Rosa Ridge

Prospects, Probably inactive

Commodities and mineralogy

Main commodities Zn
Other commodities As; Au; Bi; Cu; Pb; Sb
Ore minerals iron oxides; pyrite
Gangue minerals ankerite; quartz

Geographic location

Quadrangle map, 1:250,000-scale TN
Quadrangle map, 1:63,360-scale B-3
Latitude 65.33515
Longitude -151.2965
Nearby scientific data Find additional scientific data near this location
Location and accuracy These lode occurrences are along the south end of informally-named Rosa Ridge, which forms the divide between Bonanza and Rosa creeks, about 5 miles north of the Yukon River. The site is Alaska Division of Geological and Geophysical Surveys (ADGGS) sample station 92MW415 (Solie and others, 1993), 0.25 mile northeast of the center of section 20, T. 6 N., R. 18 W., of the Fairbanks Meridian. This location is accurate within 1000 feet.

Geologic setting

Geologic description

Bedrock in the vicinity of Rosa Ridge is chiefly Paleozoic limestone, dolomite, greenstone, and chert, and lesser amounts of schist, quartzite, phyllite, and slate (Chapman and others, 1982). The rocks are structurally complex. Bedrock at the prospects is mainly greenstone, carbonate, and micaceous quartzite with minor graphitic schist (North Star Exploration Inc., 2000 [Highly mineralized block 20]).
In 1992, the Alaska Division of Geological and Geophysical Surveys (ADGGS) investigated the Rosa Ridge area as part of a mineral resource evaluation of State-selected lands (Solie and others, 1993). Rocks collected in the area included gossanous muscovite-quartz schist, altered diabase, greenstone (with pyrite), graphitic schist, and dolomitic marble. Quartz and quartz-ankerite-iron oxide veins, some brecciated or vuggy, locally are exposed on ridges in the area. Seventeen rock samples were collected for geochemical analysis by ADGGS, and 5 (at stations 92Ha219, 92Ha220, 92MW412, and 92MW415) contained the following maximum values of one or more of the following commodities: 30 parts per billion (ppb) gold, 261 parts per million (ppm) arsenic, 13 ppm antimony, 22 ppm bismuth, 87 ppm lead, 34 ppm scandium, 186 ppm zinc, 1,534 ppm manganese, and 162 ppm copper (Solie and others, 1993).
In the mid- to late 1990s, the Rosa Ridge area was explored by North Star Exploration, Inc. (North Star Exploration Inc., 2000 [Highly mineralized block 20]). Mineralization exposed along the ridge occurs as quartz-ankerite stringers, and as veinlets with carbonate-altered halos, in greenstone and micaceous quartzite. Rock, soil, and stream-sediment samples collected in the vicinity of altered greenstone on a tributary of Rosa Creek are anomalous in lead and zinc. The tributary drains quartz-veined limestone on east Rosa Ridge that is anomalous in antimony and bismuth. No follow-up work has been reported.
Geologic map unit (-151.299019132604, 65.3346473723356)
Mineral deposit model Polymetallic veins? (Cox and Singer, 1986; model 22c?).
Mineral deposit model number 22c
Alteration of deposit Carbonate (ankerite).

Production and reserves

Workings or exploration
In 1992, the Alaska Division of Geological and Geophysical Surveys (ADGGS) investigated the Rosa Ridge area as part of a mineral resource evaluation of State-selected lands (Solie and others, 1993). Rocks collected in the area included gossaneous muscovite-quartz schist, altered diabase, greenstone (with pyrite), graphitic schist, and dolomitic marble. Quartz and quartz-ankerite-iron oxide veins, some brecciated or vuggy, locally are exposed on ridges in the area. Seventeen rock samples were collected for geochemical analysis by ADGGS, and 5 (at stations 92Ha219, 92Ha220, 92MW412, and 92MW415) contained the following maximum values of one or more of the following commodities: 30 parts per billion (ppb) gold, 261 parts per million (ppm) arsenic, 13 ppm antimony, 22 ppm bismuth, 87 ppm lead, 34 ppm scandium, 186 ppm zinc, 1,534 ppm manganese, and 162 ppm copper (Solie and others, 1993).
In the mid- to late 1990s, the Rosa Ridge area was explored by North Star Exploration, Inc. (North Star Exploration Inc., 2000 [Highly mineralized block 20]). Mineralization exposed along the ridge occurs as quartz-ankerite stringers, and as veinlets with carbonate-altered halos, in greenstone and micaceous quartzite. Rock, soil, and stream-sediment samples collected in the vicinity of altered greenstone on a tributary of Rosa Creek are anomalous in lead and zinc. The tributary drains quartz-veined limestone on east Rosa Ridge that is anomalous in antimony and bismuth. No follow-up work has been reported.
Indication of production None

References