N. Including manufactured platinum.
N. Including manufactured platinum.
In 1917, 38,831 oz. of refined platinum metals, of which 7,384 oz. is believed to have been of domestic origin, were recovered from alloy with other metals, and 72,186 oz. were obtained from the refining of scrap metal, and sweepings. The shortage was also to some extent relieved by the receipt from Russia early in 1918 of a special consignment of 20,922 oz. of crude platinum, which had been collected in 1917 by the Russian-English Bank, and which was taken out of Russia by F. W. Draper and delivered to the United States Government. It yielded 17,640 oz. platinum, 64·75 oz. palladium, 182·11 oz. iridium and 48·56 oz. of rhodium, a total of 85·725 per cent. of platinum metals, slightly above the usual 83 per cent.[65].
Alaska.—The first production of platinum in Alaska was in 1916, in which year about 12 oz. were shipped to the United States. In 1917 the output rose to 81 oz., of which 66 oz. were obtained from the Seward Peninsula and 15 oz. from the Copper River country.
In 1918 an increased output of 135 oz. was partly obtained from alluvial deposits and partly as a by-product in the treatment of copper ore of the Salt Chuck mine, Ketchikan[66].
This mine is a palladium-copper mine containing mainly bornite with a little chalcopyrite, and the alteration products covellite and chalcocite, the metals present being, besides copper and palladium, gold, silver and platinum. The ratio of palladium to platinum averages 50 to 1. The concentrates produced, representing about 3½ per cent. of the weight of the ore, contain: copper, 40 per cent.; gold, 1·2 oz.; silver, 5·3 oz.; and platinum metals, 3·15 oz. per ton[67].
In the Seward Peninsula the larger portion is derived from placer deposits in Dyme Creek, Koyuk district, where the gravels are primarily worked for gold, 1 oz. platinum being obtained for every $5,000 worth of gold. In 1918, 56 oz. were recovered. Bear Creek and Sweepstake Creek have also supplied small quantities of platinum, and a little is derived from placers on Boob Creek, in the Tolstoi district[50]p. 19.
A possible source of platinum appears to lie in the neighbourhood of the Red Mountain, on the Kenai Peninsula. The mountain is composed of fine-grained dunite, in which abundantchromite occurs. Up to 1917 no placer mining had been attempted in this locality[68].
In the Goodro Mine, at the head of Kasaan Bay, Prince of Wales Island, were found in 1918 both platinum and palladium, the latter in greater amount, and carried in bornite and chalcopyrite; some chalcocite and covellite are present also in the ore. The copper minerals are disseminated through pyroxenite, and the country rock consists of limestones, slates and other sedimentaries. The platinum content is small, but regular, whilst the amount of palladium present is proportional to the amount of copper, there being about 1 oz. of palladium to every 8 to 12 per cent. (units) of copper[69].
A Bill has been introduced into Congress providing for the incorporation of the United States Platinum Corporation, with capital stock of $30,000,000, the object of which is to secure a concession from the Government of land areas in Alaska containing platinum sands, and to pay for such privilege, as a royalty or subsidy, one-eighth of the net profits obtained from the working of the concession[70].
California and Oregon.—Platinum has been proved to exist over a wide area in placer deposits associated with gold, but the proportion of the platinum metals to the gold is usually small. Platinum is obtained from sands in streams rising in the belt of serpentine rocks in central California, and from the serpentine areas in the Siskiyou and Trinity counties in the north-west of the State, which continue north-east into Curry, Josephine and Jackson counties in south-western Oregon[52]p. 300. The sources of the platinum obtained along the foot-hills of the Sierra Nevada were old stream channels on the western slopes of the mountains, which are now buried beneath lava several hundred feet deep. These “deep leads” are also mined by drifting for their gold and platinum contents, and in a few cases a fair amount of the metals is extracted from them. Some platinum is obtained by hydraulic mining, but this is carried on with difficulty, owing to the prevailing scarcity of water[50]p. 18.
Platinum occurs in black sands found on the Pacific coast in the counties of Coos, Curry and Josephine, Oregon and Del Norte, California. Formerly these beach deposits were richin platinum, but at the present small quantities only are obtainable after stormy weather. This area has recently been examined by the United States Bureau of Mines, but the results were disappointing.
In California most of the output of platinum is produced by dredging for gold in the Butte, Calaveras and Stanislaus counties[50]p. 19. In Trinity county mining is in progress on the Trinity River, about 4 miles below Junction City, by the Valdos Dredging Co. The output from this source for sixteen months in 1916–17 was stated to be 1,950 gm. Platinum, with gold and osmiridium, is also obtained on the Yuba River, about 12 miles east of Marysville in Yuba county, by the Yuba Consolidated Goldfields[10]p. 540. Some alluvial platinum has been recovered at the Bean Hill Gold Mine, situated 12 miles south-east of Placerville, and this locality is at present under investigation[71]. Californian metal contains from 25 to 45 per cent. iridium. Its origin is believed to be the serpentine- and olivine-bearing rocks of the Sierra Nevada and other ranges.
In Oregon, in addition to the platinum obtained from the beach deposits near Bullards and Marshfield[50]p. 20, it occurs in placer deposits, rich in chromite, in south-west Oregon, the principal output being derived from the Waldo district.
Platinum also exists in small quantities in streams in the neighbourhood of the Blue Mountains, eastern Oregon, where the Powder River Gold Dredging Co., in Sumpter district, produces on a small scale. Other platiniferous localities in eastern Oregon are the Granite and Canyon districts, and Spanish Gulch in Wheeler county[10]p. 541.
Colorado.—Platinum is known to exist in the black sands from Clear Creek. Its presence has also been reported in the gold gravels of the Iron Hill placer at Como, where it occurs mechanically combined with magnetite. Another occurrence recently discovered is in a vein worked by the Rollcall Mining Co., near Villa Grove. An assay of material from this vein, taken at a depth of 1,500 ft., showed the following values: gold, 3·2 oz.; platinum, 5·09 oz.; silver, 3·05 oz.; and copper, 3·5 per cent.[9]p. 592.
Nevada.—In 1909 the occurrence of platinum in Clark county was noticed by the United States Geological Survey to be in association with copper, nickel and cobalt ores from the Key West and Great Eastern Mines, near Bunkerville. The ore bodies are contained in pegmatites and basic intrusions, which carry pyrrhotite and chalcopyrite, the platinum content in the ore averaging about 0·2 oz. per ton[72].
In 1914 platinum, with palladium, was discovered at the Boss Gold Mine, situated 10 miles west of Goodsprings, in Clark county. The mine was originally worked for copper, and later for its copper and gold contents. The country rock consists of limestone of middle Carboniferous age, intruded by sills of quartz monzonite porphyry, the ore bodies occurring in a fault zone in the limestone. The copper ores comprise mainly chrysocolla and malachite, and contain traces only of platinum. The gold ore occurs in a fine-grained siliceous matrix, containing a bismuth-bearing variety ofplumbo-jarosite(a hydrous sulphate of iron and lead). The rare metals are present in the free state, being apparently alloys of gold, platinum and palladium[73].
In 1919 the Boss Mine shipped $22,365 worth of platinum-bearing ore[74]. A plant of 300 tons monthly capacity has recently been erected at Los Angeles, California, for the treatment of its complex ores, which average 7 per cent. of copper, 4 per cent. bismuth, and 1·0 oz. of platinum and palladium, 0·75 oz. of gold, and 3 oz. of silver per ton. The pulp from ore pulverized to 80 mesh is agitated with sulphuric acid (2 per cent.). The acid solution contains the copper and about 20 per cent. of the platinum. The copper is precipitated as cement copper, together with the platinum, by means of scrap-iron. The remainder of the platinum, together with the gold and silver, is first leached with, and then precipitated from, a neutral solution of calcium chloride. The inventors of the process claim that approximately 92 per cent. of the copper, 96 per cent. of the platinum metals, gold and silver, and over 90 per cent. of the bismuth are recovered by this process[75].
Metals of the platinum group have recently been shown to exist in small quantities in the ore of the Oro Amigo Mine,situated between 1 and 2 miles north-east of the Boss Mine. This ore differs from that of the Boss Mine, in that bismuth and plumbo-jarosite are absent. According to H. K. Riddell, the platinum metals content averages from a trace to 0·1 oz. per ton of ore.
North Carolina.—At Mason Mountain, in Mason county, platinum occurs associated with rhodonite, garnet, biotite and iron sulphides in metamorphic deposits.
New York.—It was reported a few years ago that platinum existed in large quantities in alluvial sands of the Adirondack region. J. M. Clarke, the New York State Geologist, examined the occurrence in 1917, and found that platinum was present in traces only, the deposits being of no economic importance[10]p. 541.
Pennsylvania.—At Lancaster county platinum is associated with pyrite, chalcopyrite and galena in mica-schist, and also at Boyertown in black Triassic shale.
Washington.—The production of platinum on a small scale has been reported from beach deposits at the mouth of the south fork of the Lewis River near Yacolt, and also on beaches southward from the Straits of Juan de Fuca[10]p. 542. The metal has also been located at various places in the Cascade Mountains in the central part of the State.
Wyoming.—Palladium and platinum, in the proportion of 3 to 1, are obtained at the Rambler Mine, in Albany county, the metals occurring as sperrylite in copper ore, contained in the kaolinized portion of a dunite dyke, intrusive into granite gneiss. The ore consists of covellite, chalcocite, chalcopyrite and tetrahedrite, with nickel and gold[76]. It is stated that the platinum and palladium contents vary directly with the percentage of copper present, a typical assay giving the following values: copper, 5 per cent.; gold, 0·02 oz.; silver, 1 oz.; palladium, 0·4 oz.; and platinum, 0·6 oz. per ton[77].
Utah.—Platinum and gold in very fine particles occur in the Green River, east of Vernal; also in the Colorado River, near Hite, below the mouth of the Green River. Attempts to mine these deposits have so far proved unsuccessful, due largely to the inaccessibility of the region, as well as the finely-divided condition of the platinum[42]p. 11.
SOUTH AMERICA
José Vieira do Couto, in 1801, first pointed out that platinum occurs in the sands of the Lages River, near Conceiçao, Minas Geraes. According to E. Hussak[78], platinum in that region occurs only in the alluvium of rivers having their rise on the eastern slope of the Serra do Espinhaço. The platinum is accompanied by black pebbles of quartz-tourmaline rocks, magnetite, hematite, rutile, octahedrite, xenotime, monazite, senaite, pseudomorphs of rutile after octahedrite (captivos), zircon and gold, which is sometimes of a copper-red colour (palladium-gold). Palladic gold was formerly calledouro branco(white gold), by the miners.
At Condado, further north on the eastern slope of the same Serra, platinum also occurs with very similar associations. The platinum from both localities occurs in bunchy, mammillated and globular forms, concave within, with thin walls, having a radiated fibrous structure under the microscope. It is frequently in thin foliated crusts, having the characteristic structure of hematite. It was accurately described by Wollaston in 1805 and 1809. Hussak thinks the primary formation was an olivine rock, or gabbro, while the platinum is secondary, having been most probably re-deposited from solutions resulting from the decomposition of platiniferous pyrites or of sperrylite (PtAs2), minerals derived, possibly, from the neighbouring schistose quartzite, or from the overlying conglomeratic quartzite.
The platinum of Condado, although comparable, as regards density, to the Russian platinum, is very rich in palladium, is non-magnetic and contains practically no iron. An analysis by G. Florence gave the following percentages: insoluble residue, 0·92; platinum, 73·99; iridium, 0·08; palladium, 21·77; iron, 0·10 (= 96·86), undetermined (rhodium and osmium), 3·14.
In the Rio Abaeté, Minas Geraes, platinum—very different in appearance and chemical composition from that of the Serra do Espinhaço—occurs in placer deposits, associated with gold, diamonds and the following minerals: rolled pieces of ahydro-phosphate of barium and aluminium (gorceixite= “marumbé” of miners), garnet, almandite, pyrope, ashy-blue oxide of titanium (bagageira—regarded as a good indicator for diamonds), magnetite, chromite and calcium-titanate (perovskite). Pyroxene-olivine rock, a typical picrite-porphyry, rich in perovskite, and granular magnetite rocks, rich in titanium, have been observed by Oliveira in the vicinity. Hence it is highly probable that the platinum, as in the Urals, came from olivine rocks. The platinum occurs in thin laminæ, strongly rolled, and, rarely, in cubical crystals with the edges visibly rounded. It is strongly magnetic and contains no palladium. Minute crystals of osmiridium may occur with those of platinum, and in the platinum particles are found regular inclusions of osmiridium, as at Nizhne Turinsk, in the Urals, the platinum of which locality it resembles in chemical composition, magnetic properties and crystalline structure. The following analysis shows the percentage and composition of a general sample: insoluble residue, 7·57; iron, 9·62; palladium, trace; copper, trace; platinum metals, 82·81.
The auriferous alluvial of the Cuyabá and Coxim rivers in the southern part of the State of Matto-Grosso, also contain some platinum. According to Luiz Caetano Ferraz[79], platinum occurs in the River Coxipó-Mirim, where golddredging is carried on, combined with palladium, iron, osmium and iridium in small spherical grains, flattened on one side, of a brilliant white colour and strongly magnetic. It is found in alluvial deposits, associated with various kinds of quartz and oxides of iron, marcasite, arsenopyrite, rutile, anatase, almandine, garnet, black tourmaline, monazite, staurolite, white topaz, sphene, cassiterite, wolfram, graphite, galena and native silver.
In the State of Bahia, platinum has been found in Ituassú, Feira de S. Anna and Serra do Assuruá, and it is said to occur at Sâo Bartholomeu, and in the Serras do Pitango and Macahubes[80].
Platinum also occurs in Brazil as rare disseminations in the gold-bearingjacutinga, intercalated in the itabirites (e.g. at Gongo Socco Mine, long since abandoned). The jacutinga occurs as narrow bands and nuclei in the itabirites, containinga high percentage of gold, with much talc, clay and pulverulent pyrolusite. As accessory minerals zircon, rutile, cassiterite and tourmaline occur. Hussak thinks that the gold-bearing jacutinga has been derived from altered pegmatite veins.
From analyses made by Johnson (1833–41) on the Gongo Socco bullion, it would appear that the percentages of silver and platinum decreased while those of copper and palladium increased with depth (Henwood). The percentages of palladium varied from 3·89 to 4·80, and that of platinum from 0·04 to 0·12.
At Candonga, gold occurs in an eruptive rock rich in magnetite enclosed in itabirite, and is probably of contact-metamorphic origin. The gold occurs in grains of high standard, and with it are found fine indented scales of palladic gold, of a bright copper-red colour.
At Itabira do Matto Dentro gold occurs in jacutinga, lying between a micaceous iron schist, rich in quartz, and an enormous solid bed of itabirite. The palladium-gold may be copper-red, dark-brown or silver-white in colour. Native platinum also occurs with the gold.
Grains of platinum have also been found in the most northerly of the auriferous lenticular masses, which occur near the Bruscus River, near Pernambuco, in Cambrian crystalline schists. The matrix is a coarse white quartz containing small quantities of the arsenides and sulphides of iron, and the sulphides of copper, lead and zinc.
Platinum, although widely distributed in Brazil, occurs in such small quantities that so far there has been no production; but in the near future richer and more extensive deposits may be discovered, or it may be found practicable to win the metal from those already known, as an important by-product.
Palladium-gold, orporpezite, is a natural alloy of palladium and gold, and may contain up to 10 per cent. of the former metal. It is found in Brazil, in gold-washings, and also in the gold-bearing jacutinga reefs at Gongo Socco, Candonga and Itabira do Matto Dentro. In 1870 Henwood showed that the palladic gold from Gongo Socco contained, to a moderate depth from surface, from 0·04 to 0·12 per cent. of platinum. (Palladium-gold has also been reported from gold-washingsin the Caucasus, near Batoum.) Ruer concludes, from an examination of the freezing-point curves of artificial alloys of gold and palladium, that these alloys form a continuous series of mixed crystals, and that there is no indication of chemical combinations[81].
This republic is the second largest producer of platinum in the world, and in pre-war years supplied about 5 per cent. of the world’s total output. Owing to the decline of the Russian supply, and the increased demand for the metal, the industry has in recent years received a considerable stimulus, and in 1916 Colombia’s production rose to approximately one-third of the Russian output.
Platinum was first introduced into Europe from Colombia in 1735, although the metal was known in America for some time previously[48]p. 608. In 1810 the value of platinum stood at $5 to $6 (U.S.) per oz., and in 1823 the price had further dropped to from $3 to $4 per oz. As a result, platinum was rejected as waste in the operation of refining gold by the “dry-blowing” system. Later, when platinum became valuable, much of this dumped metal was recovered, notably in Quibdo, the capital of the Chocó district, where much gold-refining was carried on.
The following table gives the outputs of crude platinum from Colombia, in recent years, principally produced in the Chocó district:
The larger portion of the production is shipped to the United States, the exports to that country for the years 1910–18 being as follows:
The crude platinum is estimated at 84 to 85 per cent. fine. The price in 1917 fluctuated from £16 to £20 10s.per oz., the average for the year being nearer the latter amount.
During 1918 the United States Government fixed the price at $105 per oz., which stimulated production.
The deposits are alluvial, and consist of re-concentrates of older gravels. The principal source of supply is at the head of the San Juan River, which enters the Pacific Ocean north of Buenaventura, the richest deposits occurring in the Condoto, Opagado and Tamanal Rivers, tributaries of the San Juan[82]. Platinum is also obtained in the Upper Atrato River, which flows northward to the Caribbean Sea. It is nearly always found associated with gold. In the gravels of the San Juan River the two metals are present in about equal proportions, and in those of the Atrato the ratio is approximately 85 of gold to 15 of platinum.
The area including the watersheds of the San Juan and Upper Atrato Rivers is known as the Chocó district. T. Ospina, Director of the Colombian School of Mines[83], estimates that in the area are 5,000 sq. miles of gold and platinum deposits, the Mira River forming the southern boundary of the area. In 1916 he estimated that there were in it 68,000,000 c. yd. of actually profitable gravel, with a reserve of 336,000,000 yd. of possibly profitable ground. Platinum has also been recovered in much smaller amounts on the Micay River in the Barbacoas district, near the frontier of Ecuador. The stream beds in which platinum occurs are those in which Tertiary conglomerates have become eroded; the river gravels about the areas underlain by that formation are barren. The conglomerates are composed of rounded boulders of basic rocks, such as diabase, melaphyre, peridotite and dunite[48]p. 620.
At Novita Vieja, in the centre of the Chocó district, a bed of conglomerate 6 to 12 ft. thick has been laid bare, over an area 2½ miles long and ½ mile wide, through the sluicing away of the overlying sands. It contains 0·5 oz. of gold, and 0·5 oz. of platinum, per ton[84]. According to Castillo, the parent rock is a typical gabbro, pyroxene predominating over the felspar[85]p. 826.
Platinum has been found in the Chocó district in serpentine rock. Granite also occurs in the same district, traversed by quartz lodes containing palladium, iridium, osmium and rhodium.
Colombian crude platinum contains from 80 to 85 per cent. platinum, the remaining 15 to 20 per cent. consisting chiefly of iridium and osmium. The sands in which it occurs are described as brown in colour, and carrying, besides platinum and gold, the heavy minerals chromite, magnetite and ilmenite[85]p. 384.
In the past, mining operations have been very irregularly carried on, by primitive methods of working, but dredges are now being employed in increasing numbers. In 1915 a dredge was operated on the Condoto River, in the province of Chocó, by the Anglo-Colombian Development Company, and showed good results. Native methods of working are very simple. The alluvial gravels derived from dried-up beds of ancient rivers are hand-washed with the use of thebateaor dish. Where the metal occurs in the bed of a river it is obtained by diving girls, who work down to the platiniferous gravels, removing the gravel in small dishes, the men being employed in washing the gravels on the river banks[86]. About 90 per cent. of the total output is recovered by these primitive methods.
A large portion of the industry is in the hands of two companies, one of which is the South American Gold and Platinum Company, of New York, a Lewisohn company, which has absorbed the interests of the above-mentioned Anglo-Colombian Development Company, Ltd., the Gold Fields American Development Company, Ltd., and Johnson, Matthey & Co., Ltd., of London. The second company—the British Platinum and Gold Corporation, Ltd.—has recently amalgamated with the Paris (Transvaal) Gold Mines, Ltd., taking in the latter’s interests on the Opogodo and other places.
The question of transporting platinum concentrate to the coast is not a matter of much difficulty, as the Atrato River is navigable as far as Quibdo, and the San Juan can be ascended by vessels of moderate draught for over 140 miles inland.
An estimate of average working costs appears to be 6d.perc. yd. for dredging, and 3d.for hydraulicking[87]. In 1917 new platiniferous deposits were discovered in the Caceres district, between the Cauca and Nechi Rivers, in the department of Antioquia. The mineralized area extends along the Caceri River, a distance of 14¼ miles, the width at the north end being 1¼ miles, and 300 ft. at the southern extremity[10]p. 545.
Platinum occurs, in association with the gold obtained from steam gravels, in the area covered by the Rivers Bogota, Cachabi, Uimbi, Santiago and Cayapas, but it has not so far been found in sufficient quantities to be of economic importance.
Dredging has been employed in mining these deposits, but does not appear to have been a success, and operations are now largely confined to native washings[88].
Platiniferous gold-bearing sands are found in the Aporuague River, the metal, according to an analysis by A. Danmer, having the following composition in percentages: platinum, 41·96; gold, 18·18; silver, 18·39; copper, 20·56[89].