The Bullard mineral district is one of approximately 15 mineral districts in west-central Arizona and southeastern California that are related to large-displacement, regionally low-angle normal faults known as detachment faults (Spencer and Welty, 1986; Roddy and others, 1988). Detachment faulting occurred during regional mid-Tertiary extension in the Basin and Range province and was associated with formation of extensional basins and elevated geothermal gradients (Spencer and Reynolds, 1989a). Mineral deposits related to detachment faults formed within this tectonic setting and were the result of hydrothermal ascent of basin brines along detachment faults (Wilkins and others, 1986). One of these districts includes the Copperstone mine, which has yielded several hundred thousand ounces of gold (Spencer and others, 1988). This article briefly describes the mineral deposits of the Bullard district and summarizes gold-assay data from numerous surface samples and from two drilling programs. Geologic similarities between the Bullard district and Copperstone deposit suggest that significant gold deposits could be present in the subsurface in the Bullard district.

The eastern Gila Bend Mountains, Maricopa County, Arizona, are composed of Early Proterozoic crystalline rocks and overlying mid-Tertiary continental clastic and volcanic rocks of the Sil Murk Formation. Slightly more than half of the bedrock in the eastern Gila Bend Mountains is composed of granitic rocks, mainly located in the eastern and northern part of the map area. Except for a few scattered exposures, the Tertiary continental clastic and volcanic rocks crop out in the southwest part of the map area. The eastern Gila Bend Mountains were mapped with funds provided to the Arizona Geological Survey by the U.S. Geological Survey COGEOMAP program, contract #14-08-001-A0785. Field work was carried out from December, 1990 to February, 1991. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U.S. Government.

A workshop on the future of research on mineral resources in Arizona was held on January 12 and 13, 1987, in Tucson, Arizona. The objective was to exchange information from research on the geology of metallic mineral resources. The emphasis was on the potential for the discovery of new ore deposits and on the type of research necessary to fulfill that potential. We recognized at the outset that copper and associated metals derived from porphyry-type deposits related to calc-alkaline igneous rocks have dominated and most likely will continue to dominate metallic mineral production in Arizona. We also recognized that a large research effort has been devoted and will continue to be devoted to the understanding of these traditional deposits. As a result, the potential for other deposit types has largely been neglected. The decision was made to emphasize those geologic environments in which "nontraditional" deposits might be found. The term "unconventional" used in the workshop title simply means "nonporphyry copper deposits." 16 pages.

Brief summary of geological features and known mineral occurrences Wilderness Study Areas 4-14, 4-16 Fishhook - Day Mine 1) The Fishhook - Day Mine areas are underlain by middle - to - upper Tertiary age volcanic flows, breccias, and tuffs, and by late Tertiary-Quaternary basin-fill deposits, primarily of alluvial and lacustrine origin (sands, gravels, etc.); 2) The WSA's do not contian any known base or precious metal occurrences; 3) Secondary copper mineral deposits have been reported from fissure veins in middle Tertiary volcanic rocks along the western and southern borders of the WSA's. Other copper deposits are located several miles to the south of WSA 4-16. No production has been recorded from exploration prospects in these areas; 4) Minor occurrences of gold, silver, lead, zinc, and molybdenum are associated with the copper deposits. Mining claim reports indicate that mineral amounts are insufficient to be of economic value; 5) One known occurrence of manganese is located to the south of WSA 4-16 in middle Tertiary volcanic rocks. There are no reports of production; 6) Information concerning mineral types, claim development, and ore production is unavailable for other prospects in this region; 7) The Safford - Lone Star Mining District, to the south of the WSA's, has been actively mined and prospected since the late 1800's.

The WSA is underlain by Precambrian metamorphic rocks, Cretaceous or Tertiary granite, and middle Tertiary volcanics. Bedrock exposures are surrounded by late Tertiary-Quaternary basin-fill (sands, gravels, etc.). Three major fault systems Two groups of inactive prospects are located within the WSA; botll are situated on the northern flanks of Jackson Mountain. The Spar Fluorite Group, largest mining operation in this area, produced 1200 tons of fluorspar prior to 1953; no further activity has been reported. Minor occurrences of secondary copper, lead, silver, and zinc minerals are associated with ftuorspar; however, no significant production of these ores has been recorded. No information concerning development, mineral commodities, or production is available for the second group of prospects within the WSA; Fluorspar also occurs to the south of the WSA in Precambrian schist. Several prospect pits were located in this area. Records of production are unavailable; There are reports of uranium radioactivity from five exploration prospects to the north and south of the WSA. No uranium production has been recorded from the Jackson Mountain region; There are several copper occurrences in granitic rocks located in the south-central portion of the massive Tertiary granitic batholith to the northwest of Jackson Mountain. Minor amounts of lead, silver, and gold are associated with the copper deposits; The Stanley-Aravaipa Mining District, to the west of the WSA, has been actively mined and prospected since the late 1800's. Lead, zinc, and silver deposits are contained in Precambrian metamorphosed igneous and sedimentary formations, Paleozoic sediments, Cretaceous or Tertiary granitic rocks, and middle Tertiary volcanics.

It is becoming increasingly clear that Arizona's.Basin and Range Province contains an abundance of low-angle tectonic phenomena that are diverse in space, time and tectonic significant. It is the purpose of this field trip to examine a representative sample of·these tectonic phenomena, emphasizing their geometry, timing, kinematics and regional significance to Arizona's tectonic and mineral-deposit framework (Figure 1). With this goal in mind we will discuss from a distance the complex low-angle fault, mylonitic, and plutonic terranes in the eastern Tortolita,Santa Catalina, and Picacho Mountains (DAY 1: STOPS 1 AND 2). These mountains contain Laramide through mid-Tertiary mylonitic phenomena that geologists have variously related to early Laramide northeast-vergent thrusting, late Laramide southwest-vergent thrusting and two-mica granite magmatism, mid-Tertiary regional crustal extension. These stops will be primarily lead by Stan Keith.

This informal guidebook was assembled to serve the broad purposes of the Coal Geology Division's two-day Arizona field trip. The following remarks are intended to assist in placing the field trip locale into a regional geologic perspective. Our bus route, beginning in Phoenix, traverses a region having considerable geologic diversity (Figs. 1, 2, 2A). It begins in the classic Basin and Range Province (B&RP) and ends well into the Colorado Plateau Province (CPp). The Boundary between provinces traditionally inspires debate. The recognition of a variously defined Transition Zone (TZ) in central Arizona tends to lessen the either/or discussion that ensues if some form of TZ is not recognized (Fig. 1).

This report presents a compilation of geologic and hydrologic information for the Bullhead City-Black Mountains area of we stem Arizona. The purpose of the project is to determine the significance of mining, geology, and geohydrology in the chemistry of Bullhead City area groundwater. Mining in the Black Mountains has taken place since the 1800s, and the region provides a good opportunity to investigate any links between mining and water quality. The study encompasses the area from the crest of the Black Mountains on the east, the Colorado River on the west, latitude 350 on the south and the top of township 2IN at the north (Figure 1). Information was compiled from published and unpublished sources including U.S. Bureau of Land Management, U.S. Geological Survey, U.S. Bureau of Mines, U.S. Natural Resources Conservation Service (Department of Agriculture), Arizona Geological Survey, Arizona State Land Department, Arizona Department of Water Resources, and Arizona Department of Environmental Quality.

This map depicts both the bedrock geology and the general ages and distribution of Late Tertiary and Quaternary deposits and geomorphic surfaces in the Stewart Mountain quadrangle (see Figure 1). The Salt River, re-emerging from Saguaro Lake, slices through the middle of the study area where it separates granite pediment and of the Usery and Goldfield Mountains (respectively) to the south, from a vast expanse of Late Tertiary basin-fill sediments to the north. Mapping of the surficial deposits was based both on field observations and interpretation of color 1:30,000-scale aerial photographs (dated 6-12-88), obtained from the Tonto National Forest in Phoenix. All of the region is administered by the Tonto National Forest. Good access to the region is provided by State Route 87, the Bush Highway, and Usery Pass Road (see Figure 2). A primitive road provides access to Bulldog Canyon, but locked gates at both ends can only be opened by obtaining a permit from the Tonto National Forest Service field office in Mesa. However, even with a 4-wheel drive vehicle, the road is almost impassable in places. Saguaro Lake is a popular recreation area and the roads to the west shore and to Butcher Jones Cove are paved. At the Saguaro Lake marina boats are available for rent that will provide the only access to the northeast side of the Goldfield Mountains.

Geologic map and cross section through the northern Matzazal Mountains of Shake Tree Canyon, Central Arizona. Scale 1:24,000. Two sheets.