Geological Survey Circular 217 Preliminary Report on the White Canyon Area, San Juan County, Utah

The principal known uranium deposits in the White Canyon area are shown in figure 2 and plate 1. All the ore produced has come from the Shinarump conglomerate where the uranium, commonly associated with copper, occurs in disseminated deposits in the sandstone and in veins along fractures. Uranium and copper minerals also make up low-grade disseminated deposits and vein deposits in the sandstones of the lower part of the Chinle formation and the sandstones and siltstones of the Moenkopi formation.

Figure 2.—White Canyon and surrounding area, San Juan County, Utah. (click on image for a PDF version)

The uranium ore in the Shinarump conglomerate occurs principally in the lower third of the formation; the thickness of the ore-bearing sandstones in few places exceeds 10 feet, and in most deposits is less than 5 feet.

Localization of deposits

Relation of deposits to channel fills

In other parts of the Colorado Plateau most of the uranium minerals are reported to be chiefly in deposits that fill ancient channels in the Shinarump and Morrison formations. The belief that these channel fills are a primary factor in the localization of ore bodies has been one of the more potent arguments in favor of a syngenetic origin of the uranium. In the White Canyon area, although most of the larger ore bodies are in channel deposits, many small deposits are in the base of the Shinarump and along the contact between the Shinarump and Moenkopi formations where there is no evidence of channeling and subsequent filling. Conversely, many obvious channels have no copper or uranium minerals.

Examples of deposits in channel fills are as follows:

(1) The Hideout claim is in a channel 50 to 75 feet wide and about 7 feet deep. Uranium and copper minerals are in the lower 5 feet of the channel fill, and form a deposit about 50 feet wide. However, vertical fractures in the Shinarump conglomerate have also been mineralized at the Hideout claim.

(2) The Posey mine in Red Canyon is in a deposit filling a channel 40 to 50 feet deep and about 175 feet across.

(3) Scenic no. 2, Scenic no. 4, Frey no. 4, and Yellow John claims are all in obvious channels.

Examples of deposits outside of channel fills are as follows: (1) The deposits of the Jerry and Bankrupt claims are in a purplish sandstone 10 to 15 feet above the base of the lower unit of the Chinle formation. The uranium minerals appear to be associated with a fractured zone rather than with any channel fill.

(2) Along the southwest side of Frey Canyon the contact between the Shinarump and Moenkopi formations has been mineralized with little or no relation to the channels. Frey no. 1 claim is in a shallow indistinct channel, but east of this claim, the lower 2 feet of the Shinarump and the upper 3 feet of the Moenkopi contain sporadic uranium(?) minerals along more than one-fourth mile of their outcrop.

(3) At the Woodenshoe(?) claim the Shinarump conglomerate lies with apparent conformity on the Moenkopi formation. Uranium and copper minerals in the Shinarump appear to follow a set of east-west fractures. A channel within the Shinarump is filled with gray siltstone and fine-grained sandstone, and this fill has fewer uranium and copper minerals than the enclosing sandstone.

In addition to the above rather clear-cut examples, many of the uranium deposits in White Canyon are in beds that may or may not be channel fills. Among these is the Happy Jack mine, the largest known deposit in the district. At this locality there is no obvious channeling or scouring, but a structure-contour map prepared by the Atomic Energy Commission does show a broad shallow depression on the top of the Moenkopi formation. Whether this "sag" represents a broad indistinct channel or whether it indicates a small structure is not apparent.

Relation of deposits to structure

In many deposits, copper and uranium minerals coat fracture surfaces. Most of these exposures do not penetrate beyond the oxidized zone, and the minerals are secondary.

Deposits where the ore minerals are in fractures are as follows:

(1) The Woodenshoe(?) claim has already been mentioned as a deposit not related to channel fill. In this deposit, secondary copper and uranium minerals follow fractures and apparently spread from these fractures into and along bedding planes. Much of the secondary copper is in discrete blebs along the fractures, suggesting that small masses of sulfides had been oxidized in place.

(2) Mineralization of fractures at the Hideout claim has already been mentioned.

(3) In the Moenkopi formation on the north side of White Canyon opposite the Happy Jack mine a vertical fracture is filled with a silica vein containing uraniferous chalcocite. The vein has little lateral persistence; whereas its vertical extent is indeterminable. The top of the vein as exposed is about 20 feet below the top of the Moenkopi, which is overlain directly by shales of the Chinle formation.

(4) In the Happy Jack mine bornite, chalcopyrite, covellite, and pitchblende fill closely spaced parallel fractures in the sandstone and form veinlets as much as one-fourth inch wide parallel to these fractures. Polished sections of highly uraniferous sandstone are markedly banded as a result of this structure.

In addition to mineralized fractures, the sandstones of the Shinarump conglomerate are jointed into blocks a few inches to 10 feet across. Many of these joints are discontinuous; some have been deflected in crossing between beds. These joints are especially common above many of the higher-grade deposits and in these deposits the channel fills are generally closely jointed or shattered. In contrast, channel fills that are only slightly fractured tend to be barren or have very low grade deposits.

Relation of deposits to chemical controls

The precipitation of the copper and uranium minerals has been localized, at least in part, by the chemistry of some components of the Shinarump conglomerate. Both copper and uranium minerals replace logs and other carbonized vegetal matter, and uranium seems to be especially common in some of the charcoal fragments. In addition, some clay balls in the sandstone evidently were favorable host rocks and have been highly mineralized. On the other hand, megascopically similar balls have apparently inhibited the ore-bearing solutions. These latter remain unmineralized, although surrounded by copper and uranium salts.

Summary

It is obvious that the three factors controlling deposition of the ore minerals are interrelated, and that a locality where all are present is more likely to be the site of a large ore body than a locality that shows only one of these factors. The fact that many channels that are unmineralized are associated with only a few fractures, plus the fact that many of the uranium and copper minerals are associated with channels where fractures are abundant, suggests that the fractures were the primary routes of the ore-forming fluids and that the porous rocks of the channel fills were merely favorable host rocks in which the solutions migrated.

Mineralogy of the deposits

The uranium occurs as the oxide, either as pitchblende or uraninite, in at least three deposits: the Happy Jack, Posey, and Hideout mines. Both hard (primary?) and soft (secondary?) pitchblende have been identified. Secondary uranium hydrous sulfates, phosphates, oxides, and silicates occur with the oxide minerals in these properties, and in others where the oxides have not been found. The secondary uranium minerals in the White Canyon area include the following:

In many deposits carbonized wood, iron and manganese oxides, and veinlets of hydrocarbon are abnormally radioactive, and the source of this radioactivity is being investigated. Some of the manganese oxides are known to contain uranium.

Base-metal sulfides have been found in every deposit in the White Canyon area that has been explored beyond the oxidized zone. These sulfides include chalcopyrite, chalcocite, bornite, covellite, arsenopyrite(?), galena, sphalerite, and pyrite. At the Happy Jack mine pyrite appears to have been the earliest of the sulfides, followed by bornite, chalcopyrite, covellite, and pitchblende. The relative ages of the other sulfides have not been determined. Gold and silver have been reported in assays from the Happy Jack mine. The copper minerals are associated with the uranium in all the principal uranium deposits, and are also found in the Shinarump conglomerate where little, if any, uranium occurs. The secondary copper minerals in the oxidized zones are the hydrous sulfates and carbonates. Malachite, azurite, brochantite, antlerite, chalcanthite, and chalcoalunite have been identified. Gangue minerals include quartz, clay minerals, and iron and manganese oxides in all the deposits; and alunite, calcite, gypsum, pyrite, jarosite, vein quartz, allophane, gibbsite, opal, and chalcedony in some deposits. Erthyrite, halotrichite, and cobaltoan siderotil have been identified at the Happy Jack mine. Cobalt-bearing pickoringite has been identified at the Scenic no. 4 claim.

In some of the deposits, later silica has been introduced into sandstone of the Shinarump conglomerate, producing veinlets through the rock and crystal faces on the quartz grains. At least one period of silica veining is believed to have followed the formation of the base-sulfide minerals of the Happy Jack mine. Calcite, iron oxides, copper carbonates, and jarosite have embayed the quartz grains in some deposits, partially replacing many of the quartz out-growths.

Alunite fills some fractures and apparently has replaced siltstone and sandstone of the Shinarump adjacent to these fractures. Spectrographic analysis indicates that the alunite is the potassium variety, and not the natro or sodium type (Weeks, Alice, personal communication). Alunite has been found at the Gonway, North Point, and Markay nos. 2 and 3 claims.

Calcite is a cement in many sandstones of the Shinarump conglomerate and is a coating on fractures in the upper sandstone at the Gonway and North Point claims. It is finely crystalline and replaces both microcline and quartz.

Gypsum is a fracture filling in siltstone of the Shinarump conglomerate at the North Point and Gonway claims and replaces wood fragments in sandstone of the Shinarump at the Jacobs Chair claim.

Pyrite is disseminated in the sandstones of most of the uranium deposits, and is believed to be one of the earliest of the sulfide minerals. Brown "freckling" in some of the sandstones of the Shinarump conglomerate may be pyrite crystals that have been altered to hydrous iron oxides.

In the siltstones of the Shinarump conglomerate of many deposits, jarosite is commonly associated with carbonized wood, and in sandstones of the Shinarump, it forms a cement between the grains and replaces some of the feldspar and quartz. The jarosite is believed to be an alteration product of pyrite.

Allophane forms yellow, greenish-blue, and pale-blue opalescent coatings on fractures cutting siltstones of the Shinarump and Moenkopi formations at the North Point and Gonway claims. The mineral fluoresces intense yellow. A white clay-like mineral, identified as gibbsite, forms coatings and nodules on the allophane.

Locally tan and black opal cements sand grains and veins the sandstone at the North Point and Gonway claims. The tan opal has an intense yellow fluorescence. Both are associated with abnormally radioactive sandstone. Chalcedony forms a cement in some of the radioactive sandstones in the White Canyon area.

Siltstones of the Moenkopi formation have been bleached creamy-white for as much as 5 feet beneath some deposits in altered Shinarump conglomerate. Bleaching appears to have been more intense in the western part of the mapped area, especially the area near the Happy Jack mine. In some localities the beds of the Moenkopi formation have been bleached for as much as 1 foot from veins of copper and uranium minerals.

Origin of the ores

The origin of the copper-uranium ores of the Colorado Plateau has been disputed for many years. Two main hypotheses have arisen, each with a large and impressive number of adherents. The first and probably the most widely advocated hypothesis suggests that the ores are syngenetic, that is, they were formed at the same time as the enclosing sedimentary rocks. Later, ground water may have dissolved and reprecipitated the constituents, but the essential materials were already present in the original sediments. The second hypothesis suggests that the ores are of igneous origin and were precipitated from hydrothermal solutions. A third hypothesis, which has attracted fewer followers, suggests that the elements of the ores originated in the volcanic tuffs of the Chinle and Morrison formations and were subsequently leached and redeposited.

The study of the White Canyon area is still in its early stages. Both the general geologic mapping and the detailed mapping of the ore deposits is less than half completed; laboratory studies of the ores have just been started, It is probably too soon to draw definite conclusions about the origin of the ores of this district. Nevertheless, the field relations and the mineralogy of the deposits in the White Canyon area seem to support the hydrothermal hypothesis. The significant features can be summarized as follows:

(1) Many of the deposits apparently are controlled by fractures. These mineralized fractures are not confined to the Shinarump conglomerate, but are sparsely present in both the Moenkopi and Chinle formations. Fractures apparently controlled some of the ore deposition even in mineralized channel fills. This suggests that the fractures were the primary route of the ore-forming solutions, and that the channel fills were favorable host rocks with both physical and chemical features that favored precipitation of the minerals.

(2) The mineral suite of the area is typically hydrothermal. Especially suggestive of hydrothermal deposits are galena, alunite, hard (primary?) pitchblende, and the arsenic minerals. Although every mineral found in the district may have been precipitated from comparatively cool water, the repeated occurrences of the entire assemblage over the whole area suggests hydrothermal origin.

(3) Recent unpublished investigations by Stieff and Stern of the Geological Survey indicate that pitchblende from the Happy Jack mine has a lead/uranium ratio that would indicate an age of 55 to 60 million years (that is, early Tertiary). Other determinations by Stieff and Stern indicate about the same age in years for uranium deposits in the Shinarump and Morrison formations elsewhere in the Colorado Plateau. The youngest accepted age for Upper Triassic formations is 150 million years. This seems incompatible with the syngenetic hypothesis, unless it is assumed that some major event caused contemporaneous solution and redeposition of the ore minerals in all formations of the plateau.

Therefore, pending further investigation, the authors favor the hypothesis that the ores are of deep-seated origin and were brought to their present locations in early Tertiary time by hydrothermal solutions. This mode of origin, however, has not been proven, and the reader is reminded that these conclusions are subject to change.

Grade

Figure 2 indicates the estimated grade of rock from some of the properties in the White Canyon area. A grade in excess of 0.2 percent uranium must be maintained for most operators to realize a profit. Some ore shipped from the Happy Jack, Posey, Bell, and Yellow John mines is said to contain more than 0.3 per cent uranium.

Copper is contained in most of the ore, commonly in concentrations less than 1.0 percent, although more than 5.0 percent copper has been reported by Granger and Beroni (1950, pp. 16-19) in individual samples.

Production

Although the White Canyon area was prospected as early as 1880, the only metal produced prior to 1949 was a small amount of copper. In 1951 uranium and copper were being produced from the Happy Jack, Yellow John, and Bell mines in White Canyon, and the Posey mine in Red Canyon. Seven others with favorable possibilities are idle. These properties are the Frey no. 4, White Canyon no. 1, Hideout, Scenic no. 4, Scenic no. 2, Gonway and North Point, Dead Buck, and W. N. claims. In 1950 the Vanadium Corp. of America erected a pilot mill for the processing of uranium ore east of the Colorado River, opposite Hite, Utah. This mill has been receiving ore exclusively from the Happy Jack mine.

The ore from all other properties is trucked to Monticello, Utah, where it is crushed and shipped to the Simplot Co. mill, Salt Lake City.