Andradite Skarn Garnet Records of Exceptionally Low Δ18o Values Within an Early Cretaceous Hydrothermal System, Sierra Nevada, CA
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Contributions to Mineralogy and Petrology (2019) 174:68 https://doi.org/10.1007/s00410-019-1602-6 ORIGINAL PAPER Andradite skarn garnet records of exceptionally low δ18O values within an Early Cretaceous hydrothermal system, Sierra Nevada, CA J. Ryan‑Davis1,2 · J. S. Lackey2 · M. Gevedon3 · J. D. Barnes3 · C‑T. A. Lee4 · K. Kitajima5 · J. W. Valley5 Received: 2 March 2019 / Accepted: 12 July 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019 Abstract Skarn garnets in the Mineral King roof pendant of the south–central Sierra Nevada within Sequoia National Park, Califor- nia, USA reveal variable fuid chemistry with a signifcant component of meteoric water during metasomatism in the Early Cretaceous Sierra Nevada Batholith. We focus on andradite garnet associated with Pb–Zn mineralization in the White Chief Mine. Laser fuorination oxygen isotope analyses of δ18O of garnet (δ18O(Grt)) from sites along the skarn show a large range of values (− 8.8 to + 4.6‰ VSMOW). Ion microprobe (SIMS) analyses elucidate that individual andradite crystals are strongly zoned in δ18O(Grt) (up to 7‰ of variation). Total rare-earth element concentrations (∑REE) across individual garnets show progressive depletion of skarn-forming fuids in these elements during garnet growth. These fndings support 18 18 a skarn model of earliest red high-δ O grandite garnet consistent with a magmatic-dominated equilibrium fuid (δ O(H2O) as high as ≈ + 8‰). Later, green andradite crystallized in equilibrium with a low-δ18O fuid indicating a signifcant infux 18 of meteoric fuid (δ O(H2O) ≈ − 6 to − 5‰), following a hiatus in garnet growth, associated with late-stage Pb–Zn miner- 18 18 alization. Latest orange overprint rims have higher δ O values (δ O(H2O) ≈ 0–2‰), and depleted total REEs, suggesting infux of high-δ18O, trace-element depleted fuid derived from regional metamorphism of the carbonate host. Remarkably, low δ18O(Grt) values in the White Chief canyon skarn require a signifcant proportion of meteoric fuid available dur- ing > 400 °C andradite-forming metasomatism. Fluid fow was channelized at the pluton–wallrock contact, evidenced by the narrow extent of skarn. Keywords Skarn · Garnet · Oxygen isotope · Fluid fow · Arc magmatism Introduction Elemental and oxygen isotope zoning within hydrothermal Communicated by Othmar Müntener. skarn systems is observable at many scales: system-wide Electronic supplementary material The online version of this across a pluton, outcrop and hand-sample scale, and within article (https ://doi.org/10.1007/s0041 0-019-1602-6) contains individual minerals (e.g., Meinert et al. 2005). Microanalysis supplementary material, which is available to authorized users. by laser ablation or ion microprobe has successfully been * J. Ryan-Davis used to measure elemental and oxygen isotope compositions [email protected] within individual garnet crystals from skarns as a precise metric of fuid sources (e.g., Yardley et al. 1991; Jamtveit 1 Geological and Planetary Sciences, California Institute et al. 1993; Jamtveit and Hervig 1994; Crowe et al. 2001; of Technology, Pasadena, CA 91125, USA Clechenko and Valley 2003; Smith et al. 2004; Gaspar et al. 2 Geology Department, Pomona College, 185 E. 6th Street, 2008; Page et al. 2010; D’Errico et al. 2012). A multitude of Claremont, CA 91711, USA properties of the fuids and spatial arrangements in a hydro- 3 Department of Geological Sciences, University of Texas, thermal system (e.g., temperature, fuid pressure, oxidation Austin, TX 78712, USA state, chemistry, fuid sources, fow rate, and difusion) may 4 Department of Earth Science, MS-126, Rice University, 6100 be the cause of observable skarn zoning (Bowman 1998b), Main Street, Houston, TX 77005, USA and therefore, a multi-method approach must be used to 5 WiscSIMS, Department of Geoscience, University understand potential causes of zoning in skarns. of Wisconsin, Madison, WI 53706, USA Vol.:(0123456789)1 3 68 Page 2 of 19 Contributions to Mineralogy and Petrology (2019) 174:68 This study focuses on a narrow band of andradite-rich The pendant also contains early Jurassic (ca. 196 Ma) skarn at White Chief canyon in the Mineral King Roof Pen- tufs and exposes aerially extensive Cretaceous arc volcanic dant. Pb–Zn–Ag mineralization there drew many miners to units (132–136 Ma) (Klemetti et al. 2014). Small plutons of the Mineral King mining district in the late 1800s, simi- overlapping age (135–136 Ma) are found within and adja- lar to the rush for gold in the western Sierran foothills but cent to the Mineral King pendant and porphyritic textures in otherwise unique in the Sierra, as most other skarns in the dikes and portions of the plutons are common, and provide range harbor tungsten mineralization (e.g., Goodyear 1888; evidence that the area preserves a shallow “volcano-plutonic Newberry 1982; MacKenzie 1983). The results provide suite” transition (Sisson and Moore 2013). Because of this details on the dynamics of garnet chemistry and fuid fow shallow setting, we have assumed that the pressure of skarn in a shallow, Early Cretaceous hydrothermal system in the formation at White Chief canyon was < 1 kbar. Within the Sierra Nevada Batholith, a period of magmatic quiescence metavolcanic units are carbonate-rich units interpreted to in the Sierran Arc (Paterson and Ducea 2015), but one that represent intervals of volcanic and tectonic quiescence. Pen- preserves a critical glimpse of hydrothermal fuid fow in the dant protoliths at this location were calcareous quartz sand- arc. Comparing oxygen isotope data with from White Chief stone interpreted to have been deposited in a deep marine canyon (this study), with other skarn systems in the same environment during a break in the volcanic activity that roof pendant, provides a record of changing characteristics produced the material for the majority of the roof pendant of hydrothermal systems at key intervals in the Mineral King (Busby-Spera 1983; Busby-Spera and Saleeby 1987; Sis- roof pendant. These archives of hydrothermal processes give son and Moore 2013). The roof pendant underwent meta- unusual glimpses into upper crustal fuids in the Cretaceous morphism and deformation of the volcanic and sedimentary Sierra Nevada arc. Our investigation of the White Chief protoliths, assigned to upper greenschist and amphibolite canyon skarn has implications for the role of meteoric fuid facies (Sisson and Moore 2013), and mineral assemblages exchange in the Early Cretaceous volcanic system. in the metamorphic rocks include andalusite and cordierite A comparison of oxygen isotope ratios of garnet, calcite, suggest low pressure and high temperature associated with and scheelite (CaWO 4) from the White Chief skarn with pluton emplacement at shallow levels (Sisson and Moore oxygen isotope ratios measured elsewhere in the pendant 2013; Klemetti et al. 2014). Pressures of 2–3 kilobars are tests for contributions of fuids from distal sources (e.g., reported by Al-in-hornblende barometry on most of the metarhyolites or metapelites in the pendant). Measured large, ~ 98–100 Ma granodiorites that surround the pen- oxygen isotope values whole rock (δ18O(WR)) and zircon dant (Ague and Brimhall 1988). Calcite- and dolomite-rich (δ18O(Zrc)) from the granodiorite of White Chief Mine pro- marbles are exposed to the west and southwest of Empire vide the best estimates of δ18O of the magmatic fuid in the Mountain, and to the east and northeast of the granodiorite skarn-forming system. of White Chief Mine (Fig. 1). We report textural, major, minor, and trace-element com- Hydrothermal exchange between the granodiorite of position, and oxygen isotope ratios of near-end-member White Chief Mine and the large marble body that bounds andradite (Adr) garnets from the Pb–Zn White Chief can- it to the east drove formation of Pb–Zn skarns along a nar- yon skarn system. By combining petrologic approaches with row (~ 1–10 m wide) zone between the pluton and marble elemental and isotopic measurements, we provide details of in White Chief canyon (Figs. 1, 2). Field relations indicate garnet morphology and chemistry that record the evolution that the emplacement of the 135 ± 1 Ma (U–Pb zircon, of the hydrothermal system including spatial relations of Sisson and Moore 2013) deformed hornblende–biotite fuid fow over the time period recorded by garnet growth. granodiorite of White Chief Mine drove skarn formation (Figs. 2, 3), thus linking its formation to the Early Creta- Geologic setting ceous “volcano-plutonic suite” of Sisson and Moore (2013). The White Chief canyon skarns are typically massive gar- Complex centimeter- to meter-scale mineralogical zoning netites with subordinate green clinopyroxene and in some is apparent in the White Chief Mine skarn within the Min- cases secondary actinolite. Most of the “pockets” of gar- eral King roof pendant in Sequoia National Park (Fig. 1). netite are composed of red- to beige-colored, granoblastic The Mineral King pendant is among the largest (~ 10 km2) garnet. Olive-green and orange-rimmed andraditic garnetite, roof pendants in the south–central Sierra Nevada batholith often occurring with up to 80 volume % Pb–Zn sulfde min- (Fig. 1), and is bounded by ca. 98–99 Ma granodiorite and eralization (galena + sphalerite), occurs as more localized granite plutons (Sisson and Moore 2013). Pendant rocks domains within the skarns, with the largest of these being comprise Triassic–Jurassic metavolcanic and metasedimen- the galena-rich ore zone, where White Chief Mine was situ- tary units of the Kings Sequence group (Saleeby and Busby ated (Fig. 2a). Ore deposition is often associated with late 1993). meteoric fooding in skarn systems, which represents the retrograde stage of skarn formation (e.g., Einaudi and Burt 1 3 Contributions to Mineralogy and Petrology (2019) 174:68 Page 3 of 19 68 Fig. 1 Location and simplifed geologic map of the Mineral King ▸ Simplified Geology roof pendant, south–central Sierra Nevada, California, modifed after Sierra granodiorite of (~135 Ma, Sisson Sisson and Moore (2013).