Age and petrogenesis of volcanic and intrusive rocks in the Sulphur Spring Range, central Nevada: Comparisons with ore-associated Eocene magma systems in the Great Basin

Abstract

Widespread base-and precious-metal anomalies, oxidized sulfi de veins, silicifi ed calcareous shales and carbonates, and altered porphyry intrusions occur in the northeastern Sulphur Spring Range, Nevada, 80 km south of important gold deposits in the Carlin trend. The small historic mines and prospects in the area are spatially and perhaps genetically related to a suite of variably altered dikes, small lava fl ows, silicic domes, and related pyroclastic rocks. New major-and trace-element data and U-Pb zircon ages show that the East Sulphur Spring volcanic suite is Eo-Oligocene in age (36-31 Ma) and ranges in composition from high MgO-basaltic andesite to peraluminous rhyolite. The major-and trace-element compositions of the volcanic rocks are characteristic of continental margin subduction zone magmas and form a high-K, calc-alkaline suite with low Fe/Mg ratios. In addition, the rocks have negative Nb and Ti anomalies and elevated Ba, K, and Pb on normalized trace-element diagrams. Crustal melting is indicated by the eruption of a peraluminous garnet-bearing ignimbrite and as a component in hybridized andesite.The nature of this suite and its potential for mineralization is elucidated via comparisons to other Eocene age volcanic rocks associated with much larger gold and copper deposits in the Great Basin. The East Sulphur Spring suite is more similar to Eocene igneous rocks found along and near the Carlin trend than it is to those erupted while the Bingham porphyry copper deposit developed 300 km farther to the east. For example, the East Sulphur Spring suite and the Eocene magmatic rocks along the Carlin trend are less alkaline than the Bingham suite and lack its unusual enrichment of Cr, Ni, and Ba in intermediate composition rocks (58-68 wt% silica). Nonetheless, the Bingham and East Sulphur Spring volcanic suites both preserve evidence of mixing that created intermediate compositions. For example, an andesite has obvious mineral disequilibrium with plagioclase, biotite, clinopyroxene, orthopyroxene, olivine, and amphibole coexisting with extensively resorbed megacrysts of quartz, K-feldspar, and garnet-indicative of mixing basaltic andesite or andesite and largely crystallized garnet-bearing rhyolite. On the other hand, we found no evidence for mixing with a mafi c alkaline magma like that in the Bingham Canyon magma-ore system. We conclude that: (1) an unusual tectonic setting prevailed during the Eocene and Oligocene of the western United States that promoted the production of oxidized mafi c magma in an arclike setting, but far inland as a result of the rollback of the Farallon slab;(2) the mafi c magmas intruded or erupted separately, or mixed with more silicic magma generated by fractional crystallization and assimilation of crustal materials; and (3) these mafi c magmas may have delivered signifi cant amounts of sulfur and chalcophile metals to upper crustal magma chambers and eventually to Paleogene ore deposits in the eastern Great Basin.

Fallout tuffs in the Eocene Duchesne River Formation, northeastern Utah—ages, compositions, and likely source

“…Age (Ma) Reference Central Wasatch Range 29.45, 32.2-35.38 John and others, 1997;Biek and others, 2005;Smyk and others, 2018 Sulphur Springs Range 31.5-36.9 Ryskamp andothers, 2008 Grouse Creek 34.3, 36.3, 41.3 Egger, 2003;Strickland and others, 2011 Harrison Pass 36 Barnes and others, 2001 Bingham Canyon 37.0-38. 6 Warnaars, 1978;Deino and Keith, 1997;Vogel and others, 2001 McGinty 37 Hintze and Kowallis, 2009 Pilot Peak 37.7-38.2 Wooden andothers, 1999;Woodburne, 2004 Ibapah 39 Hintze and Kowallis, 2009 Volcanic Field Age (Ma) Reference Duchesne River Formation, northeastern Utah-ages, compositions, and likely source Jensen, M.S., Kowallis, B.J., Christiansen, E.H, Webb, C., Dorais, M.J., Sprinkel, D.A., and Jicha, B. (figure 15a) also shows that the Duchesne River Formation tuffs have compositions similar to the northeast Nevada volcanic field.…”

Distinct mantle sources for Pliocene–Quaternary volcanism beneath the modern Sierra Nevada and adjacent Great Basin, northern California and western Nevada, USA

“…The Great Basin of the southwestern United States is well known for its abundance of Tertiary mafi c to felsic igneous rocks that are associated with rollback of the shallow-subducting Laramide slab (e.g., Colgan et al, 2008;Dickinson, 2006;Du Bray et al, 2009;Farmer and DePaolo, 1983;Farmer et al, 1989;Feuerbach et al, 1993;Henry et al, 1998;Humphreys et al, 2003;Humphreys, 1995;Perry et al, 1993;Ryskamp et al, 2008;Valentine et al, 2006;Wooden et al, 1998). Most of the youngest volcanic activity is concentrated at the margins of the Great Basin (DePaolo and Daley, 2000), specifi cally along the western margin of the Colorado Plateau (Conway et al, 1997;Johnsen et al, 2010;Lee, 2005;Smith et al, 1999;Tanaka et al, 1986), in southern Nevada (Feuerbach et al, 1993;Valentine et al, 2006), and along the eastern margin of the Sierra Nevada (Ormerod et al, 1988;Rogers et al, 1995).…”

Petrography, geochemistry and isotopic analysis of paleogene volcanism in the Fish Creek Mountains, Great Basin, North-Central Nevada

“…consistent with the Sulphur Springs area. Both volcanic suites have compositions that are generally consistent with a subduction zone origin including low Mg #'s, high K 2 0, and similar "spiky" trace element patterns with LILE enrichment and HFSE depletion (Ryskamp et al, 2008). Both regions were also affected by the same Paleogene detachment or roll back of the Farallon plate, which contributed to continental arc magmatism over a wide area of western North America (Ryskamp et al, 2008).…”

“…(B) Mafic rocks (Muller and Groves, 2000). Compositions of East Sulphur Springs samples, Bingham, Carlin, Tuscarora and Emigrant Pass are from Ryskamp et al (2008) and sources within 89 (Figure 1). The area of study is primarily composed of late Paleogene volcaniclastic and volcanic rocks that overly Paleozoic metasedimentary rocks, that also cover a large portion of the Sierra Nevada of northeastern California as well as western Nevada (Stewart and Carlson, 1976).…”

“…Lavas from the Ancestral Cascades area (N. Sierra, Lassen Volcanic Centre and the Lake Taheo-Reno area) and Sulphur Springs (Ryskamp et al, 2008) also display no noticeable HREE depletions suggesting that they are also melts from the spinel lherzolite field (Staffers, 2010) (Figure 39 (Pearce, 1983;Schmidt et al, 2008). Intraplate Mojave Desert basalts also have higher Nd and lower Sr radiogenic isotopic ratios, similar to those of the Buffalo Valley Pliocene -Quaternary cones found in the FCM (Wetmore, 2011) ( Figure 36).…”