|Quadrangle map, 1:250,000-scale||JU|
|Quadrangle map, 1:63,360-scale||D-5|
|Nearby scientific data||Find additional scientific data near this location|
|Location and accuracy||This prospect is located in an east-facing cirque at an elevation of 3,200 feet. The cirque forms the east flank of an unnamed mountain, 2 miles west of Lynn Canal and 3.5 miles west of Sullivan Island in the SE1/4 section 5, T. 34 S., R. 60 E. of the Copper River Meridian. The location is accurate. This is the discovery prospect in what has been called the Dream prospect area; numerous other prospects and occurrences have been found nearby.|
This prospect consists of three distinct stratiform layers of sulfides in a zone 75 feet thick. These layers pinch and swell from six inches to four feet thick and are exposed for over 200 feet along strike. The lowest sulfide layer is characterized by disseminated to massive, well-bedded, arsenopyrite-pyrite zones containing minor erythrite or 'cobalt bloom'. The sulfide minerals include arsenopyrite, chalcopyrite, galena, pyrite, pyrrhotite, and sphalerite. Alteration is limited to postmetamorphic hydrothermal, dolomitization and pyritization (Huber and Barnett, 1988). Continuous chip samples collected every 15 feet average 0.67 ounce gold per ton and 0.37% cobalt over 200 feet of strike length. Select samples contained up to 3.25 ounces of gold per ton, 3.5% copper, and 2.4 ounces of silver per ton (Huber and Barnett, 1988). Three diamond drill holes drilled in the cirque failed to intersect massive-arsenopyrite beds. One, however, intersected two mineralized zones; An upper 2.3-foot-thick zone assayed 0.107 ounce of gold per ton; and a lower 5.4-feet-thick zone tassayed 0.22 ounce of gold per ton (Bull and others, 1989). Although the stratabound, volcaniclastic-hosted, sulfides suggest a volcanogenic origin, Placer Dome U.S. geologists interpreted the deposit as a pre- or syn-metamorphic, hydrothermal-replacement deposit, possibly related to a pluton (Bull, 1991).
This deposit is one of many in the Dream prospect area that includes numerous veins, stockworks, stratabound and stratiform sulfide deposits (also see JU002, JU006, JU009, JU011, JU013, JU014, JU016, JU019), most of which occur near a volcaniclastic-marble contact. The U.S. Bureau of Mines (Clough and Redman, 1989), International Curator Resources, Ltd. (Huber and Barnett, 1988), and Placer Dome U.S. (Bull and others, 1989) explored the area in the late 1980s and developed a general lithology of the area. They divide the rocks into four major rock units. From the base up, they are: 1) a volcaniclastic unit approximately 2000 feet thick that consists of albite-chlorite schist, chlorite schist, and chlorite-quartz-sericite schist that may in part be metaplutonic as well as metavolcanic; 2) a unit 800 feet thick of micaceous marble, pelitic schist, graphite schist, gray to white, cliff-forming marble, chlorite-amphibole schist, greenstone, and phyllitic graphite schist; and 3) a unit of very fine-grained chlorite-sericite-biotite schist over 1000 feet thick that includes metatuff and pelitic, mafic and graphitic schist. The upper contact of this unit is a thrust fault that trends N-S for several miles; quartz veining is common along the thrust contact. The rocks overlying the thrust are middle- to upper-greenschist-facies graphitic schist, argillite, phyllite, and marble. The metamorphic grade of the rocks varies from mid- to upper-greenschist facies in the south, to amphibolite facies in the north. There have been at least two stages of folding.
The Dream prospect area was the site of extensive exploration and mapping from 1987 through 1990 by International Curator Resources Ltd. and Placer Dome U.S. The area was covered by 600 federal mining claims in 1989 and more than 5000 feet of drilling was completed by the end of 1990 (Swainbank and others, 1991).The general area consists predominantly of metamorphosed Silurian and Devonian clastic rocks, limestone, and volcanic units; Permian limestone and siltstone; and small plutons of Tertiary and Cretaceous granodiorite (Brew and Ford, 1985).
|Geologic map unit||(-135.438346389714, 58.9490745125734)|
|Mineral deposit model||Possibly a metamorphosed Kuroko massive sulfide deposit (Cox and Singer, 1986; model 28a) or a metamorphosed polymetallic replacement deposit (Cox and Singer, 1986; model 19a)|
|Mineral deposit model number||28a or 19a|
|Alteration of deposit||Post-metamorphic hydrothermal dolomitization and pyritization (Huber and Barnett, 1988).|
|Workings or exploration||The Dream prospect was discovered by the U.S. Bureau of Mines in 1986; numerous other prospects were found nearby and the area is commonly called the Dream prospect area. The area was the site of extensive exploration and mapping from 1987 through 1990 by International Curator Resources Ltd. and Placer Dome U.S. The area was covered by 600 federal mining claims in 1989 and more than 5,000 feet of drilling had been completed by the end of 1990 (Swainbank and others, 1991). In 1989, 3 diamond drill holes were completed on the Dream prospect and 3 diamond drill holes were completed in the Stinging Cliffs (JU016) area for a total of 2,000 feet. Three additional diamond drill holes were completed in the area by Placer Dome during the 1990 field season for a total of 2,307 feet (Bull, 1991). Claims are still active on this prospect (Roger Eichman, oral communication, 2001).|
|Indication of production||None|
Brew, D.A., and Ford, A.B., 1985, Preliminary reconnaissance geologic map of the Juneau, Taku River, Atlin, and part of the Skagway 1:250,000 quadrangles, southeastern Alaska: U.S. Geological Survey Open-File Report 85-395, 23 p., 2 sheets, scale 1:250,000.
Bull, K.F., 1991, The Dream project--Model frustration: Journal of Alaska Miners Association, v. 19, no. 10, p. 17.
Bull, K.F., and Radford, G., 1989, Dream project 1989; Final report: Unpublished report for Placer Dome U.S., Inc., 49 p.
Clough, A.H., and Redman, E.C., 1989, Bureau of Mines mineral investigations in the Juneau mining district, Alaska, 1984-1988, Volume 2, Detailed mine, prospect, and mineral occurrence descriptions, Section C, West Lynn Canal subarea: U.S. Bureau of Mines of Mines Special Publication, 44 p.
Gehrels, G.E., and Berg, H.C., 1994, Geology of southeastern Alaska, in Plafker, George, and Berg, H. C., eds., The geology of Alaska: Geological Society of America, DNAG, The geology of North America, Vol. G-1, p. 451-467.
Huber, J.A., and Barnett, J.C., 1988, The Dream massive sulfide project; 1988 Progress Report: Unpublished report for International Curator Resources, Ltd., Denver, Colo., 51 p.
|Reporters||J.C. Barnett and L.D. Miller (Juneau, Alaska )|
|Last report date||12/15/2001|