New Mexico Geological Society Annual Spring Meeting — Abstracts

Mapping of 7 tranches during the deconstruction of the Goathill North mine rock pile in 2004 identified several consistently correlatable units downward through approximately 200 feet of mined material. Trench construction typically consisted of four benches approximately 5 feet long and 4 feet deep, and mapping units were identified based on grain size, color, and other physical properties. Unit boundaries ranged from horizontal to vertical, but most dipped between 20 and 40 degrees westward to northwestward. At the top of the rock pile, a 10- to 15- foot, nearly horizontal traffic surface unconformably overlies dipping units. Mapped units ranged in thickness from 0.5 feet to 15 feet.

Team members identified and mapped units primarily on trench walls because benches were usually covered with a thin (6 to 12 inch) traffic surface created by bulldozer movement. Section drawings and lateral measurements of unit boundaries provided data to make maps of each trench. Maps of individual trenches show a “v-shape” indicating the westward dipping beds on each trench with an apparent offset between benches due to the vertical walls separating benches. Thin units pinched out or graded vertically and laterally. Unit boundaries have been projected onto east-west cross-sections to show the vertical extent of units within the rock pile.

Detailed and generalized versions of trench maps, projected cross-sections, and contoured unit boundaries provide a structural framework for conceptual and numerical models in other parts of this study. Analysis of samples and measurements within each unit provide physical properties and boundary conditions for the models.