By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
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Sandoval County, in northwestern New Mexico, is mostly west of the Rio Grande. Small amounts of gold and silver were produced from veins in the county, and copper has been produced from sandstone deposits. The gold and silver came from the Cochiti district in the foothills of the Valles Mountains, about 30 miles west of Santa Fe.
COCHITI DISTRICT
The Cochiti district was prospected in the 1870's or 1880's, but boundary disputes with Mexico dampened any early enthusiasm to locate claims. By 1889 much exploration was underway, resulting in the discovery of the Albemarle deposit in 1894. During a period of feverish activity from 1894 through 1904 more than $1 million in gold and silver was mined (Lindgren and others, 1910, p. 150).
In 1905 mining ceased and was never resumed except for brief flurries in 1914-16 and 1932-40. The district was mostly idle from 1941 through 1959. The total gold production through 1959 was about 41,500 ounces.
The country rock of the Cochiti district consists of sandstone of probable Cretaceous age which has been intruded and domed by monzonite and related porphyries, also probably of Cretaceous age. Overlying these rocks is rhyolite 500 to 800 feet thick of probable Miocene age (Lindgren and others, 1910, p. 151).
The ore bodies consist of quartz lodes as much as 150 feet wide in shattered and brecciated zones in the monzonite. Ore minerals extend into the wallrock, but nowhere do the veins extend into the overlying rhyolite (Lindgren and others, 1910, p. 153-162). Sphalerite, pyrite, and chalcopyrite are the most abundant sulfides, but argentite is probably the principal ore mineral. Galena occurs sparingly. Gold may be associated with the pyrite.
None of the base-metal sulfides was sufficiently abundant to be of economic importance. The deepest ore known in the district pinched out at a depth of about 600 feet.
