Mineral Resources of the West-Central Arizona and Southeastern California Detachment Terrane MLA 13-92 (1992)

Potential for Recovery of Rutile and Other Byproducts From Western Copper Tailings R.I. 9158 (1987) 23 p.

In Situ Leach Mining Proceedings: Bureau of Mines Technology Transfer Seminars, Phoenix, AZ, April 4, and Salt Lake City, UT, April 6, 1989 IC 9216 (1989) 112 p.

In Situ Mining Research - Proceedings: Bureau of Mines Technology Transfer Seminar, Denver, Colo., August 5, 1981 I.C. 8852 (1981)

Tertiary sedimentary units in central-western Arizona are of interest because they evince evidence of potassium alteration and because they host Mn, Fe, and Cu mineral deposits. Little work has been done to characterize these units geochemically. Mineralization typically occurs as replacement ores and as disseminated to massive tabular ores (particularly the manganese deposits), and as fracture and fault filling deposits (Spencer and Welty, 1986). Mining districts in this province have produced copper, manganese, iron, and gold as well as lead, zinc, and silver accompanied by common gangue minerals, including: quartz, calcite, chlorite, and barite. Manganese production in the Buckskin-Rawhide Mountain area totaled approximately 24 million pounds of Mn; the Artillery Mountains district yielded more than 93 million pounds making it the largest manganese producer in the United States (Spencer and Welty, 1986). Associations between K-metasomatism and detachment-related mineralization have been suggested in the southwestern United States (Chapin and Glazner, 1983; Brooks, 1986; Chapin and Lindley, 1986). Alteration due to infiltration K-metasomatism, often associated with hematization, was the dominant process responsible for mineralization in the Tertiary strata. Similar alteration assemblages indicating K-metasomatism (secondary K-feldspar-quartz-calcite and hematite) have been previously mapped in central-western Arizona south to Picacho Peak (Brooks, 1986), north to the Artillery Mountains, and west to the Whipple Mountains, spanning over 40,000km2.

Northern Arizona has attracted pioneers in North American geology since the days of John Wesley Powell; when northern Arizona was considered to be a part of our "last frontier." Perhaps Powell, Darton, Dutton, Walcott, Noble, Gregory, Gilbert, Davis, or Robinson would not have been surprised to learn that the geology of northern Arizona would play an important part several generations later in the geologic exploration of a new frontier--that of space. Largely because of the variety of geologic terranes, good exposures, and the presence of geologic analogs of lunar features, Apollo astronauts received training in ten different field sites in northern Arizona, including operational rehearsals for lunar geologic traverses. Because of the importance of the geology of northern Arizona to both the history of the science and to an understanding of the geology of North America, papers were solicited to provide an up-to-date synthesis of this geologically varied region. The contributors represent a variety of sponsoring institutions. Most are affiliated with the U.S. Geological Survey, Northern Arizona University, or the Museum of Northern Arizona; other universities and research agencies are represented, as are state agencies and mining companies.

The Mormon Lake quadrangle is in the northern part of the Mormon volcanic field, a late Cenozoic volcanic province on the southern margin of the Colorado Plateau (Holm and others, 1989). Except for Pleistocene and Holocene surficial deposits, all of the rocks mapped on the quadrangle are Miocene and Pliocene volcanic rocks. All geologic contacts and faults were traced in the field. Map units were defined on the bases of lithology and morphology, and stratigraphic relationships were determined in the field on the basis of traditional geologic principles such as superposition and cross-cutting relationships. The mapping strategy was to map all lava flows and vent structures that could be distinguished in the field as discrete units, and to trace each flow to its source vent. Each vent structure was given an identification number (see "Vent and flow identification numbers"), and related lava flows were identified with the same number. Small vent deposits and related flows (Tys and Tyb) that lack morphologic distinction on the map were not, however, given separate identification numbers. Multiple contiguous lava flows of the same lithology from the same vent, and individual flow units of compound lava flows and lava flow fields were not mapped separately (for example, Tibv, Tobs).

Geologic map and geochemical data for the Bradshaw Mountains in the Mayer-Crown King area of Yavapai County, Arizona. Map scale 1:24,000

The U-Pb data described in this report were produced to determine the ages of granitic rocks in Arizona and the timing of metamorphic and deformational events. Two developments emerge from the data reported here that are especially significant. Two granites, one from the Mazatzal Mountains east of Phoenix and one from the Santan Mountains southeast of Phoenix, yielded dates between 1630 and 1640 Ma. This is unusually young for early Proterozoic granites in Arizona, although two granites in the Maricopa Mountains southwest of Phoenix have yielded similar dates (Eisele and Isachsen, in review; Joe Wooden, written communication, 1998). Possibly, these dated granites are part of a belt of similar-age granites that roughly occupy the boundary between Pinal Schist on the southeast and metavolcanic and metasedimentary rocks of the Tonto Basin Supergroup to the northwest (Conway and Silver, 1989; Reynolds and Dewitt, 1991).

Mafic dikes and sills intrude sediments of the Late Jurassic (Early Cretaceous?) lower McCoy Mountains Formation in western Arizona. Some units show evidence for intrusion into wet, unconsolidated sediments, indicating that intrusion was approximately contemporaneous with sedimentation. Some of the units also show evidence for subaerial crystallization, and may in fact be lava flows. Attempts to directly date these rocks have been hampered by metamorphic recrystallization and by our inability, despite repeated attempts, to extract zircons from them. Five units from the Granite Wash Mountains, and two from the Plomosa Mountains, were sampled for geochemical and isotopic study in order to place some further constraints on their tectonic setting. Major element, trace element, and isotopic data reveal a suite of high-AI basaltic to andesitic rocks that are sub-alkaline to moderately alkaline and slightly to moderately enriched in light rare-earth elements (LREE), and have epsilon Nd values ranging from +5 to -6. Two gabbroic sills from the Granite Wash Mountains have epsilon Nd of +5, indicating they were derived from depleted mantle sources. The geochemical and isotopic variation in the suite can be explained either as a product of heterogeneous mantle sources or variable interaction of depleted basalts with continental crust. These rocks appear to be transitional in composition and tectonic setting between rift-related basalts of the Bisbee basin and Jurassic diorites intruded during crustal extension in the eastern Mojave desert region.