity an d that th e tre a tm e n t of th e n ativ es on Gold Coast lines is preferable to th a t n ecessitated on the R and b y its rap id grow th and intensive developm ent.
W
H IL E it is n o t difficult to be critical of th e G overnm ent’s schem e for the protection of th e oil-from -coal in d u stry on economic grounds, th e re will be m a n y who see in th is a ju s t rew ard for m a n y years’p atien t research and m uch cap ita l expendi
tu re b y th e organization larg ely responsible for the progress m ade in th is cou n try — Im perial Chemical In d u stries. Unem ploy
m en t in th e coal and iron an d steel industries will also be relieved, while th e m oral effect of this revival of a c tiv ity in a particularly depressed area is of unquestioned value.
G overnm ent assistance is to be afforded in the form of a p referen tial ra te of 4d. per gallon over th e im p o rted p ro d u c t for a period of nine years from A pril, 1935, a t an estim ated cost of £1,000,000 an n u ally b y the loss of C ustom s’ receipts. T he projected p lan t for th e conversion of coal in to oil by hydrogenation, w ork on w hich is sta te d to have been begun already, will be capable of tre a tin g 500 tons of coal p er day, a further 500 tons a t least being consum ed in the process, w ith an estim a te d an n u al yield of 100,000 tons of first-grade p etro l— figures derived from th e results of a pilot p lan t which has been w orking for some tim e p a st, treating 10 to 15 tons daily. I t is w o rth y of note th at a p articip atin g in terest in th e Im perial Chemical In d u stries subsidiary controlling these developm ents is held b y tw o of the largest oil com panies. T here are indications th a t o th er oil-from-coal industries are likely to come into being— for exam ple, in South W ales— as a consequence of th e prom ised p rotection and low -tem perature carboniza
tion activities are also expected to increase, since th e p lan t referred to will be capable of dealing w ith products of th a t process as well as raw coal.
AUGUST, 1933 67
ttve Bela : cti&cal' o{ t f 'res In o4
u v o se on ( is combated | c Band and •
% of the opim are the strong
^unity andj lVes on Gold C
necessitated on
^ and intei;
■ - cno
®eflts scheme lor ere "ill be manp lVard (or many ^ nuch capital expet ion largely tespoE
•e in this countn iustnes. Unempi m and steel iife chile the moral ti city in a panicd
unquestioned n
! is to be afforde:
ntial rate of id orted product I om April, 1935, £ 0,000 annually by ipts. The prop in of coal into oi n which is stats ly, will he cap#
ial per day, a k lated annual yield
S ilic o sis
M iner’s phthisis, or “ silicosis,” has always been th e bane of the underground worker and it has long been held to be one of the inevitable h ealth risks to be faced b y th e
“ h a rd -ro c k ” m an all over th e world, its onslaught having become th e m ore m arked w ith the advent of m achine drilling, p a r
ticularly w ith com pressed-air m achines. In the General R ep o rt of th e M iners’ Phthisis Prevention Com m ittee for th e Union of South Africa, issued in 1916, th e m alady was defined as prim arily a fibrosis of the lung, the essential factor producing th e condition being th e “ m ore or less continuous inhala
tion, over long periods, of fine rock d u st ” ; a t la te r stages of the disease tuberculosis sets in and d eath results from th e effects of a “ tub ercu lar infection in a fibroid lung.”
A t the In tern atio n al Congress on Silicosis, held in Johannesburg in August, 1930, the definition finally accepted was th a t silicosis is “ a pathological condition of the lungs due to the inhalation of silicon dioxide,”
resulting from silica reaching the lungs in a
“ chemically uncom bined s ta te .” I t will be seen, therefore, th a t the researches con
tinuously conducted during th e intervening period did n o t alter th e general conception th a t silica d u st is the irrita n t cause of the disease. I t has to be rem em bered, too, th a t it is n o t only in the p u rsu it of m etal-m ining th a t silicosis occurs ; the coai-miner also is liable to contract the disease, while p o tte ry men, stonemasons, clay workers, and labourers in asbestos works are all subject to infection. W hat promises to be the m ost im p o rtan t contribution to our knowledge of th is dread disease is revealed in a paper published this m onth in th e Journal of Hygiene} which embodies research carried out b y Dr. W. R. Jones, of th e Geology D epartm ent of the Im perial College, whose conclusions seem to be so far-reaching in their effects, p articularly in relation to governm ent regulations and having in view the com pensation arising out of silicosis cases, as to deserve detailed consideration here, in addition to the sum m ary published elsewhere in th is issue.
D uring th e p ast two years D r. Jones has had occasion to visit certain collieries in the anthracite d istrict of S outh W ales in order to collect and exam ine specimens of rock
1 Silicotic L u n g s: T he Minerals they Contain.
W. R. Jones, Journal of Hygiene, V ol. X X X I I I , N o. 3, A ugust 4, 1933.
from working places w here m en form erly em ployed h ad contracted silicosis. Some of th e specimens could be regarded as coming w ithin the legal definition of silica rock (usually held to contain over 50% free silica), b u t others could not. These la tte r n a tu ra lly aroused the a u th o r’s interest, for it was evident th a t rocks o th er th an those em braced in th e Silicosis Scheme were responsible for th e prevalence of dangerous d u st and it was obviously a m a tte r for fu rth er inquiry. Pursuing his investigation Dr. Jones w ent on to th e exam ination of silicotic lungs and th e actual m inerals th ey contain. A precise technique was developed, th e lungs being first digested in strong nitric acid, the slime filtered, dried, rem oved from th e filter paper, and calcined. L ight m aterials were rem oved b y separation in a m ixture of brom oform and benzine having a specific g rav ity of 2 and the heavier m inerals were washed, dried, m ounted in Canada balsam, and exam ined under a petrological micro
scope. U nder high power it was speedily evident th a t the greater p a rt of these m ineral residues consisted of m inute fibres of sericite, or “ secondary w hite m ica.”
Chemical w ork carried on a t the same time fully supported this conclusion, the results of th e combined investigation showing th a t silica in an uncom bined state is present in a silicotic lung in am ounts subordinate to sericite, and the au th o r is now convinced th a t th e la tte r m ineral m ust be the chief cause of th e disease. The fact th a t the R and
“ b an k et ” —which is full of sericite—is a well-known dangerous rock from th e silicosis point of view, while th e q u artz m ined in the K olar goldfield of Mysore—practically free of sericite—is not known to have caused a single case of th e disease supports the author in his conclusion, and other similar com
parative cases are quoted. A t Broken Hill, for example, rocks containing a relatively low percentage of quartz, b u t which do contain fibrous silicates such as sericite and sillimanite, produce a dust th a t has caused a large num ber of silicosis cases. A nother point of some significance is th a t free silica present in th e residues exam ined by the au th o r occurred as relatively coarse granular particles such as m ight lodge in the bronchi or bronchioles, whereas th e m inute fibres of sericite were fine enough to penetrate m uch farth er into th e lung itself. The a u th o r’s final conclusion is, therefore, th a t it is m ainly the presence in the exploited rocks of fibrous minerals, which during drilling become
68 T H E M IN IN G M AGAZINE freed in to th e atm osphere as individual
fibres, th a t enables sufficient m aterial, in course of tim e, to en ter th e lung and cause
“ silicosis.”
R egulations affecting the m iner working under conditions th a t m ight induce “ sili
cosis ’ ’ have all been based on the idea th a t it was free silica d u st th a t caused th e trouble, so th a t it will be readily seen th a t Dr. Jo n e s’s w ork m ay dem and their drastic revision.
I t is certain, however, th a t fu rth er investiga
tion is u rg en tly necessary and m ining engineers should be in a position to help by th e collection of precise d a ta relating to m ines where q u artz has been w orked for long periods w ithout giving rise to any a u th e n ticated cases of silicosis or of mines w here “ silicosis ” cases have occurred although no “ silica rocks ” are mined. In conclusion, it is interesting to note th a t earlier w ork has been done on th e doubly- refracting particles found in microscope sections of silicotic lungs. The presence of these m inerals has been noted before, b u t it is not u ntil now th a t their tru e significance has been realized.
The E co n o m ic C on feren ce
Tow ards th e end of last m onth th e W orld Econom ic Conference “ w ent into recess,”
th e result of its deliberations being held—
on all sides—to be disappointing. In announcing th e opening of th e Conference the Ma g a z in e sta te d th a t there was a general feeling th a t if its w ork was to be of perm anent use .and of im m ediate benefit it was probably necessary th a t existing trad e barriers should be considerably modified an d th a t th e principle of n atio n al economic self-sufficiency should, in p a rt a t a n y rate, be throw n overboard. The com
p arativ e failure of th e Conference can only be due to the refusal of certain countries to e n tertain proposals th a t in a n y w ay lim ited th e ir freedom of individual action, a m a tte r well em phasized b y President R oosevelt’s a ttitu d e tow ards currency stabilization. The P resident ab ru p tly rejected all proposals w hich would prevent th e m anipulation of th e dollar to A m erica’s advan tag e and since it seems evident th a t some sort of currency stabilization is an absolutely essential prelude to a free in te r
change of goods th e proceedings of th e Conference gradually faded aw ay to an ignom inious close, since “ exchange d u m p ing ” was not one of the evils to be recognized
b y th e A m erican delegation. Meanwhile, although pious hopes are e n tertain ed for the reassem bly of th e Conference a t some fu tu re d a te — and th e new Geological M useum at South K ensington is p ro b ab ly to be k ep t available for this purpose—it seems necessary here to tak e note of tw o results of th e recent m eeting w hich are of im portance to m em bers of th e profession— th e silver agreem ent and th e effort th a t is being m ade b y th e I n te r natio n al Tin Com m ittee to secure world-wide adherence to its plans.
Schemes for th e reh ab ilitatio n of silver have been freq u en tly to th e fore d u rin g the past few years, b u t th e possibility of a general rem onetization of th e m eta l was rejected by bo th th e O ttaw a an d th e W orld conferences a t th e outset. To th e silver-producing and silver-using countries, however, th e m a tte r rem ained of suprem e im portance and it is satisfacto ry th a t th e delegates from those countries were able to arrive a t a definite agreem ent on policy while th e Conference was sitting. T he agreem ent, w hich is to run for four years, provides th a t In d ia shall not, except for w ar-debt p aym ents, dispose of m ore th a n 140,000,000 oz. of silver during th a t period and th a t the producing countries shall n o t during th e agreem ent sell any silver, b u t shall w ith d raw from th e m arket 35.000.000 oz. in each year. Silver from dem onetization in China is n o t to be sold and Spain agrees n o t to dispose of m ore than 5.000.000 oz. a year. I t is evident, therefore, th a t during th e period of th e agreem ent the position of silver is likely to be im proved, b u t th e colossal stocks th a t will be b u ilt up b y the producing countries will continue to m enace th e fu tu re position of th e m eta l and it is to be hoped th a t W orld conditions will so im prove during th e tim e of th e agreem ent th a t its extension will eith er be easy to arrange or become unnecessary.
One of th e m ost satisfacto ry features of the m etal m ark ets during th e p a st few m onths has been the stead y rise in th e price of tin to over £200 per ton and th is a t a tim e when consum ption could h a rd ly be regarded as good. This pleasing aspect of th e effect of restriction m easures has em boldened the In te rn a tio n a l Tin C om m ittee to p u t forw ard a strong recom m endation th a t all tin- producing countries not y et p articip atin g in the in tern atio n al restriction agreem ent should join in the scheme of control w ith o u t delay, a recom m endation th a t was endorsed b y the Sub-Com m ittee on Tin a t th e W orld Economic Conference. The Sub-C om m ittee
AUGUST, 1933 69 atta ch ed g reat im portance to early action
being taken in the m a tte r, as th e negotia
tions w hich are in hand for th e new three y ears’ control agreem ent cannot be very well concluded u n til th e intentions of the various governm ents in th is m a tte r have been m ade clear. The countries concerned are A ustralia, Belgium, China, France, India, Jap an , Mexico, P ortugal, th e U nited K ingdom , and the Union of South Africa, all of whom have been urged to nom inate a representative who can negotiate w ith th e In tern atio n al Tin Com m ittee w ith th e object of determ ining a qu o ta agreem ent. How far th is effort to secure all-em bracing restriction for tin will be successful rem ains to be seen.
The P e tr o le u m C ongress
The W orld Petroleum Congress— the first held since the W ar—took place in London la st m onth. The countries represented by official delegates num bered 33, well over a thousand m em bers taking p a rt in the proceedings. On J u ly 19 m em bers were welcomed by th e president, Mr. T. Dew- hurst, a t the Science Museum, South Kensing
ton, the work of the Congress commencing on the following day. Sessions were held daily in th e R oyal School of Mines, while two special lectures were given a t the Royal In stitu tio n , by Mr. J. B. A. Kessler on
“ R ationalization of the Oil In d u stry ” on Ju ly 20 and by Sir Jo h n Cadm an on “ Science in the Petroleum I n d u s tr y ” on Ju ly 21.
Following Mr. Kessler’s lecture a reception was held by th e G overnm ent a t L ancaster House, delegates and m em bers being received by the President of the B oard of Trade.
In addition to other social functions visits were paid to various industrial works during th e period th e Congress was sitting.
The w ork of the Congress was divided into three m ain sections : Geological, production, and refining, chemical, and testing. The first section considered th e geological significance of the regional distribution of oilfields and then w ent on to discuss the geological aspects of oilfield developm ent, in this connexion paying special a tten tio n to general develop
m ent schemes, u n it developm ent, the evidence provided b y coring and flush sampling, electrical logging, and m ethods of increasing oil recovery. Modern develop
m ents in geological exploration were also considered, th e value of geophysical explora
tion, aerial reconnaissance, and current field m ethods being discussed. Sum m aries of several of these papers will be found else
where in this issue. The production section first m ade a survey of m odern drilling m ethods, going on to discuss the tran sp o rt and storage of oil, while fu rth er sessions were devoted to actual production m ethods and to th e m easurem ent of oil in bulk. A very full program m e of papers was arranged for the last section, th a t devoted to refining, chemical, and testing. H ydrogenation, the subject first discussed, n a tu rally a ttra c te d a great deal of a tten tio n in view of th e Govern
m e n t’s recently-declared policy. O ther work before th is section included discussions on bitum inous m aterials and emulsions, the determ ination of gum in gasoline, viscosity and its expression, fuels for high-speed com pression-ignition engines, and problems connected w ith kerosine, lubricating oils, the refining of cracked gasolines, oil-coal fuels, knock-rating, and altern ativ e fuels, a final session being devoted to a consideration of petroleum as a chem ical raw m aterial.
To conclude the business of th e Congress a joint m eeting of all sessions was held to discuss intern atio n al co-operation in stan dardization. Here the lack of an accepted intern atio n al nom enclature for petroleum products was em phasized and th e need for co-operation betw een all th e existing standardization bodies urged. I t was con
sidered th a t co-ordination of opinions among these bodies was an essential first step tow ards th e achievem ent of an international term inology and com plete agreem ent on testing m ethods, while th e in stitu tio n of regular channels through which inform ation could be readily exchanged by the different countries was regarded as urgent. A t this m eeting it was proposed and adopted th a t, in order to avoid any overlapping or duplica
tion of work, national petroleum nom en
clature and m ethods of testing should be arranged through the m edium of an in te r
n ational body—th a t is, through Committee 28 of the In tern atio n al Standards Associa
tion. T he Congress closed on a note of optim ism , it being generally felt th a t its purpose had been fulfilled b}^ bringing together specialists in all branches of the in d u stry and b y affording the o p p o rtu n ity for frank discussion of th e m an y im p o rtan t problem s th a t had arisen through th e rapid developm ent of petroleum technology, p a r
ticularly in recent years. I t was held th a t if th e constructive w ork of th e 1933 Congress was to be carried on arrangem ents should be m ade for m eeting m ore often and a proposal favouring triennial congresses was unani
m ously approved.
R E V IE W O F M IN IN G
In tro d u ctio n .—The failure of the W orld Economic Conference has a p p a re n tly h ad no effect on business generally and conditions m ay be described as firm, m etal prices showing little change. The position w ith regard to zinc has been clarified to some ex te n t by th e decision to continue the Cartel for a year, while the silver agreem ent has so far m ade no im pression on prices. The figures relatin g to unem ploym ent in th is co u n try issued th is m o n th show th a t the p osition continues to im prove.
Transvaal.-—The o u tp u t of gold on the R an d for J u ly was 872,695 oz. and in outside d istricts 50,976 oz., m aking a to ta l of 923,671 oz., as com pared w ith 918,633 oz. in June. The num ber of n atives em ployed in th e gold m ines a t th e end of J u ly totalled 230,306, as com pared w ith 229,751 a t the end of June.
R eports from th e U nion last m onth indicated th a t South Africa was seeking drastic revision of th e M ozambique Con
vention relating to th e supply of n ativ e labour from Portuguese te rrito ry . I t has.
been sta te d th a t, failing agreem ent on th e suggested revision, th e Convention will cease on six m o n th s’ notice.
An interesting feature of the rep o rts of the R and companies covering th e three m onths to Ju n e 30 last is th e decision of some com panies to issue calculations of ore reserves based on a price of ¿6 per oz. for gold. As an exam ple calculations for the Robinson Deep m ight be quoted. F o r this m ine th e reserves a t Ju n e 30 last, w ith gold a t 84s. 9d. per oz., were estim ated to be 3.128.000 tons averaging 5’8 dw t. over a stoping w idth of 58 in., w hereas w ith gold a t 120s. per oz. th ere were estim ated to be 4.089.000 tons averaging 5-4 dw t. over th e same w idth. I t is probable th a t sim ilar calculations will soon be m ade available for all th e R and mines.
Shareholders of M odderfontein E ast have been inform ed th a t the G overnm ent has accepted th e com pany’s application for the lease of th e under-m ining rights of an area equal to approxim ately 625 claim s adjoining its eastern b oundary on the F arm s Klip- fontein No. 11 and W elgedacht No. 2.
In th e rep o rt covering operations for the three m onths ended Ju n e 30 last shareholders
of Geldenhuis Deep were inform ed th a t the repairs to th e dam aged No. 2 S haft caused by th e pressure bu rst m entioned in th e last rep o rt have been ham pered by fu rth er m ovem ents in th e vicinity of th e shaft.
W ork is sta te d to be proceeding, however, and th e 16th and 17th level statio n s have now been reclaim ed.
F u rth e r results from the boring on W est W itw atersran d A reas were announced last m o n th , Bore-hole No. 11 V enterspost in ter
secting a narrow b an d of reef a t 3,588 ft.
an d a w ider reef channel a t 3,743 ft. The second intersection is ap p ro x im ately a t the expected horizon of th e W est reef, but definite correlation will n o t be possible until th e underlying basal shale has been p en etrated.
I t was announced last m o n th th a t the Main Reef h ad been in tersected in No. 36 level cross-cut from the S outh sh aft of W est R and Consolidated Mines. A t th is point the reef was dipping a t 26° a n d averaged 11 dwt.
in value over a w idth of 42 in.
A circular to shareholders of E a st Rand Consolidated last m o n th sta te d th a t the com pany h ad acquired th e rig h t over the F arm P oortje No. 123, adjoining Tulipvale, while la te r th e acquisition of th e Farm S paarw ater from Lace P ro p rie ta ry Mines was announced. T he price p aid for th e last- nam ed p ro p e rty is sta te d to be ¿250,000 in 5s. shares of E a st R an d C onsolidated and an e x trao rd in ary m eeting will be held shortly to sanction th e increase of c a p ita l necessary to com plete th e purchase. T he com pany has com m enced boring operations on Marais- d rift, n ear th e b o u n d ary of th e Sub Nigel properties.
Shareholders of G lynn’s L ydenburg have been inform ed th a t th e cash position will enable th e com pany to p a y its accrued liab ility to th e G overnm ent u n d er th e power agreem ent, am ounting to ¿13,600, and excess profits d u ty , am ounting to ¿6,028, b u t th a t there will be no surplus for th e p ay m en t of a dividend.
The rep o rt of th e R ooiberg Minerals D evelopm ent Co. for the three m o n th s ended Ju n e 30 last sta te s th a t the Old School W orkings have been re-opened. T he alluvial p la n t is said to be w orking satisfactorily.
The accounts of th e Jo h an n esb u rg Con- 70
AUGUST, 1933 71 solidated In v estm en t Co. for 1932 show a
profit of £359,675, m aking, w ith the sum brought in, an available to ta l of £526,360.
A dividend equal to Is. 6d. per share will absorb £220,706, while £150,000 has been placed to reserve, leaving £155,654 to be carried forward. T he assets of th e com pany include £1,000,000 in B ritish G overnm ent securities.
S ou th ern R h od esia.—The o u tp u t of gold from Southern R hodesia during Ju n e was 54,442 oz., as com pared w ith 53,358 oz. for the previous m o n th and 48,441 oz. for June, 1932. O ther o u tp u ts for Ju n e were : Silver, 8,662 oz. ; coal, 46,838 tons ; chrom e ore, 935 t o n s ; asbestos, 2,703 t o n s ; iron pyrites, 682 tons.
The report of the Gold Fields Rhodesian D evelopm ent Co. for th e year to M ay 31 last shows a profit of £161,301, reducing the d eb it balance brought in to £55,527. The value of th e com pany’s investm ents a t the close of the year under review showed an appreciation of £204,194, as com pared w ith the substantial depreciation shown a t the end of the previous year.
The accounts of Falcon Mines, L td., for the year to Septem ber 30, 1932, show th a t a sum of £143 was received during th e year from th e trib u tin g arrangem ents m ade in respect of th e Falcon and A thens properties.
There was a loss of £812 for th e year, increasing th e debit balance brought in to
£176,480.
N orthern R hodesia.—The o u tp u t of gold from N orthern Rhodesia for Ju n e was 214 oz., as com pared w ith 256 oz. for the previous m onth and 467 oz. for June, 1932. O ther o u tp u ts for Ju n e were : Copper, 8,079 tons ; zinc, 1,600 tons ; manganese ore, 945 tons ; m ica, 700 lb.
Shareholders of the Rhodesian Selection T ru st were inform ed last m onth th a t it had been decided to re-open the M ufulira mine.
I t is expected th a t copper production on a restricted scale will begin tow ards the end of the year.
The rep o rt of Loangwa Concessions (N orthern Rhodesia) for 1932 reveals the arrangem ents th a t have been concluded w ith the B ritish South Africa Company whereby th e period of prospecting rights is extended to Decem ber 31, 1940. In retu rn for the extension th e C hartered com pany is to be allotted, not later th an June 30, 1935, 1,000 fully-paid shares in Loangw a Con
cessions for every 1,000 square miles or p a rt
thereof retained b y the com pany after April 30, 1935.
G old C oast.—A circular to shareholders of A riston Gold Mines (1929), issued last m onth, sta te d th a t holders of the rem aining debentures and convertible notes had exercised their option and converted into shares, so th a t the com pany has no longer an y preferential charges. A progress report
by Mr. C. B. Brodigan, which accompanies
th e circular, states th a t extensions of the old 16th level south of P restea have opened up a large com pact body of ore, which, although no t payable a t this point, is considered encouraging. The reserves of ore a t Ju n e 30 last were estim ated to be 223,000 tons, averaging 10'55 dw t. in value.
Shareholders of B ibiani (1927) have been inform ed th a t the mill was sta rte d on April 8 last and has since operated as a pilot plant.
U p to the end of Ju n e 4,679 tons of ore had been treated , yielding 1,330 oz. of gold.
These operations revealed the need of finer grinding and th is section of the p lan t is to have its capacity increased.
The rep o rt Of L yndhurst Deep Level (Gold and Silver) for 1932 shows th a t no m ining operations were carried out, the p ro p erty rem aining in charge of a caretaker.
Since the close of the year one h alf of the Boabedroo Concession, including the Akyenase mine and p lant, has been sold to Konongo Gold Mines, L td ., in re tu rn for
£250,000 in fully-paid 2s. shares in th a t com pany. The reefs being developed b y the Konongo com pany continue through the L y n d h u rst p ro p erty and arrangem ents are in h an d to prospect these occurrences.
N ig eria .—A t an ex trao rd in ary m eeting of the Ju n ctio n Tin Mine (Nigeria), held last m onth, a resolution proposing the voluntary liquidation of the com pany was approved.
A u stralia.—Shareholders of the W iluna Gold C orporation have been inform ed th a t it was expected to commence treatin g ore a t th e rate of 40,000 tons per m onth by the middle of July.
Two interesting developm ents have been reported by the G reat Boulder P roprietary.
A cross-cut in E ast Section 29, Main Shaft 1,933 ft., last m onth intersected a lode 12 ft.
in w idth, having an average value of 15 dw t., while a cross-cut 390 ft. n o rth of the Main Shaft on the 500-ft. level cu t a lode 3 ft. wide averaging 8 dw t. in value.
The accounts of B arrier South, L td., for 1932 show a profit of £127, reducing the debit
72 T H E M IN IN G M AGAZINE balance brought in to £7,249. As w ork on th e
neighbouring p ro p erty of the Zinc Corpora
tion was confined during 1932 to im prove
m ent of th e ventilation system there was nothing fu rth er to rep o rt w ith regard to the com pany’s leases.
N ew Z ealand.—The rep o rt of the New Z ealand Crown Mines for 1932 shows a profit of £708. A dividend equal to 6J% absorbed
£596, leaving a balance for the year of £112.
M alaya.—The rep o rt of Selayang Tin D redging for 1932 shows a loss of £134, increasing the d ebit balance brought in to
£2,515. The dredge recovered 94 tons of tin concentrates a t a cost of £7,072, equal to 4'9d. per cubic yard treated .
D u tch E ast In d ies.—A rrangem ents were concluded last m o n th for the taking over of th e Sinkep Tin Com pany b y th e Billiton Jo in t Mining Company. The purchase consideration is stated to be FI. 2,500,000, either in cash or 4J% debentures of the Billiton com pany. I t is probable th a t the operations of the Singkep com pany will be stopped for th e tim e being, Billiton costs being m uch lower.
B u rm a .—The final dividend announced by the B urm a C orporation in respect of th e financial year ended Ju n e 30 last was 4 annas per share, of which 3J annas is out of th e y e a r’s earnings and \ an n a from accum ulated profits. The to ta l paid for the year th u s am ounts to 5J annas per share, ta x free, as com pared w ith 4 annas per share for th e previous year.
A t an ex trao rd in ary m eeting of K a- m ounghla T avoy Tin, L td ., held last m onth, th e sale of th e com pany’s m ining properties in Lower B urm a to the T avoy Tin D redging Corporation was approved. The purchase consideration was £10,000, satisfied by the allotm ent of 50,000 shares of 4s. in T avoy Tin Dredging.
K orea.— Shareholders of th e Chosen Corporation were inform ed last m o n th of a projected hydro-electric installation on the Y alu River, in th e financing of which French and Japanese capitalists are interested. The G reat N urupi mine is said to be only 20 to 25 miles d ista n t from the proposed site.
Y ugoslavia.—The re p o rt of T repca Mines for the three m onths ended Ju n e 30 last shows an estim ated w orking surplus of £93,430, equal to 14s. l i d . per ton milled. C apital expenditure during th e q u a rte r totalled
£10,268. D uring the period under review 125,118 tons of ore was milled yielding
14,083 tons of lead concentrates and 18,272 tons of zinc concentrates.
F u rth e r details are now available of the e x te n t to w hich th e C entral M ining and In v estm en t C orporation has become in terested in Novo B rdo Mines, Kopaonik Mines, and the Zletovo Mines. T he corpora
tion has u n d ertak en to purchase a t par 200,000 5s. shares (Is. paid) in th e Novo Brdo com pany and to subscribe for 200,000 5s.
shares a t p ar in th e K opaonik an d Zletovo com panies. The tw o last-n am ed companies held e x trao rd in ary m eetings la st m onth, at which proposals to increase th e cap ital of each com pany to £225,000 were approved. In the case of Zletovo Mines th is involved the creation of 160,000 new 5s. shares, while shareholders of K opaonik Mines agreed to th e creation of 200,000 new shares of the same value.
C on so lid a ted T in S m e lte r s .— The report of Consolidated Tin Sm elters, L td ., for the y ear to Ju n e 30 la st shows th e revenue to have been £166,377, increasing the a m ount b ro u g h t in to £261,764. Of this am ount £66,122 has been absorbed in the p ay m en t of preference dividends, £74,942 paid as an ord in ary dividend, equal to 5%, and £25,000 used to w rite dow n shares in subsidiary com panies, th e balance of £95,700 being carried forw ard.
C h em ica l and M e ta llu rg ica l Corpora
tio n .—D uring 1932 th e operations of the Chemical and M etallurgical C orporation were conducted a t a profit of £2,280, a fte r allowing
£8,791 for depreciation. A circular accom
panying th e re p o rt contained full details of the offer for th e sale of th e whole of the issued cap ital of th e corporation, to which reference was m ade in th e Ju n e issue of the
Ma g a z i n e. An agreem ent w ith Imperial
Chemical In d u stries, providing for the exchange of shares in th e corporation for Im perial Chemical In d u strie s’ shares, was approved at th e annual m eeting held last m o n th .
T in.—The statistics relatin g to tin stocks a t th e end of Ju ly show a fu rth e r reduction in visible supplies am o u n tin g to approxi
m ately 1,900 tons. These stocks now stand a t 44,622 tons, as com pared w ith 57,630 tons a t th e end of th e previous year. A lthough the reduction was n o t so large as h a d been expected th e price of th e m etal continued stead y around £215 per ton. The results of th e effort being m ade to o b tain world-wide restriction are aw aited w ith interest.
SMELTING PRACTICE AT T H E ROAN ANTELOPE
By A. R U S S E L L M E R Z
Follow ing on (he article on th e R o a n C o n ce n trato r w hich a p p e a re d in the J u l y issue of th e Ma g a z i n e, the au th o r com pletes the account of m etallurgical practice at this N o rth e rn R h o d esia n c o p p er p ro d u c e r.
The o perating practice a t th e R oan Antelope sm elter is notable for its simplicity.
The character of th e concentrate produced from R oan ore is responsible for th e unique position of th is p lan t am ong copper sm elters.
The m ajor points of difference are th ree : F irst, no roasting of th e concentrate is required, owing to a deficiency in iron and s u lp h u r ; secondly, no converter slag is produced, due to th e negligible q u a n tity of iron in th e m a t t e ; and, th ird ly , no electrolytic tre atm en t is needed, owing to the rare p u rity
m ining operations progress w estw ard.
Generally speaking the concentrate is a simple m ixture of chalcocite (Cu2S) and gangue m aterial (shale), a ty p ic a l analysis showing—
Cu, 58-67% ; SiO„j 13-40% ; FeO, 3-90% ; CaO, 0-10% ; A120 3, 4-12% ; MgO, 0-70% ; and S, 16-02%. A decrease in the copper content of th e concentrate causes no corresponding decrease in th e copper content of th e m a tte produced, b u t since a lower- grade concentrate contains m ore gangue m aterial more lim estone is required to flux
Fi g. 1 .— Th e Ro a n An t e l o p e Sm e l t e r.
of th e copper produced. All these factors react tow ards reduction of sm elting costs through decreasing th e am ount of equipm ent and labour required to smelt the full produc
tion of concentrate and produce therefrom a large tonnage of copper. The sm elter commenced operations on October 15, 1931, when th e first charge was fed to th e reverberatory furnace. A ctual production com m enced five days later, when the first copper was converted and cast.
There has been no appreciable change in th e ty p e of ore m ined since the p lant was started , as m ining has been confined chiefly to th e eastern end of th e ore-body. There will be an increase in th e am ounts of iron and sulphur present in th e concentrate as
it. The course of m aterial in its passage through th e sm elting p lan t is shown in th e accom panying flow-sheet (Fig. 2).
Co n c e n t r a t e Ha n d l i n g. — The concen
tr a te is tra n sp o rted from th e concentrator by pum ping through a 3-in. pipe to three Oliver filters situ ated a t th e sm elting p lant. The filters deliver th eir product, at 8 to 10% m oisture, to a system of belt- conveyors, which discharge in to th ree stock bins of 100 tons capacity each. The original equipm ent com prised th ree Lowden dryers, one connected to each filter, arranged to receive th e product of th e filters and discharge it into th e three stock bins m entioned above.
The dryer equipm ent was rem oved after it was found th a t th e w et concentrate could be 73
74 T H E M IN IN G M AGAZINE
F i g . 2.— S m e l t e r F l o w - S h e e t , A p r i l , 1933.
AUGUST, 1933 75 h andled th ro u g h th e system w ithout difficulty.
The stock bins will accom m odate a full d a y ’s production of concentrate, which is weighed, sampled, and conveyed to th e sm elter storage bins during th e d ay shift. E ach bin is equipped w ith a belt-feeder, which delivers the concentrate on to an inclined belt- conveyor, on which it is carried to a hopper weighing m achine.
The weighing ap p a ra tu s consists of a circular steel drum , together w ith m otor an d reduction gears for revolving th e drum , all m ounted on a frame which is supported on weighing levers.
The drum is provided w ith an opening in the shell, through which th e concentrate is charged and discharged. The feeders, belt-conveyor,
by trip p ers to th e various bin com part
m ents.
All th e ingredients of th e reverberatory charge are stored in th e m ain sm elter storage bins. These consist of 18 steel com partm ents, arranged in tw o parallel rows of nine each.
Three com partm ents are reserved for crushed lim estone flux, one for crushed sm elter reverts, and th e balance for concentrate.
The m aterial in a com partm ent is tak en as a u n it lot and th e weight and analysis of each “ lot ” of m aterial is determ ined before an y of it is rem oved for smelting.
Fl u x Pr e p a r a t i o n.— F lux and sm elter reverts are delivered in sta n d a rd railw ay cars to storage bins a t the crushing p lan t. The
Fi g. 3 .— Fl u x Pl a n t.
sampler, and operating m echanism of th e hopper weighing machine are all synchronized through a system of electrical interlocks to operate from a m ain control a t th e weighing- beam . The weight cannot be p rin ted unless the scale beam is in balance. After th e drum is filled and th e w eight of th e concentrate recorded by th e ticket-printing m echanism it is revolved 180° and th e contents discharged into a 30-ton capacity receiving hopper. The drum is th en revolved to its loading position.
The concentrate is weighed in 23-ton batches. I t requires 20 m inutes to com plete the cycle of filling, weighing, and em ptying.
The receiving-hopper is equipped w ith a belt feeder, which continuously discharges the concentrate on to an inclined belt- conveyor during th e weighing operations.
The concentrate is conveyed to th e to p of th e sm elter storage bins, where it is d istributed
m aterial is fed from the bins by a travelling apron feeder on to a belt-conveyor, which delivers it to a jaw crusher situ a ted under and a t th e end of th e line of bins. The product of th e jaw crusher is carried on an inclined belt-conveyor to a 5 |-ft. Symons is reduced cone crusher, where th e limestone to | in. size and th e reverts to fin . size.
The sm elter rev erts are conveyed directly from th e Symons crusher to th e sm elter storage bins. Lim estone flux is further reduced to pass a four-mesh screen by a set of 42-in. by 16-in. rolls in closed circuit w ith tw o 4-ft. by 5-ft. H um -m er v ibrating screens.
The crushed lim estone is delivered to the sm elter storage bins by a belt-conveyor.
This system includes a sam pling plant to sam ple th e Symons crusher product, consisting of a Snyder sam pler, a set of 24-in.
by 14-in. rolls, and a vertical riffle-sampler.
76 T H E M IN IN G M AGAZINE
Fi g. 4 .— Ch a r g e Ca r u n d e r Sm e l t e r St o r a g e Bi n s.
Ch a r g e Pr e p a r a t i o n.— The ingredients of th e reverberatory charge are rem oved from th e sm elter storage bins by m eans of apron feeders a ttach ed to th e bo tto m of each bin com partm ent into a specially-designed charge car, in w hich th ey are tran sp o rte d to a receiving hopper a t th e rev erb erato ry furnace. The charge car is powered by an overhead trolley circuit and is equipped to perform all th e functions of weighing, m ixing, and tran sp o rtin g th e charge ingredients. I t consists of a circular drum 7 ft. 6 in. in tern al diam eter and 6 ft. long, together w ith a m otor and reduction gears for revolving th e drum , all m o unted on a fram e which is suspended from scale beams.
The drum is provided w ith an opening in its p eriphery for th e purpose of charging and discharging th e m aterial. This opening is fitted w ith a sliding gate operated by levers.
A system of m otor-operated cam s lifts th e load off th e knife-edges when weighing is not being done. A pointer a n d calibrated dial situ ate d in th e cab indicate the weight in pounds of each ingredient as it is fed in to th e drum .
A ty p ical charge consists of 18,800 lb. of concentrate an d 1,130 lb. of lim estone flux or when crushed m a tte is a.vailable 17,300 lb.
of concentrate, 1,050 lb. of lim estone flux, and 1,650 1b. of crushed m a tte skulls. This fills th e drum a little m ore th a n half full, which allows sufficient em p ty space for p roper m ixing. The d ru m is revolved and its contents m ixed while th e car trav els to th e point of discharge.
Re v e r b e r a t o r y Sm e l t i n g. — The rev e rb erato ry furnace is of th e usual type a n d is 100 ft. long a n d 25 ft. wide, inside dim ensions. The walls an d roof are built of silica brick. The side walls are 2 ft. thick an d th e roof is 18 in. th ick over th e smelting zone an d 15 in. th ick over th e settlin g zone.
The charge is carried on belt-conveyors from th e receiving hopper to th e charge floor of th e rev erb erato ry furnace, w here' it is d istrib u ted by a two-w ing trip p e r to trough
shaped hoppers a rran g ed on each side of the furnace over th e side walls. T he charge is dropped through 6-in. pipes in to th e furnace to form an em bankm ent against th e side walls.
There are tw elve charge pipes on each side.
The em bankm ent of charge is m ain tain ed to cover th e face of th e side walls for a distance of 60 ft. from th e b u rn er wall.
F uel for h eatin g th e furnace is coal pulverized to pass 80% th ro u g h a 200-mesh screen an d blown in to th e furnace through four p o rts in th e end wall spaced a t 4-ft.
centres an d a few inches above th e m axim um height of th e b ath .
The coal is pulverized a t a cen tral plant, which supplies th e needs of th e sm elter and also of th e direct-fired boilers a t th e power p lan t. Two Fuller K inyon pum ps blow the pow dered coal th ro u g h pipes to th e bunkers which th e y supply. E lectrically-operated valves control th e q u a n tity of coal pum ped to each bunker. There are four coal bunkers over th e rev erb e rato ry furnace, each of 18 tons capacity. E ach b u n k er is equipped w ith a Bailey feeder driven by a sm all m otor
•tixg. - I he usual |
• w ide , is:
roof are If a r e 2 ft. H i th e sm et s e t t lin g s b e lt-co n u r le ch a rge : , w h e re ':
p e r to tat c h sid e of T h e chare
th e fume h e sid e t o n each s m a in t a k fo r a f a
aace is s h a 2it e nace throE aced at t he m a s k entral p
sm elter at
: the po®
as blow th h e b a r ii y-operalf
¡1 pump#
if b m t e e a ch >
equips
a h i b #
AUGUST, 1933 through Tex-ropes a n d variable reduction
gears, so th a t th e ra te of feed to each burner can be varied from 6 to 25 tons of coal per day. E ach feeder has an individual prim ary air fan, which furnishes th e air required to carry the coal from th e feeder to th e burner.
The coal drops through a 3-in. pipe into a 7-in. prim ary air pipe, which joins a 12-in.
branch from th e secondary air m ain before reaching th e furnace. The volum e of air is controlled in b o th prim ary and secondary air lines by m eans of b u tterfly valves, which are locked in position after adjustm ent.
The m ixture of fuel and air is proportioned to produce com plete com bustion, w ith an excess of 0-6% oxygen, as determ ined by daily analysis of gas samples asp irated from the furnace.
A Stirling boiler and th e reverberatory stack are closely connected to th e furnace, so th a t th e m axim um recovery of w aste heat is m ade by th e boiler. The recovery of heat energy in the form of superheated steam averages 52% of th e to ta l calorific value of the coal burned in the furnace. The hot gas is draw n through the boiler and discharged into the stack by an induced drau g h t fan.
An air preheater situ ate d betw een the boiler and stack utilizes th e h eat of th e w aste gas from the boiler to heat th e secondary air for com bustion. The secondary air is supplied by a forced draught fan which blows th e air through the preheater and an insulated duct to th e burner end of th e furnace. The
air reaches th e burners a t a tem perature of 400° F.
The drau g h t in th e furnace is m aintained as near to zero as is practicable and ordinarily is not allowed to go above 0-02 in. w ater- gauge. Control of th e draught is obtained by regulation of butterfly dam pers a t the intake of th e induced draught fan. A native o perator w atches th e recording d rau g h t gauge and alters th e dam per position to keep the d rau g h t w ithin th e specified range. Despite th e m oisture in th e furnace charge, a very good fuel ra tio is obtained because of the high percentage of m atte-form ing elem ents present.
The average fuel consum ption is 15-5% of th e charge, th e weight of m a tte is 70% of the weight of charge, and th e weight of slag is only 26% of th e charge.
The m atte-form ing elem ents in th e charge consist of copper sulphide and iron sulphide, which m elt to form a m ixture of the following analysis : Copper, 78-7% ; iron, 0-58% ; and sulphur, 19-58%. This m aterial has a specific g rav ity of 5-5 and the slag has a specific g rav ity of 3-0, a difference which causes a clean separation of th e two in the furnace b ath .
In order to operate the furnace a t its g reatest efficiency a dep th of a t least 12 in.
of m a tte is k ep t in th e furnace a t all times.
The greatest possible safe dep th of m a tte is 24 in., which is th e level of th e doors through w hich th e slag is skimmed.
The m a tte is tap p e d through tw o 3-in.
Fi g. 5 .— Sk i m m in g Sl a g.
78 T H E M IN IN G M AGAZINE
F i g . 6.— T a p p i n g M a t t e .
holes, 9 in. a p a rt vertically, in a replaceable copper block fastened to th e side wall of th e furnace ju st beyond th e charging zone. The holes are opened by burning them out w ith oxygen. The m a tte flows through them and down a clay-lined launder into large sem i
steel ladles, which are supported on low tru ck s on a tra c k below. The tra c k extends under th e operating floor, parallel to th e side of th e furnace, into th e converter aisle. The m a tte ladle tru ck s are hauled b y m eans of a cable operated from an electric hoist.
A ladle will hold 22 tons of m olten m atte.
W hen b o th tap-holes are opened it requires from 20 to 35 m inutes to fill th ree ladles,
which is th e usual am o u n t charged to a converter. I t is custom ary to ta p from two holes a t th e sam e tim e, since a speedy tran sfer of th e m a tte from th e reverberatory to th e converter greatly decreases th e am ount of m a tte th a t freezes to th e ladles, all of which m ust be rehandled, crushed, and resm elted in th e re v e rb e rato ry furnace.
W hen th e last ladle has been filled, th e flow of m a tte is stopped by ram m ing stiff clay plugs in to th e tap-holes.
T he ingredients of th e charge are propor
tioned to produce slag having a silicate degree of 1-75. This entails a flux burden of only 6% lim estone an d produces th e minimum
Fi g. 7 .— Th e Co n v e r t e r.
AUGUST, 1933 79 q u a n tity of slag com patible w ith a fluidity
which allows read y settlem ent of m a tte particles through it and ease in handling.
An average slag analysis sh o w s: S i0 2, 47-3% ; FeO, 13-7% ; CaO, 11-4% ; A120 3, 14-7% ; MgO, 2-9%. The copper content of the slag varies from 1-0 to 2-5%, depending on the am ount of cuprous oxide in th e charge.
There are tw o skim m ing doors in th e furnace, one in th e end wall and one in the side wall. These are closed w ith clay dams, which are chipped out when th e slag is to be skimmed. R everb erato ry slag is used to provide a protective lining in th e steel ladles
in which m olten copper is handled.
The slag is carried to the dum p in ladles of 14 tons capacity. The ladles are m ounted
aro u n d th e reverberatory furnace and con
v erters for sealing openings and lining launders. This clay is ab u n d an t near th e sm elter and is m ixed to th e proper consistency in a w et pan mill, of the Chilean mill type.
Two natives operate th e mill on day shift and produce enough clay to supply all three shifts.
Co n v e r t i n g.—The converters are of the Peirce-Sm ith type, 12 ft. in diam eter and 20 ft. long inside the shell, and are lined w ith 12 in. of m agnesite brick throughout, except along th e tuyère line, where th e lining is 15 in. thick. There are 30 tuyères in each converter, each I f in. in diam eter. One converter has am ple capacity to handle the entire production of m a tte from th e rever-
F i g . 8.— C a s t i n g .
on trucks and each tru ck is equipped w ith electrically-driven gears for tilting its ladle.
An electric trolley-locomotive hauls th e slag to th e dum p, which is half a mile from th e furnace. The locomotive weighs 16 tons and handles th ree loaded trucks, a to ta l weight of 140 tons.
E ven though the furnace charge is wet, there is a considerable am ount of dust carried out of th e furnace by th e stream of gas. This dust, com bined w ith ash from the coal, settles in the boiler and connecting flues. The accum ulation of du st is rem oved and sm elted. An average analysis of this dust shows: Cu, 31-22% ; S i0 2, 19-82% ; FeO, 4-59% ; CaO, 3-13% ; A120 3, 11-37% ; MgO, 0-35% ; S, 5-7%.
A considerable am ount of clay m ud is used
beratory furnace. The other converter is kep t available as a spare.
A blowing engine, driven by a 950-h.p.
electric m otor, situ ated in th e power station, supplies th e air blast, a t a pressure of 15 lb.
per square inch, for oxidation of th e iron and sulphur in the m a tte . The h eat produced by the oxidation of the sulphur and th e small am ount of iron in the high-grade m a tte is ju st sufficient to finish th e charge at a proper tem p eratu re for casting. The converter is kept hot during its idle periods w ith pulverized coal, which is blown through a burner port in one end. Before startin g a blow the coal is shut off and th e burner port filled w ith clay. A t the end of th e blow th e clay is rem oved and th e coal fire started.
The converters are served by an electric
