Abstract
In the Santander Massif of the Eastern Cordillera of Colombia, intense Pliocene to Holocene sulfide-rich gold mineralization occurs in a six kilometers long section of the La Baja fault zone, where it crosses partially migmatized gneisses and intrusions of Triassic-Cretaceous quartz monzonites and granites. These intrusives are mineralogically and texturally similar to the neosome of the migmatites that they intrude. The mineralization occurs as medium to large veins in the gneisses and as small veins, veinlets and disseminations in the intrusives. The type, volume and metal grades of the veins are dependent on the local structure, and the chemical composition and degree of reactivity of the host rocks. Thicker and higher-grade veins of the Mascota-type occur in chemically favorable magnetite-hornblende gneisses and migmatites, deposited after phases of silicification, and brecciation along the foliation of the host rocks. The Gigante-type shear veins occur in splays of the fault, and are marked by shearing and mylonitization. Lower-grade, flat-banded veins appear in leucocratic quartz-feldspar gneiss and related migmatites. The mineralizing fluids ascended along fault planes, and invaded the gneisses in fractures oblique to them. In all deposits, gold occurs in free form, as electrum and in tellurides, and accompanied by copper and silver.
Highlights
In the Municipality of California, Department of Santander, Colombia, there is a widespread gold mineralization, with an intense concentration of deposits in a six kilometers long corridor following the La Baja fault zone, where it crosses a sequence of partially migmatized Precambrian gneisses and Triassic-Cretaceous granitic intrusives (Figs. 1 and 2, which are described further on)
Minor faults parallel to the foliation of the gneisses and to the main fault planes of the La Baja Fault Zone were observed in drill cores from Aserradero, La Rosa, Gavilán and other sites
A large portion of the Central and most of the Eastern Cordillera, the latter range only seen in Colombia, are made of Precambrian gneisses and migmatites, intruded by Mesozoic to Late Cenozoic granitic rocks
Summary
The description of the mineralization is completed with the presentation of a model for the origin of the veins, providing a basis for future exploration for vein extensions and additional veins. This information may help the identification of other styles of gold mineralization in the region. The article begins with a summary of the historical development of the exploration of the area This is followed by a review of the lithological and tectonic setting of North Colombia, outlining the possible and important participation or influence of the Caribbean Plate in the mineralization
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