Purches Creek

Occurrence, Inactive

Alternative names

Purchase Creek

Commodities and mineralogy

Main commodities Au
Other commodities Ag; Cu
Ore minerals chalcopyrite; gold; pyrite; silver
Gangue minerals quartz

Geographic location

Quadrangle map, 1:250,000-scale AN
Quadrangle map, 1:63,360-scale D-7
Latitude 61.81
Longitude -149.35
Nearby scientific data Find additional scientific data near this location
Location and accuracy 1,000 ft northwest of the head of Craigie Creek. Accurate within 2,500 ft. Locality 4 and 5 of Capps and Tuck (1935) and locality 7 of Cobb (1972).

Geologic setting

Geologic description

Two occurrences were reported by Capps and Tuck (1935). The first is a quartz vein exposed in a tributary on the divide between Craigie Creek and Purches Creek drainages (Capps and Tuck locality 4). The vein is 1 ft wide, strikes S 20 W, and dips 30 S, and can be traced for several hundred feet. It is composed of 'bull' quartz and contains chalcopyrite, gold, and silver. The second occurrence is a crushed piece of quartz float from the next tributary to the west (Capps and Tuck locality 5). It contained disseminated pyrite, gold, and silver. At the first locality described above, assays show the vein to contain 0.16 oz/ton Au and 0.2 oz/ton Ag. At the second locality described, the quartz float assayed 0.01 oz/ton Au and 0.2 oz/ton Ag.
These occurrences are located near the contact of the Willow Creek Pluton and an early Paleocene and Late Cretaceous granite body. The Willow Creek Pluton is a Late Cretaceous zoned pluton: the outer part consists of hornblende quartz diorite and lesser hornblende tonalite; the core consists of hornblende-biotite granodiorite, and lesser hornblende-biotite quartz monzodiorite and biotite quartz monzonite. The early Paleocene and Late Cretaceous granite is generally a biotite-muscovite granite with granodiorite and lesser quartz monzonite. Wall-rock alteration within a few inches of the veins is intense, but seldom extends more than 10 to 12 inches beyond the quartz filling. Sericitization and carbonate alteration predominate, but there is some pyritization and in the outer parts of the alteration zone chloritization is present (Ray, 1954).
Geologic map unit (-149.352214467986, 61.809473308094)
Mineral deposit model Low-sulfide Au-quartz veins (Cox and Singer, 1986; model 36a)
Mineral deposit model number 36a
Age of mineralization Late Cretaceous or younger based on the bedrock in the vicinity.
Alteration of deposit Wall-rock alteration within a few inches of the veins is intense, but seldom extends more than 10 to 12 inches beyond the quartz filling. Sericitization and carbonate alteration predominate, but there is some pyritization and in the outer parts of the alteration zone chloritization is present (Ray, 1954).

Production and reserves

Workings or exploration Two occurrences were sampled by Capps and Tuck (1935). At the first locality described above, assays show the vein to contain 0.16 oz/ton Au and 0.2 oz/ton Ag. At the second locality described, the quartz float assayed 0.01 oz/ton Au and 0.2 oz/ton Ag (Capps and Tuck, 1935).
Indication of production None

Additional comments

Capps and Tuck (1935) also mention that on the lower Purches Creek there are numerous pegmatite dikes, but no minerals of value were found in them. Purches Creek has also been labeled Purchase Creek on some older maps.

References

MRDS Number A011605
Reporters D.P. Bickerstaff (USGS contractor); S.W. Huss (USGS)
Last report date 7/30/1998