New Mexico Mineral Symposium — Abstracts

The Fierro-Hanover mining district in Grant County, southwestern New Mexico, is one of the state's more productive mining areas, having seen nearly continuous production of base metals, precious metals, and iron for more than a century.

The entire district is contained within the roughly triangular-shaped features known as the Santa Rita horst, which is sharply bounded on the northwest by the Barringer fault, on the northeast by the Mimbres fault, and less distinctly on the south by the Groundhog and Nancy faults. The intrusion of the Fierro-Hanover granodiorite stock uplifted and fractured the sedimentary rocks in the district. These fractures provided channels through which the mineralizing solutions invaded the limestones and formed the extensive contact-metamorphic and skarn deposits in the Combination, Princess, Kearney, Empire, and Pewabic mines in the southern and central parts of the district and the Union Hill iron deposits and the Continental mine at Fierro in the northern part.

These and other smaller mines have produced a total of more than a billion pounds each of copper and zinc, 50 million pounds of lead, 5 million ounces of silver, and 50,000 ounces of gold. The district is the state's leading producer of iron ore totalling some 8¹/₂ million short tons. Concurrent with the production has come a long and colorful mining history beginning in ca 1858 with German metallurgist Sofio Hinkle at the old Hanover mine near present-day Fierro. The richest copper ores, some grading 58% Cu, were produced here until the Civil War.

The Hanover and other mines have produced an abundance of collectible mineral species including quartz, calcite, selenite, magnetite, native copper, and turquoise, as well as wide variety of copper oxides and sulphides. Excellent specimens are still produced occasionally at the currently active Continental mine, the Union Hill iron pits, and until recently, the mines along the Barringer fault north of Fierro.