Field Trip Day Three: Skarns of the Yerington District, Nevada: A Triplog and Commentary
Marco T. Einaudi, 2000. "Field Trip Day Three: Skarns of the Yerington District, Nevada: A Triplog and Commentary", Part I. Contrasting Styles of Intrusion-Associated Hydrothermal Systems: Part II. Geology & Gold Deposits of the Getchell Region, John H. Dilles, Mark D. Barton, David A. Johnson, John M. Proffett, Marco T. Einaudi, Elizabeth Jones Crafford
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THE CONTACT between the Yerington batholith and metased-imentary and metavolcanic rocks east of Ludwig, Nevada, is exposed over 3.5 km of paleodepth (Fig. 1) due to 90° of westward rotation during Basin-and-Range faulting (Proffett, 1977; Geissman et al., 1982). Here we have the opportunity to study the effects of depth, distance, and time in the generation of metamorphic rocks and skarns. As we walk over the terrain, keep reminding yourself that “original up” is to the west. The main emphasis of the trip will be to examine the structural and lithologic controls on the formation of calc-sil-icate hornfels, skarn, and related ores, the mineralogy of these rocks, and their temporal relation to quartz monzodior-ite and granite porphyry intrusions of the Yerington batholith. This examination will yield a conceptual framework for understanding skarn-forming processes and will generate ideas useful in mineral exploration. Some background material on terminology and phase equilibria is given in the first section of the chapter, preceding the description of individual stops. The actual trip log gives descriptions of outcrops for each stop, followed by background material, interpretation, and application where appropriate. An overall summary and conclusions is beyond the scope of this chapter.
Many of the conclusions presented below rely on the parallel studies of igneous and hyrothermal events associated with emplacement of the Yerington batholith (Proffett, 1977; Proffett and Dilles, 1984; Dilles, 1987; Dilles and Einaudi, 1992; Dilles et al., 1992; Dilles and Proffett, 1995), summaries in this Fieldtrip Guidebook (Dilles et al., 2000, etc.), as well as studies by others on skarn deposits around the world (cited individually in text).