Extract from beginning of chapter: EUREKA, NEVADA During May and June [1880], I worked as a temporary assistant to Hague on the United States Geological Survey, and on the first of July, I received my appointment as assistant geologist and felt duly elated. It had been King's plan that Hague should have charge of the Division of the Pacific Coast with headquarters in San Francisco, and that he should study the volcanoes of that region beginning with Lassen Peak. But it seemed advisable that his first work should be of a more utilitarian character, so he was commissioned to investigate the geology of the Eureka Mining District in central Nevada. 1 Leaving New York on the evening of the 16 th of July, we were joined in Utica, New York, by a tall, slender, red-whiskered young man who was said to be a promising paleontologist, who had already made a reputation out of his studies of Trenton trilobites, and who had spent the previous season in the Grand Canyon of the Colorado [River]. The next morning, I made the acquaintance of Charles D. Walcott 2 and commenced a lifelong friendship full of interesting experiences and pleasant memories. At the end of the sixth day, we reached Eureka, after a journey, which, for a young geologist, became more and more fascinating and instructive as it proceeded. Nowhere can one see geological structures on a grander scale or in more easily comprehended exposures than in the barren ranges of the Great Basin desert! Its simplicity as well as its nakedness

Abstract The Archimedes gold deposit, discovered in 1992 by Homestake Mining Company, is about 1 mile northwest of Eureka, Nevada in the northern part of the Eureka minin district (Nolan, 1962). The deposit, described in further detail by Dilles et al. (1996), is a largely stratiform body of silicification within non-carbonaceous, cherty Ordovician limestones of the Pogonip Group. This zone, West Archimedes, is approximately 2600 feet long at N60°W, and averages 260 feet inwidth and 75 feet in height; the zone plunges gently east. Gold mineralization has low concentrations of Ag-Pb-Zn-Cu and correlates strongly with silicification, which is generally surrounded by decalcified but unsilici:fied limestone containing lower grade. Published reserves for the western zone are 7.62 million short tons grading 0.099 ounces per ton (opt) Au; the mineralization is oxidized. Values above 0.25 opt Au are common in the central part of the zone. This stratiform silicification is concealed by as much as 500 feet of alluvium and locally intersects the bedrock surface. No intrusive rocks or calc-silicate alteration are present within the West Archimedes deposit, although an altered sill lies more than 1000 feet below. This gold-bearing silicification is herein referred to as Type A. North-northeast and west-northwest trending normal faults are thought to have provided ingress for hydrothermal fluids in the deposit area (Dilles et al., 1996); however, the lack of bedrock exposure at the deposit has precluded thorough analysis of the structures. More strongly brecciated gold-bearing silicification (Type A) on the east side of West Archimedes is underlain

Abstract The Betze gold deposit in the Goldstrike Mine, north-central Carlin Trend, Eureka County, Nevada, is the largest known, sedimentary rock-hosted, disseminated gold deposit containing 32 million ounces of gold (Leonardson and Rahn, 1996)(Fig.1). The paragenesis of hydrothermal mineralization characterizes the nature of gold mineralization in the deposit. This paper describes stages of gold ore mineralization determined from hand specimen and thin section petrology, XRD analysis and SEM studies; mineral formulae reported are those from Frondel (1962) and may not be exact. The stages result from a poly-phase, mineralizing event that has determined the conditions under which gold was precipitated. Previous studies of paragenesis and associated hydrothermal minerals of Carlin-type deposits were conducted by Arehart et al. (1993a), Bakken and Einaudi (1986), Kuehn and Rose (1992), Peters (1996) and Peters et al. (1997) who determined relative paragenesis of mineralization in a general one or two stage hydrothermal event. Our investigations suggest that three stages of hydrothermal mineral development are associated with gold ore mineralization in the Betzedeposit: Stage I: Early (pre-primary gold deposition); Stage II: Main (primary gold deposition), and Stage III: Late (post-primary gold deposition). Pre-gold stage mineralization events include diagenesis of the sediments and metasomatic processes associated with the intrusion of the dioritic Goldstrike stock. Hydrothermal minerals associated with an individual stage generally are limited to each stage; however, overlap of the major gangue minerals, such as quartz, illite, and sericite (Fig. 2) is common. Some mineralogical overlap between stages is due to cycling of circulating fluid that