The Koyana prospect was first identified by BHP-Utah in 1986 as an area anomalous in arsenic and gold in soils. Subsequently they drilled 10 holes in the area before they dropped the property in 1990 (Stevens, 2010). The Koyana prospect is at the east end of an arcuate band of Paleozoic schist about three miles long and up to a half mile wide that extends from the mouth of Koyana Creek to the mouth of Daniel's Creek (Herreid, 1965; Mulligan, 1971; Till and others, 1986). This schist unit hosts most of the lode deposits in the Bluff area, including the Saddle (SO175), Daniel's Creek (SO006), and Idaho (SO135) prospects. The schist is bordered to the north and south by thick, extensive marble; the schist-marble contacts are probably thrust faults.

There is little outcrop in the Koyana area and most of the information about it comes from 10 BHP-Utah drill holes. As described by Ford (1993) and Ford and Snee (1996), the mineralization at the Koyana prospect is localized in extensional joints that strike easterly and dip moderately to the south in quartz-muscovite schist. The veins are discontinuous and commonly less than 3 inches thick. Gold grades are irregularly distributed; vein intersections up to 3.3 feet across contain up to 1.8 ounces of gold per ton. The quartz veins frequently contain a few percent of ore minerals, mainly arsenopyrite, but marcasite, pyrite, and pyrrhotite occur in small amounts. The veins are commonly bordered by altered zones with plagioclase, chlorite, carbonate, white mica, biotite, titanite, and tourmaline. A sample of white mica from a quartz vein gave an Ar/Ar plateau date of 109.1 +/- 0.2 Ma and metamorphic white mica in the host schist gave Ar/Ar total gas dates of 122.6 +/- 0.4 Ma and 122.4 +/- 0.2 Ma (Ford and Snee, 1996). This indicates that the mineralization at Saddle is Late Cretaceous and probably related to regional metamorphism as are many other deposits on the Seward Peninsula (Apodoca, 1994; Hudson, 1994; Ford, 1993, Ford and Snee, 1996; Goldfarb and others, 1997).

Based on their 10 drill holes, BHP-Utah concluded that the resource of the Koyana prospect was 1.81 million tonnes of material with a grade of 0.69 gram of gold per tonne, or a total resource of 1.24 million grams of gold (Heine and Kell, 1991; Stevens, 2010). However, Stevens also emphasized that the BHP-Utah 'resource' for Koyana was not 43-101 compliant.

In 2008, Millrock Resources Inc. began exploring in the area under an agreement with Bering Straits Native Corporation. As of early 2010, Millrock's work on the Koyana prospect included geologic mapping and sampling, reanalysis of some of the BHP core, and geochemical soil surveys (Stevens, 2010).