| Main commodities | Cu |
|---|---|
| Other commodities | Ag; Au; Pb; Zn |
| Ore minerals | chalcopyrite; malachite |
| Gangue minerals | calcite; calc-silicate minerals |
| Quadrangle map, 1:250,000-scale | KC |
|---|---|
| Quadrangle map, 1:63,360-scale | C-3 |
| Latitude | 55.724 |
| Longitude | -130.868 |
| Nearby scientific data | Find additional scientific data near this location |
| Location and accuracy | The Marble Copper prospect is on the north shore of Walker Cove about 1.4 miles from its mouth. The site is in section 9, T. 71 S., R. 95 E., of the Copper River Meridian. It corresponds to loc. P-19 in Berg and others (1977, p. 120-121), and to loc. 24 in Elliott and others (1978). The location is accurate within 0.1 mile. |
Geologic descriptionThe country rocks in the area of the Marble Copper prospect are Tertiary or Cretaceous foliated granodiorite and quartz diorite of the Coast Range batholith, and paragneiss and minor marble that form metamorphic roof pendants, screens, and inclusions in the batholith (Berg and others, 1977, p. 120-121; Berg and others, 1988). The metamorphic rocks represent marine strata that underwent high-grade regional metamorphism in Cretaceous or Tertiary time. The premetamorphic age of the strata is uncertain, but they probably are mainly Paleozoic and may be as old as Precambrian (Berg and others, 1988, p. 26; Gehrels and others, 1990; Crawford and others, 2000). The deposit consists of chalcopyrite and malachite in a marble-skarn zone in a paragneiss roof pendant in gneissic diorite and quartz diorite (Berg and others, 1977, p. 120-121 and fig. 33). The marble-skarn zone is about 20 feet wide, and it adjoins a zone of paragneiss and subordinate marble and skarn about 60 feet wide. The calc-silicate minerals in the skarn are not described, but their green color (fig. 33, spl. no. 2K008) suggests that they include diopside. A 22-inch-long channel sample of the most heavily copper-stained part of the marble-skarn zone assayed up to 0.7% Cu, 150 ppm Pb, 300 ppm Zn, 30 ppm Ag, and 3.5 ppm Au (Berg and others, 1977, fig. 33, spl. no. 2K009). Adjacent channel samples showed much lower assay values, and a chip sample of a second band of marble northeast of the marble-skarn zone showed only traces of copper. The prospect was explored sometime before 1972 by a shallow opencut, but there was no evidence in 1973 that any claims had been staked. | |
| Geologic map unit | (-130.869705134295, 55.7236548264792) |
|---|---|
| Mineral deposit model | Cu skarn (Cox and Singer, 1986; model 18b) |
| Mineral deposit model number | 18b |
| Age of mineralization | Probably Cretaceous or younger. |
| Alteration of deposit | Local oxidation of copper minerals. |
| Workings or exploration | The prospect was privately explored sometime before 1972 by a shallow opencut, but there was no evidence in 1973 that any claims had been staked. A 22-inch-long channel sample of the most heavily copper-stained part of the marble-skarn zone assayed up to 0.7% Cu, 150 ppm Pb, 300 ppm Zn, 30 ppm Ag, and 3.5 ppm Au (Berg and others, 1977, fig. 33, spl. no. 2K009). Adjacent channel samples showed much lower assay values, and a chip sample of a second band of marble northeast of the marble-skarn zone showed only traces of copper. |
|---|---|
| Indication of production | None |
Additional commentsProspect is in Misty Fiords National Monument Wilderness. | |
| MRDS Number | A012301 |
|---|---|
ReferencesGehrels, G.E., McClelland, W.C., Samson, S.D., Patchett, P.J., and Jackson, J.L., 1990, Ancient continental margin assemblage in the northern Coast Mountains, southeast Alaska and northwest Canada: Geology, v. 18, no. 3, p. 208-211.
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| Reporters | H.C. Berg, USGS |
| Last report date | 6/29/1999 |