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1.0 INTRODUCTION <br />The Cripple Creek gold deposit is associated with, and hosted by an Oligocene alkaline diatreme <br />complex. The rocks within [he diatreme belong to an unusual and rare class of rocks, which <br />have distinctive geochemical properties. These include high alkali concentrations for their given <br />levels of silica, and high COQ concentrations (manifested as carbonate minerals). Rocks within <br />the diatreme are dominantly phonolitic in composition, but include volumetrically subordinate <br />amounts of mafic rock types (trachy[es, tephriphonolites, trachyandesites, phonotephri[es, and <br />lamprophyres; see figure 1). The diatreme was emplaced as part of a regionally extensive <br />episode of alkaline magmatism during the mid-Tertiary. <br />The hydrothermal system responsible for the gold mineralization also had distinctive <br />geochemical characteristics. These include a markedly alkaline chemistry, low concentrations of <br />sulfur and base metals, and high concentrations of C07. The gold deposit at Cripple Creek <br />belongs to a distinctive, but uncommon class ofprecious metals deposits associated with alkaline <br />magmatism. As a group, these deposits are characterized by gold telluride mineralization, <br />significant volumes of alkali metasomatism, carbonation of wall rocks and lack of acid alteration i <br />(Bonham, 1984; Mutschler, et al., 1985; Botiltam, 1986; Bliss, et al., 199?; Mutschler, et al., <br />1993; Richards, 1996; Jensen and Barton, in press). <br />This paper will summarize the igneous and hydrothermal evolution of the Cripple Creek gold <br />deposit, describe its mineralogy and geochemistry and offer comparisons with other deposit <br />types. <br />2.0 CHARACTERISTICS OF THE IGNEOUS SI'STEMS <br />The Cripple Creek gold deposit is spatially and temporally associated with an Oligocene (~ 30 <br />Ma) alkaline diatreme complex emplaced within Precambrian rock. The Oligocene alkaline rocks <br />span an impressive range of compositions (see figure 1), from felsic phonolites to ultramafic <br />lamprophyres/silicocarbonatites. Being a diatreme, the most abundant rock types are volcanic <br />breccias, which are the oldest of the Tertiary intrusive rocks. The volcanic breccias were <br />successively intruded by a series of phonolites, tephriphonolites, phonotephrites, tepttrites and <br />ultramafic lamprophyres. In contrast with many other igneous systems, the intrusions at Cripple • <br />Cripple Crcck & nicror Go/A mining Co. SGrphrrrt Millrr, brr. <br />uDIAMONOW,DRIr'E~IOn3aMynnUrmcbmarldm 1 Alnrch 7000 <br />