| Description |
xv, 158 leaves : illustrations, maps, photographs ; 29 cm |
| Summary |
"The Escalante Silver District, Iron County, Utah, occupies a group of low hills extending to the Escalante Desert from the Black Hills to the south. Tertiary volcanics serve as host rocks for silver bearing quartz veins. Five map units, with a total of 12 members are recognized. X-ray fluorescence and field mapping enabled differentiation of the units, while thin section analysis enabled characterization of the members. The map units formed in three episodes. The oldest is extrusive doming of distinctive older lava and breccia flows. The middle group is made up of tectontic breccias, sillar-like lava flows, and volcaniclastic sediments that fill a preexisting moat. The youngest group consists of lava and breccia flows along with hot spring deposits related to regional eruptions and local hydrothermal activity. Four sets of linear features cut the area: east-west trending, northeast-trending, northwest-trending, and arcuate shaped. Most are relatable to normal faults associated to Basin and Range faulting. Arcuate fractures probably are related to tensional stress brought on by caldera activity. Silicic, or jasperoid type alteration and pervasive weak clay alteration occur throughout the district. Alteration effects are coincident with the vein distribution. The wall rock near the veins is characterized by silicification and intense replacement by calcite. A feasible checklist for exploration of vein mineralization in volcanic environments includes the following: 1) permeable volcanics or volcaniclastic sediments, 2) fracturing framework conducive to ore deposition, and 3) hydrothermal circulation set in motion by nearby intrusions or rhyolitic domes"--Abstract, leaves ii-iii. |
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