ORIGIN OF GYPSUM IN LIGHT OF A NEW 3-D GEOLOGIC MODEL OF THE CASCADE TACONITE DEPOSIT, MARQUETTE IRON DISTRICT, MICHICAN

The Cascade taconite deposit is a significant untapped mineral resource in the Marquette Iron District of Michigan. Historically, this deposit was mined on a small scale between 1872-1934. The study area is located within the Palmer Basin, situated ½ mile ESE of Palmer in Michigan's Upper Peninsula. Currently, there are two active iron mines operating near the Cascade deposit. This study incorporates 40,000+ m of drill core data, iron ore assays and bench scale testing into a 3-D geologic model of the deposit. The deposit lies entirely within Negaunee Iron Formation (approximately 2.2 Ga.) and consists of layers of silicates inter-bedded with various iron minerals including hematite, martite, magnetite, goethite and siderite/ankerite. The Negaunee Iron formation also locally contains distinct volcanic, intrusive, and clastic lithologies that are used as marker horizons and have important genetic implications. Structurally, the Palmer Basin is a large syncline that is broken into separate compartments by at least 4 individual fault systems. Gypsum is present in the deposit and its distribution is important because its solubility impacts selective flocculation in the proposed benefaction process. The abundance of gypsum was determined by quantitative XRD to a lower detection limit of about 0.1 weight %. The maximum amount of gypsum was calculated by the abundance of sulfur. The 3-D distribution of gypsum was mapped in relationship to the overall geologic model. Initial results show that there are higher concentrations of gypsum in the eastern end of the basin, but the gypsum abruptly disappears below the detection cut-off of 0.1% towards the west. A possible explanation for this may be control by a fault or other structure. Overall, the gypsum is probably related to paleo-water levels that fluctuate. This study was made possible with the assistance of the Cleveland Cliffs Mining Service Company, a subsidiary of Cleveland-Cliffs Inc.