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You searched for: Creator Personal Names Leonard, Joseph W. Remove constraint Creator Personal Names: Leonard, Joseph W. All Creators Humphreys, Kenneth King. Remove constraint All Creators: Humphreys, Kenneth King. Subject Topical Mineral industries--Economic aspects. Remove constraint Subject Topical: Mineral industries--Economic aspects. Subject Topical Mineral industries--Safety measures. Remove constraint Subject Topical: Mineral industries--Safety measures. Subject Topical Mining engineering. Remove constraint Subject Topical: Mining engineering.

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