Sierra County, NM
— March 29, 2021
New Mexico offers a much wider variety of mineral collecting opportunities than my home state of Alabama. This is certainly the case with fluorescent minerals, a major focus of my mineral collection. One mine that offers attractive fluorescent material is the Dictator Mine, located near Winston in Sierra County. The Dictator Mine is a small, former producer of zinc, lead, copper, and silver. According to the 1934 NM Bureau of Mines and Mineral Resources Bulletin 10, which details the ore deposits of Sierra County, the deposit was known to prospectors as early as 1880. Relatively shallow underground workings chased ore hosted primarily in limestone of the Madera Group contacting Tertiary porphyritic monzonite, suggestive of a carbonate replacement deposit. Based on collected mine dump material, the ore contains mostly sphalerite, galena, and willemite (Zn2SiO4) with gangue calcite. Some sparse oxide ore can be found with colorful azurite and malachite. The real fun begins as the sun goes down, provided one is equipped with a shortwave fluorescent light. Various shades of fluorescent green willemite contrast strongly against bright orange fluorescent calcite. This assemblage is reminiscent of the ubiquitous dump material from the world famous zinc mines of Franklin and Sterling Hill, New Jersey. However, the Dictator Mine’s specimens pale in comparison to the mineralogically diverse and extremely aesthetic material that could be found in the New Jersey zinc mines. Other fluorescent minerals that can be found at the Dictator Mine include bright blue-white fluorescing hydrozincite (Zn5(CO3)2(OH)6), rare grey smithsonite (ZnCO3) that fluoresces pink/purple, and probable scheelite that fluoresces bright white. Phosphorescence can also be observed in the willemite; some continues to glow for several minutes. The primary activator of fluorescence at this deposit is manganese that substitutes in small amounts into the crystal structure of these minerals (save for the probable scheelite, which is an innately fluorescent mineral and requires no activator). As it continues to warm up, you may find me with some friends back in the hills near Winston hunting for other fluorescent minerals!
— Evan Owen, NMT M.Sc. geochemistry student, E&ES