Prospect, Inactive

Commodities and mineralogy

Main commodities Cu; Mo
Other commodities Ag; Pb; Sn; Zn
Ore minerals chalcopyrite; fluorite; ferrimolybdite; molybdenite; pyrite
Gangue minerals clay; quartz; sericite

Geographic location

Quadrangle map, 1:250,000-scale GU
Quadrangle map, 1:63,360-scale D-1
Latitude 62.8
Longitude -144.17
Nearby scientific data Find additional scientific data near this location
Location and accuracy The Elizabeth prospect is on a southeast facing ridge in upper Hidden Creek about a mile south-southeast of the center of Long Lake. The coordinates are approximately the center of this low-grade molybdenum porphyry. The prospect was identified as locality 4 by Richter (1966, fig. 5). It is the same as locations 6 of both Richter and Matson (1972), and MacKevett and Holloway (1977). Cobb (1979 [OF 79-1247]) lists the site as an unnamed occurrence. It is in the SW1/4SE1/4, section 19, T. 12 N., R. 7 E., Copper River Meridian.

Geologic setting

Geologic description

This low-grade, molybdenum porphyry occurs in a complex contact region of the Pennsylvanian to Permian, Ahtell pluton. A coarse-grained, porphyritic quartz monzonite phase of the Ahtell pluton appears to intrude the Border and Grubstake phases of the intrusion in the region south of Long Lake (Richter, 1966, fig. 2). The molybdenum deposit is mostly in the Border phase and in the overlying volcanic rocks of the Pennsylvanian to Permian, Slana Spur Formation.
The molybdenum deposit trends southeasterly from the ridge crest above Long Lake. On the ridge crest, it is about 400 feet wide; it extends over the ridge to the west for about 1,000 feet. To the southeast, the deposit widens to about 2,500-3,000 feet. The deposit is probably bounded by faults. On the surface the deposit is mainly rubble crop developed over a sericite-quartz-clay alteration zone with veinlets and disseminations of pyrite and minor molybdenite. Purple fluorite occurs locally. Quartz-molybdenum fragments mark the surface of the deposit and yellowish secondary ferrimolybdite occurs in surface materials (written communications, Emery Bailey Jr., ASARCO, 1969, and Kirk W. Stanley, 1970). The extent and shape of the deposit was defined by detailed geologic mapping and by a series of soil-sample lines running nearly east and west.
Because of poor exposures, the shape and size of much of the deposit was defined by a soil survey. Soils were analyzed for copper, molybdenum, lead, and zinc. Molybdenum was considered anomalous in excess of 20 ppm; Mo values are highest in a 1200-foot wide zone on the southeast side of the ridge. Copper and lead are partly coincident with molybdenum but also show strong anomalies on the lower southeast slope. Zinc is peripheral to molybdenum, copper, and lead. The highest zinc values are in Dry Creek (a local name for the creek in the center of section 30) that drains the southwest flank of the deposit. The distribution of zinc suggests that some may have been redistributed and concentrated in stream sediments. In absolute concentration, lead exceeds copper, zinc, and molybdenum. Lead in soils locally exceeds 0.1 percent. Apparently no samples were analyzed for gold.
Drilling in 1968 and 1969 shows that most of the deposit is very low grade, but two shallow holes drilled in 1968 found intercepts of rich mineralization. Both holes F and G cut ore grade material. Hole F, drilled northwest, assayed 0.519 percent MoS2 over 26 feet; drill hole G, drilled northeast from the same location assayed 0.642 MoS2 over 41 feet. Both holes were drilled from the same location on the ridge between Dry and Moly Creeks at an elevation of about 4,500 feet (Moly Creek is a local name given to the creek in the southeast portion of section 13). None of the holes drilled in 1969 hit high grade mineralization. The maximum concentration of copper was about 0.3 percent; most samples ran 0.03 to 0.05 percent copper. Silver was not always assayed; its maximum concentration was 0.08 ounces per ton. The composite drill core was also analyzed spectrographically; tin was present in one sample at 50 ppm. Kirk Stanley later proposed two deeper holes nearer the top of the ridge where he believed better values would be found (written communication, 1970). A 2-foot-wide vein deposit that contains molybdenum reported by Richter (1966) is approximately on the northeast contact of the deposit.
The deposit is in part structurally controlled. Emery Bailey Jr., proposed that the deposit is bounded on east and southwest by post-Ahtell-pluton faults that control the courses of Moly and Dry Creeks (written communication, 1969). The deposit appears to be open to the southeast under upper Hidden Creek, but the best molybdenum zone appears to be near the top of the ridge in the northwest part of the deposit.
Geologic map unit (-144.172195930988, 62.7996064100706)
Mineral deposit model Porphyry Mo (Cox and Singer, 1986; model 21b)
Mineral deposit model number 21b
Age of mineralization Emplaced subseqent to or is related to the border phase of the Pennsylvanian to Permian, Ahtell pluton.
Alteration of deposit Argillic and sericite alteration; argillic alteration is probably accentuated by supergene acid solutions formed by oxidation of pyrite.

Production and reserves

Workings or exploration The deposit was discovered in 1957 by Au Noc Ho and Kirk W. Stanley but no work was done until 1968 (Stanley, written communication, 1970). The site was visited and mapped at a reconnaissance scale by Richter (1966). Stanley's and Richter's geologic mapping and new discoveries led to renewed prospecting in the area. The molybdenum porphyry was initially covered by 95 federal claims, Elizabeth 20 to 115, owned jointly by the Ptarmigan Company and investors. The Ptarmigan Company, a company formed by Kirk Stanley to work on prospects near the Ahtell pluton, conducted a geochemical survey in 1968 and drilled six shallow AX holes. The claims were leased to ASARCO in 1969 who mapped the area in detail and drilled seven BX holes; the deepest hole, no. 6, was 400 feet in length. Drilling was fairly difficult; holes tended to swell shut. ASARCO did not find enough mineralization to warrant further work by them and little has been done since 1969.
Indication of production None

Additional comments

Additional information can be obtained from Ahtna Minerals in Anchorage, Alaska.