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Rock alteration and mineralization is widespread in the vicinity of the San Juan <br />caldera. "Propylitic alteration has affected many cubic miles of volcanic rocks <br />throughout and beyond the [Silverton) caldera" (Burbank, 1960). In the propylitized <br />rocks "pyrite is ubiquitous and forms between 0.1 and 2.0 percent" of the rock <br />volume (Casadevall and Ohmoto, 1977, p. 1292). In excess of one billion tons of <br />pyrite are estimated to exist in rocks in the vicinity of the Sunnyside Mine (assuming <br />5 cubic miles of propylitized rocks with 1.0% pyrite). The weathering of this <br />dispersed pyrite as well as other mineralization has resulted in the pervasive staining <br />which is common in rocks throughout the area (e.g. Red Mountains 1, 2, and 3). <br />3.2 Bedrock Permeability <br />Fracture permeability in the vicinity of the Sunnyside Mine is anisotropic. Permeability <br />is greater in anortheast/southwest direction due to the dominant fracture orientation <br />within the Eureka graben. In addition, fracture permeability is greater in the welded <br />tuffs and flows than in the unwelded units. The southwest dip in the vicinity of the <br />mine results in zones of greater permeability which dip southwest along the more <br />highly fractured units. The overall effect is that the greatest permeability zones trend <br />northeast/southwest and dip about 10° - 14° southwest. Field evidence for this <br />anisotropy in permeability includes a preferred orientation for ore shoots. Figure 5 <br />shows an example of a northeastlsouthwestirending ore shoot which dips southwest. <br />sunnylwpltraci122571Mar7993.Rpt 14 <br />Nil SIiT1011 HYDRO-SERRCH <br />