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Wildcat Mining Corporation <br />Page 19 <br />• The La Plata Mountains are recognized as an example of the laccolithic type of <br />mountain. They were carved from a domal uplift of sedimentary rocks into which <br />numerous stocks, dikes and sills of igneous rock were intruded. In general the <br />strata, which range in age from Pennsylvanian to Lower Cretaceous, dip away <br />from the core of the range. The dome, approximately 15 miles in diameter, is <br />outlined by a horseshoe - shaped hinge fold, open to the south. <br />Several high - angle, down -to- the - south, faults occur along the southern margin of <br />the dome in zones where the deformation was too extreme to be accommodated <br />by folding of the sedimentary layers with resulting fracturing and fault <br />displacement (Figure 4). These faults trend approximately east -west. A series of <br />near - parallel, anastomosing faults, the May Day -Idaho fault system, border the <br />dome near Mayday and are clearly important in controlling the disposition of ore <br />in the May Day and Idaho mines. The Idaho fault, the northernmost splay, <br />offsets the rocks about 50 to 100 feet, whereas the May Day fault, the southern <br />splay, exhibits 300 to 375 feet of displacement. Although the evident <br />displacement is normal down -to- the - south, slickenside kinetic indicators exposed <br />in underground workings suggest that the last movement of the faults was largely <br />horizontal (Eckel, 1949). <br />Stratigraphy <br />Precious metal veins of the May Day mine are largely hosted within a section of <br />sedimentary rocks of Mesozoic age (Figure 5). Six sedimentary rock units of <br />Triassic and Jurassic age have been intruded by late Cretaceous to Paleocene <br />porphyritic igneous dikes. (Unit abbreviations in the following discussion are <br />keyed to map Figure 5) <br />The lowermost unit, the upper Triassic Dolores formation (TPdc) consists of <br />soft redbeds, dominantly mudstone with distinct limestone conglomerates. The <br />Dolores formation ranges from 400 to 700 feet thick and is not a productive ore <br />host unit. <br />The Jurassic Entrada sandstone (Je) is one of the most distinctive and easily <br />recognized rock units in the district and is a favorable ore host in several <br />deposits. The formation in the vicinity of the May Day mine ranges in thickness <br />from 150 to 225 feet. The Entrada consists of light- colored massive to strikingly <br />cross - bedded sandstone made up of relatively coarse, well- rounded, glassy <br />quartz grains with finer quartz grains filling the interstices; calcareous cement is <br />common. <br />0 <br />January 2007 May Day - Idaho Mine Colorado <br />