Music Valley

Location: California, United States (34.015, -115.940 approx.)

Commodities: thorium; rare earth elements

Deposit model: metamorphic xenotime and monazite · unclassified

Geology

Meager data indicate that mineralization was the result of either lit-par-lit injection of a granitic magma into a pre-existing igneous or sedimentary rock, or intrusion of the hornblende diorite. It seems most reasonable to expect that the diorite at the U-Thor deposit assimilated parts of the gneiss and in the process incorporated an occasional grain of xenotime. The contact between the two rocks here is gradational across 2 to 5 feet, and diorite near the contact contains an abnormal amount of biotite, as much as 15 percent locally. As the diorite should have been emplaced at temperatures that exceeded 700deg C, one might expect assimilated xenotime (if cerium earths were available) to be recrystallized as monazite at such temperature. For whatever reasons, the fact is that xenotime was not recrystallized. (Evans (1964)) In using figure 11 note that the three lines each have a different slope and represent trends for the samples as a whole. For example, consider the U-Thor 3 sample: for a total rare-earth content of 8.36 percent, ground radioactivity is about 0.2 mr/hr, phosphorus content is 0.73 percent, and thorium content is 0.39 percent. The points do not fall on each of the respective curves. Because of this one should not expect great accuracy in plucking values at random from the curves (rare-earth content as related to radioactivity especially). There are not enough points to strongly support the position of each line but still the trend is definite and important. (Evans (1964)) “Field work starting in March of 1959 was carried on during April of that year and during July 1960, and consisted of detailed geologic mapping through plane table and Brunton-chain surveys, and general geologic mapping with use of aerial photos. Ground radioactivity surveys were made with an Engineers Syndicate, Ltd., Model SC-10 scintillation counter used in a grid system. Net radioactivity was then recorded on the grid in milliroentgens per hour (mr/hr), and isorads drawn from these readings.” (Evans (1964)) The majority of evidence and the best evidence point to a detrital origin for the rare earth minerals, modified later by metamorphism. (Evans (1964)) A pilot run in August 1958 on a — 60 mesh (ASTM) material was fairly successful. One of the gravity and magnetic concentrate fractions was analyzed spectrographically and contained 16 percent phosphorus, 0.4 percent titanium, 4.4 percent thorium, 6.5 percent cerium sub-group lanthanides, 18.0 percent yttrium, 2.2 percent ytterbium, and 0.1 percent erbium (C. A. Richards, oral communication, August 1959). (Evans (1964)) A method based principally on the ratio of rare-earth content to radioactivity can be used for roughly estimating a part of the radioactive mineral reserves. An average anomaly reading between two isorads can be computed by adding their respective values and dividing by two. This new value is used to obtain an average rare-earth content from the solid line relation on figure 11 for the Pinto Gneiss between the two isorads, and projected, say, to a depth of 1 foot. The number of cubic feet of gneiss between the isorads and to 1 foot of depth can be closely computed by use of a planimeter. A specific gravity of 3.0 was found to be a fair average value for the gneiss. There are then 3.0 X 62.4 (wt. of 1 cu. ft. of water) or 188 lbs/cu ft, and 2000 lbs/ 188 lbs per cu ft, or 10.1 cubic feet per ton of gneiss. If 188 lbs/cu ft is multiplied by the number of cubic feet of gneiss under consideration and that value divided by 2000, the number of tons of gneiss is obtained. Multiplication of the average rare-earth content of the gneiss (value obtained from figure 11 ) by the number of tons gives the rare-earth content in tons. (Evans (1964)) Pilot tests show that mineralized Pinto Gneiss can be processed by mechanical means to obtain a xenotime-rich concentrate. After primary jaw crushing, secondary grinding in a ball mill, and screening (— 60 mesh, ASTM), material can be concentrated on Wilfley tables. Table concentrates consist of monazite (G. = 5.5), magnetite (G. = 5.2), zircon (G = 4.7), xenotime (G. = 4.5), sphene (G. = 3.5), apatite (G. = 3.2) and some biotite (G. = 3.0). The biotite has a tendency to adhere to the xenotime crystals and is difficult to remove. Possibly crushing to a finer size may prove more effective in removing the biotite. An effective magnetic separation of the dried Wilfley table concentrates can be made because of the differing magnetism of the components: magnetite is strongly magnetic, xenotime and monazite moderately so, and zircon, sphene, and apatite are practically nonmagnetic. (Evans (1964)) “Music Valley is about 10 miles southeast of Twenty-nine Palms and 2 miles east of the Gold Park gold mining district, in the Pinto Mountains of San Bernardino and Riverside Counties (figure 1). Wind that frequently blows through the valley and creates a somewhat eerie sound constitutes the "music" for which the valley apparently was named. Of the several radioactive mineral occurrences in this area, those in the southern Music Valley have by far the strongest radioactive anomalies and therefore were studied in detail.” (Evans (1964)) At the Baby Blue prospect a shallow vertical cut has exposed mildly radioactive Pinto Gneiss (figure 2 and map 1). Gneiss adjacent to the cut is coated by desert varnish and is generally weathered to a depth of about 1 foot. Locally, rock is stained rusty-brown, especially along fractures; likely the result of the weathering of magnetite and iron-rich biotite. (Evans (1964)) Much of the hilltop is underlain by highly radioactive Pinto Gneiss. An anomaly of 1.7 mr/hr was recorded in a pit near the central part of the area mapped (figures 6 and 7). An anomaly of 0.8 mr/hr was recorded in a less pronounced center of radioactivity 90 feet southeast of the pit adjacent to a steep but low cliff. An elongate radioactive zone about 270 feet by 135 feet surrounds the pit area, and roughly defines the surface shape and areal extent of mineralized gneiss. (Evans (1964)) Gneiss in the pit area is extremely biotite-rich and contains abundant orange grains of xenotime readily visible to the unaided eye (photo 3). Xenotime composes nearly 35 percent of selected hand specimens. Minor quantities of monazite and allanite are also present. (Evans (1964)) Exploratory work consists of several shallow prospect pits and open cuts. The largest pit, in the center of the area mapped, is 37 feet long in an east-west direction, 7 to 15 feet wide, and 1 to 7 feet deep. Nearly 3 miles of often steep but good dirt road lead to the area from the sandy Music Valley road. About 50 tons of mineralized gneiss have been removed from the pit, transported to the mill 3 and a half miles southeast of Twentynine Palms, and stockpiled (figure 1). (Evans (1964)) A small pit has been dug in well weathered, sheared Pinto Gneiss cut by a narrow andesitic-basalt dike. The rock in the pit is discolored along fracture surfaces in the same manner as at the Baby Blue (Dixie Girl) Prospect. Medium- to coarse-grained augens of oligoclase interrupt the thin biotite folia which contain small amounts of microscopic xenotime and monazite crystals. Foliation trends north and northwest, and dips from 35 degrees east to 60 degrees northeast respectively. Radioactivity is mild to medium in intensity and the maximum anomaly of 0.45 mr/hr was recorded in a shear zone at the northeast end of the pit (figure 3). (Evans (1964)) Highly sheared Pinto Gneiss has been exposed by a bulldozer cut and two shallow open cuts. Biotite folia in the gneiss are as much as 2 inches thick, but average only about 1 inch. Rock is weathered to a depth of 1 foot to 2 feet and is stained rusty-brown along fracture planes. The biotite is locally altered surficially to a gold-colored material. Radioactivity is nil except in one small area (figure 4) where an anomaly of 0.38 mr/hr was recorded. Thin sections of gneiss here showed minor amounts of very fine grained xenotime and monazite in biotite rich areas. (Evans (1964)) Several areas of anomalous radioactivity have been explored at the Uranus Number 4 deposit (figures 4 and 5). An anomaly of 1.8 mr/hr was reported here by Walker, Lovering, and Stephens in 1956 (p. 26). Probably this reading was recorded at Pit 2 which provided most of the 500 tons of Pinto Gneiss that has been stockpiled at the Silver Bell processing plant located 2 J/2 miles north of Twentynine Palms on Utah Trail. The radioactivity of the stockpile ranges from 0.08-0.24 mr/hr, averaging 0.11 mr/hr. Radioactivity anomalies of mild to medium intensity near Pits 2 and 4 are shown in figure 4. There are two areas that have relatively high readings; one is just south of Pit 4 (0.22 mr/hr), and the other near the face of Pit 2 (0.15 mr/hr). Radioactivity was more intense here before the removal of rock to the stockpile. A pronounced radioactive belt about 300 feet long and close to 60 feet wide extends from the area adjacent to Pits 3 and 6 through Pit 4 and open cut 5, to open cut 1 (figure 5). The central part of this belt has an anomaly of 0.12 mr/hr. (Evans (1964))

Published resource estimates

As compiled by USGS USMIN from the cited studies. Resource classes follow the source; "approximate" flags values USMIN reports as approximations. These are not current company reserve statements.

Exploration and site history

• Discovery — The USGS and the U.S. Atomic Energy Commission conduct ground and airborne reconnaissance work which led to local prospecting and the discovery of radioactive material in Music Valley, 1949–1952 (Evans (1964))
• Exploration — The USGS and U.S. Atomic Energy Commission conduct ground and airborne reconnaissance work, 1949–1952 (Evans (1964))
• Intermittent Exploration — Detailed geologic mapping through plane table and Brunton-chain surveys; Geologic mapping on aerial photos, 1959–1960 (Evans (1964))

Record imported from USGS USMIN ver. 4.0 (June 2019). Developments after that date appear on facility records, not here; see the methodology.