Laserfiche WebLink
l <br />T-4518 <br />The deposit at the Cross mine in the Caribou mining district of Boulder County, <br />Colorado contains more than 0.13 M ounces of gold and significant silver, lead., and zinc. <br />It is part of the Front Range mineral belt on the northern margin of the Idaho Springs- <br />Ralston sheaz zone of the Colorado lineament. This Precambrian fracture zone localized <br />alkaline and calc-alkaline igneous activity and associated mineral deposits during the <br />Lzramide orogeny. <br />The deposit is situated at the contact between the 1.7 Ga mica schist unit and the <br />60-63 Ma Caribou composite stock. The mica schist unit is primarily a biotite gtanite <br />gneiss with abundant granite migmatites. The mean orientation of mica schist iutit <br />foliation is N85E/34N. The Caribou stock is primarily monzonite to quartz monzonite. <br />Minor rack types occur as 0.5- to 12-inch-wide dikes. Biodte-hornblende quartz <br />monzonite dikes are mostly oriented approximately NOOE/90 but some aze oriented north- <br />northeast. Four high potassium felsic dikes occur in two orientations: approximately <br />N40W/90 and N45E/LOS. A single magnetite-biotite monzodiorite dike is oriented <br />N65E~32N. Veins occur in two primary orientations: east-striking with vertical dip, and <br />northeast-striking with variable dips to the northwest. The northeast-trending ~~eins curve <br />into east-trending veins and structures. <br />The reactivated northwest-trending Precambrian Arapahoe Pass-Junction Ranch <br />fault localized the Caribou stock in a district-scale dilationa] jog under east-trending <br />compression. East-striking quartz monzonite dikes were also emplaced in the district <br />area. An east-wending quartz monzonite dike, Precambrian dike, and segment of the <br />iii <br />