TY - JOUR
T1 - Fe-oxides in jasperoids from two gold districts in Nevada
T2 - Characterization, geochemistry, and (U-Th)/He dating
AU - Huff, Dante E.
AU - Holley, Elizabeth
AU - Guenthner, William R.
AU - Kaempfer, Jenna M.
N1 - Funding Information:
We thank P. Reiners, U. Chowdhury, and E. Able (University of Arizona) for assistance with (U-Th)/He analyses and V. Valencia at Zirchron LLC for sample separation. Comments from A. Ault and two anonymous reviewers greatly improved the manuscript. NSF EAGER awards to EH (1641142) and WRG (1641138) and a NSF CAREER award to EH (1752756) supported this research. We gratefully acknowledge Newmont Goldcorp Corporation and SSR Mining Inc. for access to sampling sites and logistical support.
Funding Information:
We thank P. Reiners, U. Chowdhury, and E. Able (University of Arizona) for assistance with (U-Th)/He analyses and V. Valencia at Zirchron LLC for sample separation. Comments from A. Ault and two anonymous reviewers greatly improved the manuscript. NSF EAGER awards to EH (1641142) and WRG (1641138) and a NSF CAREER award to EH (1752756) supported this research. We gratefully acknowledge Newmont Goldcorp Corporation and SSR Mining Inc. for access to sampling sites and logistical support.
Publisher Copyright:
© 2020 Elsevier Ltd
PY - 2020/10/1
Y1 - 2020/10/1
N2 - 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.
AB - 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.
KW - Carlin-type gold deposit
KW - Fe-oxide (U-Th)/He chronology
KW - Jasperoids
UR - http://www.scopus.com/inward/record.url?scp=85088958690&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85088958690&partnerID=8YFLogxK
U2 - 10.1016/j.gca.2020.07.014
DO - 10.1016/j.gca.2020.07.014
M3 - Article
AN - SCOPUS:85088958690
SN - 0016-7037
VL - 286
SP - 72
EP - 102
JO - Geochmica et Cosmochimica Acta
JF - Geochmica et Cosmochimica Acta
ER -