2011-08-09_REVISION - M1981185 (56)

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The Pony Express Limestone member consists of medium- to dark -gray, very thin - bedded to laminated, micritic and algal limestone. The Pony Express member is locally brecciated, intruded by sand dikes, and is a preferred host for mineralization. • Entrada formation. Light -gray to white, fine- to coarse - grained highly cross - bedded sandstone. The Entrada sandstone frequently has prominent large -scale cross - bedding. • Dolores formation. Mostly dark- red -brown to purple -brown shale and siltstone and brown, gray, and red -brown lenticular sandstone and limestone - pebble conglomerate. The Mayday -Idaho Fault System are two eastward- trending reverse faults, each with a downthrow to the south with vertical displacement along the two faults of 350 -475 feet (Eckel, 1949). Based on Eckels mapping (figure 2), the Idaho No. 1 daylights on a west southwesterly facing slope with the surface geology consisting of the Entrada Sandstone (Figure 2). The tunnel generally follows an easterly trend along the Idaho Fault. At the entrance to the Idaho, No. 1, this places the Dolores Formation (northern fault block) in contact with the Entrada Formation (southern block) in this area with the Idaho No. 1 apparently following the fault where the offset has occurred. The May Day No. 1 portal appears to daylight in the Morrison formation in close proximity to the May Day fault. Again, based on Eckels mapping, there is a thin sliver of Junction Creek sandstone on the upthrown side of the May Day fault that is in contact with the Morrison Formation on the downthrown side of the fault. In this vicinity, the Idaho fault is extremely close to the May Day fault (approximately 200 feet north) and the May Day No. 1 tunnel appears to cross both faults. While, this is based on mapping by others, this would essentially create an access tunnel to all of the major geologic/hydrogeologic units in this area. 4.0 HYDROGEOLOGY Hydrogeologically, flow in the area is characterized by both flow through porous media and along fractures and faults. Potentially, some of the non - porous media flow in the limestone can be the result of dissolution structures. Fracturing of the local formations locally increases the secondary permeability; as a result, the transmissivity also is increased locally to values as much as 100 times greater than those for the unfractured rock. Offsets due to faulting create discontinuous hydrologic blocks that impede porous flow over long distances. Generally, recharge to the groundwater system is from: o Precipitation and snow melt on outcrops; and o Stream channel loss to the formations as streams cross outcrops. Generally, discharges to the groundwater system are from: o Springs and seeps in topographically low parts of the outcrop; and