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Page 7 of 18 <br />The Idaho Springs Gneiss consists of a well-foliated and banded gneiss composed of <br />medium to coarse grained quartz-biotite-plagioclase-orthoclase with accessory <br />magnetite and apatite. The unit has a zebra appearance due to biotite banding. Granite <br />migmatites comprise nearly one-half of its total volume. The migmatite consists of coarse <br />grained, fairly planar bodies which are predominantly parallel to foliation. Mica rich schist <br />units also occur within the gneiss, hosting sillimanite that indicates a high peak <br />metamorphic grade. <br />The Caribou Monzonite Stock is variable in composition. It consists predominantly of <br />monzonite and quartz-monzonite but also ranges to mafic phases as lenses, pods and <br />dikes. The monzonite phases are composed of medium-grained plagioclase-orthoclase- <br />quartz-biotite-clinopyroxene-hornblende with accessory magnetite and apatite, giving <br />the unit a black color. <br />The Swandyke Hornblende Gneiss is present approximately one mile south of the Cross <br />Mine in two relatively continuous bodies. It consists of a dark gray to black, medium to <br />fine grained, well-foliated amphibolite unit. Composed primarily of hornblende and <br />plagioclase with lesser pyroxene, biotite and quartz. The unit likely represents small, <br />localized mafic intrusions that were subsequently metamorphosed in the Precambrian. <br />The Boulder Creek Granodiorite is located approximately one-half mile northeast of the <br />Cross deposit. It consists of a weakly foliated paleo-igneous unit. It is composed of fine <br />to medium-grained quartz-orthoclase-plagioclase-biotite and minor hornblende. It is <br />differentiated from the gneiss mainly by the lack of conspicuous banding but does have <br />well developed foliation near its contacts. <br />The contact between the Idaho Springs Gneiss and the Caribou Monzonite Stock strikes <br />northwest-southeast through the mine area, dipping near vertical. The Cross Gold Mine <br />is developed in veins near this contact. <br />3.3 Faults, Veins and Fractures <br />The Cross Mine site has a complex tectonic history. Forces in the Colorado Front Range <br />have left an overprint of regional to local scale faults and fracture zones through the <br />terrain. The Cross Gold Mine is located in highly faulted and fractured geologic units. <br />At the scale of rock outcrop, and in the underground working, pervasive blocky jointing <br />is noted in all rock types especially in the gneiss. <br />A published 1969 USGS map maps a fault at the ground surface approximately 700 feet <br />east of the Cross Mine site (Gabel, 1969). Holland (1994) refers to numerous faults <br />encountered underground within the Cross Mine deposit, and many of the veins <br />encountered in the mine are the result of mineralization along fault planes although there <br />is evidence of consolidated mineralized stockwork where fault intersections occur. The <br />major fault structures appear to be oriented along an east-west strike and dip steeply <br />north to vertical however in the gneiss there is extensive development of north-south <br />faults intersection with east-west faults.