CHAMBERS'S INFORMATION FOR THE PEOPLE. 



comparatively few countries where the mining of it is 

 found to be remunerative. In the British Islands 

 gold was worked rather extensively in the i6th 



century, at Leadhills, in Scotland, and towards 

 the end of the last century, in Wicklow, in Ireland. 

 Of late years it has been regularly worked in 

 North Wales, 20,000 oz. being obtained in 1862. 

 Hungary and Transylvania, whose mines have 

 been long famous, are the most productive of 

 European countries, yielding annually about 

 ,300,000 worth of the precious metal, but even 

 there it requires all the aid that the highest skill 

 in mining can furnish, as well as very cheap 

 labour, to yield profitable returns. 



The three most productive gold regions in the 

 world are those of the Russian empire, California, 

 and Australia. From the sand of streams in the 

 Ural Mountains, gold is believed to have been 

 obtained in ancient times, and during last century 

 much was obtained from the auriferous veins of 

 this range. These Ural sources, though still 

 worked, are small in their yield, compared with 

 those of Western and Eastern Siberia, where 

 various washings were opened up between 1829 

 and 1838, and for several years afterwards were 

 the most productive in the world. The greatest 

 supply of gold is now obtained from California, 

 where auriferous deposits were first discovered in 

 1848; but the gold-fields of Australia, discovered 

 only three years later, are nearly as productive, 

 and the two countries together now produce about 

 two-thirds of all the gold obtained. In the latter 

 country, as in most gold regions, the gold-bearing 

 veins are found inmetamorphic Silurian strata ; but 

 in California they happen to occur in a much later 

 formation namely, the Jurassic. It is, however, 



402 



* Fusible only by oxyhydrogen blow-pipe, 

 t Agglomerate, but do not melt in forge. 

 } Highest heat of forge. 



not in veins of solid rock, but in alluvial deposits, 

 where the greatest quantity of the precious metal 

 is found. The present annual yield of gold of 

 California and neighbouring states is variously 

 estimated at from 8 to 10 millions sterling; that of 

 Australia in 1871 was 7 millions; that of the 

 Russian empire, 3-i- millions ; and that of the South 

 American states, nearly 2 millions. Just before 

 the Californian discovery, the annual produce of 

 all countries did not exceed ^7,000,000 ; while for 

 the last ten years it has not, on an average, been 

 far short of .29,000,000. 



Whatever the nature of the rock inclosing 

 auriferous veins, the productive vein itself is almost 

 always quartz. The veins worked in California 

 yield for every ton of material from | to 5 oz. of 

 gold, but occasionally the quantity obtained is 

 much higher. In Victoria the average yield is i 

 ounce per ton, rising, however, in rare instances 

 to nearly 300 oz. per ton. Alluvial deposits or 

 drift contain gold which, in the long course of 

 ages, has been slowly washed out of solid veins, 

 and like the veins themselves, vary much in rich- 

 ness. In these there are what are called shallow 

 workings or ' placers,' and deep diggings ; the one 

 belonging to recent, the other to ancient river 

 systems. Gold is found most abundantly in the 

 ' gutter ' or bottom of the drift, which in Australia 

 is sometimes 400 feet thick ; and the auriferous; 

 portion, called the ' wash-dirt ' or ' pay-dirt,' may 

 vary from I foot to 12 feet thick. Where water is 

 scarce, as in Australia, such a deposit can only be 

 worked by skilful mining ; but in California, where 

 it is abundant, banks of this alluvial gravel are 

 worked by what is called ' hydraulic mining ; ' that 

 is, water under a pressure of from 50 to 200 feet in 

 perpendicular height, is conveyed by flexible pipes 

 to the face of the gravel, and by means of metal 

 nozzles directed against the bank with great force : 

 the gravelly mass rapidly disintegrates, and falls 

 down in large sections. In flowing away, the 

 water conveys the loosened gravel to a sluice, 

 where little raised pieces in its bottom catch the 

 gold as it falls. Banks of shingle 80 feet high 

 can be levelled at one operation by this process, 

 which is found to be by far the most profitable 

 kind of placer-working where water is plentiful. 

 The more simple and primitive methods of wash- 

 ing auriferous sand or gravel are by the pan and 

 the cradle. In either case the gold is separated 

 by agitating the mixed materials with water, so as 

 to allow it to collect at the bottom by reason of its 

 superior weight. 



Native gold is invariably alloyed with silver ; 

 that from Australia contains only from 3 to 8 per 

 cent. ; but sometimes the silver amounts to 40 per 

 cent, of the alloy. With all the processes in use 

 for the extraction of gold, either an alloy of it with 

 silver, or more rarely with copper, is first obtained. 

 Washing is the simplest method ; but when gold 

 exists in any gangue in a state of fine division, 

 or when, as with auriferous quartz, the whole is 

 stamped to a fine powder, the amalgamation pro- 

 cess is usually employed. This is conducted in 

 several ways, but the principle in all consists in 

 exposing the auriferous material as thoroughly as 

 possible to the mercury. The latter dissolves the 

 gold, and from the amalgam so formed the mer- 

 cury is afterwards separated by distillation in some 

 form of retort. Of late years, a concentrated solu- 

 tion of common salt saturated with chlorine gas has 



