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GIS-Based Identification of Areas that have Resource Potential for Lode Gold in Alaska

Open-File Report 2021-1041
Prepared in cooperation with the Alaska Division of Geological & Geophysical Surveys and the Bureau of Land Management
By: , , , , , , , and 
https://doi.org/10.3133/ofr20211041

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Abstract

Several comprehensive, data-driven geographic information system (GIS) analyses were conducted to assess prospectivity for lode gold in Alaska. These analyses use available geospatial datasets of lithologic, geochemical, mineral occurrence, and geophysical data to build models for recognizing different types of gold deposits within physiographic units defined by stream drainage basins that are approximately 100 square kilometers in area. The analytical methods successfully delineated areas in the State that contain known lode gold deposits and occurrences, providing some measure of confidence in their ability to predict gold prospectivity in areas of unknown lode gold potential. The results of our analyses indicate high prospectivity in a few areas scattered around the State that are not known to contain lode gold deposits.

In addition to assessing the potential for lode gold deposits in Alaska, we designed analyses to distinguish different lode gold deposit types, including orogenic, reduced-intrusion-related, epithermal, and gold-bearing porphyry. These can primarily be differentiated using their unique trace element geochemical fingerprints and elemental enrichments, which reflect the characteristics of the geologic environment and chemistry of the ore-forming fluids. We identified multiple parameters that would discriminate the different types of gold deposits, but owing to the limits of available data, the compositional similarity of ore-forming fluids among some types of lode gold deposits, and overlapping geologic environments, distinguishing deposit types at the state scale in Alaska remains problematic. These limitations resulted in overlapping areas of prospectivity for different deposit types, highlighting the challenges for targeted gold exploration in Alaska. Adjustment of some scoring parameters and recharacterization at smaller scales to highlight individual mineral systems for application of prospectivity analyses may be helpful at a district scale. At a regional scale, the aerial overlap of individual deposit type analyses reinforces confidence in prospectivity for a lode gold resource in a drainage basin. Our analysis for undivided lode gold deposits will be the most practical analysis for landuse decisions in which delineation of areas that have confident potential for gold deposits in general is the primary goal.

Data-driven GIS analysis for lode gold potential in Alaska, although limited by the size and uneven coverage of available datasets, objectively indicates prospectivity in areas where exposure is good as well as in areas under cover. The results of our analyses show medium to high prospectivity in areas that surround known deposits, indicating an overall expansion of areas that have the potential to contain gold deposits. Exploration in these areas may help improve the balance between the volume of gold produced in placer districts statewide and the relatively low volume of identified lode resources that contribute to these placer deposits. The results of our analyses can help focus future investigations in areas that show prospectivity but are not known to contain gold deposits, as well as in areas where data are lacking and the geology is poorly understood, and acquisition of additional data may help better define and constrain gold prospectivity.

Suggested Citation

Karl, S.M., Kreiner, D.C., Case, G.N.D., Labay, K.A., Shew, N.B., Granitto, M., Wang, B., and Anderson, E.D., 2021, GIS-based identification of areas that have resource potential for lode gold in Alaska (ver. 1.1, October 2021): U.S. Geological Survey Open-File Report 2021–1041, 75 p., 9 plates, https://doi.org/10.3133/ofr20211041.

ISSN: 2331-1258 (online)

Study Area

Table of Contents

  • Acknowledgments  
  • Abstract  
  • Introduction  
  • Data Types and Analytical Process  
  • GIS-Based Methods  
  • Chapter 1. Lode Gold Deposits—Undivided  
  • Chapter 2. Orogenic Gold Deposits  
  • Chapter 3. Reduced Intrusion-related Gold Deposits  
  • Chapter 4. Epithermal Gold Deposits  
  • Chapter 5. Discussion of Discrimination of Lode Gold Deposit Types  
  • Chapter 6. Gold-bearing Porphyry and Epithermal Gold Deposits  
  • Chapter 7. Reduced Intrusion-Related  
  • Chapter 8. Discussion of Discrimination of Lode Gold Deposit Types Using Model Combinations  
  • Summary and Conclusions  
  • Data Resources  
  • References Cited  
  • Appendix 1. Statistical Calculations of Levels of Background Values for Sediment and Rock  
  • Appendix 2. Lithology-Keyword Search Terms for the "Geologic Map of Alaska"
Publication type Report
Publication Subtype USGS Numbered Series
Title GIS-based identification of areas that have resource potential for lode gold in Alaska
Series title Open-File Report
Series number 2021-1041
DOI 10.3133/ofr20211041
Edition Version 1.0: Jun 2021; Version 1.1: October 2021
Year Published 2021
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) Alaska Science Center, Central Mineral and Environmental Resources Science Center, Geology, Geophysics, and Geochemistry Science Center
Description Report: x, 75 p.; 9 Plates: 11.00 x 17.00 inches or smaller; Data Release; 3 Appendixes
Country United States
State Alaska
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
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