The iron ores of Cerro Bolivar, Venezuela

Abstract

The ores were formed by leaching of silica and residual concentration of insoluble iron oxides in extensively deformed, recrystallized ferruginous cherts of the Precambrian Imataca series. Physical types include so-called crustal ores, consisting of hematite grains in a matrix of secondary goethite and characterized by a banded structure inherited from the bedding of the iron formations, and friable ores, porous aggregates of hematite grains which extend downward below a transitional zone of semifriable, platy ores to depths of as much as 800 feet. Sampling of spring waters which issue from levels at or below the lower margins of the ore bodies and other evidence indicate that silica is being removed at the rate of about nine tons per year, that iron ore is being formed at the rate of 18 tons per year, and that the amount of ore now present could have been formed (under present-day climatic conditions) in only 20 million years, or since Oligocene time.