Prospect, Active

Alternative names

Commodities and mineralogy

Geographic location

Quadrangle map, 1:250,000-scale LG
Quadrangle map, 1:63,360-scale A-1
Latitude 65.0617
Longitude -147.4466
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Dolphin intrusive body is an elongate northeast-trending stock, about 2,000 feet by 1,200 feet in plan view on the ridge between Willow Creek and Bedrock Creek. It is centered about 0.4 mile south of the junction of Bedrock and Cleary Creeks and about 0.5 mile northeast of the center of section 25, T. 3 N., R. 1 E., of the Fairbanks Meridian. The location is accurate within 1/4 mile. It is located within the Golden Summit Project area.

Geologic setting

Geologic description

Note: As of early 2012, this site and several others nearby were being explored as a single entity by Freegold Ventures Inc. (Freeman, 2008). Considerable mineralization has been discovered that indicates this prospect is part of a larger mineralized system that is described separately as ARDF site (LG207).
In 1995, Freegold discovered significant disseminated gold mineralization in granodiorite and tonalite of the Dolphin stock (Freeman and others, 1998). Soil sampling in 1995 and 1996 delineated a large northeast trending gold anomaly with gold values over 100 parts per billion (ppb). The anomaly coincides with the south contact of the Dolphin stock and is aligned with the Dolphin shear zone. The gold anomaly is also highly anomalous in silver, arsenic, lead, antimony and zinc. It is the southeast part of a broad gold-in-soil anomaly which extends from the west bank of Willow Creek to Bedrock Creek.
As recognized in early 2012 (Adams and Giroux, 2011, 2012), the Dolphin stock is roughly elliptical in plan view, trends northeast, and is about 2,000 feet long and up to 1,200 feet wide. At least five intrusive phases have been identified: 1) equigranular to weakly porphyritic, biotite granodiorite; 2) equigranular to weakly porphyritic, hornblende-biotite tonalite; 3) fine-grained biotite-granite porphyry; 4) fine-grained biotite rhyolite to rhyodacite porphyry, and 5) fine-grained mafic dikes. Drilling along the northern edge of the stock encountered calc-silicate skarn at a depth of 400 feet, suggesting that the north contact of the stock dips steeply north. The southern contact of the stock dips shallowly to the south. Drilling at the northeast end of the stock suggests that it branches into a dike swarm there and that the main stock may be faulted at depth. The deposit is open to the west toward Willow Creek, and is at least 1,000 feet deep, the bottom of the deepest hole. Three Ar40/Ar39 age determinations on sericite from the mineralization and from a shear zone vary from 88.3 to 90.1 Ma.
During 1995-96, Freegold completed 15,559 feet of reverse circulation drilling in 46 drill holes. In 1998, a single vertical core hole was drilled to a depth of 1,033 feet. Seven holes were drilled in 2004 and 26 more were drilled in 2011 when the Dolphin prospect was the center of exploration by Freegold in the Cleary area. Over the years, the prospect has also been covered by numerous geochemical and geophysical surveys and has been trenched and sampled as part of Freegold extensive work in the Cleary Hill area since 1991.
Adams and Giroux (2011, 2012) classify the Dolphin deposit as an intrusion- hosted sulfide-quartz stockwork. Four distinct assemblages of ore minerals have been identified that mark the transition from early, high temperature mineralization to late low-temperature mineralization: 1) high-temperature arsenopyrite, maldonite, gold, native bismuth, bismuthinite, pyrite, and pyrrhotite; 2) low-temperature arsenopyrite and marcasite; 3) chalcopyrite, sphalerite, and galena; and 4) tetrahedrite, and jamesonite. There are also zones with more than 50 percent sulfides that include galena, tetrahedrite, and sphalerite. Up to 2 percent disseminated scheelite is locally present. Electron microprobe analyses and polished section microscopy indicate that native gold and bismuthinite occur as inclusions in arsenopyrite. Visible gold is rare and is hosted in white, quartz stockwork veins. Preliminary metallic sieve analyses suggest little or no nugget effect (Adams, 1997). Bottle roll analyses from granodiorite from the oxide zone recovered 82 percent to 92 percent of the gold; less than 10 percent of the gold was recovered in the sulfide-rich altered granodiorite.
The gold content of the Dolphin prospect is chiefly in quartz veinlets, typically less than 1 mm wide, that cut the stock (Freeman, 2008; Adams and Giroux, 2011, 2012). Vein orientations vary with no apparent preferred orientation. At least three separate hydrothermal events can be identified in the Dolphin core as seen in multiple, flooded zones of alternating silicification and sericitization, local scheelite-bearing carbonate zones, and sulfide-rich zones containing elevated base metals. Scheelite-bearing carbonate-alteration zones generally contain lower gold values and tend to form halos around the higher-grade gold mineralization. Silica flooding occurs throughout the intrusive and the rocks locally may contain up to 90 percent silica. The silica-flooded zones often contain chalcedonic green, brown, or black quartz. In some drill holes the silicification of the granodiorite almost completely obliterates the original igneous textures. Chloritic alteration is rare.
As estimated by Adams and Giroux (2012), based on drilling through 2011 and a cut-off grade of 0.3 gram of gold per ton, the Dolphin stock has an indicated resource of 17.270 million tonnes with an average grade of 0.62 grams of gold per tonne (or 341,000 ounces of gold) and an inferred resource of 64.440 million tonnes with an average grade of 0.55 gram of gold per tonne (or 1,135,000 ounces of gold).
A total of 87 holes, totaling 24,156 m, have been drilled within the resource area since 2011 (as of Dec. 2016). In 2016, 717 soil samples were collected; they delineate a gold-in-soil geochemical anomaly west of the current Dolphin deposit. Previously completed shallow rotary air blast drilling was composited and indicates better-grade oxide material may be present to the north (Athey and Werdon, 2017).
Geologic map unit (-147.44904747222, 65.0612766500378)
Mineral deposit model Polymetallic veins (Cox and Singer, 1986; model 22c)
Mineral deposit model number 22c
Age of mineralization Three Ar40/Ar39 age determinations on sericite from the mineralization and from a shear zone that cut the stock vary from 88.3 to 90.1 Ma.
Alteration of deposit The Dolphin deposit is marked by multiple flooded zones of alternating silicification and sericitization, with local scheelite-bearing carbonate zones (Freeman and others, 1998). In some drill holes the silicification of the granodiorite almost completely obliterates the original igneous textures. Chloritic alteration is rare.

Production and reserves

Workings or exploration
During 1995-96, Freegold completed 15,559 feet of reverse circulation drilling in the Dolphin prospect in 46 drill holes. In 1998, a single vertical core hole was drilled to a depth of 1,033 feet. Seven holes were drilled in 2004 and 26 more were drilled in 2011 when the Dolphin prospect was the center of exploration by Freegold in the Cleary area. Over the years, the prospect has also been covered by numerous geochemical and geophysical surveys and has been trenched and sampled as part of Freegold's extensive work in the Cleary Hill area since 1991.
In 2012, 47 drill holes representing 48,937 feet were completed in the Dolphin/Cleary Hill area by Freegold. A revised NI 43-101 compliant gold resource was calculated (Abrams and Giroux, 2013).
In 2013, ten drill holes representing 11,392 feet were completed in the Dolphin/Cleary Hill area. A subsequent revised NI 43-101 compliant gold resource ensued (Abrams and Giroux, 2013).
A total of 87 holes, totaling 24,156 m, have been drilled within the resource area since 2011 (as of Dec. 2016). In 2016, 717 soil samples were collected; they delineate a gold-in-soil geochemical anomaly west of the current Dolphin deposit. Previously completed shallow rotary air blast drilling was composited and indicates better-grade oxide material may be present to the north (Athey and Werdon, 2017).
Indication of production None
Reserve estimates
As estimated by Abrams and Giroux (2013), based on drilling through 2013 and a cut-off grade of 0.3 gram of gold per ton, the Dolphin stock has an indicated resource of 79.800 million tonnes with an average grade of 0.66 gram of gold per tonne (or 1.683 million ounces of gold) and an inferred resource of 248.060 million tonnes with an average grade of 0.61 gram of gold per tonne (or 4.841 million ounces of gold). Included within this new resource is an oxide component.
In January 2016, Freegold Ventures Ltd. released a preliminary economic assessment (PEA) for their Golden Summit gold property near Fort Knox mine north of Fairbanks, followed by a March 2016 technical report, which was amended and restated in May 2016 (Abrams and others, 2016). Freegold’s initial development scenario for Golden Summit includes a proposed heap-leach operation focused on the existing oxide portion of the resource, with a staged approach to a larger milling scenario. Only blocks falling within the conceptual open pit are reported as a mineral resource, and using a 0.3 gram of gold per tonne cut-off, this results in an indicated resource of 61,460,000 tonnes at 0.69 gram of gold per tonne (1,363,000 contained ounces of gold) and an inferred resource of 71,500,000 tonnes at 0.69 gram of gold per tonne (1,584,000 contained ounces of gold). Using $1,300 per ounce of gold, the PEA evaluated a two-phase, 24-year, open pit mine generating two gold streams, each operating at 10,000 tonnes per day for 2,358,000 ounces of doré produced over the life of the mine; processing operations for the oxide and sulfide mineralized materials are heap leach and bi-oxidation, respectively (Abrams and others, 2016).
Production notes None.

References

Reporters C.J. Freeman, J.R. Guidetti Schaefer (Avalon Development Corporation); D.J. Grybeck (Port Ludlow, WA); V.C. Zinno (Alaska Earth Sciences, Inc.); M.B. Werdon (DGGS)
Last report date 8/26/2017