The hammer assembly completed the pilot hole with minimum wear and all tungsten carbide teeth intact. A pneumatic drill (with stiff foam), percussion hammer, foaming agent, polymers, and lubricants were used for the pilot wellbore. For the last two reamers (20 in and 24 in), the drilling fluid system was changed to a waterbased mud system.

The 205-m-long, 16-in-diameter pilot hole was completed in record time—3 d, in contrast with the anticipated 5–6 d in the hard rock and rubble. Time reduction was achieved due to our stiff foam formulation, which extends hammer life in abrasive ore formations such as lead glance (galena), quartz, and pyrite. Additionally, a hammer oil was applied to the air hose through a dispenser to protect the internal hammer assembly.