Geology and resource assessment of the Venezuelan Guayana Shield at 1:500,000 scale

Conversion of the Venezuela maps to a computerized digital format was
undertaken for the following reasons:

1) The digital format facilitates the presentation and analysis of
earth-science data. Digital maps can be displayed at any scale or projection,
whereas a paper map has a fixed scale and projection. However, the maps on this
disc are not intended to be used at any scale more detailed than 1:500,000.

A geographic information system (GIS) allows combining and overlaying of layers
for analysis of spatial relations not readily apparent in the standard paper
publication. Digital data on geology, geophysics, and geochemistry can be
combined to create useful derivative products.

2) The digital format was used to facilitate publication in both paper and
electronic form. For the Rio Caura paper map publication (Brooks and others,
1995), digital images were sent to the Gerber plotter, a vector-to-film
processor. The other 1:500,000-scale MF maps were reproduced photographically
from electrostatic plotter output on clear mylar. The published digital
formats include this CD-ROM and ARC/INFO Export files to be located on the
World Wide Web on the Internet.

The data in this CD-ROM are based on a mineral resource assessment of the
Venezuelan Guayana Shield, conducted between 1987 and 1991 by the U.S.
Geological Survey and Corporacion Venezolana de Guayana, Tecnica Minera, (USGS,
1993). The Venezuelan Shield occupies about 415,000 sq km in the south and
east part of Venezuela. The study area is bounded on the north by the Rio
Orinoco. It includes all of the Territorio Federal Amazonas, Estado Bolivar,
and part of Estado Delta Amacuro. The original resource assessment publication
USGS Bulletin 2062 consists of 121 pages of text and figures as well as eight
full-color maps:

Geographic
Geologic and tectonic
Bouguer gravity
Two mineral-occurrence maps
Side-looking airborne radar image
Two permissive domain maps

The side-looking airborne radar image and the Bouguer gravity map are not
included in this CD-ROM. The geology layer from the 1993 Bulletin was revised
and published as a series of MF and I maps.