The Red Dog ore deposit district in the Brooks Range of northern Alaska is host to several high-grade, shale-hosted Zn + Pb deposits. Due to the complex history and deformation of these ore deposits, the geological and hydrological conditions at the time of formation are poorly understood. Using geological observations and fluid inclusion data as constraints, numerical heat and fluid flow simulations of the Anarraaq ore deposit environment and coupled reactive flow simulations of a section of the ore body were conducted to gain more insight into the conditions of ore body formation. Results suggest that the ore body and associated base metal zonation may have formed by the mixing of oxidized, saline, metal-bearing hydrothermal fluids (<200°C) with reducing, HS-rich pore fluids within radiolarite-rich host rocks. Sphalerite and galena concentrations and base metal sulfide distribution are primarily controlled by the nature of the pore fluids, i.e., the extent and duration of the HS- source. Forward modeling results also predict the distribution of pyrite and quartz in agreement with field observations and indicate a reaction front moving from the initial mixing interface into the radiolarite rocks. Heuristic mass calculations suggest that ore grades and base metal accumulation comparable to those found in the field (18% Zn, 5% Pb) are predicted to be reached after about 0.3 My for initial conditions (30 ppm Zn, 3 ppm Pb; 20% deposition efficiency).
Bibliographical noteFunding Information:
Acknowledgments This project was supported by the Mineral Resources Program of the USGS. We thank Julie Dumoulin and Chris Potter at the USGS for discussions about the stratigraphy and structure of the region and for help in constructing the Anarraaq cross section. Teck Comico geologists, including Adrian King, Jeff Clark, and Brigitte Dejou, provided geological and geochemical information that in part formed the foundation for the modeling. The senior author wishes to thank Lyudmyla Koziy for technical assistance.
Copyright 2008 Elsevier B.V., All rights reserved.
- Base metals
- Lead zinc deposit
- Reactive fluid flow modeling
- Red Dog district