Geological, geochemical and mineralogical characterization of non-metallic mineral deposits in the La Paz region, Bolivia

Sammanfattning: Industrial mineral resources are a promising source of economic development in Bolivia where the mining industry’s main focus is on metalliferous deposits. The industrial mineral resources in Bolivia are of large quantity, even though they remain only locally known, as well as understudied to a large degree.This thesis aims to show the industrial mineral mining potential of La Paz and Bolivia as a whole. Bolivia’s resources of industrial minerals can potentially be used for numerous industrial applications. Three deposits have been geologically and mineralogically characterized. In addition, the potential applications of the mined products are addressed.Firstly, the Micaya deposit, located at the Micaya village south-west of La Paz city, comprising two whitish kaolinite-bearing occurrences, was investigated. The material is currently used in tableware production. The Micaya deposit is situated in a Palaeozoic sequence in the Altiplano basin. The general mineral composition of the occurrences is 56 vol.% quartz, 21 vol.% muscovite, 18 vol.% kaolinite and <5 vol.% feldspar. The kaolinite-bearing sediments were formed through enhanced weathering of the muscovite-rich siltstones aided by groundwater remobilization along permeable fault zones. Micaya kaolinite is suggested to be suitable for industrial applications.Secondly, the Choquetanga deposit, located south-east of La Paz city and currently mined for Sn and W, is associated with a coarse-grained granitic batholith that was studied for its feldspar characteristics in this work. Geologically, the Choquetanga area is dominated by a Palaeozoic sedimentary sequence intruded by the porphyritic granite from the Quimsa Cruz batholith in the south-east of the Eastern Cordillera. The Quimsa Cruz batholith is composed of megacrystalline granite with 5–10 cm long orthoclase, albite and oligoclase crystals that contain a considerable alkali content of YK2O,Na2O=7.84–10.25 wt.%.Thirdly, the La Fabulosa deposit, located north-west of the Eastern Cordillera, was studied for its feldspar occurrences hosted in granites and pegmatites. The deposit is composed of a metasedimentary sequence of Palaeozoic age intruded by the Sorata batholith, which comprises two-mica granites, granodiorites and pegmatites with an alkali content of YK2O,Na2O=7.41–14.25 wt.%, hosted in the minerals microcline, orthoclase and oligoclase.The potential raw materials from the three studied industrial mineral deposits were evaluated for use in ceramic applications. In addition, nine non-metallic occurrences, most of them currently mined and located at Oruro (one zeolite occurrence), Potosí (one diatomite and one montmorillonite occurrence), La Paz (three clay deposits and one diatomite occurrence) and Santa Cruz (two kaolin deposits) have been sampled. Mineralogical and lithogeochemical characterization of the materials have been performed to address higher-value applications for the deposits.X-ray diffraction (XRD) and inductively coupled plasma mass spectrometry (ICP-MS) were used to identify the mineralogical and lithogeochemical composition of the host rocks to the deposits. Scanning electron microscopy (SEM) were performed on the kaolinite-bearing materials to characterize the microstructure in the rocks. This indicates mineral paragenesis and has therefore implications for mineral deposit formation. Physical tests on the ceramic specimens, such as drying shrinkage (Choquetanga 0.20 vol.%, La Fabulosa 0.31 vol.%), firing shrinkage (Choquetanga 1.66 vol.%, La Fabulosa 1.59 vol.%), bending strength (Choquetanga 69.55 N/mm2, La Fabulosa 70.20 N/mm2), water absorption (Choquetanga 2.13 vol.%, La Fabulosa 0.58 vol.%) and Mohs hardness value of 7, demonstrate the potential application of the studied industrial minerals in the production of floor tile ceramics.The results of this work show the geological potential for industrial mineral exploitation in Bolivia. It is expected that these investigations will serve as a starting point and encouragement for future geological research and mineral exploration with important implications for the supply of industrial minerals for the growing industrial sector of Bolivia.