THE GEOSOL IZABAL. A CASE OF ARRESTED DEVELOPMENT OF A NICKEL LATERITE IN CENTRAL AMERICA

The Geosol Izabal is a new stratigraphic unit defined by the author within the Sierra Santa Cruz (SSC) ophiolitic complex which is located to the north of Lake Izabal, in the east-central portion of Guatemala, some 140 km northeast from Guatemala City and represents the eastern expression of the Polochic Ophiolitic Belt. The Geosol Izabal is composed of the following five pedosols:

a. Gossan or Iron Cap (a.k.a. Ferricrete) b. Limonitic Horizon c. The Stone Line Horizon d. Mottled Zone Horizon (a.k.a. Transition Zone) e. Saprolitic Horizon.

The Saprolitic Horizon lies over a Saprock Horizon, which lies directly over a less weathered bedrock of the SSC ophiolitic complex. The most complete profiles are usually present over weathered dunites and serpentinites, while on top of the less altered pyroxenites there usually forms only a limonitic zone.

The SSC ophiolitic complex overthrusted the Maya Block of the North American Continental Plate during the Early Tertiary age along a flat structure that outcrops at its base. The SSC is one of the six ophiolitic complexes identified to date in Central Guatemala that are related to the northwestern border of the Caribbean Plate and, thus, to the ophiolitic belts from Cuba and Dominican Republic.

The intrusives of this complex are composed of dunites and pyroxenites, usually strongly serpentinized. Existing data indicate that these rocks underwent fractional crystallization and probably some degree of magma mixing and crustal contamination prior to their main tectonic event.

The Geosol Izabal represents an immature wet lateritic profile, which develops mainly as large pockets controlled by tectonics and the presence of dunitic and olivine-rich lherzolite rocks. The most striking difference from the wet laterites of Cuba and the Dominican Republic is the presence of up to 30% of magnetite within the Saprolitic Horizon, which is another indication of the relatively young age of these laterites. This magnetite, which carries nickel grades of 1.5 to 2%, could represent a secondary product for a plant producing ferro-nickel or steel products.

The relative complexity of the SSC ophiolitic complex explains the variety of mineral resources in the area, which include Ni-Co-Fe ores, chromites, bauxite, MgO, and has the potential for gold and PGM.