This includes all mining establishments (firms) with at least one-hundred employees or more that were in operation at any time during the year.

These establishments consist of paid full-time and part-time employees on the payrolls during any part of the pay period which included the 12th of March. They include salaried officers and executives of corporations; employees on paid sick leave, paid holidays, and paid vacations; not included are proprietors and partners of unincorporated firms.