Christopher S. Henry
David A. John
2020
<p><span>Numerous epithermal gold-silver deposits formed during the past 40 Ma are irregularly distributed across the Great Basin. These deposits formed in six major magmatic-tectonic settings that varied during the complex evolution of the continental </span><span>margin of western North America: (1) slab rollback–ignimbrite flareup (~45–17 Ma), </span><span>(2) slab rollback–ancestral Cascade arc (~35 Ma–present), (3) Yellowstone hotspot–</span><span>bimodal (~16.7–3 Ma), (4) slab window (~16 Ma–present), (5) Basin and Range bimodal extensional (≤ 7 Ma), and (6) amagmatic extensional (≤ 5 Ma). Most large (> </span><span>1 Moz gold produced) deposits are Miocene (~20–8 Ma), low-, intermediate-, and </span><span>high-sulfidation deposits in the southern part of the ancestral Cascade arc; late Miocene post-subduction, low-sulfidation deposits formed over the slab window; and lowsulfidation deposits related to early (16.7–15 Ma) Yellowstone hotspot magmatism </span><span>formed along the northern Nevada rift and related fracture zones to the west. The </span><span>world-class Round Mountain low-sulfidation deposit is the only large deposit in ignimbrite flareup rocks despite these rocks constituting the largest eruptive volume of </span><span>Cenozoic magmas in the Great Basin. Intermediate to silicic composition lava dome </span><span>complexes are the most common setting for epithermal deposits in the western Great </span><span>Basin, whereas deposits formed in a wide range of settings and rock types during Yellowstone hotspot activity. With exception of the Round Mountain caldera, the dozens </span><span>of calderas of the ignimbrite flareup do not host large epithermal deposits. Several </span><span>young (≤ 5 Ma), “amagmatic” low-sulfidation deposits formed along Basin and Range </span><span>fault zones in sedimentary rocks that lack proximal magmatic activity. The types and </span><span>characteristics of epithermal gold-silver deposits in the Great Basin systematically </span><span>vary with magmatic-tectonic setting and magma composition, and their distribution </span><span>reflects the combined effects of tectonic setting of magma genesis; magma source, </span><span>composition and eruptive style; crustal thickness and composition; presence of crustal-scale structural zones; climate; and preservation of deposits.</span></p>
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Geological Society of Nevada
Magmatic-tectonic settings of Cenozoic epithermal gold-silver deposits of the Great Basin, western United States
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