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 pneumatolytic
 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 andesiteporphyry;
 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,