Geochemistry and Mineralogy of the Silver Pond Prospect in the Toodoggone District: Implications for Regional Exploration

Abstract

The Lawyers Property located in the Toodoggone district hosts a well-known extensively explored low sulfidation style epithermal deposit as well as an adjacent less understood target area known as Silver Pond that shares characteristics of a high sulfidation style system. The Silver Pond prospect is a large argillic alteration lithocap, with a high degree of leaching and texturally destructive clay alteration of the intermediate volcanic host rocks. This study characterizes the geochemical trends, key alteration assemblages, and paragenesis of the Silver Pond prospect. The argillic-advanced argillic clay alteration is extensive both at surface as well as in the subsurface. The results of combined spectral (Raman and SWIR) and petrographic analysis identified a characteristic high sulfidation epithermal zonation pattern, as represented by an advanced argillic alteration zone with high temperature, low pH mineralogy (alunite, dickite, kaolinite, pyrophyllite) in structural contact with a large argillic alteration envelope (smectite, illite, ± kaolinite). Geochemical analyses indicated complimentary trends that are associated with alteration type and intensity. Intense alteration focused along major fault surfaces indicate that known regional scale structures controlled fluid flow. Abrupt changes in alteration assemblages and geochemistry at structural contacts indicate that Silver Pond likely underwent displacement that postdates alteration. While advanced argillic alteration is relatively extensive, highly porous silicified rock is scarce at Silver Pond and typically associated with faulting. Therefore, either the silica cap has been removed by erosion or Silver Pond represents the proximal shoulders to a silica cap that has been structurally displaced. Structural displacement and subsequent burial has led to preservation of different levels of erosion within Silver Pond. As shown by the mining history in the region, this structural dismemberment of mineralized systems makes the Toodoggone district prospective for diverse hydrothermal deposit types including epithermal and porphyry systems.