A PRELIMINARY INVESTIGATION INTO THE OCCURRENCE OF CARBONIZED WOOD IN THE CRIPPLE CREEK VOLCANIC COMPLEX

The Cripple Creek Mining District is one of the most important gold districts in the world. Historic, current and expected future gold production will be near 1,000 tonnes. The district is located between the towns of Cripple Creek and Victor in central Colorado where the dominant geologic feature is a 34-28 Ma diatreme-intrusive complex located at the junction of four Precambrian rock units. The main portion of the complex is 6.4 km long, 3.2 km wide and consists of a heterolithic diatremal breccia that has been intruded by stocks, dikes and discordant breccias. Early volcanic and intrusive rocks include alkaline phonolites, trachytes, phonotephrites and tephriphonolites, followed by later lamprophyres. During historic underground mining operations in the late 1890s, pieces of carbonized wood, logs, and trunks were encountered. Discoveries continued through the early 20^th century where 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 Cripple Creek 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.