Study of manganese traces in fluvial sediments along the Lluta riverbanks in the Arica and Parinacota region, northern Chile: Archaeological and current implications

Abstract

The ancient coastal populations of northern Chile called Chinchorro used manganese (Mn) oxide extensively for the preparation and ornamentation of their deceased. The possible sources of extraction of this mineral have been debated in several studies. This work focuses on the study of dry sediments from the Lluta riverbed in the Arica y Parinacota region to characterize Mn concentrations in alluvially transported material at different points along the river. Six riverbed sediment samples were collected from an altitude of 1,328 masl to 6 masl. The samples were sieved into five-size fractions and Mn concentrations were measured using atomic absorption spectroscopy. It was found that Mn concentrations vary inversely proportional to altitude with a correlation coefficient of -0.91. The highest Mn levels are found in samples near the coast with the following values: total water-soluble Mn 243 µg/g, total exchangeable Mn 248 µg/g, and total acid-soluble Mn 4,607 µg/g. These levels of Mn would not correspond to a primary or important source for the extraction of black Mn ore by the archaic inhabitants for mortuary preparation of the Chinchorro mummies. Nevertheless, the presence of Mn in the riverbed raises questions about the health consequences for the ancient populations and the importance of monitoring Mn in the water due to possible bioaccumulation of this mineral in agricultural products of the area.