Tolovana Mine, Fairbanks Mining District, Fairbanks North Star Borough, Alaska, USAi

Regional Level Types
Tolovana Mine	Mine
Fairbanks Mining District	Mining District
Fairbanks North Star Borough	Borough
Alaska	State
USA	Country

Location: Cobb (1972, MF-413), loc. 38; NW1/4NE1/4 sec. 25, T. 3 N., R. 1 E., of the Fairbanks Meridian. The Tolovana mine is about 25 feet above Willow Creek at an elevation of 1,300 feet. It is approximately 1/8 of a mile upstream from the confluence of Willow Creek and Cleary Creek.
Geology: The Tolovana Mine is an old property that was first discovered before 1910. It operated intermittently until at least 1949, and was the site of considerable work in the 1980's. Three different metamorphic rock types are visible at the Tolovana prospect (LeLacheur, 1991). The dominant rock unit is a micaceous quartzite. A layer of crenulated biotite-schist and a thin layer of amphibole-biotite schist are enclosed between the quartzite layers. Strongly altered plutonic rock is exposed in several trenches at the south end of the property (LeLacheur, 1991). The dominant process of ore deposition seems to have been replacement of the country rock and fault products by quartz, sericite and sulfides, rather than vein quartz deposition (LeLacheur, 1991, p. 50). Mineralization occurs within fault gouge zones cutting through micaceous quartzite. Initial development began on a series of 1- to 3-inch quartz veinlets which trend N 75 E. These stringers contained visible gold and in one case a barren quartz-albite stringer was found suggesting an igneous affinity (Prindle, 1910). Ore in the Tolovana mine varies from ribbon texture quartz stringers to massive quartz zones which vary from a few inches to 3 feet in width. The mineralization had been traced for over 1,500 feet along strike. The Tolovana shear zone strikes east-west and dips 60 S (Smith, 1913; B 525). The 1- to 3-inch quartz stringers are separated by calcareous schist containing disseminated pyrite. The gold-bearing quartz stringers contain euhedral stibnite but do not normally contain pyrite (Smith, 1913; B 525). The gold fineness analyses, conducted through 1912, varied from 792 to 824 fine, with the highest silver content being 180 parts per thousand from the sample with a gold fineness of 792 (Smith, 1913; B 525). Several phases of quartz introduction were noted at the Tolovana prospect with gold being most common in a glassy variety which post-dates the more abundant milky white quartz (Smith, 1913; B 525). A new shear zone was discovered on the Tolovana mine prospect in mid-1913 (Chapin, 1914). The occurrence is 100 feet south of the portal of the adit; it strikes east-west and dips 50 S. The shear is 18 inches to 36 inches wide and consists of massive white quartz with gouge on each contact. This shear is parallel to the shear exposed in the Tolovana adit. Shaft sinking was in progress in 1913. This shaft, referred to here as the South shaft, was later connected to the Tolovana adit by a cross-cut. The western extension of the Tolovana shear was discovered in 1930 and was developed by the 160-foot Parenteau adit. The Tolovana shear strikes N 30-65 E and dips 30-60 SE. The mineralization is in 1- to 12-inch wide stringer zones similar to that mined from the Tolovana adit. The ore contained gold associated with arsenopyrite, stibnite, pyrite, galena and tetrahedrite (Stewart, 1933; Pilgrim, 1933). The prospect was sampled by Fairbanks Exploration Inc. in 1986 (Fairbanks Exploration Inc., unpublished report, 1986). Backhoe and dozer trenches on the Tolovana prospect exposed a large section of metarhyolite tuff, exhalite and volcaniclastic metaquartzite of the upper Cleary Sequence. These rocks contain disseminated and shear-zone-controlled arsenopyrite, pyrite, stibnite and native gold. The structures which hosted the high grade gold-quartz shear zones in the old Tolovana mine trend predominantly N 60-80 E and dip steeply southeast; they transect the flat-lying, northeast-trending Cleary Sequence. Samples collected in the Upper Pit area were chip samples across exposures of sulfide-bearing metarhyolite tuff units cut by numerous 1-6 inch thick white quartz veins. Gold values from these samples were 520 to 3600 ppb. Samples from high-grade dump material at the small mill set up near the old Tolovana shaft ranged from 0.27 to 0.52 ounces of gold per ton. The samples consisted of white, massive, quartz vein material with 1-3% arsenopyrite and minor stibnite. Country rock welded to the shear zone selvages was metarhyolite similar to that seen in the upper pit area. As a check on the efficiency of the old gravity milling circuit used in the Tolovana mill, a sample was collected from the tailings pond below the mill. This sample consisted of coarse sand-size material (20-30 mesh); it contained mainly quartz, arsenopyrite, pyrite and stibnite. The sample assayed 0.458 ounces of gold per ton, suggesting that the mill did a poor job of recovery of the fine gold in the ore (Fairbanks Exploration Inc., unpublished report, 1986). In 1988 and 1989, Yukon Tanana Mining conducted extensive surface trenching on the Tolovana and adjoining Chechako prospects and outlined an estimated 150,000 ounces of gold that could be mined from the surface pit (R. Blakestad, oral commun., 1991).
Workings: By 1910, an 85 foot adit had been driven. In July, 1911 a Huntington disc mill was installed and began operation on the prospect. The mill ran continuously through mid-November when lack of water forced it to close. The mill began operating again in March, 1912 after a well and pump had been installed on Willow Creek (Times Publishing Company, 1912). In July, 1912 a two stamp Nissen mill was erected and began crushing ore on August 23, 1912. In 1912, the mine consisted of a 400 foot adit from which several short drifts were driven; small stopes were also developed (Smith, 1913; B 525). The adit extends along the main shear zone for 130 feet where it intersects a vertical fault. The workings turn north for 30 feet and then turn east again along the offset extension of the shear zone. Approximately 100 feet from the portal of the adit, a winze was sunk to a depth of 50 feet and drifts driven to the east and west. A second winze inclined at 60 degrees south was driven from the east end of the drift but was flooded in 1912. A second winze, located 330 feet from the portal, was sunk from the adit level to a depth of 100 feet (Loftus, 1927). A shaft near the adit portal had been sunk to a depth of 100 feet and a drift driven on the 50-foot level connects with the winze in the adit. Due to flooding of the shaft near the Tolovana adit in late 1912, work was shifted to the Willow Creek-Bedrock Creek divide where a 55 foot shaft, referred to here as the Scheuyemere #1 shaft, was sunk on a 12- to 14-inch-thick shear zone (Times Publishing Company, 1912). This shaft is sometimes referred to as the Tolovana Stibnite prospect (Chapin, 1914). By 1913, the shaft and the winze had been connected by a drift on the 100-foot level and the ore between the adit and the 100 foot level was mined (Chapin, 1914). Additional stoping took place above the adit level. The Scheuyemere #1 shaft had been sunk to a depth of 100 feet by 1913 and drifting had been conducted for 50 feet to the east and 30 feet to the west on the 50-foot level (Chapin, 1914). A raise located 24 feet west of the shaft connected with the surface and the block of ground between the shaft and the raise had been stoped from the 50 foot level to the surface. In 1913, a new shear zone was discovered and shaft sinking was in progress (Chapin, 1914). This shaft, referred to here as the South shaft, would be connected to the Tolovana adit by a cross-cut drift. In 1922, the Tolovana adit was 530 feet long. A drift had also been driven from the 50 foot level of the winze for 30 feet to the east where it intersected a fault which offsets the shear zone 30 feet to the north (Stewart, 1922; Davis, 1922). In the South shaft, drifting at the 50-foot level went out 15 feet to the west and 20 feet to the east along the shear zone. A total of 150 feet of new drifting was completed on the Tolovana prospect in 1923 and 8 to 10 tons of ore milled on site (Stewart, 1923). The Tolovana mine remained inactive until 1930 when exploration was renewed (Smith, 1933; B 836). The western extension of the Tolovana shear, on the west side of Willow Creek, was discovered in 1930 and was referred to as the Parenteau adit (Stewart, 1931). This adit had been driven 160 feet to the west and 50 tons of ore had been treated in the mill in 1930. The Parenteau adit had caved about 75 feet from the portal when visited in 1931 (Hill, 1933). Antimony and gold were mined from the prospect in 1949 (Saarela, 1950). In August 1984, dozer and backhoe exploration of the prospect was conducted. A small gravity mill was constructed on the prospect near the old portal of the Tolovana adit and several large open cuts were excavated in the vicinity of the Scheuyemere #1 shaft (Freeman, 1992). Surface samples of the Upper pit area and the dump were also collected in 1986 (Fairbanks Exploration Inc., unpublished report, 1986).
Alteration: Pods and disseminations of jamesonite occur in an amorphous, green vuggy matrix in the walls surrounding the gouge zone (LeLacheur, 1991). Quartz, sericite, ankerite and carbon alteration also present.
Production: Ore was shipped from the prospect as early as 1909 (Times Publshing Company, 1912). Production through 1912 averaged $20 to $105 per ton (1 to 5 ounces per ton gold) (Smith, 1913; B 525). In 1923, 8 to 10 tons of ore were milled on site, averaging $16 gold per ton (0.8 ounces of gold per ton) (Stewart, 1923). A small amount of ore was milled in 1924 and in 1931(Stewart, 1923; Pilgrim, 1932; Smith, 1933, B 844). Antimony and gold were mined in 1949 (Saarela, 1950).
Reserves: In 1988 and 1989 Yukon Tanana Mining conducted extensive surface trenching on the Tolovana and adjoining Chechako prospects and outlined a reserve of about 150,000 ounces of gold that could be mined from a surface pit (R. Blakestad, oral commun., 1991).

Commodities (Major) - Au; (Minor) - Ag, Sb, W
Development Status: Yes; small
Deposit Model: Disseminated veins and shear zones containing gold in intrusive rocks and schist

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Link to USGS - Alaska:	LG110

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