ORES OF COPPER 83 
formed at high temperatures as they are associated with 
many basic dykes, some of which are earlier and others later 
than the lodes. The lodes in 1000 had been worked to the 
depth of over 2000 feet, and the ore contained an average 
of -8 per cent. of copper, gold worth about £2 10s. per ton of 
ore, and some nickel. The ores are clearly of hydrothermal 
origin, and support the same formation of the nickel ores 
of Sudbury (cf. pp. 114-18). 
The copper mines which saved South Australia at a critical 
stage of its early history derived their copper from a pneu- 
matolytic source. The rich oxidized ores at Burra-burra, 
which yielded 22 per cent. of copper, were discovered in 
1845, and are in altered slate and limestone. The primary 
F16. 28.—THE BrapeEn Copper MINE, CHILE. 
One stage in the development of the Braden Copper Mine, Chile. V, 
the volcanic rocks forming the country; AP, intrusive andesite- 
porphyry; BT, Braden tuffs filling the explosion crater; B, the 
intrusive breccia invading both the porphyry and the tufis. 
re was discovered at Moonta in 1861, and is a pegmatitic 
formation of quartz, microcline, tourmaline, apatite, and 
fAuorite. Five lodes occur in quartz-porphyry, which at 
Moonta has been intruded by pre-Cambrian granite; the 
lodes contain 2 to 5 per cent. of copper in chalcopyrite, 
and were covered by an oxidized zone containing copper 
carbonates, atacamite (oxychloride of copper), and native 
“opper. The Moonta Mine was once the deepest copper 
Mine in the world and has been worked to 2600 feet. 
The Braden Mine, Chile (Lindgren and Bastin, Econ. 
Geol, xvii, 1922, pp. 75-99), illustrates the relations of the 
Pheumatolytic to other copper ores (Fig. 28). It is in the 
Western Cordillera about 100 miles S.E. of Valparaiso. The 
Mine is in an extinct volcano in Kainozoic tuffs and lavas,