Van Horn Sandstone, West Texas: An Alluvial Fan Model for Mineral Exploration

The Van Horn Sandstone in southwestern Culberson and southeastern Hudspeth counties, Texas was studied in cooperation with the United States Geological Survey in order (1) to determine the gold-bearing potential of this terrigenous rock body, (2) to ascertain the geological conditions which influenced deposition of the Van Horn, (3) to correlate heavy metal occurrence or concentration with particular facies of the Van Horn, and (4) to derive a process-defined depositional model with which areas of heavy metal occurrence could be predicted and to which similar terrigenous rock bodies may be compared. Composition of the Van Horn conglomerates was determined from field pebble counts. Thin sections of sandstones and matrix of conglomerates from the various facies were examined to determine any vertical or lateral variations in composition. In addition to studies of conglomerate and sandstone composition, clay-sized (< 2 m) materials for some of the muddy sandstones were analyzed by X-ray diffraction. Samples from each textural and structural type within each facies were analyzed for gold by atomic absorption method. Heavy mineral separates were made from sandstones and matrix of conglomerates of each of the facies; separates were studied by standard petrographic methods.