We present a newly compiled geologic map of the Pine Mountain window based on available 1:24,000 (and smaller) scale geologic maps; this map provides an improved basis to reconcile long-standing issues regarding tectonic evolution. We integrate sensitive high-resolution ion microprobe (SHRIMP) single-grain U-Pb ages of igneous, metamorphic, and detrital zircons from Grenville basement rocks, associated metasedimentary units, and cover rocks to help clarify the pre-Appalachian history and to better delimit the distribution of Laurentian versus peri-Gondwanan and Gondwanan units along the southeast flank of the window. U-Pb results indicate that some units, which earlier had been correlated with Neoproterozoic to Early Cambrian Laurentian rift deposits of the Ocoee Supergroup (i.e., Sparks-Halawaka Schist), actually are supracrustal rocks deposited prior to ~1100 Ma that were intruded and metamorphosed during the Ottawan phase of the Grenville orogeny. Zircons from the Phelps Creek Gneiss are 425 ± 7 Ma and overlap in time with plutons that intruded rocks of the Carolina superterrane during the Silurian (i.e., the Concord-Salisbury suite). The host units to the Phelps Creek Gneiss had also previously been interpreted as Sparks-Halawaka Schist, but field relations combine with the Silurian intrusive age to suggest that they rather belong to the peri-Gondwanan Carolina superterrane, helping to refine the position of the Central Piedmont suture in its most southern exposures. Results suggest that the Pine Mountain window is not framed by a single fault, but by Alleghanian faults of different timing, rheology, and kinematics, some of which were reactivated while others were not. The new map and U-Pb dates reveal that the southwesternmost exposures of the Central Piedmont suture are located farther northwest, so the width of the Pine Mountain window narrows from 22 km wide in central Georgia to only 5 km in Alabama. At its narrowest, the flanks of the Pine Mountain window are marked by two relatively thin normal faults (the Towaliga and Shiloh faults, northwest and southeast, respectively) that have excised the wider, earlier-formed mylonite zones. All of the Alleghanian faults are cut by later high-angle, normal and left- and right-slip brittle faults (Mesozoic?), which also influenced the present configuration of the window.

Abstract The Coles Hill uranium property is located in Pittsylvania County, Virginia, within the Smith River allochthon in Southside Virginia's Western Piedmont Province. The Coles Hill property is bounded on the east by the listric normal Chatham fault at the Triassic Danville basin. Uranium mineralization occurs in the footwall of the Chatham fault and is hosted in healed fractures and in hydrothermal apatite in the Leatherwood granite mylonite that is intruded by the Rich Acres gabbro amphibolite. The granite is silica depleted. The mylonite is foliated with a strike of 030° and dips 30°SE; the Chatham fault strikes 030° and dips 60°SE. The structural trap for uranium mineralization is contained on the east by the Chatham fault and beneath by unmineralized Leatherwood biotite gneiss, which is underlain by the Fork Mountain schist. Hematite staining of the ground surface is from weathering of Fork Mountain schist, which outcrops west of the Chatham fault at a constant distance of half a kilometer. In the southern property, pods of uranium mineralization plunge south at 45°. In the northern property, pods of uranium mineralization plunge northeast at 12°. Saussurite, rapakivi textures, Na- and K-metasomatism, titanite, zircon, apatite, calcite, and hematite are present. One possible uranium source is remobilization from the Triassic basin by westward-flowing meteoric waters that intersected the Chatham fault at depth and migrated upward and laterally into the Leatherwood granite. Another uranium source model may be introduction of uranium mineralization by hydrothermal fluids associated with emplacement and cooling of the Leatherwood granite. These fluids would have migrated upward into a structural trap where uranium minerals were precipitated in hydrothermal fractures.