Fe-oxides in jasperoids from two gold districts in Nevada: Characterization, geochemistry, and (U-Th)/He dating

Dante E. Huff, Elizabeth Holley, William R. Guenthner, Jenna M. Kaempfer

Research output: Contribution to journalArticlepeer-review

Abstract

This study examines the whole-rock geochemistry, Fe-oxide texture and crystal morphology, and Fe-oxide (U-Th)/He date variation of jasperoids, as well as the relationships between these characteristics, in order to evaluate jasperoids as an indicator for gold mineralization. Jasperoid samples with a range of textures, appearances, and expected gold concentrations were collected from two gold districts in Nevada: the northern Carlin trend (Gold Quarry Mine), and the Battle Mountain district (Marigold Mine; Battle Mountain prospect). In our jasperoid samples, whole-rock concentrations of Au are positively correlated with As, Ag, Pb, Sb, U, W, and Tl. The following Fe-oxide textures are associated with anomalous gold concentrations: disseminated, submicron crystals; feathery and acicular crystal morphologies; concentric zonation from hematite to goethite; and botryoidal textures. Calculated closure temperatures for the (U-Th)/He system in observed jasperoid Fe-oxide morphologies within our dataset range from 26 to 136 °C, indicating variable susceptibility to He diffusion at near-surface conditions. Fe-oxide (U-Th)/He dates range from 29.4 ± 0.5 Ma to 0.11 ± 0.01 Ma, displaying intra- and intersample variation. We attribute the date variation to multiple factors including He implantation, parent isotope exchange, and He loss through closure temperature sensitivity and alpha-ejection. The intra- and intersample variation within the Fe-oxide (U-Th)/He dates limits our ability to make geologic interpretations. Our case study identifies important limitations of the (U-Th)/He method in jasperoids and provides insight on how He date variation might be avoided in future studies.

Original languageEnglish (US)
Pages (from-to)72-102
Number of pages31
JournalGeochimica et Cosmochimica Acta
Volume286
DOIs
StatePublished - Oct 1 2020

Keywords

  • Carlin-type gold deposit
  • Fe-oxide (U-Th)/He chronology
  • Jasperoids

ASJC Scopus subject areas

  • Geochemistry and Petrology

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