tas, g
The Mining Magazine
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Br a n c h Of f i c e s •
Vol. X L V I 1 I . No. 3. L O N D O N , M A R C H , 1933.
P R I C E O N E S H I L L I N GC O N T E N T S
Ed i t o r i a l
Notes ... 130
The Gold F ie ld s ’ N e w C hairm an; S kin n er’s “ M ining Y ear B o o k ’’ ; M ining R esearch a t Sheffield U n iv e r s ity ; M ines D ep a rtm en t C o m m ittee on O v erw in d in g ; Changes a t th e Cam borne S ch o o l of Mines ; W orld Rower C o n fe r e n c e ; N o m in a tio n s of the Am erican I n stitu te ; T h e F u tu re of D o lc o a th ; B ritish In dustries F a i r ; T h e A m erican D eb t.
The In stitu tio n Meeting ... 131
A n a ccoun t o f the discussion of tw o pap ers read a t the F ebruary m eetin g.
Research and In d u stry ... 132
T h e report o f th e A d visory Council o f th e D epartm en t o f Scien tific and Industrial R esearch fo r 1 9 3 1 -3 2 is review ed. R e v i e w o f M i n i n g ... 134
Ar t i c l e s
The Tin-Tungsten D eposits of Stew art Island, New Zealand
Gordon W illiam s 137 A description o f the m ode o f occurrence o f w olfram ite and c a ssiterite on this island.American Gravel- and Sand-Dressing Practice ... H. G. Sm ith 143
The auth or describes current A m erican p ractice in the preparation o f san ds and gra v el fo r th e m arket.M otor-Lorry Tests . . . . S. V. Griffith 150
A com parison o f c o s t facto rs o b tain ed d u ring a series o f te s ts w ith six ty p e s of m otor-lorry. Le t t e r t o t h e Ed i t o r“ The American D ebt ”
H . Foster B a in 15 2 Bo o k Re v i e w s W illiam s’ “ T he G enesis of th e D iam o n d ” Dr. A rth u r Holmes 154 S tu tze r a n d W etzel's “ P h o s p h a t-N itra t ” Dr. W. R . Jones G ro u t’s “ P e tro g ra p h y a n d P etro lo g y ” Dr. A . B ram m all 157 D a v is’ " A F re n c h -E n g lish V o c ab u lary in G eology a n d P h y sic a l G eology " Dr. W. R . Jones 157 Ne w s Le t t e r sJ o h a n n e s b u rg ... 158
Gold M ining In d u str y ’s N e w P o l ic y ; W estern Rand E x te n sio n ; W e st W itw atersrand A r e a s ; W itp oort N o . 14 ; P la tin u m in R h odesia.
3—2 129
P A G E V a n c o u v e r ... 159C a r ib o o ; B ridge R i v e r ; N elso n ; S h eep C r e e k ; Lardeau ; B ou n d a ry ; C oast. T o r o n t o ...
161
Sudbury ; Porcupine ; K irkland L ake ; O ther O ntario G oldfields ; N o rth -W estern Q uebec ; M anitoba. B r i s b a n e ...
163
M ount Isa ; M ount C oolon G oldfields ; M ount Morgan ; N ew G oldfields ; L ast Y e a r ’s Mineral O utp ut ; Pla tin u m in Papua ; T h e G ranites, Central A ustralia ; M ount L yell. Pe r s o n a l...
165
Tr a d e Pa r a g r a p h s...
165
C lim ax A ir-L ine L u b ric a to r ... 166
L o ngyear A ir P r o s p e c t o r ... 166
B eiliss a n d M orcom Diesel E n g in e ... 167
B ritish In d u strie s F a ir ... 168
W akefield's “ A yrlyne ” L u b ric a to r ... 170
Me t a l Ma r k e t s...
171
St a t i s t i c s o f Pr o d u c t i o n ...
173
Pr i c e s o f Ch e m i c a l s ...
175
Sh a r e Qu o t a t i o n s ...
176
Mi n i n g Di g e s t T he W edza P la tin u m Mine, S outhern R h o d esia E . Golding O re T re a tm e n t a t th e P re m ier Mine W. J . A sselstine and D. L . Coulter H e m a tite in Sierra Leone . . K . F ow ler-L unn M in erag rap h y ... F. L . Stillwell Skip C apacities ... A . Clemes A n A u to m atic-D u m p in g Cage L. G. M orrell P o tassiu m F e rro cy a n id e as a C oagulant C. T . Creed and C. F. Cayton-Boxall Gold in N o rth -W e ste rn Q uebec. .A . B uisson 177 178 183 185 186 188 188 189 156 Sh o r t No t i c e s... 19 0 Re c e n t Pa t e n t s Pu b l i s h e d ... 191
Ne w Bo o k s, Pa m p h l e t s, e t c. 191 Co m p a n y Re p o r t s ... 192
B a tu C aves T in D r e d g in g ; B a tu Selan gor Tin D r e d g in g ; G eldenhuis D e e p ; R a n ta u Tin D r e d g in g ; V illage D eep. Di v i d e n d s De c l a r e d... 192 Ne w Co m p a n i e s Re g i s t e r e d... 19 2
E D IT O R IA L
T H E ap p o in tm en t of Mr. J. A. Agnew as chairm an of th e C onsolidated Gold F ields of S outh A frica is of in terest, as it places a t th e head of th is im p o rta n t u n d e r
tak in g one who has spent m a n y y ears on th e p ra c tic a l side of m ining.
L AST m onth th e 1933 edition of S k in n er’s
“ Mining Y ear Book ” — th e forty- seventh annual issue—was published. This w ork contains particulars of th e w orld’s principal m ining companies and as m ore foreign undertakings are added each year its international character continues to grow, a fact which adds to its value for all associated w ith th e industry.
T H E U niversity of Sheffield last m o n th issued a booklet containing p articu lars of research w ork carried out in th e d e p a rt
m ents of m ining an d fuel technology during th e 1931-32 session. The efforts of th e school are alm ost entirely connected w ith coal mining, th e booklet describing in n on
technical language th e w ork th a t has been already rep o rted in th e technical press.
A COMMITTEE has recen tly been appointed by th e Mines D epartm ent to inquire into th e precautions which m ay be tak en to prevent overwinding. The chairm an is Mr. F. H. W ynne, D eputy Chief Inspector of Mines, and th e m em bers Messrs. J. M. Gillians, B. J. Marson, H. M.
Morgans, J. A. S. R itson, and R. Shirkie, Mr. J. E. H enshaw being secretary.
C HA N G ES in th e direction of th e Cam
borne School of Mines are shortly to be effected. Mr. C. V. Thom as has resigned his position as chairm an of th e Governors and is to be succeeded by Mr. H arry Rich, Mr. Thom as rem aining on th e com m ittee of th e school. In addition Mr. R. A. Thom as and Mr. T. Knowles are to retire, although th e la tte r will continue to act as secretary to th e Governors. T he appointm ent of th e new principal is aw aited w ith interest.
A SECTIONAL m eeting of th e W orld Power Conference is to be held in Stockholm between Ju n e 26 and J u ly 10
n ex t, when delegates will discuss th e energy problem s of large-scale in d u stry an d trans
port. A num ber of visits a n d excursions in Sweden, D enm ark, N orw ay, an d Finland have been arranged for those attending th e conference, which, it is felt, will afford a unique o p p o rtu n ity for th e industrialist and th e power engineer to come in to contact.
T WO nom inations are announced by the American In stitu te of Mining and M etallurgical Engineers—th a t of D r. Frederick M. Becket as president for th e ensuing year and th a t of Mr. Jam es O. E lto n as James Douglas m edallist. D r. B ecket’s election is notew orthy in th a t he is a Canadian and a g rad u ate of McGill U niversity. He has been in tim ately associated w ith the advance of electro-m etallurgy, having been connected since 1903 w ith th e Niagara Research L aboratories an d its successor companies.
S P E A K IN G recently in Cam borne, Mr.
C. V. Thom as in tim a te d th a t the receiver a t present in charge of th e Dolcoath m ine, appointed by th e G overnm ent, was likely to be w ithdraw n an d th e machinery dism antled. Mr. Thom as felt th a t such a step was m uch to be deprecated, as, if th e receiver were p e rm itte d to remain u n til tin prices im proved, som ething might be done to re sta rt th is fam ous old mine.
T his is an opinion w ith w hich one can hardly fail to agree, in view of th e deplorable unem ploym ent situ atio n in th e county.
T H E B ritish In d u stries F a ir continues to grow, although th is y ear witnessed a fu rth er falling off in th e su p p o rt accorded it by th e heavy industries. Regrettable though th is ab sten tio n m ay be, since it d etracts som ew hat from th e representative character of th e Fair, it is h a rd ly surprising in view of th e considerable expense incurred in th e tra n sp o rt of heavy p la n t, apart from th e cost of running it. As w as pointed out last year, th e tendency am ong such industries is to reserve th eir expenditure for th e specialized exhibitions generally held in London in th e au tu m n . Never
theless, as is evident from th e details published elsewhere in th is issue, there was even this year p len ty a t Birmingham to interest th e m ining m an.
130
MARCH, 1933 131
E L S E W H E R E in this issue is a letter from Mr. Foster Bain, com m enting on the article on th e American D ebt which appeared in our Ja n u a ry issue. I t will be seen th a t th e lette r is not only more lengthy but m uch m ore controversial th a n our editorial an d th e m any points Mr. Foster Bain raises will doubtless be dealt w ith by those concerned in carrying through the forthcoming negotiations. As in th e Ja n u a ry issue we clearly expressed our view, it is now only fair to give th e other side, and it will readily be conceded th a t in this respect we have erred on the generous side. In view of the banking crisis in th e U nited States, however, it is interesting to note the recently-published statem en t of th e Swedish economist, Professor G ustav Cassel, to the effect th a t “ W hen th e U nited S tates in December insisted on th e p aym ent of w ar debts this proved a final blow to A m erican economic life.”
The In stitu tion M eeting
A t the February m eeting of the In stitu tio n of Mining and M etallurgy two papers of widely different character were presented for discussion—one by Messrs. V. T. E dquist, C. Valentine, and Norman D unstan on the use of gas power at the Sons of Gwalia mine, W estern Australia, and the other by Mr. C. B. E. Douglas entitled “ N ative W ire Silver : Notes on its Form ation and Possible Significance.” The first paper was introduced by Mr. W. A. Macleod, of Messrs. Bewick, Moreing, and Co., the general m anagers of the Sons of Gwalia mine, who, it will be recalled, was himself the au th o r of a paper read before the In stitu tio n in December, 1926, on the subject of in tern al com bustion engine power for mines, in which reference was made to this p lant, a precis of this part of the paper being published in the
Ma g a z in ea t the tim e. The second paper was introduced by Sir H arold Carpenter.
B oth contributions were full of interest and the ensuing discussions fully occupied the time available.
In introducing the first paper Mr. Macleod drew atten tio n to the m anner in which the work described had developed, pointing out th a t there was a m arked tren d tow ards the simplification of equipm ent, the power used a t th e present tim e being economically produced w ith little or no trouble. The Sons of Gwalia mine is situated near M ount Leonora, in the N orth Coolgardie
goldfield, and gas power was first used there in 1911, th e original p lan t being added to in 1912. The first u n it of this original p lan t used an up-draught suction-gas pro ducer, w ith m ulga charcoal as fuel, while th e second u n it was operated b y a down
d rau g h t wood producer. In 1921 th e p lant and power house were destroyed b y fire a n d in th e course of th e reorganization which followed this disaster it was decided to operate all b u t th e winding p lant electrically and to replace th e steam -driven air-compressors b y gas-driven units. This change necessitated the installation of engines giving continuous service under try in g con
ditions, th e tem p eratu re of th e engine-room in sum m er frequently rising to over 135° F., and those installed, of th e Crossley-Premier horizontal type, have proved em inently suitable for th e conditions obtaining in such an isolated situation. As regards the producers them selves, th e tendency has been to develop th e dow n-draught ty p e and those a t present in use at the mine are th e outcome of research b y m an y workers, am ong whom m ention should be m ade of Mr. W. R. D egenhardt and th e late Messrs.
Jo rd an and Beech, as well as th e authors of the present paper. I t has to be rem em bered th a t conditions a t th e pro p erty rendered th e adoption of gas power necessary, in view of the scarcity of fresh w ater and fuel supplies. The wood fuel available is being draw n from th e bush a t a distance of 40 miles from the mine and is delivered b y rail a t a cost of 18s. per ton. F or actual details of the p la n t the reader is referred to the paper itself, which forms a valuable supple
m ent to th a t by Mr. Macleod, and m uch new practical inform ation has been m ade available b y its publication. The costs are p articu larly instructive and th e figures for the 500 h.p. No. 1 Prem ier gas-electric set, covering th e years 1926 to 1931, show th a t the running tim e was 50,020-6 hours, or 95-12% of th e full tim e possible, the o u tp u t being 13,289,460 units for an average consum ption of 3-91 lb. m oist fuel per u n it and an average cost of 0-714d. per unit.
More recent practice has im proved even on
these figures, the o u tp u t of the combined
gas-electric sets during the m onth of July,
1932, being obtained a t a ru n n in g 'c o st of
0-68d. per unit. Y et one more item deserves
m ention, th a t of w aste-heat recovery. The
first recuperators installed came from
G ermany, b u t the last was m ade in A ustralia,
the satisfactory perform ance of the equip
132
m ent being reflected in th e a u th o rs’ s ta te m ent th a t the estim ated saving in fuel cost for the steam w inding p lan t re su lta n t on th eir installation has in less th a n three years been equal to the capital cost of th e plant.
Discussion of the paper was in itiated b y Mr. D egenhardt, who referred to the keenness w ith w hich research on th e use of gas power h ad been prosecuted in W estern A ustralia and w ent on to review early difficulties, concluding w ith a com parison between th e cost of wood and oil fuels a t the mine. Messrs. A. K. Bruce and W. A.
Tookey—nam es well known in th e world of m echanical engineering—and Messrs. H.
Morgans, S. H. de la Mare, L. A. Skinner, T. J. T aplin, and th e president, Dr. Sydney Sm ith, also took p a rt in th e discussion.
T he general in te rest aroused b y th e paper seemed to show th a t th ere was some tr u th in Mr. M acleod’s contention th a t th e tim e was ripe for another general discussion on power generation.
W hile th e first paper would appeal to the m echanically m inded, th e second was of interest more p articu larly to m etallurgists and geologists. The au th o r states th a t he has n o t been convinced b y th e widely-held opinion th a t all n ativ e silver was deposited from solution and he had set out to endeavour to produce it by other means.
W ith th is end in view he h ad b u tto n s of silver sulphide m ade w ith which to experi
m ent, the b u tto n s being prepared by m elting freshly-precipitated silver sulphide in glazed crucibles in an electric furnace, th e surface of the b u tto n s being protected b y a charcoal cover. U nder these conditions it was found th a t some m etallic silver h a d separated and fu rth er .work a t lower tem p eratu res con
firmed this, m etal of the “ wire ” form growing in each case. The au th o r was th u s able to show th a t m etallic silver can grow on th e sulphide a t low tem peratures under oxidizing conditions and he draw s the obvious inference th a t there is no reason w hy th e n ative m etal should n o t have been formed from argentite a t tem peratures not m uch above norm al in th e course of geological tim e. The im portance of th e results of these simple experim ents was m entioned by Sir H arold C arpenter in his introduction and although, as D r. Fisher ultim ately pointed out, th e results are n o t strictly new th e low tem peratures a t w hich th e reaction can tak e place have been sharply b rought to th e notice of research workers. The author, m odestly enough, suggests th a t th e work m ay be w o rth y of fu rth e r investigation
b y others b e tte r equipped to c a rry it out and one was able to g ath er from th e intro
d u cto ry rem arks th a t his suggestion is not likely to rem ain unheeded.
R esearch and In d u stry
In review ing th e re p o rt of th e advisory council of th e D e p artm en t of Scientific and In d u stria l R esearch last year it was pointed out th a t th e w ork of this departm ent is of considerable im portance to th e mining m an, for, if research on production methods is a necessity for th e p rim ary commodity, it is equally im p o rta n t th a t th e utilization of th e com m odity should be actively investigated. F or th is reason, although so m uch of th e routine of th e departm ent is concerned w ith th e uses to w hich th e raw m aterials of production can be put, its activities m a y be considered w orthy of review. The new re p o rt,1 covering the year 1931-32, contains an adm irable summary of th e progress of in d u strial research in this c o u n try and th e g rad u al aw akening of the scientific m in d to in d u stria l realities is as well illu strate d as is th e tard in ess with which in d u stry utilizes new m aterials placed a t its disposal. I t is to be observed th a t in n early every in d u stry to -d ay movements are on foot to find new uses for old materials and m ining m en will be well aw are, for exam ple, th a t such an organization has been formed under th e auspices of th e Tin Pro
ducers’ A ssociation to u n d ertak e research and to conduct p ro paganda an d development w ork for extending th e uses of th a t metal.
Clearly, therefore, it is recognized that in d u stry is best able to help itself in this direction, for th e atte n tio n of the Depart
m ent should be directed to w ard s finding suitable uses for new pro d u cts. Industry often seems slow to realize, however, that science has m an y p ractical results waiting to be applied a n d there is an appreciable lag here which m ay well be speeded up. It is possible th a t if m ore business concerns could be induced to give financial support to th e w ork th a t is being done w ith the p articu lar products in w hich th e y are interested a step would have been taken tow ards lessening th e tim e gap between discovery and in d u strial application. It is interesting to note, therefore, th a t the advisory council to th e D ep artm e n t has given some consideration to a suggestion
1 R e p o rt of th e D e p a rtm e n t of Scientific and I n d u s tria l R e se arc h , 1931-32. H .M . Stationery Office. P ric e 3s.
MARCH, 1933 133 that Research Associations should be placed
in a stable financial position by m eans of an Enabling Bill passed by P arliam ent, which would give a u th o rity to raise funds from industry for purposes of industrial research.
Inquiry in this direction, however, served clearly to indicate th a t the general tren d of opinion was th a t if industries could not be persuaded to support research little was to be gained by forcing them to do so. I t is w orth observing th a t it was generally feared th a t statu to ry action of this n atu re would m ean a loss of lib erty of action b y th e various members of the research organizations and th a t in this m anner personal enthusiasm , such an im p o rtan t asset in the developm ent of new activity, m ight begin to wane. I t is probably tru e th a t live m em bers of a research organization would be the first to profit by a new discovery, b u t th e y have paid for it by their contributions and it seems unfair th at others, standing outside the organiza
tion’s activities, should be able to m ake use of its published results. The m a tte r is at present left in abeyance, b u t it is felt th a t something m ust be done by v o lu n tary effort to place the finances of particular organiza
tions on a sound footing or com pulsory levies m ay be necessary.
The report notes th a t in no branch of the D epartm ent’s activities was the depression so seriously felt as at the N ational Physical Laboratory, where the fall in receipts from testing fees and for special investigations m ade it especially difficult to m aintain a trained staff which would be in readiness for a return to better times. The w ork of the Laboratory’s m etallurgical d ep artm en t is mainly concerned w ith the physical structure of metals and alloys and w ith their properties under a set of specified conditions. Passing on to the activities of the Fuel Research Board, one of its m ost im portant tasks has been the continuation of the physical and chemical survey of th e national coal resources, while im portant w ork in connexion w ith low-temperature carbonization has been actively carried on, the horizontal reto rts at the Fuel Research Station having been rebuilt and set to work and two new brick retorts erected and tried out. The good results achieved by these new reto rts were recently described in a Technical Paper 1 and it is believed th a t considerable
1 “ L o w -T em p eratu re C arb o n iz atio n : N arro w B rick R e to rts a t th e F u el R ese arc h S ta tio n .” Fuel R esearch T echnical P a p e r N o. 35. H.M . S ta tio n e ry Office.
progress is being m ade tow ards solving some of th e outstanding problem s of low- tem perature carbonization. This new re to rt is cheap in capital cost, is easy to work, and gives good results w ith small labour requirem ents, w ithout producing unpleasant fume. As regards the hydrogenation of tar, the stu d y of the m ost suitable and economic catalysts has been continued, b o th static converters and small continuous plants being used for the purpose, while it is intended to proceed w ith th e erection of a plant capable of dealing w ith one ton of ta r per day. The use of the “ Elm ore ” flotation p lan t for experim ents in the cleaning of coal is said to have given very promising results and th e effects of “ w eathering ” are being investigated. The w ork of the Geological Survey of G reat B ritain in regard to geophysical investigations has been suspended, th e Survey’s ap p aratu s having been handed on loan to the Professor of Geophysics a t the Im perial College, where researches on this subject are being continued as p a rt of th e activities of th e new School of Applied Geophysics. In this connexion it is interesting to note th a t th e results obtained b y Professor A. H. Cox and Mr. S. W. Rice, of Cardiff, on th e use of electrical m ethods of survey for detecting approach to w ater-logged areas in coal m ining have been of a negative character.
W ork carried out a t various places for the M etallurgy R esearch B oard has included investigations into the behaviour of m etals a t high tem peratures, into the properties of light alloys and of th e m inor m etals, into th e casting of ordinary and alloy steels, and into th e cracking of boiler plates.
Electro-deposition is being investigated at Woolwich and Farnborough, while the B ritish N on-Ferrous Metals Research Association has continued its successful program m e.
A lthough th e results achieved by intensive
research of this character m ay sometimes
seem small, it should be rem em bered th a t
th ey often have far-reaching results. In this
connexion it m ay be recalled th a t the
presence of a trace of silver in th e copper
used for boiler tubes has m eant an immense
im provem ent in th e ir perform ance. The
m ain feeling in reviewing the activities of
this G overnm ent departm ent is one of
satisfaction th a t such m achinery exists as
will tak e care of the developm ent of
industrial uses for the m etals the miner
produces.
R E V IE W O F M IN IN G
In tro d u ctio n .—The m ajor event of the
p ast m o n th has been th e banking crisis in America, w hich has tem porarily affected business. A lthough th e U nited S tates has for a short period been v irtu ally driven off th e gold stan d a rd , th ere seems no reason w hy th is should last for a n y length of time, especially as such energetic m easures have been tak en b y those in control. In th e base- m etal in d u stry th e outlook for zinc has been im proved b y th e agreem ent reached betw een producers to prolong th e existing cartel u n til J u ly 1 next, while copper seems so far to have been b u t little affected b y th e cessation of agreed restriction a t th e end of 1932. The notice of an e x tra 2% cut in th e A p ril-Ju n e tin production of th e F.M.S.
appears to have acted favourably on th e price of th a t m etal.
T ran svaal.—T he o u tp u t of gold on the
R an d for F eb ru ary was 835,931 oz. and in outside districts 47,214 oz., m aking a to ta l of 883,145 oz., as com pared w ith 967,457 oz.
in Jan u ary . The num ber of natives em ployed in th e gold mines a t th e end of F eb ru ary totalled 222,589, as com pared w ith 222,005 a t th e end of Jan u ary .
The rep o rt of Crown Mines, L td., for 1932 shows a profit of £1,192,623, m aking, together w ith th e balance brought in and sundry item s, an available to ta l of £1,652424. Of, th is am ount, £730,873 was d istrib u ted as dividends, equal to 77 J% , while after m aking various allowances there was a balance of £503,493 to be carried forward.
The ore milled totalled 3,332,000 tons, yielding 1,042,063 oz. of gold w orth
£4,419,903, osm iridium and silver recovered bringing th e to ta l revenue to £4,427,983.
The to ta l ore reserves a t th e end of th e year were estim ated to be 13,742,950 tons, averaging 6'64 dw t. in value, as com pared w ith 12,997,390 tons, averaging 6 5 dw t., at th e end of the previous year. Shareholders of th e com pany have been inform ed th a t th e G overnm ent has accepted their application for a lease of th e underm ining rights of an area equal to approxim ately 829 claims adjoining th e com pany’s southern boundary.
The Anglo American Corporation has been granted the right to prospect over the tow n lands of Potchefstroom and to purchase m ineral rights for £12 10s. per m orgen, the ex te n t of such options to be n o t less th an 5,000 morgen. Meanwhile rich developm ents have been reported by th e W est Springs
com pany below th e 2 S.E. haulage. Driving w est from a new incline has exposed reef going 38-15 dw t. over 39 in., while to the east th e ore has been stru ck b y bore-hole 30 ft. below th e drive and is found to assay 14 dw t. over 50 in.
Shareholders of W itp o o rt Gold Areas (in liquidation) have been inform ed that th e whole of th e purchase m oney due from B rak p an Mines, L td ., has been received and th a t a first an d final dividend is to be made to shareholders registered on F eb ru ary 28.
W est R an d C onsolidated Mines, L td., has announced th a t it is proposed to increase th e cap acity of th e p lan t to 120,000 tons per m o n th and th a t th e necessary additions should be com pleted before th e end of the cu rren t year.
In publishing th e ore-reserve estim ate for the end of 1932 th e directors of th e Wit- w atersrand D eep announce th a t th e life of th e m ine for incom e-tax purposes has been determ ined b y th e G overnm ent mining engineers at six years from J a n u a ry 1 last, no allowance being m ade in th is estim ate for ore th a t m ay be added to th e reserves consequent on the d ep a rtu re of th e Union from th e gold sta n d ard . T he available ore reserves at D ecem ber 31 la st were estimated to be 596,000 tons, averaging 6-2 dw t. in value over a stoping w id th of 51 in.
In th e last issue of th e
Ma g a z i n ethe decision of th e directors of th e Sub Nigel to increase th e cap ac ity of th e reduction p lan t to ap p ro x im ately 41,000 tons a month was announced an d it is now know n that a new issue of cap ital is contem plated. In addition to th e installatio n of additional equipm ent, a new sh aft is projected in the n o rth ern section of th e p ro p erty , which it is expected will go down ab o u t 5,000 ft.
V ogelstruisbult Gold Mining Areas, in w hich th e Gold Fields, R an d Mines, and Anglo A m erican groups are interested, has now been registered in S outh A frica with a cap ital of £507,500. T he new company is to acquire an d exploit a large mining area on th e F a r E a st R and.
I t is sta te d th a t th e H .E . P ro p rie ta ry has secured an option over a large area in the W est W itw atersrand, close to th a t recently acquired by th e Gold Fields Com pany. I t is expected th a t th e com pletion of negotiations will e v en tu a te in th e flo tatio n of a company capitalized a t £500,000 to u n d e rtak e the developm ent of th e area.
134
MARCH, 1933 135
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received end is to lee
® February
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t to 120,1:
ecessary addfc re the end of serve estimaa :tors of tie f :e that the I purposes has :■
vemment i m January 1i I to the r a ture of the t
The avaOabk ast w e estk aging 6-2 dm h o f 51 in.
h e M
a g mof the Sol S of the red®
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is projected it: property. ® n about 5,OOOi Mining A ®
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are ! South A f® i The new coup ,it a large
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Me area»to that 0 -, Compi
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i
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undertaieD ia m o n d s.—The rep o rt of th e Prem ier
(Transvaal) D iam ond Mining Co., L td., for the year to October 31 last shows a loss of
£60,554, which has been m et from the balance in hand of th e trad in g fund, which now am ounts to £149,205, th e deficit including a loss of £37,666 on exchange.
Diamond sales to talled £83,587, as against
£278,403 for th e previous year. Operations at the com pany’s mines were closed down on March 31 last, b u t th e yield of the-g ro u n d treated during th e period w orked was 22 carats per hundred loads, th e highest average obtained for some tim e.
Southern R hodesia.—The o u tp u t of gold
from Southern Rhodesia during J a n u a ry was 48,656 oz., as com pared w ith 52,096 oz.
for the previous m onth and 42,706 oz. in January, 1932. O ther o u tp u ts for J a n u a ry were : Silver, 8,342 oz. ; coal, 31,520 tons ; chrome ore, 2,006 tons ; asbestos, 2,675 tons ; mica, 1 t o n ; tin, 1 ton ; iron pyrites, 657 tons.
The report of the W anderer Consolidated for the three m onths to December 31 last shows th a t work in connexion w ith the sinking of the W anderer incline shaft was commenced and good progress m ade w ith the prelim inary excavations, while actual sinking and rising is in hand betw een the 5th and 8th levels. D evelopm ents in the Ashton section are said to have given satis
factory results, good values over a large area having been disclosed on the 6th level.
Shareholders of the Cam and M otor Gold Mining Co. (1919), L td., were inform ed last m onth th a t the reduction of capital decided upon in Ja n u ary last had been sanctioned by the Court and th a t paym ent would be made during the present m onth.
The directors of the B ritish S outh Africa Company have decided not to recom m end the paym ent of a dividend a t the m eeting to be held this m onth.
Northern R hodesia.—The report of Roan
Antelope Copper Mines, L td., for the three m onths to December 31 last shows th a t 406,000 short dry tons of ore, averaging 3-68% total copper, was m ined and milled, 9,398-91 long tons of blister copper being produced. The average to ta l costs for the quarter were estim ated to be equal to
£22 8s. 2d. per long ton, before allowing for debenture interest and depreciation.
Single-stage grinding has been successfully developed and this is said to result in a substantial reduction in power consum ption, as well as increasing the capacity of the mill.
A circular to shareholders of Luiri Gold Areas last m onth sta te d th a t as the additional funds necessary for developm ent had not been secured it was proposed to create a series of debentures for £40,000 to provide the working capital required.
Shareholders of the N orth C harterland E xploration Com pany have been inform ed th a t the public inquiry into the com pany’s title is to be reopened, in order th a t fu rth er evidence and inform ation m ay be laid before the Commissioner.
G old C oast.—A t
an extraordinary m eeting of th e A tta Gold Com pany held this m o n th it was approved th a t th e capital of th e com pany should be increased to
£100,000 by the creation of 600,000 additional 2s. shares. The com pany has agreed to purchase th e Besiasi concession, in the K w ahu district, the purchase price of
£30,000 being taken in shares, while 100,000 new shares are offered to the existing shareholders a t par.
Resolutions proposing th a t the capital of th e Central W assau Gold Mines, L td., should be increased b y £50,000 to £150,000 in 2s. shares were approved a t an e x tra ordinary m eeting held this m onth. The com pany, which u ntil recently held a one- fourth interest in th e Beposo p ro p erty on the A shanti belt, has now acquired a fu rth er one-fourth interest, th e vendors accepting fully-paid 2s. shares in settlem ent of the purchase price of £20,000.
B elgian C ongo.— I t has been announced
th a t from April 1 nex t th e Union Minière du H a u t K atan g a will increase its production of copper from 40,000 to 56,000 tons per annum .
U ganda.—A progress report issued by
K agera (Uganda) Tinfields, L td ., states th a t the 1932 o u tp u t totalled 308 tons of con
centrates, production costs showing a sub
sta n tial im provem ent over those of previous years. T he capacity of the existing plan t is to be extended, while arrangem ents have been m ade to resume exploratory work at Nam herere.
K enya.—The o u tp u t of gold from Kenya
during 1932 was estim ated to be 10,731 oz., of which 6,221 oz. was produced on the K akam ega field.
A u stralia.—The report of the Broken
Hill P ro p rietary Com pany for th e four
weeks to F eb ru ary 19 last states th a t good
progress has been m ade w ith th e erection
of a small treatm en t p lant a t the H annans
N orth m ine, Kalgoorlie, purchased last
136
year. O ther gold-mining activities of the com pany are reflected in the news th a t th ey are drilling th e E nterprise G roup Leases, Kalgoorlie, and hold options over alluvial properties near W ellington and Bingara, New South Wales.
Shareholders of Lake View and S tar, L td., were inform ed last m o n th th a t th e New Consolidated Gold Fields h ad exercised its option over 100,000 Lake View shares of 4s. each a t 10s. per share. The Lake View has recently declared a second interim dividend of 6d. per share.
Advice from th e G reat Boulder P ro p rietary Gold Mines states th a t the ore reserves a t Decem ber 31 last were estim ated to be 204,792 tons, containing 81,792 oz. of gold, in addition to 333,208 tons of probable ore. The reserves in sight a t th e end of the previous year were estim ated to be 132,139 tons, containing 53,694 oz.
An im p o rtan t com pany has been registered in Melbourne under th e title of th e W estern Mining Corporation, w ith a cap ital of
£500,000. The chairm an of th e new com pany is Mr. Colin F raser and it has been formed to carry on m ining business thro u g h o u t A ustralia. The m em bers of th e W estralian advisory com m ittee are Messrs. H. E. Vail, R ichard H am ilton, and J. W. Sutherland.
N ew G uinea.—The discovery of new
dredging areas by New Guinea Goldfields was announced in these columns last m onth.
A rrangem ents have now been m ade to send out a well-known engineer to estim ate th eir value and to advise on plans for their working.
India.— I t was announced la st m onth
th a t some exceptionally wide patches of ore h a d been encountered while stoping in the O riental section of th e N undydroog mine.
This com pany has ju st declared a dividend of 4s. per share, m aking a to ta l distribution of 6s. per share, equal to 60% , as com pared w ith 2s. 9d. per share in th e previous year.
The breakdow n of an underground winding engine on th e Ooregum mine last m onth was expected to interfere seriously w ith th e m o nthly ou tp u t.
B u rm a .—The Anglo-Burm a Tin Company
announced last m o n th th a t it h ad purchased a t p ar £6,150 of its debentures, which have been cancelled.
M alaya.— An advance rep o rt of Petaling
Tin for th e year to O ctober 31 last shows a profit of £50,635, which, w ith £26,679 brought in, gave an available to ta l of
£77,314. Of th is £46,667 has been dis
trib u te d as dividends, equal to 20% , leaving
£30,647 to be carried forward.
' An issue of £400,000 4% prior lien debenture stock has been placed privately b y th e P erak R iver H ydro-E lectric Power Co., in accordance w ith a scheme of arrange
m ent w hich th e com pany en tered into w ith its d ebenture holders in Ja n u a ry , 1931.
C anada.— A special general m eeting of
the In te rn a tio n a l Nickel C om pany of Canada is to be held to confirm th e reduction of th e share capital by cancelling 167 shares of preferred stock and 14,454 shares of com m on stock surrendered for cancellation since Decem ber, 1929. T he authorized capital stock is to be increased by the am ount of th e reduction.
S w ed en .—The rep o rt of th e Boliden
Mining C om pany for 1932 sta te s th a t after w riting off kr. 3,318,000 th e accounts show a profit of kr. 8,134,000, as com pared with kr. 549,000 in th e previous year, a first dividend equal to 10% being proposed.
D uring th e year 220,000 tons of ore was mined and sent to th e mill, w hich has now been enlarged in order to handle 350,000 to 400,000 tons annually.
C orn w all.—T he reduction of th e capital
of Geevor T in Mines, L td ., from £180,000 to £97,878, b y cancelling cap ital lost, has now been sanctioned b y th e H igh Court.
B r itish T in In v e stm e n t C orp oration .—
T he accounts of th e B ritish Tin Investm ent Corporation for th e eight and a half months from its incorporation to D ecem ber 31 last show a profit of £11,726. A fter allowing
£5,465 for income ta x an d £5,930 for prelim inary expenses, th ere rem ained £331 to be carried forward.
C ord eroy M ines.—The
rep o rt of Corderoy Mines, L td ., for th e period to Decem ber 31 last shows th a t arrangements have now been concluded for th e cancellation of th e existing debentures, while a t an extra
ordinary m eeting held last m o n th it was agreed th a t the existing " B ” shares should be subdivided in to five shares of 4s. each, ranking in all respects w ith th e existing 4s.
shares. These arrangem ents will enable the com pany to proceed w ith negotiations for w hat is sta te d to be a prom ising property.
E xp loration C o m p a n y .— T he accounts
of th e E x ploration C om pany for 1932 show
a realized loss of £1,742. T he com pany’s
interests in subsidiary com panies an d other
investm ents had a m a rk e t value of £123,359
a t th e end of th e year, against a book value
of £326,627.
* u
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High Court
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T H E TIN-TUNGSTEN DEPOSITS OF STEWART ISLAND, NEW Z EALA ND
By G O R D O N W IL L IA M S , B.E., M.Sc., D.I.C.
T h e au th o r d escrib es the m ode of o ccurrence of the w olfram ite and cassiterite found on this island off th e south coast of N e w Z e a la n d .
In t r o d u c t i o n.
— The only p a rt of New Zealand where cassiterite and wolfram ite can be regarded as being more th a n mineralogical curiosities is Stew art Island, lying off the southern coast. S tew art Island consists of a series of rugged granite peaks rising to 3,200 ft. and separated by to rtu o u s drowned valleys, which form sheltered bases for the fishing fleets th a t w ork in th e surrounding seas and for a Norwegian whaling com pany operating in th e A ntarctic. A heavy rainfall encourages a dense forest grow th and only on the sum m its of th e highest hills does th e thick bush give w ay to an im penetrable wind-swept interlocking scrub an d to peat and tussock, whilst in places areas of bare rock appear. The “ prevailing westerlies ” sweep across the bleak highlands, which are constantly buried in cloud.
The mineral deposits lie am ong th e hills behind P ort Pegasus, a tin y fishing base at the extrem e south of th e island. The deposits are in the form of lodes containing wolframite and cassiterite and placers con
taining these m inerals and also gold. The deposits have been known for m any years and unsuccessful a tte m p ts were m ade to work them tow ards the end of last century, b u t the field has since been neglected, except for a brief period in 1913. The d istrict was visited by Alexander M cKay, of th e New Zealand Geological Survey, in 1888, b u t th e present w riter’s work is th e first a tte m p t to m ap th e deposits and to describe th e mineralogical relationships and genetic processes.
Su m m a r y o f Ge o l o g y.
—S tew art Island is a rem nant of an extensive granite mass lying in the extrem e south of New Zealand.
The granite b a th o lith has been deroofed by erosion and th e extrem e tips of th e pen d an ts of the invaded m etam orphic rocks th a t lay deepest in th e b ath o lith now rem ain only on th e tops of the highest hills. In th e m ineralized region th e invaded rock is a biotite-schist and it is in an inlier of th is rock, capping the Tin R ange behind P o rt Pegasus, th a t th e w olfram ite-cassiterite lodes appear. The stream s th a t rise in th e Tin Range and cross granite country on th e ir w ay to th e coast contain concentrations of m inerals derived
from th e lodes and also th e heavy accessory m inerals of th e granite th ey traverse.
Me t a l l i f e r o u s Lo d e s.
— Q uartz veins appear throughout the rem nants of biotite- schist th a t cap th e higher hills behind Port Pegasus, b u t only those running along the sharp eastern crest of th e Tin Range are m etalliferous. The useful m ineral is wol
fram ite, b u t small am ounts of cassiterite also occur. The m etalliferous m inerals are restricted to th e actual veins— they are entirely absent from th e country-rock.
Structure.—The m etalliferous veins occur
in a zone varying in w idth from a few yards to several chains. The useful m inerals first appear about half a mile south of Trig. J and from th is point th e veins m ay be followed southw ards for two miles as a series of dis
connected outcrops to th e extrem e southern end of th e Tin Range, where th e lode-zone
Fi g. 1 .— Sk e t c h Ma p o f Ne w Ze a l a n d s h o w i n g p o s i t i o n o f St e w a r t Is l a n d.
137
| G r a n ite and, gneiss.
m | j B i o i i i e - s c h j u s t
m Metalliferous lodes.
|° ° :| High-level heach g Sire euro gravel.
| % T t | E h u /la l deposits.
M A P O F
PECASUS DISTRICT
iT EW ART IS L A N D
N E W Z E A L A N D D rawn toshowthe distribution of P LA C E R DEPOSITS conraining wolframite,cassiterite, gold, manazite.efc., and LO D ES of wolframite and cassiterite.
Fi g. 2 .
MARCH, 1933 139 swings round and disappears. M ineralization
is strongest a t th e extrem e south.
The regional tre n d of th e biotite-schist is W. 20° N ., a direction th a t is observed only at the extrem ities of the long tongues of schist th a t project w estw ards from th e m ain body of the inlier in which th e m ineral lodes occur.
In successive zones to th e east a progressive swinging of th e tre n d is observable and along the straig h t eastern boundary of th e schist the strike is a t rig h t angles to th e regional direction. The m ineralized belt ru n s along the eastern flank of th e inlier—i.e., it occupies th a t p a rt of th e schist which has received a superimposed orientation a t right angles to the regional tren d . I t is suggested th a t the more or less m eridional stru ctu re of the eastern flank of the inlier was im pressed along the forefront of a newer granite m ass (occupy
ing the R obertson R iver basin) which was introduced under a pressure directed perpen
dicularly to th e pre-existent foliations.
The fugitive constituents of th e m ain in tru sion would be concentrated in th e later intrusion. As it cooled, peripheral shrinkage p arted th e folia of th e intensely-com pressed schist along th e forefront and afforded passages for the percolation of the late-stage m etal-bearing ichors. In a w esterly direction from the m ineralized zone pneum atolytic effects became progressively less prom inent and such q u artz veins as appear are barren. At the southern end of
T o p a jije d . Bi.otCOe.-Muscovi.te Sclúst GreLSen” | , r v | Mineral Lodes
Fi g. 3 .
th e Tin Range, where th e lode-zone swings round, it follows th e crest of an isoclinal fold pitching steeply along th e contact of th e granite th a t had im pressed th e fold structure.
Form of M ineral V eins.—The individual
veins in th e m etalliferous zone are irregular and anastom izing and form a typical com
posite vein system (Fig. 3). Only rarely do th e veins exceed six inches in w idth, the average being of th e order of one inch.
Small scale “ folding ” of th e veins, such as th a t shown in Fig. 3, is common. Close observation shows th a t wherever the veins
Fi g. 4 . — Co m p o s i t i o n o f t h e Me t a l l i f e r o u s Lo d e s : W = W o l f r a m i t e ; C = Ca s s i t e r i t e ; Q = Qu a r t z ; G = Ga r n e t; T = To p a z.
140
present th e appearance of having been folded th e y follow th e bends of tw isted lam inæ of schist enclosed w ithin th e greisen. The m inerals of th e folded veins are n o t crushed.
The contortions of th e schist inclusions are not shared by th e gneissosity of th e host, which flows round them (Fig. 3, left-hand side). H ence it m u st be concluded th a t th e folded veins were never plane an d th a t th e bends occur where th e fracturing was guided by contacts betw een tw isted fragm ents of schist and th e “ g re ise n ” which encloses them . I t is not p ty g m atic folding as defined by Sederholm.
Tenure in Depth.—The granite-schist con
ta c t b eneath th e m etalliferous lodes is not
fractures in ore m inerals. G arnet (almandine w ith 2-33% MnO) is as ab u n d a n t as topaz and also appears in cracks in th e ores. The masses of w olfram ite th a t are so clearly seen in hand- specimen are com posed of aggregates, the individual grains of which reach as much as one centim etre in diam eter. T he m argins are rounded in d etail an d often surrounded by m inute idiom orphs isolated in th e gangue.
C assiterite is n o t com m on an d occupies cavities in th e surfaces of th e wolfram ite clusters. The pleochroic colours v a ry from greyish brow n to brow n an d th e mineral has th e ch aracteristic b lo tch y appearance.
In ad d itio n to these five m ain lode-forming m inerals m uscovite also appears, b u t in
Fi g. 5 . — Pe g a s u s Cr e e k— Fa l l o v e r Ba n d o f Sc h i s t i n t o Pe g a s u s Ha r b o u r.
exposed, consequently th e veins cannot be traced down into th e g ran ite ; b u t from observations on non-m etalliferous veins in schist p endants fu rth e r n o rth (the em place
m ent of which m ust have been controlled by sim ilar dynam ic conditions) it m ay be inferred th a t th e lodes do not persist in th e granite.
The dep th of th e schist p endant in which the lodes app ear is probably n o t greater th an 200 ft., so th a t th e ten u re in dep th of th e veins m ay n o t be expected to exceed this distance.
M ineral Relationships in Lodes.—U nder
th e microscope th e lode m aterial is seen to be m ade up predom inantly of coarse-grained quartz. Topaz, which is usually tu rb id w ith m inute inclusions of biotite, is unevenly d istrib u ted th ro u g h th e gangue in crystal aggregates, which frequently appear in
close association w ith re m n a n ts of felspar, showing its derivation from th a t mineral.
Spinel (gahnite), sillim anite, an d biotite appear only as xenocrysts th a t have been to rn from th e co n tact-altered vein-walls during injection.
Order of Crystallization.— W olfram ite and
cassiterite were th e first m inerals to crystal
lize. The perfect cleavage of th e former
m ineral rendered it susceptible to mechanical
disintegration and each of th e gangue minerals
m ay be seen occupying p a rte d cleavages and
fractures, th e sides of w hich were to some
ex ten t rounded by reaction w ith th e vein-
form ing solutions, w hich la te r deposited
a crop of m inute idiom orphs ro u n d the
periphery of th e w olfram ite clusters—a
redeposition th a t followed th e crystallization
of garnet and topaz. Of th e gangue minerals,
MARCH, 1933 141 garnet crystallized before topaz and quartz
followed. I t is n o t clear a t w hat stage in relation to th is sequence th e felspar cry stal
lized and reacted w ith th e aqueous m aterial of th e lode-solutions to form m uscovite.
Country Rocks.—The country rocks are
of tw o kinds—a topaz-biotite-schist and a “ greisen.” The rock th a t is here called
“ greisen ” encloses th e lodes and consists of a fine-grained aggregate of quartz, topaz, and biotite. I t has a sugary appearance in hand-specimen and crum bles on weathering, leaving the m ineral veins in relief. I t occurs in long well-defined zones, following broadly the structure of th e schist. In the
th e topazized schist. The intrusive n atu re of the lodes is also suggested by the fact th a t the in ten sity and disposition of th e greiseni- zation bear no relationship to the proxim ity of th e m ineral veins.
There appears, then, to have been th ree stages in th e production of th e rocks spacially related to th e m ineral zone— (a) th e pneu- m atolytic topazization of th e m uscovite and felspar and th e bleaching of the biotite of th e granitized b io tite -sc h ist; (b) the intrusion along fissures of highly siliceous (liquid) ichor (the greisen) containing fluorine and water, which to some ex ten t reacted w ith th e topazized biotite-schist to ab stra ct the
Fi g. 6 . — So u t h e r n En d o f Ti n Ra n g e: Th e h i l i, i s c a p p e d b y s c h i s t, w h i c h c a r r i e s t h e M E T A L L I F E R O U S L O D E S . T H E F O R E G R O U N D I S T H E G R A N I T E T H A T E X T E N D S B E N E A T H T H E H I L L .
mineralized area th e schist consists solely of a coarse-grained aggregate of m ore or less bleached biotite and tu rb id grains of topaz.
Ge n e s i s o f Lo d e s.
— I t seems clear th a t the rock which is called “ greisen ” is intru
sive into th e topazized biotite-schist, for
(1) the bands of greisen are sharply defined against the topazized biotite-schist and th eir margins contiguous to th a t rock do not present gradational stages in a process of progressive topazization and silicification of the biotite-schist, (2) contorted fragm ents of the schist appear w ithin th e greisen, and (3) a poorly-defined gneissic stru ctu re in the greisen flows round these included fragm ents.
I t is equally clear th a t th e lodes, in tu rn , are intrusive into th e greisen. This is shown by th e existence betw een th e lodes and the greisen of relationships analogous to those ju st sta te d to occur between th e greisen and
m aterial necessary for th e form ation of biotite in tin y plates in th e greisen ; (c) the greisen crystallized an d la te r cracked along a series of anastom izing fissures following in a general way such rudim entary gneissic stru ctu re as it possessed. The cracks were occupied by tin -tu n g sten bearing fluids introduced soon afterw ards.
Most m ineral veins of th e tin-tungsten ty p e are believed to have been deposited pneum atolytically, b u t th e w riter’s observa
tions suggest th a t th e Stew art Island veins
formed from liquid solutions th a t entered a
fissure system in a greisen-like rock. This
conclusion is based on the following features :
(1) The m etalliferous m inerals are restricted
to th e lodes, (2) vein-banding or comb
stru ctu re were not observed, (3) garnets
occur in th e lodes in sim ilar association
and of th e same v ariety as garnets appearing
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in th e pegm atites associated w ith th e granite, (4) felspar (which was la te r alm ost entirely sericitized) crystallized in th e veins, a n d (5) th e ore m inerals were introduced in to th e veins in crystal fo rm — th is is shown by th e ir fracturing, by slight resolution of th e fracture surfaces an d redeposition of a late crop of m inute idiom orphs around th e crystal groups, b y th e crystallization in th e fractures of all th e gangue m inerals, a n d by th e general disposition of th e ore-m inerals aw ay from th e walls (although th e y are clearly th e first m inerals of th e veins to have crystallized).
It is th o u g h t, then, th a t th e m ineral lodes were introduced in liquid form in m uch th e
same w ay as a pegm atite dyke is injected, th a t th e ores were brought up from below as crystals w ith these solutions, and th a t the veins m ay be regarded as advanced peg
m atites.
Pl a c e r De p o s i t s.
—The placer deposits m ay be divided into three groups—eluvial, alluvial, and beach concentrations.
E luvial Deposits.—U nder th is head are
included sparse deposits of cassiterite and wolfram ite th a t are scattered over the surface of the Tin Range and represent only an elem entar}' stage in n a tu ra l m ineral concen
tra tio n through w'hich all m inerals found in alluvial ground m ust pass. U nder the abnorm ally wet an d rigorous clim atic con
ditions, th e cou n try rock surrounding the lodes is rapidly decomposed and rem oved, leaving piles of com m inuted vein m aterial th a t forms scree-slopes, b en eath w hich the
rain-w ash effects a rough con cen tratio n of cassiterite, w olfram ite, an d gold. Owing to th e co n stan tly changing surface of these slopes, however, th e drainage is seldom con cen trated in well-defined courses for any length of tim e, consequently such concentra
tions as form in riffles in th e underlying bed-rock are p a tc h y , b u t th e occasional discovery of such a pocket in ev itab ly leads to u n w a rra n te d optim ism an d subsequent disappointm ent. T he p o sition of these pockets, of course, bears no relatio n to the present contour of th e scree-slope.
A lluvial D eposits.— D eposits such as those
described (w ith some latitu d e) u n d er th e term
“ eluvial ” grade im perceptibly in to true alluvial ground. On account of th e high relief of th e island a n d th e p ro x im ity of all p arts to one or o th er of th e deep coastal em baym ents, th e form ation of gravel and th e concentration of valuable d e trita l minerals in well-defined d rifts is re stric te d to narrow strips along th e beds of th e larger stream s—
th e R obertson R iver an d Pegasus Creek—
in which local concentrations of gold and cassiterite were w orked in th e ’80’s. Small accum ulations of gravel also ap p ear here and th ere on th e steep flanks of th e Tin R ange behind constrictions w here stream s cross h ard b ands in th e granite.
Beach Deposits.—A th in veneer of m etal
