Geology, geochemistry, and mineral resources of the upper Caura River area, Bolivar State, Venezuela

Abstract

A sample of andesitic dike material contains anomalous values of Cu (334 ppm), As (153 ppm), and Mo (7 ppm). A mineral deposit model for epithermal precious metal veins best represents the occurrences in the upper Caura River area.

Geology of the Venezuelan Guayana Shield and its relation to the entire Guayana Shield

“…For example, field and petrographic evidence of metamorphism is not present in samples of volcanic rocks from the upper Caura or Paragua River areas (Sidder, unpublished data, 1990;Sidder and Martinez, 1990). Indeed, as noted above, vitroclastic and eutaxitic textures are abundant.…”

“…Broad, open folds are common, and structures such as faults and lineaments generally strike northwest to north-northwest and north-northeast. The El Viejo Formation, the volcanic suite of the Parucito Valley, and other relatively unmetamorphosed volcanic and plutonic rocks in the Amazon Federal Territory, the Uatuma Supergroup (including the Surumu and Iricoume Formations and the granodiorite of Serra do Mel) in northern Brazil, the Kuyuwini and Burro-burro Groups in Guyana, and the Dalbana Formation in Suriname correlate with the Cuchivero Group (Mendoza and others, 1975;Talukdar andColvee, 1975, 1977;Berrange, 1977;Mendoza and others, 1977;Tepedino, 1985;Gibbs, 1987;Sidder and Martinez, 1990;Machado and others, 1991). Rocks equivalent to the Cuchivero Group are not present in French Guiana or the West African craton.…”

“…1). They include a thick pile (greater than 3 km in thickness) of felsic to intermediate and mafic volcanic, subvolcanic, and plutonic rocks, and associated volcanogenic sedimentary rocks of the Cuchivero Group; sandstone and conglomerate with lesser siltstone, shale, chert, and interlayered felsic volcanic rocks (jasper) of the Roraima Group; continental tholeiitic dikes, sills, inclined sheets, and small irregular intrusive bodies of the Avanavero Suite; and rapakivi granite of the Parguaza Province (Rios, 1972;Mendoza and others, 1975;Ghosh, 1985;Gibbs, 1986;Sidder and Martinez, 1990).…”

“…The rocks are aphyric to porphyritic, with both crystal-rich and crystal+lithic-rich varieties. Vitroclastic and eutaxitic textures with devitrified glass shards and collapsed pumice fragments are common (Rios, 1972;Mendoza, 1977b;Sidder and Martinez, 1990). The Caicara Formation is comprised dominantly of rhyolite, with subordinate rhyodacite and dacite and minor proportions of andesite, basaltic andesite, and basalt.…”

“…The silicic rocks are mainly tuffs, whereas andesite and basalt occur as lava flows and dikes. Together, these rocks form a comagmatic calc-alkaline series (Talukdar andColvee, 1975, 1977;Mendoza, 1977b;Sidder and Martinez, 1990). Briceno and others (1989) described felsic to intermediate volcanic and volcaniclastic rocks near Ichun tepui (pi.…”