Geology and timing of Zn-Pb-Ag mineralization, northern Brooks Range, Alaska
Title:
Geology and timing of Zn-Pb-Ag mineralization, northern Brooks Range, Alaska
JLCTITLE245:
by Melanie Beth Werdon.
Personal Author:
Publication Information:
1999.
Physical Description:
130 leaves : illustrations, maps ; 28 cm
General Note:
"May 1999."
Includes abstracts for chapters 2, 3, and 4.
Dissertaton Note:
Ph. D. University of Alaska Fairbanks 1999
Abstract:
"The north-central and northwestern Brooks Range of Alaska hosts widespread Carboniferous Zn-Pb-Ag ... [plus/minus] Ba shale-hosted massive sulfide (Sedex) deposits, and Zn-Pb-Ag ... [plus/minus] Cu vein-breccia and disseminated sulfide occurrences. The Sedex deposits are hosted by black carbonaceous shale and siliceous mudstone of the Mississippian to Pennsylvanian Kuna Formation and are spatially associated with minor (e.g. Red Dog) to locally abundant (e.g. Drenchwater) volcanic and hypabyssal intrusive rocks. The vein-breccia and disseminated sulfide occurrences show no obvious igneous association and are hosted by a deformed but only weakly metamorphosed package of Upper Devonian to Lower Mississippian mixed continental and marine clastic rocks (the Endicott Group). Textural, mineralogical, isotopic, chemical, and fluid inclusion data indicate that sulfides, quartz, and lesser carbonates in the Kady vein-breccia and disseminated sulfide prospect were deposited from slightly acidic, low salinity, carbon-destructive, relatively oxidized, low temperature (<250 C) hydrothermal fluids, under evolving chemical conditions (i.e. decreasing temperature and pressure, increasing pH, fo2, fs2). The lack of known Sedex mineralization in the north-central Brooks Range and the presence of sulfide mineralization within the Endicott Group suggests that Kady represents the hydrothermal fluid pathway below a failed or non-existent Sedex system. Trace element analysis of volcanic rocks and 40Ar/39Ar laser step-heating ages indicate the following geologic history for the north-central and northwestern Brooks Range: within-plate alkaline volcanic rocks at Red Dog and Drenchwater were emplaced from approximately 344 Ma to 336 Ma in a continental extensional environment. This presumably set up an elevated geothermal gradient, which heated basinal fluids. Sedex mineralization is estimated to have formed between 337 and 3̃14 Ma by basinal dewatering. 40Ar/39Ar ages of recrystalized white mica in Upper Devonian sandstone adjacent to large sulfide-bearing vein-breccia zones fall within the independently estimated time frame for Sedex mineralization. Tholeiitic gabbro magmatic activity occurred around 276 ... [plus/minus] Ma. The transition with time from within plate alkaline to tholeiitic magmatism suggests progressive episodic extension in a continental basin"--Leaf 3.
Bibliography Note:
Includes bibliographical references.
Additional Physical Form Available:
Online version available via The University of Alaska Fairbanks https://scholarworks.alaska.edu/handle/11122/9553
Contents:
Ch. 1. Introduction -- Ch. 2. Drenchwater, Alaska: Zn-Pb-Ag mineralization in a mixed black shale--volcanic environment -- Ch. 3. Geologic setting of Mississippian vein-breccias at the Kady Zn-Pb-Cu-Ag prospect: plumbing system for a failed Sedex deposit? -- Ch. 4. Dating the undateable using 40Ar/39/Ar laser step-heating: an application in the northern Brooks Range Zn-Pb-Ag district, Alaska -- Ch. 5. Conclusions -- Appendix A. Host rock and mineralization data for the Kady vein-breccia prospect -- Appendix B. List of publications related to this study.