2010-03-16_REVISION - M1981185 (29)

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Wildcat Mining Corporation Page 21 • The Jurassic Wanakah formation (Jw) contains two members: the Pony Express limestone and an overlying thicker marl member. A thin sandstone, the Bilk Creek sandstone, occurs locally between the Pony Express and the marl member. Because it is easily recognized and commonly hosts high -grade ore zones, the Pony Express limestone is one of the most important stratigraphic units in the district, even though it is but rarely greater than 20 feet thick. The Pony Express limestone member is a thin unit of dark -blue to gray to black relatively pure limestone. In places, the limestone consists of a single massive bed; elsewhere it comprises three or more thinner beds. The upper beds are commonly massive and the lower beds thinly laminated. The Bilk Creek sandstone, where present, consists of a sandstone, generally about 20 feet thick, with horizontal and locally nodular bedding. The marl member of the Wanakah formation is 25 -200 feet thick and consists of slightly pink to green -gray marl, mudstone, and sandstone in lenticular beds. The Jurassic Junction Creek sandstone (Jjc) ranges in thickness from 200 -500 feet and is made up in large part of massive white cross - bedded sandstone, closely resembling the Entrada sandstone. The Morrison formation (Jm) consists of an upper member, the Brushy Creek member, and a lower member, the Salt Wash member. The Brushy Creek member is chiefly a greenish -gray bentonitic mudstone and claystone. The Salt Wash member is mainly light -gray fine- to medium - grained sandstone • interbedded with thin beds of green -gray mudstone. The unit is 350 -400 feet thick and does not host gold ore. The stratigraphic sequence was intruded by dikes and sills of diorite to monzonite porphyry of variable texture, but always marked by phenocrysts of white feldspar and dark -green to black hornblende. The porphyry intrusions throughout the La Plata Mountains are of highly irregular form, generally described as dikes, sills, small laccoliths, and small stocks (Figure 5). Prior to 1949, geologists in the district used a different stratigraphic terminology, now considered obsolete, as summarized in the following table. Table 2. Stratigraphic terminology in the May Day and Idaho mines. Current Terminology Older Terminol Morrison formation McElmo formation Junction Creek sandstone Upper La Plata sandstone Wanakah formation Marl member Middle La Plata shale Pony Express limestone member La Plata limestone Entrada sandstone Lower La Plata sandstone Dolores formation Dolores formation 0 January 2007 May Day — Idaho Mine Colorado