Abstract 0.0 Oatman Hotel. Take paved road to Kingman. 0.8 Dumps of the United Western mine on the left side of the road. 1.0 Intersection with road to Bullhead City to the left; continue on the pavement straight ahead. Dumps of the Oatman Amalgamated mine at 10:00. 1.5 Road parallels compositional layering in lati-andesite at Oatman. 1.9 Road goes around sharp bends, paralleling bedding in lati-andesite at Oatman. Contact of Gold Road Latite up the hill to the right about 100 ft. 2.5 Dumps straight ahead are of the Gold Road mine. Spectacular steeply dipping vein system was mined as an open cut about 15 ft wide to a depth of more than 500 ft (Shrader, 1909). Open cut is now covered by steel plates and chain link fence. 2.9 First of two hairpin turns above the Gold Road mine. One-tenth of a mile farther we cross the Gold Road fault and vein. Major adits along the highway on our right were access points to the Gold Road vein. Outcrops of Gold Road Latite on the right and left. 3.8 Adit in very bleached zone in Gold Road Latite. Possible fault contact. Contact of Sitgreaves Tuff just above us. 4.0 First of two small hairpin turns. Climbing uphill. To the left and downhill is the Sitgreaves Tuff. Capping basalt flow unconformably overlies Sitgreaves Tuff at Sitgreaves Pass, straight ahead. 4.3 Sitgreaves Pass. View to the east is of the Hualapai Mountains south of Kingman, Arizona. High peaks to the left in

Abstract 0.0 Exit to eastbound Interstate Highway 40 toward Flagstaff from Andy Devine Avenue in Kingman. 0.1 Behind and to the left in the foothills of the Cerbat Mountains is the Kingman Feldspar mine, a 1700 Ma zoned pegmatite (Heinrich, 1960; Wasserburg and Lanphere, 1965) that intrudes Early Proterozoic granitic rocks. Minerals of principal economic interest are microcline and allanite. 0.9 Prominent strata at the top of the Grand Wash Cliffs (fig. 26) in the far distance at 9:00 are Cambrian through Mississippian limestone and associated sedimentary rocks. Rocks beneath the Paleozoic section are mainly Early Proterozoic foliated to gneissic granite to granodiorite. Most of the Proterozoic rocks of the Grand Wash Cliffs are unmapped; only the Garnet Mountain area (Blacet, 1975; Theodore and others, 1982) has been mapped in any detail. 2.6 To the left and north is Hualapai Valley, which drains to the north into the playa of Red Lake at the northern end of the Cerbat Mountains. One of the thickest accumulations of halite in Arizona (minimum of 4,000 ft; possibly as thick as 10,000 ft) underlies Red Lake and the Hualapai Valley south of Red Lake (Peirce, 1973; 1976). 3.8 Crossing Rattlesnake Wash. Hills to our right are composed of mildly flow foliated, 1400 Ma coarse-grained porphyritic granite of Rattlesnake Hill 1400 (Kesler, 1976). 5.1 Outcrops on the right that weather into large bouldery piles are the granite of Rattlesnake Hill (fig. 24). 6.2 Exit 59, DW Ranch Road, provides access into the northern Hualapai Mountains. Roadcuts

Abstract This field conference of the Society of Economic Geologists, held in conjunction with the 1987 Annual Meeting of the Geological Society of America in Phoenix, Arizona, investigates various Proterozoic ore deposits in southeastern California and western and central Arizona. The trip starts in Las Vegas, Nevada, and ends in Phoenix, Arizona. Although Proterozoic ore deposits and geology are emphasized, the field trip traverses a variety of tectonic provinces, each containing ore deposits of various ages. Many geologic features and ore deposits that are not Proterozoic in age will be discussed during the course of the trip, but no stops will be made to investigate any of these, features. The morning part of the trip starts in the Mesozoic foreland fold and thrust belt of Nevada and southeastern California, goes just east of the Mesozoic batholith belt of California, and ends in crystalline basement containing Early and Middle Proterozoic metamorphic and plutonic rocks. Within this basement is exposed the Middle Proterozoic Mountain Pass Carbonatite deposit, the largest source of rare-earth elements in the world. The Mountain Pass Carbonatite will be the focus of our morning stops. The afternoon part of the trip crosses Early Proterozoic high-grade metamorphic rocks and plutonic rocks east of Mountain Pass. Ore deposits noted along the afternoon portion of the trip include middle Tertiary epithermal, gold-rich veins at Searchlight, Nevada, and disseminated gold deposits in Tertiary volcanic rocks near Hart Peak in the New York Mountains. The trip continues across the Colorado River trough along the border of California and Arizona, where crystalline basement and its cover of Tertiary volcanic rocks and plutons have been greatly extended along listric normal faults and low-angle detachment faults. The afternoon part of the trip ends in Oatman, Arizona, a district famous for its middle Tertiary epithermal, gold-rich deposits. The ore deposits at Oatman will be the subject of a slide show and talk after supper on the first night of the trip. The first day ends with an evening drive across a middle Tertiary volcanic pile near Oatman. The first night will be spent in Kingman, Arizona. Assemble at the Las Vegas Convention Center, south of the Hilton Hotel. Take any main street south to Tropicana Avenue. Turn west on Tropicana, past the Las Vegas Strip, and continue to Interstate Highway 15. Turn south on Interstate 15 toward Mountain Pass, California. Mileage starts at 0.0.

ABSTRACT This field trip will visit the southern Black Mountains volcanic center (SBMVC) and its associated products in northwestern Arizona. Post-volcanic extension and erosion of this semi-arid area afford the opportunity to examine a Miocene-aged (ca. 19–17 Ma) volcanic terrain in detail, using an approach that integrates fieldwork, petrography and geochemistry, and remotely sensed data. This approach was recently used in a three-year National Science Foundation Research Experience for Undergraduate (NSF REU) program, from which some results will be highlighted. This integrated approach can provide insight into the amounts and types of information that can be gleaned from various types of remotely sensed data of a volcanic terrain. Over three days, we will work our way through the volcanic section associated with the SBMVC as exposed near Oatman and Kingman, Arizona, to observe: (1) felsic to mafic shallow intrusions; (2) deposits from felsic to intermediate explosive and effusive eruptions; (3) deposits from sedimentary processes; and (4) the results of subsequent extensional faulting. The petrologic, physical volcanic, and morphologic characteristics of observed outcrops will be discussed at each field stop, and will be used as points of discussion while in the field, for observations of presumably volcanic terrains on other planetary bodies. An appended road log serves as a geologic guide to this volcanic center and associated rocks.

Abstract A heap-leachable, open pit and underground gold reserve of about 173,000 ounces has been delineated by drilling at the America Mine, San Bernardino County, California. The reserve is contained within a 346,000 ounce geologic resource. The principal control for the gold mineralization is the ENE-striking, 20° to 40° NNW -dipping America Mine shear zone. The shear zone is up to 150 feet thick, is marked by mylonitic fabric in footwall rocks, and is overprinted by brittle fracturing and shearing. Ore-grade gold mineralization is up to 110 feet thick and occurs inN60°E- to N70°E-trending ore shoots which are up to +3000 feet long and up to 600 feet wide. These elongate ore shoots are axial-parallel to sub-horizontal flexures developed within the shear. The America Mine shear zone juxtaposes assemblages of rocks with contrasting origins and metamorphic grades, suggesting a terrain boundary. Footwall rocks are amphibolite-grade granitic gneisses with sparse marble lenses. Hanging wall rocks are metadiorite and metagabbro which intruded greenschist facies volcanic and sedimentary rocks. The shear contains tectonic slices (or is perhaps intruded by) a leucocratic granite and is intruded by a laterally extensive hypabyssal quartz-eye dacite. Both intrusives, confmed to the footwall side of the shear zone, are sheared, altered, and gold-mineralized. Post-mineral, NW -striking, NE-dipping, dacite dikes related to a regionally developed dike swarm in the Bullion Mountains, cut the shear, but are also slightly offset by the shear. Mineralization consists of micron-sized gold associated with intense quartz-sericite-pyrite alteration which overprints all shear zone lithologies. Accessory minerals include galena, sphalerite, tetrahedrite, chalcopyrite, and their oxidation products. Gold-free, carbonatebarite- pyrite fissure veins were emplaced along NNW-striking listric normal faults. The listric faults, which dip steeply west, cut, offset, tilt and rotate the ore shoots. The listric faults generally have minor offset (<200 feet), and related post-mineral rotation is estimated at 20°, consistent with the weak-tomoderate mid-Tertiary extension related to the Mojave Rift structural province. The gold deposit at the America Mine is interpreted as mesothermal mineralization hosted by ductile-brittle shearing along a late Mesozoic or early Tertiary thrust or a rotated subvertical (60°-70°) shear zone. The deposit is structurally complicated by mid-Tertiary extension and rotation, postmineral dacite dike emplacement, and Tertiary-Quaternary transpressional faulting.

Abstract The Modoc prospect is a Plio-Pleistocene epithermal gold-bearing hot springs system located in the northwestern Salton Trough. To date, Modoc offers the best preserved and developed fossil analogue of the currently active geothermal systems in the continental rift. A surficial hot springs origin for the system is evidenced by interbedded, nearly flat-lying chalcedonic sinter beds exhibiting a strong layered morphology, hummocky pool structures and well preserved fossil reed casts. The primary structural control on the hot springs system is a major ENE-striking, southerly dipping, oblique-slip fault system separating Jurassic granodiorite on the north from Plio-Pleistocene continental sediments on the south. This “Truckhaven” fault system appears to be coincident with the edge of a large basin related to crustal thinning and progradation of the Colorado River Delta into the proto Gulf of California. Gold mineralization occurs as electrum and native gold (8 to 1800 microns) and is associated with sheeted and banded chalcedony veins, silicified and adularized sandstone and conglomerate, and siliceous sinter beds. Gold and chalcedony precipitated simultaneously in numerous episodes and preliminary fluid inclusion data indicate temperatures ranging from 90 to 135°C. Gold mineralization is locally high grade (up to 1.4 ounces of gold per ton over a 20′ (6.1 m) width) and is found in highly anomalous concentrations over an area measuring 8,000′ (2,438 m) long by up to 2,000′ (610 m) wide. Correlation coefficient data indicate a strong gold, silver, copper affinity. The typical hot springs pathfinder elements As, Sb and Hg are present in unusually low concentrations. The Modoc hot springs system is more akin to the active geothermal fields situated on the margins of the rift than those in the center of the Trough. It is strikingly similar to the high-silica Dunes geothermal system, which has no surface expression largely due to the development of hydrothermally induced caprocks. The rediscovery of the Modoc hot springs gold prospect leaves exploration geologists wondering how many other such occurrences underlay the seemingly barren sediments of the Imperial and Mexicali Valleys.

Abstract The morning part of the trip starts in Kingman, near the western edge of the Colorado Plateau, and traverses the Transition Zone of Arizona. Proterozoic rocks are abundant along this section of the trip and consist mainly of foliated to undeformed Early Proterozoic granite to granodiorite (~ 1700 Ma) cut by undeformed Middle Proterozoic leucocratic and potassic granite (~1400 Ma). Relatively small belts of Early Proterozoic meta-sedimentary and metavolcanic rocks are preserved within the terrane dominated by Proterozoic intrusive rocks. Much of the Early Proterozoic geologic history in this part of Arizona is unknown. Ore deposits characteristic of this part of the Proterozoic are: 1) 1700 Ma volcanogenic massive sulfide deposits in metasedimentary and metavolcanic rocks (Hualapai metallic mineral district, northern Hualapai Mountains); 2) 1700 Ma gold-rich quartz veins related to Early Proterozoic granodiorite and diorite (Cottonwood district in the Cottonwood Cliffs); 3) 1700 Ma pegmatite deposits related to evolved granites (Aquarius Mountains district in the Aquarius Mountains and the Kingman Feldspar mine north of Kingman); and 4) 1400 Ma tungsten-rich quartz veins related to potassic granites (Ophir, Fluorescent, and Three-In-One districts in the Hualapai Mountains. Phanerozoic deposits include base-metal-rich veins and copper-rich disseminated and stockwork systems related to Laramide intrusives in the central Cerbat Mountains and Hualapai Mountains, and middle Tertiary vein systems on the west side of the Hualapai Mountains. Our arrival in Bagdad in the late morning will bring us to the first major 1700 Ma volcanogenic massive sulfide ore deposits in Arizona, those in the Old