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 cr ........

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

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