Circular 68—Niobium-bearing Sanostee heavy minreal deposit, San Juan Basin, northwestern New Mexico

By E. C. Bingler, 1963, 63 pp., 15 plates, 15 figs., 1 sheet.

The sedimentary sequence exposed near Sanostee, New Mexico, includes undifferentiated Jurassic rocks; Upper Cretaceous Dakota (?) Sandstone, lower Mancos Shale, Gallup Sandstone, and upper Mancos Shale; and tertiary Chuska Sandstone. Heavy mineral and clay mineral zones in the section are correlated with similar zones at Todilto Park, NM. Littoral marine, lagoonal, and nonmarine facies are represented in the Gallup Sandstone. Mineralogic composition, grain morphology, and inclusions in quartz indicate that during deposition of the Gallup Sandstone sediments, the immediate source area contained both crystalline and sedimentary rocks with the latter predominating.

Six en echelon heavy mineral lenses occur within the littoral marine unit of the Gallup Sandstone. The principal minerals constituents are quartz, ilmenite, zircon, tourmaline, leucoxene, and brookite. Both the heavy minerals and the normal Gallup Sandstone contain niobium-bearing heavy minerals and similar mineral suites. It is concluded that the heavy mineral lenses were formed by local concentrations of heavy mineral during deposition of the Gallup Sandstone sediments. Niobium-bearing ilmenite, leucoxene, anatase, and brookite impart a high niobium content to the deposit. Twenty-seven quantitative X-ray fluorescent analyses of three heavy mineral lenses reveal a range of 0.09 to 0.15 weight % niobium pentoxide. The deposit is also estimated to contain 9 weight % zircon and 10 weight % titanium dioxide. Probable (57,400 tons), possible (266,100 tons), and maximum possible (2,064,500 tons) tonnage estimates are made.

It is the purpose of this study to examine in detail heavy mineral lenses which occur within the Gallup Sandstone near Sanostee, NM. Similar deposits have been located in other parts of the San Juan Basin, but none has been studied in detail. All known deposits of heavy minerals in the upper Cretaceous of northwestern NM contain substantial amounts of radioactive zircon which has led to their discovery by uranium prospectors. These deposits have been found to contain substantial amounts of titanium, and hence the common reference to them as "titaniferous black sand deposits." The Sanostee deposit has been studied especially because it has an unusually high niobium content which may make it a commercial source of this metal. Field work consisted of preparing a reconnaissance geologic map and a plane table geologic map of the deposit; an organized sampling program was carried out during the summer of 1960. Laboratory work was performed at the NMIMT during the fall of 1960. In this report, data are presented substantiating the opinion that the lenses are beach placers formed from pre-existing sediment and were concentrated by the reworking of these sediments during upper Cretaceous time. The mineralogy of the deposit is determined and conclusions are presented with respect to the source of the heavy minerals. The niobium content of the individual lenses is determined by X-ray fluorescent spectroscopy.