A dredge-dragline equipment combination is being used to remove over 32 meters of overburden and to recover 13 meters of phosphate ore at Texasgulf’s Lee Creek Mine. The area is a low-lying swampy terrain only about three meters above mean sea level. Over eight million tons per year of this clayey ore are presently being mined.
Mining began in 1966 as an all-dragline method using a single dragline with a bucket capacity of 55 cubic meters. In 1976 a second dragline (38-cubic -meter-capacity) was put into service. In the original mining method, 30 meters of overburden were stripped in two separate cycles. The top 12 meters of unstable sediments, mostly Pleistocene in age, were dug as chopdown (Fig. 1). The draglines were established at nine meters below mean sea level and dug above their bases, spoiling the material in the adjacent mined-over strip. The lower 18 meters of overburden (Tertiary) were then stripped In the conventional method and spoiled. In a third cycle, 13 meters of ore were recovered and cast to the surface to be slurried and pumped to the beneficiation plant.
The upper 12 meters of overburden, composed of Irregularly bedded silty clays, peat, oozy silts, sand and shell presented a severe problem for dragline handling. All these sediments were saturated; the sands released large quantities of water, and the uncompacted silts and clays frequently flowed as mud slides. The undisturbed material would not support the ore piles, which frequently failed and inundated the dragline on the mining
Figures & Tables
Southeastern United States–Guidebook is comprised of twelve field trips that were organized for the Third Annual Midyear Meeting held in Raleigh, North Carolina in 1986. The spectrum of geologic time represented in the Upper Precambrian, Lower Paleozoic, Mesozoic, Cenozoic and the very Recent. The geologic provinces are the Valley and Ridge, Blue Ridge Mountains, Piedmont, and the Coastal Plain. Besides North Carolina, trips include Virginia, South Carolina and West Virginia.