Page 124 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

MINING DISTRICTS 123
with abundant manganese oxides and limonite, and in the shaft much of the ore is found in a soft, highly decomposed limestone stained with iron and manganese oxides. West of this shaft for 3,000 feet the contact has been exposed by shallow pits and shafts and by short drifts and tunnels. In all openings the ground is impregnated with contact-metamorphic minerals, and ore miner- als are present in notable quantities. For the entire distance of over 6,000 feet along the length of these claims the limestone adjacent to the intrusive porphyry is contact-metamorphosed and well mineralized.
CONFIDENCE GROUP
About 3,000 feet west of the Covington ground, and on the
west side of the mountain, the Confidence group of six claims has been located in the limestone overlying the porphyry along and adjacent to a northerly trending dike of rhyolite. In one place on the group a 250-foot tunnel, 65 feet of crosscuts and a short winze constitute the development work, and in another place an 80-foot tunnel has been driven and a 50-foot shaft sunk. Seme ledges of magnetite and hematite on this group are similar in ap- pearance to those in the northern end of the mountain. Associ- ated with these are other contact-metamorphic minerals, and in places there are good showings of the sulfides of copper and iron, with accompanying oxidation products such as malachite and chrysocolla.
RIFLE SHOT GROUP
This group of claims includes an area of limestone that un- derlies the monzonite porphyry sill on the west side of the moun- tain. The ore occurs along the tops of minor folds in the lime- stone, in fractures that strike slightly north of east. Oxidized ores shipped to the smelters in Chloride and Fairview in early days are described as being of very high grade. Sulphide ores encountered at some distance from the outcrops down the pitch of the ore shoots are said to contain 10 to 12 per cent copper. It is stated that there are in this group large areas of mineralized ground that have not yet been adequately explored. The extent of the underground workings could not be ascertained.
TIN DEPOSITS
On the east slope of the Sierra Cuchillo and overlooking the
valley in which the small village of Monticello is situated, the rocks consist of a thick succession of rhyolite flows, agglomerates and tuffs, dipping gently to the northeast and finally disappear- ing under the gravel that composes the alluvial fans and degradi- tional plains on the west side of the Alamosa River. One of these flows consists of flow-banded rhyolite, glassy in places, and hav- ing a much crackled appearance which may have been caused from rapid cooling. Surges in the flow caused fracturing of the solidified crust, and molten rhyolite from the interior of the flow- ing mass welled up through these cracks to form small dikes.