Detailed field and laboratory studies have resulted in the determination of a general paragenetic sequence of the minerals in the Tri-State ore involving 7 periods of mineralization, each characterized by its own mineral suite and sequence, and each separated from the next by a period of tectonic activity, a period of solution, a hiatus of deposition or by a return to the crystallization of earlier formed minerals. Local deviations from the general paragenetic sequence have been noted, but the recurrence of crystallization of several minerals has been found to be more common than previously believed. Chalcopyrite and pyrite were found to have been deposited during 8 intervals, sphalerite and marcasite during 6, and galena and quartz during 5. Significant variations in paragenetic sequence with areal or with stratigraphic distribution are absent. The authors interpret these paragenetic relationships to indicate repetitive deposition over a long period of time from ore-forming solutions that were remarkably uniform and not very different from the ground water circulating in the district today.