Abstract The Lavender open pit is approximately 80 mi (130 km) southeast of Tucson, Arizona, and can easily be reached by car from either Tombstone or Douglas on paved roads (Fig. 1). The overlook or observation site for the Lavender open pit copper mine is on U.S. 80 between Bisbee and Lowell. The topography and a few of the more famous landmarks—such as the Copper Queen mine, which was the first discovery, the Irish Mag mine, and Sacramento Hill (Ransome, 1904)—are shown on Figure 2. Unlike many of the porphyry copper deposits of the Lavender open pit mineralization is in a fluidized [intrusive] breccia pipe, not porphyry, and is Nevadan (130 Ma), Laramide, in age. The fluidized breccia is composed of exotic ments and boulders that have been transported from below in fine-grained or rock flour matrix of pulverized rock and ported sulfides. The transporting media was a circulating water slurry flowing along preexisting fractures. The ore actually mined in the Lavender pit were not in the porphyry rocks but were transported fragmental sulfides in the matrix mineralized fragments and boulders with later supergene chalcocite enrichment. The mineralization in the porphyrins limited to pyrite with a thin coat of chalcocite, and was very grade.

Abstract This trip crosses a wide-expanse of typical Valley and Ridge geology and topography before reaching the gentler structure of the Powell River anticline with its numerous zinc and lead occurrences. The largest of these, the New Prospect mine, is Stop 3. Here the mineralization occurs in Maynardville Limestone along fault and shear zones rather than in collapse breccias. Stop 4 will be at the famous Thorn Hill section where the roadcut for highway US-25E traverses strata from lower Cambrian to lower Mississippian in age. Selected sites will be examined. The remainder of this trip will cover the area northeast and southeast of the Mascot-Jefferson City district, concentrating on the post-Knox unconformity and its solution features. Stop 5, just south of Dandridge along Douglas Lake, provides a look at a quartz sand-filled depression in the erosion surface. At Stop 6, west of Dandridge at the Shady Grove area, two large, relic sinks filled with blocks of dolomite and chert will be seen. This karst development is believed related to the development of the large breccia bodies which are common to the upper Knox dolomite and which are ore hosts in the mineralized districts.

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).