The Empire Copper Company papers (including its predecessors, the White Knob Copper Company, White Knob Copper and Development Company, and Macbeth Lease, and its successors, Idaho Metals Company, Mackay Metals, and Mackay Exploration Company) are contained in 293 small file boxes, bound journals and letterbooks. Included are a great deal of correspondence, both corporate and personal, legal papers, scrapbooks, financial journals, and a variety of company reports.

The correspondence of the Empire Copper Company spans the years 1900 to 1946 and includes the routine business correspondence, letters ordering supplies and equipment, correspondence with the smelter and railroad, and official reports to government agencies. Among the more interesting letters are those between company officials detailing mine operations, and more especially the personal letters of the general manager, Frank M. Leland, from which one learns the early history of the mine.

Other material contained in this archival group includes leases, deeds, contracts, accident reports, articles of incorporation of Mackay Metals, several financial ledgers, a 1907 scrapbook containing newspaper articles about the company, information on stocks, cancelled checks, and various reports from departments of the company.

In addition to the Empire Copper Company papers there is also material relating to the investment company of Hobbs and Seeley, the Mackay Development Company, the Balaklala Copper Company in California, the Waldo Consolidated Gold Mine Company in Oregon, and several smaller mines with which either Frank Leland or LeRoy Eccles were associated.

This collection is extremely important for students of mining as it provides a virtually complete record of the operation of Idaho's largest copper mine during its most productive years.

The contents of this archival group are related in more detail in the following Description of Series.