54 



THE PROSPECTOR'S HANDBOOK. 



TELLUBIDES IN GOLD ORES. 



The tellu rides have usually a light grey colour, though 

 some are dark grey and some have a slightly yellowish 

 tint, are usually brittle (though one is sectile), and some- 

 times scaly, or film-like; and all have a metallic appearance. 

 The specific gravity of the most valuable is high, viz. : 

 7 to 10. Most can be scratched by the nail, and all by a 

 copper coin. 



Before the blowpipe, a brilliant greenish-blue luminosity 

 is distinctly seen near the test-piece. When boiled in sul- 

 phuric acid, a telluride imparts a pinkish colour to the 

 liquid, which becomes greyish if water be added afterwards. 

 A telluride can usually be soon fused to a globule. 



Native Gold. 



Found as grains ; laminae, sometimes threadlike ; nuggets, 

 etc. There is always a small 

 amount of silver in the gold 



FIG. 37. SECTION SHOWING THE TWO CONDITIONS UNDER WHICH GOLD is 



USUALLY FOUND. 



1, Granitic and gneissic rocks, often containing gold finely") Traversed by quartz 

 disseminated. 2, Micaceous, taloose, and argillaceous ? veins containing 

 slaty rocks, Laurentian and Cambrian. ) gold. 



3, Silurian and Devonian strata. 4. Carboniferous limestone and grits. 5, 

 Coal measures. 6, Permian and newer rocks. 7, 7, 7, 7, Drift filling hollows 

 in rocks, with gold, especially at the base of the dxift. 



(sometimes, as in California, nearly 10 per cent.), and fre- 

 quently other metals. 



Colour yellow. 



H. 2-5 to 3; S.G. 12 to 20. 



With carbonate of soda or charcoal before B.F. it yields 

 a yellow bead, easily hammered out or cut. If the pow- 

 dered ore be dissolved in aqua regia (4 parts hydrochloric 

 and 1 part nitric acid), a purple precipitate will be formed, 



