Update geus_mineral_occurrences.py citation

[twilamoon-science]

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Description

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Checklist

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• [ ] The PR description links to issues that it resolves with closes #{issue_number}
• [ ] Config lockfile updated (inv config.export > qgreenland/config/cfg-lock.json)
• [ ] Environment lockfile updated if needed (conda-lock)
• [ ] Version bumped if needed (bumpversion (major|minor|patch|prerelease|build))
• [ ] CHANGELOG.md updated (for user-facing changes)
• [ ] Documentation updated if needed
• [ ] New unit tests if needed