Abstract: A mineralogical study by the Bureau of Mines and the University of Utah of the shale beds on the 1600 ft level of the Ophir Hill mine, Utah, disclosed that the micaceous minerals in the shale were altered as a function of proximity to the sulfide ore zones. The principal mineral in the shale distant from ore is 2M sericite. Within 100 ft along the bedding plane and 15 ft normal to the bedding plane, the sericite was altered successively to a modified form of sericite, two polymorphs of chlorite, and finally phlogopite.
A general sequence of the mineral changes from barren to ore-bearing ground was: (1) sericite; (2) modified sericite; (3) modified sericite and 7 Å chlorite; (4) modified sericite, 14 Å chlorite, and phlogopite; (5) 14 Å chlorite and phlogopite; and (6) phlogopite. This sequence of alteration of sericite in the shale was not noted in the mine areas barren of ore.