The Apollo-Sitka Mine was the site of Alaska's first underground gold mine which from 1886-1922 produced a historically reported total of approximately 150,000 gold ounces at a historically reported grade of approximately 10 g/t gold.
The 8km Trend stretches from the Heather prospect on the south coast of Unga Island through the closed Apollo and Sitka mines in the NE and to showings beyond. The structure is a NE striking fault with an average strike of 075 and a dip of 70° SSE that separates porphyritic from aphanitic andesite flows.
(NOTE: Redstar Gold Corp observes that a qualified person has not done sufficient work to classify historical estimates as current mineral resources or mineral reserves and Redstar is not treating the historical estimates as current mineral resources or mineral reserves).
The Apollo mine was in production during 1892-1904 and 1908-1913, with two tunnels 350m and 975m long plus two shafts 140m and 240m deep, producing an estimated 240kt of ore at a grade of 0.4 oz/ton (12.5 g/t; Berg and Cobb, 1967, USGS Survey Bulletin 1246). Most of the mined ore was free milling at shallow depths, whereas Au in deeper ore is associated with sulfides. A 1935 report referenced by Brown (1947, Alaska Territorial Department of Mines Report MR 138-1) suggested that there were four ore shoots 120-240m long, along 1500m strike to a depth of 400m. Most of the ore mined came from two shoots the largest of which was up to 5m wide and extended down dip for 150m, with a plunge of 60° to 70°NE (Wilson et al., 1996, USGS Miscellaneous Field Studies Map MF- 2155-F).
In 1983, Alaska-Apollo Gold Mines compiled the results of underground sampling from the 1920s and conducted trenching and drilled nine holes totaling 2900m. They suggested a resource of 748kt at a grade of 23g/t Au, with 3:1 Ag:Au ratio (http://mrdata.usgs.gov/ardf/show-ardf.php?ardf_num=PM079).
Most of this would have been in the shallow oxide zone, as the deeper sulfide zone is base metal rich (reportedly galena, sphalerite, chalcopyrite and tetrahedrite, with vein intersections containing up to 25% Pb+Zn; Pilcher, 1983), higher Ag:Au than in the overlying oxide zone, and relatively low Au values.
Strandberg (1993) showed a longitudinal section of the Apollo workings which indicated that below sea level they had blocked out 400 short tons of “ore” with combined Au+Ag values of 0.12 opt Au, with 12 – 15% combined Pb-Zn sulfides.
The Sitka gold vein system is the most northeastern part of the Apollo – Sitka Trend that has been exploited to date. The east-west shaft zone comprises a steeply south dipping open stope for about 70m that extends underground following remnants of a sulfidic-banded vein in coarse, cockscomb quartz with adularia in vugs. Mineralization consists of epithermal gold, silver, lead, zinc, and copper and was mined between the 1880s and 1922. Workings at Sitka included underground development to 76m below surface on three levels ending in primary/sulphidic mineralization.
Descriptions of the Sitka mineralization are variable but Redstar has reported an east-northeast trending quartz vein/stockwork zone containing pyrite, galena, sphalerite, and lesser quantities of chalcopyrite hosted in andesite.
Lithology and alteration
Typically district scale propylitic alteration is overprinted by quartz-sericite-pyrite around central veins in an andesite host. Argillic alteration is restricted to faults zones and is likely supergene. Adularia is found in two veins and float. Approximately 10% of the veins have iron oxide staining in vugs and on surfaces which appear to have contained sulfide minerals.
There are four north-south trenches on the south side of the shaft that expose an extensive sphalerite, galena and chalcopyrite bearing, quartz vein/ stockwork zone that dips consistently south, extending 50m south of the shaft and striking northeast.
The bulk of the mineralization visible in the trenching is complex quartz veining and silicification with hydrothermally brecciated veins and wall rock varying from 20-60m in width. Most veins are fracture and fill with rare local replacement veins. Breccias contain both vein and wall rock fragments and are both clast and matrix supported. The matrix is most commonly massive white quartz with some crustiform, open-space filling quartz crystals in concentric bands around clasts.
An earlier description by Van Wyck et. al. (2005) stated that mineralization at the Sitka mine is located at the intersection of northeast- and northwest-striking quartz-sulfide veins and:
“The Sitka deposit is composed of west-northwest trending auriferous quartz–sulfide veins in propylitically altered Tertiary andesite units which cut across the dominant N 40° E Apollo Trend. The west-northwest trending vein/shear zone dips steeply south while the northeast trending veins dip 40° to 50° to the east. The open stope trending away from the shaft reflects a more east-west orientation. In the first trench to the north of the shaft, the dominant N. 40° E. vein trend is cut by a series of N 30° W trending quartz sulfide veins with visible galena, sphalerite, pyrite and rare chalcopyrite. Vein material exposed in the vicinity of the old shaft and on dumps indicates comb quartz with fine and medium-grained galena, sphalerite, pyrite and rare chalcopyrite at the base of the quartz. From the Sitka to the northeast, veins in the Apollo Trend horsetail or splay into individual veins rather than continue in one dominant structure. The west-northwest Sitka shear post-dates the Apollo trend and may have been down-dropped relative to the volcanic units to the northeast”.
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