Westward’s geology group was responsible for designing and performing a limited exploration project at a site located in the foothills east of El Paso, Texas. The primary target was the Hueco Limestone formation, which is actively mined by other operators in the region for the production of aggregate products. However, prior to this project, no subsurface exploration had been conducted at the Site.
The Site encompasses approximately ~440 acres and features more than 500 feet of topographic elevation change. The region exhibits a complex geologic history, characterized by multiple episodes of tectonic activity, settlement, and weathering. The Hueco Limestone at this location is documented to exceed 5,000 feet in thickness and comprises several distinct stratigraphic units.
Current quarry activities are limited to extracting hard limestone present at the surface along the eastern flank of the foothills, near the property boundary, where stripping was limited. No exploratory drilling had been performed prior to mining so only the surface rock was being quarried. The depth and extent of the formation in the subsurface was unknown.
During Westward’s initial site visit, notable features included near vertical bluffs along the eastern boundary. This appearance was in stark contrast to the more rounded and uniformly weathered hills in the immediate vicinity. It appears vertical movement had occurred here in the distant past creating a possible fault scarp of ~200 ft. tall.
The first location cored was in the flats near the toe of the bluffs just south of the active mine area. The client did not expect there to be any rock present in the subsurface in this area, which is why there had not been any mining there, or in any of the other ‘flats’ areas west of the bluff.
Hard, cohesive dolomitic limestone was encountered at roughly 10 ft. below ground surface. Apart from a few, relative thin shaley intervals scattered throughout, the hole was completed at 200 ft. while still in the dolomitic limestone. This supported the theory that the near vertical bluff was indeed a fault scarp.
The second location cored was in the lowest level of the mine to a depth of 400 feet to establish an inferred lower limit of hard rock in the active extraction area. As in the first hole, hard, dolomitic limestone, with some scattered shale, was encountered all the way down.
The northern most core hole in the flats encountered overburden in the form of sand, silt and clay to a depth of 68 feet where fault breccia was then observed. At this depth, the material turned into the same hard, dolomitic limestone, as encountered in the other coring locations, to a depth of 200 feet. The presence of the breccia also supports the theory of faulting in this area.
The client had a rotary hammer rig that was used to drill holes for blasting. Westward drilled ten (10) holes, to approximately 60 feet each (max depth the rig could drill), to help delineate the top of the hard rock to the west. One of the rotary holes was drilled adjacent to Core Hole 1 to help calibrate the driller on the target conditions we were seeking.
Of the 10 hammer holes drilled, five (5) encountered the top of the hard rock between 4 feet and 17 feet. A minimum of 10 feet was drilled into this layer to check for cohesiveness. The results from the coring and air rotary drilling allowed Westward to partially delineate the western horizontal extent of the hard rock. The vertical extent of the target formation was not delineated during this limited exploration event. Total depths drilled were used in modeling the thickness of the mineable unit.
This exploration initiative provided critical subsurface data to drive decisions in planning for future development. A life of mine time frame as well as an initial economic value of the mine were also determined based on the exploration data collected.