Date of Award
Master of Science (MS)
This study was done for the Erie Hining Company after periodic problems with the quality of pellets from taconit2 of the Biwabik Formation had been linked to the presence of carbonate minerals. The carbonates found in the cherty members of the Precambrian Biwabik Formation are predominantly siderite, ankerite, and calcite. Siderite is the only primary carbonate mineral and occurs in three forms: nicrogranular, granular (oolitic), and crystalline aggregates (recrystallized). Ankerite is a secondary mineral occurring as crystalline aggregates and alteration rims on granular siderite. Calcite is found only in fractures and fault zones. Siderite formed from the original precipitate and early in the diagenetic history of the rock. The alteration of siderite to fine-grained, euhedral magnetite appears to be the major part of the pellet-quality problem at Erie. The fine-grained magnetite causes small amounts of siderite to be incorporated with magnetite in the magnetic separation process. This siderite breaks down when the pellet is roasted and carbon dioxide is given of£ causing the pellet to disintegrate. Ankerite formed in two periods: the ankerite rims on siderite granules formed early in epigenesis and the crystalline ankerite formed much later. Calcite formed late in the epigenetic history of the formation. It appears that the carbonates of the cherty members of the Biwabik Formation can be used as indicators of an environment of deposition having reducing conditions and as indicators of the extent of metamorphism caused by the intrusion of the Duluth Gabbro.
Honeyman, Leslie R., "Description and origin of carbonate minerals in the upper and lower cherty members of the Biwabik Formation, Minnesota" (1973). Theses and Dissertations. 142.