Geology, mineralogy and geochemistry of the Cerro Matoso nickeliferous laterite, Córdoba, Colombia

1986 Spring. ; Includes bibliographical references. ; The Cerro Matoso nickeliferous laterite, located in northern Colombia near the town of Montelibano, was developed in pre-Late Cretaceous ultramafic rocks consisting principally of slightly serpentinized harzburgite. The peridotite body is flanked by ferruginous sandy sediments with interbedded coal beds of the Cienaga de Oro Formation (early Oligocene-early Miocene) and Recent alluvial gravels and sands. The harzburgite consists predominantly of olivine with lesser amounts of orthopyroxene and secondary serpentine. Intense serpentinization is primarily confined to areas of faulting and brecciation particularly along the western and eastern boundaries of the peridotite body. Development of the nickel laterite profile was greater in weakly serpentinized peridotite both in vertical extent and in the degree of enrichment of nickel-rich secondary products than in strongly serpentinized peridotite. The Cerro Matoso peridotite was affected by two major tectonic events. Compressional stresses associated with the late phases of the Pre-Andean orogeny in middle Eocene-late Eocene time brought the peridotite to the surface and also generated a major NE trending fault system in the peridotite body arid local serpentinization particularly along fault zones. Lateritization of the harzburgite probably began in late Eocene-early Oligocene time and chemical weathering and erosion favoured by a tropical humid and rainy climate with probable alternating wet-relatively dry seasons, continued throughout the Oligocene period. A major NW trending fault system developed in the peridotite body during the late Miocene-Pliocene Andean orogeny and the southwestern part of the weathered peridotite body was uplifted relative to the northeastern part. This uplift apparently was sufficient for intense erosion to remove most of the laterite profile from the uplifted block while the northeastern block was being only slightly modified. The laterite profile consists of an upper Canga zone ...