New Mexico Mineral Symposium — Abstracts

Since its discovery in 2005, Mina Herradura in Sierra County has continually produced amazing "Herkimer" style quartz crystals from quartz-calcite veins in the Cretaceous Mesa Verde sandstone. Mineralization appears to have exploited a regional structural architecture of extensional faults within the Jornada de Muerto basin. Abundance of organic material within the host sandstone allowed infiltrating fluids a high silicic acid chemistry that precipitated double terminated quartz crystals at temperatures more amenable to chalcedony formation (100°C) based on fluid inclusion evaluation. Multiple species of hydrocarbons are also present and inclusions and bubbles are responsible for the UV fluorescence of certain samples. The "Covid Leap Year Pocket" uncovered in February 2020 has to date produced the largest, finest, and most impressive specimens from the property.

The Magdalena district of Socorro county has an infamous mining history and is best known for the wonderful blue smithsonite from the Kelly mine. The nearby Graphic mine tailings (privately owned) have been very productive over the past several years as well. Very nice cabinet specimens of azurite and malachite can still be found with permission of the owner. If you venture beyond these popular areas and go "off the map" there are treasures to be found. A few years back, in the scrub brush of the steep mountain cliffs I located a deposit of large (up to 6 inches) double terminated prismatic milky quartz crystals. This was unusual as most quartz in the district are of a pyramidal morphology in Pennsylvanian limestone. These specimens, however, were extracted from a rare quartz arkosic unit interbedded within the limestone. I hypothesize that the mineralizing fluids deposited this anomalous prismatic morphology due to chemical and thermodynamic changes as they interacted with the arkose host rock as opposed to the limestone.

The Sierra Ladrones in Socorro County have long served as a legendary location of hidden gold, thieves hideout, and a buried silver altar stolen from a local church. With good reason; it is hot, cactus laden, bug infested, no shade, no water, always uphill, rattlesnakes, and a great spot to hide treasure near the Camino Real. Due to federal and private property ownership it is not very accessible. Mina Rosita is a new prospect on the steep slopes of the peak that produces milky, strawberry, and amethyst quartz crystals. It is an unusual deposit hosted in a rapakivi granite gneiss with a spectrum of quartz colors. In one area, complex double terminated milky quartz specimens up to two inches in length are suspended in a carbonate powder down to a minimum of four feet in depth. This is enigmatic as I had presumed it was a kaolinite alteration by-product of the fluid-granite interaction until I poured some acid on it out of curiosity and it fizzed.

Catron County is host to the commonly known "Luna Agate" used for lapidary and the occasional crystalline quartz specimens. Nearby, "Luna Leopard" agate reveals a very complex paragenesis of phreato-magmatic clastic pumice injection into Tertiary volcanic host rocks and subsequently altered to a celadonite-gmelinite zeolite association followed by silicification. In some areas quartz overgrowths of dog tooth calcite and stalactitic quartz specimens are present.