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Porphyry copper deposits are copper orebodies which are associated with porphyritic intrusive rocks and the fluids that accompany them during the transition and cooling from magma to rock. Circulating surface water or underground fluids may interact with the plutonic fluids. Successive envelopes of hydrothermal alteration typically enclose a core of ore minerals disseminated in often stockwork-forming hairline fractures and veins. Porphyry orebodies typically contain between 0.4 and 1 % copper with smaller amounts of other metals such as molybdenum, silver and gold.
The first mining of low-grade copper porphyry deposits from large open pits coincided roughly with the introduction of steam shovels, the construction of railroads, and a surge in market demand near the start of the 20th century. Some mines exploit porphyry deposits that contain sufficient gold or molybdenum, but little or no copper.
Porphyry copper deposits are currently the largest source of copper ore. Most of the known porphyrys are concentrated in: western South and North America and Southeast Asia and Oceana - along the Pacific Ring of Fire; the Caribbean; southern central Europe and the area around eastern Turkey; scattered areas in China, the Mideast, Russia, and the CIS states; and eastern Australia.[1][2] Only a few are identified in Africa, in Namibia[3] and Zambia;[4] none are known in Antarctica. The greatest concentration of the largest copper porphyrys is in Chile. Almost all mines exploiting large porphyry deposits produce from open pits. |
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发表于 2011-11-21 01:49:35
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