The Summit Mine and Steeple Rock District lie on the southern edge of the mid-Tertiaryage, Datil-Mogollon volcanic field. The volcanic sequence comprises up to 8,000 feet of highly diverse volcanic and volcaniclastic rocks representing multiple eruptions from different vents. Thick sequences of andesitic and dacitic lava flows are interbedded with volcaniclastic and fluvial sediments. The flow rocks are typically porphyritic. Numerous high-silica rhyolites (Miocene-age) have intruded the lava flows. Thin tuffaceous units are associated with some of these intrusive bodies. The rock units generally trend northwesterly and dip moderately to gently to the northeast.

Small outcrops of Precambrian igneous rocks, Cretaceous sedimentary rocks and Cretaceous-Eocene sedimentary rocks crop out south of the district. Although these rocks are not exposed in the Steeple Rock district, they probably underlie the thick Tertiary volcanic sequence exposed in the district.

Gold and silver mineralization occur in an epithermal, low-sulfidation system containing less than 1% very-fine-grained, disseminated pyrite and trace amounts of galena, sphalerite and chalcopyrite. Most of the gold and silver mineralization occurs as grey streaks of finely-divided sulfide minerals in brecciated quartz and other siliceous material. Lesser amounts are associated with calcite. Brecciation and silicification have occurred in multiple episodes. Chalcedonic banding is common and late-stage crystalline quartz, frequently amethystine, fills vugs. Oxidation in the form of iron and manganese oxides is prevalent throughout the mineralized zone and is quite strong in the Inspiration level (elevation 5750 feet). At the water table (elevation 5300 feet), oxidation, although still present, is greatly reduced.

The Summit gold-silver deposit is a structurally controlled, vein-type deposit occurring in the lower footwall portion of a 50- to 100-foot-wide, steeply dipping, siliceous fault breccia within a segment of the northwesterly striking Summit fault. A flexure in the structure may have provided some of the conduits for ascending mineralizing solutions. The model for the deposit is a low-sulfidation, epithermal system in which gold and silver mineralization associated with silica were deposited within an approximate 1000-foot vertical zone governed by temperature and pressure. Above this zone the system is notably calcareous, and the mineralization is low grade and erratically distributed. Below the mineralized zone, on the basis of limited drilling, the structure appears to be virtually barren.

The Summit Mine is an underground operation in an advanced stage of development. At full production, the mine is expected to produce 144,000 tons per year. The mine is operated utilizing mobile, rubber-tired, diesel equipment.

The development plan for the Summit Mine is based on a vertical, long-hole-stoping method. Some of the Resource Blocks may be better suited to a more selective mining method. The S-2 stope, which is smaller, narrower, and higher grade, has been developed for cutand-fill mining. The block will be mined from bottom to top with waste development rock being used for fill.

Some lenses of above-cutoff-grade mineralization with widths of 8 feet or less occur in close proximity to the minable resources. These likely will be mined with jack-leg drills or with single-boom jumbos designed for narrow widths

Processing involves crushing run of mine material through a jaw and cone crusher in closed circuit with a triple-deck screen. The ball mill feed material is crushed to minus 1/4 inch while the smelter flux is sized to minus 3/8 and plus 1/4 inch. Fines remaining from crushing of flux are added to the mill feed stockpile.

Mine-run material is fed by front-end loader into a portable, two-stage, Cedar Rapids crushing-screening plant. A nominal minus 3/8-inch product is stockpiled by a stacker conveyor over a mill feed reclaim tunnel. Storage capacity is about 4000 tons. The crushing plant has a 25 x 40-inch jaw crusher and a 45-inch cone crusher operating in a closed-circuit system.

Vibrating feeders in the mill feed reclaim tunnel place the fine crushed material onto a conveyor for transport to a 7-ft x 10-ft, 300 H.P., rubber-lined ball mill where the feed is ground to a nominal 80% passing 100 mesh. The ball mill discharge goes to a conditioner tank and then to banks of Denver flotation cells including roughers, scavengers and cleaners. The flotation concentrate is pumped to a 24-ft x 10 ft-diameter, concentrate thickener for storage and thickening.