Geologic, Geochemical, and Geophysical Characterization of the Gold Deposits of the Horseshoe Bend Mining District, Idaho: Building a Four Dimensional Model for Ore Exploration

The Eocene aged Trans-Challis Fault System of central Idaho provides the tectonic and magmatic framework for a series of Au-Ag and Cu-Mo ore deposits. From its northernmost extension near Butte, Montana to its southwestern terminus in the Boise Basin of south-central Idaho the Trans-Challis Fault System is associated with some of the richest precious metal deposits found in Idaho. However, the southernmost tip of the Trans-Challis Fault System, composed of the Horseshoe Bend and Pearl mining districts, remains understudied, receiving little economic or academic attention. As a result, how the Pearl to Horseshoe Bend mining districts fit within the established framework of the Trans-Challis Fault System and associated mineralization is poorly characterized. Significantly, no high-resolution mapping or modern geochemical and geophysical techniques have been applied to areas within these historically productive mining districts. This study employs detailed bedrock mapping, high-precision U/Pb geochronology, high-resolution soil geochemistry, ground-based magnetic anomaly mapping, and electrical resistivity and induced polarization geophysical imaging to characterize spatial patterns to create a model for structurally controlled mineralization within the Horseshoe Bend Mining District. Integration of these datasets with knowledge gained from other studies along the Trans-Challis Fault System has led to the characterization of the structural framework hosting mineralization near Horseshoe Bend, Idaho. Geologic mapping reveals NE-SW and E-W trending dike swarms and associated en echelon mineralized vein systems oriented sub-parallel to the NE trend of the Trans-Challis Fault System. U/Pb ages on zircon grains within the dikes date emplacement during the late Early Eocene to the Early Oligocene. Surficial geochemistry surveys reveal east-west oriented, en echelon, zones of anomalously high gold concentrations with subordinate north-south oriented arms. Magnetic anomaly mapping reveals lineaments of sharp magnetic gradients spatially correlated with mapped dike patterns, as well as zones of magnetic lows spatially correlated with surface geochemical gold concentration anomalies. Electrical resistivity and induced polarization subsurface imaging techniques outline a series of east-west oriented, northeast stepping, conductivity, chargeability, and metal factor highs that correlate with a similarly oriented magnetic anomaly over the survey area, and en echelon mineralized vein systems mapped in adjacent bedrock. The Early Oligocene age of the andesite dike phase reported to follow mineralization either extends the duration, or changes the timing, of the mineralizing events associated with this section of the Trans-Challis Fault System. Mapping, geochemical and geophysical data strongly suggest the controlling factor in mineralization location and geometry is the underlying structural framework of the system. Based on these geometries and orientations, a dextral Riedel shear array oriented 070° is proposed to adequately model the structural architecture controlling mineralization within the Horseshoe Bend Mining District

Draco

This poster for the Natural Sciences Poster Session at Parkland College features the constellation Draco, which is positioned between the big and little dipper in the Northern sky. It is also circumpolar and contains a galaxy and a nebula in its boundaries. The student identified ten different key stars in the constellation, observed when they rose and set. He then graphed their altitudes and azimuth and identified their life spans

Shall Be Bright at Last: Reflections on Suffering and Hope in the Letters of Paul

These nine essays on suffering offer exercises in Christian hope. The contributors reveal honest and tender wounds of the many harsh realities of life in a broken world awaiting full redemption. They meditate on Paul\u27s holy words that teach us to pray with expectation and live by faith. They encourage fellow pilgrims to trust the path and stick together. Shall Be Bright at Last is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License, except where otherwise noted. CC BY-NC-SAhttps://digitalcommons.georgefox.edu/monographs/1000/thumbnail.jp

Geochronology in the Exshaw Formation: correlation with the Hangenberg extinction event.

The Hangenberg mass-extinction event defines the boundary between the Devonian and Mississippian geologic Periods, and is recognized by the common occurrence of black shales associated with marine anoxic environments. Biostratigraphy and radiometric dating have been used to globally correlate these end-Devonian black shales; however, much of the biostratigraphic record is missing and past radiometric ages have not had the resolution necessary to provide clear insight into the causes of the Hangenberg event. Here we apply high resolution U-Pb zircon dating methods to volcanic tuffs collected from four locations in the Exshaw Formation, along the eastern of edge of the Western Cordillera in Alberta, Canada, and compare these results to high-precision ages for the Hangenberg Event (359.3 ± 0.1 Ma) in the type sections of the Rhenish Mountains of Germany. The Exshaw Formation is divided into lower black shale and upper silty carbonate members; the exact location of the Hangenberg event within the Exshaw is unknown due to the sparse fossil occurrence. Two correlated tuffs exposed in the Jura Creek and Rundle Range sections have been dated to 360.0 ± 0.1 Ma, and constrain the position of the Hangenberg event to the upper portion of the lower black shale member of the Exshaw Formation. Ongoing analysis of additional overlying tuffs in the Rundle Range section will further constrain the exact position of the Hangenberg event. Zircon dates of 362.7 ± 0.1 Ma and 363.0 ± 0.1 Ma from Nordegg and Crowsnest sections, respectively, are significantly older than the Hangenberg Event. These new zircon ages confirm and clarify the presence of unconformities in the relatively condensed sections at these locales, and show that anoxic sedimentation began earlier in the Western Canadian Sedimentary Basin compared to correlative strata in Europe