Laserfiche WebLink
The second rock type in the AGVLF Phase I -IV area is Tertiary aphanitic phonolite, most <br />frequently occurring as narrow, often discontinuous dikes intruding the granodiorite in a <br />northeasterly direction. Phonolite dikes generally are blue -gray in color (depending on degree of <br />alteration) and porphyritic (with low percentages of K- feldspar phenocrysts set in an aphanitic <br />groundmass) and may range from massive to fissile in character. Dikes typically range in width <br />from 0.5 feet to 10 feet. Phonolite also occurs as an intrusive plug that forms Beacon Hill. At <br />the surface, the plug measures approximately 2,000 feet long in a north - northeasterly direction <br />and 1,200 feet wide. It is interpreted to taper considerably downward below 8,400 feet amsl and <br />is much the same as the dikes described above in terms of composition and texture. <br />The third rock type in the AGVLF Phase I -IV area is the lapilli breccia. Based on the <br />geotechnical investigations performed on the breccia occurring on Beacon Hill, it is weathered to <br />an average of about three feet below the ground surface. More specifically, the slopes of Arequa <br />Gulch were covered with a thin layer of colluvium and soil. Bedrock outcrops at the surface <br />were noted but are not dominant. No notable alluvial deposits were present within the footprint <br />of Phase 5 of the AGVLF. <br />Mapping in the Arequa Gulch area for the AGVLF Phase I -IV indicated the existence of four <br />important structural orientations. The strongest trend is about N20E and is in the central portion <br />of Arequa Gulch. These linear features are small faults or shears consisting of narrow clay <br />gouge seams (0.1 to 1.0 foot in width), surrounded by five- to eight -foot wide envelopes of <br />highly fractured, oxidized and weakly clay - altered granodiorite. A less strong lineation trends <br />N70E primarily along the northern portion of the Arequa Gulch site. These lineations are <br />schistose shear zones and range up to five feet in width. The other lineations are at a N40 -50E <br />structural orientation delineated by discontinuous phonolite dikes that increase in frequency to <br />the north, and a N45W trend of discontinuous, narrow faults observed only in the northern <br />portion of the site. There appears to be minimal displacement (less than 10 -30 feet) along the <br />observed faults. <br />Four rock types compose the general bedrock geology of the Phase 5 AGVLF area. The <br />predominant bedrock unit is granodiorite, which is a massive to foliated, medium to coarse <br />grained, hornblende biotite granodiorite. The second most common unit is the Cripple Creek <br />lapilli breccia, which is generally massive, structureless, matrix- supported breccia that is poorly <br />sorted, typical, diatremal crater -fill breccia. Clasts are sub - angular to sub - rounded and primarily <br />composed of various phonolite units with occasional Precambrian fragments. The breccia <br />commonly shows varying degrees of weak argillic to potassic alteration. The third and fourth <br />rock types are the biotite phonolite and phonolite, respectively. The biotite phonolite is generally <br />Cripple Creek & Victor Gold Mining Company <br />Cresson Project Mine Life Extension 2 <br />4 -5 <br />