Geology, petrology, and iron deposits of the Guiana shield, Venezuela

Feldspathic gneiss and other metamorphic rocks of the Imataca series, middle or upper Precambrian in age, and metavolcanic rocks of the Pastora series in the northern Guiana shield area of northeastern Venezuela may represent the respective products of shallow-water sedimentation in an early stage of geosynclinal development and ofvolcanism later in the history of the same geosyncline. These series may be continuous and may be correlative with the Barama-Mazaruni complex of British Guiana, which exhibits similar facies changes. Ferruginous quartzites intercalated in the Imataca feldspathic gneisses are the host rocks of extensive iron deposits (as at Cerro Bolivar) whose formation was due to oxidation of magnetite to hematite and leaching of quartz. The great size of the ore deposits is attributable to repetition of the iron-bearing beds in tight folds.