géologie de la mine de CHUQUICAMATA

chuquicamata est la plus grande mine à ciel ouvert au monde ,on exploite le cuivre et le molybdéne .
elle se situe au Nord de Chile dans le desert d'Atakama.

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Geology of the Chuquicamata Mine: A Progress Report  

GUILLERMO OSSANDÓN C.,

Abstract

Chuquicamata, in northern Chile, is the world’s greatest copper orebody. It was controlled, from the initial

intrusions (probably at 36–33 Ma) through mineralization (last major hydrothermal event at 31 Ma) to postmineral

brecciation and offset, by the West fault system. East porphyry, West porphyry, Banco porphyry, and

Fine Texture porphyry make up the Chuqui Porphyry Complex. East porphyry, the dominant host rock, has a

coarse, hypidiomorphic-granular texture. Intrusive contacts between most porphyries have not been found, but

early ductile deformation, subsequent pervasive cataclastic deformation, and faulting affects all of the rocks and

makes recognition of intrusive contacts very difficult.

Potassic alteration affects all porphyries, comprises partial K feldspar and albite replacement of plagioclase,

and more widespread biotite replacement of hornblende, with igneous texture largely preserved. It is accompanied

by granular quartz and quartz-K feldspar veinlets, which contain only trace disseminated chalcopyrite

± bornite remains from this early stage. Fine-grained quartz-K feldspar alteration, with destruction of biotite

and apparently following albitization of plagioclase, accompanies strongest cataclastic deformation and destruction

of igneous texture. A band of quartz-K feldspar alteration, up to 200 m wide and 1,500 m long, lies

along the southward extension of Banco porphyry dikes and is the locus of the bornite-digenite center of the

sulfide zoning pattern. This passes east through chalcopyrite-bornite to chalcopyrite-pyrite as sulfide abundance

fades out. Sulfides in quartz-K feldspar alteration are abundant only where there is intense crackle brecciation.

Propylitic alteration is superimposed on biotitic alteration at the eastern edge of the deposit, but there

is no pyritic fringe. Westward, this zoning is interrupted by the superposition of pyritic main-stage veins with

pervasive quartz-sericite. Veins of quartz-molybdenite, up to 5 m wide and cutting all porphyries, were emplaced

between the early and the main stages. These veins and early-stage quartz veins are commonly segmented

and sheared, with fine recrystallization of quartz that eliminates all original fluid inclusions. It is not

clear whether quartz-K feldspar alteration was formed later or earlier than quartz-molybdenite veins.