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.

Abstract Metavolcanic and metasedimentary rocks of the Yavapai Series (Anderson and Creasey, 1958) crop out within the area described in this study. These rocks were originally subdivided into the Ash Creek Group and Alder Group (Anderson and Blacet, 1972). Isotopic data led Anderson and others (1971) to replace the name Alder Group with the Big Bug Group, which includes all the rocks of the Yavapai Series exposed in the Prescott-Jerome area. The Big Bug Group is divided into three formations. From oldest to youngest they are: 1) Green Gulch Volcanics; 2) Spud Mountain Volcanics; and 3) Iron King Volcanics (Anderson and Silver, 1976). The Green Gulch Volcanics are not present in the area of this study and will not be discussed. The thickness of the Big Bug Group cannot be measured with confidence because of the probability that unrecognized small folds on the flanks of major folds duplicate the section, and because of probable thinning and thickening of units during deformation (Anderson and Blacet, 1972c). The Iron King Volcanics are composed of a thick sequence of metamorphosed, pillowed and amygdaloidal andesitic and basaltic flows. Locally the Iron King contains thin interbeds of metamorphosed rhyolitic tuff and flows units. The youngest part of the Iron King is a mixed metatuff of andesitic to rhyolitic composition that crops out in the trough of an overturned syncline. The Iron King Volcanics have been informally subdivided into members (O'Hara, 1981; unpublished map) in order to facilitate mapping for industry. The area encompassing the Montezuma, Swindler

Abstract During 1983, one hundred-sixteen samples were collected at the Bell Ranch prospect and analyzed for major elements plus zirconium, gold, silver, arsenic, antimony, mercury, copper, lead, and zinc. Thirty-eight samples were collected from rocks interpreted to have a felsic volcanic protolith. These geochemical data are part of a regional study of Early Proterozoic hydrothermal systems associated with strata-bound mineralization. The regional study includes lithologic and alteration mapping as well as analysis of more than 1,300 geochemical samples from eleven properties. The original purpose of the study was to classify polymetallic massive sulfide types empirically and to derive generative models of the hydrothermal-geological environment associated with mineralization. During 1983, two gold-bearing, base-metal-poor hydrothermal systems were included in the database.

Abstract The Bell Ranch prospect is 5 km southeast of the Iron King massive sulfide deposit in the Agua Fria metallic mineral district. The prospect is strata-bound, exhalative in nature, and syngenetic with submarine volcanic and sedimentary strata of the Proterozoic Yavapai Series (1750 – 1780 Ma). In this region the Yavapai Series is characterized by greenschist grade metamorphism, steeply plunging penetrative folds, and steeply dipping foliation. The rocks hosting the prospect are distal (1.5 km) to a rhyolite dome to the north, but may be proximal to hydrothermal vents associated with growth faults at the prospect.

Abstract Coincident with and largely confined to the sulfide-bearing strata are anomalous amounts of Au, As, Sb, Cu, Pb, Zn and Ag with associated silicification, sericitization and carbonatization. Geochemical and alteration changes are complex normal to bedding planes, probably reflecting continual and abrupt changes in exhalite precipitation. In the plane of bedding, they show a more general systematic pattern indicating relatively stable sea floor topography. Facies changes of mineralization observed along strike are believed to reflect varying Eh and pH conditions during exhalite deposition (6, 7). A crude generalization of the pattern, starting from the rhyolite dome and proceeding south, can be summarized as: Carbonate facies (strike length = 0.8 km), Sulfide facies and carbonate facies (strike length = 4 km), Carbonate facies (strike length = 1.6 km) (Fig. 4).