By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Colfax County, which lies just south of the New Mexico-Colorado border, has been an important source of lode and placer gold. Small quantities of silver, copper, and lead have also been mined. The metal mining districts in Colfax County are centered in the Cimarron Range which is along the western edge of the county. Martin (1953, p. 645) reported a total gold production for Colfax County through 1952 of 282,717 ounces. This may be too low; the amount credited to the two principal districts in this report totals about 358,000 ounces through 1959.
The most productive placer deposits are in the Moreno Creek valley near Elizabethtown on the west side of the Cimarron Range, and the most productive lode deposits are in the Baldy (Ute Creek) area on the east side of the range, east of the Elizabethtown district.
Copper float, found by an Indian on the upper slope of Baldy Peak, was exhibited at Fort Union early in the 1860's (Graton, in Lindgren and others, 1910, p. 92-93). This was the first mineral discovery in the Elizabethtown-Baldy district, and some of the men stationed at the fort located claims where the float had been found. In the fall of 1866, men sent by the owners to do assessment work did some panning along Willow Creek and discovered rich placer deposits; a boom followed in the spring of 1867. Although some locations were made on lodes, including the famous Aztec lode, most were on placers. To provide sufficient water for placering, a ditch about 41 miles long was dug from the headwaters of the Red River and was completed in 1868.
The placer deposits along Grouse and Humbug Gulches, tributaries of Moreno Creek, each yielded more than $1 million in placer gold and silver. Another $2 million worth of placer gold and silver was recovered from the valleys of Moreno and Willow Creeks (Anderson, 1957, p. 38-39), and some gold also came from the gravels along Ute Creek. Graton (in Lindgren and others, 1910, p. 93) estimated the placer production of the Elizabethtown-Baldy district prior to 1904 at $2.5 million, and C. W. Henderson (in U. S. Bureau of Mines, 1929, pt. 1, p. 740) estimated the production through 1929 at about $3 million (145,138 ounces). The total placer production through 1959 was about 146,980 ounces.
Most of the lode gold of Colfax County has come from the Baldy area. Graton (in Lindgren and others, 1910, p. 93, 97) estimated production at about $2 million (96,760 ounces) through 1903. The Aztec mine, discovered in 1868 and one of the oldest and richest gold mines in the State, accounted for more than half of the early output. The lode mines were virtually idle from 1941 through 1959. Through 1959, total lode production was about 221,400 ounces, and total lode and placer production was 368,380 ounces.
The Cimarron Range consists of eastward-tilted and faulted sedimentary rocks - the Pierre Shale of Cretaceous age and the Raton Formation of early Tertiary age. These two formations are separated by an unconformity and both are intruded by dikes and sills of quartz monzonite porphyry (Lee, 1916, p. 327-329).
The principal ore bodies are in pockets and stringers in the basal conglomeratic sandstone of the Raton Formation along the unconformity. Much ore is in the underlying Pierre Shale, as much as 5 feet below its contact with the Raton Formation. Minute fissures filled with ore minerals interlace the shale and extend upward into the conglomerate. The gangue is mainly calcite, and ore minerals are pyrite, chalcopyrite, sphalerite, and possibly galena. Native gold is present as wire gold and irregularly shaped masses (Lee, 1916, p. 329-330). Most of the deposits are associated with the porphyry intrusive bodies. Chase and Muir (1923, p. 272) noted that some ore bodies are in contact metamorphic deposits in calcareous rocks adjacent to quartz monzonite porphyry. These are few in number and have been less productive than the veins.
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