Studies by the U.S. Geological Survey in Alaska, 2007
View southwestward from the southern outcrop of the Lakeview deposit across Lake 573 toward the Stack barite
occurrence. The white and dark knob in the center midground is an outcrop of limestone informally named the Stack.
Barite occurs in three low rubble and outcrop mounds a few meters to tens of meters north (to the right) of the limestone
outcrop.
Abstract
Longview and Lakeview are two of the larger stratiform barite deposits hosted in Mississippian Akmalik Chert in the Cutaway Basin area (Howard Pass C-3 quadrangle) of the southern National Petroleum Reserve, Alaska (NPRA). Geologic studies for the South NPRA Integrated Activity Plan and Environmental Impact Statement process included an attempt to evaluate the possible size of barite resources at Longview and Lakeview by using potential-field geophysical methods (gravity and magnetics).
Gravity data from 227 new stations measured by the U.S. Geological Survey, sparse regional gravity data, and new, high-resolution aeromagnetic data were forward modeled simultaneously along seven profiles perpendicular to strike and two profiles along strike of the Longview and Lakeview deposits.
These models indicate details of the size and shape of the barite deposits and suggest thicknesses of 15 to 24 m, and 9 to 24 m for the Longview and Lakeview deposits, respectively. Two groups of outcrops span 1.8 km of strike length and are likely connected below the surface by barite as much as 10 m thick. Barite of significant thickness (≥5 m) is unlikely to occur north of the presently known exposures of the Longview deposit. The barite bodies have irregular (nonplanar) bases suggestive of folding; northwest-trending structures of small apparent offset cross strike at several locations. Dip of the barite is 10 to 25° to the southeast. True width of the bodies (the least certain dimension) is estimated to be 160 to 200 m for Longview and 220 to 260 m for Lakeview. The two bodies contain a minimum of 4.5 million metric tons of barite and more than 38 million metric tons are possible.
Grades of the barite are relatively high, with high specific gravities and low impurities. The potential for the Cutaway Basin to host economically minable quantities of barite is uncertain. Heavy-mineral concentrate samples from streams in the area, trace-element analyses, and physicalproperty measurements of bulk samples derived from trenching or drilling would be valuable for future assessment work.
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