Rocio Quispe, BSc

R. Quispe¹, N. Jimenez¹, G. Uzquiano²

¹Geological Engineering, Universidad Mayor de San Andrés, La Paz, La Paz, Bolivia

²Colegio de Geólogos de Bolivia, La Paz, La Paz, Bolivia

Cerro Manomó is interpreted as a silicified ferrocarbonatite complex with a highly complex geological history involving multiple geological processes that significantly modified the original rocks. Since the first studies conducted in the 1980s, its geological interpretation has been the subject of debate due to the extensive replacement of the original lithologies by metasomatic, hydrothermal, and supergene processes. Despite this complexity, Cerro Manomó is of high scientific and strategic interest because of its anomalies in rare earth elements (REE) and radioactive minerals, positioning it as a relevant target within Bolivia’s growing interest in critical minerals.

The objective of this study was to characterize the geology of the northeastern sector of Cerro Manomó and to contribute to the understanding of its genetic evolution by addressing uncertainties related to lithological origins, structural controls, and the processes responsible for the observed geochemical enrichment. The scope of the work focused on integrating field, laboratory, and remote sensing data to propose a coherent and preliminary evolutionary model for the complex.

To achieve this, a multidisciplinary approach was applied, including photogeology, satellite image analysis, detailed geological field mapping, petrographic and mineragraphic studies, X-ray fluorescence (XRF) geochemical analyses, and fluid inclusion investigations. This methodology allowed the identification of key structural features, including the presence of possible annular carbonatite dikes, as well as zones of intense hydrothermal alteration.

The results indicate a polyphase evolution dominated by pervasive silicification and hydrothermal alteration at temperatures close to 400 °C, with secondary mineral assemblages characterized by quartz, hematite, kaolinite, limonite, barite, and bastnaesite. Geochemical data show significant enrichment in REE, Nb, Th, and U, consistent with carbonatitic affinities and comparable to other regional alkaline–carbonatite complexes. Available geochronological data indicate a basement interpreted as a possible Banded Iron Formation (BIF) dated at approximately ~1.2 Ga and a Cretaceous carbonatite intrusion dated at ~139 Ma.

Overall, this study confirms that Cerro Manomó represents a highly evolved ferrocarbonatite complex enriched in REE, whose exploration potential may be structurally controlled by annular features. Further exploration is recommended through geophysical surveys and drilling, as well as detailed evaluation of the rare earth element potential in residual soils, in order to assess the economic viability of the system and its potential future development.