Laserfiche WebLink
• the surrounding granitic rocks. The volcanic rocks, consisting primarily of phonolites <br />and volcanic breccias (volcanoclastic sediments to coarse heterolithic eruption breccias), <br />occupy a diatreme, which has the general aspect of asleep-walled crater with a crudely <br />elliptical outline at the surface. More recently, Birmingham (S.D, 1990, Petrology a~tcl <br />Rb-Sr Isotope Chemistry of Alkaline Rocks of the Cripple G-eek I~olcmiic Field. <br />Colorado, Contributions to Mineralogy and Petrology) has used the following li[hologic <br />designations for the Tertiary alkaline rocks of the District: Phonolite, Plagioclase <br />Phonolite (lathe phonolite), Tephriphonolite (syenite), Phonotephrite (trachydolorite), <br />Lamprophyre (alkali basalt), and Breccia. Much of the breccia is cemented by a <br />dolomitic carbonate, which, with small pyrite crystals, has replaced the original mineral <br />fragments and impregnated the other minerals. (See, e.g., Covering, T.S. and E. N. <br />Goddard, 1950. Geology and Ore Deposits of the Front Range Colorado; U.S. <br />Geological Survey Professional Paper 223, p. 292; Pontius, Jeffery A., 1996. Field <br />Guide Gold Deposits of the Cripple Creek Mining District Colorado, USA). The <br />dolomitic carbonate plays a major role in the ground water chemistry of the area, as <br />• evidenced by the alkaline nature of water draining from the Carlton Tunnel. <br />The mineralogy of the Main Cresson Mine area is quite diverse. Intrusive and <br />breccia lithologies spanning the entire alkaline suite from leucocratic phonolites through <br />ultramafic lamprophyres occur in the Main Cresson Mine area. Volumetrically, the main <br />lithologies are volcanic breccia, phonolitec breccia, and phonolite. Alteration in the <br />mineralized azea is variable. Irregularly oxidized assemblages of K-feldspaz t pyrite and <br />sericite-clay t pyrite aze most common within the ore body, while propylitic and sericite- <br />clay facies aze most common adjacent to the ore. Accessory cazbonate, while believed to <br />be partially leached from the mineralized areas in the Main Cresson Mine azea near the <br />surface and therefore not identified in every core, is widely noted in the District by <br />Lindgren & Ransome (Lindgren, W. & Ransome, F.L., 1906, Geology and Gold Deposits <br />of the Cripple Creek District, Colorado; U.S. Geological Survey Professional Paper No. <br />54, 516 pp.). <br />• <br />16 <br />