Abstract
Solid organic matter is an important constituent not only in coal, but also in black shale-hosted ore deposits. The reliable recognition and quantification of organic carbon—as well as its microfabric relation to associated inorganic minerals—plays a crucial role in characterization by scanning electron microscopy-based image analysis. However, the use of conventional epoxy resin in the preparation of grain mounts does not allow for recognition of solid organic carbon compounds. In this study we illustrate that the use of iodized epoxy resin readily overcomes this bottleneck. Best results are obtained with an addition of 15 wt% iodoform to the epoxy resin. With process samples of black shale-hosted polymetallic Kupferschiefer-type ore as a case study, it is shown that recognition and quantification of solid organic carbon are easily achieved and that tangible parameters such as particle and grain sizes, association and liberation for ore and gangue minerals can be determined in the presence of solid organic matter. Due to the inherent uncertainty of the exact chemical composition of the kerogen contained in Kupferschiefer, it was not possible to attain exact comparability between chemical Corg assays and assays calculated from MLA data. However, the results are still found to closely agree with one another. The strength of iodized resin lies in its ability to distinguish organic matter with high hydration ratios in addition to the easy integration in sample preparation. It could therefore be an attractive supplement in the analyses of other raw materials containing complex organic-matter.
Highlights
With process samples of black shale-hosted polymetallic Kupferschiefer-type ore as a case study, it is shown that recognition and quantification of solid organic carbon are achieved and that tangible parameters such as particle and grain sizes, association and liberation for ore and gangue minerals can be determined in the presence of solid organic matter
Difficulties arise, when the studied raw materials are rich in solid organic carbon, such as coal or polymetallic base metal ores hosted by carbonaceous shales [2] [3] [4]
The precise total organic carbon (TOC) content cannot be calculated from the Mineral liberation analysis suite (MLA) results, as it is known that the maturity of kerogen in the Kupferschiefer is rather variable with carbon contents ranging from, ~60 wt% to more than 90 wt% [24]
Summary
Automated mineralogy is widely accepted as an analytical tool well-suited to quantify mineralogy and relevant microfabric parameters [2] [16] [17] It combines highresolution backscatter electron (BSE) images with energy-dispersive X-ray (EDX) measurements to determine the chemical composition and distribution of minerals on a defined polished surface. Solid organic carbon residues can generally not be differentiated from the epoxy resin that is used to produce grain mounts for granular process samples. In such cases, the organic carbon remains unnoticed—resulting in erroneous results. Within this study we document that the addition of iodoform to epoxy resin is an attractive and practical alternative that is well suited to recognize and quantify the abundance of organic carbon in metalliferous black shales
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