WALL
TUNGSTEN MINERAL PRODUCTION DEVON AND
Page 76 TABLE XX
(tons concentrates of 65 per cent. WO3 content)
218
1943
RAL
.... 155. of tworus volum nov 1944 a bow
1938 1939. 1940 1941 A 1942
...u 200 m ma
cam128. ven 171.
310
207-6 3560 P2C
110
. 89.
ansonjbe ore „11945) .
1946 (il sted, he 1947 bango 1:166 (For production figures prior to 1938 see page 11)
General Information
nwor
235. The two important tin mines now in operation are Geevor Mine, St. Just, near Penzance (Geevor Tin Mines, Ltd.) and South Crofty Mine, Carn Brea, near Camborne (South Crofty Ltd.). They employ together between 600 and 700 men. The two mines were examined by us in January, 1947, and our preliminary views formed at that time and now confirmed were communicated to you in July, 1947, and are now largely incorporated in this Report.
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236. South Crofty mine is situated within the long-famous Cornish tin- producing district of Camborne-Redruth which has supplied most of the Cornish production. This area is famous also as a training ground for miners and technicians many of whom have carried Cornish mining traditions to all the chief metalliferous mining fields of the world. In our examination of this area we had the advantage of access to a valuable technical report of a Committee under
the Chairmanship of Mr. Robert Annan appointed by the Minister of Fuel and Power to enquire into the resources of this area in June, 1945.
237. Both of the operating mines suffer from a shortage of underground labour, and this restricts output and increases costs per ton. Even so, at the current price of tin metal (£569 per ton) Geevor mine is operating profitably, although if operations are to continue there for any length of time, the mine will be faced with considerable capital expenditure in connection with the exploration and development of new ground into which the present workings could be extended with a reasonable prospect of success. South Crofty mine is at present continuing to operate under a Ministry of Supply wartime contract whereby output is purchased at cost. Apart from the adverse effects on costs per ton of shortage of labour, working costs at South Crofty are abnormally high due to inadequate pumping facilities. The amount of water to be pumped has been much increased due to the closure of an adjoining mine (East Pool) in 1945, the workings of which, with those of other shallower old mines, are connected with those of South Crofty.
Resources
-
238. In undeveloped areas adjacent to the two operating mines there is available geological information favourable for the occurrence of lode forma- tions, which with other evidence suggests that considerable tonnages of ore of economic grade may still be found. Although most of the larger and better known lodes in the highly mineralised Carn Brea area have been worked extensively, geological and other evidence, although by no means conclusive, suggests that further development from the existing workings of South Crofty and from those of East Pool, would be likely to prove substantial quantities of tin ore of economic grade based on present standards. Unfortunately, actual underground development at South Crofty is so little ahead of existing workings that not more than one or two years' supply of ore on the present
51
**
T$
scale of operations can be said to be proved. At the moment, however, development prospects are reasonably good. There was little proved ore in East Pool when it closed, but here again there are unexplored areas of promise.com
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2008
239. Ore reserves at Geevor mine amount to at least three years' supply. Present workings, moreover, are adjacent to an area of ground known to be geologically favourable for the discovery of new resources, but it would have to be opened up and explored before any estimatelöf reserves could be made.
240. Owing to the lag in development and exploration the future of the tin mining industry as a whole, particularly in the Carn Brea district, can only be regarded as uncertain beyond two or three years. The proving of probable new deposits of commercial size and grade in the neighbourhood of the existing mines will necessitate greatly increased expenditure on develop- ment or new exploration before the industry can count safely on operations
190 UN Bac Wd Rodwod continuing for a longer period.
ma tnd 241. The possibility of new mines of long-term economic importance being opened in other parts of the Cornwall and Devon mining district must be considered in relation to the fact that the area has been worked for a long time and the more accessible ore deposits are probably exhausted. This naturally increases the normal element of speculation attached to lode mining of the Cornish type, and especially to new projects. The increasing depths of working which would probably be necessary would enhance the difficulties and would increase costs, due to many factors of which mine drainage is usually the most important. Outside the immediate areas of the two operating mines there is little precise information of any substantial proved reserves, either of tin or of wolfram (with the possible exception of Hemerdon, para. 250). It has been submitted to us that there are likely to be found tin and wolfram resources of national importance in various parts of Cornwall and Devon, and many instances have been mentioned to us of mines which have closed for reasons other than exhaustion of the ore body being worked. It is certainly true that in Cornwall many cases exist where a multiplicity of mineral ownerships have led to many small mines being opened up where fewer but larger mines would have had a better chance of survival. In certain cases there is supporting geological evidence justifying a case for further exploration, but little or no other evidenceThe financial risk, therefore, would be considerable and projects of this kind, which might be successful only if carried out on a relatively large scale, cannot be attractive to private enterprise as offering reasonable commercial possibilities until more knowledge of the existence of new deposits has been obtained: 10/
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242. It has been further suggested to us that the production of tin in Cornwall can be greatly increased. While there is always the chance that this might be realised, our examination has not brought to light any confirma tory evidence, and there are no proved, or even probable reserves, to support such suggestions. It would be most unwise to assume that any particular increase in output could be achieved beyond that possible from existing mines until such time as a thorough exploratory campaign has established the exist- ence and workability of resources of ore in sufficient quantities to support new mines f
s for a reasonable length of time,
J
.1
243. It is important to remember in connection with proposals to revive tin mining in Cornwall that at present there is an acute shortage of under- ground labour There has undoubtedly grown pup over recent years a prejudican Comwall against underground work. This is no doubt due in part to the uncertain future of the industry. But equally important factors
52
1
appear to be the deterrent of silicosis to recruitment of new labour and, it has been stated beg us the unfavourable comparison of rates of pay in Cornwall with those, for instance, in coal mining. or un vino few blow
1
244. The approach to the question of shortage of underground labour and indeed to the whole future of Cornish mining, should be, in our view through scientific examination of the evidence available in specific localities with a view to carrying out properly conducted schemes of exploration to ascertain whether ore reserves of long-term importance occur. Such schemes would have to deal comprehensively with relatively large areas, and be pres pared to carry exploration to considerable depth. If favourable results were obtained, there would be a better case for making a real attempt to attract new manpower, particularly if increasing, attention, were paid, to anti-silicosis measures and to raising the standard of working conditions. In other words, once there was a prospect of a flourishing industry, being re-established con- fidence would be restored, and there would then be a much better prospect of the labour situation righting itself.
Research
1
T
C
Ragu i 201 pidiegogeti Jguesio Ja gaird done? to wainiM sut
245. It is important that much more attention should be paid to research, primarily with the object of improving present mineral dressing practice in this industry, Modernisation of existing treatment plants, where necessary, is mainly a long-term economic question related essentially to the ore-reserve position. On the other hand, substantial economies could be effected if losses of tin ore in the mills, now amounting, we believe, to something between 25 per cent, and 35 per cent could be reduced. Although the position in this respect is probably no worse than in tin öre extraction plants elsewhere in the world, the benefit of any improvement of recovery to the Cornish tin- mining industry should be emphasised since it might be the means of bringing into the realms of profitability certain known and extensive low-grade Cornish deposits not at present economic to work woontibusque Isungs azot you an aoni oz vodomo odt vd zbosbivib to ansurveq Isis The Special Position of Tin Mining in the Carn Brea District of
A
SENPFL
"
246. We have referred above to difficulties at present facing South Crofty mine, which is the sole remaining operating mine in what is probably one of the most intensely mineralised tin lode districts in the world. It is essential in our opinion for this mine to be kept in operation at least until such time as certain areas of unexplored ground to which its present workings give access have been thoroughly investigated. Otherwise the closure of the mine, and the consequent flooding of its extensive workings and those in the vicinity would probably mean that the cost of exploration later would be prohibitive, if ever it became necessary for strategic or other reasons to find out whether any further tin resources existed. It must not be forgotten that as the alluvial supplies of tin in the world (for instance, those of Malaya and Nigeria) now being rapidly drawn upon, became exhausted, it may be necessary once again to re-examine those areas carrying tin lodes, to see whether further resources can be found. From this point of view the Carn Brea district must continue to be regarded as of potential value to the Nation, and it would be unwise to neglect to take any reasonable measures now when the facilities are available. The cheapest and technically the most efficient way of carrying out an exploratory programme in the favourable areas adjacent to South Crofty mine would be to run it in conjunction with normally conducted mining operations. weng at belved asan is bad Abil
247. If South Crofty mine is to be kept open, it is urgently necessary for new pumps to be provided to avoid the risk of total closure of the mine through breakdows of the existing, out-of-date, Cornishgpumpsof Moreover,
53
38
88
the management of the mine believe that new centrifugal pumps would result in an annual saving of at least £20,000 they state that the latter would nagonly foff men for their operation sagompared with the 42 at present required, and would result in a substantial saving of fuel. The cost of new centrifugal pumps is estimated by the management at between £70,000 and £80,000, a sum which they state the company is not in a position
to raise.
248. The risk of South Crofty mine closing must be removed until more development exploration in its immediate vicinity has been carried out. This must be considered as a matter of urgency and apart from our other general recommendations in this Report, since if the latter are accepted, the interim period until they are implemented should not be lost. We make a special recommendation, therefore, designed to ensure that the chance of exploring for possible reserves of tin ore in the Carn Brea area is not lost, or made too hazardous or uneconomic.
249. We recommend that:-
HOL
The Minister of Supply, being at present responsible for tin supplies, should replace his existing contract with South Crofty, Ltd., by a new contract which would :-
(a) provide for the purchase of the output of tin concentrates from the mine at a guaranteed minimum price for a period of not less than three and not more than five years.
to momen (b) enable special provision to be made for new centrifugal pumps, if necessary by a loan from public funds or by a hire-purchase agreement.
:
(c) empower the Minister to appoint one or more representatives on the Board of South Crofty Ltd. and enable him to prescribe the annual expenditure on underground development and maximum annual payment of dividends by the Company, so long as any loan to the Company from public funds is outstanding.
Hemerdon
:
250. An attempt to work the low-grade wolfram-tin deposit at Hemerdon about ten miles N.E. of Plymouth, was made under Government auspices during the 1914-18 War, but the project was uneconomic and operations were suspended soon after hostilities ceased.
251. In 1939, a private Company (Hemerdon Wolfram Ltd.) erected a small plant which commenced operations in 1941. The lease of the property was then assigned to the Ministry of Supply and the assets of this Company were taken over by agreement in 1942.
agreement in 1942. From January of that year to September, 1943, the plant was operated by Non-Ferrous Minerals Develop- ment Ltd. on behalf of the Ministry of Supply pending the erection of a much larger plant as an emergency war measure.
,
*V
252. Sampling and testing of the ore body by the Ministry of Supply confirmed previous testing and established the existence of at least 4,000,000 tons of ore of a probable grade of 3.19 lbs. and 0.82 lbs. of equivalent 65 per cent. wolfram and tin concentrates respectively per ton of ore, of which 2.78 lbs. and 0.7 lbs. respectively were estimated to be recoverable. The tests, which had not been carried to a greater depth than 60 ft. indicated no deterioration of values, and on these and other geological considerations there is reason to suppose the existence at depth of a considerably greater tonnage of ore than that already proved. The output of the small plant from
January 1942 to September 1943, from about 8000tons of pre milled
54
was equivalent to a recovery of 2.45 lbs. of 65 per cent. wolfram concentrate and 0.45 lbs of 65 per qegt tin concentrates, showing abreasonable comparison with sampling results. Dates,
ZAGG 190 600 62 1
al vonanosaisen bis 0182
253. The small mill was partly dismantled to make way for the new mill, capacity up to 3,000 tons per 24 hours, which came into operation in October, 1943. It continued until June 1944, when it was necessary to close owing to a favourable change in the wolfram supply position. In this period 201,580 tons of ore were quarried and treated, yielding approximately 181 tons of mixed wolfram and tin concentrates in the proportions 42.61 per cent. WO, and 11.86 per cent. Sn. The recovery in this case was only 48 per cent. of that expected from the sampling results, it is believed mainly on account of technical adjustments necessary to sections of the new mill and not because of any known deterioration in the grade of ore quarried. The adjustments might cost upwards of £25,000, but no precise estimate has been made.
254. During the six months January 1944 to June 1944, the plant operated at an average rate of 82.6 tons per hour capacity equivalent to a rate of approximately 2,000 tons per 24 hours. The Mill actually ran, however, for only 71 per cent. of the total possible time available due to mechanical troubles and this reduced the overall milling rate for the period. The project employed about 200 workers, of whom 40 were women.
255. The total cost of the plant including the assignment of the lease of the property was approximately £368,000.
256. The Ministry of Supply have kindly made available to us all the reports and data relating to the operation of the plant during the 1939-45 War. Some of us also had the opportunity of inspecting the plant which is at present on a care and maintenance basis.
257. For various reasons, some of which are mentioned below, the cost of producing wolfram from Hemerdon during the War was considerably higher than had been estimated. The average cost of wolfram, omitting the trial weeks at the beginning when the plant was "running in was approxi- mately of the order of 190s. per unit. This is allowing for a credit in respect of the tin produced as a by-product.
258. The question of the disposal of the Hemerdon plant or its continued retention on a care and maintenance basis is one which, in our view, must be considered in relation to the potential economic and strategic importance to the country of the mineral deposit. Our provisional opinion (which should be confirmed or otherwise by a detailed examination) is that with suitable modifications the existing plant is admirably fitted and equipped for long-term operation. It is the most modern plant of its kind in the country, and has a capacity about twelve times that of any other tin or wolfram plant in Devon and Cornwall. The Hemerdon project, though so far not proved to be economic, represents the first attempt in this country to work a low-grade ore-body on a large scale and on modern lines.
259. It would seem to us, therefore, that Hemerdon presents a strong argument for the outlay of capital with the object of proving the extension in depth and value of the mineral deposit. Without this essential information it is useless to consider the possible economic importance of the plant when an ore supply of, at the most, only 4-5 years' duration is at present proved. We have considered various schemes of exploration drawn up by the Hemerdon Management, and while the final method selected could only be arrived at pafter lose 6tudy, it is probable that Paris off exploratory
55
39
shafts and galleries would be most suitable. The cost might be as much as £50,000 and the work would take about two years to complete but this estimate 6und be verified by a more detailed examination. The cost of care and maintenance is about £3,000 per annum.
or betins
260. Without plant modifications to improve recovery and efficiency of operation, as indicated above, it is unlikely that costs could be much reduced from the high figure attained during the War. We could only recommend that the plant be re-started as a temporary measure on the assumption that uneconomic production of wolfram is required for important strategic or national considerations in which cost is not the most important factor. Subject to this, we recommend that no further steps be taken at Hemerdon, either with a view to temporary operation or disposal of the plant, until further exploratory work has been undertaken. cand for
to Divide nateng on and Jonesa o ebiswan den. Jagia aladinjeuįbe
obnox asor
WITHERITE ¿dinum xil edi pritud 226
Ang
all
ܙ
bsh
na taki onus 261. Witherite, although not mineralogically rare, is now worked in economic quantities in this country only in the Settlingstones Mine near Fourstones, west of Hexham, Northumberland, and in the adjacent Louisa and Craghead collieries of the National Coal Board at South Moor about ten miles S.W. of Gateshead, Co. Durham Chemically, it is barium carbonate (BaCO). These two localities are the only commercial source of witherite in the world.
mqu káv choqnta
Pro Theses
1
2
and pobum viong seed gigquè in queniff ofT ME
Fulg see to gok gage det be wiplet støb bun ahoss 262. earliest records of witherite
records of witherite production relate to the Fallowfield lead mine near Hexham, which closed in 1912, having been worked for this mineral, as well as lead ore, since before 1850. Certain mines in Alston Moor, as well as the Snailbeach mine in Shropshire, also yielded the mineral but in small amount. qpisu, potrocif mo. trentov ypbuking (?) fetera bed bad, audt norbald 263. Production began in Settlingstones Mine some time before 1869 when the working of galena was coming to an end, and at the two Durham collieries about 1932. Both concerns operate gravity separation plants for dressing the mineral.
264. The annual output has reflected the state of trade in the chemical industry, being as high as 13,890 tons in 1923 and as low as 5,111 tons in 1933. Recent figures are given below:
.
TABLE XXI
1.800. 8
PRODUCTION OF WITHERITE
m. (tons)
475
1939
9.8810
1940
12,965
1941
9,709
1942.
12,813
1943
11,835
1944
10,839
1945
10,766
1946
14,376
1947
14,727
་
265. The mineral is readily soluble in acids and therefore finds its main use inpthe preparation of barium chemicals of which the principal are the precipitated barium sulphate known as blanc fixe, the sulphide, chloride, hydroxide and nitrate.
56
må
266. Other uses include brick-making, to check white efflorescence, and porcelain and glass-making
rod lupage 82 of 662 Paredes vir ha85.02.01.02.096 21 11 abletons on
.. Reserves
Ives on oven blow badorgiobau asomote Istento ven goleren, of 267: The reserves
of mineral at the South Moor Collieries are stated to be of the order of 150,000 tons and something slightly less than that amount at Settlingstones.onReserves at the latter are not wholly proved but further exploration might reveal larger tonnages On the information at present probably sufficient to
;
E
2.5. P
available, however, we estimate that reserves are etion at both, mines.
last from ten to twenty years at the present rate of production at both, mines.
wal devtaler gantiupor soustokra rule or encidoph teral is to emails,
sÅT
ased oyun doldw bus biCHAPTER SIV KOM 19/5 SET AT
--sas berebieron
290
to
*** MINERAL RESOURCES
RESOURCES (SCOTLAND)
baal 30 2010 268. The information contained in this Chapter is based on a report by our Scottish Sub-Committee (see page 8) which was appointed în January, 1947, and whose conclusions we have accepted.
269. The Sub-Committee held ten meetings in Edinburgh, including a joint meeting with the Scottish Council (Development and Industry). In addition, they visited the following mines or mineral-bearing districts:-
Leadhills and Wanlockhead (lead and zinc), Tyndrum (lead),
RETOU
are not on pegat/
Killin (Corrycharmaig) (serpentine, chromite, talc and magnesite), ** tiane Gasswater (barytes), noimatta tek bonftros gouemol v2 SET ARC
Muirshiels (barytes), seod of bas koshow gaisd you she hold w Shetland Islands (talc, chromite, serpentine). *dan olulinnup josi
Olure
·
270. Much of the technical information has been furnished by the Scottish Office of the Geological Survey and Museum and our thanks are due to Mr. T H. Whitehead, Assistant Director (Scotland), and to his staff for the care which they have taken in the compilation and geological assessment of the data available, and for the work which they have put into the geological reports on mineral resources supplied to us.
271. The procedure was generally to review all the geological evidence and to supplement it by an examination of records of mining operations, other technical reports, and, where desirable, by visits to the areas con- cerned. The Sub-Committee were fortunate in many cases to have had access to special reports on lead and zinc resources, haematite and mag- netite iron ores, mica, felspar, diatomite, etc., made on behalf of the Ministry of Supply during the War, many of them by Mr. Gordon S. Duncan, A.R.S.M., M.I.M.M.
272. Most proposals to explore or develop Scottish minerals, particularly in the Highlands and Islands, will have to be considered in relation to probems of labour supply and transport. While any proposal must not be rejected for these reasons alone until the potential value of the mineral deposit has been assessed, it is clearly essential to consider these two factors and their economic implications at an early stage, particularly in relation
to other planning and development schemes.? Jo Page 82 of 662
57
40
273. Apart from those few places where mines are still in operation, and in the Leadhills-Wanlockhead area, mining labour is practically non-existent in Scotland Sutside the coalfields. It is apparent,Ptherefore, that any schemes to develop new mineral resources underground would have to take this into account, and to plan sufficiently far ahead if an attempt were to be successful. This is one reason in our view why adequate exploration is necessary first, in order to prove the existence of economic minerals on which long-term projects can be based, before labour is encouraged to leave other employment and to be trained for mining. On the other hand, there are areas, particularly in the Highlands, where local unskilled labour is available in small numbers and this might influence any mineral development schemes, or at least decisions to start exploration requiring relatively few
men.
:
:
274. The chief MDC minerals found in Scotland and which have been considered are:-
Metalliferous
Ores of lead
zinc
Non-metalliferous
Barytes Diatomite
99
""
"
39
Beryl
99
,, copper
""
""
nickel cobalt
antimony
manganese
chromium
Magnetite iron ore
Haematite iron ore
Mica Talc
Magnesite
Chromite, serpentine and olivine
rock
Felspar
Glass sand
Fluorspar Graphite
275. The Sub-Committee confined their attention mainly to those minerals which are now being worked and to those that seem likely to occur in sufficient_quantity to make their economic development in future a possi- bility. Some of these are barytes, ores of lead and zinc, haematite and magnetite iron ore, diatomite, talc, serpentine and olivine rock, felspar, mica, and glass sand. Some of the others, for instance, ores of copper, nickel, and manganese and graphite, have been worked in small quantities here and there in the past, but with one or two exceptions mentioned below the possibility of discovering further resources of value is remote.
276. By far the most important minerals in the past have been the ores of lead and zinc (chief area Wanlockhead and Leadhills) and barytes (Isle of Arran and Gasswater). Today no lead or zinc ore is being produced, but barytes is still important (the Arran source is believed to be exhausted, but Gasswater and another mine recently re-opened, Muirshiels, are pro- ducing on an expanding scale). Other minerals being worked today are talc (Banffshire), serpentine and talc (Shetland) glass sand (Loch Aline). Arrangements have also been completed recently to develop the diatomite deposit in the Isle of Skye (para. 289).
277. A synopsis is given below of the present position about resources, the supporting data for which is, for the most part, the reports received from the Geological Survey (Scotland). When there is sufficient information, the Sub-Committee have endeavoured to distinguish between mineral occur- rences where, in their opinion, further exploration would be worthwhile, and others of doubtful value which it would seem on present evidence need not be furth301662
pfurther conside
considered. The arrangement is alphabetical of 662
of
58
BARYTES
278. Baryteg has beenfound at several localities Ragdiffeteaf parts of Scotland but at the present time it is only being worked at Gasswater Mine, Cronberry, Ayrshire, and Muirshiels Mine, Lochwinnoch, Renfrewshire. Pre- viously an important producer was Glen Sannox Mine in the Isle of Arran, but this closed shortly before the War. Among other places where barytes has been worked are Occumster, in Caithness, Aberfoyle in Perthshire, Barlocco and Auchencairn in Kirkcudbrightshire. It is also found at Stron- tian near Loch Sunart in Argyllshire (see also paragraph 302). Some ex- ploration work has also been done recently on an occurrence at Myres Burn in the Ochil Hills. Elsewhere in Scotland the mineral is common con- stituent of other mineral veins such as those of lead and zinc but is not usually present in sufficient quantities to justify exploitation.
I
·
279. Evidence provided by the company operating Gasswater Mine indi- cates that at present about 40,000 tons of barytes are proved and blocked out, which is sufficient to last the mine two years at the present rate of
output. It is reasonable to suppose, moreover, that normal development
3
will enable the mine to continue in operation for at least five years with good prospects of a considerably longer life.
280, Muirshiels Mine was still being developed at the time of the visit by the Scottish Sub-Committee in January, 1948. It is now understood that further development has indicated that reserves of about 70,000 tons are proved with probable reserves of a further 50,000 tons. Beyond this the possibilities of the extensions of the ore-shoot in depth are good. Further development is in progress, but until this has been done, however, it is not possible to estimate what other reserves may be found.
281. Diamond drilling at both Gasswater and Muirshiels Mines would enable a more accurate estimate to be made of reserves and prospects, but up to the date of the visit of our Sub-Committee the companies had not been able as a matter of policy to spend money to prove reserves far ahead of existing workings.
::
282. Regarding other occurrences of barytes, with the possible excep tion of that now being investigated in the Ochil Hills, no information about proved or probable reserves is available, as little or no exploration has been carried out. In some of the lead veins in Scotland barytes occurs as an associated mineral and there is the possibility of working it in conjunc- tion with lead. Scottish barytes production was about 18,500 tons in 1947.
CHROMITE, SERPENTINE, AND OLIVINE ROCK*
.
283. These minerals have been recorded in workable quantities at two localities, Balta Sound, Unst (Shetland), and Corrycharmaig, Killin (Perth- shire). When first worked in Unst, from 1823-1876, chromite was sold for use as a pigment, but later for refractory purposes. In neither of the deposits has the mineral been exploited as an ore of chromium.
284. Balta Sound, Unst. Chromite is found as concentrations within serpentine rocks. The individual occurrences are either steeply inclined, irregular, and sheet-like bodies, or nodular masses. The sheet-like masses worked so far have been up to 12 ft. in thickness, and the largest has yielded 3,000 tons of chromite rock. The largest nodular masses have yielded up to 500 tons. It is estimated that about 40,000 tons of chromite rock were produced during the per1823-1876; 5,757 tons (inging410656 (tans of
*"Talc, other Magnesium Minerals and Chromite associated with British Serpentines," Geological Survey, Wartime Pamphlet No. 9, 1946, and Supplement No. 1, 1949.
59
41
concentrates) between 1908-1927; and 3,907 tons from 1936-1944. The ore produced has so far averaged 26 per cent. Cr2O, content. Working has been by quarries and it is said that all workable bodies exposed at the surface had been discovered inf 1909, and that the quarries baye ngostly been worked as deep as open quarrying will safely and economically allow. There has been
BA ASOUD
IN G
QS VIAUON no chromite production since 1944.
CONTA 70% salt stoled vinoda hozvio al S 285. An attempt was made in 1918 to concentrate the chromite by gravity. If this had been successful, it might have been possible to work lower grade material, but practical difficulties due to the nature of the oren were encountered,
› rus no quesos, sauh negi ozle and drew toitamolg WR 10. sdi ni 286. Since chromite production ceased in 1944, occasional small shipments of serpentine have been made for refractory purposes svg filmed
ni save 287. Geological evidence suggests that other occurrences similar to those worked at the surface are likely to be discovered underground, and that further exploration is justified. The mineralogical nature of the ore bodies indicates that one or more methods of geophysical surveying could be utilised, com- bined with inclined diamond drilling from the surface. In the event of new chromite ore bodies of reasonable size being discovered; there would be justification for a thorough metallurgical examination of representative bulk samples to ascertain whether modern developments in mineral dressing technique could be applied, since an effective concentration plant on the site might favourably influence the economics of production. At the same time the possibility of producing a chrome-serpentine refractory, on which some research has been done already, might be further investigated.
•
100
nomegalovab
288. Corrycharmaig, Perthshire*. At this locality chromite (or chromium- bearing magnetite) occurs as scattered aggregates in various degrees of con- centration within serpentine which forms part of a small intrusion of igneous rock. Parts of the serpentine are altered to talc (para. 310). The occur rence was worked for chromite in a small way about, the middle of last century and it is stated that about 60 tons of ore were raised and sold in 1855-6. Recent work by the Geological Survey suggests, however, that the mass as a whole contains very little chromite, and that it is unlikely to prove a source of chrome ore, or of chrome refractory material. On the other hand, a considerable area of the serpentine mass has been found to consist of a mineral known as breunnerite (an iron-bearing magnesite), and it is evident that further investigation is justified to ascertain whether a serpentine- magnesite rock could be worked on a large scale for refractory purposes. There is also the possibility of proving and developing the occurrence as a source of talc.
DIATOMITE
.:
289. The only deposit which, on present information, is likely to be of economic importance is that situated at Loch Cuithir in Skye which has already been worked to a small extent some years ago. Exploratory work at that time, including over 100 boreholes, showed the existence of a large deposit some 22 acres in extent. The diatomite underlies a few feet of surface peat and varies from 2 to 35 ft. in thickness. On a conservative estimate several hundred thousand tons of material is present. The crude diatomite is relatively low grade and it will have to be beneficiated to enable it to compete with imported diatomite. Previous attempts to work the Skye deposit have shown that in other respects the main economic factors are the cost of tagspoɓt and the cost of drying on the sitegatwouldppear that the
*See footnote, page 59. 60
existence of large resources of this material in Skye would justify expenditure on research into methods of dressing and processing in an attempt to raise the grade. Weaged&starfdothat a private firm has relengly &arried out tests with this object in view, and that arrangements are now in hand to develop the deposit.
290. Other known occurrences of diatomite are of doubtful importance, with the possible exception of that at Dinnet Muir, Aberdeenshire, which merits further investigation.
42
FELSPAR
291. A good deal of information about the occurrence of this mineral in Scotland has been recorded by the Geological Survey in a recent publica- tion.*
Some of the occurrences have been considered as of potential commercial interest but only one so far has been worked, and then only as a wartime measure. The chief uses of potash felspar in this country are for the production of various porcelain products, whereas soda felspar is used for the glass industry. Normally requirements are obtained from Scandinavia and also in recent years to some extent from Canada.
292. Potash felspar is mainly found as intrusive veins or irregular lenti- cular masses, usually small in size and of limited distribution, whereas soda felspar (in those places where it may be of commercial interest) occurs as one of the mineral constituents in larger bodies of intrusive rock. There are four main potash felspar localities:
(a) Island of S. Harris.
(b) N.W. Sutherland. (c) Wester Ross.
(d) S.E. Inverness.
The chief localities for soda felspar are Ben Loyal and two other places in Sutherland.
•293. During the 1914-18 War, some potash-bearing felspare deposits were examined as possible sources of potash for the manufacture of fertilisers, but the project did not materialise. This use was not considered again during the last War, but instead a re-examination was made to see whether any of the Scottish occurrences could be worked to produce high grade potash felspar for the ceramic industry to replace lost Scandinavian imports. Occurrences in South Harris were tested and two of these were subsequently worked, one of which supplied the greater proportion of home requirements throughout the War. The cost, however, was much in excess of the pre-war imported material and the quality was inferior in respect of colour which is an important consideration.
294. Although at the moment it does not seem that any of these occur- rences can be worked commercially under ordinary conditions, the number of occurrences of the felspar deposits and their composition suggests that further examination should be undertaken, combined with research work to ascertain whether any method of processing could render lower grade material acceptable to the home market. This applies particularly to the large masses of intrusive rocks which are rich in soda felspar. It has recently been suggested that these latter deposits might be examined to ascertain whether there was any possibility of their development and use for making soda Pashe 86Fxflation at most of the Page 86calities 2would * "Scottish Sources of Alkali Felspar ". Wartime Pamphlet No. 44, 1945.
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encounter transport difficulties, although other development schemes in the Highlands might mean that in some places these difficulties would decrease in futurePage 87 of 662