Abstract The northern Black Hills of South Dakota and Wyoming contain a large number of mineral deposits that range in age and type from Quaternary placers to Early Proterozoic or Late Archean pegmatites. Classification of the different deposits according to age, metals present, and structure of the deposits (DeWitt et. al., 1986) allows the delineation of twenty-two metallic mineral districts, which contain 303 mines or mineral deposits. These districts and mines are shown on four maps across the northern Black Hills. The mines or mineral deposits are listed numerically and alphabetically in Tables 1 and 2. These metallic mineral districts differ significantly from conventional mining districts, which generally had geographic or political boundaries and could contain mineral deposits of differing age and genesis. In contrast, metallic mineral districts are defined by geologic criteria and are classified by age of mineralization, metals present, and structure of the deposit. Therefore, one district contains only one age and type of mineral deposit. Metallic mineral districts across the northern Black Hills are present in four major clusters: in the Bear Lodge Mountains of Wyoming (Fig. 1); at Tinton on the South Dakota-Wyoming border (Fig. 2); in the Lead area of South Dakota (Fig. 3); and in the Galena area of South Dakota (Fig. 4). Mines and mineral deposits on all figures are given a letter designation (C, T, etc.) and a plotting symbol (filled circle, filled square, etc.) that indicates the deposit type. Plotting symbols are consistent from one figure to the next.

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

Abstract 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. 0.0 Tropicana exit on Interstate 15. Head south toward Mountain Pass. McCarran International Airport on the left. Spring Mountains on your right at 3:00. The impressive range is made up of thrust plates of the foreland fold and thrust belt (Armstrong and Oriel, 1965; Armstrong, 1968; Burchfiel and Davis, 1972). In the low morning sun the bold cliffs of the Aztec Sandstone are clearly visible. The Keystone thrust plate, consisting of dark Cambrian limestone and dolomite, overlies the Aztec Sandstone (Longwell and others, 1965; Burchfiel and others, 1974). Lower and presumably older thrust faults, which aren't very obvious from here, include the Red Springs thrust (Davis, 1973) and the Bird Spring thrust (Hewett, 1956). Behind and to your left, at approximately 7:00, is Frenchman Mountain, a titled and listrically rotated fault block containing most of the Paleozoic shelf sequence of carbonate rocks (Longwell and others, 1965). 2.9 Mountains at 9:00 are the northern end of the McCullough Range extending south from Henderson, Nevada (fig. 1). Northern part of the range consists predominantly of Tertiary volcanic rocks. View to the right in the Spring Mountains shows Keystone and older thrust plates. Strata in the thrust plates at 3:00 are relatively horizontal, but to

Abstract 0.0 Drive north past abandoned gas station on the right and old bowling alley on the left. 0.2 Turn left on residential street. Just after left turn the road forks; stay to the left on North Park Road. 0.3 Take the left fork in the road, around a satellite television dish. Just past the satellite dish turn off the paved road and take the well-traveled dirt road to your left. This dirt road goes toward an active waste dump, but turns south at the base of the waste dump. Follow the road around the south side of the waste pile, traveling west, parallel to the Interstate Highway on your left. The dumps on the right are some of the older waste piles at the mine and are no longer used because deep mining by open pit methods of the carbonatite beneath the waste piles would entail moving the dumps. The fence around the waste piles is the property boundary of Moly Corp. Inc.; we should not go inside the fenced area. Gray rocks on the dump are 1700 Ma high-grade metaigneous and metamorphic rocks. Tan rocks on the dump are 1700 Ma granite and 1400 Ma carbonatite material. Carbonatite on this dump averages less than 3 percent combined rare-earth oxides. When this waste dump was active the cutoff grade of ore at the mine averaged 5 percent rare-earth oxides; currently the cutoff grade of ore is approximately 9 percent rare-earth oxides. 0.9 Road turns to the right (north) around the

Abstract 0.0 Bailey Road interchange at Interstate Highway 15. Go south over the Interstate and take the northbound entrance ramp toward Las Vegas. 1.4 Large roadcuts on the right in 1700 Ma foliated granite and high-grade metamorphic rocks. 1.6 Outcrops to the left contain low-angle faults cutting high-angle foliated metaplutonic rocks. At 12:00 are Castle Peaks on the far horizon in the northern New York Mountains (Miller and others, 1986). These sculptured peaks are Tertiary volcanic rocks which rest depositionally on 1660 Ma (Wooden and others, 1986) Ieucocratic granite (unit Xg1, fig. 3). 2.4 Roadcuts in Tertiary fanglomerate. Past roadcuts, views to both left and right show pronounced foliation and layering of light-colored Early Proterozoic granitic rocks that intruded darker ampibolite and mixed gneiss. Mineral Hill on the right; 1400 Ma syenite and granite crop out on the ridge at 3:00. Farther south along Mineral Hill are numerous prospect pits containing thorium-rich, rare-earth-element-rich veins. The extent of mineralization related to the Mountain Pass Carbonatite south, past Mineral Hill, is unknown. 3.7 View into Ivanpah Valley and across Ivanpah Lake. Mountains in the distance are the McCullough Range, which contain granulite-facies gneissic rocks (Clarke, 1985; Anderson and others, 1985) and 1700 Ma plutonic rocks. Rectangular ponds at the southern end of Ivanpah Lake are waste water storage for the Mountain Pass mine. 4.6 Nipton Road exit. Take the exit to the right. 4.9 Stop sign. Turn right onto highway leading to Nipton, California, and on to Searchlight, Nevada. Entering East Mohave National

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 Bastnaeaite, a rare-earth fluocarbonate, was found in the Mountain Pass district in April 1949. Subsequent geologic mapping has shown that rare-earth mineral deposits occur in a belt about 6 miles long and 1½ miles wide. One of the deposits, the Sulphide Queen carbonate body, is the greatest concentration of rare-earth minerals now known in the world. The Mountain Pass district is in a block of metamorphic rocks of pre-Cambrian age bounded on the east and south by the alluvium of Ivanpah Valley. This block is separated on the west from sedimentary and volcanic rocks of Paleozoic and Mesozoie age by the Clark Mountain normal fault; the northern boundary of the district is a conspicuous transverse fault. The pre-Cambrian metamorphic complex comprises a great variety of lithologic types including garnetiferous mica gneisses and schists; biotite-garnet-sillimanlte gneiss; hornblende gneiss, schist, and amphibolite; biotite gneiss and schist; granitic gneisses and migmatites; granitic pegmatites; and minor amounts of foliated mafic rocks. The rare-earth-bearing carbonate rocks are spatially and genetically related to potash-rich igneous rocks of probable pre-Cambrian age that cut the metamorphic complex. The larger potash-rich intrusive masses, 300 or more feet wide, comprise 1 granite, 2 syenite, and 4 composite shonkinite-syenite bodies. One of the shonkinite-syenite stocks is 6,300 feet long. Several hundred relatively thin dikes of these potash-rich rocks range in composition from biotite shonklnite through syenite to granite. Although a few thin fine-grained shonkinite dikes cut the granite, the mafic intrusive bodies are generally the oldest, and granitic rocks the youngest. The potash-rich rocks are intruded by east-trending andesitic dikes and displaced by faults. Veins of carbonate rock are most abundant in and near the southwest side of the largest shonkinite-syenite body. Most veins are less than 6 feet thick. One mass of carbonate rock near the Sulphide Queen mine is 700 feet in maximum width and 2,400 feet long. About 200 veins have been mapped in the district; their aggregate surface area is probably less than onetenth that of the large carbonate mass. The carbonate minerals, which make up about 60 percent of the veins and the large carbonate body, are chiefly caleite, dolomite, ankerite, and siderite. The other constituents are barite, bastnaesite, parisite, quartz, and variable small quantities of croeidolite, biotite, phlogoplte, chlorite, muscovite, apatite, hematite, goethite, fluorite, monazlte, galena, allanite, cerite, sphene, pyrite, chaleopyrite, tetrahedrite, malachite, azurite, strontianite, cerussite, wulfenite, aragonite, and thorite. The rare-earth oxide content of much of the carbonate rock is 5 to 15 percent; in some local concentrations of bastnaesite the rare-earth oxide content is as high as 40 percent. The foliation and inclusions in the Sulphide Queen carbonate body, and the discordant contacts between this body and the gneissic wall rocks, show that the carbonate rock was intruded as a mass into its present position. Radioactive age determinations on monazite from the Sulphide Queen carbonate body indicate a tentative age of about 900 to 1,000 million years (pre-Cambrian), and the potash-rich rocks are at least as old and thus are of pre-Cambrian age. Four tentative determinations of 800 to 900 million years for the age of zircon in shonkinite at the Birthday shaft also indicate the pre-Cambrian an of the potash-rich rocks. The relation of the carbonate rocks to alkalic igneous rocks is Similar to rock associations found in certain other parts of the world. Because of structural reasons, as well as the pre-Cambrian age of the monazite, the rare-earth-bearing carbonate rock could not have originated as sedimentary limestone or dolomite of Paleozoic age or through assimilation of sedimentary rocks of Paleozoic age by the parent magma of the potash-rich rocks. The carbonate rock might have had a sedimentary origin in the pre-Cambrian gneissic complex as limestone or evaporate, subsequently modified and squeezed into discordance with the foliation of the metamorphic rocks. A magmatic origin of the rare-earth-bearing carbonate rock by differentiation of an alkaline magma from shonkinite to syenite to granite, with a carbonate-rich end-product containing the rare elements, is in harmony with the field relations. This late differentiate might rare been introduced either as a relatively concentrated magmatic fluid, highly charged with volatile constituents such as carbon dioxide, sulfur, and fluorine, or as a dilute hydrothermal fluid.

Abstract Shonkinite, syenite, and granite at Mountain Pass, California, differ from typical alkalic rocks associated with carbonatites in other areas by being saturated to oversaturated in silica rather than undersaturated, displaying strong light rare-earth element (LREE) enrichment, and by being enriched in K rather than in Na (by later fenitization?). New major and REE data suggest that the shonkinite and syenite are probably comagmatic and related by crystal fractionation. The granite, however, is spatially, but not genetically related to either the syenite or shonkinite. Shonkinite is characterized by high total REE abundances (REE = 715-1214 ppm) and high Ce/Yb N (22–37). Syenite has similar REE contents (REE = 900 ppm, Ce/Yb N = 24), but has lower CaO, P 2 O 5 , MgO, TiO 2 , Ba, and Cr, and higher Al 2 O 3 , FeO, Hf, Zr, and Ta concentrations than shonkinite. This elemental distribution can be explained by mineralogic differences due to crystal fractionation. Granite is lower in total REE (REE = 397–488 ppm), but shows greater LREE enrichment (Ce/Yb N = 37–50). The lack of a Euanomaly suggests that feldspar fractionation was not important in the formation of the granites. The following petrogenetic model is proposed: (1) generation of shonkinite liquid by 1% partial melting of a REE enriched mantle (garnet peridotite), (2) 20% crystal fractionation of the shonkinite to produce syenite, and (3) generation of an alkali-granite liquid by the partial melting of garnet pyroxenite in the upper mantle.

Abstract The age of the Mountain Pass carbonatite, the largest source of rare-earth elements in the world, is an important constraint in the search for similar bodies. Emplacement of the carbonatite was the last event in the intrusion of a 1400-Ma alkalic complex. Based on field relationships, the intrusive sequence was 1) shonkinite, 2) syenite and granite, and 3) carbonate bodies, dikes, and veins. Late shonkinite dikes cut syenite and granite, but not the carbonate bodies. Alkalic igneous rocks were emplaced between 1410 and 1400 Ma. Apatite from the shonkinite has a U-Pb date of 1410±2 Ma. Phlogopite from the shonkinite has a 40 Ar/ 39 Ar plateau date of 1400±8 Ma. Arfvedsonite from the syenite has a 40 Ar/ 39 Ar plateau date of 1403±7 Ma. Zircon from the syenite are highly discordant and have Pb-Pb dates as old as 1330 Ma; their U-Pb dates were not made appreciably older by abrasion techniques. Monazite from the carbonate body have Th-Pb dates of 1375±7 Ma and imply that the carbonatite was emplaced about 25 Ma after syenite and granite. Bastnaesite and parisite from the carbonatite contain considerable common lead and suggest that the body was open to lead migration after emplacement. Clear parisite has an older Th-Pb date (1332±7 Ma) than coexisting bastnaesite, but that date is anomalously young if compared to the Th-Pb dates from monazite. The least radiogenic common-lead ratios of galena from the carbonatite and potassium feldspar from alkalic igneous rocks (204:206:207:208 = 1:16.08:15.23;35.61) indicate that the parent magma for both rock types was

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

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 0.0 Copper Plaza in Bagdad, Arizona. Proceed east on Arizona Highway 96 toward Hillside, Arizona. 0.1 Intersection of North Lindahl Road and Arizona Highway 96. Turn left (north). A small Bell Telephone building is on the left as you proceed north; the Bagdad Fire Station is on the right. 0.7 Roadcuts in Hillside Mica Schist intruded by aplite-pegmatite. Sanders Mesa on the left at 9:00. One-half mile farther, pass Faye's Pizza Parlor on the right. 1.7 Turnoff to the left to the Bagdad landfill. Proceed straight ahead on the paved road. Outcrops to the right and on Granite Mountain at 1:30 are light-colored Early Proterozoic aplite-pegmatite, which intrudes Hillside Mica Schist. 2.1 Prominent gray peak, straight ahead in the distance, is Blue Mountain. The pluton contains considerable magnetite, and stand out as an aeromagnetic high (Dempsey and others, 1963; Aero Services, 1983). 2.9 Trailer park on right. 3.1 Pavement ends. “Y” in the road; take the heavily traveled fork to the left that climbs to the top of Nelson Mesa. 3.4 View of Blue Mountain, elev. 5,550 ft, which is underlain by a Laramide pluton that is similar in composition to the diorite porphyry dike swarm associated with the porphyry copper deposit west of the town of Bagdad (Anderson and others, 1955). Big Shipp and Little Shipp Mountains are at 1:00, and 2:00 to 2:30, respectively, in the distance. Both peaks are composed of aplite-pegmatite. 3.9 Top of Nelson Mesa. “Y” in the road at construction site. Stay to the

Abstract 0.0 Copper Plaza in Bagdad. Proceed east on Arizona Highway 96 toward Hillside, Arizona. Drive past the basketball courts on the right and the small park past that. 0.4 Turn right at the sign for Warehouse A. Go across cattleguard. 0.5 Take the first right turn possible. Just past that turn, about 100 feet, is a paved road topped with gray gravel. Take that paved road, which turns off to the right from the housing subdivision that we are driving through. The paved road traverses the hillside slightly above the houses, then climbs through outcrops of Lawler Peak Granite and Hillside Mica Schist. 1.0 Housing subdivision on our left ends. Pavement also ends; continue on tbe gravel road around a hill and toward the Bruce mine. Outcrops on the left are Lawler Peak Granite that intrudes Hillside Mica Schist. 1.5 Low, rounded hills that we are crossing are Hillside Mica Schist intruded by Lawler Peak Granite. The schist is darkly desert-varnished and crops out poorly. 2.4 View to the right past the hi1ls in the near foreground is of Proterozoic granitic rocks east of the Santa Maria River. On the skyline are high peaks in the Weaver Mountains north of Yamell, Arizona. 2.6 “Y” in road; stay to the right. Left fork goes to the Kellis Ranch. Bouldery outcrops to the left are Lawler Peak Granite.

Abstract 0.0 Copper Plaza in Bagdad, Arizona. Proceed east on Arizona Highway 96 toward Hillside, Arizona. 0.4 Turnoff to the right to the Bruce mine. Outcrops ahead, on the left, and for the next one-half mile are Hillside Mica Schist intruded by Lawler Peak Granite. 1.0 Roadcut in Hillside Mica Schist intruded by Early Proterozoic foliated granodiorite. 1.2 Small creek from below the Cowboy mine enters Bridle Creek on the right. Outcrops are of dark metabasalt of the Bridle Formation (Anderson and others, 1955). Light-colored rocks are intrusive and extrusive metarhyolite. Roadcuts 0.4 miles ahead in light felsic metavolcanic rocks on the right, dark mafic metavolcanic rocks and Hillside Mica Schist on the left. 1.8 Eastern margin of of metavolcanic belt. Roadcuts in Hillside Mica Schist intruded by aplite-pegmatite. 2.3 Large roadcut contains Hillside Mica Schist intruded by numerous sills and dikes of aplite-pegmatite. 3.4 Tertiary fanglomerate in roadcut. Large dike of aplite-pegmatite projects across the highway. Outcrops ahead about one-quarter mile on the left are light aplite-pegmatite intruded by tan-weathering, ocher-stained, strongly jointed Lawler Peak Granite. On the right are outcrops of strongly jointed Lawler Peak Granite. 4.3 Junction of Arizona State Highways 96 and 97. Arizona State Highway 91 turns off to the right and connects with U.S. Highway 93 to Wickenburg and Phoenix. We continue along Arizona Highway 96 straight ahead through the roadcuts of Lawler Peak Granite. Road narrows through these roadcuts; please drive carefully. Most of the roadcuts are in Lawler Peak Granite, but some aplite-pegmatite

Abstract Wolframite-bearing quartz veins that have peripheral greisen-type wall rock alteration products are present in and around the Black Pearl mine (about 18 km northeast of Bagdad, Arizona). The veins are spatially related to a small albitite stock, and the largest vein, which was the only one mined, is at the apex of the stock. On the basis of field relations, this stock is interpreted to be a late differentiate related to the 1400 Ma Lawler Peak Granite, which crops out within 3 km of the mine. Other, similar albitite bodies are common in the Black Pearl mine area. Sharp contacts with country rocks (schist, monzogranite, and granodiorite), relatively unaltered xenoliths, and consistent mineralogy throughout indicate that the albitite bodies are igneous, and have undergone relatively minor postmagmatic alteration. A thin (1- to 2-m-wide) border pegmatite unit (“stockscheider”) exists at the contact of the albitite of the Black Pearl mine and the country rock. Directional indicators and other evidence indicate that the pegmatite was formed from a volatile-rich phase at the time of magma emplacement. The sudden change from potassium-feldspar-rich pegmatite to fine-grained albitite suggests a pressure-quench of the system, perhaps owing to fracturing of and escape of volatiles up the Black Pearl vein at the apex of the stock. Similar stockscheider textures are typical of the borders of productive plutons in tungsten and tin districts worldwide.