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Page 8 of 18 <br />Last movement on these faults was associated with the late Laramide orogeny and they <br />are now considered inactive. <br />Holland (1994) noted two episodes of fault movement. The earliest was left lateral strike- <br />slip movement along the east-west striking structures. This was overprinted by right <br />lateral strike-slip movement along minor east-northeast striking structures. The <br />northeast-trending veins on Caribou Hill are interpreted as occupying shear zones and <br />the east- and west-trending veins are interpreted as occupying tension fractures <br />branching from the shear zones. <br />Holland (1994) proposed that the structures present at the Cross Gold Mine tie into the <br />regional Arapahoe Pass Fault and the Junction Ranch Fault. The Arapahoe Pass Fault <br />is mapped along strike to the west where it disappears under glacial cover. The Junction <br />Ranch Fault is also mapped along strike but to the southeast. <br />The veins are distributed within two main sets. One striking north-northeast with most of <br />the veins considered to be open along strike and depth, except where they enter the <br />monzonite. In contrast, the east-west striking veins located west of the historic mine <br />area do not decrease in magnitude where they cross into the monzonite. <br />Holland (1994) proposed that left lateral movement created a dilatational fault jog <br />betweentheArapahoePassFaultandtheJunctionRanchFault.Thissamemodelisthen <br />used to explain the presence of the large open space fill veins at the Cross Mine. The <br />north-northeast striking vein sets appear to be largely dilatational structures. The east- <br />west striking set of veins appear to be localized along earlier fault structures. <br />Individual steeply dipping veins range in width from inches to tens of feet and consist of <br />open space fill zones containing quartz and disseminated sulfides flanked by mineralized <br />and non-mineralized alteration zones. A late stage of carbonate mineralization was the <br />last emplacement before weathering and supergene enrichment of the upper ore body <br />ore body at Caribou must of which has been eroded at Cross. Weathering has partially <br />oxidized sulfide minerals in the upper 200 ft or so of the deposits. These tend to be high <br />infiltration pathways during snowmelt. <br />4HYDROLOGY <br />4.1 Aquifers and Adjacent Use <br />The groundwater beneath and adjacent to the Cross Mine is present in a single aquifer, <br />the Mountain Crystalline Bedrock Aquifer as mapped in the ON-010 Colorado <br />Groundwater Atlas (Barkmann et al., 2020). However, water is especially flow may be <br />different in the gneiss where the higher apparent transmissivity occurs. A more <br />comprehensive hydrogeological investigation is needed to verify the aquifer regimes and <br />source water chemistry. Unlike sedimentary rock aquifers, igneous and metamorphic <br />crystalline rocks have no primary porosity; water is stored in fractures and stopes in the <br />older mine working, many of which have been unmapped. Groundwater flow proximal <br />to and within the compliance boundaries is wholly with the Idaho Springs