The Mining Magazine
Managing Director : W . F . Wh i t e. Assistant : S t. J . R . C. Sh e p h e r d,
A .R .S .M ., D .I.C ., F .G .S .
E d ito r : Ed w a r d Wa l k e r, M .Sc., F.G .S.
A ssis ta n t: F . Hig h a m,
A .R .S.M ., M .Sc., F .G .S . P u b l i s h e d o n t h e 1 5 t h o f e a c h m o n t h b y M i n i n g P u b l i c a t i o n s , L i m i t e d ,
a t S a l i s b u r y H o u s e , L o n d o n , E .C . 2.
T e lep h o n e : L o ndon Wall 8938. T e le g ra p h ic A d d r e s s : Oligoclase. C o d e s : M c N e ill, b o th E d itio n s , & B e n tle y . Y o r k : A m e r. I n s t . M. & M .E . i 12s. p e r a n n u m , in c lu d in g p o s ta g e . Br a n c h Of f i c e s^ C h ic a g o : 3 60, N . M ic h ig a n B lv d . Su b s c r i p t i o nj y g A _ $g p e r an n u m ? in c lu d in g p o s ta g e .
Vol. XLI. No. 5. L O N D O N , N O V E M B E R , 1929.
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 ... 258
A W a r B o o k ; P r e s id e n tia l a d d re s s to th e I n s t i tu t io n ; B o ra x C o n so lid a te d ; Q u a rry in g a n d th e C o u n try sid e . The In stitu tio n in S w a n s e a ... 259
T h e r e c e n t v isit to th e w o rk s o f th e M o n d N ic k e l Co. a n d th e N a tio n a l S m e ltin g Co., S o u th W a le s , is d escrib ed . Boring for Oil in K ent ... 260
C o m m en t is m a d e o n a p ro p o s a l to s in k a w ell fo r oil n e a r H y th e . The Protection of Investors ... 261
T h e new C o m p a n ie s A c t c a m e in to fo rc e o n N o v e m b e r 1, a n d a lre a d y a c a m p a ig n fo r th e i n tr o d u c tio n o f f u r th e r m e th o d s of p r o te c tin g in v e s to rs h a s b e e n la u n c h e d . R e v i e w o f Mi n i n g ... 262
Ar t i c l e s The M ount Isa Lead-Zinc Mines, N orth Queensland ... 265
D iam ond Mining on th e Gold Coast 5 . V. Griffith 271 Southern M alayan Tin Dredges ...282
Bo o k Re v i e w s W ilsk i’s “ M ark sch eid ek u n d e,” P a r t I D r. H en ry L o u is B ow en’s “ T h e E v o lu tio n of th e Igneous Rocks ” Dr. A rth u r Holmes “ P e tro le u m D e v elo p m en t a n d T echnology ” H . B . M iln e r B u sk ’s e tc .” E a r th F lex u res T h e ir G eom etry, . . H . B . M iln e r 283 285 287 288 N e w s L e t t e r s J ohannesburg 289 L o w -g ra d e M ines P r o b l e m ; T o n s o f D i a m o n d s ; A llu v ia l D ia m o n d s ; S t a te D ia m o n d s S a les ; T r a n s v a a l E m e r a l d s ; J a d e ; B e ry lliu m S u p p l ie s ; M an g an ese D e v e lo p m e n ts ; F a lse B a y F o rm a tio n . Brisbane ... 291
Q u e e n sla n d Oil P r o s p e c t in g ; D r. W o o ln o u g h ’s R e p o r t ; C oal fro m A b ro a d ; M o u n t I s a M ines ; B ro k e n H ill M ines ; A B ig C e n tra l P o w e r P la n t. V a n c o u v e r ... 293
A lice A r m ; B o u n d a r y ; T h e K o o t e n a y s ; P o r tla n d C a n a l ; V a n c o u v e r I s la n d ; Y u k o n T e r rito r y . T o r o n t o ... 295
S u d b u r y D i s t r i c t ; P o rc u p in e ; K irk la n d L a k e ; R o u y n ; M a n ito b a . C a m b o r n e ... 297
U n e m p lo y m e n t a n d a P ro p o s e d R e m e d y ; T h e P ric e of T in . P e r s o n a l ... 298
T r a d e P a r a g r a p h s ... 298
M e t a l M a r k e t s ... 299
S t a t i s t i c s o f P r o d u c t i o n ... 301
P r i c e s o f C h e m i c a l s ... 303
S h a r e Q u o t a t i o n s ... 304
Mi n i n g Di g e s t T h e Seism ic M ethod in G eophysics E . H . Neville 305 E le c tro ly tic Z inc a t A naco n d a (concluded fro m October issue) A . E . W iggin and R . B . Capíes 307 C a ssiterite D eposits in U g an d a E . J . W ayland 309 M odern M ining E xplosives Dr. W illia m Cullen 312 T in M ining in B a n k a . . . . J . B . Scrivenor 313 L ead-Z inc D ep o sits on G re a t S lave L ak e D r. J . M ackintosh B ell 315 B ritis h Som aliland M inerals ... 316
S h o r t N o t i c e s ... 317
R e c e n t P a t e n t s P u b l i s h e d ... 317
N e w B o o k s , P a m p h l e t s , e t c ... 317
C o m p a n y R e p o r t s ... 318
C am a n d M o to r ; C h o sen ; E a s te r n S ia m T in D re d g in g ; G ly n n ’s L y d e n b u rg ; J a n t a r (Cornw all) ; J u g a V a lle y T in A re a s ; K a g e ra (U g a n d a ) T in f ie ld s ; N a r a g u ta K a r a m a A r e a s ; N ig e ria n B a se M e ta ls ; S h e rw o o d S t a r r ; S u b N i g e l ; T e m o h T in D r e d g in g ; Y a rd e K e r r i G ro u p T in M ines ; Z a a ip la a ts T in M ining. D i v i d e n d s D e c l a r e d ... 320
N e w C o m p a n i e s R e g i s t e r e d ... 320
5—3 257
E D IT O R IA L
M
ANY books hav e been w ritte n on th e w ar giving th e personal experiences of th e w riters, b u t th e re is still room to be found on our shelves for th e la te st one published : “ W ar L e tters to a W ife,” b y Colonel R ow land Feilding. F o r four years, from 1915 to 1919, th is g allan t soldier, who is well know n to m a n y of our readers, was present on th e w estern fro n t in N orthern F rance and Belgium, and his account is in the form of a vivid d iary chronicling th e events as th ey happened, w ith th e im pressions m ade on his m ind a t th e tim e. Exigencies of space p rev en t us from saying m uch ab o u t w ar books, b u t we cannot let th e publication of Colonel F eilding’s diary pass w ith o u t th is appreciative if brief m ention.T
H E delivery of th e address by th e president of th e In stitu tio n of Mining and M etallurgy has been a m ovable function in each session recently. This year it has been found advisable for Dr. W illiam Cullen to take th e first evening of th e 1929-30 session because th e annual m eeting in April will be distu rb ed by th e E m pire Congress in S outh Africa. Accordingly th e m eeting held on O ctober 17 was occupied alm ost entirely w ith his address on “ Modern Mining E xplosives.” Coming from one who has been so long associated w ith th e m anufacture of explosives his rem arks were n a tu ra lly of considerable value. Elsewhere in th is issue e x trac ts are m ade from th e address, dealing w ith azide detonators, sem i-instantaneous fuses, and non-freezing nitroglycerine explosives, which are all com p a rativ ely new features of explosive practice.T
H A T B orax Consolidated should n o t be able to p ay its usual dividend on th e deferred shares comes to m an y as a surprise, seeing th a t th e com pany tw o years ago m ade an im p o rta n t discovery of a v a st deposit of a new m ineral w hich can be worked more cheaply th a n th e colem anite (calcium borate) w hich has been th e chief source of b o rax an d boracic acid during recent years. This new m ineral is kernite, N a2 B 4 0 7-4 H 20 , or rasorite as it is called by th e com pany, nam ing it after th e ir engineer. I t differs from borax in having four molecules of w ater instead of ten. The reason why no dividend is being paid is th a t th e com pany requires funds for equipping m ines and building new refineries.D uring th e last y ear or tw o th e m arket
price of b o rax has dropped considerably and it was supposed in m any q u arters th a t the discovery of I th e new m ineral was th e cause.
I t appears, however, th a t th e fall is due to th e Searles L ake producers selling their borax as a by-product, relying entirely on th e p o tash content of th e brine for their profit. No doubt w hen B orax Consolidated is w orking th e new deposit to advantage th e price will stead y itself again, b u t at a lower figure th a n was custom ary until recently.
P
E R IO D IC A L L Y th e m arring of n atu re’s face b y m ining an d quarrying operations comes up for discussion am ong people of refinem ent. T h a t th e production of useful m inerals should so often entail an offence to a rtistic feeling is, of course, to be reg retted , b u t th is draw back has been obvious from th e daw n of civilization and th e objection to these scars has been m iti
g ated by th e knowledge th a t th e general advan tag e to m an k in d overbalances a local irritatio n . So th e com m u n ity has been content to view w ith resignation th e riddling of Cornwall w ith tin m ines and clay-pits, the spoiling of th e D erbyshire ravines b y lime
stone quarries, an d th e wholesale rem oval of P enm aenm aw r. As th e p opulation and its requirem ents increase, so do th e scale of operations. A t th e present tim e th e b attle of opposition to wholesale quarrying rages round th e M alvern Hills, w hich for genera
tions have yielded an unobtrusive supply of stone, b u t are now th re aten ed , it is alleged, w ith to ta l extinction. T he facts cannot be denied, b u t th e opposition is p itched in too- h y sterical a key. If m odern m ethods of tra n sp o rt call for good roads an d plenty of them , th e stone m u st be obtained, th e best a n d easiest quarried, an d th e owners of such deposits are obliged in these days of financial pressure to realize th e ir possessions to th e b est advantage. T here is also another point of v ie w : Supposing th e im ports of stone from foreign countries increased, w ould there n o t be an o u tcry in various q u arters and resolutions passed to th e effect th a t th e n a tu ra l resources of th is co u n try should be developed an d th e tra d e th u s kept w ithin our own boundaries ? So th e engineer or business m an connected w ith mineral production suffers from onslaught on both sides and th e co n trad icto ry criticism s are a p t to leave him indifferent to public com m ent.
NOVEM BER, 1929 259
T h e I n s titu tio n in S w a n se a Invitations having been extended to the Institution of M ining and M etallurgy to visit the works of th e Mond Nickel Company, Ltd., and of th e N ational Sm elting Company, Ltd., an enjoyable expedition to Swansea was undertaken by some six ty members, who were well repaid for having found tim e to break aw ay for tw o or th ree days from their ordinary routine. A considerable proportion of th e travellers also visited the new tin-plate works of Baldwins, L td. I t is to be hoped th a t th e In stitu tio n will in th e coming years be th e fo rtu n ate recipients of many like a ttra c tiv e summonses, for there can be no question th a t these journeyings and m eetings of a more or less inform al character are nothing if not beneficial in their consequences. A part from th e oppor
tunities afforded of paying privileged visits to works of specific technical interest, these occasions bring about a m arked increase in social intercourse in serving as m eeting places of old associaties and friends, wherein also many new allegiances have their beginning.
It is im portant in th is connection to compare the In stitu tio n w ith th e In stitu te of Metals, the Iron and Steel In stitu te , th e A ustralasian Institute of Mining and M etallurgy, and the American In stitu te of Mining and M etal
lurgical Engineers, all of which hold m eetings in different m ining or m etallurgical centres year by year. The E m pire M ining and M etal
lurgical Congress undoubtedly acted as a spur to the In stitu tio n in th is m atter, of which the first evidence was th e highly successful m eeting in Cornwall last year.
The latest event is especially interesting, however, in th a t it signalizes a departure from a policy long pursued by the Mond Com
pany of discouraging—in fact, forbidding — the admission of visitors. This does not, of course, m ean th a t the whole of the secrets of practice were laid bare to all and sundry, for they still h ad to accept th e words of th e guides as to the reactions occurring w ithin certain lofty towers. Many of th e p a rty were d o u b t
less fam iliar w ith th e nickel carbonyl process, but none h ad previously seen th e p lan t in which th is exceptional m etallurgical opera
tion is carried out. I t is hardly necessary to remind th e curious th a t th e gas content of those carefully-sealed cham bers is one of the most deadly poisons known to m an and th a t for th is reason, if no other, there has been little inclination to extend the carbonyl process. I t is understood, however, th a t
certain work is being done in G erm any by the I. G. F arbenindustrie on th e purification of iron and cobalt by forming th e carbonyls of these m etals.
In th e spelter works a t Swansea Vale some visitors m ade their first acquaintance w ith the distillation process, while others h ad it borne home to them y et again how laborious is th is ancient m ethod of obtaining th e m etal from th e flotation concentrates w hich are now reaching th is country b o th from A ustralia and Canada. T he difficulties experienced in handling these concentrates in virtu e of th e ir fine sta te of subdivision, and th e consequent necessity for sintering furnaces to render them suitable for retorting, were m ade apparent. The contact acid p la n t was new to m any and is specially no te
w orthy because these plants usually require sulphur or high-grade pyrites for their operation, th e gases from blende and galena concentrates being too dusty, im pure, and of too low a grade, and only recently has the process been im proved sufficiently to adm it of its use here. The tin -p late works visited b y some of th e p a rty are th e m ost m odern in th is country. Here th e tin-plate is m ade from which Shell petrol tins are m anufactured an d th e lay o u t whereby there is an easy flow from m ild steel strip to finished tinned plate in a m inim um of operations is adm irable.
An account of th is excursion would be incom plete w ith o u t some reference to the generosity of th e hosts. The Mond Nickel Com pany en tertain ed th e ir guests, under the chairm anship of Mr. D. O. Evans, in th eir own in stitu te. N ot the least enjoyable feature of th e ir h o sp itality was th e m usical accom
panim ent supplied b y th e works orchestra.
Mr. J. L. Agnew, th e vice-president of th e In te rn atio n al Nickel Company, spoke a few words of encouragem ent th a t will surely have been very welcome in Swansea when he rem arked th a t it was not th e intention of the combined nickel companies to close the Clydach works, which would continue to p lay th e ir p a rt in spite of th e extensive production of th e m etal in Canada. The N ational Sm elting Com pany were hosts to th e p a rty a t dinner th e same evening and Mr. Stanley Robson, who presided over this entertainm ent, gave a concise sketch of the process of distillation and alluded guardedly to th e future technical policy of th e com pany w ith regard to th e treatm en t of concentrates a t A vonm outh. W hile distillation is to be th e m ethod, his hearers gathered th a t some m odification of th e process m ay be expected.
260 T H E M IN IN G MAGAZINE Finally, a w ord of appreciation is due to
th e officials of th e In stitu tio n and of th e com panies m entioned for th e sm ooth w ay in w hich th e functions were developed. In particular, Dr. Cullen is to be con g ratu lated on th e genial w ay in w hich he m arshalled his p a rty and Mr. M cDermid for his efficient organization.
B o r in g fo r O il in K e n t
Statem en ts have been m ade in th e press th a t an oil-well is to be sunk on R om ney Marsh, to th e west of H y th e, in K ent, and th e sponsors of th e scheme are sufficiently optim istic to expect a supply of oil a t 1,000 ft. Seeing th a t th e surface deposits give no evidence of underground oil storage, th ere m u st be some o th e r technical reason for th e new activity. I t is safe to an ticip ate a considerable thickness of Kim m eridge Clay a t no g reat d ep th below H y th e , an d as th is form ation is consistently associated w ith oil-shale th e present venture is probably based on a hope of finding an oil pool in th e clay or in adjacent stra ta . As such a hope is of th e flimsiest, it is ap p ro p riate to review th e question once m ore, so th a t those who m ay th in k of tak in g a financial in tere st shall know th e risk involved.
The K im m eridge Clay as an oil-bearing deposit is a well-worn them e of geological discussion, an d is seldom left to rest for long.
U p and down its visible outcrop it has been studied for all kinds of interests, academ ic and economic, while in its subm erged develop
m ent it has frequently been vested w ith th e glam our of lim itless resources of oil or gas, or both, to say nothing of its genuine credit as a rep u tab le oil-shale horizon. W herever it is m et w ith, either a t outcrop from D orset to N orfolk or in sam ple from in
num erable borings, it is one of th e m ost rem arkably consistent deposits w ith w hich we are fam iliar. As a m other-rock of petroleum it certainly once possessed great p o ssib ilitie s; as m aterial it was fu n d a
m entally a good, m u d d y slime, extrem ely uniform in character and grade ; as an environm ent for th e peaceful b urial of a prolific m arine fau n a an d flora it was alm ost id e a l; in response to th e sim pler stresses of consolidation it behaved m uch as m any oth er b itu m in o u s rocks of sim ilar n a tu re an d geological age have done ; b u t som e
where in th e m echanism of its form ation, as we know it to-day, th ere was a m issing p a rt, a condition essential to th e conception
of free oil which it is n o t easy to define.
T he geo-chemical processes im plied by the deposition an d subsequent h isto ry of this clay were decidedly inim ical to th e segrega
tion of qu an tities of fluid hydrocarbon, or even if th is did form a t an y phase there was a p p aren tly no reservoir in th e shape of sand-lenses in to w hich th e oil m ight be expelled and u ltim ate ly trap p ed , so its organic energies were directed to enriching th e deposit itself, to th e production of oil- shale and sporadically occurring natural gas pockets. In th e face of all th e evidence, it is inconceivable th a t, h ad th e Kimmeridge Clay been a favourable oil-bearing rock, it would n o t have shown appropriate signs of such condition long ago, an d th a t measur
able yields of petroleum w ould have been realized in such deep borings as have in the p a st p e n e tra te d it ; b u t beyond th e natural gas m entioned, it has alw ays proved singularly, or perhaps we should say in
evitably, sterile of free oil, and we are unaw are of an y new ly-discovered character w hich would lead to a supposition th a t it could behave differently.
Of th e oth er “ p o ssib ilities” under H ythe th e P urbeck rocks, well-known from the Sub-W ealden borings, from outcrops in the cen tral W eald, and from water-wells, may be ruled out, even though certain limestones an d gypsiferous shales m ay smell strongly of No. 1 petrol, as is th e case a t th e gypsum mines in Sussex. These are too much fra ctu re d an d d istu rb e d to form eith er good m other- or reservoir- rocks, and, besides, it has been shown conclusively th a t th e y have borrow ed m ost of th e ir bitum inous (fluid) content from th e K im m eridge Clay via the intervening P o rtla n d form ation, incidentally th e present source of th e H eathfield gas.
T he P u rb eck beds m ay or m ay not be preserved a t H y th e ; sim ilarly there is the doubt ab o u t th e P o rtlan d ian , which, if present, would a t least serve as a reasonable reservoir to an y K im m eridge oil or gas available. If we descend deeper, to pre- K im m eridgian horizons, m uch th e same scientific objections apply, w hether it be to Corallian, Oxfordian, Lower Oolites, or Lias, and in any case to reach th e base of the Kim m eridge Clay below H y th e — th a t is, practically a t sea-level—w ould require drilling to considerably m ore th a n 1,000 ft.
We cannot credit even th e in stig ato rs of th is contem plated oil-well w ith th e idea th a t an upw ard m igrating Palaeozoic oil has been trap p e d a t a convenient shallow horizon ;
NOVEM BER, 1929 261 apart from th e fact th a t we do n o t believe
in the existence of Palaeozic oil anywhere in this p a rt of th e country, any theory th a t involved such m igration through a rock- column composed of th e types known in the concealed Mesozoic would be wildly fantastic.
T h e P r o te c tio n o f In v esto rs The Companies Act of 1928 cam e into force on th e first of th is m onth, b u t public interest in it has w aned considerably since the days of th e long discussion th a t took place in P arliam ent and elsewhere a year or two ago. A lready another cam paign for further im proving com pany law and protecting the investor has been launched and m any of th e suggestions th a t formed part of the propaganda of reform during past years b u t failed to receive general support are being revived. The case for additional action was vigorously tak en up at the m eeting of th e Law Society held last month by th a t ard en t protagonist, Mr.
Charles L. Nor don. He pointed out th a t much of th e recent legislation is futile in preventing fraudulent or ill-advised prom o
tions and th a t penalties for gross infractions of com pany law do n o t save th e investor from losses. I t is no consolation to th e disappointed shareholder to know th a t those responsible for swindles m ay possibly receive a term of penal servitude, and Mr. N ordon therefore pleads for laws and regulations which will kill th e dangerous schemes a t their inception.
One of th e recom m endations he p u ts forward is th a t all prospectuses should be issued in standardized form, th e inform ation being given in uniform order under headings of prom inent type, and th a t perm ission to publish a prospectus should not be given without a certificate of approval from the Registrar of Jo in t Stock Companies, after due verification of every statem en t of fact.
In addition th e prospectus should contain copies of all m aterial docum ents or full abstracts of such docum ents as approved by the Registrar. This would be far more useful th a n th e present com pulsory printing of the M em orandum of Association and the names and addresses of th e clerks who have signed it, for th is M emorandum is seldom read by intending shareholders a n d usually contains no useful inform ation.
O ther suggestions m ade b y Mr. N ordon are th a t every director shall be required to state in th e prospectus his qualifications for the position ; th a t no underw riting shall be
referred to in a prospectus unless th e under
w riters have deposited w ith th e com pany’s bankers th e am ounts due on application and allotm ent, th u s preventing “ t r u s t s ” and
“ corporations ” w ithout adequate financial resources entering into obligations th ey cannot carry o u t should th e public applications fall short of th e required am ount ; and th a t th e B oard of T rade should assum e th e d u ty of enforcing penalties laid down by th e Act an d of investigating grievances an d com plaints on behalf of shareholders. Among th e foregoing sugges
tions perhaps th a t relating to th e qualifica
tions of directors will be th e m ost difficult to carry out, for u n d oubtedly m any influential men, w ith little or no special business a p titu d e b u t able to com m and capital, expect some recompense and claim a seat on th e b o ard in order to w atch th e interests of th e ir financial supporters. Then again m an y people w ith experience in th e technical p a rt of a venture m ay n o t be business experts and th eir directorships m ay have disastrous results. However, th e inclusion of a provision in th e A ct such as th a t suggested w ould effectively sc atter crowds of w h at inoffensively m ay be called am ateu r directors. Mr. N ordon is inclined to recom m end a still more drastic regulation in th is connection by m aking it compulsory for all directors to be licensed.
One of th e crying grievances of th e present day is th e grow th of “ tru s ts ,” th e ostensible object of which is to enable an investor to do his business all in one transaction, a t th e same tim e giving him an o p p o rtu n ity of p articip atin g in favourable new flotations issued under th e auspices of th e " tr u s t.”
Theoretically, and when th e directors are experienced and tru stw o rth y financiers, such an in stitu tio n serves an excellent purpose, b u t now adays there is no guarantee th a t th e funds subscribed will be used to the advantage of th e subscriber and n o t applied to purely speculative and indeed risky transactions. W hether Mr. N ordon has any specific cure for th is u n fo rtu n ate sta te of things is not quite clear, b u t one of his suggestions m ay possibly cover these cases, nam ely, th a t every issuing house shall be licensed by th e B oard of T rad e and be re
quired to m ake a substantial deposit to m eet claims in th e same w ay as insurance com
panies. Such a requirem ent m ight effectively help in regularizing th e use of m oney sub
scribed in this way, b u t probably other pro
visions would also be necessary to remove one of th e sinister features of current finance.
R E V IE W O F M IN IN G
I n tr o d u c tio n . — The dullness w hich ushered in th e au tu m n has continued and b o th th e Stock E xchange a n d th e M etal E xchange have ex h ib ited weakness. In spite of considerable a c tiv ity am ong tin producers w ith th e object of stabilizing prices, tin has continued to fall. The general collapse on th e New Y ork Stock E xchange following over
speculation caused some excitem ent here, b u t th e adverse effect was n o t so g reat as m ight have been expected. Political events in B ritish coal circles are causing some uneasiness, for th e G overnm ent, th e coal owners, an d th e m iners all seem to have different views as to th e expected decrease in th e hours of em ploym ent and a settlem ent of th e new conditions appears a t present to be far off. T he form ation of a G overnm ent com m ittee to exam ine banking practice m ay be of even tu al value in m aking it possible for banks to give b e tte r and cheaper facilities for in d u strial loans. On th e o th er hand, some objection m ay be m ade to th e G overn
m e n t’s financial proposals for in augurating public works for th e relief of unem ploym ent.
T r a n sv a a l.—The o u tp u t of gold on th e R an d during O ctober was 853,609 oz. and in outside d istricts 35,081 oz., m aking a to ta l of 888,690 oz., as com pared w ith 849,553 oz. during Septem ber. A t th e end of O ctober th e num b er of n a tiv es engaged a t th e gold m ines was 189,739, as com pared w ith 190,567 a t th e end of Septem ber.
The results a t Sub Nigel for th e y ear ended J u n e 30 la st are given elsewhere in th is issue. I t will be seen th a t developm ents have n o t fully m ain tain ed th e reserve of rich ore, th e to ta l reserve being e stim ated a t 891,000 tons averaging 18-2 dw t. over a stoping w idth of 22 in., as com pared w ith 986,000 to n s averaging 19-7 dw t. over 24 in. th e year before a n d 1,013,000 tons averaging 20 dw t. over 25 in. tw o years ago. A large a m ount of developm ent w ork has been done, th e footage being 42,367 ft., as com pared w ith 22,559 ft. th e y ear before.
Of th e footage sam pled 36-7% was payable, as com pared w ith 4 2 -9% .
S o u th e r n R h o d e s ia .—T he o u tp u t of gold during S eptem ber was re p o rted a t 45,025 oz., as com pared w ith 46,473 oz.
in A ugust an d 47,716 oz. in Septem ber, 1928. O ther o u tp u ts during S eptem ber were : Silver, 5,837 oz. ; coal, 90,279 tons ; chrom e ore, 17,976 to n s ; asbestos, 3,674 to n s ; arsenic, 20 t o n s ; corundum , 16 t o n s ; mica, 16 t o n s ; iron, 210 t o n s ; scheelite,
3 t o n s ; tin , 2 t o n s ; b ary tes, 59 t o n s ; diam onds, 17 carats.
The Gold Fields R hodesian D evelopm ent Co. m ade a profit of £181,604 during the year ended May 31 last an d has d istributed
£125,711 as dividend, th e ra te being 10%.
D uring th e previous y ear th e profit was
£169,019 an d th e dividend was th e same.
No new in terests of im portance have been acquired recently, b u t holdings in the W anderer, M ayfair Gold, and Loangwa Concessions hav e been increased.
O perations a t th e W anderer Consolidated Gold Mines com m enced on O ctober 8 and from th en u n til th e 16th of last m o n th 2,312 tons of ore averaging 5-56 dw t. per ton was tre a te d for a yield of 567 oz., equal to 4-91 dw t. per ton. I t is expected th a t th e plant will be w orking a t full cap acity ab o u t the m iddle of th e cu rren t m onth.
I t will be rem em bered th a t, on th e poor prospects a t th e Copper Queen being dem o n strated b y Dr. McCann, th e Southern R hodesia B ase M etals C orporation decided to suspend w ork th ere a n d tra n sfe r th e plant to th e A laska copper m ine. The report now issued shows th a t th e first u n it started in th e m iddle of S eptem ber an d from then u n til th e m iddle of O ctober 155 tons of high-grade co n cen trate was produced and is to be shipped to E urope. I t is hoped th a t in th e course of a sh o rt tim e th is u n it will reach its norm al cap acity an d be producing 200 to n s of co n cen trate p er m onth.
N o r th e r n R h o d e s ia . — News from Loangw a Concessions is n o t v ery cheerful, as th e first diam ond-drill hole has registered 10 ft. of ore averaging only 0 -9 % copper.
Those who have read th e article last m onth on estim atin g ore reserves by bore-hole will realize, however, th a t th e y need n o t be alto g eth er discouraged.
The R hodesian Selection T ru st and the R hodesian Anglo A m erican are b o th issuing new cap ital for th e purpose of extending th e ir copper operations in N o rth ern Rhodesia, p articu larly in connection w ith th e Mufulira a n d Cham bishi m ines. The Rhodesian Selection T ru st is o p eratin g these properties u n d er agreem ent w ith B w ana M’Kubwa, w hich com pany is controlled b y R hodesian Anglo American. The Selection T ru st, which is th e parent com pany of th e Rhodesian Selection T rust, has also increased its capital and some a t any ra te of th e new m oney will be used in developing R hodesian copper mines.
262
NOVEM BER, 1929 263 Gold C o a st .— I t will be rem em bered
that A shanti Goldfields C orporation acquired the old B ibiani gold mine in 1927 w ith a view to reopening it an d conducting exploratory work. A t th e m eeting of shareholders held last m onth it was state d that progress has been slow owing to th e dangerous condition of th e workings. The shaft has been cleared and lined w ith steel setts to the deepest level—No. 3, a t 368 ft.
—opened up b y th e old com pany, and th e rest of the sh aft— 100 ft.— is being cleared and similarly lined.
N igeria.—Three com panies of the Latilla group are to be am algam ated, w ith the idea of cu ttin g expenses in face of th e present low price of tin. These are th e Nigerian Base M etals Corporation, th e Anglo- Nigerian Tin Mines, and th e Nigerian Power and Tin Fields. The la tte r has recently handed over its K u rra Falls h y d ro electric undertaking to th e A nglo-Oriental group. The chief m ining properties of th e three companies are in th e same district and this fact, together w ith th e expected supply of electric power, is hoped to m ake it possible to work them more economically.
The Ribon Valley Tinfields, a com pany belonging to the L atilla group, finds itself in financial difficulties owing p artly to the fall in th e price of tin an d p a rtly to th e new plant n o t sta rtin g operations as early as was expected. The rep o rt for th e tw o years ended M arch 31 last shows credits of
¿41,796 from the sale of 316 tons of tin concentrate and costs of £41,984, leaving an adverse balance on w orking of £187.
The position is rendered unsatisfactory by an interim dividend having been paid in February, 1928, when 7£%, absorbing
£11,500, was d istrib u ted . This am ount n o t only absorbed the balance carried forw ard on March 31, 1927, b u t results in an adverse balance of £4,130 being shown a t March 31, 1929.
India.— In th e last annual report of the Mysore Gold Mining Co. it was m entioned th a t a new lode h ad been cut by bore-holes from th e surface a t a distance of 1,600 ft. east of the outcrop of th e m ain lode. A pilot shaft was sunk and th e news is now to hand th a t th e lode has been cut a t a dep th of 280 ft., where it is 10 in. wide and assays 3 oz. 2 dwt. per ton. I t will be rem em bered th a t Mr. Thom as Pryor, in his paper on the geology of th e K olar goldfield six years ago, m entioned th a t there are a t least 26 lodes in th is district and th a t only th e Champion and O riental lodes have been developed, the
m ain, or Cham pion, lode having accounted for nearly all th e gold ou tp u t. The lodes all dip to th e w est and th e O riental is about half a mile to th e west of th e m ain lode, while th e new lode now struck is to th e east of the m ain lode. I t is about four years since exploration b y diam ond-drill was a d o p ted a t th e K olar group of m ines. So far th e results published have concerned underground w ork an d th e presen t case is presum ably th e first of discovery an d develop
m ent from surface.
M a la y a .—K am p ar M alaya T in Dredging, L td., was form ed by th e A nglo-O riental group in 1927 to acquire from th e London Tin Syndicate tin-bearing lan d on th e K am par R iver, Perak. The dredge sta rte d in May last. D uring Ju n e it tre a te d 123,700 cu. yd. for 50 tons of tin concentrate an d th e o u tp u t gradually increased u n til in Septem ber 227,500 cu. yd. was tre a te d for 80 tons. D uring th e four m onths 250 tons was e x tracted from 716,700 cu. yd., th e yield per y a rd being 0-78 lb.
The present position of tin was discussed early th is m o n th in th e F ederal Council by Sir W illiam Peel, th e Chief Secretary, when m aking his statem en t relating to th e finances of th e F ed erated Malay States.
H e expressed him self as doubtful of any advantage to be gained by th e curtailm ent of o u tp u t on th e p a rt of existing producers, but, in response to com m unications m ade by th e Cham ber of Mines, he and his colleagues were considering th e question of th e alienation of land for m ining purposes.
H e stressed th e im portance of conserving th e tin resources of th e country and said th a t th e present increase in th e o u tp u t of tin was n o t helpful either to th e G overn
m ent or th e industry.
A u str a lia . — The W est A ustralian M inister of Mines has agreed to advance
£10,000 free of interest to Boulder Perseverance to help in th e building of a new brom o-cyanide p lant, which is to cost
£30,000. I t is believed th a t w ith th is p lan t a saving of 6s. per to n will be effected in th e cost of extraction. W hen th e cost is reduced by 4s. or more per to n repaym ent of th e advance is to be m ade b y a ro y a lty of Is. per ton.
A notew orthy victim of th e low price of tin is th e M ount Bischoff Tin Mining Co., of Tasm ania, which has shut down its mines and sm elter aw aiting b e tte r tim es. This com pany has been in operation since 1873, w ith never a break u n til now.
Owing to th e continuance of th e coal
264 T H E M IN IN G MAGAZINE lockout in New S outh W ales, w hich has
caused a lower o u tp u t of iron an d steel an d a higher cost of production, th e B roken H ill P roprietory Co. has been unable to declare th e usual half-yearly dividend.
C a n a d a .—A serious fire occurred on O ctober 28 a t th e Dom e Mines, Porcupine, w hen th e m ill was com pletely destroyed.
C o r n w a ll.— In these days of depression in Cornish tin m ining owing to th e low price of th e m etal it is p leasant to be able to record th a t th e Geevor m ine, a t Pendeen, has declared an interim dividend for th e half year ended Septem ber 30 last. D uring th is period 28,562 tons of ore yielded 422 tons of concentrate, selling for £42,750.
A pproxim ately th e yield per to n was w orth 36s. 7d., th e cost per to n 29s. 6d., an d th e to ta l gross profit £10,000. The interim dividend, a t th e ra te of 5% , will absorb
£8,212. D evelopm ent continues to disclose ore of a satisfactory character.
Polhigey Tin, L td ., in its re p o rt for th e y ear ended A pril 30 last, states th a t milling s ta rte d on F e b ru a ry 21 and from th a t d ate to th e end of th e y ear covered b y th e re p o rt 10,500 tons of ore was m illed, th e o u tp u t of co ncentrate being 34 tons. F o u r lodes are being developed, th e chief one being e stim ated to average 22 lb. of tin oxide p er to n over a w id th of 49 in. T he reserve of ore blocked out is given a t 115,400 tons, sufficient to keep th e m ill going for 20 m onths.
K e n t.—A year ago it was announced in these columns th a t th e Tilm anstone (Kent) Collieries, L td., h a d o btained powers to build an aerial ropew ay from th e m ine to Dover harbour. L ast m onth th e section of th e ropew ay from Tilm anstone to Pineham , tw o-thirds of th e w ay to Dover, was com pleted and it is expected th a t th e rem ainder will be a t w ork in D ecem ber, so th a t shipm ents from D over h arb o u r should commence early in th e new year. I t will be rem em bered th a t th is m ethod of tra n sp o rt from th e m ine to th e sea was ad o p te d on account of th e high cost of th e sh o rt railw ay journey. The ropew ay will be 9 miles long and will carry 3,000 tons of coal per day.
M e x ic o .— L ast m o n th reference was m ade in th is column to encouraging develop
m ents a t th e Dos Carlos mine of th e S an ta G ertrudis com pany. Since th en it has been announced th a t on th e 19th level a cross-cut has disclosed 32 ft. of ore averaging 6 dwt.
gold and 50 oz. silver, of w hich 19 ft. was in th e lode assaying 67 oz. silver and 13 ft.
was m ineralized hanging wall assaying 25 oz. silver.
The E l Oro gold m ine was closed in 1926 after a prosperous career, b u t th e com pany has continued in existence, as it h a d a num ber of m inor investm ents. To m eet th e altered conditions th e capital was reduced a year ago from £1,147,500 to £286,875 by cancelling 15s. per £ l share. T h e com pany has b y th is m eans been able to re tu rn to th e dividend-paying list, Is. Ojd. per 5s.
share now being paid, less incom e ta x , for th e y ear ended J u n e 30 last. T he com pany’s chief assets a t present are th e railw ay and th e L a N oria silver mine. D uring th e year th e railw ay m ade a profit of £14,091 and th e silver m ine a loss of £2,977, o th er items bringing th e y e a r’s profit to £25,386. At th e silver m ine 169,083 sh o rt to n s of ore was tre a te d , averaging 16 • 4 oz. silver and 0-38 dw t. gold per ton, an d th e yield was 3,301 to n s of concentrate, selling for
$1,343,722, to g eth e r w ith 31 to n s of ore realizing $3,070.
P a n a m a .—As readers w ill remember, Mr. H ugh F. M arriott some tim e since joined th e b o ard of th e P a n a m a Corporation and subsequently v isited th e pro p erty . A t the annual m eeting on O ctober 31 he delivered a len g th y address, w hich is rep o rted in full elsewhere in th is issue. Mr. M arriott corroborated th e views of th e engineers with reg a rd to th e value of th e alluvial gold deposits in th e Sabalo R iver, a t E l Mineral, and a t San Jose H ill an d spoke favourably of exploration w ork on th e lode-gold deposits around th e old Cana m ine. The most im p o rta n t news he h a d to give, however, was in connection w ith q u ite recent develop
m ents a t Mina B lanca m ines and a t tw o other properties w hich were n o t specifically named.
A y ear ago th e M ina B lanca was described as a lead-zinc deposit, b u t since th en the accom panying gold has added g reatly to its im portance. T he o th er properties contain copper an d silver an d th e grade is described as being very high, assays over stoping w idth showing 14% copper an d 36 oz. silver.
N o rw a y .—T he D u n d erlan d Iro n Ore Com pany has struggled for existence for over a q u a rte r of a cen tu ry , b u t it appears from th e rep o rt for 1928 ju s t published th a t th e co n centrating difficulties h av e been overcome and th a t satisfa cto ry co n tracts have been m ade for th e sale of th e products.
I t is e stim ated th a t th e deliveries during 1929 will am ount to 90,000 to n s and eventually an o u tp u t of 16,000 to 20,000 tons m onthly is expected. T he m an ag e
m en t of th e com pany is now w ith th e Tilden Sm ith group.
T H E MOUNT ISA LEAD-ZINC MINES
N O R T H Q U E E N S L A N D
This article is based on reports published by the Company and deals with the geology and present mining operations. In further articles to be published next month Mr. C. A. Mitke will give an account of the comprehensive method of mining to be adopted, and Mr. J. M. Callow will describe the concentration and metallurgical plant now in course of erection.
I n t r o d u c t i o n . — The lead-zinc-silver deposits a t M ount Isa, N o rth Queensland, are already sufficiently well know n to readers of th e M a g a z i n e to m ake it un
necessary to give here an account of their discovery and early developm ent. Suffice it to say th a t since th e m iddle of 1927 the finance and technical m anagem ent have been in th e hands of th e U rq u h art group, that is to say, a t first th e Russo-Asiatic Consolidated and la te r th e newly formed
w ork will have progressed sufficiently to deliver regular supplies of ore to th e mill.
The plan t provides for th e handling of 1,000 tons of carbonate ore and 500 tons of sulphide ore per day, fine grinding of b o th classes, tabling th e coarser carbonate on Deisters, and flotation in M acintosh cells of th e rest of th e carbonate and th e whole of th e sulphide ore ; th is to be followed by sintering and sm elting in lead blast-furnaces, the zinc concentrate from th e sulphide ore being
GO V E RN M E N T R t ï FR O M O U C H E S S
Fi g. 1.— Pl a n o f
Mining T rust, L td. The operating com pany continues to be th e M ount Isa Mines, L td., some of th e shares in w hich are still held in A ustralia. W ith th is brief introduction it is possible to proceed a t once w ith a description of th e ore-bodies and of the general geology, leaving th e m ethod of mining and th e concentration and m etallurgy to be described in future articles. A fter a period of full investigation th e construction of th e concentrator and sm elter is a t present in h an d and th e mill and sm elter will probably be com pleted early n e x t year, when th e rearrangem ent of underground
265
____ ^e / c f> fia r/ _ /? / ______
Mo u n t Isa Mi n e s.
sold u ntil such tim e as a zinc p lan t is erected.
Though th e to ta l capacity of th e concen
tra tin g p lant is given a t 1,500 tons, it is probable th a t it will be capable eventually of treating 2,000 tons. Connection is already m ade w ith th e Queensland railways. Coal will be obtained from Collinsville, 50 miles south-w est of Bowen, and an electric power p lan t is being erected on th e mine employing th is coal in powdered form, th e p lan t operating on th e Fuller-B onnot system.
W ater for th e dressing and power p lan t and for dom estic purposes will be obtained from a reservoir b u ilt 20 miles aw ay a t Rifle
266 T H E M IN IN G M AGAZINE Creek, and fu rth e r supplies will be available
from th e m ines itself as w ater has been stru c k in depth.
T h e O r e - B o d i e s . —There are a num ber of ore-bodies on th e p ro p e rty an d of these th e R io Grande, B lack Rock, an d M ount Isa contain high-grade carbonate ore w ith sulphides ’ appearing in depth, while th e B lack S tar is of lower grade and th e sul
phides m ake th eir appearance m uch nearer th e surface. In th e first th ree th e delim ita
tion of th e carbonates and sulphides has not y e t been com pleted.
The following table gives an estim ate of th e ore reserves a t th e present tim e :—-
Ca r b o n a t e s—
R io G ran d e . . . . . .
B lack R o c k . . .
M o u n t Is a . . . . . .
B lack S ta r . . . . . .
Su l p h i d e s, Bl a c k St a r— M easurable to 750 ft. d e p th F u r th e r e x p ec te d to 750 ft. d e p th I n ad d itio n , a p p ro x im a te ly
As already m entioned, th e deposits lying w ithin th e boundaries of th e p ro p erty are of tw o classes, th e high-grade lodes, including th e Rio Grande, B lack Rock, a n d M ount Isa, w hich form a m ineral belt extending n o rth a n d south th e full length of th e property, or two and a half miles, and th e second or lower grade ty p e of lode, represented b y th e B lack Star, lying parallel to th e first, ab o u t
1.000 ft. d istan t to th e west.
The Rio G rande m ine is served b y th e three-com partm ent vertical Lawlor Shaft, from w hich a t a d ep th of 175 ft. a cross
cu t in th e hanging wall cuts th ro u g h th e lode. This is here com posed of four distinct veins of sulphide ore from 4 ft. to 12 ft. wide, separated b y from 5 ft. to 15 ft. of co u n try rock. N ot far above th is level th e sulphide gives place to oxidized ore or carbonates.
On th e 130 ft. level tw o of th e veins, b o th com pletely oxidized, hav e been opened b y drives and cross-cuts an d prove th e so-called m ain vein to be 620 ft. in length an d 13 ft.
m ean w idth, while No. 2 vein is 600 ft. long an d averages 14 ft. wide. Allowing 160 ft.
dep th of oxidation and a m ean specific g ra v ity of 2 5 , th e m ain vein contains 90.000 tons of carbonate ore carrying 15'8%
lead and 9’2 oz. silver per ton. No. 2 vein contains an equal am ount of ore of like grade, or a to ta l of 180,000 tons in th e tw o veins. Bore-holes cu ttin g th e lode a t 300 ft.
to 400 ft. dep th have proved th e continuation to these depths of th ree principal veins from 5 ft. to 22 ft. wide, while one, from which th e best results were n o t expected, cut a 12 ft. vein, well above th e average in lead, a t a d ep th of 530 ft. Again, a t 1,000 ft.
depth, various veins were encountered of which one carried 20% lead an d 23 oz.
silver on a w idth of 13 ft. A lthough the diam ond-drilling has n o t y e t proceeded far enough to p erm it a sta te m e n t of th e sulphide ore reserves, it has nevertheless already proved persistence in d e p th to 1,000 ft., an d has given no cause to d o u b t further considerable extension. Therefore, pending
Tons. L ead . Zinc. Silver.
200,000 %
15-8 % Oz.
9-2
120,000 2 2 -4 — 10-6
100,000 12-0 — 4-4
3,100,000 8 -0 — 3 0
3,520,000
14,700,000 6 -2 8 -0 3 -9
3,000,000 6 -2 8 -0 3 -9
500,000 of m u ch h ig h e r assay.
fu rth e r exploratory w ork, it is permissible to apply to th e sulphides th e dimensions used in estim ating th e carbonates while introducing th e specific g rav ity , 3-6. Thus, 150,000 tons of sulphide ore per 100 ft.
d ep th can be counted on or, betw een the 160 ft. an d th e 500 ft. horizons, very pro
b ab ly half a m illion tons. In lead content th e sulphide ore is som ew hat lower th a n the carbonate, b u t th e deficiency is m ore than offset by th e higher silver tenor. Moreover, it contains 6% or m ore zinc.
T he B lack R ock m ine is opened up to a d ep th of 250 ft. below th e outcrop by the O ’D o h erty Shaft, a three-co m p artm en t in
cline of 37°. This horizon m arks closely the lower lim it of th e zone of oxidation, and the level w hich develops it is p a rtly in carbonate ore an d p a rtly in sulphide. The ore-shoot is 350 ft. long by 20 ft. wide, an d disturbances of th e form ation a t th e ends have hindered a d eq u ate exploration in b o th directions.
A tte m p ts to prove th e ore-body in dep th by m eans of diam ond-drills h av e n o t been altogether successful. Of th e th ree bore
holes a ttem p ted , th e so u th ern m o st was stopped owing to difficult ground before cu ttin g th e ore-body, th e m iddle bore failed to cut th e ore-body a t all, b u t a t a d e p th of 500 ft. disclosed a vein, h ith e rto u n discovered, in th e foot-wall, a p p a re n tly 21 ft. wide and carrying 10-1% lead, 6-2%
N OVEM BER, 1929 267 zinc, and 6-3 oz. silver. The developed
reserves of carbonate ore am ount to 120,000 tons, carrying 22-4% lead and 10-6 oz.
silver. I t is prem ature to hazard a forecoast of the q u a n tity of sulphides available.
On th e M ount Isa m ine, from th e three- com partm ent vertical Bushell Shaft a cross
cut, 165 ft. in depth, intersects th e ore-body at about th e level of tran sitio n from carbonate ore to sulphide. Two bore-holes closely spaced prove th e extension of th e lode to a d ep th of 365 ft. where th e w idth is 11 ft., b u t th e difficulty of boring in such ground and th e u n tru stw o rth y results dis
courage fu rth er a tte m p ts a t diam ond-drilling.
So far as developed, th e ore-shoot has a length of 400 ft. and a w idth of 20 ft., corresponding to a carbonate reserve of 100,000 tons of ore containing 12% lead and 4-5 oz. silver. Good exposures a t No. 23 Shaft, 540 ft. n o rth of th e Bushell, and at No. 6 Shaft, 220 ft. still fu rth er north, pro
mise a su b stan tial extension of th e lode in this direction. A t th e present tim e it is not intended to push developm ent in the Mount Isa.
On th e Black S tar, th e lode has been traced by surface and mine working and by boring over a length of 2,000 ft. and a variable w idth up to 250 ft., while th e greatest depths th u s far dem onstrated b y th e “ B ” line of bores is over 800 ft. below th e o u t
crop. (See Fig. 2.) The three-com partm ent vertical D avidson Shaft is in th e hanging wall and a t th e 200 ft. level a cross-cut intersects th e lode a t about th e perm anent water level, which corresponds to th e transition of th e oxidized zone to th e sulphide zone. Above th is horizon th e oxidized zone has been adequately explored by m eans of trenches across the outcrop, by num erous shafts and churn-drill bores and b y drives and cross-cuts. The d a ta available m ake it possible to determ ine th e volum e and the m etallic content of th e carbonate ore w ith sufficient accuracy. On th e basis of a specific gravity of 2-3, th e carbonate reserves am ount to 3,100,000 tons containing 8-0% lead and 3-0 oz. silver per ton. The “ A ” row of bore-holes from 7 to 14 proves to th is date a length of 2,000 ft. a t 500 ft. depth. The
" B ” line of bores, c u ttin g th e lode a t 750 ft.
depth, dem onstrates the unim paired q u ality of th e ore to th e lowest horizon th u s far atta in ed , nam ely 800 ft. Bore-holes B 1, 4, and 8 are now finished. Based on th e volume actually delim ited a t this date a n d applying th e specific g rav ity 3-3,
14,700,000 tons of sulphide ore are m easured, carrying 6-2% lead, 8-0% zinc, and 3-9 oz.
silver.
G e o l o g y .—The following account of the geology of th e d istrict comes from Mr. H. H.
K nox’s report.
The m atu re topography of th e district is characterized by low north-south trending ridges rarely a ttain in g a height of 400 ft.
above th e intervening level valleys. An ancient peneplain after elevation has been
Fi g. 2 .— Se c t io n a c r o ss t h e Bl a c k St a r l o d e S H O W IN G B O R E - H O L E S .
dissected down to th e present level of th e valleys a t an altitu d e of about 1,200 ft.
above th e sea. The course of th e hills and prom inences conforms in general w ith th e strike of th e form ation, and it is clear th a t th e relief, save where h ard igneous rocks or q u artz have invaded th e sedim ents, has been determ ined by th e selective silicifica
tion of certain beds which thereby become highly resistant to weathering, leaving the unaffected s tra ta an easy prey to erosion.
This phenom enon of superficial silicification, so common in arid regions, is here unusually pronounced. The effect is cum ulative at
Da v i d s o n
k3 § î I 8
_i i 1--- 1---1-- »
Sc a l e in Fe e t.
268 T H E M IN IN G MAGAZINE th e surface and does n o t extend dow nw ard
m ore th a n 8 or 10 ft.
W ithin a few miles b o th to th e south and n o rth of th e m ines ap p ear bosses of coarse
grained granite trav ersed b y dykes of u ltra - basic rocks, some of w hich can be identified as olivine-pyroxenite or its uralitized derivative. Paralleling th e granite intrusion to th e n o rth huge lenses of q u a rtz extend for miles an d as snow-white hills form a conspicuous feature of th e landscape. T hey m ay reasonably be regarded as representing th e u ltra-acid phase, as th e pyroxenite m arks th e extrem e basic phase of th e gran itic m agm a. These occurrences harm onize w ith th e earlier silicification and la te r dolom itiza- tio n observed of th e rocks adjoining th e ore-bodies.
W estw ard (on th e hanging w all side) of th e B lack S ta r lode a bod y of greenstone of aphanitic te x tu re outcrops a n d has been followed dow nw ard 2,000 ft. by deep, bore No. 1. This rock or series of rocks displays all stages of alteration, culm inating a t d ep th in a biotite-chlorite schist. In age it precedes th e close of th e dynam o-m etam orphic episode. A t 2,000 ft. d e p th it is succeeded by th e norm al m etam orphic sedim ents.
The predom inant rocks of th e d istric t are sedim entary and m ay be classed provisionally as Precam brian. A lternating th in beds of original lim estone, calcareous shale, an d clay shale have undergone a lteratio n , wholly or in p a rt, to crystalline lim estone and silicified lim estone an d shale, while th e so unaffected lim estone has la te r to a large ex ten t been changed to dolom ite. N o t
w ithstanding th e in tro d u ctio n of m uch
silica and m agnesia, th ere is evident a n e tt reduction of volum e m anifest in unfilled solution cavities. T he final a lteratio n under th e action of acid surface w aters has resulted in th e kaolinization of those shales which have escaped th e a tta c k s of silica, thereby rendering th em extrem ely porous, and the low specific g ra v ity (2-3) of th e B lack Star lode above w ater level testifies th a t the superficial as well as th e deep m etam orphic processes have a b stra c te d m ore m aterial th a n th e y have contributed.
The general strik e of th e stratification is n o rth -so u th an d th e dip approxim ates 60° W. Compressive stresses, doubtless associated w ith th e igneous activ ity , have produced zones of folding also trending no rth -so u th , an d in th e v ic in ity of the ore-
bodies th e plication is often severe w ithout, however, inducing ru p tu re save on a small scale ; indeed, dislocations of m ore th a n a few inches are uncom m on. Seams of iron sulphides as p y rite an d p y rrh o tite, introduced a t th e m etam orphic stage, p a rta k e of the folding w ith o u t ap p a ren t ru p tu re . This g eneration of sulphides replaces th e rock as dense aggregates of m in u te grains.
On th e eastern ore b elt a group of m ajor folds has throw n th e alignm ent to th e right and a t th e extrem e n o rth e rn end of th e pro
p e rty a gossan outcrop several feet wide cuts squarely across th e form ation. The economic significance, if any, of these phenom ena is subject to la te r investigation.
The n ex t stage in th e h isto ry of th e deposits appears to hav e ensued a fter a long tim e-interval. T ensional strain s, acting along th e old lines of w eakness, opened
Fi g. 3 .— He a d f r a m e a t La w l o r Sh a f t.
channels for th e circulation of solutions which deposited th eir m etallic burden p artly in the passages so form ed and p a rtly as a replacement of th e rock and th e older iron sulphides. This later m ovem ent, causing shearing and fracture, is distinguished in mode from th e older, w hich is characterized by plication, although shearing forces have also caused local folding. D ifferential m ove
ment along th e bedding planes of tw o beds which them selves rem ain undeform ed m ay produce th e m ost fan tastic convolutions of a plastic stra tu m lying betw een them . And here it is w orthy of note th a t a tendency of the folds caused b y bedding faults to pitch
N OVEM BER,
(1) The introduction of p y rite and, some
w hat later, p y rrh o tite as b ands from a m illim etre up to several feet wide, replacing sedim entary laminae and beds, a t a period preceding or coinciding w ith th e local folding of the stra ta . The p y rite is distinguished from la te r generations by its extrem ely fine grain.
(2) The second or shearing period opened passages for solutions which a t first deposited fine-grained zinc blende an d a coarser grained py rite as replacem ents of older m inerals and as veinlets in th e gangue.
(3) Chalcopyrite (in places subsequently altered to bornite) slightly precedes and th en accom panies th e deposition of argentiferous
1929 269
Fi g. 4 .— Ri f l e Cr e e k Damfr o m b e l o w.
rather flatly tow ard the north suggests a possible connection w ith th e pitch of th e ore-shoots. Since, however, these new shear zones do n o t conform stric tly w ith th e stratigraphic strike b u t cut it a t an acute angle, th e tendency of th e ore-bodies is tow ard an alignm ent en echelon, an effect to be tak en into account in exploration.
The p rim ary economic m inerals are th e common sulphides of lead, zinc, and silver, w ith accessory copper (principally chalco
pyrite w ith a little bornite). The gangue minerals are calcite, dolom ite, and th e iron sulphides, w ith accessory m anganese m ineral and carbonaceous m a tte r in flakes resem bling graphite.
The succession of events involving th e deposition of ore has been as follows :—
galena. Besides replacing th e older m inerals and rocks and occupying m inute joints, fissures, and bedding faults, th e galena finds favourable lodging in saddles and troughs of sharp folds where th e strain has fractured th e rock.
(4) The calcium -m agnesium carbonates extend throughout th e whole range of ore deposition as does th e quartz.
(5) F rom th e surface to a d ep th of 150 to 200 ft. corresponding in a general w ay w ith th e perm anent w ater-table, th e m etallic sulphides have been oxidized to lead carbonate w ith m inor am ounts of sulphate and other lead salts, and to zinc carbonate, th e m ajor portion of which has been rem oved in solution, leaving th e m ore stable lead and silver salts in place. Copper where present
