Paper No. 2-11
Presentation Time: 11:40 AM
DEVELOPMENT OF AN INDUSTRIAL MINERALS DEPOSIT IN EASTERN LATAH COUNTY, IDAHO, PROCESSING PRIMARY CLAY TO PRODUCE PRODUCTS OF QUARTZ, K-FELDSPAR, KAOLINITE, AND HALLOYSITE
The Bovill Kaolin Project of I-Minerals Inc. features the exploration of a clay-quartz-feldspar deposit for more than 10 years in an old clay-producing district located about 5 miles northwest of Bovill in Northern Idaho. The deposit is hosted within the Thatuna Granodiorite of Cretaceous age, interpreted to be a lobe of the Idaho Batholith injected into Precambrian metamorphic terrane. Miocene basaltic lavas dammed streams and created lakes in the area, which was subsequently subjected to an intense period of tropical weathering during the later Miocene. Earlier lithologies were deeply weathered, particularly and most importantly the granodiorite, forming a primary clay. Clay layers in the Latah formation resulted from erosion of the primary clay and deposition of sediments into the lakes.
I-Minerals is focusing efforts on the weathered granodiorite that occurs typically along the ridges in order to streamline permitting by avoiding wetlands. During weathering, Na-spar is altered to clay, while the K-spar is residual and more resistant. The Na-spar weathers to kaolinitic clays, mixtures of halloysite and kaolinite. The four mineral components to be upgraded by processing are quartz, K-spar, halloysite, and kaolinite. A sand circuit in the plant includes a flotation process to float the K-spar. Grinding to <30-mesh liberates most of the K-spar and yields a product containing K 2 O as high as 13% and less than 0.1% Fe as Fe 2 O 3 . Quartz is the sink product in the flotation process. Three quartz products can be produced with an additional flotation step per product. The three products can be targeted to contain SiO 2 abundances, for example, of 99.85%, 99.92%, and 99.97%. The latter product contains around 300ppm non-SiO 2 contaminants. Grinding to <50-mesh is required to liberate all the quartz, and the presence of mineral and fluid inclusions must be at a minimum to reach that high purity. The halloysite can be upgraded to a 90%+ purity product. This deposit yields halloysite with a high aspect ratio that is low in heavy metals, characteristics that make it advantageous for many different high value markets, especially cosmetics and pharmaceuticals. The kaolinite fraction is calcined at about 900°C to produce a metakaolin that makes an excellent pozzolan for cement. Over 200,000 tons of total products will be sold each year.