Geology and Ore Deposits of Central Atacama Province, Chile
Geologically, the central part of Atacama Province straddles the north-striking intrusive contact between the Andean batholith of western Chile and the stratified rocks to the east. Apophyses of the Andean batholith and other intrusions, some of them in the form of sills, interrupt the continuity of the rocks to the east. The layered sequence consists of Lower Jurassic and Lower Cretaceous marine sedimentary rocks and lavas, which are unconformably overlain by Upper Cretaceous and Tertiary continental sedimentary rocks, tuffs, and lavas. A marked contact zone of skarn rocks and meta-andesite separates the diorite, granite, and related rocks of the batholith from the unmetamorphosed sedimentary and volcanic sequence. The sedimentary rocks have been folded into a major, north-northeast-trending, north-plunging anticlinorium in the middle of the area and into a doubly plunging synclinorium in the eastern part. Several small domes and a structural basin occur in the southwestern part. Minor overthrusts occur on the limbs of member folds of the anticlinorium and synclinorium. Most high-angle faults and other fractures strike north to northwest; some older faults strike northeast. The entire area is in the copper metallogenetic province of Ruiz and Ericksen (1962), and parts of it are in the overlapping gold, silver, and iron provinces. The zones of supergene enriched and oxidized rock in this area are related to deep weathering of an old surface which has existed since middle Tertiary time. At least seven of the 14 major types of hypogene ore deposits in Chile are represented in the central part of Atacama Province. However, most of the production of metals has been from supergene ores, with the important exceptions of iron ore from the contact metamorphic zone and hypogene copper ore from near the deep valley of the Rio Copiapo. The discovery localities of five rare supergene minerals—re-molinite, nantokite, copiapite, bordosite, and chanarcillite—are in the area.