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a gray, fine- grained porphyry with euhedral biotite and alkali feldspar phenocrysts. The <br />phonolite is light- to medium -gray, porphyry with subhedral to euhedral, medium- to coarse - <br />grained phenocrysts of alkali feldspar with minor amounts of feldspathoids, glassy apatite and <br />pyroxenes. <br />The Squaw Gulch area general lithology is composed of four rock types. The predominant <br />bedrock unit is the Cripple Creek lapilli breccia, which generally consists of a massive, <br />structureless, matrix - supported breccia that is poorly sorted, typical of diatremal crater fill <br />breccia. Clasts are sub - angular to sub - rounded and primarily composed of various phonolite <br />units with occasional Precambrian fragments. The breccia commonly shows varying degrees of <br />hydrothermal alteration. The second and third rock types are the plagioclase phonolite and the <br />phonolite, respectively. The phonolite is light- to medium -gray, porphyry with subhedral to <br />euhedral, medium- to coarse- grained phenocrysts of alkali feldspar with minor amounts of <br />feldspathoids, glassy apatite, and pyroxenes. The fourth unit is biotite bearing plagioclase <br />phonolite. This material is generally a gray, fine- grained porphyry with euhedral biotite and <br />alkali feldspar phenocrysts. <br />4.5 Geochemistry <br />The ground water hydrology and geochemistry of the District have been investigated since 1906 <br />(Lindgren and Ransome, 1906). Extensive investigations of the ground water hydrology and <br />geochemistry of the District have been conducted for permitting of Cresson Project extensions <br />for Amendment No. 8 (Adrian Brown Consultants, 1998; Shepherd Miller Inc., 1998) and MLE <br />(Adrian Brown Consultants, 2008). For MLE2, additional investigations of the ground water <br />hydrology and geochemistry of the system were conducted, in particular to allow determination <br />of the effects of mining and overburden storage in the Grassy Valley drainage, and to allow <br />determination of the effects of covering a significant portion of the Squaw Gulch drainage with <br />the proposed new SGVLF. The most recent study for Grassy Valley is reported in Appendix 1 in <br />Volume II of this document. <br />The prior studies evaluated the acid - generating potential and acid - neutralizing potential of sulfur <br />oxidation of the rockmass within the District. The environmental effects of weathering of <br />overburden and exposed rock slopes were evaluated in detail by the performance of detailed <br />testing of rock samples from the District, including: <br />• Sulfur and carbonate content (35,000 samples) <br />• Total metal content (352 samples) <br />• Net Acid Generating Tests (352 samples) <br />Cripple Creek & Victor Gold Mining Company <br />Cresson Project Mine Life Extension 2 <br />4 -6 <br />