Remote Sensing and Biogeochemical Prospecting for Uranium and Associated Mineralogical Elements in Argentina
Creators: name: BERG, TALIA CARINA
Publisher: name: University of Surrey
Year: 2021

description: Remote sensing systems is widely used for mineral exploration. Many minerals have distinctive spectral patterns and can also be identified using linear features linked to geologic structures of mineralisation or the recognition of hydrothermally altered rock formations that may be associated with mineral deposits. Landsat and ASTER satellite imagery was used to characterise potential uranium deposits in northern Santa Cruz, Argentina. Field-based gamma-ray radiometry was carried-out to identify sampling sites and an aerial-based survey for the generation of a regional radiometric anomaly map, followed by biogeochemical prospecting, which is based on using plants to indicate the presence of minerals in the underlying substrate. In Argentina, mineral ores are abundant but few studies of the chemical analysis of native vegetation growing in such areas have been reported. Moreover, uranium deposits may also have raised levels of Th, V, As, Zr and rare earth elements (REEs). Two campaigns were coordinated for the purpose of this research: a preliminary study in Nov. 2014 which covered the collection of soils and plant species, along with radiometric field data, from 2 areas, a control or ‘background’ (sites 3 to 8) and possible U-deposit at Laguna Sirven (sites 9 to 13). Hyperspectral data was obtained at Hytec Alto Americas for plant and soil samples. Preliminary studies confirmed that the preferred digestion method was dry ashing with subsequent acid dissolution of the ‘ash’ with aqua regia (plants) or aqua regia/hydrofluoric acid (soils) for elemental analysis (for more than 35) by inductively coupled plasma mass spectrometry. The Laguna Sirven ‘mineralised’ values confirmed sites of higher U-levels, with the translocation and distribution of U being roots &gt; leaves ~ stems &gt; flowers. Soil depth profiles at Laguna Sirven confirmed U-deposit layers at site 11-2 (mg/kg U d.w.): a surface value of 3.32 (0 cm), 119.87 (15 cm), 713.13 (30 cm), 282.51 (50 cm) and 10.30 (70 cm), respectively. Pearson correlation coefficient analysis confirmed the relationship between the gamma-ray radiometry equivalent uranium (eU) signal and the U levels at the Laguna Sirven sampling sites. A highly statistically significant relationship (two-tailed t-test) exists in plant material between U and V or U and As A similar relationship exits between these elements for surface soils, suggesting Laguna Sirven has calcrete uranium deposits in which the U6+ mineral is carnotite or hydrated potassium uranyl vanadate. In April 2018, a follow-up trip was undertaken at Laguna Sirven using information obtained from new remote sensing satellite images and data processing techniques, which helped identify two new sampling areas, namely, gypsum and carbonate-based sites. This study confirmed the data from 2014, although the plant uranium (and some other elements) had lower levels, especially samples from the carbonate sites. This may be due to seasonal fluctuations causing variations in elemental uptake by aerial plant tissues. Correlation maps for all plant and soil samples confirmed highly positive relationships between U, V and As, already establish in the 2014 study. Principle component analysis of soil and plant data also confirmed the above correlations between these elements and clustering with other elemental groups – REE, Ba-Sr-Th, alkaline earths. This data helped postulate the possible U mineralization process and involvement of other elements in this region of Laguna Sirven, Santa Cruz, Argentina.