2017-03-27_REVISION - M1981185 (27)

Home Browse Search

• Wanakah Formation. Consists of two members. The upper marl member is mostly white to tannish to pale-reddish colored, fine-grained sandstone, mudstone, and marl. 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 host for mineralization. • Entrada formation. Light-gray to white, fine-to coarse-grained highly cross-bedded ore- bearing sandstone. The Entrada sandstone frequently has prominent large-scale cross- bedding and hosts gold mineralization • 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 May Day Idaho Fault System consists of two eastward-trending reverse faults, each with a downthrown to the south with vertical displacement along the two faults of 350-475 feet (Eckel, 1949). Based on Eckel's mapping(Figure 7), the Idaho No. 1 portal is situated on a west southwesterly facing slope with the surface geology consisting of the Entrada Sandstone (Figure 7). The Idaho No. 1 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 be in the Morrison formation proximal to the May Day fault. Again, based on Eckel's mapping, there is a thin sliver of Junction Creek sandstone on the up thrown 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 entry appears to cross both faults. While,this is based on mapping (by others),this would presumably create an access to all of the major geologic/hydrogeologic units in this area. The Mayday and Idaho mines are located within southward-dipping sedimentary rocks cut by a series of east-west faults. The sedimentary units associated with the mines are presented in Table 1. Ore-bearing veins are north-trending, mainly found within the Entrada Formation (Eckel, 1949). The Mayday Idaho Fault System includes two eastward-trending reverse faults, each with a down throw to the south with vertical displacement along the two faults of 350-475 feet. There is little published information regarding groundwater conditions in the vicinity of the mine site. A review of well permits (Appendix A) indicates that most wells are located either within La Plata River alluvial material, the sandstone (presumed to be the Morrison Formation) north of the fault system or the Mancos Shale south of the fault system. May Day Idaho Mine Complex M-1981-185 January 19, 2017 Page I -9-