Bonanza Creek (lode)

Prospect, Active?

Commodities and mineralogy

Main commodities Au
Ore minerals arsenopyrite; gold; pyrite
Gangue minerals ankerite; calcite; dolomite; mariposite; quartz

Geographic location

Quadrangle map, 1:250,000-scale EA
Quadrangle map, 1:63,360-scale D-3
Latitude 64.9789
Longitude -142.3816
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Bonanza Creek prospect covers about one-third of a square mile near the midpoint of Bonanza Creek, mainly on the east side of the creek. Bonanza Creek is a small south tributary of the Seventymile River. The coordinates are the approximate center of the prospect, at the southeast corner of section 23, T. 2 N., R. 26 E., of the Fairbanks Meridian; this location is accurate within 500 feet. Bonanza Creek is locality 3 of Cobb (1972 [MF-393]) and locality 5 of Eberlein and others (1977). The Bonanza Creek prospect is located within Doyon, Ltd. selected or conveyed land.

Geologic setting

Geologic description

The Bonanza Creek prospect is one of a northwest-trending set of ophiolite-hosted gold prospects informally referred to as the Flume trend. Other lode gold prospects within the Flume trend include Flume Creek (EA009), Alder Creek (EA013), and Flanders (EA015). One-half mile to the south, and subparallel to the Flume trend, the Deep Creek trend of volcanic-hosted lode gold prospects includes the Deep Creek (EA017) and Kill Zone 2 (EA016) prospects and the Jay Creek and Kill Zone 3 gold anomalies that are defined by soil sampling.
The Flume trend prospects are in weakly metamorphosed ultramafic, mafic, and oceanic sedimentary rocks of the Seventymile terrane (Foster and others, 1985). Rocks of the Seventymile terrane are deformed and cut by internal thrust faults. These rocks are bordered by Paleozoic metamorphic rocks to the north and south along northwest-trending strands of the Tintina strike-slip fault. Bimodal Tertiary(?) dikes, including porphyritic rhyolite and diorite-gabbro, intrude all older rocks.
At the Bonanza Creek prospect, stockwork veining and widespread gold mineralization occurs in multiple zones associated with extensive silica-carbonate alteration (WGM Inc., 1998 [DLR 98-19]). The prospect consists of fault-controlled stockwork veining spatially associated with the steeply dipping contact between strongly altered serpentinite to the north and strongly altered volcaniclastic rocks and tuffaceous rocks to the south. The hanging wall consists of interlayered, folded, crystal lithic tuff and volcaniclastic rocks; the footwall consists of serpentinite, gabbro, crystal lithic tuff, and volcaniclastic rocks. Mineralized zones occur above and below the fault in several sub-parallel, tabular zones. The deposit is cut by a late high-angle fault.
Three types of mineralization have been distinguished by WGM Inc. (1998 [DLR 98-19]): (1) sulfide-poor, visible gold-bearing, quartz stockwork veins cutting dolomite-altered serpentinite and gabbro; (2) sulfide-bearing silica-ankerite alteration in tuffs and tuffaceous siltstone cut by arsenopyrite-quartz stockwork veins; and (3) quartz veins in argillite, locally with pyrite, with little apparent alteration. Hydrothermal white mica from wall rocks adjacent to a gold-bearing quartz-arsenopyrite vein at the nearby Flume Creek prospect (EA009) gives a 40Ar/39Ar plateau age of 100 +/- 3 Ma, interpreted to estimate the age of the gold mineralization (Newberry and others, 1996). Geologic similarities between the two prospects suggest the Bonanza Creek gold mineralizing event is of the same age.
The prospects along the Flume trend form a semicontinuous 4-mile-long soil anomaly with greater than 10 ppb gold and elevated arsenic. At the Bonanza prospect, the soil anomaly in gold is about 3,000 feet long and 1,000 feet wide, and values reach 470 ppb gold (WGM Inc., 1998 [DLR 98-19]). Adjacent gold anomalies extend an additional 1,200 feet east and 3,000 feet west. Samples from trenches include 20 feet with 0.192 ounce of gold per ton. An interval 200 feet long and 7.8 feet thick averaged 0.17 ounce of gold per ton. Intercepts from seven drillholes include 7.5 feet with 0.32 ounce of gold per ton, 27 feet with 0.055 ounce of gold per ton, and 10 feet with 0.08 ounce of gold per ton. The highest grade reported is in a narrow quartz vein with 3.36 ounces of gold per ton. A 143-foot-thick zone in hole FC90-4 averages 0.038 ounce of gold per ton. Drilling has been confined to about 1,200 feet of the strike of the soil anomaly, only 12 percent of the total length. WGM Inc. concluded that there is the potential for a bulk tonnage deposit with 0.07 to 0.12 ounce of gold per ton (WGM Inc., 1998 [DLR 98-19]).
The Bonanza Creek prospect was discovered during reconnaissance mapping by the U.S. Geological Survey in 1967 (Clark and Foster, 1971). A channel sample 5 feet long of silica-carbonate rock contained 11 ppm gold, and a channel sample across the contact zone contained 7 ppm gold.
Reconnaissance exploration by WGM Inc. in the mid-1970s located several gold targets in the Seventymile region (WGM Inc., 1998 [DLR 98-19]). In 1989 and 1990, Central Alaska Gold Co. explored the Flume Creek (EA009) and Deep Creek (EA017) areas. In 1996, WGM Inc. expanded soil grids at the Flanders (EA015) and Deep Creek (EA017) prospects, conducted ridgetop sampling along a 13-mile-long segment between the Crooked Creek trend and Flume and Deep Creek trends, and had an airborne geophysical survey flown over the Flume, Deep Creek, and Crooked Creek trends.
Geologic map unit (-142.383940382965, 64.978574373712)
Mineral deposit model Listwaenite (altered ophiolite) gold (Newberry and others, 1998).
Age of mineralization Hydrothermal white mica from wall rocks adjacent to a gold-bearing quartz-arsenopyrite vein at the nearby Flume Creek (EA009) prospect gives a 40Ar/39Ar plateau age of 100 +/- 3 Ma, interpreted to estimate the age of gold mineralization (Newberry and others, 1996). Geologic similarities suggest the Bonanza Creek gold mineralizing event may be of the same age.
Alteration of deposit
At the Bonanza Creek prospect, stockwork veining and widespread gold mineralization occur in multiple zones associated with extensive silica-carbonate alteration (WGM Inc., 1998 [DLR 98-19]).
Quartz-carbonate-mariposite alteration accompanies the gold mineralization here, and this alteration is a favorable indicator of gold at other prospects along the Flume trend (WGM Inc., 1998 [DLR 98-19]). Greenstone, diorite, gabbro, and serpentinite next to the veins and in the stockwork zone are intensely altered to an assemblage of quartz, dolomite, ankerite, mariposite, arsenopyrite, and pyrite.

Production and reserves

Workings or exploration
The Bonanza Creek prospect was discovered during reconnaissance mapping by the U.S. Geological Survey in 1967 (Clark and Foster, 1971). A channel sample 5 feet long of silica-carbonate rock contained 11 ppm gold, and a channel sample across the contact zone contained 7 ppm gold.
Reconnaissance exploration by WGM Inc. in the mid-1970s located several gold targets in the Seventymile region (WGM Inc., 1998 [DLR 98-19]). In 1989 and 1990, Central Alaska Gold Co. explored the Flume Creek (EA009) and Deep Creek (EA017) areas. In 1996, WGM Inc. expanded soil grids at the Flanders (EA015) and Deep Creek (EA017) prospects, conducted ridgetop sampling along a 13-mile-long segment between the Crooked Creek trend and Flume and Deep Creek trends, and had an airborne geophysical survey flown over the Flume, Deep Creek, and Crooked Creek trends.
Work by WGM Inc. and Central Alaska Gold Co. indicates the prospects along the Flume trend form a semicontinuous 4-mile-long soil anomaly with greater than 10 ppb gold and elevated arsenic. At the Bonanza prospect, the soil anomaly in gold is about 3,000 feet long and 1,000 feet wide; values reach 470 ppb gold (WGM Inc., 1998 [DLR 98-19]). Adjacent gold anomalies extend an additional 1,200 feet east and 3,000 feet west. Samples from trenches include 20 feet with 0.192 ounce of gold per ton. An interval 200 feet long and 7.8 feet thick averaged 0.17 ounce of gold per ton. Intercepts from 7 drillholes include 7.5 feet with 0.32 ounce of gold per ton, 27 feet with 0.055 ounce of gold per ton, and 10 feet with 0.08 ounce of gold per ton. The highest grade reported is in a narrow quartz vein with 3.36 ounces of gold per ton. A 143-foot-thick zone in hole FC90-4 averages 0.038 ounce of gold per ton. Drilling has been confined to about 1,200 feet of the strike of the soil anomaly, only 12 percent of the total length. WGM Inc. concluded that there is the potential for a bulk tonnage deposit with 0.07 to 0.12 ounce of gold per ton (WGM Inc., 1998 [DLR 98-19]).
Indication of production None
Reserve estimates WGM Inc. concluded that there is the potential for a bulk tonnage deposit with 0.07 to 0.12 ounce of gold per ton at Bonanza Creek (WGM Inc., 1998 [DLR 98-19]).

Additional comments

The Bonanza Creek prospect is located within Doyon, Ltd. selected or conveyed land. For more information contact Doyon, Ltd., Fairbanks, Alaska.

References

MRDS Number A015109

References

Foster, H.L., Cushing, G. W., Keith, T. E. C., and Laird, J., 1985, Early Mesozoic tectonic history of the Boundary area, east-central Alaska: Geophysical Research Letters, v. 12, p. 553-556.
Freeman, L.K. and Puchner, C.G., 1990, Geology of the Bonanza and Flume Creek gold occurrences, east-central Alaska--Report prepared for Central Alaska Gold Co.: Doyon, Ltd. Report 90-16 (Report held by Doyon, Ltd., Fairbanks, Alaska).
Rogers, Bob, and Bradley, Laura, 1998, Gold deposits of the Seventymile Belt: Extended Abstracts of the 16th Biennial Conference on Alaskan Mining, Second Rush of 98; Alaska Miners Association meeting March 2-7, 1998, Fairbanks, Alaska, p. 22.
WGM Inc., 1977, Doyon Project, 1976 annual progress report, volume 1a, Blocks 1, 4, 5, 7, 8: Doyon, Ltd. Report 77-02a. (Report held by Doyon, Ltd., Fairbanks, Alaska).
WGM Inc., 1998, Ventures Resource Alaska projects, 1997 progress report, Seventymile property exploration, volume 1: Doyon, Ltd. Report 98-19. (Report held by Doyon, Ltd., Fairbanks, Alaska).
WGM Inc., 2000, Seventymile property summary, in Ventures Resource Alaska project overview and properties summary: Ventures Resource Corporation report.
Reporters M.B. Werdon; R.L. Flynn
Last report date 5/1/2002