New Mexico Mineral Symposium — Abstracts

Gold has been produced from the Cripple Creek mining district since its discovery in 1891. Historic production from underground mines and small, shallow surface mines is approximately 20 million ounces (622 tonnes) of gold. Recent gold production, since 1995, by Cripple Creek and Victor Gold Mining Company (a wholly-owned subsidiary of AngloGold Ashanti, Ltd.) is nearly 4.5 million ounces (140 tonnes). Current reserves include 5.9 million contained ounces (184 tonnes) of gold while the exclusive resources include an additional 7.0 million ounces (218 tonnes). This puts the total district endowment at nearly 37 million ounces (1,164 tonnes) of gold. This endowment makes Cripple Creek one of the most important gold districts in the world.

All ore tons are currently processed on the Valley leach facility where a dilute solution of sodium cyanide is percolated through the crushed rock. The gold goes into solution, and this pregnant solution is collected and pumped to the recovery facility. The leach pad currently holds over 300 million tons of rock. It will be filled with ore tons in late 2015 when it reaches its capacity of 400 million tons. Annual gold production from the operation is approximately 260,000 ounces.

Exploration activities have successfully replaced depletion for several years, and sufficient reserves exist to justify the construction of a second Valley leach facility. The construction of the second leach pad, with a capacity of 218 million tons, is currently underway, and the first gold will be poured from the new pad in 2016. In addition to this project, a new mill is also under construction to process higher-grade material and to increase gold recoveries with a gravity circuit, flotation, and CIP.This mill will process nearly 2.0 million tpa (tons per annum) of higher grade/lower recovery material that is intersected in the open-pit mining operations.

Mining activities are currently permitted to 2024 as this will allow the construction of both the second leach pad and the mill. Opportunities exist to add additional years to the mine life if exploration is successful. These opportunities include the re-introduction of underground mining in the district.

During historic underground mining operations in the late 1890s, pieces of carbonized wood, logs, and trunks were encountered. Discoveries continued through the early 20th century when additional carbonized wood specimens were found in several underground mines in the district. In 2003, the deep directional drill program beneath the main Cresson surface mine, yielded a core sample of diatremal breccia from a depth (beneath the surface) of 938 m that hosted a fossil wood fragment. Since then, much larger specimens (up to 15 cm long) of carbonized wood were found in the same general mine area at a shallower depth (152.4 m below the surface). This recent discovery was on the north side of the Cresson pipe, a late-stage, lamprophyre breccia near the center of the largest open-pit mine.

The occurrence of these carbonized wood specimens, and other pieces of petrified wood found in various locations on the surface, suggest that trees were growing during periodic lulls in the volcanic activity. Succeeding explosive volcanic events and the subsequent subsidence likely incorporated trunks, branches, and other organic debris into the resulting diatremal breccia. Further studies are being planned on the carbonized wood to determine the metamorphic temperatures to which they reached, including Raman spectra analysis.

Cripple Creek and Victor Gold Mining Company (CC&V) supports historic preservation in the district. They put the Independence Headframe and Mill on the National Register of Historic Places, relocated the Cresson headframe and ore sorting house, relocated and preserved the Hull City headframe and ore sorting house, moved the Gold Sovereign headframe to the Cripple Creek district museum, and they maintain a display of historic mining equipment at the Victor Lowell Thomas museum. Through their partnership with the Southern Teller County focus group, CC&V preserves historical sites throughout the mining district and provides public access to some of those areas. Five trails have been developed by the focus group on CC&V property.

The Cripple Creek district museum houses a fantastic collection of photographs and other ephemera, as well as tools, costumes, house wares, and Victoriana relating to the district's rich late-19th- and 20th-century mining history. Included is a large (not yet fully inventoried) collection of mineral and rock samples from the district and elsewhere. The collection contains excellent examples of the district's ores and other minerals, as well as the original rock specimens collected by Whitman Cross and R.A.F. Penrose, Jr. when compiling their historic work on the district's geology.

In 2012, three semi-retired geologists, Carl Carnein, John Rakowski, and Steven Veatch, began the task of developing an inventory and computer database that documents this collection. Once or twice a month, they meet with a museum docent and fully describe, measure, photograph, and number specimens. This work requires careful examination of each specimen, which often involves discussions of identities among the participants. Many of the district's telluride minerals cannot be identified by eye, and we consider this to be a preliminary inventory. Thus far, we have inventoried about 300 specimens, and we estimate that the work will take several more years.

Thanks to financial help from CC&V and support from the staff of the Cripple Creek district museum, we hope to help the museum to make its geologic collections accessible and available to future generations of scientists, historians, and the interested public.