MCR-GeoChem: A harmonized, quality-flagged open compilation of whole-rock and mineral geochemistry for the 1.1 Ga Midcontinent Rift in Michigan, Minnesota, and Wisconsin
Abstract
Nickel, copper, cobalt, and the platinum-group metals are all on the final 2025 U.S. List of Critical Minerals, and the 1.1-billion-year-old Midcontinent Rift around Lake Superior hosts some of the largest domestic resources of them. The rock chemistry needed to study these systems is public but fragmented: it is spread across the U.S. Geological Survey (USGS) National Geochemical Database, project-level USGS data releases, the GEOROC compilation, and individual EarthChem datasets, each with its own units, method codes, and conventions for values below or above analytical limits. We present MCR-GeoChem v1.0.0, an open, versioned, reproducible compilation of 3,524 Midcontinent Rift samples and 168,748 geochemical determinations (88 analytes) from Michigan, Minnesota, and Wisconsin. Every value is converted to a common unit scheme (oxides in wt%, trace elements in ppm, Auand platinum-group elements in ppb) while retaining its original form; censored values are decoded into an explicit qualifier and limit; 89 source method codes are mapped to a common vocabulary of technique, digestion, and completeness; and each sample carries a rift-membership label tied to the USGS State Geologic Map Compilation. An open checker, mcrqa, adds value- and sample-level flags for below-detection results, uninformative detection limits, semi-quantitative and partial-digestion methods, unit errors, oxide-total problems, likely post-magmatic alteration, coordinate quality, and cross-source duplicates. The compilation shows that 27% of determinations derive from legacy semi quantitative emission spectrography, that 501 of 1,304 platinum results are below-detection values whose limits are too high to constrain the rock, and that 488 of 2,821 igneous whole-rock samples carry at least one alteration flag. The full pipeline rebuilds the release from public sources with identical results. The dataset, the method and detection-limit crosswalk, and the checker are released under open licenses to support critical-mineral research in the Lake Superior region.
Related
- Prospectivity model for magmatic Nickel, Copper, Cobalt, and Platinum-Group Elements in the Midcontinent Rift
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- Ultramafic weathering in tropical volcanic arcs: Geochemistry and inverse modeling of rivers draining the Zambales Ophiolite Complex (ZOC), Philippines
- Surface Geochemistry of Natural Hydrogen: Modelling of Soil Artefacts Versus Active Hydrogen Seeping
- Sedimentology and geochemistry of the Pleistocene-Holocene fluvial-lacustrine colluvial sedimentary sequence in the Pegalan River section, NW Borneo: Implications for regional tectono-climatic conditions and landscape evolution
BibTeX
@misc{danso2026mcrgeochem,
title = {{MCR-GeoChem: A harmonized, quality-flagged open compilation of whole-rock and mineral geochemistry for the 1.1 Ga Midcontinent Rift in Michigan, Minnesota, and Wisconsin}},
author = {Bezali Kwame Danso and Saadatu Abdullah},
howpublished = {EarthArXiv},
year = {2026},
month = oct,
doi = {10.31223/x5zv47},
url = {https://eartharxiv.org/repository/view/15631/},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - MCR-GeoChem: A harmonized, quality-flagged open compilation of whole-rock and mineral geochemistry for the 1.1 Ga Midcontinent Rift in Michigan, Minnesota, and Wisconsin
AU - Bezali Kwame Danso
AU - Saadatu Abdullah
PY - 2026
DA - 2026/10/21
PB - EarthArXiv
DO - 10.31223/x5zv47
UR - https://eartharxiv.org/repository/view/15631/
AB - Nickel, copper, cobalt, and the platinum-group metals are all on the final 2025 U.S. List of Critical Minerals, and the 1.1-billion-year-old Midcontinent Rift around Lake Superior hosts some of the largest domestic resources of them. The rock chemistry needed to study these systems is public but fragmented: it is spread across the U.S. Geological Survey (USGS) National Geochemical Database, project-level USGS data releases, the GEOROC compilation, and individual EarthChem datasets, each with its own units, method codes, and conventions for values below or above analytical limits. We present MCR-GeoChem v1.0.0, an open, versioned, reproducible compilation of 3,524 Midcontinent Rift samples and 168,748 geochemical determinations (88 analytes) from Michigan, Minnesota, and Wisconsin. Every value is converted to a common unit scheme (oxides in wt%, trace elements in ppm, Auand platinum-group elements in ppb) while retaining its original form; censored values are decoded into an explicit qualifier and limit; 89 source method codes are mapped to a common vocabulary of technique, digestion, and completeness; and each sample carries a rift-membership label tied to the USGS State Geologic Map Compilation. An open checker, mcrqa, adds value- and sample-level flags for below-detection results, uninformative detection limits, semi-quantitative and partial-digestion methods, unit errors, oxide-total problems, likely post-magmatic alteration, coordinate quality, and cross-source duplicates. The compilation shows that 27% of determinations derive from legacy semi quantitative emission spectrography, that 501 of 1,304 platinum results are below-detection values whose limits are too high to constrain the rock, and that 488 of 2,821 igneous whole-rock samples carry at least one alteration flag. The full pipeline rebuilds the release from public sources with identical results. The dataset, the method and detection-limit crosswalk, and the checker are released under open licenses to support critical-mineral research in the Lake Superior region.
ER -