By A. H. KOSCHMANN and M. H. BERGENDAHL - USGS 1968
Santa Fe County is in north-central New Mexico, along the western edge of the Great Plains physiographic province.
Gold has been mined from placers and lodes along the western boundary of the county in the Cerrillos Hills, Ortiz Mountains, and San Pedro Mountains. These ranges are circular in outline and were formed by doming of Carboniferous and Cretaceous sedimentary rocks by laccolithic sheets of Tertiary monzonite porphyry (Lindgren, in Lindgren and others, 1910, p.163-165).
Gold placers were mined as early as the 1830's; therefore, the early production can only be estimated. The principal gold districts are the Old Placer and the New Placer; each produced an estimated $2 million in gold (Lindgren, in Lindgren and others, 1910, p. 75, 168). Total county gold production through 1959 probably was between 150,000 and 200,000 ounces.
NEW PLACER DISTRICT
The New Placer (San Pedro) district is on the west side of the San Pedro Mountains between the towns of San Pedro and Golden. Most of the gold production came from placers that were mined before 1880, but after 1904 there was also an appreciable output of lode gold. The placer deposits were discovered in 1839 (Lindgren, in Lindgren and others, 1910, p. 174), 11 years after those of the Old Placer district were discovered. The placers are in Lazarus Gulch and in branches of Tuerto Creek near Golden on the west side of the mountains.
It has been estimated that the New Placer district produced about $2 million (96,759 ounces) from beginning of production to 1904 (Lindgren and others, 1910, p. 75). This figure represents chiefly placer gold but it may also include some lode gold; figures on lode production before 1904 are not available. From 1904 through 1957 the district produced 2,931 ounces placer gold and about 16,000 ounces of lode gold. Total gold production was about 115,700 ounces. There was no recorded production from 1957 through 1959.
The San Pedro Mountains consist of Carboniferous formations at least 700 feet thick intruded by a laccolith, sheets, and dikes of monzonite and related porphyries probably of Late Cretaceous or early Tertiary age (Lindgren and others, 1910, p. 170-175). Numerous small gold-bearing veins, containing quartz, calcite, pyrite, and free gold, occur both in the porphyry and in the sedimentary rocks. In the lower part of the laccolithic roof are found small copper-bearing contact metamorphic deposits, and in limestone farther away from the igneous contact are found replacement deposits rich in galena.
The placer gold is found in alluvial fans along the mountain front and in the gravels of streams that have reworked the alluvial fans.
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