2009-05-19_REVISION - M1977416 (37)

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depositing large sequences of sandstones and mudstones. The streams often cut back across previously deposited sediments, reworking the sands and mudstones. This back and forth reworking of the sands and mudstones has led to the formation of long, lenticular, tabular ore deposits. F.W. Cater (1955) shows that the Brushy Basin shale ranges from 350 to 430 feet in thickness across the Gypsum Valley anticline, however the only evidence of the Brushy Basin within the study area is a thin 15 foot thick section consisting primarily of light yellow, gray and maroon bentonitic claystone in the upper part of drill holes SC-0509 and SC-0709. The bentonitic clay, which forms much of the Brushy Basin was deposited under very quiet conditions probably as broad mud flats of a flood plain, is probably volcanic in origin and suspected source of uranium mineralization within the underlying Salt Wash. The contact between the two members is difficult to indentify in the drill cuttings and the contact is primarily identified as an increase in resistivity on the geophysical logs. • • The contact between the Salt Wash and underlying Summerville Formation (Js) occurring at interpreted depths of 280- 440 feet is difficult to determine because the overlying beds of shale and mudstones of the Salt Wash are similar to uneven upper beds of the Summerville. Beds of the Summerville are predominantly light red to gray sandy shale and mudstones. The Summerville has a fairly uniform thickness of 40-45 feet when fully penetrated by the drilling, and roughly half of that reported by F.W Cater (1955) which may be representative of the thinning of the Summerville along the flanks of the Gypsum Valley anticline. The Summerville rests on the Entrada (Je) sandstone, as shown in the geophysical log for SC-0509 at 357 feet. A sharp, flattening decrease in the natural gamma log along with a sharp increase in conductivity marks the contact. However, the sharp contrast between the Summerville and Entrada is seen in no other holes. The Entrada sandstone consists of a massive 200 foot thick section of light yellow to brown, fine grain subrounded to subangular quartz sandstone. The thickness of the Entrada sandstone within the Gypsum Valley anticline area per F.W. Cater (1955) is only 110 to 120 feet thick, which suggest that SC-0509 actually was stopped (total depth (TD)) within the underlying Navajo Sandstone (in). A small bump in the conductivity log at 506 feet may be evidence of the Entrada/Navajo contact Tahle 2- Drill hole reports (lithology based on cuttings) holeno from to Lithology color. SC-0109 0 90 Fine Grained Sand Lt Y1/13r SC 0109 90 113 Claystone Wh SC-0109 113 144 Siltstone Wh SC-0109 144 163 Claystone Wh SC-0109 163 175 Siltstone Wh SC-0109 175 224 Fine Grained Sand Wh SC-0109 224 237 Siltstone Lt Gy SC-0109 237 250 Fine Grained Sand Wh SC-0109 250 295 Siltstone Lt Gy SC-0109 295 304 Claystone Wh SC-0109 304 340 Fine Grained Sand Lt Gy SC-0209 0 25 Fine Grained Sand Br SC-0209 25 54 Siltstone Lt Br SC-0209 54 62 Fine Grained Sand Lt Br SC-0209 62 96 Siltstone Wh SC-0209 96 123 Claystone Wh SC-0209 123 144 Fine Grained Sand Lt Br SC-0209 144 157 Claystone Wh SC-0209 157 256 Fine Grained Sand Lt Gy/Wh SC-0209 256 282 Siltstone Wh SC-0209 282 295 Fine Grained Sand Wh SC-0209 295 316 Siltstone Lt Br/Gy SC-0209 316 352 Fine Grained Sand Lt Gy/Wh SC-0209 352 380 Siltstone Lt Gy/Wh SC-0309 0 44 Fine Grained Sand Wh SC-0309 44 64 Claystone Wh SC-0309 64 85 Fine Grained Sand Wh SC-0309 85 112 Mudstone Wh SC-0309 112 156 Fine Grained Sand Lt YI SC-0309 156 177 Poorly sorted silty Sandstone Wh OENISONOII MINES 3