Abstract Alkaline igneous rock-related gold deposits, primarily of Mesozoic to Neogene age, are among the largest epithermal gold deposits in the world. These deposits are a subset of low-sulfidation epithermal deposits and are spatially and genetically linked to small stocks or clusters of intrusions possessing high alkali-element contents. Critical-, near-critical, or energy-critical elements associated with these deposits are F, platinum-group elements (PGEs), rare earth elements (REEs), Te, V, and W. Fluorine and tungsten have been locally recovered in the past, and some other elements could be considered as future by-products depending on trends in demand and supply. The Jamestown district in Boulder County, Colorado, historically produced F from large lenticular fluoritebearing breccia bodies and Au-Te veins in and adjacent to the Jamestown monzonite stock. Several hundred thousand metric tons (t) of fluorspar were produced. Some alkalic epithermal gold deposits contain tungstenbearing minerals, such as scheelite, ferberite, or wolframite. Small tungsten orebodies adjacent to and/or overlapping the belt of Au telluride epithermal deposits in Boulder County were mined historically, but it is unclear in all cases how the tungsten mineralization is related genetically to the Au-Te stage. Micron-sized gold within deposits in the Ortiz Mountains in New Mexico contain scheelite but no record of tungsten production from these deposits exists. The most common critical element in alkaline igneous-rock related gold deposits is tellurium, which is enriched (>0.5%) in many deposits and could be considered a future commodity as global demand increases and if developments are made in the processing of Au-Te ores. It occurs as precious metal telluride minerals, although native Te and tetradymite (Bi2Te2S) have been reported in a few localities. Assuming that the Dashigou and adjacent Majiagou deposits in Sichuan province, China, are correctly classified as alkalic-related epithermal gold deposits (exact origin remains unclear), they represent the only primary producers of Te (as tetradymite) from this deposit type. It is worth noting that some epithermal veins (and spatially or genetically related porphyry deposits) contain high contents of Pt or Pd, or both. The Mount Milligan deposit typically contains >100 ppb Pd, and some values exceed 1,000 ppb. However, owing to the presence of other large known PGE resources in deposits in which PGEs are the primary commodities, it is unlikely that alkaline-related epithermal gold deposits will become a major source of PGEs. Similarly, many epithermal gold deposits related to alkaline rocks have high vanadium contents, but are unlikely to be considered vanadium resources in the future. Roscoelite (V-rich mica) is a characteristic mineral of alkalic-related epithermal deposits and is particularly abundant in deposits in Fiji where it occurs with other V-rich minerals, such as karelianite, Ti-free nolanite, vanadium rutile, schreyerite, and an unnamed vanadium silicate. A few alkaline intrusive complexes that contain anomalous concentrations of gold or were prospected for gold in the past are also host to REE occurrences.The best examples are the Bear Lodge Mountains in Wyoming and Cu-REE-F (±Ag, Au) vein deposits in the Gallinas Mountains in New Mexico, which have REE contents ranging up to 5.6% in addition to anomalous Au.

Abstract The architecture of the critical zone—the distribution of mobile regolith, the thickness of weathered rock, and their characteristics, as well as the topography of the land surface—is shaped by erosion and weathering processes that depend upon both lithology and climate. In this trip we explore the Boulder Creek watershed, a landscape that juxtaposes uplifted Precambrian crystalline rocks of Colorado’s Front Range against Mesozoic marine sedimentary rocks underpinning the western edge of the High Plains. The landscape is strongly shaped by Quaternary climate cycles operating on this template inherited from the Laramide orogeny. Stop 1 will provide an overview of the abrupt topographic step at the Front Range–High Plains join, where we will discuss fluvial strath terraces on the Plains. At Stop 2 in Betasso Preserve, we will discuss the impact of the canyon cutting set off by late Cenozoic exhumation of the High Plains on the hillslopes and groundwater systems lining the master stream. At Stop 3, we will hike 2 miles down Gordon Gulch, a focus site in the Boulder Creek Critical Zone Observatory. At stops on the hike, we will discuss exhumation rates, climate-modulated weathering, hillslope hydrology and hillslope sediment transport, and the influence of slope aspect on these processes. Our goal is to focus on the history of climate-driven erosion and weathering processes, and how to incorporate these processes into quantitative models of landscape evolution.