The Mining Magazine
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Vol. X L V I . No. 3. L O N D O N , M A R C H , 1932.
O N E S H IL L IN GP R IC EC O N T E N T S
P A G E E d i t o r i a l
Notes . .
130Skinner’s “ M ining Y ear B o o k ” ; Cam borne H o lid a y Course in E co n o m ic G eo lo g y ; O il versu s Coal as Fuel ; A Course of L ectures o n T ropical H y g ie n e ; T he G eo lo g y o f N o rthern R h od esia.
The In stitu tio n Meeting
130Three papers presen ted a t th e F ebruary m eetin g are review ed.
The B ritish Industries F a i r ... 132
The p o sitio n o f B ritish in d u stry , as ev id en ced b y this y ear’s fair, is ex am ined.
The Technician in Commerce ... 133
Som e co n clu sio n s are drawn from the su b sta n ce o f a lecture recen tly d eliv ered a t th e R o y a l S ch o o l o f Mines.
R e v i e w o f M i n i n g
... 134
Ar t ic l e sThe Sub Nigel Gold Mine
G. Carleton Jones 137
The author, w h o is co n su ltin g en g in eer to th e N ew C onsolidated G old F ield s, L td., in the T ransvaal, describes op era tio n s a t th is H eidelberg d istr ict m ine.
Bucket Dredge Losses
7 . /,. W illan 149
A presentation o f certain factors w hich govern the loss of va lu es in E astern b u ck et-d redging practice.
U g a n d a •.
E . J . W ayland 151(C oncluded fr o m the F eb ru a ry issu e, p. 93.)
The I.M.M. Benevolent F u n d ... 160
F irst L ist of Subscriptions.Bo o k Re v i e w s
S h a n d ’s “ T he S tu d y of R ocks ”
Dr. E rnest Parsons 160 Ries a n d W a ts o n ’s “ E n g in eerin g Geology ”
Dr. M u rra y Stuart 160 Ne w s Le t t e r s
Johannesburg ... 160
N igel A rea ; W est R an d C on solidated ; N e w H ydraulic P r o c e s s ; R h odesian C opper M in e s ; G eological Survey.
B r is b a n e ... 162
P rogress a t M ount Isa ; M ount Isa O u tp u t ; Q ueen s
land M ineral P ro d u ction ; M ount M organ’s P o sitio n ; N ew nes Shale O i l : B roken H ill A sso cia ted S m elters ; R evival o f B en d ig o ; G uinea G old Com pany.
Ipoh ... . ,:C
H o lid a y s ; Sub-L eases ; B ritish E xp orters ; N ew R egulations.
V ancouver...
P rospecting A ctiv ities; Phillips Arm ; Bridge R iv e r ; N elso n Area ; B o u nd ary ; B ritan nia Beach.
Toronto ...
Porcupine ; K irkland Lake ; Sud bury ; R o u y n ; Patricia D istrict.
Pe r s o n a l
Tr a d e Pa r a g r a p h s . T h e G rit P u m p ...
B ritish In d u strie s F a ir Me t a l Ma r k e t s ...
St a t i s t i c s o f Pr o d u c t i o n Pr i c e s o f Ch e m i c a l s...
Sh a r e Qu o t a t i o n s ...
Mi n i n g Di g e s t
Sand-P'illing a t a C um berland Mine
A . A . Jones V e n tilatio n a t th e R o binson D eep
J . P. Rees and E. C. W hittaker T he M easurem ent of R efractoriness
Dr. H . A . White T h e S h ab an i A sbestos M ines, S o u th ern
R h o d e s ia ... J . Spalding M ineral D evelopm ents in th e C an ad ian N o rth w e s t D. F. K id d M ining G old-Silver O re a t Ja rb rid g e, N ev ad a / . F. Park Sh o r t No t i c e s...
Re c e n t Pa t e n t s Pu b l i s h e d . Ne w Bo o k s, Pa m p h l e t s, e t c. Di v i d e n d s De c l a r e d
P A G E
1G3
164
166
167 168
168 169
171 173 175 176
177 180 182
184 188
190
191 191 192 192
3—3 129
E D IT O R IA L
T H E forty-sixth annual issue of Skinner’s
“ Mining Y ear Book ” ap peared last m onth. The policy of including particulars of foreign m ining com panies has been still fu rth er expanded in th e present issue, th e in tern atio n al ch aracter of th e book increasing its value to all associated w ith th e m ining industry.
T H E holiday course in economic geology, w hich has been a feature a t the Camborne School of M etalliferous Mining (Cornwall) since 1919, will be held this year from Ju ly 11 to A ugust 20. The course is designed to appeal to engineers and geologists home on leave and comprises both lab o rato ry and field work, including geological excur
sions, visits to mines, and field m apping.
L E C T U R IN G last m onth before th e R oyal In stitu tio n , Sir J o h n Cadm an chose as his subject “ P etroleum —A Record of A chievem ent in Applied Science.” The lecturer laid g reat em phasis on th e advantages of oil over coal as a fuel, p a r
ticularly in connexion w ith railw ays. In view of recent w ork on th e recovery of oil from coal in th is country, his figures, regarding th e com
p arativ e consum ptions of oil and coal m ade a g reat im pression on his hearers.
A dem onstrations on tropical hygiene, COURSE of seven lectures and b y M ajor D. T. R ichardson, of th e R oyal A rm y Medical College, will be given nex t m onth a t th e room s of th e B ritish R ed Cross Society, Chesham Street. The lectures will be given on M ondays, W ednesdays, and Fridays, comm encing on Monday, A pril 4, a t 5.30 p.m ., and will cover such questions as food, clothing, and th e m edical and sa n itary precautions necessary for h ealth in h o t countries. The fee for th e course is 5s.
for m em bers of th e society and 7s. 6d. for non-m em bers.
R EC E N T progress in th e elucidation of the geology of N orthern R hodesia was clearly dem o n strated a t a m eeting of th e Geological Society of London held last m onth. A fter the intro d u ctio n of a paper on th e geology of th e N ’Changa district, by D r. G. C. A.
Jackson, a brief account of th e general geology of th e copper belt was given by Mr. G. V ibert Douglas, who m ade reference
to the clim atic cycle since T e rtia ry tim es and to m eans of distinguishing betw een the older and younger granites (the two-granite question being still som ew hat controversial), his lecture concluding w ith a sketch of the general stru c tu re of th e country. Speakers co n trib u tin g to th e discussion w hich followed included Dr. A nton Gray, Mr. R. Murray- Hughes, and Dr. L. H aw kes.
T he In stitu tio n M eeting
T he three papers down for presentation a t the F eb ru ary m eeting of th e Institution offered som ew hat m ixed fare to th e large num ber of m em bers atte n d in g . Two of th em — “ Sand-Filling M ethods a t Hodbarrow (H æ m atite) Mines, S outh C um berland,”
by Mr. A. Alec Jones, and “ T he Asbestos Mines a t Shabani, in Southern Rhodesia,”
b y Mr. Ja c k Spalding—doubtless attracted th e m iners, th e th ird — “ F lo tatio n : Some O perating D etails,” by Mr. Kenelm E.
A rm ytage, draw ing those in terested in ore- dressing practice. A ctually, only two of the papers were introduced and discussed on this occasion, th a t dealing w ith S habani being left—in th e absence of th e au th o r—for am plification by w ritte n contributions to th e T ransactions. T he papers on sand- filling an d flotation, how ever, h ad evidently created some in terest an d th e ir presentation and discussion fully occupied th e available tim e.
T he first paper to be considered was that by Mr. Jones, full e x tra c ts from which will be found elsew here in th is issue. I t will suffice here, therefore, if some idea is given of th e conditions which led to th e adoption of such a m ethod of filling a t th is Cumberland property, w here a large m ass of hæmatite ore lying u n d er th e seat was m ined during th e years 1860-1922 b y a top-slice caving m ethod. B y th e la tte r y ear it was estimated th a t ab o u t n in e-ten th s of th e Hodbarrow m ass h ad been ex tra c te d and it h ad become increasingly a p p a re n t th a t some other way would have to be found of tak in g out the rem ainder, owing to th e danger, in the no rth e rn section, of in u n d atin g th e mine by th e collapse of w ater-laden sedim ents and, in th e south, of flooding th e m ine w ith sea
w ater through caving of th e sea-bottom.
In 1905 th e “ O uter B arrier ”— a large
em b an k m en t—was com pleted, an area of
130
MARCH, 1932 131 200 acres previously below the high-w ater
m ark being th ere b y reclaim ed, so th a t the ore lying below th is ground m ight be re
covered b y th e use of th e old caving m ethod.
The ore is found in th e Lower Carboni
ferous lim estone, which, in th e south of the property, is overlain by glacial clays and sands. Carefully controlled caving in the limestone h a d heretofore led m erely to gentle subsidence of the im pervious clays above the caved ground, danger of flooding by surface w ater th u s being minim ized. Too rapid extraction of th e ore during th e W ar period, however, when th e mine was under th e con
trol of th e M inistry of M unitions, h ad led to severe faulting of the overlying glacial beds and there had, in consequence, been several abnorm al inrushes of sea-w ater. In another part of th e m ine, where the ore outcropped directly b en eath th e cover of glacial sedim ents, developm ent of th e ore-body h ad been fre
quently atte n d e d b y th e inrush of sand.
In these two areas, therefore, some alternative m ethod of m ining h ad to be adopted and con
trolled sand-filling, in the opinion of those in charge of th e property, offered the best solution of th e problem . The m anner in which this has been carried out will, as was previously stated , be found elsewhere and it will be sufficient to say here th a t m ost of the ex tractio n difficulties appear success
fully to have been overcome, well over a million tons of ore having th u s been brought into the reserves. In his introductory remarks th e a u th o r laid stress on th e care which had to be tak en in this w ork and in the sinking of the bore-holes used as sand feeders. He was also able to add some details as to costs, the absence of which had detracted som ew hat from th e value of the paper. He calculated th a t, excluding over
head charges, the actual cost of sand-filling in this p ro p erty w orked out a t about lOd.
for every ton of ore replaced, three-fifths of this am ount going as wages and two- fifths for fuel and lubricants, th e filling m aterial being present in alm ost unlim ited quantities a t th e surface. A t the present rate of e x tractio n th is adds approxim ately 4d. to 5d. to th e costs per ton raised. The discussion was opened b y Mr. R. E. Palm er, who proceeded to com pare sand-filling w ith
h a n d - f illin gas adopted by him self in similar work elsewhere. Mr. P alm er also called a tte n tio n to th e m erits of pneum atic stow ing, w hich is being successfully applied on the C ontinent. Following Mr. Palm er, Col.
E d g ar P am showed how extensively the
use of sand for filling purposes h ad been applied on the R and, pointing out its use in packing ground where hand-stow ing would be impossible. Professor Lawn endorsed Mr. P alm er’s rem inder th a t top- slice caving m ethods of mining, while widely practised in America, were originally developed in Cum berland, and Mr. W hite- house, who concluded th e discussion, while differing w ith Col. P am as to the wide range of application of sand-filling m ethods, dem onstrated its usefulness in certain circumstances.-
The rem ainder of tim e available at last m o n th ’s m eeting was occupied by the introduction and discussion of Mr.
A rm ytage’s paper on flotation details. The a u th o r describes flotation as an art, but points out th a t various mechanical devices can be usefully em ployed by the artist in order to sim plify his labours, going on to say th a t in th e production of a brittle, well-mineralized froth an expert operator will be able, owing to his experience, to produce such a froth as a result of constant observation, relying a t th e same tim e on certain definite factors.
These factors, such as accuracy in m aintain
ing alkalinity of the circuit, in th e rate of reagent addition, in the sizing of th e ore- particles, and in th e tim es of contact w ith reagents, can be suitably controlled by the use of certain practical aids, these aids forming th e m ain subject-m atter of th e thesis. The author th en considers these factors in detail, concluding his paper w ith an essay on relative floatability. H ere he points out th a t, while investigating a complex ore for the first tim e, it m ay be useful to fractionate th e froth into a num ber of products, each representing the results of a tw o-m inute bulk float of all th e ore minerals, no change being made in the circuit except for the addition of the frother and collector.
In this way, it is said, some idea of relative floatabilities can be gained and an y unusual features will im m ediately become apparent.
T he whole presentation of th e paper and th e
o p p o rtu n ity given to m em bers a t the m eeting
of inspecting th e “ gadgets ” used by
th e au th o r bore ample testim ony to his
acquaintance w ith his subject and of
th e ingenuity and the workshop handiness
which are so useful in this practical-scale
lab o rato ry work. Discussion of th e paper
was opened b y Mr. Sulman, who was able to
am plify several points m ade b y th e author
and to show how m odern m ethods have
brought flotation practice under more
accurate control. O ther speakers included Mr. B utler-Jones, Dr. Sidney Sm ith, and Mr. J . C. Allan.
The th ird paper, by Mr. Ja c k Spalding—
details of w hich will be found elsewhere in th is issue—was, in th e absence of th e a u th o r in In d ia, left for discussion in w riting.
T his paper describes th e chrysotile asbestos deposits a t Shabani, in Southern Rhodesia, an d gives details of th e m ethods em ployed in m ining a n d handling th e large tonnages extrac ted . T he geology of th e Shabani belt has been fully described by D r. F. E.
K eep in his m onograph appearing in B ulletin No. 12 of th e S outhern R hodesia Geological Survey an d Mr. Spalding’s description of th e deposits is based on th is work. As regards th e m ining of th e ore-bodies, however, th e au th o r was able to give th e results of first
h an d experience and his description covers th e organization of th e w ork and th e quarrying m ethods, b y w hich m ost of th e o u tp u t is a t present obtained. This is followed by a description of th e m ethods of handling th e ore, th e developm ent of new ore-bodies, th e stoping m ethods em ployed in th e Nil D esperandum mine a n d m odifications contem plated elsewhere, and th e subsequent tre a tm e n t of th e asbestos m ineral, concluding w ith an account of th e general surface equipm ent and of labour conditions. I t m ight be as well here to m ark th e care w hich has to be ta k en in tre atin g th e chrysotile ore in order to preserve the fibre in an undam aged condition an d to em phasize th e a u th o r’s note th a t m illing suitable a t one p ro p erty has often been found unsuitable for ap p aren tly sim ilar ore from neighbouring mines. The im portance of these deposits, especially w hen th e pre-em inent position of th e Em pire as an asbestos producer is considered, lends additional in terest to this com plete descrip
tion of th e m ining and tre a tm e n t m ethods em ployed in Southern Rhodesia.
T he B r itish In d u stries F air
This y e a r’s B ritish Industries F air was an event of more th a n usual im portance, coming as it did a t a crucial tim e in th e economic h isto ry n o t only of this co u n try b u t of th e world. On th is account it m erits more a tte n tio n th a n is usually given it in these columns, n o t so m uch by reason of its direct intere st to mining m en as because of th e indication it affords of th e probable course of B ritish industry, which, in common w ith
th a t of all o th er countries, has declined in consequence of certain forces th a t, while variously diagnosed, are generally felt to be outside in d u strial control. M ining men realize th a t th e ir own in d u stry is n o t likely to w itness th a t p ro sp erity enjoyed b u t a few years since u n til those m an u factu rin g con
cerns w hich are th e consum ers of th e raw m aterials produced re tu rn to norm al activity.
T h a t such a re tu rn m ay reasonably be a n ticip ated before an y g reat lapse of tim e is th e inevitable conclusion reached after an extensive to u r of all sections of th e fair.
T here was certain ly one featu re which d istinguished th is y e a r’s fair from those previously held. I t has ta k en place a t a time w hen th e B ritish m an u factu rer is afforded a double ad v an tag e—th e increased purchasing power of several foreign currencies, as a result of th e depreciation of sterling on foreign exchanges, following th e abandon
m ent of th e gold sta n d a rd by th is country, a ttra c ts th e foreign buyer, w hilst th e pro
tection afforded b y a long-aw aited change in th e fiscal policy p ro te c ts th e home industries against th e influx of m anufactured articles of o th e r th a n B ritish origin. T hat th is double factor has proved a beneficial one was evidenced b y th e larger num ber of visitors from abroad and b y th e increased business done.
T h a t th e fair should have been so well a tte n d e d —th e increase is said to have am ounted to over 50 per cent, as com pared w ith last y ea r—and have done m ore business is not, perhaps, surprising having regard to th e causes alluded to, b u t th a t it should have p resented a greater and more com prehensive display th a n in th e p a st was as rem arkable as it was creditable to all concerned. The B irm ingham section—w hich is referred to in some d etail elsewhere in th is issue—was som ew hat more extensive th a n last year, for, while th ere were some notable absentees, there were a num ber of new comers. Metals an d th e articles into w hich th e y are or can be fabricated were th e principal features here. T he electrical in d u stry w as also well represented an d some of th e h e av y engineer
ing industries, th e la tte r n o t so well as they
m ight have been. I t m u st be borne in m ind,
however, th a t th e exhibition of running
p lan t is an expensive u n d ertak in g for the
m an u factu rer an d th a t there is a tendency
for such to be reserved for specialized
exhibitions. T he running ex h ib it staged
out of doors—designed to d em o n strate "the
em ploym ent of excavating, tra n sp o rt, and
MARCH, 1932 133 crushing m achinery in contracting opera
tions—was a notable new d eparture, which well deserves special com m endation and, when open-air space is available—as it certainly was here—is likely to prove a useful field for extension in th e future.
A ltogether th is y e a r’s fair m ay be regarded, not m erely as a w orthy successor to those preceding it, b u t as a convincing dem onstra
tion of th e B ritish m an u factu rer’s intention to overcome all th e obstacles presented by an economic u p heaval an d of his recognition of th e necessity of m eeting his custom ers’
requirem ents.
The T ech n icia n in C o m m erce
In an o th er column an im pending revival in B ritish in d u stry is suggested as th e outcome of th e im pressions conveyed by a visit to th is y e a r’s B ritish Industries Fair.
Another aspect of th is all-im portant topic opportunely presents itself for discussion in the form of some reflections on th e subject- m atter of a lecture by Mr. W. E. Gooday, delivered last m onth a t th e Royal School of Mines, on “ The Technician in Commerce.”
While Mr. Gooday was dealing particularly with th e m arketing of lubricating oils—
a sphere of com m ercial activ ity of which he is specially qualified to speak—he made some observations of a general character and there are a num ber of points of interest to engineers and m etallurgists arising th ere from which deserve exam ination.
As Mr. G ooday pointed out, there ought to be, and in the view of m any there is, a big field of usefulness for th e technically- trained m an in com m erce—in commerce, it should be em phasized, and not in industry, where th e technician is already extensively and inevitably em ployed on th e research and production sides. The em ploym ent of a scientifically-educated m an on the sales organization is, however, relatively exceptional, b u t th a t th is conception of the engineer’s com paratively lim ited value to industry is beginning to disappear is as evident as it is fortunate. This was the burden of Mr. G ooday’s contention and it is th e purpose of this brief review to endorse as em phatically as possible b o th its tru th and its im portance.
A similar thesis has already been adm irably presented b y Mr. G ilbert Rigg, th e well- known m etallurgist, in a fascinating s to r y 1 of his early experiences, when, as a fully- fledged chem ical engineer, he dealt w ith a
1 T h e Sales E n g in e er : M ining P u b lica tio n s, L td .
num ber of commercial problem s in the zinc industry, b u t Mr. Rigg only p artially covers th e subject. Thus th ere are broadly speaking two kinds of salesm anship—the selling of a specific product and the selling of service. Sometimes one, som etim es the other, b u t more often th a n not b o th are required. Mr. Rigg w rites alm ost exclusively of service after sales, in which field of com
merce th e m an who has technical qualifica
tions to equip him for the ta sk is indisputably w ithout equal. In the other sphere also the educated salesman has become increasingly necessary and, when in d u stry appreciates this and the young m en show them selves adaptable to the special requirem ents of commerce, im proved results are confidently believed to be a foregone conclusion.
T h at the foregoing rem arks are not idle speculation will surely be generally appreciated. How otherwise can inefficiency in B ritish selling m ethods be accounted for, except it be in the shortcom ings of the personnel. I t is obviously bad policy to send m en to sell m achinery, for example, who, when th e y have exhausted their sales talk, have no reserves on w hich to draw in order to counter inform ed criticism, such as m ay be anticipated from the potential buyer who is himself a practising engineer.
And y et how often has this happened.
Many who read th is indictm ent—m ade in no carping spirit, b u t w ith every desire to help—will have some knowledge and experience of m anufacturing works. Will th e y not readily agree th a t in too m any instances there is a gulf fixed between the selling organization and th a t responsible for research and production ? Conversation w ith sales m anagers and their executives reveals th a t, while th ey are fully con
versant w ith their firm ’s products, th ey
frequently have b u t a slight acquaintance
w ith th e operations for which th ey are
designed to be used. In the absence of
this knowledge, how are th e y to m ake
those outside contacts th a t are required
of them ? This m ay seem to be a counsel
of perfection, y et a change such as th a t
indicated is surely taking place. Our
younger engineers who have th e requisite
personality—an indefinable quality—should
be encouraged to present them selves for
service in engineering commerce, and industry
should adm it them and thus secure b etter
relations betw een research, production, and
sales on the one hand and m anufacturer
and custom er on the other.
R E V IE W O F M ININ G
In tro d u ctio n .— S entim ent in th is c o u n try
has, p articu la rly during th e p a st week or so, been cautiously optim istic and, although it is realized th a t it m ay be some tim e before m ining affairs can expect to be favourably affected to an y e x ten t, it is hoped th a t th e tide of depression is nearing th e tu rning point, if it has n o t already reached it. The recent spectacular rise in th e value of sterling is regarded w ith m ixed feelings, for, w hilst it m ay be ta k en as evidencing a revival of confidence in th is c o u n try ’s financial sound
ness, it is n o t calculated to benefit its export trad e.
T ran svaal.— The o u tp u t of gold on th e
R an d for F e b ru a ry was 869,711 oz. and in outside d istricts 44,301 oz., m aking a to ta l of 914,012 oz., as com pared w ith 936,784 oz.
in Ja n u a ry . The num ber of n atives em ployed on th e gold m ines a t th e end of th e m onth to talled 216,171, as com pared w ith 215,752 a t th e end of Ja n u a ry .
T he rep o rt of M odderfontein B Gold Mines for 1931 shows a working profit of
£424,173, o th er revenue bringing th e to ta l profit up to £449,465. T he to ta l sum avail
able was £774,147, of which £420,000 was d istrib u ted as dividends, equal to 60% , and, a fte r m aking various allowances, £275,127 was carried forward. T he ore-reserve position, w hen com pared w ith th a t a t th e end of 1930, is n o t quite so good, th e to ta l a t 1,177,460 tons, averaging 6-57 dw t. in value over a stoping w idth of 49-3 in., showing a decrease of 48,940 tons in am ount, of 0-46 dw t. in value, and of 2-6 in. in w idth. D uring th e year under review 887,000 tons was milled, 264,895 oz. of gold being recovered, w orth £1,123,775, th e revenue showing a decrease of 4s. 5d. per to n milled when com pared w ith th e previous year. W orking costs am ounted to £704,565, equal to 15s. lOd. per to n milled, a decrease of Is. Id . from th e previous y e a r’s figures. I t is felt th a t, while th e present scale of milling opera
tions will be m aintained during th e current year, th e profit, in view of th e lower ore- reserve value, will be som ew hat reduced.
The accounts of G eldenhuis Deep for 1931 show a working profit of £72,351. A fter allowing for su n d ry item s of revenue and adding th e sum of £113,686 unapp ro p riated a t th e end of 1930, th e to ta l available was
£190,431, of which £56,667 was d istrib u ted as dividends, equal to 10%. A fter m aking various allowances, th e sum of £118,309 was carried to the n ex t account. T he ore reserves
a t 654,200 tons, averaging 5-55 dw t. over 51-7 in., show a decrease of 32,700 tons in am ount, of 0-11 dw t. in value, an d of 0-3 in.
in w idth. D uring la st y ear 861,900 tons of ore was milled, 198,843 oz. of gold being recovered, valued a t £843,603, or 19s. 7d.
per ton milled. W orking costs am ounted to
£772,718, equal to 17s. l i d . per ton. The tonnage m illed was a record for th e mine.
D uring 1931 th e w orking profit of th e Rose Deep was £30,856, th e n et profit being
£30,372. A fter adding th e balance of
£92,462 brought in and su n d ry revenue, the to ta l sum available was £122,871, of which
£16,574 was d istrib u ted as a dividend, equal to 2 \% . A fter m aking various allowances, th e sum of £81,622 was carried forward. Ore reserves, estim ated to be 1,019,800 tons, averaging 4-7 dw t. over 61 in., show a decrease of 71,500 tons an d of 0-2 dw t. in value w hen com pared w ith th e previous year.
D uring th e y ear u n d er review 741,500 tons of ore was m illed, 153,029 oz. gold being recovered, w orth £649,093, silver and osm iridium recovered bringing th e total revenue to £650,495, or 17s. 7d. per ton milled. W orking costs am ounted to £619,638, or 16s. 9d. per ton.
The accounts of th e Village D eep for 1931 show th a t th e subsidiarj^ clean-up is still proceeding, £14,284 being recovered during th e year. A fter m aking allowance for the rep ay m en t of 4s. 6d. cap ital on each of the shares during 1931, th ere was a balance available a t th e end of th e y ear of £79,765.
A t an e x trao rd in ary m eeting, to be held following th e an n u al m eeting n e x t m onth, it will be proposed th a t th e c ap ital of the com pany be reduced from £475,053 in shares of 9s. 6d. each to £425,048 in shares of 8s. 6d. each, by retu rn in g to th e holders the sum of Is. per share in cash.
D etails of th e proposed sale of th e assets of the W itpoort Gold A reas to Brakpan Mines, L td ., were given in th e last issue of the
M a g a z i n e .A m eeting of shareholders of W itpoort Gold Areas, L td ., has been called for th e last d a y of th e prese n t m onth, when th e y will be asked to approve th e sale.
An e x trao rd in ary m eeting of Moodies
Gold Mining and E x ploration C om pany is to
be held in Johannesburg th is m onth for the
purpose of considering an offer to purchase
m ade by th e T ran sv aal E xploring L and and
Minerals Com pany. T he la tte r has agreed to
ta k e over the whole of th e assets of the
form er in re tu rn for 680,000 fully-paid shares
134
MARCH, 1932 135 of Is. each. If th e offer is accepted the
Moodies C om pany will go in to v o lu n tary liquidation. T he T ransvaal Com pany has also offered to ta k e over McCreedy Tins (Swaziland), L td ., in re tu rn for 200,000 fully-paid shares in its own com pany, and a t an ex trao rd in ary m eeting to be held next m onth its shareholders will be asked to approve these tw o purchases, as well as the necessary increase of cap ital to £217,803 10s.
to m eet th e purchase consideration.
I t was announced last m onth th a t the Union Corporation intended to carry out certain prospecting w ork on th e Marievale Nigel property.
Preference shareholders of th e Consoli
dated Gold Fields of South Africa have been informed th a t th e dividend on th e Second Preference shares, postponed from O ctober 1 last, will be paid on April 1 and th a t the dividend for th e cu rren t half-year will be paid at the same tim e. P ay m en t on the preference share capital of this com pany will thus be brought up to date.
D iam on d s.—The
expectation of Sir Ernest O ppenheim er th a t th e South African diamond mines would soon be compelled to close down was noted in the last issue of the
M a g a z i n eand has since been confirmed by the announcem ent th a t the De Beers mines would cease w ork a t th e end of March, the decision to ad o p t th e same course being subsequently announced by th e Prem ier and the Consolidated D iam ond Mines of South- West Africa com panies. The situation thus created is said to have come as a surprise to the Union G overnm ent, which was investigating the problem , and a t the beginning of M arch it was announced th a t a commission, consisting of Judge Gardiner, Mr. Ross F ram es, a form er chairm an of De Beers, and Mr. F. W. Beyers, ex-M inister of Mines, had been appointed to investigate conditions in th e industry. Advices from the Union show th a t th e to ta l production of stones in 1931 am ounted to 2,119,155 carats, valued a t £4,182,523, as com pared w ith 3,163,590 carats, valued a t £8,340,719, in 1930.
S ou th ern R h o d e s i a . —
The o u tp u t of gold from Southern R hodesia during J a n u a ry was 42,706 oz., as com pared w ith 50,034 oz. for the previous m onth and 45,677 oz. for Jan u ary , 1931. O ther o u tp u ts for th e m onth of J a n u a ry were : Silver, 25,942 oz. ; coal, 47,073 tons ; asbestos, 755 tons ; copper, 4 tons ; mica, 3J tons ; tin, 1 ton.
It was announced this m onth th a t the
A frican and E uropean In v estm en t Co., L td., and th e Lonely Reef Gold Mining Co., L td., have jo in tly acquired an option over the Charliesona mine, 12 miles due south of the Lonely m ine. This p ro p erty has only been p artially prospected, the proved reef at 100 ft. d e p th having a w idth of 26 ft. over a length of 300 ft., th e average value being betw een 8 and 9 dw t. T he Lonely Reef com pany has also acquired rights over th e P e te r P an ore-body, which is w ithin four miles of th e mine. H ere 100,000 tons of ore, of an average value of 4-1 dw t., has been proved down to 70 ft.
W ith regard to the petition of the Globe and Phoenix com pany to be allowed to appeal against th e decision of th e H igh Court granting perm ission to the Rhodesian Corporation, L td., to m ake a complete inspection of th e Globe and Phoenix mine, th e la te st news is to th e effect th a t th e right to appeal against th e judgm ent has been refused.
N orthern R h od esia.—D uring th e three
m onths to December 31 last the Roan A ntelope produced 7,872 short tons of blister copper, while 8,453 d ry short tons of concen
tra te s was shipped to A m erica for sm elting and refining. All production is now in the form of blister copper. Costs during th e first full m o n th ’s operation a t th e sm elter—
D ecem ber—were £2-532 per short to n and for th e q u arter £2-88 per short ton of blister copper, including startin g up expenses.
C onstruction w ork has alm ost been com pleted and the num ber of both E uropean and native employees shows a big reduction when com pared w ith the previous quarter.
Kenya C olony.—A small gold rush has
ta k en place to the K akam ega district, n o rth of the Yala River. The auriferous d istrict is said to cover an area of approxim ately 300 square miles.
India.— Shareholders of B alaghat Gold
Mines, L td., have been inform ed th a t, in view of th e heav y cost of deep developm ent w ork on the mine and the difficulty of m ain
taining an adequate scale of o u tp u t, th e directors have approached th e board of N undydroog Mines, L td., w ith a view to th a t com pany acquiring th e ir property.
B u rm a .—A prospecting licence over the
Mwedaw gold area, covering a square mile
of co u n try below Kalaw, near th e Southern
Shan Railw ay, has been granted to th e
K afue Copper D evelopm ent Company. I t
is said th a t the existence of a gold reef in the
area has been established and developm ent w ork is to comm ence im m ediately
M alaya.—The re p o rt of Gopeng Con
solidated, L td ., for th e year ended Septem ber 30 last shows th e profit to have been ¿29,251.
A fter adding th e sum b ro u g h t in from the la s t account and m aking various allowances, th ere was an available to ta l of ¿54,836, of which dividends absorbed ¿26,385, equal to Is. 4d. per share, leaving ¿28,451 to be carried forw ard. D uring th e y ear 1,705,600 cu. yd.
of ground was tre a te d , 719 tons of tin ore being recovered, w orth ¿49,295. W orking costs again show a reduction from 10-56 cents to 9-55 cents (2-67 pence) per cu. yd., th e lowest figure a ttain ed by th e com pany. I t has been announced recen tly th a t the com pany has arranged to ta k e over the qu o ta allotted to th e K en t (F.M.S.) Tin D redging com pany and th a t consequently th e dredge of th e la tte r will n o t recommence production th is m onth.
The accounts of P etaling Tin, L td ., for th e year ended O ctober 31 la st show a n et profit of ¿29,444. A fter adding th e sum of
¿26,402 brought in, th e am ount available was ¿55,846, of which ¿29,167 was d istrib u ted as dividends, equal to 12^% , th e balance of
¿26,679 being carried forward. T he am ount of ground tre a te d during th e year was 4,054,060 cu. yd., as com pared w ith 4,854,630 cu. yd. in th e previous year, th e tin recovered am ounting to 1,580 tons, against 2,124 tons. The price realized for th e concentrate was ¿102,282.
N ew G uinea.— Shareholders
of the Oroville Dredging Com pany have been inform ed th a t a su b stan tial interest has been acquired in Bulolo Gold D redging, which owns a large area of alluvial gold pro p erty on th e Bulolo and W a tu t Rivers.
M exico.—The rep o rt of th e Mexican Cor
poration for the q u a rte r ended Decem ber 31 last shows th a t owing to low m etal prices the suspension of sulphide ore production at Fresnillo is under consideration, while th e Teziutlan p ro p erty was closed down a t th e end of th e year.
B r itish -A m e r ic a n Tin C orp oration .—
At an ex trao rd in ary m eeting of share
holders of the B ritish-A m erican Tin Corpora
tion, L td., held th is m onth, it was agreed th a t th e unissued capital of th e corporation, am ounting to ¿500,000, should be called preferred ordinary shares of ¿1 each and th a t th e whole of th e com pany’s assets, except its stock of m etallic tin, should be sold to a new com pany, th e B ritish Tin In v estm en t
Corporation, L td ., in re tu rn for 1,750,000 shares of 10s. each, credited as fully paid.
I t is proposed th a t th e co rp o ratio n ’s stock of tin m etal should be acquired b y a separate com pany, Tin Holdings, L td ., for ¿112,500, to be satisfied b y th e allotm ent of 2,250,000 shares of Is. each in th e new company, credited as fully paid. P resen t shareholders will th u s receive one fully-paid 10s. share in th e new investm ent corporation and three fully-paid Is. shares in Tin Holdings, Ltd., in re tu rn for each share now held.
B r itish S ou th A frica C om p an y. The
accounts of th e B ritish S outh Africa Com
pan y for th e y ear to Septem ber 30 last show th e n et profit to have been ¿262,151, against ¿409,762 in th e previous year, to which m ust be added th e sum of ¿647,053 b rought in from th e previous account. A dividend equal to 9d. per share absorbed
¿261,720, leaving ¿647,484 to be carried forw ard. A ccom panying th is rep o rt is an account of m ining activ ities in R hodesia by Mr. E. H . Clifford, in w hich he notes the serious decrease in th e value of th e mineral production of S outhern R hodesia, due principally to declines in th e coal, chrome, an d asbestos o u tp u ts, owing to th e depressed condition of in d u stry . In N o rth ern Rhodesia the curtailm en t of copper production has m eant a slowing down of activ ities on the copper b elt, although prospecting for other m inerals has been actively continued, and a deposit of m anganese ore a t Luano, six miles west of N ’Changa, is now being exploited to provide flux for th e N ’K an a sm elter.
C ord eroy S y n d ica te.— A
circular to shareholders of th e Corderoy Syndicate that accom panied th e rep o rt for 1931 intim ated th a t some decision regarding th e fu tu re of the com pany w ould have to be m ade. The altern ativ es before th e shareholders were eith er to tak e up an option over an alluvial gold area in New Mexico or th a t th e company should go into v o lu n tary liquidation, and the first course was approved a t th e annual m eeting. To provide th e necessary capital for th e developm ent of th is area shareholders are to surrender one-half of th eir holdings to tru stees appointed b y th e directors, the shares so surrendered being available for re-purchase a t Is. per share for a period of 21 days, a fte r w hich th e y m ay be sold by the trustees. The p ro p erty to be exam ined lies on th e R iver H ondo, a trib u ta ry of th e Rio Grande, and it is sta te d it embraces 10,000,000 cu. yd. of ground, averaging 2s.
per cu. yd. in recoverable value.
T H E SUB NIGEL GOLD MINE
By G. C A R L E T O N J O N E S
In this article the au th o r, w ho is consulting engineer to th e N ew C on so lid ated G o ld Fields, L td ., in the Transvaal, d escrib es operations at this H e id e lb e rg district mine.
The usual article dealing w ith th e general description of a m ine lays m ost stress on th e straight technical features involved, b u t in w riting of th e Nigel district, and of the Sub Nigel mine in particular, th e au th o r feels th a t there is so m uch of interest con
nected w ith th e pure rom ance of th e early days, which is not generally known, th a t an outline of th e vicissitudes of those tim es should not be out of .place.
One of th e earliest and richest discoveries of gold in th e W itw atersrand banket was
up of towns and villages along th e line of outcrop, th a t on the other hand it has taken practically 40 years to establish th e fact definitely th a t th e Main Reef Series is continuous between R andfontein and Nigel.
Gold in th e Nigel district was first dis
covered in a reef outcropping on th e farm V arkensfontein No. 217, which was pro
claim ed in 1888. The property was acquired by th e Nigel Gold Mining Company, L td., which a t once commenced operations, thus
Ge n e r a l Vi e w o f Re d u c t i o n Wo r k s, Su b Ni g e l Mi n e.
that in th e Nigel district, which followed immediately upon th e startlin g reef discoveries near Johannesburg, upcfn which world-wide a tten tio n had already been focussed. In those early days it was little thought th a t th e “ Nigel ” Reef, as it was then term ed, belonged to the identical reef series being opened up a t th a t tim e in the Johannesburg district, in fact the conception of a W itw atersrand, which would embrace th e eighty-m ile strip of country lying betw een R andfontein and Nigel was undream t of. E ven to-day the Sub Nigel mine, although exploiting th e reef series which has come to be acknowledged as being the continuation of th e Main Reef Series, is still excluded from th e W itw atersrand district in m ost of th e official retu rn s and reports. I t seems alm ost paradoxical, when considering on th e one hand th e rapid advance of th e in d u stry and th e springing
becoming th e first property in th e F ar E a st R an d district to produce.
Mining was first sta rte d in Ju ly 1888, th e m ethod consisting of blasting th e ore on to sheep skins and removing th e pro
duct by m eans of wheel-barrows or small trucks draw n by mules. The ore was then conveyed by m eans of ox-waggons to a five-stam p mill situ ated on th e Blesbok Spruit, nearly two miles from th e workings.
The gold recoveries in th e first treatm en ts surpassed all expectations and a t tim es showed over 5 oz. per to n for days on end.
F or th e y ear 1891 th e extraordinarily
high average of 2-23 oz. per ton was actually
obtained for 4,417 tons treated, and it m ust
be rem em bered th a t this high recovery
resulted from treatm en t by am algam ation
only. To such an extent had public interest
been aroused by this E ldorado th a t w ithin
a few years th e ground on all sides of
137
V arkensfontein was also proclaim ed, and
" Nigel ” added to th e nam e of an y pro
posed com pany was sufficient to ensure successful flotation, if th e acquisition of claims w ithin th e elastic boundaries of th a t district was th e new co m p an y ’s object.
By 1897 th irte en different “ Nigel ” com panies, w ith an authorized c ap ital of
£3,455,000 h a d been “ flo a te d ” from th e farm s V arkensfontein, D roogebult, Noyce- dale, B ultfontein, and M arievale, besides innum erable syndicates and individual claim holders ; b u t only th ree concerns cam e to actu al production. One p a rty of ad venturers banded together to prospect for diam onds in th e bed of Blesbok Spruit, indicating
which h ad intersected th e reef a t depths of 883 ft. and 686 ft. A t th e sam e tim e th e C entral Nigel Deep, L td ., beyond the Nigel Deep, had, w ith courageous enterprise, laid out th ree vertical sh afts in line to intersect th e reef a t an estim ated dep th of ab o u t 2,000 ft., and these shafts h a d been sunk to depths of 636 ft., 1,136 ft., an d 792 ft.
betw een th e years 1895 an d 1899. In the case of No. 2 Shaft, subsequent operations have proved th a t h a d th is sh aft been con
tin u ed a fu rth e r d ep th of 920 ft. it would have intersected th e phenom enally rich shoot which has now come to be known as th e Sub Nigel Main Shoot. U nfortunately all shaft sinking operations were stopped in
Su b Ni g e l Mi n e— So r t i n g f r o m Me c h a n i c a l Sh a k e r.
th e unbounded faith held a t th a t tim e in th e possibilities of th e district. N atu rally such liveliness, com bined w ith its distance from th e Reef towns, tended to m ake Nigel village a populous centre, th e re being no fewer th a n th irteen hostelries an d th e usual com plem ent of shebeens to cater for th e refreshm ent and am usem ent of the com m unity ; in fact th e village becam e a h ub of a c tiv ity an d according to th e “ old tim ers ” a very gay place indeed, com pared w ith th e quiet village of to-day.
Sub Nigel, L td., was form ed in 1895, w ith a cap ital of £350,000 to acquire 483 claims on Droogebult. T he com pany’s activities in its early years were confined to exploring th e reef b y diam ond drilling and to acquiring additional claim areas.
Meanwhile th e Nigel Deep, L td., form ed in 1894, an d com prising 659 claim s on V arkensfontein on th e im m ediate dip of th e Nigel G. M. Com pany’s ground, was m ining and producing from tw o shafts
1899, owing to th e C om pany’s funds having become practically exhausted. In 1903 a bore-hole was p u t dow n from th e surface to a d ep th of 3,404 ft., b u t encountered a dyke, which is now know n to be the dyke which is associated w ith th e main divisional fault betw een th e “ C ” Shaft and No. 1 Shaft area of th e Sub Nigel.
H ad th e No. 2 S haft been continued to
reef, or h a d th e site of th e bore-hole been
selected a few h u n d red feet to th e West,
th e m ain shoot of th e present Sub Nigel
m ine would have been encountered, an d it is
safe to say th a t th e developm ent of th e Far
E a st R an d w ould hav e been advanced by
at least 20 years ; in fact th e en tire layout
of th e W itw atersran d m ight to -d ay have
been to tally different, since advancem ent
would in all p ro b ab ility have been West
from Nigel instead of, as has been th e case,
E a st from Johannesburg. This will be the
m ore readily ap p reciated w hen it is realized
th a t th e Sub Nigel Main Shoot, which came
MARCH, 1932 139 so near to being intersected a t depth, has
not y et been surpassed in richness anyw here on th e W itw atersrand.
In 1909 th e Nigel Deep, although producing, h a d h a d a ru n of b a d luck and, through heav y faulting, was seriously ham pered in its operations b y lack of funds, while th e C entral Nigel Deep was in liquida
tion, w ith o u t even having reached th e reef.
The Sub Nigel, on th e oth er hand, h ad been able to conserve its resources by adopting the policy of aw aiting developm ents on th e neighbouring properties before com m itting itself to a production program m e, although in th e m eantim e acquiring th e 175 claims belonging to th e French W estern Nigel
from east to west over a distance of 3-8 miles in th e direction of th e strike, and from south to n o rth over a distance of 4-8 miles on th e dip of th e reef, em bracing a to ta l area of about 10-5 square miles.
I t will be seen from th e foregoing th a t th e Nigel mine, which sta rte d crushing in 1888, was th e im m ediate forerunner of deep level mining on th e Nigel Deep, which is now p a rt of th e Sub Nigel Mine. This Company, therefore, although only coming into pro
minence during th e past few years as a leading gold producer, can really be looked upon as one of th e pioneer m ining companies of th e W itw atersrand fields. Strangely enough th e W estern area of th e mine, which includes
Su b Ni g e l Mi n e— Na t i v e Dr i l l i n g, w i t h Sc r a p e r i n Op e r a t i o n i n Ba c k g r o u n d.
and a portion of th e Nigel Deep ground, 139 claims in ex ten t and including th e “ E ” Vertical Shaft. Accordingly, w ith th e help of a financial reconstruction, it was able to acquire th e rem aining assets of th e Nigel Deep, and commenced active operations on its own account on Decem ber 18, 1909, with a to ta l holding of 1,375 claims.
Various additional areas were taken up between 1914 an d 1919, including th e southern m y npacht of 500 claims on Groot- fontein, which was acquired a t a cost of
£131,956. In 1923 various worked out and barren areas, totalling 362 claims, in th e upper portion of th e mine were abandoned, an d in May, 1926, th e lease of 2,373 claims on G rootfontein was granted to th e Com pany by th e Union Governm ent.
The area held under m ining title a t the present tim e is 4,555 claims. A t its Southern end, which is th e wider, th e property extends
th e 483 claims on th e farm Droogebult on which th e original Sub Nigel Company was formed, was never exploited u n til five years ago, and th en only in a m inor degree by exploratory driving on th e 19th level.
The m ain concentration of effort has been on th e line of extension of th e pay streaks of th e Nigel mine, which have been, and still continue to be, parallel to th e longitudinal axis of a sharply defined a n ti
cline, th e tre n d of which is approxim ately N orth 30° W est. In th e eastern flank of this anticline occurs th e clearly defined and rich p ay streak which has now come to be locally know n as th e “ Main S hoot.”
The persistence of th is enriched zone can
best be gauged when it is realized th a t
it has been practically continuous from the
surface through to th e present dep th of
3,650 ft., equivalent to a length on dip
of over 22,000 ft., while th e w idth of th e
zone has averaged ab o u t 700 ft. A com
parison betw een th e richness of th e Main Shoot an d th e rem aining shoots of th e mine is clearly brought hom e by figures recently ta k e n out, which show th a t th e Main Shoot averages 64 dw t. over a 15 in. reef w idth, while th e rem aining shoots of th e mine average 35 dw t. over nine reef inches.
The h isto ry an d fortunes of th e Sub Nigel have always been w rapped up in th e difficulties of regularly following th e Main Shoot, th e chief com plication having been th e extrem ely serious dislocations which have ta k e n place through heav y faulting, th e fluctuations in value being of relatively m inor im portance.
P a y S h o o t s . —
The reef, which has a n o rth erly dip, is overlain by th e qu artzites an d underlain by th e slates of th e W itw aters- ra n d Series. The w idth of th e reef varies from a mere co n tact to as m uch as three feet and this v ariation generally supplies a fair indication of th e value, wide reef being pay, while conversely narrow reef is found to be u n p ay ; th is theory, however, is not infallible, an d occasionally stretches of a ttra c tiv e looking reef are encountered which are found to be below th e profitable m argin, while contacts are som etim es m et w ith which carry exceptionally high values.
The gold content is not evenly distributed, b u t pay zones are found along certain well- defined shoots which run more or less parallel to th e axis of th e m ain Nigel anticline.
These shoots are scattered over th e pro
p e rty from east to w est and are separated by large stretches of u n p ay rock, while in th e shoots them selves unaccountable barren areas occur.
As is to be expected from th e presence of th e anticline, th e faulting is b o th com plicated and extensive, m aking it extrem ely difficult to p u t into operation an y h ard and fast scheme for developm ent layout.
The m ain faulting, which roughly resembles a bad ly conditioned rectangle w ith its m ajor axis running approxim ately n o rth and south, constitutes block faulting, the faults having throw s varying from 200 to 500 ft. W ithin this rectangle subsidiary faulting has tak en place, w ith throw s varying from 50 to 200 ft., th u s causing fu rth e r com plication. D ykes occurring in th e mine, which are identified w ith th e V entersdorp and K arroo Systems, do not seriously in te r
fere w ith m ining operations, w ith th e excep
tio n of a sill which occurs a t depths of from 40 to 180 ft. below th e reef, and which at
tim es has been responsible for some costly developm ent.
On th e Sub Nigel some fourteen p ay streaks have been exposed, an d of these, as previously m entioned, th e m ost im p o rtan t is th a t known locally as th e Main Shoot. B etw een th e 11th and 14th Levels th is shoot varies in width from 600 to 800 ft., an d splits up into three shoots se p arated b y sm all areas of unpay ground. These shoots range in value from 200 to 500 inch-dw t. w ith patches of p ay ground up to 1,000 inch-dw t. Between th e 14th an d 19th Levels th e value increases, th e m inor shoots coming to g eth er to form a large block of highly p ay ground varying in value from 500 to 2,000 inch-dw t. On th e 18th Level a fault striking n o rth and south w ith a throw of 500 ft. divides the p ay shoot, which on th e “ C ” Shaft side continues w ith a slight tu rn from its normal course, while on th e No. 1 Shaft side the area ad jacen t to th e fault has been heavily distu rb ed by a series of dip faults, associated w ith erratic reef w idths an d values. Away from th e area of disturbance th e shoots come together again to form a large section of highly p ay ground ab o u t 700 ft. wide on th e strike an d extending in a com pact and highly payable body as far as th e 26th Level, divided on th e 24th Level, b u t n o t otherwise affected by a fault having an upthrow of about 300 ft. Below th e 26th Level th e shoot is sep arated into tw o portions b y an area of u n p ay ground, each portion, however, continuing to carry high values. N orth of this very little stoping has been done, but th e shoot has been exposed as far as a strike fault below th e 27th Level, by which it has been throw n up app ro x im ately 280 ft.
In this developed area values range from 500 to 2,000 inch-dw t. a n d over. Below this fault th e shoot has been encountered on the 27a a n d 28th Levels, th e average w idth being 700 ft., w ith values ranging u p to 4,000 inch-dw t., a n d interspersed w ith patches of barren ground. The Main Shoot below the 28th Level is being followed up w ith current developm ent.
As in th e case of th e Main Shoot, all other shoots m ay be roughly tra c e d from one level to another. The correlation is s tra ig h t
forw ard except in faulted or d isto rte d areas, where a certain a m ount of subsidiary developm ent is often necessary to obviate th e m ining of isolated barren patches.
To enable th e tre n d of th e shoots to be
closely followed an d th e changes in value
and conglom erate w idths to be shown up
MARCH, 1932 141 rapidly, special colour contour plans of both
value and reef w idth are k ep t up to date at the mine. On th e contour assay plan the inch-dwt. values obtained by sam pling are segregated into groups ranging from low through m edium to high values by m eans of contour lines of equal value. The direction of the observed long axis of th e conglom erate pebble—where obtainable—is also indicated on this plan. On th e conglom erate w idth plan, contours of equal w idths are drawn.
These plans have proved them selves of great value w hen laying out th e future developm ent of th e mine, as th e change in direction and tenor of the pay streaks
are shown a t a glance.
Opening up a new stope by th e old m ethod was laborious an d slow, owing to th e need for clearing th e tracks a t th e beginning of every shift to allow th e passage of cars.
Now th e stope is im m ediately equipped w ith a scraper, and broken ore is quickly and easily scraped to a box a t th e bottom . W hen stoping commences th e broken ore is throw n back into th e winze or “ gully ” in which th e scraper works. D uring the opening up period a considerable q u an tity of w aste is produced, b u t care is taken to see th a t this w aste is sorted and stacked for future use in supports.
W hen th e stope has advanced approxi
m ately 25 ft. from th e winze, th e scraper
Su b Ni g e l Mi n e— Sc r a p e r i n Op e r a t i o n, t h e Ph o t o g r a p h Sh o w i n g Me t h o d s o f Ha n g i n g- Wa l l Su p p o r t.
M i n i n g M e t h o d s .
