DZ Prospect, Juneau Mining District, Juneau, Alaska, USAi

Regional Level Types
DZ Prospect	Prospect
Juneau Mining District	Mining District
Juneau	City Borough
Alaska	State
USA	Country

Location: The prospect is at an elevation of about 2,350 feet, on the ridge northeast of upper Johnson Creek. It is about 2 miles south-southeast of Lions Head Mountain near the center of section 11, T. 35 S., R. 62 E. of the Copper River Meridian. The location is accurate.
Geology: In 1984, Bear Creek Mining Company delineated a N 40 W-trending, 300- to 800-foot-wide band of quartz veins with disseminationed pyrite. The veins carry elevated gold values, accompanied by wallrock alteration similar in style to that at the Jualin Mine (JU044) and Kensington Mine (JU029)(Barnett, 1989). The veins are traceable for over 7,000 feet. Bear Creek collected 140 vein samples of which nearly 20% assayed 0.05 ounce or more of gold per ton, the highest was 1.205 ounces of gold per ton. In 1987 and 1988 additional mapping and sampling was conducted by International Curator Resources, Ltd. (Barnett, 1989). The DZ prospect is in the Berners Bay district at the north end of the Juneau Gold Belt. The district is characterized by a series of structurally-controlled, mesothermal, gold-bearing quartz veins. Most of the veins are in Early Cretaceous (105 Ma) Jualin Diorite, which intrudes Upper Triassic metabasalt. The Jualin Diorite is generally massive, jointed, blocky, quartz monzonite to quartz monzodiorite. Gold occurs in low-sulfide, quartz-carbonate veins that contain pyrite and tellurides; the veins are marked by distinctive ankeritic alteration zones. There are both extensional and shear veins that generally strike north to northwest and dip east. Discrete vein systems are defined by one or more through-going quartz veins, many of which are in shear zones. Levielle (1991) and Knopf (1911) describe other gangue minerals near vein margins including albite, chlorite, muscovite, and lesser tourmaline, rutile, and apatite. Hydrothermal alteration adjacent to the veins is characterized by reddish-brown ferroan dolomite (Miller and others, 1995). Other alteration includes sericitization of plagioclase, chloritization, sulfidization of mafic minerals, and albitization of feldspars (Leveille, 1991). Pyrite is the most abundant sulfide mineral, with lesser amounts of chalcopyrite, galena, sphalerite, arsenopyrite, and tetrahedrite. Gold occurs in the native state, in pyrite, and in various telluride minerals such as calaverite, hessite, and petzite (Leveille, 1991; Redman and others, 1989). The vein paragenesis consists of early quartz, carbonates, albite and pyrite, followed by deposition of base and precious metals. Gold, galena and the tellurides were the last to be deposited (Leveille, 1991). The age of hydrothermal muscovite from veins at Kensington Mine (JU029) varies from 53.4 Ma to 56.5 Ma (Miller and others, 1994). This coincides with the 55 Ma age of the other mesothermal gold vein deposits in the Juneau Gold Belt (Goldfarb and others, 1997).
Workings: The DZ deposit was discovered and sampled by Bear Creek Mining Company in 1984. International Curator Resources and Placer Dome U.S. conducted additional mapping and sampling in 1987 and 1988. Currently (2001) held by Coeur Alaska.
Age: The age of mineralization in the Berners Bay district is about 55 Ma, the same as the other mesothermal gold-quartz-vein deposits in the Juneau Gold Belt (Goldfarb and others, 1997).
Alteration: The alteration adjacent to the veins is characterized by reddish-brown ferroan dolomite alteration, sericitization of plagioclase, chloritization and sulfidization of mafic minerals, and albitization of feldspars (Leveille, 1991).

Commodities (Major) - Au; (Minor) - Ag, Cu, Pb, Zn
Development Status: None
Deposit Model: Low-sulfide Au-quartz vein (Cox and Singer, 1986; model 36a)

Other Databases

Link to USGS - Alaska:	JU040

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References