Abstract

The structural relations, rock alteration and sulphide mineralization of the Chuquicamata Mine are described in detail. Attention is directed to the zonal arrangement of the different types of alteration and of the sulphide mineralization.The mineralization is associated with strong N-S fissures and several N 10 degrees E shear zones. Several systems of tension fractures are found between these shear zones.The host rock has the mineralogical characteristics and the chemical composition of a granodiorite. Five different types of alteration phases of this rock have been mapped. The following wallrock alteration processes have been recognized beginning with the fresh granodiorite in the eastern part of the orebody to the siliceous zone in the western part.Enargite is the predominating primary sulphide of copper. Bornite and chalcopyrite are always present but in minute quantities. Tennantite and tetrahedrite are found in specimens from veins near the pit.Molybdenum as molybdenite occurs in the net of quartz veinlets near the highly silicified zone. The amount of molybdenum present is very small. Most of the source of molybdenum in present workings comes from the oxide minerals such as lindgrenite and molybdenum ochres. In the course of this study the writer found a new molybdenum ochre so far undescribed in the geologic literature.Within the orebody are bands of a fine grained rock of a texture and mineralogical composition similar to that of leuco-granite porphyry.

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