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The volcanic rocks occupy a diatreme, which has the general aspect of a steep - walled crater with <br />a crudely elliptical outline at the surface. More recently, Jensen (2003) used the following <br />lithologic designations for the alkaline rocks of the District: volcanic breccias, phonolites, <br />tephriphonolites, phonotephrites, tephrites, nepheline syenites, nepheline monzosyenites, <br />nepheline monzodiorites and, in the last intrusive event, lamprophyres. Following the <br />emplacement of the lamprophyres, large volumes of rock were subjected to intense potassium <br />metasomatism, hydrothermal brecciation, and gold mineralization. Carbonate -rich styles of <br />alteration post date the precious metal mineralization event. The carbonate alteration plays a <br />major role in the ground water chemistry of the area, as evidenced by the alkaline nature of <br />regional ground water flowing from the Carlton Tunnel portal. <br />The mineralogy of the Main Cresson Mine area is quite diverse. Intrusive and breccia <br />lithologies, spanning the entire alkaline suite from leucocratic phonolites through ultramafic <br />lamprophyres occur. Volumetrically, the main lithologies are volcanic diatremal breccia, <br />phonolitic breccias, and phonolite. Alteration in the mineralized area is variable. Irregularly <br />oxidized assemblages of K- feldspar ± pyrite and sericite -clay ± pyrite are most common within <br />the ore body. Accessory carbonate, while believed to be partially leached from the oxidized <br />areas in the Main Cresson Mine area near the surface, was widely noted in the District by <br />Lindgren and Ransome (1906). <br />The geology of the East Cresson Mine is similar to that of the Main Cresson Mine with the <br />exception that there are volumetrically more phonolites than diatremal breccias in the East <br />Cresson. The East Cresson Mine is focused at the intersection of the northeast - trending <br />Pharmacist Vein and the northwest- trending Isabella -Buena Vista vein systems, in the area of the <br />former Gold Star Mine. Diatremal breccias occur between thick phonolite sills and are cut by <br />later, north - northwest - trending phonolite and lamprophyre dikes. <br />The East Cresson Mine area is located in the north central portion of the District where the gold <br />mineralization is hosted by an assemblage of shallow- dipping diatremal breccias, porphyritic <br />phonolite flows, and Precambrian granodiorite and biotite gneiss along, and within, north- and <br />northwest- trending structural zones associated with the diatreme - Precambrian contact. <br />The ECOSA is located directly north of the East Cresson Mine area, and is underlain by up to <br />1,500 feet of the moderate permeability Tertiary phonolites and breccias of the Cripple Creek <br />diatreme. Within this unit, and underlying the ECOSA footprint, are the small historic School <br />Section Mine and the Cameron Mine, hosted by northeast- trending structures. Calcarious <br />sediments have been identified in the volcanic rocks underlying the ECOSA footprint. Loughlin <br />Cripple Creek & Victor Gold Mining Company <br />Cresson Project Mine Life Extension 2 <br />4 -3 <br />