Listvenites: new insights of a hydrothermal system fossilized in Cerro Matoso peridotites, Montelíbano, Córdoba Department, Colombia

Abstract

The products of metasomatic alteration (e.g., carbonation) of peridotites are called listvenites. Based on a description of the outcrops in the laterite deposit at Cerro Matoso located in the NW of Colombia, the mineralogical composition confirmed by petrography, and a chemical analysis performed with XRF and WDS/EDS, the previous unit called tachylite is redefined as listvenite. Two types of listvenites are described: listvenite A, with the mineralogical association of quartz + siderite + phyllosilicates + goethite +/- magnetite, and listvenite B, with the association of siderite + phyllosilicates + goethite. Cr-spinel relics accompanied by Mn-siderite and neoblastic textures, indicate their origin from peridotites, where Mn-Fe would have been deposited by hydrothermal fluids. Hydrothermal reducing environments with alkaline fluids and low temperatures should have favored the formation of listvenites that are observed along a fracture zone, oriented WNW-ESE at Pit-1 in Cerro Matoso. Due to exposure to climatic conditions since the Eocene, but definitively since the last Andean Orogeny, listvenites were affected, like all the rocks in the Cerro Matoso deposit, by intense supergene weathering and leaching processes, which could make their true origin unclear.

Mineralogical, petrographic, and geochemical analyzes which confirm the hydrothermal origin of the sediments that overlie the peridotites of Cerro Matoso, Colombia

“…Although the less depleted δ 13 C values are in the range of meteoric siderite line (MSL) (Figure 8) that could reflect biological processes related to the degradation of organic matter, these values may also record anaerobic oxidation of methane or bacterial oxidation/sulfate-reduction (Irwin et al, 1977). The ancient hydrothermal activity in the Cerro Matoso peridotites is supported by the identification of listvenites (Castrillón and Guerrero, 2020), precisely rocks that are underlying the Fe-rich mudstone succession. If this interpretation is correct, then it suggests that serpentinization-derived fluids flow was active for a considerable time according to the mounds and tabular unit thickness, as well as during the formation of listvenites, and this process was localized in the north area of the Cerro Matoso peridotites.…”