y. i ^ ü p 3 ¡X
The Mining M agazine
Mant ... , „ „ . w f W h i t e . A s s is ta n ts : S t . J. R . C. S h e p h e r d , A.R.S.M ., D .I.C ., F .G .S .;
Director and E ditor . W . i l Higham> a . r . s . m . , M .Sc., F.G .S.
P u b i i s h e d o n t h e 1 5 t h o f e a c h m o n t h b y M i n i n g P u b l i c a t i o n s , L i m i t e d , a t S a l i s b u r y H o u s e , L o n d o n , E .C . 2.
T eleg rap h ic A d d ress: Oligoclase. Codes: M cN eill, b o th E ditions, & Bentley.
Su b s c r ip t,on J }2s. p e r a n n u m , in c lu d in g p o s ta g e . ( U.S.A., $3 p e r annum , including postage Telephone : Metropolitan 8938. & M È
Bra n ch 0 „ ic e , { B .v d !
V o l .
X L V I 1 I .
No. 1. L O N D O N , J A N U A R Y , 1933. PRIf cO N E S H I L L I N G
C O N T E N T S
Ed i t o r i a l
N otes ... -
The A nglo-Persian Oil D isp u te ; T estin g Air-Com
pressors ; C anadian M ineral O u tp u t for 1932 ; New Y ear H o n o u rs ; Basic Bessem er S te e l; D ecentraliza
tion in M alaya ; T he K akam ega Coldfield ; South A frican Affairs ; T h e In s titu tio n B enevolent Fund.
N on-Ferrous M etals in 1932... 3
An ex a m in a tio n of th e base-m etal position a t the end of la s t y ear.
The In stitu tio n Meeting ... 4
Proceedings a t th e D ecem ber m eeting rexiewed.
The Am erican D e b t... 5
The q u estio n of the d eb t position is exam ined from a new angle.
Re v i e w o f Mi n i n g... 6 Ar t i c l e s
The Recovery of Alluvial Diamonds R. Kenneth McLeod 9 A com parison of the pan plants and mechanical trom m el
p la n ts used for the concentration of alluvial diam onds in G old Coast Colony.
L i g h t n i n g —H I John F. Shipley 19 In th is th e third of a series of fo u r articles, th e au th o r
discusses the protection of life and p ro p erty against lightning.
on an Andean Mine
S . V . Griffith 22
nf four separate m ethods of tra n sp o rt used in a S n e in the Andes are com pared.
The Ankole Tinfield of South-W est U g a n d a ... Dr. A . W. Groves 26
P of two recent publications dealing w ith this T Id and a statem en t of th e results of th e au th o r's
observations.
The I.M-M. Benevolent F u n d ... 30
E l e v e n t h List of Subscriptions.
Le t t e r s t o t h e Ed i t o r
The Measurement of Air-Compressor Efficiencies ... R. L. Qnertier The I.M-M. Benevolent F und
Hugh F . K . Picard
Bo o k Re v i e w K abone’s “ F lo ta tio n T r a n s p o r t
3 0
31 P la n t P ra ctice ”
P. E . M arm ion JvjEVVSLe t t e r s
Johannesburg ...
YVaterberg G old Belt : R andfontein Extension ; W estern Areas : Liquid O xygen Explosives.
-2
B r is b a n e ...
Mount Isa A ctivities ; M ount W andoo Goldfield ; Cracow F ie ld ; M ount Morgan A g ain ; Lake View and S ta r ; Gold in C entral A ustralia.
Toronto ...
Metal P ro d u ctio n of O n tario ; Porcupine ; K irkland Lake ; S ud b u ry ; O th er O ntario Goldfields ; N orth- W estern Quebec ; M anitoba.
V ancouver...
Bridge R iver ; P ortla n d Canal ; C ariboo ; Nelson ; V ancouver ; E a st K o o ten ay ; B oundary ; H ope ; A tlin.
P A G E 3 3
3 5
3 7
Pe r s o n a l... ... 4 0 Tr a d e Pa r a g r a p h s ... 4 0 Rico-W ilfley M agnetic S e p a r a t o r ... 41 H o lm an S ingle-D rum In tern a l-G ea red H o ist 41 Geco D ouble-A cting Classifier ... 42 M errill P re c ip itatio n Process ... 42 Me t a l Ma r k e t s ... ... .. 4 3 St a t i s t i c s o f Pr o d u c t i o n ... 4 5 Pr i c e s o f Ch e m i c a l s... 4 7 Sh a r e Qu o t a t i o n s... 4 8 Mi n i n g Di g e s t
A ir-C om pressor T e s t i n g ... 49 O re -T re a tm en t a t P io n eer Gold M ines,
B ritish C olum bia
H. J . C ain and P. Schutz 52 H an g in g -W all C ontrol in D eep-L evel M ines
B . T . A ltso n 55 N a tu ra l an d M echanical V en tilatio n
R. A . H . Flugge-de S m id t 57 S cheelite a t K ra m a t P u lai
E. S. W illbourn and F. T . Ing h a m 60 O p en -P it a n d U n d erg ro u n d G ypsum M ining
W. G. Bradley 61 Ore T re a tm e n t a t M c In ty re P orcupine
W. F. Boericke 61 Sh o r t No 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 ... 6 2 Ne w Bo o k s, Pa m p h l e t s, e t c... 6 2 Co m p a n y Re p o r t s ... 6 3 A m ari N igeria Tin ; A yer H ita m ; B aba R iver Tin ; C henderiang ; Chosen C orporation ; C yprus and General Asbestos ; F o ld al C opper and Sulphur ; H ongkong Tin ; Jo s Tin A rea ; 31 K am unting Tin D red g in g ; K epong D red g in g ; Killinghall T in ; Offin R iver Gold ; P a tta n i T in ; Tarkw a B an k et W e s t; Zletovo Mines.
3 2 Di v i d e n d s De c l a r e d... 6 4 Ne w Co m p a n i e s Re g i s t e r e d... 6 4
S
INCE our last issue both p arties to the A nglo-Persian oil dispute have agreed to lay th eir case before the Council of the League of N ations and the m a tte r stands adjourned u ntil Ja n u a ry 23.A
T T E N T IO N m ay be directed to a letter, appearing elsewhere in th is issue and dealing w ith th e testing of air- compressors, from th e P resident of the B ritish Compressed Air Society. The test referred to by Mr. Q uertier is reproduced in th e m ining digest.P
R ELIM IN A R Y figures are already available w ith regard to Canada’s mineral production in 1932. The to ta l value is estim ated a t $182,701,000, as compared w ith
$228,029,000 in 1931. The outstanding feature of the returns is the increased pro
duction of gold, which totalled 3,055,168 oz., w orth $63,155,925, in 1932, as compared with 2,693,892 oz., w orth $55,786,588, in 1931.
A
MONG the New Year Honours mining men will note the names of Mr. H. W.Gepp, consultant to th e A ustralian Govern
m ent and a gold m edallist of the Institution, who receives a knighthood ; Dr. S. W.
Smith, this year’s president of th e Institution and chief assayer at the Royal Mint, who receives th e C.B.E., and Mr. A. V. Elsden, of the Royal Arsenal, Woolwich, who receives th e O.B.E.
L
AST m onth reference was m ade to the scheme for th e m anufacture of basic Bessemer steel in this country. I t is interesting to note in this connexion th a t celebrations were held in Paris in December, organized by the Société des Ingénieurs Civils de France, in commemoration of the introduction into France of the basic process, widely known on the Continent as the Thomas process, after the name of its principal inventor.
T
H E prim ary object of the visit to Malaya of th e Perm anent U nder-Secretary of S tate for th e Colonies, Sir Samuel W ilson, was to study decentralization, a subjectwhich has frequently been m entioned by our Ipoh correspondent. I t m ay be said, perhaps, th a t th e unofficial view th a t a m easure of local control be given th e individual S tates was fairly presented to th e representative of H.M. G overnm ent and th a t th e visit is bound to have h ad a beneficial effect.
D
e v e l o p m e n t of th e K akam ega goid- field appears likely to present th e K enya G overnm ent w ith a difficult problem , in view of th e fact th a t th e discoveries lie w ithin a n ativ e reserve. The m ineral rights of reserved te rrito ry have, doubtless wisely, been retain ed b y th e adm inistration, whose ta sk it m u st be to find fresh lan d for th e natives displaced by m ining operations.M onetary com pensation seems h ard ly adequate and it w ould appear th a t, in the present depressed sta te of agriculture, it should be easy enough to re-purchase any land th a t m ight be required for re-settling the native.
A
F F A IR S in South Africa, consequent upon th e U nion’s d ep artu re from th e gold stan d ard , appear to be in a sta te of flux.R approchem ent betw een th e opposition leaders, Mr. Tielm an Roos and G eneral Sm uts, does n o t appear com plete and th e form ation of a coalition has n o t yet been decided upon. Meanwhile it is evident th a t labour troubles—consequent on th e desire of th e workers to share in th e prem ium
—are in th e offing, while it is rum oured at th e same tim e th a t a heavy prem ium ta x will be im posed by General H ertzo g ’s G overnm ent. T he gold m ines, therefore, m ay n o t benefit by th e devaluation to th e ex ten t th a t o th er p rim ary producers are likely to.
E
L S E W H E R E in th is issue is a le tte r from Mr. H ugh P icard w ith regard to th e appeal m ade in th e M a g a z i n e of F eb ru ary last on behalf of th e Benevolent F u n d of th e In stitu tio n of Mining and M etallurgy. The success m et w ith is gratifying, in view of th e prevailing depression, and speaks well for th e generosity of th e profession an d those associated w ith it.
W hilst a t all tim es read y to help in any
JA N U A R Y , 1933 3 direction desired, th e publication of the
m o n th ly subscription list should not be continued indefinitely. In this issue will be found the E leventh List and we propose ceasing publication after th e appearance of the Tw elfth L ist in our F eb ru ary issue. I t does nol follow, of course, th a t either individuals or companies need subsequently b u tto n up th e ir pockets.
N o n -F erro u s M etals in 1932 Once again no very favourable account can be given for the year th a t has recently closed, so far as non-ferrous m etals are concerned. From every standpoint it was an unsatisfactory one for the copper industry.
Production, which was reduced to 2 6 |% of capacity a t th e beginning of the year, was cut further to 20% in April, b u t even then the unwieldy stocks stubbornly refused to shrink. Consumption has fallen to little more th an one-third of the peak levels established in 1929, but fortunately production costs have been reduced to a rem arkable extent. Standard copper to-day is selling at about half the pre-war price and th a t on a paper basis against gold. Despite the rapid growth of low-cost capacity, producers adhered to their unpopular and uneconomic methods of trying to control prices through Copper Exporters, Inc., which organization came to an inglorious end following the imposition of a d u ty of 4 cents per pound in th e United States in June. I t is doubtful w hether any b u t high-cost producers, who should have retired from th e race two years ago, will m ourn its decease. F u rth er complications to th e industry were introduced by the proposed tariff of 2d. per pound on non- Em pire electrolytic copper im ported into this country and, although so far this duty has not been imposed, it remains an ever
present possibility. The proposed duty, how
ever, carried the proviso th a t Em pire producers m ust supply consumers here a t a price not exceeding th e world-price and latterly enthusiasm for its application seems to have waned somewhat. In December there was a conference of producers in New York to discuss the possibility of renewing the output- curtailm ent plan for 1933 and to arrange a m utually agreeable m arketing policy.
Em pire producers, however, definitely opposed any further attem p ts to control prices or to lim it their daily sales, but the conference actually broke down on the demand of some of the newer low-cost producers—especially
in Rhodesia—for more equitable production quotas. The present situation is ex tra
ordinarily complicated and th e outlook more th a n usually obscure. A t present there is probably enough productive capacity w ith a cost price of 5 cents per pound or there
abouts to supply twice the current needs of consumers. Despite this, thanks to the misguided efforts of Copper Exporters, Inc., most of the old higher-cost producers are still operating, having been induced to continue production even a t a loss, in the vain hope of an early return to higher prices. The effect of th e American tariff has been largely to immobilize the enormous stocks in the U nited States—probably fully 700,000 tons of refined copper—which a t present are sufficient to supply about two years’ domestic requirements. In Rhodesia, after expending enormous sums on development work, up-to- date and large-scale properties have recently come into operation, which cannot very well refrain from turning out m etal. In Canada there is a big productive capacity from mixed m etal mines which enables copper to be produced a t extrem ely low prices. France has given a protection of 2% to Belgian copper, whilst exchange difficulties in Germany ham per business in th a t direction. The possibility of a tariff here on non-Empire copper complicates the position further. The only possible solution appears to be for higher- cost properties to close down, b u t this takes time, and, whilst consumption remains as small as it is a t present, the outlook for prices is anything but favourable.
The continued falling-off in the consumption of tin during 1932 necessitated further drastic curtailm ent of output in countries comprised in the Government-controlled production restriction plan. Despite this the reduction in the large surplus supplies has been dis
appointingly meagre. Prices in the latter p a rt of th e year m ade a more favourable showing th a n in the earlier m onths, due largely to th e fact th a t the International Tin Pool is holding 21,000 tons off the m arket and th a t another pool has utilized large financial resources to sustain prices. A t the higher level now prevailing new properties are coming into operation, notably in the Belgian Congo. As to lead, stocks during the past year have increased throughout the world and, w ith m any producers still unwilling to curtail output on any substantial scale, together w ith a considerable output now coming from Mount Isa, production at present remains rather in excess of consump
tion. Practically all branches of th e con
suming trades have shown a falling away during 1932, the last country to be affected m aterially being the U nited Kingdom, b u t even now this country is b etter situated th a n m ost others. E verything seems to hinge on a general trad e revival, failing which the im m ediate outlook for lead seems unsatis
factory. The efforts of th e International Zinc Cartel to reduce stocks by curtailing output have been more successful during the past year th a n those of any similar body. P ro
duction was further curtailed to 45% of the agreed basis in August and stocks fell by some 35,000 tons during the first 11 m onths of th e year. Consumption continued un satisfactory, owing largely to the depression in the galvanizing industry. Nevertheless, when the tim e came to consider the renewal of the cartel for 1933 and th e continuation of production quotas a t 45%, some members pressed strongly for permission to produce on a larger scale and th e situation a t th e mom ent is rath er precarious. U ntil the cartel settles its affairs definitely one w ay or the other the outlook m ust rem ain obscure.
The In stitu tio n M eeting
The attendance a t th e December m eeting of the In stitu tio n was somewhat affected—
as usual—by seasonal calls on m em bers’ time, b u t there was, nevertheless, a good num ber present to hear th e presentation of two interesting papers. The first of these—
“ Reduction W orks Practice a t Morro Velho, B ra z il” —was by Messrs. J . H . French and H arold Jones and dealt w ith the activities of the St. John del Rey Mining Company, while the second— “ Notes on a Tunnel driven at Stan Trg Mine, Yugoslavia,” by Mr. D. J. Rogers—described development at the property of Trepca Mines, Ltd. The programme was, therefore, attractiv e to both mill-men and miners, to both precious-metal and base-metal interests, and those who went to the trouble of attending m ust assuredly have felt th a t their evening was by no means wasted.
In introducing the paper on St. Jo h n del Rey th e president—Dr. Sydney Sm ith—reminded his hearers th a t inform ation on procedure at this mine had always been difficult to obtain, a fact which lent it additional interest. The authors—who were unavoidably absent—refer in this paper to the com plexity of the ore m ined at Morro Velho and the associated properties, which th ey describe as a finely-
crystalline m ixture of quartz, carbonates, p y rrh o tite, pyrite, and arsenopyrite, together w ith small am ounts of chalcopyrite and chlorite and traces of other minerals. The gold content of th e ore averages about 12 dwt.
per long ton and the process of extraction—
a system of g rav ity concentration, followed by cyanidation, w ith roasting of some of the concentrates—is rendered especially interest
ing to m etallurgists, as those in charge feel th a t they have successfully conquered w hat th ey consider to be th e “ b o g e y ” of the cyanidation process—pyrrhotite. The authors sta te th a t th is sulphide cannot be ignored to the ex ten t th a t it has been in th e past owing to its occurrence in new goldfields and th ey point out th a t its potent effects m ay require radical departure from standard milling practice if commercial extractions of gold and silver are to be made. The complete flow-sheet attach ed to th e paper fully illustrates th e processes described, but, as th e authors point out, it is chiefly in the cyanidation practice th a t the m ethod of treatm en t stands ap a rt from general pro
cedure, the cyanide solutions becoming so foul th a t they cannot be returned to circulation and, in consequence, volumes have to be kept low and cyanidation in thick pulp employed.
Discussion of the paper was in itiated by Mr. H. K. Scott, who, in rem iniscent vein, recalled the vast am ount of good work done by the late Mr. Chalmers. Mr. H arley B.
W right, who followed, sum m arized th e m etal
lurgical work described and added his quota to the praise generally accorded to th e paper.
O ther speakers included Mr. A. J. Bensusan, who dealt w ith his Brazilian days ; Mr. E. T.
McCarthy, who referred to native practice w ith similar ores in Korea, and Messrs. W. H.
M errett, F. Yeates, and Mr. W. H. Goodchild.
Not all the speakers could agree th a t p y rrh o tite was necessarily such a p otent cyanicide as th e authors would suggest, b u t there was scarcely a reference to the possibility of salving cyanide, although it would seem th a t the installation of some process of cyanide regeneration at St. John del Rey m ight result in im portant savings.
From Brazil to Yugoslavia— from the new world to th e old—is a far cry, as far as from ore treatm ent to tunnelling, yet th e second paper, dealing w ith th e driving of a deep adit at the Stan Trg mine of Trepca Mines, Ltd., was followed w ith as close a tten tio n as the first had been. This is th e second paper th a t the In stitu tio n has had on tunnelling in recent m onths and readers will no doubt rem em ber
JA N U A R Y , 1933 th e first, by Messrs. Francis and Allan, on
work at H alkyn, referred to in the Ma g a z i n e
for F ebruary last. A t th a t tim e it was recalled th a t tunnelling records had been achieved at various tim es in both the H alkyn and Stan Trg projects—as well as in the Haweswater tunnel of th e M anchester Corporation— and, in consequence, all these projects have been somewhat in th e public eye. The driving of th e Stan Trg tunnel, as Mr. Rogers recalls, had a dual purpose, being intended to open up the Trepca ore-bodies at a deeper horizon and to drain a large tra ct of limestone country.
The first p a rt of the tunnel— 2,387 m etres in length—was driven through schist and required support, the remaining 288 m etres required to connect up w ith th e shaft sunk from th e 760-metre level being in limestone and ore. F or details of the work carried out the reader is referred to th e paper itself, appearing in th e December Bulletin of the In stitu tio n , b u t it m ight be pointed out here th a t, whilst a t H alkyn the drilling was done by m achines m ounted on bars, a t Stan Trg a drill-carriage was used and th a t at H alkyn slusher mucking found favour w ith those in charge, whereas a t Stan Trg a Butler shovel was installed. Such details were referred to more th an once by those taking p art in the discussion, which was m ost appropriately in itiated by Mr. J. C. Allan, while Professor Truscott, who followed, compared details of th e tunnelling exploits m entioned by Mr. R. E.
Palm er in th e course of the discussion of Messrs. Allan and Francis’ paper. This brought Mr. Palm er to his feet and his able resume of th e m ain points arising in such work and of the difficulties of concrete emplacement was much appreciated. Several other members were able in the short time still available to express their views, the discussion being closed by a few well-chosen words from the president, the evening having proved a w orthy ending to the old year.
The A m erica n D ebt
Like th e poor, the D ebt question seems to be alw ays w ith us. To w hat e x ten t this incubus is responsible for th e world-wide depression which has prevailed for so long and still shows little sign of departing m ay be open to doubt, b u t there would seem to be no tw o opinions on th e point th a t under the conditions now ruling b o th creditor and d eb to r nations are adversely affected. I t would seem, therefore, th a t even from the lowest sta n d p o in t— th a t of self-interest— it
is incum bent on the U nited S tates to come to some settlem ent and th e sooner the b e tte r for all concerned. There are, of course, divergent views as to th e n atu re of this settlem ent and it has been h in ted th a t some am elioration m ay be forthcom ing in re tu rn for g ranting certain tra d e advantages. In other words, we are to be asked to ru n th e risk of losing in one direction an y th in g we are likely to gain in another. This is a suggestion, in view of th e experiences of the last year or two, which is hardly likely to be seriously considered.
T h is m a tte r should, however, be viewed from a very different angle th a n th a t of self- interest. I t has to be borne in m ind th a t the debtor countries were engaged in th e W ar for som e considerable tim e before th e U nited States. F u rth er, th e whole of th e m oney borrowed by th e various countries—for which this country stood responsible—was expended in th e U nited S tates on W ar supplies, greatly to th e benefit of th eir own industries. Those who carry th eir m inds back to th e period ju st prior to th e U nited S tates joining the Allies in April, 1917—more th a n tw o and a half years from the com m encem ent of hostilities—will recall th e views th en expressed by m any prom inent Americans to th e effect th a t it was as m uch th e ir W ar as th a t of E ngland and th e enthusiasm shown by th e large num ber of A m ericans who atten d ed th e D edication Service a t St. P a u l’s C athedral on “ The en try of th e U nited S tates of America into th e G reat W ar for Freedom ” confirmed th is view, although one well-known m ining engineer who was present p ertin en tly rem arked, when congratulated on the good m uster of his friends : “ Yes, bu t it should have been held long ago.” How m any thousands of lives h ad been lost prior to th e advent of th e U nited S tates is well known and afterw ards the sacrifice of life continued to fall far m ore heavily on those previously engaged in th e conflict. To refer, therefore, to th e necessity, in effecting any D ebt settlem ent, of com pensation being m ade to th e U nited S tates for th e “ sacrifices ” th ey have undergone can hardly be regarded as commendable. N ot only in th is country, b u t in th e U nited States, m any on th e term in a
tion of th e W ar held—and still hold—the view th a t h ad all debts to th e Allies been forthw ith wiped out Am erica would have done no more th a n an act of justice, for even th en she would have paid m ainly w ith dollars, whereas th e other countries paid m ainly w ith lives.
Introduction.—Metal m arkets opened in th e New Year in a somewhat disheartened atm osphere, owing to uncertainty as to the statistical position, chiefly of tin and copper.
In the case of tin th e small decline in supplies was disappointing ; it is believed, however, th a t th e stocks held b y th e principal holders are not so large as is generally imagined. As to copper, the failure of th e conference in New Y ork natu rally affected th e price of the m etal, although it m ust generally be felt th a t th e Rhodesian producers have done more th a n their share in the direction of assisting th e high-cost producers.
T ra n sv a a l.—The o u tp u t of gold on the R and for December was 931,749 oz. and in outside districts 48,869 oz., m aking a to ta l of 980,618 oz., as com pared w ith 978,716 oz.
in Novem ber. L ast m o n th ’s figures bring th e to ta l for th e year to 11,553,564 oz., which is a record. The num ber of natives em ployed in th e gold m ines a t th e end of December totalled 221,008, as com pared w ith 219,024 a t th e end of November, also a record.
The accom panying table gives th e dividends declared by th e R an d gold m ining companies on account of th e p a st half-year.
Figures for th e preceding three half-years are given for com parison and from these it will be seen th a t Simmer and Jac k and L uipaards Vlei have retu rn ed to th e list, from which
1st b ali, 1931.
2nd half, 1931.
1st half, 1932.
2nd half, 1932.
B r a k p a n ... ."... s. d.
4 0 s.
4 d.
0 s. d.
3 0 s. d.
4 0
C onsolidated M ain R eef. . 1 3 1 3 1 3 1 3
Crown ... 3 6 3 6 3 6 4 3 D u rb an R o o d ep o o rt D eep 0 9 U 9 0 9 0 9 E a st G e d u ld ... .— 1 0 1 9 E a st R a n d ... — 0 fi 0 3 0 3 G eduld ... 3 3 3 fi 3 6 4 0
G eldenhuis D eep ... 1 0 1 0 1 0 1 0
G o v ern m en t A r e a s ... 2 3 2 3 2 3 2 3 L an g laag te E s ta te ... 2 0 2 0 2 0 2 0
L u ip a a rd s V le i... — — 0 3
M odderfontein B ... 1 6 1 fi 1 3 1 3
M odderfontein D e e p . . . . 3 0 3 0 2 9 2 9
M odderfontein E a st . . . . 2 0 2 0 2 0 2 0
New M odderfontein . . . . 6 0 5 (Ï 5 3 5 0
N ew S ta te A reas ... 2 0 2 0 2 (1 2 3
N ourse Mines ... 0 9 0 9 0 9 0 9
R an d fo n tein ... — n fi 0 9 1 0
R obinson D eep (A Is.) . 1 6 i fi 1 6 1 6
Robinson D eep ( B ) ... 41 (i fi 0 G 0 71
Rose D e e p ... 0 fi — —
S im m er and J a c k ... — 0 2 •—• o n
S p rin g s M ines... 3 9 4 11 3 9 3 9 S ub N ig e l ... 3 0 3 fi 4 0 4 0
V an R y n ... 0 6 0 9 1 0* 1 0*
V an R y n D e e p ... 2 6 2 fi 2 0 2 0
W est R a n d ... — 0 3 0 4J
W est S p r in g s ... 0 9 0 9 0 9 0 9
W itw a te rsra n d Gold ... 0 6 Ü 6 0 3 0 3
* F ree o f tax .
6
Rose Deep is still absent, w hilst increases are shown by Crown Mines, G eduld an d E a st Geduld, New S tate Areas, R andfontein, Robinson Deep B, an d W est R a n d Con
solidated and a decrease by New Modder- fontein. W ith th e exception of th e Van R yn paym ent, all dividends are declared in South African currency a t th e ra te of exchange ruling on J a n u a ry 27.
Shareholders of the Meyer and Charlton Gold Mining Co., Ltd. (in liquidation), have been inform ed th a t a first dividend of 15s.
(South A frican currency) will be paid during the present m onth.
The accounts of th e R an d Selection Corpora
tion, L td., for th e year ended Septem ber 30 last show a profit of £150,365, which, added to the sum brought in, gave an available total of £242,893. Of this am ount £150,000 has been transferred to a special exchange reserve account, leaving £92,893 to be carried forward.
D uring th e year th e com pany successfully tendered to th e G overnm ent for a lease of th e underm ining rights of th e eastern portion of th e farm D aggafontein No. 9.
C ape P r o v in ce.— A circular to share
holders of th e N am aq u a Copper Com pany issued th is m o n th sta te s th a t an o p p o rtu n ity has occurred for investm ent of th e com
p a n y ’s cash assets in an established com pany working a well-known sulphur an d copper m ine. This com pany has ex h au sted its cash resources on developm ent an d is in need of fu rth er capital. The p ro p erty in question is sta te d to have been exam ined by Mr.
E dw ard H ooper, chairm an of th e N am aq u a com pany, who will lay th e whole m a tte r before an ex trao rd in ary m eeting convened for Ja n u a ry 16.
Southern R hodesia.—The o u tp u t of gold from Southern Rhodesia during N ovem ber was 48,082 oz., as com pared w ith 50,416 oz.
for th e previous m onth and 44,516 oz. for November, 1931. O ther ou tp u ts for Novem ber were : Silver, 7,927 oz. ; coal, 35,426 tons ; chrome ore, 197 tons ; asbestos, 2,519 tons ; mica, 1 ton ; scheelite, 3 tons.
Some dislocation in the running of th e p lant a t th e Sherwood S tarr, owing to a portion of the new plant being brought into action and to an increase in the stibnite content of the ore, was announced in th e last issue of the
Ma g a z i n e. I t has since been stated th a t the residue from th e roaster was nearly norm al, treatm en t having been slightly altered and
JA N U A RY , 1933 the q u an tity of ore from the antim onial
stopes restricted.
Shareholders of W anderer Consolidated Gold Mines have received a dividend equal to 5%, th e first distribution m ade by the com pany since its form ation in 1928.
N orthern R hodesia.—The Rhodesia Broken Hill com pany announced early this m onth th a t th e zinc plant had been brought into operation and was running satisfactorily.
The accounts of th e Bwana M’Kubwa Copper Mining Co., L td., for the year to Ju n e 30 last show a debit balance of ¿50,880, which was carried forward. The com pany now holds 550,000 shares in th e R hokana Corpora
tion, valued at £3,388,117.
D uring 1931 the N orth C harterland Explora
tion Co. (1910), L td., suffered a loss of
£17,308, increasing th e debit balance carried forward to £70,259. I t is stated th a t the trib u to r a t the Sasare mine has installed crushing machinery. The company is con
sidering th e advisability of throwing open its country to prospectors.
Gold Coast.—The Ashanti Goldfields Corporation has declared a final dividend of 25% , m aking a to tal of 75% for the year to Septem ber 30 last. In addition, a bonus of 2s.
per share is recommended.
The accounts of the Fanti Consolidated Investm ent Co., L td., for 1932 show a profit of £19,440, after allowing for depreciation of investm ents equal to £61,739 at December 31 last.
Shareholders of Tarkw a B anket W est have been informed, in connexion w ith the reopen
ing of the Obuom mine, th a t two adits are being driven on the South Section.
A capital reconstruction, w ith an assess
m ent, has been proposed by the directors of Sefwi Goldfields. A new com pany—Colonial Mining T rust—is to be formed, having a nominal capital in 5s. shares.
Tanganyika.—At an extraordinary meeting of Bukoba (Tanganyika) Tinfields, held last m onth, it was decided th a t the com pany should go into voluntary liquidation.
A ustralia.—The report of the Sulphide Corporation for the year ended June 30 last shows a n et loss of £55,844, which has been m et from reserves, the balance in “ Reserve for Contingencies ” now am ounting to £38,000.
Operations were resum ed a t the Central mine in April last and up to the end of June 31,522 tons of ore was raised, against 73,438 tons in the previous year, the output of th e mill totalling 4,918 tons of lead concentrates and 7,461 tons of zinc concentrates. The ore
reserves at the Central mine at the close of the year were estim ated to be 691,130 tons, as com pared w ith 707,834 tons at the end of the previous year. Operations at Cockle Creek were severely restricted, productive work being closed down during the first nine m onths of th e year on all b u t th e acid plants.
The retu rn of the Boulder Perseverance mine for Novem ber last gives some details of th e running of the new plant, which treated 6,529 tons of ore during the m onth, a t a cost of 15s. lOd. per ton. The change over took place on November 5 and the early difficulties were stated to have been overcome by the end of the m onth.
Shareholders of the W iluna Gold Corpora
tion were informed last m onth th a t exhaustive tests upon cyanide residues had been com
pleted and had shown th a t such m aterial could be profitably treated. A p lant for this purpose is being erected and is expected to be in operation by th e end of April. In the power plant th e first additional Diesel unit is now in operation.
It was announced last m onth by th e Sons of Gwalia com pany th a t £28,499 had been repaid to the W estern A ustralian Government on account of th e loan and th a t a further
£15,000 would be paid before the end of 1932, thus clearing off the whole of th e original loan of £76,132.
The report of the Mount Lyell Mining and Railway Company, Lim ited, for th e year ended September 30 last shows a profit of
£43,979. Of the balance of £595,523 standing at th e credit of profit and loss on Septem ber 30, 1931, £500,000 has been transferred to reserve, which now stands a t £1,246,684. A dividend equal to 6d. per share, absorbing
£38,750, was paid out of the profits for the year. The output of ore from the mines am ounted to 362,591 tons, 69,761 tons more th an in the previous year, the copper produc
tion being 10,956 tons. In addition 162,858 oz.
of silver and 4,769 oz. of gold were recovered.
The to tal ore reserves a t the end of the year were estim ated to be 4,285,653 tons, averaging 2-74% copper and 0-28 oz. silver and 0-02 oz.
gold per ton.
M alaya.—During the year ended Ju ly 31 last the Pahang Consolidated treated 84,900 tons of ore, recovering 1,515 tons of black tin, against 2,799 tons from 174,100 tons of ore in the previous year, these figures showing the effect of restriction. The profit for the year am ounted to £19,287, which, added to the sum brought in, gave an available to tal of
£58,672. Of this am ount £7,000 was required
for the paym ent of preference dividends and
£6,098 for depreciation, while £10,000 was transferred to reserve, leaving £35,574 to be carried forward. The com pany’s appeal against th e Tin and Tin Ore (Restriction) E nactm ent, which was dismissed by th e Court of Appeal in the F.M.S. in Ja n u a ry last, was heard before th e Judicial Committee of the P rivy Council in November and was again dismissed.
The report of M alayan Tin Dredging, L td., for th e year to Septem ber 30 last shows a profit of £33,336, increasing th e sum brought in to £146,759. Of th is am ount £32,500 has been d istributed as dividends, equal to 16J% , while £211 has been w ritten off property account, leaving £114,048 to be carried forward. U nder restriction a to tal of 1,117 tons of tin concentrates was produced, which realized £87,046, or an average of £77 17s. l i d . per ton, against 1,459 tons sold for an average price of £72 6s. 6d. per ton in the previous year.
The accounts of Southern M alayan Tin Dredging, L td ., for th e year ended June 30 last show a profit of £28,372, which, ad d ed to th e sum b ro u g h t in, gave an available to ta l of £47,158. Of th is am ount
£24,643 was d istrib u ted as dividends, equal to 7 |% , leaving £22,515 to be carried forw ard. T he q u a n tity of tin ore produced w as 1,129 tons, which realized an average price of £77 13s. 7d. per ton, as com pared w ith 2,075 tons, selling for £71 12s. 2d. per ton, in th e previous year. The reduction of o u tp u t was due to th e incidence of restriction.
D uring th e year to Ju n e 30 last Southern P erak Dredging, L td ., m ade a profit of
£4,586, increasing th e sum brought in to
£19,160, w hich was carried forward. The o u tp u t for th e year was 338 tons of tin concentrates, w orth £27,472, or £81 5s. 7d.
per ton, as against 491 tons, averaging
£72 8s. 7d. per ton, in the previous year, restriction being responsible for th e decreased o u tp u t.
The report of R am butan, L td., for the year ended Ju n e 30 last shows a loss of
£2,022, decreasing the credit balance brought in to £3,840, which was carried forward. The y e a r’s o u tp u t am ounted to 67J tons of concentrates, w orth £4,879. Since th e close of the year arrangem ents have been m ade w hereby th e com pany’s qu o ta will be pro
duced by Tekka-Taiping, L td., on a profit- sharing basis.
Shareholders of Sungei Besi Mines, L td., were inform ed early th is m onth th a t arrange
m en ts h ad been m ade for th e sale of th e com pany’s hydro-electric installation to th e F.M.S. G overnm ent for £200,000. In addition th e com pany will be en titled to receive 4,000,000 u n its of electricity per annum free of charge for a period of 20 years.
The sum received will enable th e com pany to p ay off th e m oney borrow ed in respect of its holding in P elepah Tin D redging, L td ., th e pontoon for whose dredge was success
fully launched last m onth.
The rep o rt of Serem ban for th e year ended Ju n e 30 last shows a loss of £803, reducing th e credit balance brought in to £576.
P eru .— I t is proposed th a t th e cap ital of the A nglo-French T icacam pa Silver Mining Co., L td ., be reduced from £200,000 to
£100,000 by cancelling 10s. on each of the issued £1 shares,
S p ain .—A t an e x trao rd in ary m eeting of San F in x Tin Mines, held last m onth, a scheme for th e reconstruction of th e com pany was approved. A new com pany is to be form ed under th e title of San F in x Tin Mines (1932), w ith a cap ital of £20,000 in 5s. shares. P resen t shareholders will be en titled to one share in th e new com pany, credited w ith Is. paid, for ev ery nine shares held, th e d ebenture holders accepting four fully-paid 5s. shares for each £1 of d ebenture stock.
P o r tu g a l.—A t a m eeting of- B eralt Tin and W olfram , L td ., to be held this m o n th , it will be proposed th a t th e cap ital of th e com pany be increased from £170,000 to
£250,000 b y th e creation of 320,000 new 5s.
shares. I t is sta te d th a t no issue of shares is contem plated a t present.
A pex (T rinidad) O ilfield s. — The accounts of Apex (Trinidad) Oilfields, L td ., for th e year to Septem ber 30 last show oil profits am ounting to £332,457, th e final figure, after allowing for am o rtizatio n and head office expenditure, being £213,443.
A fter adding the am ount brought in, there was a to ta l sum of £313,558 available, of which £40,000 was placed to general reserve,
£40,528 to Incom e T ax reserve, a n d £125,000 d istrib u ted as dividends, equal to 25% . A fter m aking oth er allowances a sum of
£101,780 was carried forw ard. P ro d u ctio n of oil during th e year under review to talled 542,624 tons, as com pared w ith 522,194 tons in th e previous year, while th e enlarged casing-head gasolene p la n t produced 1,308,389 Im perial gallons, equal to ap p ro x i
m ately 3,950 tons.
T H E RECOVERY OF ALLUVIAL DIAMONDS
By K E N N E T H M cL E O D , A . R . S . M . , Assoc.M .I.M m .E.
T h e author d e s c r ib e s p a n p la n ts a n d m e c h a n ic a l tro m m e l p la n ts fo r th e w a s h in g an d con centration of alluvial d ia m o n d s o p e r a tin g in G o ld C o a s t C o lo n y a n d c o m p a r e s th e tw o ty p e s.
In t r o d u c t i o n;— The m ethod of working
alluvial diam ond areas in th e Gold Coast Colony by pan plan ts has already been described in these pages,1 b u t th e w riter has found no reference in technical literatu re to th e m echanical trom m el plan ts th a t operate in th e same field. The object of th e present article, therefore, is to describe th e m echanical trom m el p la n t an d com pare it with th e pan p lant. The tw o types of plant are exam ined in detail w ith th e object of disclosing th e province of each. The types of plant described are common in W est Africa and in th e Belgian Congo. F u n d a m entally similar, b u t w ith variatio n in design, th e v form a class of p lan t th a t is
series of powerful jets to assist in the breaking down of th e consolidated m aterial as it is buffeted, pounded, and throw n to and fro in its disordered passage through the trom m el.
The undersize from th e screen is received in an apron for delivery to th e pans. The plus § in. m aterial th a t is discharged consists of lum ps of clay th a t have not been sufficiently reduced in size and countless stones from f in. to 4 in. or 5 in. diam. A copious and strong w ater service over this screened area helps to clean th e stones, etc., prior to their discharge and to provide th e w ater for th e pans.
The oversize is received in an apron, from
id e ly used for th e washing and concentra-
i0p \tf
“ i S r ec o S « t i o n in a an p lan , (Fig. 1) I n to a f e dbelt conv® y°Lai" h vvlth a strong je t of opper, from > j main trom m el.
¿ * . 1S - * £ trommel is blind, the w o-thirds oi ^ g jn screen, which
e m a m i n g ag r u , rqjze for concentration andtl m * X^-r* c n n r p n + r a + i n n n n r l C 6 p t S the6 o v e r s i z e p a r t l y for further dis
ects m e , n a rt l y as barren w aste in egration an grauon v ,stones. A series of baffle\ C fortT1 this b l i n d length, together w ith the
a t e S .in a c t i o n o f large stones as th ey are )undin^ounCj t be trom m el and fall on the irried r rnucb the same w ay as m a tte r is ass a ball-mill), help in the p artial
ushU r a t i o n o f the clayey gravel. A pipe
‘sia1 trom m el impinges w ater in a
lSl .. M i n i n g Ma g a z i n e, No v. , 1 9 2 9 , a n d
which it grav itates down a steeply inclined steel-lined chute for delivery to th e washer, together w ith th e w ater supply from a 2 in.
pipe. The washer is a hollow steel cylinder, m ounted horizontally on rollers and kept in its slightly inclined position by suitable thrust-bearings. A series of internal baffles, sim ilar to those in the m ain trom m el, en
courage fu rth er breaking down of the m aterial and are assisted by th e continual pounding of th e large stones as th ey seek their discharge. For this reason it is advisable to allow m oderately large stones to pass into th e plant and not to restrict their entrance by an unduly narrow m outh to the elevator hopper or to remove them by hand from th e conveyor belt.
It is im p o rtan t th a t the washer be adequately loaded and supplied with sufficient w ater to ensure as clean a dis
charge as possible. The discharge end of the washer is equipped w ith a f i n . screen of a
for th e paym ent of preference dividends and
£6,098 for depreciation, while £10,000 was transferred to reserve, leaving £35,574 to be carried forward. The com pany’s appeal against th e Tin and Tin Ore (Restriction) E nactm ent, which was dismissed b y th e Court of Appeal in th e F.M.S. in J a n u a ry last, was heard before the Judicial Committee of the P rivy Council in Novem ber and was again dismissed.
The report of M alayan Tin Dredging, L td., for th e year to Septem ber 30 last shows a profit of £33,336, increasing the sum brought in to £146,759. Of this am ount £32,500 has been d istrib u ted as dividends, equal to 16J% , while £211 has been w ritten off property account, leaving £114,048 to be carried forward. U nder restriction a to tal of 1,117 tons of tin concentrates was produced, which realized £87,046, or an average of £77 17s. l i d . per ton, against 1,459 tons sold for an average price of £72 6s. 6d. per to n in th e previous year.
The accounts of S outhern M alayan Tin D redging, L td ., for th e year ended Ju n e 30 last show a profit of £28,372, which, ad d ed to th e sum bro u g h t in, gave an available to ta l of £47,158. Of th is am ount
£24,643 was d istrib u te d as dividends, equal to 7 J% , leaving £22,515 to be carried forw ard. T he q u a n tity of tin ore produced was 1,129 tons, w hich realized an average price of £77 13s. 7d. per ton, as com pared w ith 2,075 tons, selling for £71 12s. 2d. per ton, in th e previous year. The reduction of o u tp u t was due to the incidence of restriction.
D uring th e year to Ju n e 30 last Southern P erak D redging, L td., m ade a profit of
£4,586, increasing the sum brought in to
£19,160, w hich was carried forward. The o u tp u t for th e year was 338 tons of tin concentrates, w orth £27,472, or £81 5s. 7d.
per ton, as against 491 tons, averaging
£72 8s. 7d. per ton, in th e previous year, restriction being responsible for th e decreased ou tp u t.
The report of R am b u tan , L td ., for the year ended Ju n e 30 la st shows a loss of
£2,022, decreasing the credit balance brought in to £3,840, which was carried forward. The y e a r’s o u tp u t am ounted to 67J tons of concentrates, w orth £4,879. Since th e close of th e year arrangem ents have been m ade w hereby th e com pany’s q u o ta will be pro
duced by T ekka-Taiping, L td ., on a profit- sharing basis.
Shareholders of Sungei Besi Mines, L td., were inform ed early th is m onth th a t arrange
m ents h ad been m ade for the sale of the com pany’s hydro-electric installation to the F.M.S. G overnm ent for £200,000. In addition th e com pany will be e n titled to receive 4,000,000 u n its of electricity per annum free of charge for a period of 20 years.
T he sum received will enable th e com pany to p ay off th e m oney borrow ed in respect of its holding in Pelepah Tin D redging, L td ., th e pontoon for whose dredge was success
fully launched last m onth.
The re p o rt of Serem ban for th e y ear ended Ju n e 30 last shows a loss of £803, reducing th e credit balance bro u g h t in to £576.
P eru .— I t is proposed th a t th e cap ital of th e A nglo-French T icacam pa Silver M ining Co., L td ., be reduced from £200,000 to
£100,000 b y cancelling 10s. on each of the issued £1 shares,
S p a in .— A t an e x tra o rd in a ry m eeting of San F in x Tin Mines, held last m o n th , a scheme for th e reconstruction of th e com pany was approved. A new com pany is to be form ed u n d er th e title of San F in x Tin Mines (1932), w ith a cap ita l of £20,000 in 5s. shares. P resen t shareholders will be en titled to one share in th e new com pany, credited w ith Is. paid, for ev ery nine shares held, th e d ebenture holders accepting four fully-paid 5s. shares for each £1 of d ebenture stock.
P o rtu g a l.— A t a m eeting of- B eralt Tin and W olfram , L td ., to be held th is m onth, it will be proposed th a t th e cap ital of the com pany be increased from £170,000 to
£250,000 b y th e creation of 320,000 new 5s.
shares. I t is sta te d th a t no issue of shares is contem plated a t present.
A pex (T rinidad) O ilfield s. — The accounts of A pex (Trinidad) Oilfields, L td., for th e year to S eptem ber 30 last show oil profits am ounting to £332,457, th e fina'l figure, after allowing for am o rtizatio n and head office expenditure, being £213,443.
A fter adding th e am ount brought in, there was a to ta l sum of £313,558 available, of which £40,000 was placed to general reserve,
£40,528 to Incom e T ax reserve, an d £125,000 d istrib u ted as dividends, equal to 25% . A fter m aking o th er allow ances a sum of
£101,780 was carried forw ard. P roduction of oil during th e year under review to talled 542,624 tons, as com pared w ith 522,194 tons in th e previous year, while th e enlarged casing-head gasolene p lan t produced 1,308,389 Im perial gallons, equal to ap p ro x i
m ately 3,950 tons.
T H E RECOVERY OF ALLUVIA L DIAMONDS
By K E N N E T H M cL E O D , A.R.S.M., Assoc.M.I.Min.E.
T h e a u t h o r d e s c r ib e s p a n p la n ts a n d m e c h a n ic a l tro m m e l p la n ts fo r th e w a s h in g a n d c o n c e n tra tio n of a llu v ia l d ia m o n d s o p e r a tin g in G o ld C o a s t C o lo n y a n d c o m p a re s t h e tw o ty p e s.
In t r o d u c t i o n.—The m ethod of working alluvial diam ond areas in th e Gold Coast Colony by pan plan ts has already been described in these pages,1 b u t th e w riter has found no reference in technical literatu re to the m echanical trom m el plan ts th a t operate in th e same field. The object of th e present article, therefore, is to describe the m echanical trom m el p lan t an d com pare it w ith th e pan plant. The tw o ty p es of p lant are exam ined in detail w ith th e object of disclosing th e province of each. The types of p lan t described are common in W est Africa and in th e Belgian Congo. F u n d a m entally similar, b u t w ith variation in design, th e y form a class of p lant th a t is
series of powerful jets to assist in th e breaking- down of th e consolidated m aterial as it is buffeted, pounded, and throw n to an d fro in its disordered passage through th e trom m el.
The undersize from th e screen is received in an apron for delivery to th e pans. The plus | in. m aterial th a t is discharged consists of lum ps of clay th a t have not been sufficiently reduced in size and countless stones from § in. to 4 in. or 5 in. diam. A copious and strong w ater service over this screened area helps to clean the stones, etc., prior to their discharge and to provide th e w ater for the pans.
The oversize is received in an apron, from
Fi g. 1 .— De t a i l s o f a Pa n Pl a n t.
widely used for th e washing and concentra
tion of diam ond-bearing gravels.
P a n P l a n t s .— F o r concentration in a pan p lan t (Fig. 1) th e gravel is elevated by a belt conveyor and discharged into a feed hopper, from which, w ith a strong jet of w ater, it is w ashed into th e m ain trom m el.
Tw o-thirds of th e trom m el is blind, the rem aining th ird is of § in. screen, which accepts th e undersize for concentration and rejects th e oversize p a rtly for fu rth er dis
integration and p a rtly as barren waste in the form of clean stones. A series of baffle plates in this blind length, together w ith the pounding action of large stones as th ey are carried round the trom m el and fall on the m ass (in m uch th e same w ay as m a tte r is
c r u s h e d in a ball-mill), help in the partial d i s i n te g r a ti o n of the clayey gravel. A pipe
¡nside the trom m el impinges w ater in a
i T h e M i n i n g M a g a z i n e , N o v 1 9 2 9 a n d , 0 ne, 1 9 3 1 .
which it gravitates down a steeply inclined steel-lined chute for delivery to the washer, together with the w ater supply from a 2 in.
pipe. The washer is a hollow steel cylinder, m ounted horizontally on rollers and kept in its slightly inclined position by suitable thrust-bearings. A series of internal baffles, similar to those in the m ain trom m el, en
courage further breaking down of the m aterial and are assisted by the continual pounding of the large stones as they seek their discharge. F or this reason it is advisable to allow m oderately large stones to pass into the plant and not to restrict their entrance by an unduly narrow mouth to the elevator hopper or to remove them by hand from the conveyor belt.
It is im p o rtan t th a t the washer be adequately loaded and supplied with sufficient w ater to ensure as clean a dis
charge as possible. The discharge end of the washer is equipped with a § in. screen of a
Fi g. 2 . — Ha n d- Pi c k i n g Di s c h a r g e f r o m Se c o n d Wa s h e r.
sm aller diam eter th a n the washer itself, so th a t a bed of gravel and w ater can be m aintained, over which th e discharged m aterial m ust ride to find an exit. Once m ore m inus f in. and plus f in. products are form ed as undersize and oversize. The undersize is received in a chute and carried sideways to a dew atering box, from which it is tran sp o rted periodically to th e elevator an d so to th e pans for concentration.
The w asher oversize m ay be clean, in which case it is tra n sp o rte d and retu rn ed to the cut to level out th e w orked-out ground, or it
m ay be m oderately clean so th a t th e clay balls can be hand-picked (Fig. 2) an d set aside for fu rth er tre a tm e n t, or, lastly, th e im perfectly-w ashed oversize m ay be so excessive th a t th e whole of th e discharge requires re tre a tm e n t an d is dum ped for w eathering before it can be broken down easily. In some places th e ground is so com pact a n d clayey th a t it is extrem ely difficult to break th e clay balls as th e y are discharged, b u t a period of w eathering in th e open usually renders them so readily am enable to tre a tm e n t th a t expensive m achinery can be dispensed w ith in favour of n a tu ra l m ethods a t no cost.
F o r efficient w ork it is only necessary to retain th e gravel in th e w asher for th e tim e ju s t required to w ash it. The baffles can be so arranged, w ith a little care, th a t th e ra tio betw een th e plates th a t advance th e w asher product to those th a t re ta rd its progress is such th a t th e feed is retain ed only for th e tim e required to produce as clean an oversize as possible an d to break down th e gravel sufficiently to allow it to pass th e § in.
screen. W here th e ground is difficult to tre a t tw o w ashers m ay be used in series (cf. Figs. 3 and 4). The § in. m aterial th a t passed through th e la tte r end of th e m ain trom m el by w ay of th e § in. screen is led to No. 1 pan by an ap p ro p riate chute tan g en tial to it, so th a t th e gravel is received a t th e periphery of th e pan.
C oncentrating pans v a ry in size an d shape, b u t those w ith which th e w riter has h ad experience are 10 in. deep an d 8 ft. in diam eter, w ith vertical sides. These pans are m ore common an d are to be preferred in the w rite r’s opinion to those w ith sloping sides. A vertical spindle, resting on a journal bearing an d driven by crown wheels from the m ain shaft, supports eight horizontal arm s, braced to each oth er b y angle irons.
Fi g. 3 . — Pa n Pl a n t w i t h On e Wa s h e r.
