Geologic Map of Southern Venezuela: the Venezuelan Guayana Shield

by Jeff Wynn, Dennis Cox, Floyd Gray, and Paul Schruben

(From: U. S. Geological Survey Digital Data Series 46) and USGS Bulletin 2062)


|| Background || The maps and how to access them || About the compilation || References ||

Background

Thumbnail version of the Guayana Shield geology map.
Map of the geology of the Guayana Shield

World-class reserves of iron, bauxite, gold, diamonds, and many other commodities were known to exist in the once poorly-understood Precambrian Guayana Shield of Venezuela. Mapping and assessment of these resources were the products of a unique cooperative agreement between the U.S. Geological Survey (USGS) and CVG-Técmin C.A., the mineral resource inventory arm of the Venezuelan government. From 1987 until 1991 the USGS maintained an advisory mission in Puerto Ordaz, in east-central Venezuela. This mission was invited and funded completely by the Corporación Venezolana de Guayana (CVG), a Venezuelan government ministry, and included four resident USGS scientists and up to 12 visiting USGS scientists each year. The mission objectives were to provide training, technology transfer, a geologic and mineral resource inventory, and direct hands-on guidance in mineral exploration to CVG-Técmin C.A. The focus of the effort was the poorly-understood and incompletely-mapped Precambrian terrane (called the Guayana Shield) that underlies the southern half of Venezuela. In Venezuela, it underlies most of Bolívar State and all of the Amazonas Federal Territory. The Precambrian Guayana Shield ( not to be confused with the neighboring country of Guyana), includes some of the oldest known rocks in the world, and also covers parts of neighboring Guyana, Surinam, French Guiana, Colombia, and Brazil. This region is almost completely covered with jungle and even today has roads only on the northern and eastern fringes. Access for over 90% of the southern half of Venezuela is exclusively by helicopter and motorized dugout canoe.

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The maps and how to access them

The geologic map shown here in thumbnail sketch represents only one of the products of the five-year advisory mission. Other components include:

All these maps were first compiled at 1:500,000 scale and were then combined at 1:1,000,000 scale. They are included, along with explanatory text, in USGS Bulletin 2062 and in a new CD-ROM (U. S. Geological Survey Digital Data Series DDS-46) recently issued by the USGS. The contents of this CD-ROM is available on-line, at: http://minerals.usgs.gov/vz/

The bound version of USGS Bulletin 2062 (about 5 cm. thick, with maps), along with individual geologic maps, interim products, and specialized searches, may be ordered from:

USGS Information Services
Box 25286, Denver Federal Center
Denver CO 80225-0046
Phone: 1-888-ASK-USGS

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About the compilation

The 1:1,000,000-scale geologic map of the southern half of Venezuela combines earlier country-scale mapping (Bellizzia and others, 1976; Mendoza, 1977; Pimentel de Bellizzia, 1984) with more recent data from a large number of people from both Venezuela and the USGS (see list of contributors below). Where jungle cover, remoteness, and inaccessibility preclude direct sampling of the rocks, geophysical (magnetic and gravity) signatures, and LANDSAT and SLAR imagery were used to extend areas with known geology to areas not directly mapped in this difficult region. Whenever possible, an extensive suite of samples collected by the CVG-Técmin Geologic Inventory Group (Grupo Inventario) from 1985 through 1991 was consulted to verify or modify previous geologic interpretations.

This map represents a new kind of geologic interpretation of the Venezuelan Guayana Shield. It is an important new contribution (and crucial to the resource assessment) because the distribution of mineral resources is controlled by generally hidden geologic features such as deep faults, shear zones (single and intersecting), volcanic calderas, and intrusive bodies (among other things). Geophysical interpretive information was incorporated to make a quasi-three-dimensional representation of the geology and structure; that is, a two- dimensional geologic and tectonic map has been combined with elements of the third (or buried) dimension that were gleaned from the geophysical data. The final map was plotted using a Venezuela-specific Lambert Conformal projection (66oW Central Meridian and conic intersections at 4 degrees and 9 degrees north latitude) locally called Proyección Cónico Secante Compensada.

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Map compiled by: Jeff Wynn, Dennis Cox, Floyd Gray, and Paul Schruben

Other USGS contributors include: William E. Brooks, Warren Day, Sherman Marsh, and John H. Stewart

Venezuelan contributors include: Enrique Acosta, Juan Acosta, Jesús Arespón, Cruz Briceño, Henry Briceño, Juan Candelaria, Gloria Contreras, Yasmin Estanga de Sánchez, Luis Franco, José Jesús Freites, Andrés García, Acenk Guerra, Yolanda López, Glenda Lowry, Elis Lugo, Freddy Malavé, Iris Marcano, Félix Martínez, Miguel Martínez, Vicente Mendoza, Alredo Menéndez, Fernando Nuñez, Inés Rendón, Haydée Rincón, Ivan Rivero, Nelson Rivero, Edixon Salazar, Henry Sánchez, Gustavo Sardi, Frank Tovar, Urbano Ubencio, Manuel Uso, and Galo Yánez

Other American contributors include: John C. Dohrenwend (formerly USGS, now a private consultant in Tucson, AZ), Stephen D. Olmore (formerly USGS, now a private consultant in Denver, Colorado), Norman Page (formerly USGS, now a private consultant in Tucson, Arizona), and Gary B. Sidder (formerly USGS, now a private consultant in Denver, Colorado)

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References

Bellizzia-G., Alirio, Pimentel-M., Nelly, and Bajo-O., R., 1976, Mapa geológico estructural de Venezuela: Ministerio de Minas e Hidrocarburos, Dirección Geológica, Caracas: Caracas, scale 1:500,000.

Mendoza-S., Vicente, 1977, Evolución tectónica del Escudo de Guayana, in Petzall, C., ed., Memoria Segundo [II] Congreso Lationoamericano de Geologia, Tomo III, Caracas, November 11-16, 1973: Venezuela, Dirección de Geología, Boletin de Geología, Publicación Especial 7, v. 3, p. 2237-2270.

Pimentel de Bellizzia, Nelly, 1984, Mapa geológico estructural de Venezuela, Caracas: Ministerio de Energía y Minas, Dirección de Geología, scale 1:2,500,000.

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