Three structural belts paralleling the north-northeast trend of the main Andes chain in northwest Argentina differ in age and character of igneous activity and in mineralization. In the gently folded ranges of the eastern belt, where Precambrian-Permian, Cretaceous, and Miocene-Recent formations are represented, there are no post-Cambrian granites, few basic intrusive or volcanic rocks, and only limited occurrences of metallic ores. The sedimentary section is less complete in the strongly folded and thrust-faulted cordilleras of the central belt; late granites (probably late Tertiary) are numerous, and associated vein and replacement deposits contain lead, zinc, silver, copper, and other metals. In the high block-faulted plateau of the western belt (the Puna region), iron and copper are associated with Precambrian granite masses, molybdenum, columbite-tantalite, and some bismuth with pegmatites of similar age, and gold, silver, antimony, tin, and lead with widespread Miocene-Quaternary volcanic rocks.

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