Analyzing relationship between Fe–Mn Crust Composition and Water Depth with Collocated Co-Kriging to Study Potential Improvements in Estimation
A.P. Kollamparambil (TU Delft - Civil Engineering & Geosciences)
M. W.N. Buxton – Mentor (TU Delft - Resource Engineering)
RLJ Helmons – Mentor (TU Delft - Offshore and Dredging Engineering)
Steinar Ellefmo – Mentor (Norwegian University of Science and Technology (NTNU))
K. Pashna – Mentor (TU Delft - Resource Engineering)
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Abstract
The global transition to green energy has intensified demand for critical raw materials, increasing interest in deep-sea mineral resources such as cobalt-rich ferromanganese (Fe-Mn) crusts on seamounts like Tropic Seamount in the NE Atlantic. This thesis investigates the relationship between water depth and Fe-Mn crust composition and evaluates whether incorporating this relationship through Co-kriging (CK) improves resource estimation compared to Ordinary Kriging (OK). Geochemical and bathymetric data were analyzed using exploratory data analysis. The estimation workflow included block model generation, isometric log-ratio (ILR) transformation, Landmark-ISOMAP embedding for locally varying anisotropy, variogram modeling, and geostatistical estimation with Ordinary Kriging, Simple Co-Kriging (SCK) and Intrinsic Collocated Co-Kriging (ICCK) as well as Inverse Distance Weighted (IDW) Estimation. Model performance was assessed using Quantitative Kriging Neighborhood Analysis (QKNA) metrics and leave-one-out cross-validation (LOOCV), with a critical evaluation of LOOCV’s limitations.
Results demonstrate a significant relationship between water depth and Fe-Mn crust composition, with a significant improvement in estimation accuracy and confidence when water depth is used as the secondary variable in Co-Kriging, with SCK and ICCK providing more accurate and confident resource estimates than OK. ICCK also performed better than IDW. For the first time, tonnage calculations for metals in Fe-Mn crusts based on a 3D block model and real geochemical data are presented, highlighting Tropic Seamount’s potential as a substantial mineral resource for Europe. The workflow developed in this study, including ILR transformation and L-ISOMAP embedding, proved effective for handling compositional data and spatial anisotropy. The study also identifies methodological limitations, such as the need for improved variography, better sampling distribution, consideration of non-metallic elements, and more advanced cross-validation techniques. The assumption that the top 1 cm of crust represents the entire deposit is noted as a simplification, and future research should address vertical stratigraphy and sampling distribution.
The findings indicate that integrating ILR transformation and Landmark-ISOMAP embedding with Co-Kriging leads to better resource estimation for Fe-Mn crusts, enabling more confident and accurate assessments. This methodology offers significant potential for mineral resource exploration and future research in both marine and terrestrial environments.