688 GOLD 



dissolved out with a strong brine, from which the silver is precipitated by zinc. The 

 silver cake obtained in this way is sold from prices varying from 6s. to 105. the ounce, 

 the additional sum, above 6s. Qd. the ounce for pure silver, being given for the gold 

 it contains. See PYBITES. 



Principal Gold Mines. 



Gold exists in the primitive strata, disseminated in small grains, spangles, and 

 crystals. Brazil affords a remarkable example of this species of gold mine. Beds of 

 granular quartz, or micaceous specular iron, in the Sierra of Cociies, 12 leagues beyond 

 Villa Rica, which form a portion of a mica-slate district, include a great quantity of 

 native gold in spangles, which in this ferruginous rock replace mica. 



The auriferous ores of Hungary and Transylvania, composed of tellurium, silver 

 pyrites, or sulphide of silver, and native gold, lie in masses or veins in a rock of 

 trachyte, or in a decomposed felspar subordinate to it. Such is the locality of the 

 gold ore of Konigsberg, of Telkebanya, between Eperies and Tokay in Hungary, and 

 probably that of the gold ores of Kapnick, Felsobanya, &c., in Transylvania; an 

 arrangement nearly the same with what occurs in Equatorial America. The auriferous 

 veins of Guanaxuato, of Real del Monte, of Villalpando, are similar to those of 

 Schemnitz in Hungary, as to magnitude, relative position, the nature of the ores they 

 include, and of the rocks they traverse. Breislak and Hacquet have described the 

 gold mines of Transylvania as situated in the crater of an ancient volcano. The 

 trachytes which, in some districts, form the principal portions of the rocks including 

 gold, are regarded as of igneous or volcanic origin. 



It would seem, however, that the primary source of the gold is not in these rocks, 

 but rather in the syenites and greenstone-porphyries, which in Hungary and Transyl- 

 vania are rich in great auriferous deposits ; for gold has never been found in the 

 trachyte of the Euganean mountains, of the mountains of the Vicentin, or those of 

 the Auvergne ; all of which are superposed upon granite rocks. 



If it be true that the ancients worked mines of gold in the island of Ischia, it 

 would be another example, and a very remarkable one, of the presence of this metal 

 in trachytes of an origin evidently volcanic. 



Gold, from whatever rocks derived, is common in the alluvial deposits near the 

 primitive rocks just described. It is found disseminated in the siliceous, argillaceous, 

 and ferruginous sands of certain plains and rivers, especially in their re-entering 

 angles, at the season of low water, and after storms and temporary floods. It has 

 been supposed that the gold found in the beds of rivers has been torn out by the waters 

 from the veins and primitive rocks, which they traverse. This opinion, suggested 

 at first by Delius, and supported by Deborn, Guettard, Robitant, Balbo, &c., appears to 

 be founded upon just observations : 1. The soil of these plains contains frequently, at 

 a certain depth, and in several spots, spangles of gold, separable by washing. 2. The 

 beds of the auriferous rivers and streamlets contain more gold after storms of rain 

 upon the plains than in any other circumstances. 3. It happens almost always that 

 gold is found among the sands of rivers only in a very circumscribed space. Thus it 

 is known that the Oreo contains no gold, except from Pont to its junction with the Po. 

 The Ticino affords gold only below the Lago Maggiore, and consequently far from the 

 primitive mountains, after traversing a lake, where its course is slackened, and into 

 which whatsoever is carried down from these mountains must have been deposited. 

 The Rhine gives more gold near Strasburg than near Basle, though the latter bo 

 much closer to the mountains. The sands of the Danube do not contain a grain of 

 gold, while this river runs in a mountainous region ; that is, from the frontiers of the 

 bishopric of Passau to Efferding ; but its sands become auriferous in the plains below. 

 The same thing is true of the Ems ; the sands of the upper portion of this river, as it 

 flows among the mountains of Styria, include no gold ; but from its entrance into the 

 plain at Steyer, till its embouchure in the Danube, its sands become auriferous, and 

 are even rich enough to bo washed with profit. 



The greater part of the auriferous sands in Europe, Asia, Africa, and America, are 

 black or red, and consequently ferruginous ; a remarkable circumstance in the geolo- 

 gical position of alluvial gold. M. Napiono supposes that the gold of these ferru- 

 ginous grounds is due to the decomposition of auriferous pyrites. The auriferous sand 

 occurring in Hungary almost always in the neighbourhood of the beds of tignitc, and 

 the petrified wood covered with gold grains, found buried at a depth of 65 3 f arcls in 

 clay, in the mine of Vb'rospatak near Abrabanya in Transylvania, might lead us to 

 presume that the epoch of the formation of the auriferous alluvia is not remote from 

 that of the lignites. The same association of gold ore and fossil wood occurs in South 

 America, at Moco. Near the village of Lloro have boon discovered, at a depth of 20 

 feet, large trunks of petrified trees, surrounded with fragments of trap rocks intor- 

 ppersed with spangles of gold and platinum, But tho alluvial uoil aflbrds likewise all 



