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The Miocene Marnoso-arenacea Formation (Italy) is the only ancient sequence where deposits of individual submarine density fl ow deposits have been mapped in detail for long (>100 km) distances, thereby providing unique information on how such fl ows evolve. These beds were deposited by large and infrequent fl ows in a low-relief basin plain. An almost complete lack of bed amalgamation aids bed correlation, and resembles some modern abyssal plains, but contrasts with ubiquitous bed amalgamation seen in fan-lobe deposits worldwide. Despite the subdued topography of this basin plain, the beds have a complicated character. Previous work showed that a single fl ow can commonly comprise both turbidity current and cohesive mud-rich debris fl ows. The debris fl ows were highly mobile on low gradients, but their deposits are absent in outcrops nearest to source. Similar hybrid beds have been documented in numerous distal fan deposits worldwide, and they represent an important process for delivering sediment into the deep ocean. It is therefore important to understand their origin and fl ow dynamics. To account for the absence of debrites in proximal Marnoso-arenacea Formation outcrops, it was proposed that debris fl ows originated within the study area due to erosion of mud-rich seafl oor; we show that this is incorrect. Clast and matrix composition show that sediment within the cohesive debris fl ows originated outside the study area. Previous work showed that intermediate and low strength debris fl ows produced different downfl ow-trending facies tracts. Here, we show that intermediate strength debris fl ows entered the study area as debris fl ows, while low strength (clast poor) debris fl ows most likely formed through local transformation from an initially turbulent mud-rich suspension. New fi eld data document debrite planform shape across the basin plain. Predicting this shape is important for subsurface oil and gas reservoirs.Low strength and intermediate strength debrites have substantially different planform shapes. However, the shape of each type of debrite is consistent. Low strength debrites occur in two tongues at the margins of the outcrop area, while intermediate strength debrite forms a single tongue near the basin center. Intermediate strength debrites are underlain by a thin layer of structure less clean sandstone that may have settled out from the debris fl ow at a late stage, as seen in laboratory experiments, or been deposited by a forerunning turbidity current that is closely linked to the debris fl ow. Low strength debrites can infi ll relief created by underlying dune crests, suggesting gentle emplacement. Dewatering of basal clean sand did not cause a long runout of debris fl ows in this location. Hybrid beds are common in a much thicker stratigraphic interval than was studied previously, and the same two types of debrite occur there. Hybrid fl ows transported large volumes (as much as 10 km 3 per fl ow) of sediment into this basin plain, over a prolonged period of time.

The study of unconformity-type deposits major sources of uranium that were discovered in the past 15 years in Australia and Canada was part of the U.S. Department of Energy National Uranium Resource Evaluation (NURE) program. Pancontinental Mining Limited kindly gave Dick Grauch and I access to Jabiluka core and made their geological and geophysical data available for inclusion in our reports. Samples were collected from 19 cores. Data and interpretations from the study of Jabiluka should aid in defining characteristics and settings of these world class deposits and guild exploration for similar deposits in the United States. This paper is a description of drill-hole T129V, located in Jabiluka 2 (fig. 2). Nutt and Grauch (1983) gave a description of regional and mine geology at Jabiluka; that paper provides the regional geologic setting of drill-hole T129V. Figure 3 shows the general stratigraphy of the mine sequence. T129V drill hole was drilled to a depth of 232 meters through the Kombolgie and Cahill formations. Figure 4 shows the north-south 129 cross section through Jabiluka 2 that contains drill-hole T129V. Both ore and barren zones were cored. Description of the core consists of a stratigraphic column from 60 to 232 m (fig. 5), compiled from Pancontinental Mining Limited and my logging record; brief descriptions of minerals, identified by microscope, microprobe Energy Dispersive System (EDS), and powder camera; and thin-section descriptions from selected samples (table 1). Uranium distribution and veins are also described. Rock types The rocks in T129V are typical of the Jabiluka sequence (Nutt and Grauch, 1983, gave detailed descriptions of the rock types). The metamorphic rocks, consisting of quartz, chlorite, muscovite, and graphite in a matrix of chlorite and (or) sericite, are: chlorite schist, chlorite-muscovite ± sericite schist, chlorite-sericite ± muscovite schist, and graphite schist. These schists are fine grained with occasional pseudomorphs (most commonly chlorite after garnet) and coarse-grained muscovites and chlorites as large as 2 mm. Tourmaline-bearing pegmatite is the only recognizable igneous rock in T129V. Hybrid zones of mixed pegmatite and metamorphic rocks occur along pegmatite contacts. The Kombolgie Formation is a quartz-rich sandstone; above the unconformity, the sandstone has interstitial chlorite and crosscutting veins of chlorite and hematite.

At the request of the BLM, over 100 square miles (260 square kilometers) in the Comudas Mountains of southern Otero County, New Mexico, were evaluated for their potential for undiscovered mineral resources. There are three BLM-designated study areas in the Cornudas Mountains: Alamo Mountain, Wind Mountain, and Comudas Mountain Areas of Critical Environmental Concern (ACEC). All three ACECs include scenic peaks comprised mainly of Tertiary alkaline igneous rocks that rise above the surrounding gently rolling topography. This report incorporates geological, geochemical, and geophysical data collected in 1996 by the authors as well as compilation of existing data. The Comudas Mountains are at the eastern edge of the Basin and Range Province and within the Tertiary Trans-Pecos magmatic belt. The area is underlain by easily eroded Permian carbonate rocks and Cretaceous clastic rocks that are intruded by more resistant alkaline plugs and sills. Permian rocks exposed are, from oldest to youngest, the Hueco, Yeso, and San Andres Formations. Outcrops of Lower Cretaceous rocks are restricted to areas near intrusions, and much of the exposed Cretaceous occurs as blocks in landslide deposits along the edges of intrusions. Intrusion of the plugs and sills caused folding and warping of the Paleozoic and Cretaceous rocks; fold axes are predominantly east-trending. Surface folding, as well as geophysical data, indicate unexposed intrusive rock underlying the Comudas Mountains. The Comudas Mountains have been explored for nepheline syenite for industrial use and a resource is identified at Wind Mountain for industrial grade glass. No other exposed intrusion has potential for industrial grade glass. The area has been explored for metallic deposits associated with alkaline igneous rocks-uranium, beryllium, rare-earth elements, niobium, and gold and silver but has low potential for these deposit types. The geochemical environmental consequences of future mining would have minimal impact on the water chemistry of subsurface waters. Nepheline syenite in the Comudas Mountains, if mined, has a limited buffering capacity and contains little or no pyrite or other sulfide minerals that generate acid and degrade the water. Previous Investigations U.S. Bureau of Mines (USBM) geologists, at the request of the BLM, independently conducted an examination of identifiable mineral occurrences in the Wind and Alamo Mountains ACECs in 1992 and 1993 (Korzeb and Kness, 1994) and in the Chess Draw area northwest of Wind Mountain in 1992 (Schreiner, 1994). The only potential mineral resource identified in these evaluations was industrial grade nepheline syenite that underlies Wind Mountain. Previous investigations by the U.S. Geological Survey in this area are restricted to reconnaissance mapping by G.O. Bachman and associates during the compilation of the Geologic Map of New Mexico (Dane and Bachman, 1965).

Nevada also contains significant Tertiary epithermal Au-Ag deposits and Tertiary and Cretaceous porphyry-related base metal-Au deposits (John et al., 2003). Examples of Tertiary porphyry Cu-Au deposits (Fig. 1A) include the Battle Mountain district (Theodore, 2000) and the world-class Bingham deposit near Salt Lake City, Utah (Babcock et al., 1995, and references therein), which is located along a westerly mineral trend that extends into Nevada (Shawe, 1977). Less common and smaller Cretaceous Cu-Mo-Au deposits and related base metal-Au skarn and replacement deposits are present near the towns of Ely (Westra, 1979) and Eureka (Nolan, 1962; Fig. 1B). Distal disseminated Au deposits, with some features resembling Carlin-type Au deposits, are commonly associated with the Cretaceous and Tertiary porphyry systems. Jurassic igneous rocks are typically associated with nil or minor Au concentrations and generally are not targets for exploration. In the eastern Great Basin, minor Au is associated with intrusive rock in the porphyry-related Cu deposit at the small Victoria mine in the Dolly Varden Mountains (Atkinson et al., 1982), replacement Ag, Pb, and Au deposits in the Cortez Range (Stewart and McKee, 1977), and base and precious metal skarn and polymetallic veins associated with the Goldstrike pluton in the northern Carlin trend (Emsbo et al., 2000; Heitt et al., 2003). In the western Great Basin, the Jurassic Yerington porphyry system has low Au (Dilles and Profett, 2000). The Bald Mountain mining district is in east-central Nevada, about 115 km south-southeast of Elko and about 100 km northwest of Ely (Fig. 1B). The district contains 11 orebodies (Fig. 2) that cluster in and around the Bald Mountain pluton and are hosted by Cambrian to Jurassic rocks. In this paper, the deposits in Figure 2 are classified as follows: central and deep (Top, Mahoney, Sage Flat); peripheral and deep (LJ Ridge, LBM, Rat, 1-5 pits); central and shallow (RBM; acronyms are actual mine names). The deposits are enriched in base and precious metals and several trace elements (Table 1), particularly As, Sb, Zn, and Bi. Disseminated Au mineralization occurs along high-angle faults, in certain strata, and in stockworks and veins. In and near the Bald Mountain pluton, quartz stockworks and veins host ore at the Top, Mahoney, and Sage Flat deposits, whereas in the peripheral Rat and LJ Ridge deposits, ore is both discordant and concordant to bedding.