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CC BY-NC-ND V4.0, Open Access
Thesis
GEOCHEMICAL CHARACTERIZATION OF HYDROTHERMAL ALTERATION IN THE EOCENE SCATTER CREEK FORMATION, REPUBLIC, WASHINGTON
Washington State University
Master of Science (MS), Washington State University
01/2022
DOI:
https://doi.org/10.7273/000004431
Handle:
https://hdl.handle.net/2376/125172
Abstract
Hydrothermal alteration is widespread in a series of Eocene intermediate dikes and sills known as the Scatter Creek Formation, which are hosted in Permian-Triassic sedimentary rocks across the Republic Graben, in northeastern Washington. Input of multiple magmas during regional extension resulted in a complex unit of variable texture and composition. These intrusions have been interpreted as conduits for hydrothermal ore mineralization via geochemical interaction with contact metamorphosed sediments. However, mineral exploration has not accounted for the widespread propylitic alteration often seen in conjunction with orebodies. As such, this study provides new analyses dedicated to the distribution of geochemical signatures and hydrothermal alteration minerals in the Scatter Creek Formation, with a broader goal of linking surface observations to a possible source as a case study for future exploration.
Hand sample and thin section observations, along with electron microprobe, whole rock major and trace element, and X-ray diffraction analyses suggest that the Scatter Creek Formation geochemically links intrusive and extrusive equivalent rocks. However, hydrothermal alteration has resulted in feldspar albitization and mafic minerals reacting to magnetite-epidote-calcite-chlorite-pyrite; vesuvianite, barite, and zeolites are sometimes present. Chloritization is widespread and varies in iron content. Coarse quartz is mainly an alteration phase. Unreacted igneous minerals include rutile, zircon, sphene, pyroxene, and magnetite-ilmenite with occasional inclusions of Pb- Ni- sulfides; REE’s were also detected. Alteration had little effect on non-alkalic oxide and trace element concentrations, but elevated concentrations of As and Sb possibly relate to Au mineralization. Stable oxygen and carbon isotope ratios do not show strict connections to hydrothermal alteration progress but do relate to proximity with nearby replacement ore bodies. Continued circulation of an evolving fluid during propylitic alteration is indicated by the relation of low to high isotopic ratios with achieved reaction progress.
These observations are consistent with a distal propylitic alteration shell resulting from interactions of magmatic and meteoric water surrounding a magma body, which served as a heat source to drive the hydrothermal system. As such, widespread propylitic alteration in the Scatter Creek Formation, in association with Au-mineralization, suggests that a porphyry-type deposit may lie at depth in a hidden parent intrusion.
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Details
- Title
- GEOCHEMICAL CHARACTERIZATION OF HYDROTHERMAL ALTERATION IN THE EOCENE SCATTER CREEK FORMATION, REPUBLIC, WASHINGTON
- Creators
- Jonathan Stanfield
- Contributors
- Peter B Larson (Advisor)Kurtis M Wilkie (Committee Member)Sean P Long (Committee Member)
- Awarding Institution
- Washington State University
- Academic Unit
- Environment, School of the (CAHNRS)
- Theses and Dissertations
- Master of Science (MS), Washington State University
- Publisher
- Washington State University
- Number of pages
- 311
- Identifiers
- OCLC#: 1370910367; 99900883240401842
- Language
- English
- Resource Type
- Thesis