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GIS-Based Identification of Areas that have Resource Potential for Sediment-hosted Pb-Zn deposits in Alaska

Open-File Report 2020-1147
By: , , , and 
https://doi.org/10.3133/ofr20201147

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Abstract

A state-wide Geographic Information System analysis was conducted to assess prospectivity for lead (Pb) and zinc (Zn) in sediment-hosted deposits in Alaska. The datasets that were utilized include publicly available geospatial datasets of lithologic, geochemical, and mineral occurrence data. Key characteristics of Pb-Zn deposits were identified in available datasets and scored with respect to relative importance. To evaluate resource potential, drainage basins of the smallest size were chosen, each of which covers approximately 100 square kilometers (km2). Drainage basins are the most logical and efficient unit for evaluation because the most regionally robust dataset comes from stream sediment geochemistry.

Sediment-hosted Pb-Zn deposits in Alaska include those contained in carbonate rocks (similar to Mississippi Valley Type or MVT deposits) and those contained in clastic-dominated (CD) sequences (CD Pb-Zn), historically referred to as SEDEX (sedimentary exhalative). The latter include the deposits currently being mined in the Red Dog district in the western Brooks Range. Host rocks for the two subtypes are distinct: carbonate versus fine-grained clastic rocks for CD Pb-Zn deposits. However, there are exceptions: some CD Pb-Zn deposits are hosted in carbonate layers within a thick clastic-dominated rock sequence. The statewide geologic map database contains units that commonly include mixed carbonate-clastic sequences that cannot be subdivided. The most significant difference between the two deposit types is their respective depositional environments and tectonic settings, but at the reconnaissance level of mapping in most areas of the state, these distinctions are not possible. Furthermore, nearly all critical geochemical parameters (silver [Ag], barium [Ba], Pb, Zn) are common to both types, and therefore it was not possible to do separate assessments for carbonate-hosted and CD Pb-Zn deposits.

Areas identified that have moderate to high potential for sediment-hosted Pb-Zn deposits include the (1) western and central Brooks Range, referred to in this report as the Brooks Range zinc belt; (2) Seward Peninsula (and adjacent St. Lawrence Island); (3) Farewell terrane in Interior Alaska; (4) two spatially distinct belts in east-central Alaska; and (5) the central Alaska Range. All areas contain some known deposits, and that provides credibility to the scoring process. Some hydrologic unit codes (HUCs) that have high potential for sediment-hosted Pb-Zn deposits are located adjacent to areas of known deposits and indicate the potential for expansion of known Pb-Zn districts. There are a few areas that have high potential but contain no known sediment hosted Pb-Zn occurrences, prospects, or deposits. In such areas, future investigations could be focused on better defining and constraining prospectivity with additional data.

Suggested Citation

Kelley, K.D., Graham, G.E., Labay, K.A., and Shew, N.B., 2021, GIS-based identification of areas that have resource potential for sediment-hosted Pb-Zn deposits in Alaska: U.S. Geological Survey Open-File Report 2020−1147, 37 p., 1 app., 2 pls., scale 1:10,500,000, https://doi.org/10.3133/ofr20201147.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Purpose and Scope
  • Sediment-hosted Pb-Zn Deposit Definitions
  • Analytical Process and Data Sources
  • GIS-Based Methods
  • Mineral Resource Potential Estimation Method
  • Results and Discussion
  • Summary and Conclusions
  • References Cited
  • Appendix 1. Boxplots of select elements in rock samples from areas with high potential
Publication type Report
Publication Subtype USGS Numbered Series
Title GIS-based identification of areas that have resource potential for sediment-hosted Pb-Zn deposits in Alaska
Series title Open-File Report
Series number 2020-1147
DOI 10.3133/ofr20201147
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston VA
Contributing office(s) Alaska Science Center Geology Minerals, Central Mineral and Environmental Resources Science Center, Geology, Geophysics, and Geochemistry Science Center
Description Report: v, 37 p.; 2 Plates: 15.41 x 15.11 inches and 15.53 x 15.17 inches; Data Release
Country United States
State Alaska
Online Only (Y/N) Y
Google Analytic Metrics Metrics page
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