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Research about Chile

Source-linked reports with geographic coverage including Chile.

117 records · Page 7Linked to original sources
USGS1969

Water resources investigation program for Rio Aconcagua Valley, Chile

This report, prepared at the request of the Government of Chile under the auspices of the U. S. Agency for International Development (US AID), is based on a 2-month assignment (Oct. 22 to Dec. 31, 1969) of the author and outlines a program of water resources studies. The study program, if followed to its conclusion, will provide the basic hydrologic and hydrogeologic information and analysis essential for planning optimum future development and use of the water resources of the valley.

Open-File Report↗
USGS1965

Structural geology of aconcagua province and its relationship to the central Valley Graben, Chile

Aconcagua Province is herein divided into three major structural provinces which, for the sake of simplicity, are named the Coastal Cordillera, Central Valley graben , and Andean Cordillera structural provinces to correspond to the three geomorphic provinces recognized farther south. The coastal structural province includes the Coastal Cordillera which is underlain mainly by layered sedimentary and effusive rocks that strike north and dip homoclinally to the east, range from Triassic to Late Cretaceous in age, and are intruded by Cretaceous granodioritic and dioritic rocks. Igneous and metamorphic rocks largely of Paleozoic age comprise the western coastal margin, Along the eastern edge of the province is the Los Angeles fault zone, a wide, poorly defined band of semiparallel, arcuate faults which show downward displacement to the east and which appear to have resulted mainly from intrusion and uplift on the west. The Coastal Cordillera, therefore, may be considered a large horst with an intrusive granodiorite core. The Central Valley graben is bounded on the west by the Los Angeles fault zone and on the east by the Pocuro fault zone. Between these two fault zones is an area 20-30 km wide in which volcanic rocks of Late Cretaceous age are flat lying to gently folded and block faulted. In places, pipelike stocks of andesitic to dioritic igneous rock intrude the area. The Pocuro fault zone is a prominent lineament that marks the eastern limit of the Central Valley at Santiago and has been traced northward for 150 km. It may, however, have a mappable length of more than 1200 km. Vertical displacement downward to the west has been measured near Los Andes to be at least 2000 m. Consequently, this fault zone may rank among the major faults of the world. The Andean structural province is subdivided into the Las Ollas and Juncal subprovinces. The Las Ollas is a mountainous front range that lies east of the Pocuro fault and extends eastward for about 25 km. Upper Cretaceous volcanic strata are gently warped into broad, open, north-trending folds, with local sharp flexures and faulted mainly by normal faults. The eastern part of the subprovince is cut by a narrow belt of Tertiary plutonic rocks, some of which are associated with porphyry copper deposits. The Juncal structural subprovince extends eastward into Argentina. It is typified by close, overturned folding, vertical bedding, and thrust faulting. In general, structural deformation increases in intensity from west to east, with imbricate overthrusting to the east in Argentina. Present evidence indicates that major graben formation began during early Tertiary (pre-Miocene) time as a result of tensional stress developed by strain release of earlier compressional forces that folded the Andes. Post-Miocene uplift of the central Andean region renewed tensional stress and opened deep-seated, north-striking fractures and reinitiated volcanism. Most of the active volcanos of Chile may be aligned along such fractures.

Geological Society of America Bulletin↗
USGS1964

Paleo-channels at the Guayacan copper mine, Cabildo District, Aconcagua Province, Chile

An uneven erosion surface separates calcareous sedimentary rocks above and vesicular andesite porphyry below at the Guayacan mine of central Chile . Channel -like depressions filled with sedimentary rock flank elongate, stratiform bodies of disseminated copper ore which impregnate the vesicular crests of andesite lava flows. The " channels " lie parallel to and mark the margins of tongues of lava. Erosional features such as scour surfaces, conglomerate and crossbedding mark some of the channels . Other channels show no evidence of erosion, suggesting that some, at least, represent depressions or spaces that were not filled during extrusion of the lava. The flows strike east. Their crests are vesicular and impregnated with copper sulfide minerals, mainly bornite, to depths as much as 3 m below the contact. Bornite fills vesicles and fractures, impregnates the andesite ground mass, and replaces andesine phenocrysts, mainly along cleavage planes. Chalcopyrite is mixed with bornite in the upper, more vesicular part of the flows and occurs with fine-grained pyrite as disseminations and replacing fossils in the base of the overlying sedimentary rock. The channel axes also strike roughly east and, in most places, are underlain by barren ground. These mappable features, when recognized, are valuable in determining the size, shape, and orientation of adjacent ore bodies and, thereby, assist in the evaluation, exploration and mining of these stratiform copper deposits.

Economic Geology↗
USGS1963

Matureland of northern Chile and its relationship to ore deposits

The old surface that extends over a long north-striking belt in northern Chile probably reached the mature stage of erosion by middle Tertiary time. Low areas are mantled by the piedmont deposits of the pampa, and the higher parts exhibit rock decay, oxidation, leaching, and super-gene enrichment of sulfide mineral deposits as a result of deep weathering. The surface and its deposits are deeply eroded south of the main pampa by the Río Copiapó and its tributaries. Numerous ore deposits in the thick secondary zones have not been eroded, but ore deposits are few in the youthful valleys where the primary zones extend to the surface.

northern Chile↗
USGS1963

Geology of the salt deposits and the salt industry of northern Chile

The study of the salt deposits of northern Chile is a cooperative project of the Institute de Investigaciones Geologicas (IIG) of Chile and the United Nations Special Fund and is part of a mineral resources survey, undertaken by these two organizations, of selected regions of northern Chile, during 1960-1963. The writer, an employee of the United States Geological Survey, worked in cooperation with the IIG and its predecessor organization, the Seccion Geologica of the Corporacion de Foment de la Produccion, during the period December 1954-March 1962, under the auspices of the United States Technical Aid program (AID). The work on salt deposits, which was started during 1961, has been under the auspices of the United Nations since April 1962, during completion of field work and preparation of this report. This report summarizes the data gathered during the field investigation, including information on reserves, production, and composition of salts supplied by private companies and government bureaus. As such, it is in the nature of a progress report, lacking: 1) a comprehensive review of the literature which, at least in regard to the well-known nitrate deposits, is extensive; 2) completion of laboratory investigations of chemical, mineralogical, and isotopic composition; and 3) a review of theories of origin of the salts, mainly nitrate. The salt deposits of northern Chile comprise the well-known nitrate deposits as well as salars that have been exploited principally for sodium chloride, sodium sulfate, and borate; bedded salt deposits and salt domes, and secondary salt deposits formed in the oxidation zone of metalliferous sulfide deposits. This report will discuss the nitrate deposits and associated sodium sulfate deposits, salars, and those secondary deposits, such as aluminum-magnesium sulfates or iron sulfates, which have been exploited for chemical use. Bedded salt deposits and salt domes, consisting mainly of halite and evidently restricted to one small area, were not studied. The numerous and important secondary copper deposits, as well as other metalliferous salt deposits, are beyond the scope of the report.

northern Chile↗
USGS1962

Metallogenetic provinces of Chile, S. A

The metalliferous deposits of Chile tend to be restricted to well denned metallogenetic provinces, each characterized by a dominant mineral or mineral assemblage. The most important ore deposits are those of copper, iron, silver, gold, and manganese. The primary minerals are few in number and most are simple sulfides and oxides; more complex sulfosalts are scarce. Secondary minerals in great variety are important constituents of the ores. Many of the ore deposits are situated along well defined structural lines, several hundred kilometers long, that parallel the structural grain of the Andes.The deposits, with few exceptions, are found in sedimentary or volcanic rocks that range in age from Jurassic to Late Cretaceous or in intrusive rocks of Late Jurassic to Late Cretaceous age. Most deposits are genetically related to intrusive bodies, which have an average composition within the range of granite-diorite.The metalliferous deposits can be classed as hydrothermal, sedimentary, contact-metasomatic and magmatic. Copper deposits are typically hydro-thermal, manganese deposits are sedimentary, and most of the iron ore deposits are contact-metasomatic. A unique group of iron ore deposits apparently formed by near-surface intrusion and surface flows of a magma consisting of iron oxides. Hydrothermal deposits, the most abundant and most important economically, were formed under conditions ranging from low to high temperature and pressure. © 1962 Society of Economic Geologists, Inc.

Economic Geology↗
USGS1961

Ages of batholithic intrusions of northern and central Chile

Their stratigraphic setting demonstrates that three batholithic intrusions in northern and central Chile are respectively pre-Jurassic, Jurassic, and Cretaceous. Radiometric age determinations, by the lead-alpha (Larsen) method, indicate ages of 265 ± 30, 120 ± 15 to 125 ± 15, and 95 ± 10 to 130 ± 15 million years respectively for samples from the batholiths whose stratigraphic setting has been established or is inferred. With one exception, the radiometric ages are consistent with the stratigraphy. The exceptional determination of 130 ± 15 million years was for a sample of granite that intrudes Cretaceous rocks. Three other samples of Cretaceous granitic rocks were within the range of 95 ± 10 to 105 ± 10 million years. Angular unconformities whose ages are correlative with the intrusions suggest that the three batholiths can be related respectively to Hercynian, Late Jurassic, and middle Cretaceous orogenies.

Geological Society of America Bulletin↗
USGS1948

Geology and ground water of the Casablanca Basin, Chile

"In the uplands the Cretaceous granodiorite and granite contain water in the weathered zones, and in joints and fractures. These yield small supplies of good water to springs and to shallow domestic and stock wells. The alluvial fill of the lowlands contains a zone of saturation that is sustained by infiltration from rainfall and from the runoff of the uplands.... Where present in the zone of saturation, the coarse-grained members of the alluvial fill yield moderate to large supplies of good water to wells."

Casablanca Basin↗