The Platinum Metals

IMPERIAL INSTITUTE — Advisory Committee on Mineral Resources — MINERAL SECTION

The Right Hon. Viscount Harcourt, D.C.L. (Chairman).

^[A]Admiral Sir Edmond Slade, K.C.V.O., K.C.I.E. (nominated by the Admiralty), (Vice-Chairman).

Edmund G. Davis, Esq.

^[A]Wyndham R. Dunstan, Esq., C.M.G., LL.D., F.R.S., Director of the Imperial Institute.

J. F. Ronca, Esq., M.B.E., A.R.C.S., Department of Industries and Manufactures (nominated by the Board of Trade).

^[A]Professor J. W. Gregory, F.G.S., Professor of Geology, University of Glasgow, formerly Director of Geological Survey, Victoria, Australia.

Sir Robert Hadfield, Bart., F.R.S., Past-President Iron and Steel Institute.

Captain A. L. Elsworthy, Intelligence Department, War Office (nominated by the War Office).

W. W. Moyers, Esq. (Messrs. A. Watson & Co.), Liverpool.

R. Allen, Esq., M.A., B.Sc., Imperial Institute (Secretary).

PREFACE

The Mineral Resources Committee of the Imperial Institute has arranged for the issue of this series of Monographs on Mineral Resources in amplification and extension of those which have appeared in the Bulletin of the Imperial Institute during the past fifteen years.

The Monographs are prepared either by members of the Scientific and Technical Staff of the Imperial Institute, or by external contributors, to whom have been available the statistical and other special information relating to mineral resources collected and arranged at the Imperial Institute.

The object of these Monographs is to give a general account of the occurrences and commercial utilisation of the more important minerals, particularly in the British Empire. No attempt has been made to give details of mining or metallurgical processes.

CONTENTS — CHAPTER I PLATINUM METALS: THEIR OCCURRENCES, CHARACTERS AND USES — Introduction — Occurrences — Properties of the Platinum Metals — Metallurgical Treatment — Platinum-Refining Agencies — The Uses of Platinum and its Allies — Alloy Substitutes for Platinum — Scrap Platinum — World’s Output of Platinum

The metals which comprise the Platinum group are the following: Platinum, Palladium, Iridium, Osmium, Ruthenium and Rhodium.

Up to the year 1914 Russia produced over 90 per cent. of the world’s supply of platinum, the Republic of Colombia, South America, ranking next in importance with about 5 per cent. Owing, however, to the war and to the chaotic conditions brought about by the revolution, the output of Russia has considerably decreased, and although the Colombian production has been steadily increasing, the increased demand in connection with munition manufacture caused a somewhat serious shortage during the latter stages of the war, which was especially felt in the United States. As a result much exploratory work has recently been carried on in an endeavour to discover new deposits of importance; but up to the present, although several fresh occurrences have been brought to light, results have on the whole been disappointing.

Platinum usually occurs in nature as native metal alloyed with one or more of its allied metals in the form of very fine grains more or less flattened; sometimes in the form of irregular nuggets; and occasionally, though rarely, in small cubic crystals. It is sometimes coated with a black layer of iron 2oxide, which may be magnetic, in which case it is not easily recognizable. When unrefined it is referred to as “crude” platinum.

With the exception of a certain amount of the platinum metals, obtained from the refining of copper and gold bullion, particularly from the copper-nickel deposits of Sudbury, Ontario, about 99 per cent. of the whole supply is derived from alluvial deposits. Several occurrences of platinum in situ are known, but so far few are of commercial importance: however, in view of the indications of exhaustion shown by some of the placer deposits, notably in Russia, the exploration of primary ores is now receiving more attention and practical results have already been achieved in Russia and in Spain.

The mother rocks from which the deposits are derived, in the large majority of known cases, consist of basic and ultra-basic igneous rocks, including peridotites, pyroxenites and dunites. The two first are composed of iron magnesian silicates, pyroxene, augite and hornblende with olivine, chromite, ilmenite and magnetite: the dunites consist principally of olivine with some chromite. These rocks are often found to have undergone more or less alteration to serpentine. In addition, platinum has been found in quartz veins, notably at the Boss Mine, Nevada, and in a few known cases it has been derived from formations in schistose, or altered sedimentary rocks.

When present in serpentine, platinum is usually disseminated through the rock in fine particles. It seldom occurs in a lode-formation. In sedimentary rocks it usually occurs in sandstones. In cases where alluvial deposits have been derived from the basic igneous rocks, the associated minerals are usually chromite, magnetite, ilmenite, iridium and osmiridium. In sedimentary deposits the metal is commonly associated with quartz, copper, nickel, silver and palladium.

Platinum has been found in certain varieties of the copper ores tetrahedrite and bournonite. It has occasionally been located in shales and in coal, although not in recoverable quantities. In the latter case, in an Australian coal, it is associated with vanadium^[1] p. 992.

Several cases are known of platinum being present in meteorites, 3two well-authenticated instances having been reported from Mexico. Platinum has been shown to exist in meteoric iron from New South Wales.

Crude platinum, as recovered, contains from 70 to 90 per cent. of the metal, and, as mentioned above, is really an alloy of platinum with one or more of the allied metals, the chief impurities consisting principally of iron and copper.

The table on the next page gives the analyses of typical samples of crude platinum from the Urals, California, British Columbia, and other places.

Platinum also occurs in combination with arsenic in the mineral Sperrylite (PtAs₂), in the form of minute octahedral crystals. The colour of this mineral is tin white, its lustre is metallic and brilliant, its hardness varies from 6 to 7, and its specific gravity is 10·6. The mineral is brittle and breaks with a conchoidal fracture. It is very rare, and is interesting as being the only mineral of platinum known besides the native metal. It occurs associated with sulphide minerals of magmatic origin in gabbros and diabases, notably in the nickeliferous pyrites of Sudbury, Canada, and in the copper ores of the Rambler Mine, Laramie, Wyoming.

It is probable that the palladium, which is also found in these deposits, is similarly present in the form of an arsenide, but such a mineral has not yet been definitely proved to exist.

The following is an analysis of a sample of sperrylite: platinum, 54·47 per cent.; rhodium, 0·76 per cent.; palladium, trace; arsenic, 42·23 per cent.; antimony, 0·54 per cent.^[2] p. 69.

Platinum.—The colour is white with a greyish tinge. When pure it is very malleable and ductile. Its coefficient of expansion is less than that of all other metals. Platinum fuses at about 1750° C., but the presence of impurities lowers the melting-point. Its specific gravity is 21·5, and its hardness is from 4 to 5. Its electric conductivity is low, being 13·4 at 0° C.^[3] p. 398.

5Platinum is not acted upon by either nitric, sulphuric or hydrochloric acid, but is soluble in aqua regia (1 part of nitric to 2 parts of hydrochloric acid), or in other mixtures liberating chlorine, with the formation of platinum tetrachloride (PtCl₄). It is not acted upon by air or moisture, even at high temperatures. It is corroded by caustic alkalis, sulphides, sulphates, phosphates and arsenides, if heated in contact with them. It will not amalgamate with mercury unless sodium is present, in this respect differing from gold and silver.

Platinum, in a finely-divided condition, absorbs large quantities of hydrogen or other gases, which on occlusion become more active: hence its value as a catalytic agent.

Palladium.—This metal resembles platinum, but is sometimes fibrous, the colour being between that of platinum and of silver. It possesses a lower melting-point than platinum—about 1550° C. It is malleable, has a hardness of from 4·5 to 5, and a specific gravity of 11·5. As already stated, palladium, when found in copper ores, is probably present in combination with arsenic. Porpezite, a rare mineral, containing gold and up to 10 per cent. palladium, has been identified in gold-bearing veins in Brazil [see p. 54].

Palladium is produced from the refining of copper matte and of base gold bullion from Australia and elsewhere.

Iridium is a brilliant white brittle metal, with a specific gravity of 22·4, and hardness of 6 to 7. Its fusion point is very high—about 2200° C.—and under ordinary conditions it is not attacked by any acid. At 1100° C. it begins to oxidize to a purple oxide. Iridium usually occurs either in crude platinum, or alloyed with osmium, as iridosmine, or as native metal. The bulk of iridium is derived from the platinum placer deposits of the Urals, but the Californian metal is more valuable, on account of its better quality. It is also obtained in small amounts from copper bullion.

Osmium is a hard and brittle metal, bluish-grey in colour. Its specific gravity is 22·5, and it has a very high melting-point, in this respect being the most refractory of the group.

Iridosmine, or Osmiridium, an alloy of iridium and osmium, occurs as hexagonal crystals, or flattened grains of lighter colour than platinum. It may contain from 40 to 77 per cent. 6of iridium, and from 20 to 50 per cent. of osmium. If the iridium predominates, the alloy is called Nevyanskite, and Siserskite if the osmium content is high. It is distinguishable from platinum by the brittleness of the flakes. Siserskite gives off a pungent odour, if strongly heated, caused by the volatilization of osmium. Iridosmine has a hardness of 6 to 7, and a specific gravity of 19 to 21.

Ruthenium is a white metal, with a specific gravity of 12·1. It is scarcely acted upon by aqua regia. Ruthenium occurs mainly in small amounts in iridosmine. It is also found in the copper ores of Sudbury and other places. Laurite is a very rare sulphide of ruthenium (RuS₂), containing a small amount of osmium, which has only been recognized in the Borneo deposits.

Rhodium is a white metal resembling aluminium, with a specific gravity of 12·1, and a melting-point of about 2000° C. It is ductile and malleable at red heat. In addition to its occurrence in crude platinum, the metal is also contained in small quantities in the sperrylite found in the copper ores of Sudbury, Canada^[5] p. 779.

Colloidal Platinum.—This has only recently been detected in ores, and therefore its occurrence might not be detected qualitatively. By destroying its colloidal condition, however, its presence can be discovered in the ordinary ways^[4].

Crude platinum can be refined either by dry or by wet methods, the following being brief outlines of the two processes:

By the wet method, the crude platinum is dissolved in aqua regia, with excess of hydrochloric acid. Evaporation is continued until the whole of the nitric acid is expelled. By addition of a solution of ammonium chloride, the platinum is then precipitated as ammonium platini-chloride. This precipitate is heated to redness, when chlorine and ammonium chloride are given off, and spongy platinum remains. The last is next granulated, after fusion by the oxy-hydrogen blowpipe in a small lime furnace. Platinum obtained by this 7method may contain small amounts of iridium, rhodium and palladium.

In the dry method, introduced by Delville and Debray, the crude platinum is smelted with galena in a small reverberatory furnace. A portion of the lead is reduced to the metallic state by the iron in the charge, and forms a fusible alloy with the platinum. The osmiridium present settles to the bottom of the furnace, and may thus be removed. Litharge is then thrown in to form more alloy, and some glass to act as a flux. The alloy is cupelled, and the residual platinum is then melted in a lime furnace with the oxy-hydrogen flame. The platinum thus obtained often contains iridium and rhodium.

A combination of these two methods is also sometimes employed^[3] p. 403.

The electrolytic process of gold-refining was introduced to treat platiniferous gold. In the gold chloride, or Wohlwill method, iridium and osmiridium are insoluble, and remain with the anode slime. Platinum and palladium, if nearly pure, are also insoluble, but when present alloyed with gold and silver, pass into the solution and remain there. In a hot bath it is stated that the platinum present should not exceed 50 gm. per litre. According to T. K. Rose, a cold bath containing only 20 gm. per litre causes a certain quantity of platinum to be deposited with the gold^[6].

H. F. Keller, in “Platinum, the Most Precious of Metals” (Journal of the Franklin Institute, November 1912) deals fully with the extraction and refining of platinum.

The following contains a list of the principal firms engaged in the refining of platinum metals:

In England: Johnson, Matthey & Co., Ltd., Lees & Sanders, Warstone Smelting Works, Sheffield Smelting Works, Johnson & Sons. (This is the list of the Ministry of Munitions.)

In France: Legende et Cie., Compagnie Internationale du Platine, Lyon Allemand, Lecht Lyonnais, Henrique Marrett, Bonnen, Hesse Fils.

8In Germany: W. C. Heraeus, G. Siebert, F. Eisennad & Co.

In the United States: Baker & Co., American Platinum Works (N.T.), Irvington Smelting and Refining Works, J. Bishop & Co., H. A. Wilson & Co., Belais & Cohn, Kastenhuber & Lehrfeld, Roessler & Hasslacher Chemical Co., Wildberg Bros., and others handling scrap.

According to Russian information about 25 per cent. of the Russian output before the war was refined in Germany. In Russia there are practically no platinum-refining facilities^[7].

Platinum.—In the chemical industry platinum is largely used for catalyzers in the manufacture of sulphuric, acetic and nitric acids; for stills for the final concentration of sulphuric acid; and in the electro-chemical industry.

In the making of “contact” sulphuric acid a “contact mass” is charged into the chambers of the plant. This is formed by soaking asbestos, or anhydrous magnesium sulphate, with platinic chloride solution, and baking the mass to drive off the chlorine. The contact mass usually contains from 7 to 8 per cent. platinum, in a very finely-divided state. In the making of acetic acid from a mixture of air and alcohol vapour, platinized asbestos is used. For the catalyzer used in the conversion of ammonia into nitric acid a very fine-meshed platinum gauze is used; this is strengthened at its edges with platinum-iridium wire. One ounce of platinum is required for the production per annum of 25 tons of catalytic acid, or of 40 tons of nitric acid from ammonia.

In the finely-divided state all the other metals of the platinum group, especially palladium, have also the facility of absorbing great quantities of certain gases, and can be used as catalysts.

Owing to its high melting-point, and to the resistance to the action of acids at high temperatures, platinum is largely used for chemical ware in the form of crucibles, dishes, etc. Platinum crucibles are indispensable in the chemical analysis of rocks.

9In the electrical industry platinum is largely used for contact points, in telegraph and telephone apparatus, in magneto-contacts, and in the construction of the thermo-couples of pyrometers. In the manufacture of jewellery, especially in the crown-setting of diamonds, platinum has been much used in the place of gold: alloyed with a little iridium it can be worked into delicate designs, which are durable. During the war, however, when platinum was largely wanted in the making of munitions, its use in jewellery manufacture was much restricted. Platinum was formerly largely used in dentistry. In photography potassium platino-chloride is required for producing platinotype prints. In the form of barium platino-cyanide it is used in X-ray photography as a coating for the projecting screen.

Platinum is required in the manufacture of certain parts of chronometers, theodolites and watches; also for standard weights and measures, and for various types of self-lighting lamps^[4] p. 561.

Palladium has its chief value as a substitute for platinum, in palladium-gold alloys, which are used extensively in dentistry, for jewellery and for chemical ware. It is also utilized in the manufacture of astronomical instruments and watches, also for plating metal ware^[1] p. 1002. The use of palladium as a catalyzer is well known.

Iridium, when pure, is of small value, being difficult to manipulate on account of its brittleness. It is principally used in alloy with platinum for hardening purposes. Jewellers’ platinum usually contains 10 per cent. iridium, and in the electrical industry an alloy composed of from 15 to 50 per cent. iridium is usually employed. Alloys with up to 10 per cent. of iridium are ductile and malleable, but with over that amount are hard and difficult to work.

The metal is used in the manufacture of fountain-pen points, for which purpose the grains require careful selecting^[8] p. 106; also for standard weights and for contact points. Iridium black, an oxide, is of value as a pigment for chinaware^[1] p. 1001.

Iridium is suitable for sharp surgical instruments, and gold needles with soldered iridium ends are employed for stitching 10wounds. It is also used in photography. Iridium is of greater scarcity than platinum, hence its greater value.

Osmium.—There is now little or no market for osmium. It was formerly in considerable use for the manufacture of incandescent lamps. Osmic acid is used for staining anatomical preparations in microscopic work. On account of the poisonous nature of its vapour the extraction of osmium is costly and dangerous.

Ruthenium is also of little or no commercial value. Both these metals possess the disadvantages of being brittle and easily oxidized.

Rhodium is of small commercial use. It is used principally in alloy with platinum. An alloy containing 10 per cent. rhodium is used for some thermo-couples of pyrometers, and in the making of laboratory utensils.

Platinum Alloys.—Platinum forms alloys with a number of metals, but only a few are of industrial importance^[3] p. 400. Platinum and iridium form a hard and elastic alloy, which is unaffected by air, and takes a high polish. Alloyed with 10 per cent. iridium platinum is used for one of the wires in thermo-couples of pyrometers; and with 10 to 20 per cent. iridium for making standard measures of length and weight.

Platinum and copper form various alloys. An alloy with 18·75 per cent. copper, called “coopers’ gold,” takes a high polish and closely resembles 18–carat gold.

An alloy of platinum and silver containing 66 per cent. silver is used as a standard of electrical resistance. An alloy containing 20 to 30 per cent. silver is used in dentistry.

Platinum alloys with lead, zinc and other metals at low temperatures; it is usually recovered from these alloys by cupellation.

Platinum alloys with steel in all proportions. With 10 per cent. platinum, rusting is prevented. A very elastic metal is produced by alloying platinum with from 5 to 10 per cent. gold.

The melting-point of silver is raised by alloying it with platinum, but its thermal conductivity is lowered.

On account of the scarcity and high price of the platinum metals, much attention has lately been directed towards the discovery of suitable substitutes.

In the electrical industry an alloy of 3 parts of palladium and 2 parts of silver is in use, also an alloy of nickel and chromium. Platinite, an iron-nickel alloy, containing 46 per cent. nickel and 0·15 per cent. carbon, has the same coefficient of expansion as glass, and, when coated with copper, is used to replace the platinum connection wires of incandescent lamps. Tungsten is sometimes used for certain ignition devices. For cathodes an alloy of 90 per cent. gold and 10 per cent. copper can be used to replace platinum; the same alloy, if electrically coated with platinum, and then carefully polished and burnished, is suitable for platinum anodes.

For platinum chemical laboratory ware, there are several substitutes, such as fused quartz; various iron, chromium, and nickel-chromium alloys; palau, a gold-iridium alloy marketed in California; rhotanum, a general name for gold-palladium 12alloys containing from 60 to 90 per cent. of gold, which are suitable for most chemical purposes, except for use with hot concentrated nitric acid, and for electrolytic anodes; amaloy, which is a complex alloy containing nickel, chromium, tungsten, etc., highly resistant to corrosion and to cold nitric and sulphuric acids^[9] p. 600.

In the jewellery trade platinum has been replaced by an alloy of 90 per cent. palladium and 10 per cent. rhodium. For certain surgical work various stellite alloys, containing cobalt and chromium, and hardened by the addition of tungsten and molybdenum, are valuable substitutes for platinum, and are not affected by antiseptic solutions. In dental work pins are now made of tungsten coated with palladium^[10] p. 549. For most technical purposes an alloy of tungsten and nickel with gold or silver is used in Germany; it may be cast, rolled or forged, is acid-resisting, and capable of taking a high polish^[11]. White gold, another substitute for platinum, contains fine gold, from 75 to 85 per cent.; pure nickel, from 10 to 18 per cent.; and zinc, from 2 to 9 per cent. Illium, a chromium-nickel-copper alloy reported recently as the discovery of S. W. Parr, of Illinois, is a substitute for gold or platinum, costing only 25 cents per ounce. It is stated to have been a “50 per cent. standard of success.” The alloy withstands hot or cold, strong or diluted acid, can be both cast and machined, and is already used largely in the manufacture of calorimeter bombs^[12].

The results of researches made to discover substitutes for platinum, and undertaken by the National Dental Association of America, are described at length by F. A. Fahrenwald, in a paper read in January 1916 before the American Institute of Mining Engineers.

A considerable amount of platinum in the form of old and worn articles is now collected for return to the refineries, where it is re-treated, and sold again as new metal. The trade in scrap platinum has been particularly active in the United 13States, official statistics showing that in 1916, 49,400 oz. of refined platinum were recovered.

According to J. L. Howe, the estimated limits of the total world-production of crude platinum, up to January 1917, were as follows^[13]:

On the other hand, James M. Hill^[14] states that possibly 5,000,000 oz. was the total world’s production to June 1917, which he distributes according to the uses made of it as follows:

It is difficult to obtain exact figures of the annual production of crude platinum. This is particularly so in the case of Russia, where there appears to have been a tendency for private enterprises to keep their published outputs as low as possible, in order to avoid registration. The discrepancy between the official and actual figures of production in Russia is variously estimated at from 20 to 60 per cent.

The table on the next page is compiled from the sources considered most reliable.

Canada.—The recoveries of platinum at the works of the International Nickel Company in New Jersey for the years 1910–1912 were 258,666 and 497 oz. respectively, chiefly from Canadian matte.

Russia.—The actual productions of platinum as quoted in Mineral Industry in oz. were: 1910, 300,000; 1911, 280,000; 1912, 300,000; 1913, 275,000; 1914, 240,000; 1915, 124,000; 1916, 90,000; 1917, 50,000.

15The market value of platinum has risen considerably since 1880. In that year the price was 12s. 7½d. per oz. troy, in 1890 it was 25s. 3d., and in 1900, 63s. 1½d. The average prices in London and New York for the years 1910–1919 were as shown on the accompanying tables:

1910, 1915, 1916 and 1917—Metal Market Year Book. 1911, 1912, 1913 and 1914—Mining Magazine.

1910, 1914, 1915, 1916 and 1917—U.S. Geol. Surv. Mineral Resources.

1911, 1912, 1913, 1918 and 1919—Eng. and Min. Journ., vol. 107, No. 2, p. 77.

CHAPTER II SOURCES OF SUPPLY OF PLATINUM AND ALLIED METALS ( a ) BRITISH EMPIRE — EUROPE — United Kingdom — ASIA — India — AFRICA — Rhodesia — Union of South Africa — NORTH AMERICA — Canada — Newfoundland — AUSTRALASIA — Australia — New Zealand

The outputs of platinum metals in different parts of the British Empire are shown in the table on p. 14.

There is no known occurrence of platinum in the United Kingdom, but there has always been much trade done there in the platinum metals, England having been the second largest importer of the big consuming nations. The following were the importations of Russian platinum for five periods since 1863:

The above figures do not include receipts of platinum for seven different years since 1863, for which there are no records.

The table on the next page gives a summary of total imports of platinum metals for the years 1910–1918, with the countries of origin.

The platinum market in London was controlled by the Government from January 1916 to December 1918, Johnson, Matthey & Co., Ltd., acting as buyers. On December 26, 1916, platinum was declared contraband.

18About 7 per cent. of the Russian and one-half of the Colombian outputs were sold to England during the war, as well as most of the Australian and Indian production. Much of this metal was refined in the United States.

According to J. E. Orchard^[17], the commercial control (financial) of the world’s output of platinum of 267,233 oz. of 1913 was divided as follows: France, 74 per cent.; Russia, 18 per cent.; United States, 4 per cent.; British Empire, 2 per cent.; other countries, 2 per cent.; whilst the political control (territorial) was divided as follows: Russia, 93 per cent.; Colombia, 6 per cent.; other countries, 1 per cent.

Traces of platinum and iridium have been noticed in association with the gold obtained from native workings at Bonai City. The gold occurs in a deposit of iron oxide, which forms the cementing material in a hard stratum of quartz pebbles. The oxide is separated by pounding, and then washed away to extract the gold. The proportion of platinum to gold is probably less than 1 to 20.

Platinum occurs, associated with gold, in the gravels of the Irawaddy River in Burma. A small quantity of platinum is obtained at Myitkyina by the Burma Gold Dredging Company. During the years 1911–13, 152 oz. were won by this company. In 1915 the output was 17·7 oz., and in 1916, 9·25 oz. In 1917, 4 oz. only were produced^[18]. Owing to the cessation of the golddredging operations at Myitkyina, Burma has ceased to produce platinum, the quantity recovered during the year 1918 being only 0·31 oz.^[19].

It has also been located with iridosmine in the auriferous gravels of the rivers draining the slopes of the Patkoi Ranges, both on the Assam and Burma sides^[20].

Platinum has recently been located in the Gwelo district, about 6 miles north-east of Indiva siding, where it occurs in the great dyke of norite, which is here about 4 miles 19wide. A. E. V. Zealley, the late assistant Government geologist, made this occurrence the subject of a special report^[21].

The country rock is a serpentinized dunite. The deposit is capped by a ferruginous siliceous gossan from 4 to 5 ft. wide, which may be traced on the surface for about 100 ft., and is comparable to a fissure vein. The gossan consists largely of hæmatite and chalcedony, with occasional veinlets of copper and nickel minerals. Although the presence of platinum in the ore could not be detected by panning, the possibility of its occurrence on geological grounds was considered, and a sample of concentrate from an unstated amount of ore was forwarded to the Imperial Institute for analysis. The sample was found to contain platinum to the amount of 1 dwt. 20 gr. per ton. A report on the further development of this deposit is awaited with interest.

A sample of concentrate from an unstated amount of material from the gem-bearing gravels of Somabula Forest, Gwelo district, was received at the Imperial Institute from the Director of the Geological Survey of Southern Rhodesia in November, 1918. On analysis this sample yielded the following per ton: platinum, 3 oz. 12 dwt.; osmiridium, 7 oz. The concentrate also contained a large proportion of gold. As shown by the latest information available, the deposits, although undoubtedly rich, appear to extend over a limited area. According to an analysis made at the Imperial Institute, a sample of chromite from Southern Rhodesia (Selukwe) contained 0·17 per cent. copper and nickel oxides, and a trace of platinum^[22].

H. B. Maufe^[23] has stated that as the River Umtebekwe drains two areas of ultra-basic rock containing chromite, it might be expected to contain alluvial platinum, as well as gold, and, as a matter of fact, platinum has actually been discovered in a reef in the Great Dyke (norite), at the head of the Umtebekwe valley.

The presence of platinum was recently reported at Willoughby’s Halt, 12 miles south of Gwelo.

Cape Colony^[24].—Platinum is present in varying quantities in the copper-nickel deposits at Insizwa, situated in the Cape 20Province, close to the boundary between East Griqualand and Pondoland.

The rock formation consists of a basin-shaped mass of intrusive norite, averaging from 2,000 to 3,000 ft. in thickness, and lying in the shales and sandstones of the Beaufort Series of the Karroo System.

The ore body consists of sulphides of copper and nickel, in association with pyrrhotite, the minerals occurring disseminated near the basal margin of the intrusive in olivine picrite. Gold and silver are also present in small quantities.

The average copper and nickel contents in the ore are each about 4 per cent., and the platinum content averages from 2 to 3 dwt. per ton, the platinum being unequally distributed through the ore^[25] p. 14.

It is not certain in what form the platinum occurs. It does not appear to be present as sperrylite. In the opinion of W. H. Goodchild it may occur in close association with the silver^[25] p. 35.

Mining operations have been intermittently carried on here during the last fifty years, the last exploratory work coming to an end in 1911. Operations were, however, resumed early in 1920.

Transvaal.—Small amounts of platinum and its allied metals have from time to time been noticed in black sands from the battery “clean-ups” on the Rand at Klerksdorp and other gold-mining districts, and platinum to the amount of 2½ dwt. per ton is reported to have been present in residual slimes at the Rietfontein mines^[26]. A specimen, consisting of about 85 per cent. osmiridium and 15 per cent. platinum, recently received at the Imperial Institute, was stated to have been taken from a compact shale, immediately underlying the banket reef in one of the mines of the Klerksdorp district. In the large majority of the gold mines, however, the platinum metals, if present, appear to exist in such small quantities as to escape detection.

A series of samples of chromite from Kromdaal, near Rustenburg, showed from a mere trace to 1 dwt. of platinum per ton, and one sample of chromite from the Secocoeniland deposits showed as much as 1½ dwt. of platinum per ton^[27].

The occurrence of platinum in Canada was first observed in 1862, in the course of gold-mining operations on the Rivière-du-Loup and the Rivière-des-Plantes in the province of Quebec^[28] p. 210.

Since that time platinum has been found in a number of localities associated with auriferous gravels, but the crude metal has only been obtained commercially from the Similkameen district in British Columbia. These deposits first attracted attention in 1885. All the workings are alluvial, although the platinum has in several cases been traced to its parent source.

Alberta.—Platinum and gold in minute grains, closely intermixed, are found in the North Saskatchewan River, near Edmonton. In 1918 certain platinum occurrences were examined by the Munitions Resources Commission, visits being paid to Fort Saskatchewan and the Peace River district, in Alberta. These deposits, however, proved to be disappointing. In the former locality, which was carefully tested by drilling, the values of the samples obtained averaged less than 10 cents in gold and platinum per c. yd. of gravel^[29] p. 427.

British Columbia.—Platinum, associated with gold, which is the dominant metal, occurs in the Tulameen River and its tributaries, the principal of which is Slate Creek, others being Cedar, Eagle, Bear and Granite Creeks. The metal is present in small rounded grains, or pellets. Chromite is often found intergrown with the platinum, olivine and pyroxene usually occurring in association. The heavy minerals remaining with platinum in the concentrate are titaniferous magnetite, chromite and native copper. The platinum is sometimes magnetic, probably due to the covering of the grains by small particles of magnetite^[30].

The following analysis, according to G. C. Hoffmann, is representative of an average sample of crude platinum from the Tulameen River:

Owing to the presence of osmiridium in considerable proportion, the ore is classed as “hard metal,” and on that account fetches a higher price. Many of the richer placers have become exhausted, and work is now carried on by a few individuals, principally Chinese, who work during the summer months only. In some cases high benches, 50 to 100 ft. above the creek bottom, are being worked. Much of the platinum and gold is of a coarse texture, with a rough surface, and the latter is sometimes found embedded in quartz. Nuggets are sometimes found encrusted with chromite, and are thus liable to be overlooked. The deposits are therefore not of great age, and the metals have not been transported long distances from their sources.

Kemp is of opinion that the platinum is derived from pyroxenite dykes cutting through peridotites, which outcrop on Olivine and Grasshopper Mountains.

It is of interest to note that some diamonds and rubies have been discovered with the platinum in the Tulameen deposits. They are of good quality, but of small size, and occur in a matrix of dunite^[28] p. 210. American capital dominates the platinum industry in the district. In 1918, at the request of the Imperial Munitions Board, special investigations in this area were undertaken by members of the Geological Survey, and several prospecting bores were put down to bedrock. Full reports of the work done are not yet available, but it is understood that the results are considered to be promising, and to warrant further examination of the district^[29] p. 429.

Platinum was in 1918 discovered at Franklin Camp, near Grand Forks, B.C., in the “Black Lead,” so-called, which is a mixture of augite, 75·13 per cent.; orthoclase and microcline, 17·06 per cent.; hornblende, 1·47 per cent.; and magnetite, 6·06 per cent., as determined by microscopic measurements on a typical specimen, with accessory minerals, chalcopyrite, 23bornite and apatite. A sample of chalcopyrite assayed 0·38 oz. crude platinum per ton. Samples of the “Black Lead” assayed from 0·02 to 0·17 oz. per ton^[31].

At Burnt Basin, on the Mother Lode claim, an auriferous quartz vein carries platinum, in amounts varying from a trace to 0·25 oz. per ton. The quartz also contains chalcopyrite, pyrite, galena, sphalerite and molybdenite^[31]. Native platinum in small quantities has been found associated with gold in the following localities: Tranquille River, Fraser River, Rock Creek, Yale District, North Thompson and Clearwater Rivers. It has also been reported to occur in a dyke across the Kootenay River upon the Granite Poorman Mining Company’s property a few miles from Nelson^[32]. At Siwash Creek, in the Tulameen district, small flakes of platinum, associated with chromite, often occur in shear zones in granite. Dredging for gold and platinum is being carried on, on the Peace River, North British Columbia.

According to J. B. Hobson the heavy concentrate produced on the Consolidated Caribo hydraulic mine at Quesnel, contains, besides gold and silver, platinum, palladium and osmiridium, one analysis giving a total value of $3,873 per ton. The gold and silver being non-amalgamable are probably included in particles of pyrite and galena, whilst the platinum metals are found as minute grains or are enclosed in particles of chromite and magnetite. A system of “under-currents” is being installed to properly dress this concentrate^[33].

In 1917 the recorded output of crude platinum from the placer gravels of the Tulameen district in British Columbia was 57 oz., that for 1918 being 39 oz. For the five years preceding 1892, this district produced on an average over 1,500 oz. per year.

Manitoba.—Samples of gold ore containing platinum have been obtained in the Star Lake district of south-eastern Manitoba^[34]. Analyses of the samples from different auriferous reefs were made by the Department of Mines in 1917, and yielded platinum varying in amount from a trace to 0·1 oz. per ton. In addition to gold and platinum, the veins carry small quantities of galena, zinc blende, pyrite, chalcopyrite and arsenopyrite in a gangue consisting mainly of quartz.

24Platinum is reported to occur in auriferous quartz veins in several mines and prospects in Le Pas district; a picked sample of ore from the mine of the Northern Manitoba and Development Company, assayed $49 gold and $17 platinum per ton^[35]. McCafferty’s Prospect, about 5 miles away, contains platiniferous quartz.

Nova Scotia.—According to E. R. Faribault in Summary Report, 1918, Part F, of the Canadian Department of Mines, platinum has been found, mostly in traces, in some of the old gold districts of Halifax county and, lately, in the tungsten concentrates of the Moose River mines. So far, all occurrences are in quartz veins in the lower quartzite and slate formation of the gold-bearing series of the Atlantic coast. The platiniferous mineral is supposed to be sperrylite, with which is associated arsenopyrite.

Ontario.—Sudbury is one of the few places where platinum is profitably extracted from deposits in situ. The metal, which was first discovered in this region in 1889, is found mostly in combination with arsenic, as sperrylite associated mainly with chalcopyrite in the well-known copper and nickel-bearing deposits of the district.

The origin of the ore bodies has not yet been settled. They are either marginal deposits in, or off-shoot deposits to, a norite laceolith, which has intruded sedimentary rocks, the ores consisting principally of chalcopyrite, pyrrhotite, and pentlandite. Metallic platinum, gold, silver and palladium occur in the ore, the last also, probably, as an arsenide. The highest platinum content is associated with the highest copper content; the highest palladium with the highest nickel. According to Roberts and Longyear^[36] the mean analysis of rocks of from sixteen drill holes gave an average ore content of: copper, 1·11 per cent.; nickel, 1·95 per cent.; silver, 0·223 oz.; gold, 0·022 oz.; and metallic platinum, 0·0068 oz. per ton. The ore is principally worked for its nickel and copper content, and yields a large proportion of the world’s supply of nickel. The ore is first smelted at the mines, and a portion of the low-grade matte so produced is then shipped to South Wales for final treatment, the remainder being sent to the recently-constructed refinery of the International Nickel Co., at Port 25Colborne, Ontario, and to the United States. It was stated in 1903 that this matte contained on the average 1·25 oz. of the platinum metals per ton of nickel content of the matte, of which about 80 per cent. was extracted^[37] p. 10. The Victoria Mine, owned by the Mond Nickel Co., is stated to carry a high percentage of the precious metals, as is also the Vermilion Mine, although in the latter case the ore body is very small. In 1917 the total output of copper-nickel ore from these deposits amounted to 1,506,828 tons, of which the Canadian Copper Co. raised 1,139,629 tons, the Mond Nickel Co. 361,335 tons, and the Alexo Mining Co. 5,864 tons. The nickel content of the ore of the Canadian Copper Co. was about 2·5 times that of the copper, whilst the ore mined by the other two companies contained the two metals in approximately equal proportions. The matte produced by the Alexo Mining Co. is smelted by the Mond Nickel Co. According to the report of the Royal Ontario Nickel Commission, the matte produced by the Canadian Copper Co. in 1916 was estimated to contain 4,640 oz. platinum and 8,460 oz. palladium, corresponding to 0·10 oz. platinum and 0·15 oz. palladium per ton of matte, the International Nickel Co. recovering in that year 1,093 oz. platinum and 257 oz. allied metals. This company is now reported to have improved its methods of recovery. In 1918 the total matte shipment by the Canadian Copper Co. is stated to have contained, among other precious metals, 8,677 oz. platinum and 13,016 oz. palladium^[38].

According to information supplied by the Mond Nickel Co., their nickel residues derived from the refining of the matte are taken over by Johnson, Matthey & Co., Ltd. During the years 1915–18 the residues disposed of were estimated to contain the following amounts of platinum metals:

26Messrs. Johnson, Matthey & Co., Ltd., have kindly supplied the following figures of platinum-extraction from these residues:

The British America Nickel Corporation, who are developing some large deposits in the same district, are also erecting a refinery near Hull on the Ottawa River. It is stated that they will employ the Hybinette process of electrolytic refining, and expect to obtain a high recovery of the precious metals^[29] p. 425.

With gradual improvements in the refining process, and with the refining of the whole of the matte produced, instead of a portion only, as at present, it seems probable that the production of platinum metals by the three nickel companies may in time exceed 10,000 oz. per annum.

The 1919 report of the Ontario Bureau of Mines shows that in 1918 the International Nickel Co. treated 62,250 tons of matte for 650 fine oz. of platinum, 787 oz. of palladium, and 473 oz. of metals of the rhodium group. This cannot be used as a basis of calculation, as the proportions are not constant.

On the Quinn claims, near the Crœsus Mine, Munro Township, is auriferous quartz containing platinum. Five assays gave a platinum content of value ranging from $180 to $1,800 per ton (with platinum at from $40 to $50 per oz.)^[31]. The Abro Mine in the Timiskaming district in 1915 shipped between 5,000 and 6,000 tons of ore, containing 0·03 oz. of palladium and platinum per ton. The ore consists of pyrrhotite, chalcopyrite and pentlandite, in a gangue of altered peridotite and serpentine^[7].

Yukon Territory.—Platinum occurs associated with gold in small quantities in most of the tributaries of the Yukon River, notably at the mouth of the Hootalinqua River, and in the River Lewis^[37] p. 12.

Chromite derived from the serpentinized area in the region of Mount Cormack, situated in the central part of the island, has been found to contain small quantities of platinum^[39].

The most important occurrences of platinum in the Commonwealth are at Fifield and at Platina, in New South Wales.

The outputs of crude platinum in Australia in recent years were all exported to the United Kingdom as under:

Note.—These figures do not include the osmiridium produced in Tasmania.

Recent imports of manufactured platinum were as under:

The question of the refining of platinum in Australia has been under consideration for some time; so far the crude material has all been sent to England. The outlook for future production of crude platinum in Australia is not promising, with the exception of that of Bald Hill district, Tasmania.

New South Wales.—Platinum is obtained at Platina, in the Fifield division, in the east central part of the State, from a buried gravel channel, in which it occurs in association with gold and osmiridium. The rocks in the vicinity of the “leads” consist chiefly of slates, but the source of the platinum is not known^[4] p. 557. These deposits were first exploited in 1894, and from that year to 1918 inclusive, the total output of platinum from New South Wales was 14,680 oz.^[40]. The gravels have yielded amounts of 6 dwt. platinum and 2 dwt. 28gold per ton, but according to Government reports the richer deposits are nearly worked out; mining operations are carried on with great difficulty, as there is a great scarcity of water and a deep overburden, varying from 20 to 80 ft. in depth. It is estimated that there are 200 acres of platinum-country available, sufficiently rich to pay, were it worked on a large scale with an abundant supply of water^[41].

A new occurrence has recently been discovered about 1 mile distant from the old Platina deep “lead,” the platinum being associated with small quantities of gold. The “lead” has so far been proved to extend over an area about 1 mile in length, and from 60 to 150 ft. in width, the wash varying in depth from a few feet to up to about 80 ft. The pay gravels, which rest on shales and sandstones of Silurian and Devonian age, intruded by dioritic dykes, are stated to be from 1 to 3 ft. thick. The following analysis is representative of the crude platinum produced:

Platinum is frequently found in beach sand deposits on the coastal border between Queensland and New South Wales, notably at Ballina, close to the mouth of the Richmond River; at Evans Head, further south; and at Currumbin, near the mouth of the Tweed River. In this locality black sands containing platinum, associated with gold, cassiterite, monazite and osmiridium, accumulate on the beaches during stormy weather. At Ballina and Evans Head, the platinum predominates over the gold, but at Currumbin, further south, the gold is in the greater quantity^[4] p. 557. The minerals are present in a very finely-divided state, and separation of the valuable metals is a matter of considerable difficulty. The problem does not appear to have been satisfactorily solved up to the present time, although promising experiments have recently been carried out with screening and magnetic treatment. The deposits are, unfortunately, very low grade.

29The sources of the metals are uncertain. The platinum and osmiridium appear to have been derived from the western edge of the Clarence coal measures, which now exist only as fragmentary outcrops. The gold, tin and monazite may have their origin in granite and other rocks of the New England tableland. Chromite is present in some of the Currumbin sands, which suggests serpentine as the probable source of platinum^[4] p. 557. Other associations are zircon, garnet, tourmaline, ilmenite, magnetite and sapphire.

In the Broken Hill district, principally at Little Darling and Mulga Springs Creek, platinum has been proved to extend over a considerable area in a copper-nickel gossan, closely associated with gabbro, decomposed gneisses and schists. In addition to platinum, the amounts of which vary from a trace to 16 dwt. per ton, gold, silver, iridium and palladium are also present^[43]. The deposits bear some resemblance to the nickel deposits of Sudbury, Ontario, and it is thought that here, too, the platinum occurs combined with arsenic, as sperrylite.

Queensland.—In addition to the beach deposits between Southport and Currumbin, described above, platinum has been found in Coopooroo and Wairamba Creeks on the Russell Goldfield, near Innisfail; also in the Lucknow and Alma “reefs” of the Gympie Goldfield, where it is present in quartz lodes with native gold, and arsenopyrite, the accompanying rocks consisting of slates, alternating with volcanic tuffs and conglomerates; the metal also exists in the neighbouring gold-bearing alluvial deposits of Brickfield Gully.

Another occurrence of alluvial platinum is known at the head of the Don River in Central Queensland^[4] p. 556.

Victoria.—Platinum occurs in the Walhalla Copper Mine, where it is associated in a hornblende-diorite lode-formation with copper pyrites, gold and silver. The ore is stated to contain from 2 to 7 dwt. platinum per ton. In the Thompson River Copper Mine platinum is found in a hornblendic rock rich in chalcopyrite.

Tasmania.—Iridosmine has been produced from the Bald Hill district near Waratah, in the north-western part of the state, since 1900, the metal being obtained from placer deposits in Nineteen Mile Creek and its tributaries, Linger-and-Die, 30McGinty’s and Barren Creeks, and from Savage River. It has been located in situ in the rocks of Bald Hill, principally in serpentine, but also with chalcedony and opaline silica in lode-formations. In the former case, it is associated with magnetite, pyrite, pyrrhotite, nickel and gold. The iridosmine in the placer deposits is sometimes coated with iron oxide, and is also at times found enclosed in chromite. The following analysis in percentages, made at the Imperial Institute, is typical: osmium, 57·09; iridium, 33·80; platinum, 0·37; ruthenium, 8·19; palladium, 0·21; gold, 0·04; iron, 0·30; copper, trace.

Other localities in Tasmania at which osmiridium has been located are Heazlewood River, Whyte River, Castray River, Huskisson River, Wilson River and Boyes River; also the Badger gold diggings, west of Savage River, and the Salisbury goldfield near Beaconsfield.

The following table gives the recent annual output of osmiridium in Tasmania:

South Australia.—In the north-east part of the State traces of platinum have been recognized by analysis as occurring in the outcrop of a lode near Boolcoomatta. Further information on this occurrence is not available.

Papua.—Osmiridium, associated with small amounts of gold only, is known to occur as alluvial in the neighbourhoods of various serpentine areas; in the Lakekamu district, in flaky form; in the Yodda Valley, in appearance similar to native bismuth; and in other places in shot-like granules^[44].

Platinum is only obtained commercially in New Zealand from the Orepuki district of Southland, where it is produced 31by the Round Hill Gold Mining Company as a by-product in the washing of auriferous gravels. According to information recently supplied by the Mines Department, the annual output of crude platinum for the last ten years has averaged 30 oz., but in view of the recent falling-off of the gold production in this locality, the prospects of any increase in the output of platinum seem small.

In South Island the presence of platinum has been reported on the Thames River in quartz lodes, in a region of serpentine and diorite, and in a pyritic lode near the Taramakau River in the district of Westland, in close proximity to sheets of altered magnesian eruptive rocks^[4] p. 557. The platinum in the latter case occurs in association with silver, in the proportions of about 7 parts of the latter to 1 of the former, together with pyrite and limonite. Samples taken from the lode have been stated to have an average content of 3 dwt. 8 gr. platinum per ton^[45].

Other localities in South Island where platinum has been located are the Taraka and George Rivers, which flow into Awarua Bay; the east coast of Otago, in beach sands and river gravels; the Clutha River; and the Nelson gold district.

Concentrates containing up to 2·5 per oz. per ton are reported to have been obtained from the Parapara sub-division. Platinum in New Zealand is often associated with gold, and the deposits are in many cases similar to those of the Urals.