Editing Copper extraction (section)

===Late 20th century trends===
In the 1960s and 1970s large copper mining operations by U.S. companies [[Nationalization|were nationalized]] in many of the main copper producing countries.<ref name=valenz>{{Cite book |title=La Gran Minería en Chile |last=Valenzuela Rabí |first=Iván |publisher=Ocho Libros |year=2014 |isbn=978-956-335-192-7 |pages=135–152 |language=Spanish |trans-title=Large Scale Mining in Chile |chapter=El boom minero de los 90 |trans-chapter=The mining boom of the 90s}}</ref> Thus by the 1980s state owned enterprises overtook the dominant role U.S. companies like [[Anaconda Copper]] and [[Kennecott Utah Copper|Kennecott]] had had until then.<ref name=valenz/> In the late 1970s and early 1980s various oil companies like [[ARCO]], Exxon ([[Exxon Minerals]]) and [[Standard Oil Company]] expanded into copper mining for a few years before selling their copper assets.<ref name=valenz/> Reportedly gains were not as high as anticipated.<ref name=valenz/> Investments in copper mining concentrated in Chile in the 1980s and 1990s given that copper mining in other countries faced problems like political instability ([[Peru]]), increased environmental requirements (developed countries) or overall disinterest in foreign investment in a nationalized mining industry ([[Zaire]], [[Zambia]]).<ref name=valenz/>