The Mining Magazine
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Vol. XLV. No. 4. L O N D O N , O C TO B ER , 1931
ONE SHILLINGPRICEC O N T E N T S
Ed i t o r i a l
Notes ... 194
A New H andbook of D eterm inative M ineralogy ; C ontract for New R ailw ay in N o rth ern R hodesia ; Local Association of In s titu tio n M embers form ed in Rhodesia ; F a ra d a y ’s M etallurgical Researches ; Silver S ta b iliz atio n ; Tunnelling R ec o rd s; “ Oil- from -C oal” Papers a t B ritish A ssociation Meeting.
Petrology an d O re-G en e sis... 195
196
Proceedings a t one of the B ritish A ssociation discussions are sum m arized.Diesel-Electric T raction ...
The position of an im p o rtan t developm ent in th e applica tion of in tern al com bustion engines to railw ay tra n sp o rt is exam ined.Copper
Factors affecting the w orld’s p resen t p ro d u ctio n of copper are reviewed.197 198
201208
211 Re v i e w o f Mi n i n g ... Ar t i c l e sChromite in Sierra Leone W. H . Wilson
A description of th e C hrom ite D eposits of the K am bui Hills, in th e P rovince of K enem a.Novel F eatures of a New Copper Refinery ... W . M . Goodwin
Details are given of some of th e new eq u ip m en t of the Canadian Copper Refiners a t M ontreal E ast.The E stim ation of A ntim ony and A rs e n ic ... J . E . Clennell
[Concluded fr o m the S ep tem b er issu e, p. 153) Bo o k Re v i e w s F in k e y ’s “ T he Scientific F u n d a m e n ta ls of G ra v ity C o n cen tratio n ” B . W . H olm an 218 F e rsm a n n ’s “ Geochem ische M igration der E le m en te ” ... D r. A . B ram m all 218 N e w s L e t t e r sB r is b a n e ... 219
W ork an d P roduction a t M ount Isa ; C loncurry Copper ; A ustralian Gold M in in g ; Exchange P rem ium on Gold ; P alm er Gold D redging ; Central A ustralian Gold. I p o h ... General C onditions ; E x c av ato rs ; R ecent D evelop m en ts ; S tatistics ; Gold Mining. 221
Johannesburg ... 223
L o st Gold Reef Believed F ound ; A P ro sp e cto r’s Prom ising Find ; R hodesia’s New In stitu te .
V ancouver... 224
Bridge R iver ; Big B end D istrict ; Nelson ; Placer M ining ; T a k u R iver ; Osoyoos.
Toronto ... 227
M ineral P ro d u ctio n of C anada ; Sudbury ; Porcupine ; K irkland Lake ; R ouyn ; P atricia D istrict. Pe r s o n a l
230
T r a d e P a r a g r a p h s ...231
Shipping, E n g in eerin g , a n d M achinery E x h ib i t io n ... 232
T h e D iskon G e a r ... 233
A N ew S haking S c re e n ... 234
M e t a l M a r k e t s ...
235
S t a t i s t i c s o f P r o d u c t i o n ...
237
P r i c e s o f C h e m i c a l s ...
239
S h a r e Q u o t a t i o n s ...
240
Mi n i n g Di g e s t T h e Geology of th e K a ta n g a . . . .M . Robert 241 M ica in B ih ar, In d ia ...B .C . L u f f 243 T he Use of Ore S crapers . .A . R . Lawrence 246 T re a tm e n t of W ilu n a C o n cen trates W . G. Clarke and B . H . Moore 248 R o c k -B u rst E ffects in S o u th A frica W . A llen 250 K algoorlie M ining P ra c tice . .C . M . H a rris 252 T h alliu m ... A . V. Petar 253 L ead-Z inc F lo ta tio n a t M idvale, U ta h E le c trica l R e sistiv ity an d d u c tio n M e a su re m e n ts. . . R . A . Pallanch E le ctrica l In - . . .E . V. Potter 254 255 S h o r t N o t i c e s ...
255
R e c e n t P a t e n t s P u b l i s h e d ...
255
N e w B o o k s , P a m p h l e t s , e t c ...
256
D i v i d e n d s D e c l a r e d ...
256
4—3 193
E D I T O R I A L
H O W E V E R extensive th e literatu re, there is always room for a new contribution w hich either sheds fu rth e r light on a subject or is able to present it in a new way.
“ Simple D eterm inative M ineralogy,” by H. R. Beringer, a form er lecturer a t the Camborne School of Mines, published by Mining Publications, L td ., th e proprietors of
T h e M i n i n g M a g a z i n e ,which m akes its appearance this m onth, is a useful addition to th e books on m ineralogy of a really p ractical n a tu re an d should be of value to th e prospector as well as th e stu d en t.
R AILW A Y developm ents in C entral Africa have been closely followed in these columns, th e extension of m eans of com m uni
cation into th e great continent being of m uch im portance in th e opening up of po tential m ineral fields. I t is satisfactory to record, therefore, th e placing of a contract in th is co u n try for th e construction of a railw ay connecting Cham bishi and M ufulira in N o rth ern Rhodesia. This new line will be 19f miles in length an d will be carried over th e K afue R iver by a new bridge of th ree spans of 75 feet each.
T H E form ation of a local association in Southern R hodesia is announced by our Johannesburg correspondent. The new body has for its prim ary objects th e prom otion of th e in te rests and th e m aintenance of th e sta tu s of th e In stitu tio n of Mining and M etallurgy in N o rth ern and Southern Rhodesia, as well as th e fostering of professional and social intercourse betw een local m em bers of th a t body. Those connected w ith th e form ation of th e new association include m any engineers well known both in South A frica and in this country.
A L IT T L E known aspect of F a ra d a y ’s im p o rtan t researches is th a t covering investigations in m etallurgy. Sir R obert H adfield, in a paper to th e R oyal Society, published in connexion w ith th e recent cen ten ary celebrations, deals fully w ith this branch of th e g reat scientist’s work. As th e result of an exam ination of th e contents of a box containing F a ra d a y ’s specimens of steel and alloys Sir R obert has been able to show th a t extensive w ork had been done on th e effects of alloying m any different elem ents w ith iron. W hile it is tru e th a t nothing of lasting value cam e out of this
research, it is a p p a re n t th a t F a ra d a y ’s inquiring m ind h ad an tic ip a te d similar labours by m etallurgists who followed him.
S U P P O R T for some m eans of stabilizing silver prices continues to grow, largely owing to th e p ersistent p ropaganda of those who hold th e view th a t th e resto ratio n of the m etal to a place in th e w o rld ’s m onetary system would be an im p o rtan t step tow ards creating th e confidence necessary to combat th e present depression. Reference was made here last m onth to a conference convened b y th e China Association to consider the situ atio n created b y th e fall in silver prices.
A t this m eeting it was unanim ously resolved th a t th e governm ents concerned should be urged to call an early conference to discuss this m atte r. Sir R o b ert H orne, who presided, m ade it plain th a t increase of silver prices alone could not ren d er stabilization im potent by causing over-production, as such a large proportion of th e w orld’s o u tp u t comes from base-m etal producers as a by-product.
I N th e last issue of th e
M a g a z i n ereference was m ade to w h at was th en believed to be a new E uropean tunnelling record which had been set up in connexion w ith the M anchester Corporation H aw esw ater Scheme, an advance of 181 feet being recorded in one week. I t has since tran sp ired th a t in driving th e 610 m etre deep ad it on the S tan trg m ine, in Y ugoslavia, a distance of 459-3 feet was driven in a period of 15 days during Septem ber, 1930, equivalent to a weekly footage of 214-2. E ven this figure has now been surpassed in th e H aw esw ater tunnel, th e ir m ost recent achievem ent being equal to a weekly footage of 220. On the M anchester project th e w ork is being done by H olm an drifters, using Sullivan m echanical slushers, w hilst a t T repca the drills used were m ade b y Ingersoll-R and, th e m ucking being carried out w ith a Butler m echanical shovel.
T WO papers p resented a t th e recent cen ten ary m eeting of th e British Association m ade extended reference to the p resent position in th is co u n try of the
“ oil-from-coal ” in d u stry and ' oil fuel developm ents. T he first, by Mr. H. T.
Tizard, R ector of th e Im perial College, dealt
w ith th e progress of h y drogenation and he
was able to say th a t recen t w ork pointed
OCTOBER, 1931 195 to th e conclusion th a t it would soon be
possible to produce a heav y oil from coal a t a cost which, while not m uch lower th an th e cost of producing petrol, would m ake available a valuable source of supply for heavy-oil engine plants. Sir Jo h n Cadman, in th e second paper referred to, dealt w ith recent developm ents in oil utilization, referring p articu larly to th e rap id increase in th e nu m b er of oil-fired steam ships and m otor vessels. H e considered oil to be th e fuel of speed, th e vitalizing power of m odern transport.
P e tr o lo g y a n d O r e -G e n e sis
The centenary m eeting of the B ritish Association, to which reference was m ade in the
M a g a z i n elast m onth, concluded a t the end of Septem ber. The F a ra d a y celebrations and th e com m em oration of th e fiftieth anniversary of th e present N a tu ra l H istory Museum com bined w ith th e A ssociation’s centenary to a ttra c t m any notabilities from other countries and all th e m eetings were very well atten d ed . The reference in these columns last m onth m ade note of several of th e discussions before th e Association which were likely to be of especial interest to m em bers of th e m ining profession, b u t generally these took th e form of sym posia rath er th a n real discussions, sum m arizing advances m ade during th e past year in the various subjects, little th a t was really new arising from them . In th e geological section, however, th e discussion on th e genesis of ores in relation to pétrographie processes contained m uch interesting m a tte r and more extended reference to th is item of the proceedings is justified.
Problem s of ore-genesis an d th e stu d y of the m eans by which m ineralization takes place are ra th e r viewed askance b y practical m ining men, who are often inclined to take the philosophical view th a t ore is just where it is a n d th a t ta lk ab o u t th e reasons as to w hy ore is where it is does not really affect th e situation. P ractical geologists, of course, ta k e a co n trary view and are inclined to th in k th a t th e indifference of m any m ining companies tow ard research on th eir chief asset—th e ore-body—is, in fact, a disservice to themselves, th e h a sty removal, for “ economic ” reasons, of the first of th eir finds often destroying much valuable evidence th a t m ight have been applied to th e search for new prospects. The present tre n d of th o u g h t on ore-deposition brings th e stu d y of its effects m ore closely
in to contact w ith petrography, ore-deposits being considered as local concentrations in which valuable m inerals are in g reater con
centration th a n in average rocks. As Professor Cullis pointed out in opening the discussion on this subject at the B ritish Association meeting, “ these concentrations, being naturally-form ed m ineral aggregates, cannot logically be distinguished from rocks.”
This point of view has been well expressed by Professor Niggli and th e tran slato r of his book “ Ore-Deposits of M agmatic Origin ” — Dr. H. C. Boydell—in his preface to the work, expresses this view-point as one which envisages as necessarily connected phenom ena rock differentiation, earth tectonics, emplace
m ent, th e subsequent production of ore- bearing solutions as a later or last stage of differentiation, and, finally, the deposition of ore w ithin a recipient rock structure.
In his contribution to th e present discussion Professor Niggli emphasizes the fact th a t the genetic description of an ore-body should take three points into consideration—first, th e prim ary geochemical concentration process ; secondly, the m ineral paragenesis consequent on the original process, and, thirdly, subsequent alterations w ithin the geological body, alterations which m ay have accom panied th e process of form ation or be due to m etam orphism or to w eathering processes. The sam e worker also pointed out th a t th e ex ten t and im portance of sedim entary deposits could only be fully estim ated by a tte m p ts to reconstruct the land and w ater distribution an d th e clim atic factors which obtained a t th e tim e of their form ation. A nother im p o rtan t contribution to this discussion was th a t of Dr. A.
Bram m all, who, while a supporter of the Nigglian view-point, goes much farther, holding th e opinion th a t differentiation alone, working on fixed quantities of initial m agm a, does not cover th e whole case, as both the assim ilation and fusion (palin
genesis) of existing rocks m ust be involved to explain some of the m any departures from existing general rules connecting ore-deposits w ith igneous rock types. Dr.
Bram m alTs work on the W est of England
granites is well known and this has led him
inevitably to th e conclusion th a t these rocks
are essentially hybrid, containing from 2-5
to 16-3 per cent, of assim ilated basic igneous
rocks, differentiation and assim ilation having
proceeded sim ultaneously u ntil viscosity
has p u t an end to both. As th e result of this
w ork it has been suggested th a t all the
196 T H E M IN IN G M AGAZINE H ercynian granites, from Spain to th e W est
of E ngland, have originated by palingenesis in th e roots of deep-sunk orogenic folds.
Among th e in terestin g points arising from this intensive stu d y of th e granites of D evon and Cornwall are th e conclusions— first, th a t th e b ariu m oxide content of th e granite can be used as a delicate basis for checking th e q u a n tita tiv e im portance of shale assim ila
tio n and, secondly, th a t spectroscopic evidence has led to th e conclusion th a t a large proportion of th e b io tite in th e granites is derived from assim ilated pyroxene-bearing basic igneous rocks, chrom ium , nickel, cobalt, m olybdenum , lead, silver, gold, strontium , an d iridium being traceable to th e hornblendic basic xenoliths. Assays for gold an d silver in these granites show an average for g ran ite to contain 1-2 grains per to n of gold an d 21-3 grains of silver, whereas a dem onstrably h y b rid am phibole- bearing p egm atite contains 64-8 grains per to n of gold and 117-9 grains of silver.
P rospectors who have spent long periods in granite or granite-gneiss co u n try searching for a source for th e constantly-occurring colours of gold m ust see th a t a h y b rid granite m agm a m ay often be th e source itself.
The m ain conclusion to be draw n from th e discussion seems to be th e fa ct th a t there is general agreem ent th a t th e problem s of ore-deposition are only p arts of th e problem s of igneous petrology.
D ie s e l-E le c tr ic T r a c tio n
A possible revolution in railw ay tra n sp o rt in this co u n try m ay be regarded as a good reason for introducing a topic which super
ficially m ay n o t appear to be of direct concern to th e m ining com m unity. Its effect not only on tra n sp o rt facilities - b u t also on th e coal m ining in d u stry —which m ay still be regarded as th e basic B ritish in d u stry — is, however, sufficiently far-reaching to appeal to a w ider circle th a n those im m ediately affected. Those readers of th e
M a g a z i n ewho s tu d y th e report of th e W eir Com m ittee on th e electrification of th e m ain-line railw ays of G reat B rita in will find it contains th e im p o rta n t conclusions th a t only a wholesale electrification scheme could be contem plated an d th a t such a scheme w ould cost a sum am ounting to over
£300,000,000. In addition, it was estim a ted th a t this expenditure, after a construction period set a t tw en ty years, w ould only give a re tu rn of 6-7 per cent., w hich would, it is ad m itted , allow of little or no reduction in tra n sp o rt costs. As th is is one of th e m ost
v ita l needs of th e c o u n try a t th e present tim e it is, therefore, not surprising th a t more a tte n tio n is being given to th e internal com bustion engine, especially th e Diesel type, using a heav y oil w hich is b o th cheaper and safer th a n petrol. The use of Diesel- electric tra c tio n on rail cars is now well p ast th e experim ental stage a n d th e increasing a tte n tio n w hich is being p aid to th is type of power u n it was v ery evident a t th e exhibition ju st concluded a t O lym pia.
The ty p e of in te rn a l com bustion engine w hich is usually called afte r its inventor, Dr. Diesel, m ade its appearance in the concluding decade of la st cen tu ry a n d much of th e developm ent of th is engine took place on th e C ontinent. The m ain feature of the engine lies in th e use of cylinder compression to develop such tem p e ra tu res th a t injected oil is ignited, th e expanding gases providing th e m otive power. F rom its invention the developm ent of th e Diesel engine has proceeded rap id ly a n d u n its are now constructed capable of producing as much as 25,000 h.p. I t has to be remembered, however, th a t in com petition w ith th e steam engine th e Diesel engine h as an im portant defect. The m erits of th e steam engine are its high over-load capacity, maximum torque a t low revolution, flexibility of speed, a n d good acceleration— in fact, a steam engine is a co n stan t-to rq u e engine, whereas a Diesel is a co nstant-speed u n it. This was th e fact w hich led to th e failure of those early experim ents to couple a Diesel unit directly to th e driving wheels of a locomotive, although it is considered th a t th e use of supercharging m ay be th e first step towards overcom ing th e difficulties of direct coupling.
In practice, however, th e difficulty has been avoided b y th e use of connecting media betw een th e power u n it an d th e wheels.
Such m edia are eith er or b o th gear trans
m ission a n d electric transm ission units,
th e solution of th e problem lying in the
acceptance of th e Diesel engine as a prime
m over pure a n d sim ple. As such it has
im p o rta n t advantages, those of low cost,
sm all running a n d m ain ten an ce charges,
high speed, reliability, easy sta rtin g , and
freedom from v ib ratio n , noise, smell,
smoke, an d fire risks. As for th e relative
m erits of tw o-stroke an d four-stroke systems,
although th ere seems to be a tendency in
favour of th e tw o-stroke for large units, the
four-stroke seems to be m ore in favour for the
purposes of locom otion. R esearch on this
ty p e of engine has co n stan tly been in the
OCTOBER, 1931 197 direction of sim plification and th e im prove
m ent of m echanical injection pum ps—the so-called airless-injection system —has been a notable factor in th is direction.
Bearing in m ind th a t the desired end of locomotive developm ent—or railw ay develop
m ent, for th a t m a tte r—m ust be th e provision of cheaper tra n sp o rt facilities, it is obvious th a t th e Diesel-electric locomotive is one means to th a t end. Such a locomotive would certainly have a greater in itial cost th a n the steam locomotive it is designed to replace, but its running costs, allowing for interest and depreciation, would only be about half.
At present th e use of pow dered fuel on steam locomotives is another a tte m p t to provide greater fuel economy and th e continued use of home supplied fuel is n atu rally of param ount im portance. The developm ent of processes in th is country, however, having the aim of producing cheap oil from coal are extrem ely im p o rtan t in th is connexion, as Diesel-electric tractio n using hom e-produced heavy oil seems to have im p o rtan t advantages over complete electrification of th e railways, at any ra te for short branch or suburban lines.
C o p p er
The decision of G reat B ritain to allow its currency to d e p art from th e gold stan d ard im m ediately resulted in a rap id advance in the price of m etals, an ad ju stm en t of values to the depreciated pound sterling. Although the position has since suffered a relapse, followed by another advance, an exam ination of the present figures shows th a t after all allowance has been m ade to bring present prices on to a gold basis the values of the principal base m etals show a decline. The position as regards copper has been emphasized by th e decision of th e Rio T into Company not to m ake any interim dividend paym ent on its ordinary shares th is year, ft is tru e th a t m any factors other th a n price considerations have adversely affected this company, notab ly affairs in Spain, where a dem and for tax es on profits and dividends covering th e years 1923-25 has m ade a serious drain on its available resources.
In addition th e ore position a t Rio T into is regarded as being far from satisfactory, as it is feared th a t th e continued decline in the copper co n ten t of th e ore will m ean a gradual increase in production costs, a factor which was one of the m ain reasons influencing the decision of this com pany to invest in N orthern Rhodesia. N evertheless th e u n certain ty as regards th e position of copper
is extrem ely im p o rtan t to m any m ining m en and it is well w orthy of some exam ina
tion.
D uring the la tte r half of A ugust and the beginning of Septem ber an im p o rtan t factor affecting th e copper situation became very apparent in the U nited States. The official price set by Copper E xporters was per
sistently underquoted by custom s sm elters and other outside interests, all of whom were pressing m etal for forw ard delivery at 7 cents per pound, a figure a t which m any of the large companies in the U nited States can only be producing a t a loss. In spite of th is fact, however, th e production in th a t country during A ugust was nearly equal to th a t of July, being ju st under 39,000 tons. I t is probably tru e th a t the relative am ount of cheap copper available is only sm all when com pared w ith available stocks, b u t it is still enough to m eet the present poor dem and, and consequently has im m ediate effects on th e m arket situation, creating an u tte r lack of confidence in the position. A sim ilar situ atio n was ap p aren t on th e B ritish m arkets during th e same period, free offerings and absent buyers forcing prices ever downwards, w ith the result th a t new low records for the m etal were created daily. I t has become increasingly evident, therefore, th a t steps will have to be taken to curtail copper supplies unless economic factors tak e control of th e situation.
In view of th e prevalent state of affairs outlined here it w ould seem th a t th e chief in terest for th e n ex t few weeks will be in th e decisions of th e conference of producers which is to be held in New York this m onth.
R epresentatives of Canadian, Belgian,
Rhodesian, and U nited S tates interests will
be present and it is intended to consider th e
details of a scheme to restrict th e o u tp u t
of copper to 90,000 tons a m onth, which is
estim ated to entail a cut of 28 per cent. The
present world consum ption of copper is
about 100,000 to n s per m onth and the
lower figure chosen as a basis for agreem ent
m akes allowance for th e production of
other countries, such as Russia, Germany,
and Jap an . Although copper outputs
have to a certain ex ten t been previously
restricted, it is now evident th a t much
firmer measures are intended to deal with the
situ atio n and copper will join th e other
m etals—tin, zinc, and lead—in coming
under artificial control, w hether for the
benefit of th e in d u stry or not rem ains to
be seen.
R E V I E W O F M I N I N G
In tro d u ctio n .—A fter w hat has seem ed
an u n d u ly p ro tra c te d period of u n c e rta in ty P arliam en t has been dissolved and a general election is to ta k e place on O ctober 27.
T he N ational G overnm ent has m ade a un ited appeal to th e cou n try and th e general opinion th a t such a G overnm ent will receive th e m an d ate it desires tends to m aintain com m ercial confidence. Since th e d ep artu re of this cou n try from th e gold sta n d a rd m etal prices have been som ew hat erratic, b u t th e tendency generally is tow ards im provem ent.
T ra n sv a a l.—T he o u tp u t of gold on th e
R an d for Septem ber was 872,053 oz. and in outside d istricts 43,971 oz., m aking a to ta l of 916,024 oz., as com pared w ith 916,425 oz. in August. T he num ber of natives em ployed on th e gold m ines a t the end of th e m onth to talle d 209,424, as com pared w ith 209,409 a t th e end of August.
T he rep o rt of th e New M odderfontein Gold Mining Com pany for th e y ear ended Ju n e 30 last shows th a t th e ore reserves have suffered an o th er decline, decreasing to 6.789.000 tons, averaging 8-0 dw t. over a stoping w idth of 49-9 in., from 7,431,900 tons, averaging 8-6 dw t. over 50-2 in. Once again this is considered to be largely due to th e lower proportion of p ay ab ility of ore developed on th e S outh R eef and U pper L eaders in com parison w ith th e Main R eef Leader. The ore milled during th e year am ounted to 1,933,700 tons, yielding 838,082 oz. of gold, w orth £3,554,118, silver and osm iridium recovered bringing th e to ta l u p to £3,368,550, equal to 36s. l i d . per ton.
W orking costs am ounted to £1,550,782 and th e w orking profit to £2,017,768, dividends paid during th e year absorbing
£1,750,000, equal to 125 per cent.
Lor th e year ended Ju n e 30 last th e ore reserves of Sub Nigel show an increase of 241.000 tons, th e fully developed reserves being estim ated a t 1,206,000 tons, averaging 17-3 dw t. over a stoping w idth of 27 inches.
T he value is lower by 0-7 dw t., b u t th e w idth is higher b y 4 in., in order to conform to current stoping practice. T he ore milled was 378,000 tons, 333,551 oz. of gold being recovered. T he revenue am ounted to
£1,413,214, working expen d itu re being
£707,568 and th e working profit £705,646.
D ividends declared during th e year absorbed
£450,000, equal to 6s. per share.
T he retu rn s of th e E a st Geduld m ine for Septem ber show a ste ad y im provem ent in
operating results. Ore crushed during the m o n th am ounted to 42,000 tons, working costs being estim ated a t £47,230 an d revenue a t £44,626, th e absorption of gold in the plan t being still considerable. The develop
m ent rep o rt for th e last q u a rte r shows an advance of 2,399 ft., of which 1,490 ft. was sam pled, 965 ft. being payable, having an average assay value of 16-6 dw t. over 43 in.
The Mines D e p a rtm e n t of th e Union G overnm ent has in v ited applications, for th e leasing of areas ad jac en t to th e Sub Nigel mine on th e farm s G rootfontein and Dagga- fontein, th e ground available together representing 6,333 m ining claims. Tenders for this ground are re tu rn a b le on February 1 next.
The accounts of N o rth e rn Platinum E xploration, L td ., covering th e year ended Ju n e 30 show th a t no operations were carried out on th e com pany’s properties, these being in charge of a caretaker. In order to bring th e holding in Potgietersrust P latinum s, L td ., to m ark et value a sum of
£20,382 has been w ritte n off, lowering the value of th e com pany’s available balance, in cash an d in v estm en ts, to £33,667.
Shareholders of T ran sv aal Gold Mining E sta te s have been inform ed th a t no dividend could be declared th is year.
S o u th e rn R h o d esia .—T he o u tp u t of gold
from Southern R hodesia during August was 43,292 oz., as com pared w ith 44,765 oz.
for th e previous m o n th an d 46,152 oz. in A ugust, 1930. O ther o u tp u ts for August were : Silver, 5,892 oz. ; coal, 51,847 tons;
chrom e ore, 8,962 tons ; asbestos, 1,412 tons ; mica, 2 tons.
T he re p o rt of th e Sherwood S tarr Gold
Mining Com pany for th e y ear ended June 30
last shows th a t th e ore reserves have risen
to 151,300 tons, b u t th e value has declined
from 66'7s. to 46'6s. per ton. The ore milled
d uring th e year was 56,000 tons, 1,800 tons
less th a n was tre a te d in th e previous year,
th e increase in th e percentage of concentrates
produced and th e lim ited cap acity of the
roasters necessitating th e reduction. In
addition 46,532 tons of cu rren t slimes and
54,154 tons of accum ulated slimes were
re -tre a ted a n d th e to ta l revenue for the year
was £138,464, as com pared w ith £132,966
in th e previous year. W orking costs increased
from 22s. lOd. per to n to 24s. 3d., b u t the
profit also rose from 23s. 2d. p e r ton to
25s. 3d., th e gross w orking profit being
198
OCTOBER, 1931 199
£70,698. Dividends paid during th e year absorbed £30,000, equal to 30 per cent.
The report of th e Toronto (Rhodesia) Syndicate for the seven years to Decem ber 31, 1930, show th a t th e w orking of th e m ine by tribute ceased in April last, b u t th a t negotiations are proceeding w ith th e object of re-letting it. The response of shareholders to the reorganization scheme sanctioned in 1927 proved so poor th a t no shares were allotted, b u t these will again be offered when a favourable o p portunity occurs.
N orthern R hodesia.— Shareholders of
R hokana Corporation were inform ed last m onth of an accident a t th e N ’Changa W est Mine, where a rush of w ater occurred which reached th e shaft. A lthough this will cause some delay in th e developm ent of N ’Changa West, it will, it is stated , in no w ay affect operations at N ’K ana, w hich is expected to provide the m ajor p art of th e production in the earlier operating stages a t th e com
m encement of th e new year.
N igeria.—D uring th e year ended March 31
last the production from th e Fedderi areas of Tin Fields of Nigeria, L td ., was 58 tons, as compared w ith 5 9 | tons in th e previous year, while in addition 38J tons was produced from the areas of R ukuba Tin Mines, L td., which are under trib u te. T he price realized for the concentrates was only £68 5s. lOd.
per ton, as com pared w ith £113 17s. 5d.
obtained in th e previous year, and th e y ea r’s working resulted in a loss of £161, reducing the balance carried forw ard to £48.
The report of R ibon Valley (Nigeria) Tinhelds, covering th e year ended March 31 last, shows th a t 206J tons of tin concentrates was produced, th e operations for th e period m entioned showing a profit of £3,942. A fter writing off th e d ebit balance brought in, there remains a sum of £61 to be carried forward.
Gold C oast.—The re tu rn of the A shanti
Goldfields Corporation for Septem ber shows the m onthly profit to have been a record one at £39,599, in addition to which £6,753 was received on account of th e gold prem ium , which was only available during th e la tte r half of th e m onth. Septem ber is also the last m onth of th e financial year for this com pany, and th e n e t profit for th e period is estim ated a t over £400,000, equal to more th an 100 per cent, on the issued capital.
A circular to shareholders of T aquah and Abosso Mines states th a t arrangem ents have been m ade w hereby th e New Consolidated Gold Fields, which has acquired a substantial in tere st in th e com pany, will assist in
extending its operations. The Gold Fields com pany will be represented on th e new board, of which Mr. J. H. B a tty becomes chairm an, Mr. G. W. Campion continuing his connexion w ith th e com pany as technical adviser.
A u stra lia .—The accounts of th e Broken
Hill P ro p rietary Com pany for th e year ended May 31 last show a n et profit of
£83,257, after providing £232,752 for depre
ciation and £64,659 for debenture interest.
O perations a t Broken Hill ceased on Ju n e 30, 1930, where sufficient staff has been retained to look afte r the plant. The production of th e Newcastle steelworks shows only a slight reduction on th a t of the previous year.
As was announced in th e
M a g a z i n efor Ja n u a ry last, th e com pany has decided to investigate gold-mining propositions brought to their notice, b u t so far these investigations have been w ithout tangible results.
Advice from A ustralia is to th e effect th a t th e net profit of A m algam ated Zinc (De B av ay ’s) for th e first half of th e current year was £3,497. I t is sta te d th a t th e negotiations w ith regard to th e inauguration of a paper in d u stry in H uon Valley, T asm ania, are being continued.
A circular to shareholders of th e W iluna Gold C orporation issued last m onth stated th a t during A ugust 23,279 tons of ore was treated , yielding bullion w orth £26,370, working costs in A ustralian currency being
£24,278. I t is fu rth e r sta te d th a t Mr. C. O.
Lindberg, who is investigating th e position a t th e mine, has suggested th a t the assistance of a flotation expert would be desirable, and Mr. T. Owen, form erly of the American Smelting and Refining Company, has been engaged. T he m anagem ent have reiterated their confidence in th e deep-seated origin of th e W iluna deposits.
New Z ealand.—R ecent investigations by
G overnm ent geologists into th e huge cem ented gravel deposits in th e T uapeka d istrict of Otago are sta te d to have revived th e interest of mining m en and an A ustralian syndicate has engaged experts to go into the m atter.
India.— A progress report issued by the
In d ian Copper Corporation, covering the
first half of 1931, shows th e mine production
to have been 79,153 tons of ore, developm ent
having k ep t pace w ith depletion. T he ore
tre a te d by the mill was 79,089 tons, averaging
3-26 per cent, copper, th e recovery being
estim ated a t 97-25 per cent., milling costs
during th e period showing a reduction of
200 T H E M IN IN G M AGAZINE 12 per cent, as against th e previous year.
T he o u tp u t of th e sm elter was 2,105 tons of refined copper, over-all operating costs being 38-7 per cent. less. A t th e rolling mill costs were also lowered by ap p ro x im ately
£2 per ton, sales being well m aintained, th e o u tp u t of yellow m etal sheet for th e period am ounting to 1,581 tons.
Shareholders of th e Mysore Gold Mining Com pany have been inform ed th a t recent rockbursts in th e stoping section of th e mine have so seriously interfered w ith th e m o nthly o u tp u t of gold th a t it is deem ed advisable to postpone th e declaration of an y dividend u n til th e resu lts of th e whole y e a r’s w ork are ascertained.
B u rm a .—T he rep o rt of th e T avoy Tin
D redging Corporation for 1930 is th e first issued since th e absorption of th e N orthern Tavoy, Theindaw , and T hingandon com panies and shows th a t th e new com pany now possesses a fleet of six dredges, all of which are in excellent condition. T he ground tre a te d during th e y ear am ounted to 1,472,581 cu. yd., th e o u tp u t of tin con
c e n trates being 318f tons, while 12 tons was produced from trib u te, th e whole realizing an average price of £130 per to n of m etal.
T he y e a r’s working resulted in a loss of
£1,925, th e to ta l loss for th e y ear being
£4,669, a fte r transferring £22,231 from reserve account.
M alaya.—D uring th e year ended Ju n e 30
last th e o u tp u t of tin by th e Renong Tin D redging Com pany am ounted to 539-9 tons from th e tre a tm e n t of 1,221,894 cu. yd. of ground b y th e two dredges on th e R asa property. Continued exem ption has been given from w orking th e G om bak Valley pro p erty , activities on which have been confined to th e close-boring of certain areas.
The profit for th e period under review was
£13,983 an d £10,463 was d istrib u ted as dividends, equal to 5% on th e ordinary shares, th e balance carried forw ard being increased to £22,493.
A t an ex trao rd in ary m eeting of Anglo- E astern Tin held last m onth it was resolved th a t th e capital should be increased b y th e creation of 100,000 new ordinary 2s. shares, th e subscription of w hich " has been guaranteed.
D u tch E ast In d ies.—T he rep o rt of th e
G overnm ent B anka Tin Mines for 1930 shows th a t profits am ounted to £870,000, as com pared w ith £1,785,000 in" th e ten m onths covered in th e 1929 report. P roduction
increased from 168,737 to 219,400 quintals and w orking costs rose from FI. 79-74 per q u in tal to FI. 86-91, while th e selling price fell from FI. 239-38 to FI. 172-12.
M exico.—D uring th e y e a r ended June
30 last th e operations of th e E l Oro Mining and R ailw ay C om pany resulted in a profit of £9,766, receipts as interest from the Inversiones C om pany a n d oth er sources raising th is to £38,766. T he to ta l profit, after allowing for exchange losses an d expenses, am ounted to £34,203 and, a fter adding the sum of £11,486 b ro u g h t in, th ere was an available to ta l of £45,689, from which a dividend of 7d. per share is to be paid.
D uring th e period under review 170,955 tons of ore was raised a t th e N oria mine of the Inversiones Com pany, 172,209 tons, averaging 20-77 oz. of silver an d 12-03 grains gold per ton, being sent to th e mill. The ore reserves a t this m ine were e stim ated a t th e end of the y ear to be 201,011 tons, averaging 18J oz.
silver per ton.
C orn w all.— I t is proposed to resume
p roduction a t S outh C rofty as soon as the necessary arran g em en ts hav e been made.
S p a in .—T he rep o rt of th e Tigon Mining
and Finance C orporation for th e year ended M arch 31 last sta te s th a t b y th e end of the current year th e o u tp u t of sulphur from the m ine in Spain should am o u n t to 2,000 tons per annum , w hen it is e stim ated th a t it would be self-supporting. On th e Chilean properties production has ceased, con
siderable stocks being available.
F ra n ço is C e m e n ta tio n C o m p a n y .—The
accounts of th e François C em entation Com
p an y for th e y ear ended M arch 31 last show a trad in g profit of £63,964, increased by dividends from subsidiary com panies to
£67,544. A fter m aking allowances for depreciation, p a y m e n t of preference dividends, and o th er item s, a balance of
£44,330 was carried forw ard. T he most im p o rta n t new w ork u n d e rta k e n by the com pany is th a t being done a t Haweswater in connexion w ith th e M anchester Cor
p oration w ater supply schem e.
M urex.—T he tra d in g profit of Murex,
L td ., for th e year ended Ju n e 30 la st was
£48,666, o th er item s bringing th e gross profit u p to £82,872. A fter m aking various allowances an d adding th e sum of £26,776 brought in, th ere was an available to tal of
£86,219. D ividends paid d u rin g th e year
absorbed £49,660, equal to 35 p er cent., and,
after m aking provision for depreciation, etc.,
th e sum of £28,908 was carried forward.
CHROM IT E IN SIERRA LEONE
By w . H. W ILSO N , A.R.S.M., A.I.M.M.
In this article th e a u th o r describes the chrom ite d eposits of th e K am bui H ills, in the P ro v in ce of K enem a.
I n t r o d u c t i o n .
— In spite of its alm ost unique range of usefulness, chrom ite, the one and only com m ercial source of chrom ium , is not a well-known m ineral, and this prelim inary review of its com position and uses, together w ith other particulars, which in a paper dealing w ith a specific deposit of any of th e b e tte r known m inerals m ight be superfluous, m ay here serve as a suitable preface and guide for those who have not had an o p p ortunity to stu d y this m ineral.
Chromite contains, in varying proportions, chromium sesquioxide (Cr20 3), protoxide of iron (FeO), alum ina (A120 3), silica (S i02) and m agnesia (MgO). Commercially valuable ore contains a m inim um of 40% chromic oxide (Cr20 3), and although ore containing as m uch as 55% Cr20 3 is m ined in New Caledonia, by far th e m ajor proportion of the world’s production contains 48% or less of chromic oxide. The proportion of th e other constituents varies in different ores, b u t the following scale gives th e common lower and upper lim its :—FeO, 12% -21% ; A120 3, 6%—21 % ; S i0 2, l% - 9 % ; MgO, 9 % -16% . It is a black m ineral, w ith a sub-m etallic to m etallic lustre, has a specific g ravity of 4T-4-5, a hardness factor of 5-5, and is extrem ely refractory an d obdurate.
Occurring as m agm atic segregations in ultra-basic igneous rocks, usually peridotites altered to serpentine an d talc, it is commonly found massive, w ith a perfectly crystalline, com pact structure, disintegrating on w eathering into typical octahedral crystals.
Of recent years th e uses of chrom ite have increased an d in th e future it is certain to find fu rth e r applications.1 As ferrochrome, an alloy of chrom ium an d iron, containing a t least 60% of th e form er, it is added, together w ith nickel, to certain alloy steels.
These can be divided into three classes : Corrosion resisting, or stainless steels ; steels of high tensile strength ; and high tem perature, or heat resisting steels, all of which have an immense range of usefulness.
Nickel and chrom ium are also being increasingly used in cast iron. F or th e m anufacture of ferrochrome, which is
1 A no n ., " T h e G row ing D em an d for C h ro m iu m ,”
South A fr ic a n M in in g and Engineering Journal, vol. x l, p a r t 1, p. 268, M ay 4, 1929. Jo h a n n esb u rg .
produced from chrom ite in th e electric furnace, only th e b e tte r grades of chrom ite, containing a m inim um of 45% chromic oxide, can be employed, as difficulty is experienced in producing ferrochrome con
taining the requisite m inim um of 60%
chrom ium from lower grades of ore. In addition, th e iron oxide content m ust not exceed one-third of th e chrom ic oxide content.
Chromium plating is earning a well- deserved position of im portance, owing to its b ea u ty and durability. Chromium sulphate and chromic acid are used in th e plating solution.1 Compounds of chrom ium have num erous other uses. H. A. D oerner2 states th a t th e chemical trad e requires an ore containing from 50 to 55% chromic oxide, while F. E. K e e p 3 states th a t,
“ chrome ore of as low a value as 13%
chromic oxide is used in th e m anufacture of chemicals, bichrom ates, chrom e yellow etc.”
There is an increasing dem and for chrom ite for refractory bricks and cement. F or this purpose a m inim um chrom ic oxide content of 40% is necessary an d a low silica and iron content desirable. The ore, moreover, m ust possess certain mechanical characteristics, including th a t of rem aining solid and uncracked when subjected to heat.
Chromite is usually used as it comes from th e mine, w ithout dressing. Certain low- grade ores are, however, w ater concentrated, to raise th e grade to a m arketable value.
The bulk of th e w orld’s chrom ite is produced in Rhodesia, South Africa, and New Caledonia. The U nited S tates is the largest consumer of th e m ineral, w ith a negligible production. The m ineral is sold on a chromic oxide content basis, th e price rising a little more rapidly th a n the proportionate per
centage increase of Cr20 3. In 1929, 47%
ore was valued a t 22 dollars per long ton
1 " A M odern E le c tro -P la tin g P la n t.” N ickel B u lletin , vol. iv , no. 1.2 H . A. D o ern er, " B en eficiatio n of L ow -G rade C h ro m ite O re s.” R e p o rt of In v e s tig a tio n s
2999.
U n ite d S ta te s B u reau of M ines.
3 F . E . K eep, “ T h e Geology of th e C h ro m ite an d A sbestos D e p o sits of th e U m v u k w e R an g e, L om a- g u n d i a n d M azoe D is tr ic ts .” S o u th e rn R h o d e sian Geological S u rv ey B u lle tin No. 16.
201
202 T H E M IN IN G MAGAZINE an d 51% ore a t 2 3 | dollars, while th e current
q u o tatio n (August, 1931) is £4 or 19 dollars per to n c.i.f. for good 48% ore. The present basis allows a bonus of 2s. per u n it for every 1% above a stan d a rd value of 48% m ineral.
C h r o m i t e D e p o s i t s i n t h e P r o v i n c e o f K e n e m a , S i e r r a L e o n e .
— In reviewing th e h isto ry of th is recently-discovered chrom ite area, it should be said th a t Mr.
J. D. Pollett, of th e Sierra Leone Geological D epartm ent, found th e first chrom ite as boulders lying on a bush p a th crossing th e K am bui Hills an d fu rth er prospecting resulted in th e discovery of an outcrop of good-grade chrom ite an d of widely distributed d e trita l chrom ite. These dis
coveries were announced in th e R eports of th e Geological D ep artm en t for th e years 1927-9 and in th e 1929 R eport the following statem en t, since tra n sla te d into
The K am bui H ills.— The following is a
description of th e geological form ation in which th e chrom ite deposits occur (Fig. 1).
The K am bui Hills consist of a low ridge ab o u t 40 miles in length a n d attain in g in places a height of 1,500 ft. above sea level.
T hey are com posed of an ancient series of Schists—th e K am bui Schists 1—lying a t a steep dip of from 60° to 70° W., and striking app ro x im ately N. 30° E. (Mag.
1930). A lthough th e schists are of a width of from 1 to 1-| miles, th e w id th of th e range is som ew hat wider, since th e schists graduate on th e w estern side in to a series of hills com posed of granite a n d on th e eastern side slope gently down to a g ran ite plain, lying some 500 ft. above sea level.
A dense, hard, grey hornblendic schist is th e predom inant rock ty p e of the hills, an d this is of sedim entary origin. The
g«ai«>c [lid
r
*5
I
Fi g. 1 . — Pl a n o f p a r t o f t h e Ka m b u i Hi l l s, s h o w i n g t h e s i t e o f t h e Ch r o m i t e De p o s i t s.
fact, occurs :— “ No detailed exam ination of th is p a rt of th e cou n try has been m ade a n d it is practically certain th a t several other deposits of chrom ite will be found w hen th e district is m ore carefully exam ined.”
A cting under th e direction of Major A. D. Lum b, Senior Mining Geologist of th e U nited A frica Company, b y whose kind permission this paper is being published, Mr. T. H irst m ade a short to u r of th e locality, obtaining sufficient d a ta to confirm th e possibility of th e existence of chrom ite deposits. D uring th e following year the area was vigorously prospected, tw o large deposits being discovered by th e author, in addition to th e original deposit discovered by th e Geological D ept., which proved on developm ent to be of considerable size.
O ther small deposits were located, which on exam ination proved to be valueless an d of which no fu rth e r m ention will be m ade.
chrom ite deposits, however, are associated w ith a series of irregular intrusive dykes of ultra-basic igneous schists, consisting largely of serpentine rock a n d soft decomposition rocks—talc, an thophyllite, an d chlorite schists
—lying near th e eastern co n tact of the sedim entary hornblendic schist and the granite.
Surrounding th e schists is an intrusive biotite granite, which passes in th e contact zone by assim ilation of the schists to biotite and hornblende gneisses. O utliers of schists exist in th e g ranite as far as 2 miles from the actu al co n tact an d intrusions of granite are found far in to th e schists, in which veins of q u a rtz an d p eg m atite are also common.
M idway along th e range of hills, at a position 8° 3' N. L at., an d 11° 13' W. Long., th e three larger chrom ite deposits occur in th e ultra-basic igneous schists, w hich are
1 N. R . J u n n e r, “ G eology of S ie rra L eo n e ."
Th e Mi n i n g Ma g a z i n e, J a n ., 1930,
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OCTOBER, 1931 203
pIG>2.—GeologicalPlanof theChromiteDeposits: Thebrokencirclesinthelongitudinalsectionand theunshadedportionsinthe TRANSVERSESECTIONSREPRESENT POSSIBLEEXTENSIONSOF THECHROMITELENSES.
204 T H E M IN IN G M AGAZINE of a w idth of from \ to \ mile a t th is region.
T he deposits lie parallel to th e strike of th e adjacent rocks and are close together, th e distance from end to end of th e deposits approaching 1 mile. Three miles d ista n t is a m otor road, six miles along which is th e railw ay statio n of H angha, 180 miles v ia th e Sierra Leone R ailw ay from Freetow n, th e p o rt and capital of th e colony.
Dense forests cover th e hills, which although rendering prospecting difficult, promise an endless supply of tim ber for use w hen th e deposits are opened up.
T h e C h r o m i t e D e p o s i t s . —
D etails of the form ation, mode of occurrence and grade of th e th ree large deposits are shown in Fig. 2.
from chrom ite to talc being a b ru p t and the walls of th e deposit sm ooth an d hard.
O utcrops of serpentine occur in the bed of a stream near th e deposit. The chromite is m ineralogically pure, an d contains no en train ed im purities, such as t a l c ; it is coarse grained, perfectly crystalline, and of a black colour, w ith a sub-m etallic lustre.
A ty p ical analysis of th e m ineral gave :—
Sesquioxide of chrom ium 47-72 %
P rotoxide of iron 13-98
A lum ina . 20-30
Silica 1-92
M agnesia . 15-98
99-90
Fi g. 3 . — Ou t c r o p o f Ch r o m i t e ( 2 0 f t. w i d e) o n De p o s i t No. 1 . Th e m e n a r e s t a n d i n g a t t h e E X T R E M E E D G E S O F T H E O U T C R O P .
Deposit No. 1.— This deposit consists of
a series of dyke-like lenses, of uneven shape and thickness, lying along a line parallel to th e strike of th e schists an d dipping a t the sam e angle, i.e. N. 30° E. an d 60° W.
respectively. The lenses have a to ta l length of 500 ft., and w idths varying from 12 ft.
to 23 ft. O utcrops have been exposed by trenching, b u t as no underground explora
tion, or boring, have y et been undertaken, th e dep th is entirely a m a tte r of surm ise and is discussed late r in this paper.
The deposit occurs in th e ultra-basic igneous schists, near th e contact of these rocks and th e sedim entary schists, an d m ay be regarded as a flattened, irregular form ation of lenses, lying in th e hanging wall of th e intrusive rocks. On either side of th e chrom ite is a soft, talcose rock, th e tran sitio n
Deposit N o. 2.— S ep arated from No. 1
deposit by a distance of 1 mile, in another
developm ent of th e igneous schists, is the
second, or No. 2 deposit, also consisting of a
series of dyke-like lenses, approxim ately
in line, of to ta l length 1,000 ft. and widths
varying from 3 ft. to 23 ft. In places the
lenses have a parallel form ation, b u t maintain
th e sam e alignm ent. Considerable local
v ariatio n s occur in th e strikes an d dips, but
th e average corresponds w ith those of the
schists— N. 30° E. a n d 60° W . The deposit
lies near th e co n tact of th e intrusive and
sedim entary schists, close to th e hanging-
wall of th e form er series. In ad d itio n to
surface exploration b y deep trenching,
shafts an d ad its prove th a t, a t a d e p th of
50 ft., th e w idths of th e deposit are
m aintained.
OCTOBER, 1931 205
"ptat:
and i in |
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talc- ■•
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srable 1
T i e # trusive;
e W
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A very soft, decomposed, brown, talcose schist surrounds th e deposit. This schist is free from chrom ite, except betw een the parallel lenses, where it is interspersed w ith chromite crystals an d has a som ew hat granular appearance. Occasional nodules of serpentine are found in th e talc, which is crossed by bands of quartz-schist an d by numerous q u artz veinlets. Small outcrops of serpentine occurring near th e chrom ite are also in tru d ed w ith q u artz veins. Certain of the chrom ite lenses are sh attered and contain soft, brow n talc in th e fissures ; but the m ajo rity are sound an d unbroken.
Perhaps one-half of th e chrom ite is of good grade—coarse-grained, hard, a n d black. The other half, comprising certain entire lenses and portions of others, is composed of chromite rendered friable and of greyish appearance by films of talc occurring in the interstices betw een th e crystals. An analysis of typical m ineral gave :—
Sesquioxide of chrom ium Protoxide of iron' Alum ina . Silica Magnesia .
°/ /o 45-75 14-40 15-50
8-65 14-70 99-00
planes, exposed by trenching and blasting aw ay th e w eathered surface ore, m easure as m uch as 9 ft. across. A typical analysis of th e ore, analysed for chromic oxide content only, gives this figure as 43-5%.
M o d e o f O r i g i n o f t h e C h r o m i t e D e p o s i t s .
— In considering the genesis of the chrom ite, th e relative age of the three series of rocks associated w ith th e deposits—
th e sedim entary schists, th e intrusive igneous schists, and the granites—is one of th e prim ary
Deposit No. 3.— Lying on a prolongation
of the line of No. 2 deposit, a t a distance of 700 ft., and in th e same developm ent of the igneous schists, is th e th ird , or No. 3 deposit, consisting of tw o parallel dykes or lenses, of length 140 ft., and m axim um widths of 20 ft. and 7 ft. respectively, separated by an interval of 50 ft. The strike of the deposit is N. 12° E . (Mag.), and the dip 70° W., corresponding w ith th e schists, which are bending tow ards th e n o rth a t this point and tre n d N. 12° E. to N. 5° E., as compared w ith N. 30° E. in th e region of deposit No. 1. As w ith th e other deposits, it occurs close to th e hanging-wall of th e intrusive schists.
Surrounding th e deposit is a hard, brow n talc schist and betw een th e dykes is a banded zone, composed of a hard, grey rock consisting of a talcose m ineral and granules of chrom ite in varying proportions, w ith partings of soft, decomposed brown talc. Large outcrops of serpentine occur near th e deposit, in tru d e d by large and small veins of q u artz and pegm atite. No underground exploration or boring have yet been u n dertaken on this
deposit. <
The chrom ite is black, lustrous and unshattered. Certain faces of cleavage
Fi g. 4 . — Ch r o m i t e Ou t c r o p ( 2 3 f t. w i d e) o n D e p o s i t No. 2 , t h e p o s i t i o n o f t h e m e n S H O W IN G T H E E X T R E M E E D G E S O F T H E O U T C R O P .
factors. I t is clear th a t th e sedim entary
schists are the oldest rocks and have been
in tru d ed by th e granites and it rem ains to
determ ine th e position of th e intrusive
schists as pre- or post-granite. These
schists are found only in th e sedim entary
schist belts an d not in th e granite, which
indicates th a t th ey are of pre-granite origin,
and this is su b stan tiated by the fact th a t they
are in tru d ed by veins of quartz and pegm atite,
obviously of contem porary age w ith the
granite.
chrom ium -rich ultra-basic m agm a from which th e eutectic chrom ite, by v irtu e of its high freezing point, crystallized in advance of the rest of th e m agm a, an d descended by g rav ity to form flattened, bedded aggregates, or masses of crystals, a t th e b o tto m of the intrusions, b u t p rev en ted from making contact, w ith th e w all rocks by th e rapid solidification of th e outer m argin of the m agm a, cooled by th e wall rocks. A further fall in tem p era tu re w ould hav e solidified th e bulk of th e m agm a.
A n essential condition of th is proposed th eo ry of origin is th a t th e basic magma should have been in tru d e d in to a horizontally bedded series of rocks, an d th e deposits form ed as horizontal, flatten ed beds or masses. To fulfil th is condition th e igneous schists m u st be of pre-g ran ite age and have been in tru d e d w hen th e sed im en tary rocks were in th eir original horizontal position, the gigantic upheaval, possibly contem
poraneous w ith th e in tru sio n of th e granites, lifting th e entire series of rocks into their present position. Complete evenness and
206 T H E M IN IN G MAGAZINE
Fi g. 5 . — Ch r o m i t e Ou t c r o p o n De p o s i t No. 3 E X P O S E D A L O N G T H E S T R IK E .
I t has already been shown th a t th e deposits are in th e form of series of nearly vertical, dyke-like lenses, lying in th e igneous schists n ear th e contact of these schists w ith th e sedim entary schists and parallel to th e strike and dip of these rocks. The possibility of th e chrom ite having been in tru d e d into this position, plausible as it m ight appear after a superficial exam ination, is rem ote, since chrom ite has a very m uch higher m elting point th a n th a t of th e surrounding rocks, which would therefore be liquid a t a tem p eratu re far below th e m elting p o in t of chrom ite. The theory of th e form ation of chrom ite as intrusive masses has never been strongly supported, and is adm irably dis
proved by F. E. K eep,1 who also gives particulars of em inent geologists who condem n the theory.
If th e th eo ry of m agm atic segregation, generally accepted for th e form ation of other chrom ite deposits, is adopted, the igneous schists m ust have been in tru d ed as a
1 F . E . K e e p , op. cit. Fi g. 6 . — Ch r o m i t e Ou t c r o p o n De p o s i t No. 3 .
