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INTRODUCTION <br />gulch below the Johnson tunnel where Belden Formation rocks are <br />exposed to 400 feet at the Bushwacker shaft, less than 1,500 feet <br />to the northeast. For approximate ages of the units illustrated <br />see the Geologic Time Scale as well as their individual <br />descriptions in the GLOSSARY oe TERMS below. <br />Geologic Structure <br />In the Aspen district, structural complexity, specifically <br />folding and faulting, increases from Hunter Creek south through <br />Smuggler mountain and Aspen mountain to the southern limits of the <br />district near the headwaters of Castle Creek. Very generally the <br />bulk of the richest Aspen ore deposits occur in the Leadville <br />Limestone in a faulted syncline that both plunges and broadens to <br />the northwest. On Aspen mountain this syncline is tight and <br />intensely faulted. On Smuggler mountain the syncline is <br />essentially a monocline (the western limb partially represented by <br />Red Butte, over two miles west) cut by a series of significant <br />cross faults and near-bedding plane faults. In all areas the <br />faults are significant in localizing the richest ore deposits <br />although their direct relationship to mineralization is unclear. <br />The Smuggler orebody is contained in a sedimentary breccia <br />at the top of the Red Cliff Dolomite member of the Mississippian <br />Leadville Limestone." The breccia represents a significant <br />erosional event of early Mississippian age (approximately 345 <br />million years ago). Smaller amounts of primarily base-metal (Pb- <br />Zn) ore are present in a much younger solution collapse breccia at <br />the base of the Pennsylvanian Belden Formation, which overlies the <br />Leadville, and in unbrecciated calcareous and carbonaceous shales <br />and limestones of the Belden itself. Fragments of the Laramide <br />Aspen mountain sill are present in the second breccia, so this <br />breccia is younger than the sill, which is between 69 and 74 <br />million years old. The Della-Smuggler fault system, a series of <br />normal faults that strike northwesterly and dip to the southwest at <br />30° to 55° and which cut the Aspen mountain sill, is frequently <br />mineralized. The Smuggler orebody is thickest at the intersection <br />of these faults and the earlier breccia at the top of the Red Cliff <br />dolomite. <br />Mineralization <br />Mineralization occurred in three primary precipitation <br />(hypogene) stages. The early stage consisted of open-space <br />deposition of barite (barium sulfate), pyrite (iron sulfide), <br />" Largely from the abstract of R. J. STEGEN, D. W. BeATx, AND T. B. <br />THGMPSGN, THE ORIGIN OF TXE AG-PB-ZN-BA DEPOSITS AT ASPEN, COLORADO, BASED ON GEOLOGIC <br />AxD GEOCxeKICAL STUDIES oP Txe SMUGGLER ORE BODY, cited and annotated as the <br />"STEGEN REPORT". <br />Bruce A. Collins - XX1V - SMUGGLER BIBLIOGRAPHY <br />