Christoph Gauert

Spaceborne mine waste mineralogy monitoring in South Africa, applications for modern push-broom missions: Hyperion/OLI and EnMAP/Sentinel-2

Remote sensing analysis is a crucial tool for monitoring the extent of mine waste surfaces and their mineralogy in countries with a long mining history, such as South Africa, where gold and platinum have been produced for over 90 years. These mine waste sites have the potential to contain problematic trace element species (e.g., U, Pb, Cr). In our research, we aim to combine the mapping and monitoring capacities of multispectral and hyperspectral spaceborne sensors. This is done to assess the potential of existing multispectral and hyperspectral spaceborne sensors (OLI and Hyperion) and future missions, such as Sentinel-2 and EnMAP (Environmental Mapping and Analysis Program), for mapping the spatial extent of these mine waste surfaces. For this task we propose a new index, termed the iron feature depth (IFD), derived from Landsat-8 OLI data to map the 900-nm absorption feature as a potential proxy for monitoring the spatial extent of mine waste. OLI was chosen, because it represents the most suitable sensor to map the IFD over large areas in a multi-temporal manner due to its spectral band layout; its (183 km × 170 km) scene size and its revisiting time of 16 days. The IFD is in good agreement with primary and secondary iron-bearing minerals mapped by the Material Identification and Characterization Algorithm (MICA) from EO-1 Hyperion data and illustrates that a combination of hyperspectral data (EnMAP) for mineral identification with multispectral data (Sentinel-2) for repetitive area-wide mapping and monitoring of the IFD as mine waste proxy is a promising application for future spaceborne sensors. A maximum, absolute model error is used to assess the ability of existing and future multispectral sensors to characterize mine waste via its 900-nm iron absorption feature. The following sensor-signal similarity ranking can be established for spectra from gold mining material: EnMAP 100% similarity to the reference, ALI 97.5%, Sentinel-2 97%, OLI and ASTER 95% and ETM+ 91% similarity.

New geometric hull continuum removal algorithm for automatic absorption band detection from spectroscopic data

Modern imaging spectrometers produce an ever-growing amount of data, which increases the need for automated analysis techniques. The algorithms employed, such as the United States Geological Survey (USGS) Tetracorder and the Mineral Identification and Characterization Algorithm (MICA), use a standardized spectral library and expert knowledge for the detection of surface cover types. Correct absorption feature definition and isolation are key to successful material identification using these algorithms. Here, a new continuum removal and feature isolation technique is presented, named the ‘Geometric Hull Technique’. It is compared to the well-established, knowledge-based Tetracorder feature database together with the adapted state of the art techniques scale-space filtering, alpha shapes and convex hull. The results show that the geometric hull technique yields the smallest deviations from the feature definitions of the MICA Group 2 library with a median difference of only 8 nm for the position of the features and a median difference of only 15% for the feature shapes. The modified scale-space filtering hull technique performs second best with a median feature position difference of 16 nm and a median difference of 25% for the feature shapes. The scale-space alpha hull technique shows a 23 nm median position difference and a median deviation of 77% for the feature shapes. The geometric hull technique proposed here performs best amongst the four feature isolation techniques and may be an important building block for next generation automatic mapping algorithms.

Multi-stage formation of REE minerals in the Palabora Carbonatite Complex, South Africa

Abstract The 2060 Ma old Palabora Carbonatite Complex (PCC), South Africa, comprises diverse REE mineral assemblages formed during different stages and reflects an outstanding instance to understand the evolution of a carbonatite-related REE mineralization from orthomagmatic to late-magmatic stages and their secondary post-magmatic overprint. The 10 rare earth element minerals monazite, REE-F-carbonates (bastnäsite, parisite, synchysite), ancylite, britholite, cordylite, fergusonite, REE-Ti-betafite, and anzaite are texturally described and related to the evolutionary stages of the PCC. The identification of the latter five REE minerals during this study represents their first described occurrences in the PCC as well as in a carbonatite complex in South Africa. The variable REE mineral assemblages reflect a multi-stage origin: (1) fergusonite and REE-Ti-betafite occur as inclusions in primary magnetite. Bastnäsite is enclosed in primary calcite and dolomite. These three REE minerals are interpreted as orthomagmatic crystallization products. (2) The most common REE minerals are monazite replacing primary apatite, and britholite texturally related to the serpentinization of forsterite or the replacement of forsterite by chondrodite. Textural relationships suggest that these two REE-minerals precipitated from internally derived late-magmatic to hydrothermal fluids. Their presence seems to be locally controlled by favorable chemical conditions (e.g., presence of precursor minerals that contributed the necessary anions and/or cations for their formation). (3) Late-stage (post-magmatic) REE minerals include ancylite and cordylite replacing primary magmatic REE-Sr-carbonates, anzaite associated with the dissolution of ilmenite, and secondary REE-F-carbonates. The formation of these post-magmatic REE minerals depends on the local availability of a fluid, whose composition is at least partly controlled by the dissolution of primary minerals (e.g., REE-fluorocarbonates). This multi-stage REE mineralization reflects the interplay of magmatic differentiation, destabilization of early magmatic minerals during subsequent evolutionary stages of the carbonatitic system, and late-stage fluid-induced remobilization and re-/precipitation of precursor REE minerals. Based on our findings, the Palabora Carbonatite Complex experienced at least two successive stages of intense fluid–rock interaction.

The African Metallotects of Southwest Gondwana

The African portion of Southwest Gondwana is endowed with an enormous wealth of mineral resources. Certain types of ore deposits occur in metallotects that share common geological and metallogenetic features. These can include host rocks, the age and mode of origin of the mineralisation, the commodity elements or minerals, and the geodynamic significance of formation. This chapter describes metallotects that are significant for the regional and supraregional geological and plate tectonic evolution, and bear metallogenetically and economically important mineral resources. The size of metallotects or individual deposits described here is variable, from the world-class Cu-Co-resource of the Central African Copperbelt (CACB) to economically insignificant but metallogenetically relevant tin deposits in the Cape Peninsula of South Africa. The chapter includes settings such as Late Mesoproterozoic extensional, volcanosedimentary continental to shallow marine basins with the deposits contained therein. It also describes the Neoproterozoic, more continuous, deeper-water and locally seafloor-basalt-bearing Damara Belt with its metabasalt-hosted massive sulphide Cu–Zn deposits and sediment-hosted Pb–Zn deposits along the basin margins. However, for some of the metallotects, the age of the mineralisation is epigenetic and unrelated to the period of deposition of the host rocks. The comparatively poorly exposed, studied and explored West Congo Belt is also included, particularly since it bears a lithologically, structurally and metallogenetically strong resemblance to the Damara Belt further south. Orthomagmatic copper sulphide deposits, such as the ones of the Mesoproterozoic Okiep District, represent a comparatively small but historically and metallogenetically important metallotect in the Northern Cape Province of South Africa. In contrast, ore deposits related to highly fractionated felsic to exotic magmatic rocks have formed during the late to post-orogenic stages in collisional plate tectonic settings.

Investigation of the Metal Contamination in the Upper Olifants Primary Catchment by Using Stream Sediment Geochemistry, Witbank Coalfield, South Africa

The Olifants primary catchment area, consists of nine sub-catchments marked from B1 to B9, extends over the border between South Africa and Mozambique, and has a total area of approximately 87,000 km2. The B1 catchment, where most of the mining activities surround the major towns of Witbank (Emalahleni) and Middleburg, in turn straddles the provinces of Mpumalanga and Limpopo. Although industrial and agricultural activities are also important, the contribution of contamination from the mining activities within the catchment is significant as the result of intense mining activities of various mineral commodities such as coal and from ferrochrome processing plants located in Emalahleni and Middleburg towns with in the catchment area and yet not fully quantified. This paper investigates the severity of the mining impacts on the water resources and the ecosystem of the Olifants primary catchment area and in particular, the upper reaches of the catchment. The paper discusses the results of research which focused on deciphering the severity and the sources water contamination, and on how to minimise the dispersion of these metals into the streams, and on the relationship of the water quality and metal loadings on the sediments. Stream sediment and water samples have been collected and analysed. The sediments were analysed by Simultaneous X-ray Fluorescence and Inductively Coupled Plasma-Mass Spectrometry techniques for metal loadings. The areas were marked by anomalous level determined at 50th percentile threshold of Fe, Mn, Ni, Cr, Co, V, Pb in Emalahleni and Al, Fe, Mn, Cr, As, Zn, Pb and U in Middleburg. The ICP-MS and IC analytical techniques were used in the assessment of water quality data. From the stream sediments regional geochemistry at catchment level and for this investigation, the sediments that were found marked by high levels of Na, K, Mg, Al, Ca, Mn, and Fe signature can be attributed to the coal mines as a probable source. Whereas the sediment quality of the areas like Emalahleni and Middleburg towns, where mining of coal (with many abandoned mines) and ferrochrome processing is happening simultaneously, there are anomalous level of Cr, Ni, V and As, which is a signature of the Bushveld PGE mines material. The SO4 2− concentration of above 500 mg/kg on the water quality, which has exceeded the Department of Water Affairs water quality guideline for domestic and industrial use, is an evidence for contamination. The approach adopted herein suggests that the stream sediment and water quality data can be used in characterizing or fingerprinting impacted areas.