Summary:
Gold and silver at the Bruner property occur within narrow quartz + adularia +/- pyrite veins and veinlets, along fractures, and in disseminations that are manifested as sheeted/stockwork zones, vein swarms, and rare 0.3-2 meter wide veins, hosted by high-silica rhyolite flow domes and encasing and surrounding volcaniclastic units that overlie a mostly unaltered andesite base. The mineralization style is classified as low-sulfidation epithermal (LSE) with occasionally highgrade gold+quartz+adularia veins occurring within broad zones of hydrothermal alteration containing low-grade gold and silver.
Three zones of gold-silver mineralization have been outlined by drilling: the Historic Resource Area, and the Paymaster zone, which are located on patented mining claims, and the Penelas Zone, including both the historic Penelas Mine and the relatively newly discovered Penelas East area, which is located entirely on unpatented mining claims. All three areas have seen limited mining activity and production in the past, largely by selective underground methods.
Outcrop in the Historic Resource Area is dominated by moderately (30-55°) north-dipping biotite-rich Tbl rocks with intruding rhyolite dikes (Tr1) and rare occurrences of rhyolite tuffisite dikes (Ttd) and mafic intrusive rocks (Tba).
Structural measurements from the Historic Resource Area show that veins, faults, and joints are consistently north-trending and steeply-dipping and display normal and dextral-normal slip (Dering, 2014). Surface and underground mapping highlight older northwest-trending faults that are offset by these north-trending structures. The weak surface expression of these structures suggests slip on the north-striking structures has been tens of meters or less.
Textural evidence suggests that acanthite was partially leached out of primary electrum + acanthite assemblages in the Historic Resource Area. Although gold is typically hosted within and adjacent to high-angle structures the morphology of a widespread halo of lower-grade goldbearing rock subparallel to the current topography is present in the Historic Resource Area. The Ag:Au ratio is highly variable throughout the Bruner property and pervasive oxidation of the host rocks in the Historic Resource Area is extensive, all indicating that supergene remobilization of silver ± gold likely occurred.
Underground mapping at the Paymaster Mine revealed moderately-dipping (50-75°) north- to northeast- trending structures, and a series of shallow- dipping (30-40°) listric faults.
At Paymaster the host rocks are similar to those in the Historic Resource Area, where mineralized zones are concentrated in fractured, silicified, and adularized biotite-rich Tbl rocks. Rocks mined from the Paymaster Vein in the historic Paymaster Mine are described as fragmented vein material, analogous to some ore material mined at July-Duluth in the Historic Resource Area. Mineralized rocks at Paymaster are located just above the Tbl/Ta contact and appear to be confined by the underlying Ta unit. Based on recent and historic drilling this contact appears to be shallow- dipping and moderately offset structurally, creating a relatively flat-lying mineralized zone compared to other areas of the Bruner property.
The Penelas Area hosts the Penelas Mine, which is historically the most productive mine in the Bruner district. The Penelas East Area is a newly discovered zone approximately 400 meters east of the historic Penelas Mine. The host rocks at Penelas East are similar to those found at the Penelas Mine.
Gold- and silver-bearing veins and veinlets in the Penelas Mine Area occur along a northstriking, moderately east-dipping fault in Trp rocks forming the Penelas Vein. The Penelas Vein is 1-2 meters wide and has a strike length of at least 500 meters. Historic workings followed this vein to at least 300 meters depth in the Penelas Mine. Mineralized intervals contain electrumand acanthite-bearing quartz + adularia (up to 50%) veinlets and veins with lesser illite, montmorillonite, amethyst quartz, and iron-rich micas. Mineralized structures display textures indicative of open-space filling and boiling including colloform banding, bladed quartz and adularia after calcite, and vugs. Some structures contain fault breccias with mineralized vein fragments similar to parts of the Historic Resource Area (e.g. the Crag Fissure). Importantly, gold- and silver-bearing veins are not commonly found away from the Penelas Vein in the Penelas Mine Area.
Mineralized zones in the Penelas East Area are hosted in Trp rocks similar to the Penelas Mine. At the Penelas Mine gold-bearing veins occur in a discrete vein zone (i.e. the Penelas Vein), though at Penelas East gold-bearing veins form stockwork zones of 1-10 mm quartz + adularia + iron oxide (± illite ± montmorillonite ± amethyst quartz ± iron- rich micas) veinlets. Iron oxide minerals include hematite, goethite, and limonite and are interpreted to have formed, in part, by oxidation of vein-hosted pyrite. In the Penelas East Area these stockwork vein intervals have been intersected at multiple levels in the stratigraphy, unlike at the Penelas Mine, along a series of steeply-dipping structures. The Penelas Mine and Penelas East Areas are cutoff to the south by a major northwest-trending down-to-the- northeast structure that continues to the south of the Historic Resource Area.