Abstract

Archean greenstone belts contain volcanic complexes characterized by gradation from early mafic effusives to late felsic pyroclastics and sedimentary rocks. The three complexes described have areas of about 500 sq mi and stratigraphic thicknesses of 20,000 to 40,000 feet, and appear to represent volcanic extrusive-intrusive piles, with a domical structure masked to different degrees by east-west faults and folds. Some 79 percent of all base-metal and gold deposits, 87 percent of producers, are located within areas of volcanic complexes, and main occurrences are in or close to upper stratigraphic divisions. Metal concentrations are viewed as products of the later stages of igneous activity that gave rise to complexes.

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