A heavy-mineral study was made of the following formations in the Lucero uplift: Triassic: Chinle Formation and Wingate Sandstone; Jurassic: Carmel Formation, Entrada Sandstone, Todilto Formation (not analyzed), Summerville Formation, Bluff Sandstone, and Morrison Formation; Cretaceous: Dakota Sandstone. Emphasis was placed on the pre-Morrison Jurassic rocks.

Heavy minerals identified from these rocks consist dominantly of zircon, garnet, tourmaline, rutile, and several opaque minerals, and very minor epidote, biotite, staurolite, and apatite. This limited suite of mostly rounded, stable heavy minerals indicates that the rocks concerned are multicycle sediments, and agrees with the conclusion previously derived from utilizing other stratigraphic tools in studying these rocks. Thus, in this respect, the usefulness of heavy minerals as a stratigraphic tool is demonstrated.

Furthermore, the pre-Morrison part of the section, in which relatively abundant amounts of magnetite-ilmenite occur, is readily distinguishable from the Morrison Formation in which these minerals are virtually absent. When the pre-Morrison Jurassic rocks are viewed in sequence, it appears that the Carmel and lower Entrada are characterized by low zircon-garnet and high magnetite-ilmenite content, the upper Entrada by a high zircon-garnet and low magnetite-ilmenite content, and the Summerville and Bluff by a high zircon-low garnet and variable magnetite-ilmenite content. Nevertheless, with the exception of the upper Entrada, the differences in per cent distribution of the heavy minerals are not sufficient to unequivocally characterize any single pre-Morrison unit. Thus, in this respect the heavy minerals are not as useful a stratigraphic tool as they might be if the suite were mineralogically more varied.

Prior to the determination of the heavy-mineral content by using standard techniques of counting individual grains, an attempt was made to estimate the heavy-mineral content. A comparison of the results of the two methods shows that, even with a simple suite of easily identifiable heavy minerals, an estimated per cent distribution is not reliable and does not justify the apparent saving in time.

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