Geological Survey Bulletin 1229 Geology of the Circle Cliffs Area, Garfield and Kane Counties, Utah

The best known and partly developed prospects in the Circle Cliffs area are described below, and their locations are plotted in figure 14. Claims were staked nearly everywhere on exposures of the Chinle and Morrison Formations, but not all claims have been equally explored. Several thousand feet of wagon drilling was done by private companies and by the U.S. Atomic Energy Commission on the mesas capped with Shinarump, in areas adjacent to prospects, and elsewhere; however, none of this drilling revealed ore bodies large enough to encourage extensive development. Analyses of ore samples from several prospects are combined in table 2. Uranium content, determined by chemical analysis, is reported as U; the radioactivity of the rock, converted to equivalent uranium content, is reported as eU.

TABLE 2—Analyses of uranium content in samples from the Buff and Red Cliff prospects
[Analysts: C. G. Angelo, R. R. Lipp, J. S. Wahlberg, D. L. Schafer, and D. L. Ferguson]

The Black Widow, Hotshot, Yellow Jacket, and Stud Horse prospects and the Rainy Day mine are the only workings in the Circle Cliffs district from which more than a few truckloads of ore had been shipped as of 1956; the Rainy Day mine had produced more than 75 percent of the total. During the period of the study, shipping costs required that trucked ore average at least 0.25 percent U₃O₈ to make a mining operation profitable.

BUFF AND RED CLIFF PROSPECTS

The Buff (fig. 14, No. 1) and Red Cliff (fig. 14, No. 2) prospects are on the same small Shinarump channel in the northwestern part of the Circle Cliffs area. Exploration consists of 30-40 feet of drift at the Buff and about 70-80 feet of inaccessible drift at the Red Cliff.

The Shinarump channel is 800-1,000 feet wide and about 10 feet deep at the Buff prospect and no more than 20 feet deep at the Red Cliff prospect. Except for the ore-bearing unit described below, the Shinarump sandstone filling the channel is moderately well sorted medium-grained sandstone. The Moenkopi Formation underlying the channel-filling sandstone is reddish-brown siltstone or mudstone that is bleached light greenish gray in a 1- to 2-foot-thick zone under the channel base. Stringers of gypsum fill fractures in both the Shinarump and the Moenkopi.

The better grade ore is in the bleached Moenkopi at the Buff prospect and in the Shinarump at the Red Cliff prospect (table 2). The mineralized rock at the Buff prospect is so badly out of equilibrium that the actual uranium content is only one-fifth of the equivalent uranium content, indicated by radioactivity (table 2). The uranium ore is low grade and spotty in distribution and is confined to the upper 1 foot of the Moenkopi and the lower 2 feet of the Shinarump.

At the Red Cliff prospect the ore occurs in the lower part of a 2- to 6-foot-thick bed of brown, iron oxide-stained conglomerate composed of fragments of gray to light-yellow mudstone and black, charcoaly wood imbedded in a kaolinite-cemented matrix of medium-grained sandstone. The lower 1-3 feet of the ore-bearing bed contains copper minerals on fracture surfaces and is stained brown by iron oxide.

COOL PROSPECT

The Cool prospect (fig. 14, No. 3) consists of about 200 feet of drift and crosscuts. The Shinarump above the contact with the Moenkopi is interlayered medium-grained brown and light-yellow sandstone and gray siltstone. It contains very abundant charcoaly fragments and a few large charcoaly logs. Most of the radioactivity detected is in the large logs, but some radioactivity was detected in a 6-inch-thick zone at the contact. Radiometric examination of mineralized logs indicated that the highest grade is about 0.5 per cent equivalent uranium.

BART, CENTIPEDE, AND MIDAS PROSPECTS

The Bart, Centipede, and Midas prospects are along a closely spaced system of Shinarump channels that trends N. 70° W. in the northwestern part of the Circle Cliffs area. The sandstone of the Shinarump is medium grained and kaolinitic and generally contains moderate amounts of mudstone and charcoaly wood fragments.

The Bart prospect (fig. 14, No. 4) is a 6-foot-long north-trending adit driven near the north edge of a channel that is about 400 feet wide and 10-40 feet deep. The base of this channel was covered by talus at the time of examination, but on the channel flanks the Moenkopi is bleached gray for as much as 6 feet beneath the Shinarump-Moenkopi contact. A weakly radioactive zone only a few inches thick occurs at the Shinarump-Moenkopi contact in the adit.

The Midas (fig. 14, No. 6) and Centipede (fig. 14, No. 5) prospects are on a small channel a few tens of feet south of the Bart prospect. This channel is 200-400 feet wide and 25-40 feet deep. The radioactive rock is in a 1-foot-thick zone that straddles the Shinarump-Moenkopi contact at both prospects. At the Midas prospect most of the radioactive rock is in the bleached Moenkopi and is localized on the channel flank in a small ridge of fractured rock that trends parallel to the channel.

The Centipede prospect, near the central part of the channel, was actively prospected during this study. Figure 15 shows the workings, geologic contacts, and the location of channel samples. The highest radioactivity in the Centipede prospect is in sandstone of the Shinarump Member where it contains moderate to large amounts of mudstone and charcoaly wood fragments. This material, in the ground opened, is confined to a 2-foot-thick bed at the base of the Shinarump, but some radioactivity was detected in a 2-inch-thick bed of charcoal-rich sandstone (table 3, sample 261156) in the back of the end of the drift. The radioactivity in the prospect is probably caused by uraninite. Chalcopyrite and pyrite are present in the radioactive sandstone. Sphalerite and galena probably are also present, as spectrographic analyses show more lead and zinc in radioactive rock than in nonradioactive rock. The visible metallic minerals fill interstices and replace the quartz, feldspar, and kaolin of the rock matrix. Some of the quartz-grain boundaries show stylolitic intergrowths, which indicate solution of silica.

TABLE 3—Analyses of uranium content in samples from the Centipede prospect
[Analysts: W. W. Niles, eU; H. H. Lipp and D. L. Ferguson, U]

FIGURE 15.—Map of Centipede prospect and longitudinal section of drift, generalized from both walls. Mapped by E. S. Davidson and G. A. Miller, 1957. (click on image for a PDF version)

HORSEHEAD PROSPECT

The Horsehead prospect (fig. 14, No. 7) is similar to the Centipede prospect in occurrence and mineralogy. The prospect is in the center of a channel filled with Shinarump that is 400-600 feet wide and about 30 feet deep. About 50 feet of drifting N. 87° W. along the deepest part of the channel had been completed at the time of the examination.

The sandstone of the Shinarump that fills the channel is thick bedded, medium grained, and kaolinitic, and it contains small amounts of charcoaly material and mudstone fragments. The basal bed of the Shinarump is a medium-grained sandstone containing abundant fragments of gray mudstone and moderate amounts of charcoaly material. Gypsum stringers cut across, and lie along, bedding planes. The most radioactive rock is in a 1- to 3-foot-thick zone at the base of the Shinarump and in the upper 1 foot of gray Moenkopi. Chalcopyrite and pyrite are associated with the radioactive rock, and secondary yellow and green uranium minerals occur in fractures and along bedding planes. A grab sample of highly radioactive sandstone had an equivalent uranium content of 2.57 percent, an actual uranium content of 3.44 percent, and trace amounts of zinc, nickel, and lead. A 1-foot-long vertical channel sample collected in the drift 12 feet from the entrance contained 0.13 per cent uranium.

BLUE GOOSE PROSPECT

The Blue Goose prospect (fig. 14, No. 8) is near the center of a shallow but wide northwest-trending channel. The channel is about 800 feet wide, trends about N. 55° W., and is generally about 10 feet deep, although in places it is almost 20 feet deep. At this prospect the channel base of the Shinarump transects the mottled-siltstone unit of the Chinle and a few feet of the topmost beds of the Moenkopi. About 65 feet of northwest-trending drift had been completed at the time of this study. The sandstone of the channel is moderately clean, light brown, and fine to medium grained, and it contains only a few mudstone fragments and layers of charcoaly material. Low-grade radioactive material and associated copper minerals occur in the lower 2 feet of the Shinarump and in the upper 6 inches of the Moenkopi. The ore host is a lens 1-2 feet thick and about 25 feet wide of fine- to medium-grained sandstone containing abundant mudstone fragments and moderate amounts of carbonaceous material. Copper staining is obvious on rocks exposed at the face of the cliff. Green and yellow uranium minerals coat fractures and bedding planes.

HORSE CANYON PROSPECT

The Horse Canyon prospect (fig. 14, No. 9) consists of about 30 feet of drift in sandstone of the Monitor Butte Member of the Chinle Formation. The sandstone fills a small channel about 300 feet wide and 10-15 feet deep cut into the underlying mottled-siltstone unit of the Chinle. The Shinarump is absent at this prospect. The sandstone is medium grained and contains moderate amounts of stringers and chips of greenish-gray mudstone and many gray mudstone interbeds in the lower few feet. It also contains as much as 1 percent of charcoaly fragments, and some of this material is highly radioactive. Radioactive material (mainly green zeunerite (?)) and copper staining are present in the lower 10 feet of the sandstone, but appreciable radioactivity is distributed sporadically only in the lower 1 foot.

STUD HORSE PROSPECT

Several hundred feet of exploratory drifting, complemented by several hundred feet of exploratory drilling, yielded discouraging results at the Stud Horse prospect (fig. 16), on one of the Stud Horse Peaks (fig. 14, No. 10).

FIGURE 16—Occurrence of uranium ore at Stud Horse prospect. Letters and number indicates location of sample listed in table 4.

The drifts are on the west side of the largest channel filled with Shinarump in the Circle Cliffs area. Here the channel is at least 4,500 feet wide and slightly more than 100 feet deep and trends northeast (fig. 14). The highest grade ore was mined from a pod at the top of the Moenkopi along a small "bank" on the northwest flank of the channel. The pod is 1—1-1/2 feet thick, less than 10 feet wide, and 70 feet long (fig. 16). Some lower grade ore is present in a 1-foot-thick basal bed of sandstone of the Shinarump, which contains abundant fragments of mudstone and chips of charcoaly material. Zeunerite, autunite, and uraninite were identified in the ore zone. Megascopic chalcopyrite, pyrite, and carbonaceous material (probably oil residue) accompany the ore, and spectrographic analyses indicate that galena and sphalerite are also present. Copper staining is evident on the cliff outcrop from 10 feet above the Shinarump-Moenkopi contact to 6 feet below it. The Moenkopi is bleached gray for 6 or 7 feet, and in places 10 feet, below the contact. The location of two channel samples of the ore zone is shown in figure 16; the sample analyses are given in table 4.

TABLE 4—Analyses of uranium content in samples from the Stud Horse prospect
[Analysts: D. L. Schafer, R. P. Cox, J. S. Wahlberg, and R. H. Lipp]

GLEN RAE PROSPECT

The Glen Rae prospect (fig. 14, No. 11) is on the west edge of a channel that is about 2,000 feet wide and is 30-40 feet deep at its lowest point. Downcutting at the prospect is no more than a few feet, and the Shinarump rests on the mottled-siltstone unit of the Chinle. Workings consist only of a 10-foot-long drift and two 5-foot-long angled crosscuts. Some copper staining, pyrite cubes altered to limonite, and low to moderate radioactivity occur in the lower 2 feet of the Shinarump and in the upper 1 foot of the mottled-siltstone unit. The Shinarump here is moderately clean sandstone containing only small amounts of clay pellets and charcoaly material. Two uranium-indicator plants, princessplume and ricegrass, were noted on slopes below the prospect.

BLUE BIRD PROSPECT

The Blue Bird prospect (fig. 14, No. 12) is on the west edge of the same channel as the Glen Rae. It consists of two adits, each driven about 50-60 feet. Copper minerals and low to moderate radioactivity are localized in the lower 2 feet of a pebbly sandstone at the base of the Shinarump. In general, the highest count of disseminated radioactivity is found where the percentage of clay fragments in the sandstone is greatest. In places some carbonaceous material is present that also is radioactive.

LONE B PROSPECT

The Lone B prospect (fig. 14, No. 13) is in the center of a channel that is about 1,400 feet wide and not more than 20 feet deep. Exploration consists of two large 100-foot-long adits.

The lowest 4-5 feet of the Shinarump in the prospect area is medium-grained sandstone that contains abundant fragments of charcoaly material and moderate to small amounts of clay pellets. The underlying Moenkopi is bleached to gray from reddish brown for 3-4 feet under the contact. No uranium minerals were identified at this prospect, and radioactivity is confined to charcoaly material in the lower few feet of the Shinarump. Some of the charcoaly material is very radioactive, but the radioactivity is very spotty and the overall uranium-ore grade is probably very low. Some of the charcoaly fragments have been replaced by pyrite, but these fragments are not necessarily radioactive. Locally the upper 1 foot of the Moenkopi contains abundant pyrite cubes, but the Moenkopi is virtually devoid of uranium.

BLACK WIDOW PROSPECT

The Black Widow prospect (fig. 14, No. 14) is high on the west edge of the main Shinarump channel, where the channel is only 15-20 feet deep. Exploration at this prospect consists of slightly more than 100 feet of drift. The main adit, which yielded the only ore, and a 5-foot-long doghole are shown in figure 17. The other drifts, 600 feet south of the main adit, consist of one 40-foot-long adit and two 10-foot-long dogholes.

FIGURE 17—Prospect localities in typical channels filled with the Shinarump Member of the Chinle Formation; Moenkopi Formation (Trm) and Shinarump Member of the Chinle Formation (Trcs). A, Sneaky-Silver Falls prospect. B, Black Widow prospect. C, Yellow Jacket prospect.

The geology is rather unusual at the main adit in that the uranium minerals are disseminated in and near a pod of Shinarump sandstone that appears to underlie siltstone of the Moenkopi Formation (fig. 17). The pod of sandstone probably filled an undercut streambank in the Moenkopi. The cliff rim now exposes the undercut podlike filling and the overlying Shinarump as separate deposits divided by siltstone of the Moenkopi, but the two Shinarump deposits were probably continuous before the present slope was exposed. The pod pinches out in the drift a few feet from the adit entrance. Locally, the pod is heavily asphaltic and contains some charcoaly material, much of which is radioactive. The highest radioactivity is at the bottom of the pod. Copper minerals are disseminated through the sandstone pod and form a halo around it. Some copper minerals were found on joints in the red unbleached Moenkopi adjacent to the pod near the lower right, corner of the adit (fig. 17B). The doghole (fig. 17B), 3 feet above the thickest part of the pod of Shinarump sandstone, and the adits are in a more typical position at the Shinarump-Moenkopi contact on the sloping channel edge.

Radioactive minerals occur in the exploratory drifts of the Black Widow prospect in a 1- to 2-foot-thick mudstone-fragment conglomerate above the contact and in the upper 6 inches of the Moenkopi. The Moenkopi is bleached light to dark gray in a 2- to 3-foot-thick zone under the contact. Near the pod of Shinarump the bleached zone is 6-8 feet thick. The uranium ore is very low grade and discontinuous and consists mainly of secondary green uranium minerals on joint and bedding-plane surfaces.

MESA PROSPECT

The Mesa prospect is on a small butte in the central part of the Circle Cliffs area (fig. 14, No. 15). The Shinarump capping the butte is a remnant of channel-filling sandstone which is about 4,000 feet wide and 60-70 feet deep at the south end of the butte. Exploration consists of more than 100 feet of drift in several places. The lower 3 feet of the Shinarump contains moderately abundant fragments of mudstone and as much as 1 percent of charcoal material that decreases in amount upward. No significant radioactivity was noted in the adits during the examination.

YELLOW JACKET PROSPECT

The Yellow Jacket prospect (fig. 14, No. 16) is on a cliff that cross-cuts a deep narrow channel filled with Shinarump; the channel is 1,500 feet wide and 90 feet deep (fig. 17). This prospect comprises three adits totaling slightly more than 200 feet in length (fig. 18). The northernmost adit is on the north side of the channel, and the two other adits are in the central and lowest part of the channel. Except for the lower few feet, the Shinarump is a clean white medium-grained sandstone containing only a few mudstone and charcoaly wood fragments. As much as 4 feet of conglomerate containing abundant fragments of sandstone and charcoaly material occurs in the central and lowest part of the channel. The lower foot of Shinarump at the northernmost adit is interlaminated light-brown sandstone and gray mudstone. Some organic material, probably "dead oil" or asphaltic residue of oil, occurs in the lower few feet of the Shinarump and in the upper few inches of the Moenkopi. In the adits exploring the central part of the channel, uranium minerals are localized almost entirely in the lower few feet of the conglomerate and the uranium grade increases downward toward the contact. In places in the conglomerate, fragments of charcoal and mudstone are moderately radioactive. In the northernmost adit on the flank of the channel, the most continuous and highest grade uranium ore occurs in the upper 6-8 inches of the Moenkopi, and only spotty radioactivity occurs in the interlaminated sandstone and mudstone of the Shinarump. The upper surface of the Moenkopi is cut into ridges and rills paralleling the channel trend. Uranium minerals tend to be concentrated in the ridges. The Moenkopi underlying the channel is bleached gray in a zone as much as 4 feet thick near the northern adit and as much as 2 feet thick near the deepest part of the channel. The bleached zone ranges from several inches to several feet in thickness in the area.

FIGURE 18—Yellow Jacket prospect. Mapped by E. S. Davidson and G. A. Miller, 1957. Letters and number indicate location of sample listed in table 5.

Copper minerals accompany the uranium minerals but have a slightly wider and more continuous distribution than the radioactive minerals. Some typical sample analyses are given in table 5; the sample locations are shown in figure 18.

TABLE 5—Analyses of uranium content in samples from the Yellow Jacket prospect
[Analysts: D. L. Schafer, R. P. Cox, J. S. Wahlberg, R. R. Lipp, D. L. Ferguson, C. G. Angelo, and W. W. Niles]

HOTSHOT PROSPECT

The Hotshot prospect (fig. 14, No. 17) is in the central and lowest part of a channel about 400 feet wide and 10-15 feet deep. Exploration consists of about 50 feet of drift across the trend of the channel.

The Shinarump in the mined part is medium-grained limonite-stained sandstone containing moderately abundant layers of conglomerate. The conglomerate contains numerous fragments of charcoaly material and greenish-gray mudstone. Copper staining is noticeable in the Shinarump and in the upper few feet of the Moenkopi. Some asphaltic material also is present. This deposit attained some notoriety during the early days of extensive uranium mining on the Colorado Plateaus because it is so weathered that the uranium minerals are badly out of equilibrium. Radioactivity indicates much greater amounts of uranium than are detected by chemical analyses. Sample HS—1 in table 6 is typical of most of the uranium ore taken from this prospect. Sample CCR—54—1 was taken 6 feet inside of the portal on the north wall of the drift and at right angles to the Shinarump-Moenkopi contact. Copper minerals and yellow uranium (?) minerals were recognizable in the sample, which is higher in grade than typical rocks of the prospect.

TABLE 6—Analyses of uranium content in samples from the Hotshot prospect
[Analysts: C. G. Angelo, H. H. Lipp, J. S. Wahlberg, D. L. Schafer, and R. P. Cox]

SNEAKY-SILVER FALLS PROSPECT

The Sneaky-Silver Falls prospect (fig. 14, No. 18; fig. 17A) is on the north edge of a Shinarump channel which is as much as 4,000 feet wide and 100-130 feet deep. The channel is about 20 feet deep at the north adit and 65-70 feet deep at the southernmost adits. Exploration consists of about 200 feet of drift along the north flank of the channel.

Radioactive minerals are restricted to the lower 1 foot of the Shinarump Member of the Chinle Formation and to the upper few inches of the Moenkopi Formation. The uranium distribution is spotty and discontinuous. The highest grade rock in the Shinarump is in a conglomerate composed of mudstone and charcoaly wood fragments in a medium-grained sandstone matrix. Some radioactivity occurs in interlaminated gray mudstone and white sandstone. Clean sandstone, the dominant rock type filling the channel, is almost devoid of radioactive minerals. The highest grade and most continuous uranium-bearing rock in the Moenkopi is localized along ridges that parallel the channel trend. The main southern adit exposed such a ridge for 30 feet of drift nearest the cliff face; beyond, the ridge flattens out into the smooth flank of the channel, and the uranium minerals are disseminated along the Shinarump-Moenkopi contact. Chalcopyrite and pyrite accompany and envelop the uranium ore. Copper staining is evident on the cliff outcrop at the Shinarump-Moenkopi contact and in areas of anomalously high radioactivity.

DUKE PROSPECT

The Duke prospect (fig. 14, No. 19) is on the same channel as the Sneaky-Silver Falls prospect, and the geologic conditions are very similar in both. However, the mudstone-fragment conglomerate at the base of the Shinarump may be less continuous and more lenticular at the Duke prospect. Exploration has consisted mainly of about 100 feet of bulldozing on the Shinarump-Moenkopi contact. A 1-1/4-foot-long channel sample of the basal part of the Shinarump yielded 0.004 percent uranium on analysis.

SUN DOG PROSPECT

The Sun Dog prospect is in the southeastern part of the Circle Cliffs area (fig. 14, No. 20) and consists of a 130-foot-deep vertical shaft sunk almost entirely in the Shinarump. Red and gray mudstone of the Moenkopi lies on the dump. None of the Shinarump on the dump is very radioactive, but some of the sandstone is stained with copper minerals. The Shinarump in the Circle Cliffs area is generally about 40-50 feet or less thick, except where it fills channels in the underlying Moenkopi. Because the Shinarump exposed in this shaft is more than 100 feet thick, the shaft is almost certainly sunk in a channel deposit. The crossbeds on the surface exposure trend northeast, but they may not reflect the trend of the channel. The shaft was inaccessible at the time of examination, and the lower part of the sandstone was not examined.

BETTY JACK PROSPECT

The Betty Jack prospect (fig. 14, No. 21) is in a small outlying outcrop of the Shinarump Member. The Shinarump at the prospect is a white kaolinitic fine- to medium-grained sandstone with local streaks and partings of fine charcoaly woody material. It rests on the mottled-siltstone unit of the Chinle, and no channeling is apparent. The Moenkopi underlying the mottled unit is not bleached in this prospect. Workings consist of a 125-foot-long incline and about 70 feet of crosscuts (fig. 19). In places the thin beds containing charcoaly material are highly radioactive; one small grab sample contained 1.58 percent uranium. The highest radioactivity was found near the center point of the incline; radioactive minerals are sporadically distributed in the stringers of charcoaly material opened at the bottom of the incline.

FIGURE 19.—Map and longitudinal section of Betty Jack prospect. Mapped by E. S. Davidson and G. A. Miller.

RAINY DAY MINE AND ROCKY MOUNTAIN CO. PROSPECTS

The Rainy Day mine and Rocky Mountain Co. deposits (fig. 14, Nos. 22, 23) have been described previously (Davidson, 1959). The channel in which the deposits occur is about 3,500 feet wide and not more than 25 feet deep. The Rainy Day mine is on the steep south bank of the channel, and the Rocky Mountain prospects are along the gentle north flank of the channel.

Uranium ore in the Rainy Day mine occurs in a pod 1,800 feet long but only a few square feet in cross section. This pod is localized in the top of a small ridge or bank of Moenkopi at the edge of the channel. Chalcopyrite and pyrite occur in a zone that envelops the ore. Organic material, consisting of charcoaly material and asphalt or "dead oil," is ubiquitous in the Shinarump, and 1.68 percent asphaltic material was contained in one sample of the ore.

The Rocky Mountain prospects explore the Shinarump-Moenkopi contact with several hundred feet of drift. In these drifts, most of the radioactive minerals are in the upper few inches of Moenkopi and along the Shinarump-Moenkopi contact.

COPPERHEAD PROSPECT

The Copperhead prospect (fig. 14, No. 24) is on one of the several small channels associated with the main Shinarump channel crossing the Circle Cliffs area. The adit is at the base of the deepest part of the channel; the channel here is about 1,800 feet wide and 30-40 feet deep. Workings consist of about 80 feet of drifts and crosscuts. The sandstone filling the channel is white and medium grained and contains abundant pebbles of chert and quartz, some 6 inch to 1 foot in diameter fragments of mudstone, and small amounts of charcoaly material and asphalt. The lowest 1 foot of Shinarump contains moderate amounts of pyrite, marcasite, and chalcopyrite; and where these sulfide minerals impregnate the rock, scattered concentrations of radioactive minerals occur. One analyzed grab sample of ore contained 1.38 percent uranium.

HOPE PROSPECT

The Hope prospect (fig. 14, No. 25) consists of bulldozer cuts on the east edge of the main Shinarump channel. The channel is no more than 30-40 feet deep at this prospect. The Shinarump consists of a few feet of interlayered micaceous gray mudstone, very fine grained sandstone, and medium-grained sandstone overlain by kaolinitic medium-grained pebbly sandstone. Copper stain appears on fractures in the Shinarump and Moenkopi. Low-count radioactivity was detected at a few places along the Shinarump-Moenkopi contact.

ZELDA PROSPECT

The Zelda prospect (fig. 14, No. 26) is in the Moenkopi Formation, about 20 feet beneath the base of the main Shinarump channel. Exploration consists of a 150-foot adit.

The Moenkopi at the adit is weathered yellow in outcrop; the fresh rock ranges from gray to black, but weathered rock on the dump is light bluish gray. The coloration, which probably was the cause for exploration, is due to moderate amounts of pyrite-bearing asphalt or "dead oil" in pods and stringers along bedding planes and fractures. In the general area, about 10 feet of the Moenkopi underlying the Shinarump-Moenkopi contact is bleached light gray, but some of the Moenkopi that is exposed between the contact "bleached zone" and the prospected rock is reddish brown. No radioactivity or copper stain were noted at this prospect.

THREE PARDNERS PROSPECT

The Three Pardners prospect (fig. 14, No. 27) consists of a 25-foot-long adit and several dogholes along the cliff face. It is on the west edge of the main Shinarump channel where the channel depth is probably about 40 feet.

At the prospect the basal part of the Shinarump consists of 6-8 feet of medium-grained sandstone that contains abundant mudstone chips. The basal unit is overlain by interlayered mudstone and sandstone. Copper stains occur in the lowest 1 foot of the mudstone-chip sandstone and in the uppermost 1 foot of the Moenkopi. Some copper stain occurs at the contact of the mudstone-chip sandstone with the overlying interlayered sandstone and mudstone.

Uranium minerals coat grains and bedding planes in the basal and upper parts of the mudstone-chip sandstone and in the upper 1 foot of the Moenkopi, but their distribution is not continuous. Although the lithology of this prospect is promising, the distribution and grade of uranium content are not encouraging.

DODIE PROSPECT

The Dodie prospect (fig. 14, No. 28), also known as the Midas No. 3, is near the center of a channel that may be distributary to the main Shinarump channel. The channel on which the prospect is located is about 1,300 feet wide and as much as 50-60 feet deep; at the Dodie prospect it is 15-25 feet deep.

The Shinarump in the channel is uniform in lithology and consists of medium-grained kaolinitic sandstone that contains a few discontinuous lenses of mudstone-chip conglomerate. Copper stain occurs in a 2-foot-thick zone of Moenkopi under the Shinarump-Moenkopi contact. Moderate radioactivity occurs at the contact and in the upper few inches of the Moenkopi.

RED HEAD PROSPECT

The Red Head prospect (fig. 14, No. 29), also known as the Torpedo Head, is on the flank of the main Shinarump channel where the channel is about 40 feet deep. Exploration consists of two 6-foot-long adits.

The Shinarump at the prospect is white medium-grained pebbly sandstone. The lower few feet contains small amounts of charcoaly material, green mudstone stringers, and mudstone fragments 1/2-1 foot in diameter. Some gypsum stringers occur along bedding planes and fractures in the upper 1 foot of the Moenkopi and in the lower few feet of the Shinarump. Limonite, probably altered from pyrite, has colored the lower few feet of the Shinarump and the upper few feet of the Moenkopi light yellow to light brown. Copper stain, probably due to weathering of chalcopyrite, occurs in the upper 1 foot of the Moenkopi and in the lower few inches of the Shinarump. Radioactive minerals are distributed unevenly in the copper-stained rock and are concentrated mainly in the Moenkopi where its contact with the overlying Shinarump is irregular. Uranium mineralized rock in the prospect is too low in grade to encourage additional exploration.

MOQUI PROSPECT

The Moqui prospect (fig. 14, No. 30) consists of two adits, which are 60 feet and 40 feet long, respectively. The basal 15 feet of the Shinarump explored by these adits is an interlayered sequence of 2-foot-thick fine-grained sandstone beds and 1-foot-thick gray mudstone beds. The interlayered beds are overlain by white kaolinitic medium-grained pebbly sandstone. Very little copper stain or radioactivity was noted in either adit.

OLYMPIC PROSPECT

The Olympic prospect (fig. 14, No. 31) is an adit driven about 40 feet horizontally across the northeast-dipping contact between the Salt Wash Sandstone Member of the Morrison Formation and the underlying Summerville Formation. The Salt Wash is composed of slightly carbonaceous medium-grained sandstone that contains a few green mudstone interbeds near the base. A sample of the mudstone contained 0.033 percent uranium and 2 ppm (parts per million) selenium.

DREAM PROSPECT

Exploration at the Dream prospect (fig. 14, No. 32) consists of a 100-foot-long inclined shaft, a 10-foot-long drift to the north at the bottom of the shaft, and bulldozer trenches and cuts at the surface. Details of the exploration, the geologic contacts, and the radiometric and chemical analyses of samples collected at this prospect are shown in figure 20.

FIGURE 20.—Dream prospect, Garfield County, Utah. Numbers indicate location of scintillometer reading and value, in milliroentgens per hour.

The bed of economic interest is a 4-foot-thick very fine grained to medium-grained light-brown limonite-stained sandstone that is evenly interlaminated with 1/8- to 1.4-inch-thick layers of dark carbonaceous clayey material. Where exposed in a bulldozer trench 240 feet north of the Dream portal, the mineralized bed is less carbonaceous and less sandy than in the shaft. In the shaft the bed is coarser grained near the base and locally conglomeratic in the lower 1 foot. Flecks of carnotite are disseminated evenly on bedding planes in the carbonaceous material. The basal unit of the Salt Wash underlies the mineralized bed and grades laterally from a whitish-gray very calcareous siltstone to medium-grained crossbedded gray very calcareous sandstone. It contains abundant chert nodules about 2 feet below its upper contact and is more lime-rich in that zone. No carbonaceous material or notable radioactivity were found in this unit.

Above the main mineralized bed is about 1 foot of slightly to moderately radioactive gray fine-grained ripple-laminated sandstone containing a small amount of carbonaceous material. The next overlying units consist of crossbedded light-yellow medium-grained sandstone containing little carbonaceous material and a few 4- to 5-inch-thick interbeds of gray mudstone with virtually no radioactivity.

Moderate to high levels of radioactivity occur in the carnotite-bearing bed for about 50-60 feet along the strike near the shaft, and slight radioactivity is noted in the trench exposure 240 feet to the north. In the shaft the mineralized bed averages about 0.10 percent or less uranium and contains 15-625 ppm selenium. A picked grab sample contained 0.53 percent uranium and 2,250 ppm selenium. The grade does not improve with depth, nor does the ore bearing bed thicken substantially downdip.

SOLITUDE PROSPECT

The Solitude prospect (fig. 14, No. 33) is explored by an 180-foot-long adit through the upper part of the Summerville Formation and about 54 feet of the overlying Salt Wash Sandstone Member of the Morrison Formation. The adit crosscuts the strata, which strike northwest and dip 48° NE. The basal beds of the Salt Wash are not radioactive, but the 6-inch- to 1-foot-thick carbonaceous mudstone beds and interlayered fine-grained white sandstone beds at the end of the adit are slightly radioactive. Channel samples of the beds exposed at the end of the adit were analyzed (table 7) and show that the uranium grade is too low to encourage further prospecting.

TABLE 7.—Analyses of uranium and selenium in samples from the Solitude prospect
[Analysts: H. R. Lipp, D. L. Ferguson, G. T. Burrow, and W. W. Niles. Stratigraphically, SO-1A is the highest bed and SO-1F is the lowest]