Margerie Glacier prospect (Margarie Glacier prospect; Porcupine prospect), Glacier Bay Mining District, Juneau Mining District, Alaska, USAi

Regional Level Types
Margerie Glacier prospect (Margarie Glacier prospect; Porcupine prospect)	Prospect
Glacier Bay Mining District	- not defined -
Juneau Mining District	Mining District
Alaska	State
USA	Country

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The deposit is within Glacier Bay National Park and Preserve where exploration and development is restricted.
Location: This prospect is in Glacier Bay National Monument on the south side of the Margerie Glacier between elevations of 1,100 feet and 3,200 feet. It is about 2 miles from tidewater on the west side of Tarr Inlet in the NW1/4, section 16, T. 33 S., R. 50 E. of the Copper River Meridian. It is shown as location 7 in figure C-2 and in figure C-39 of Brew and others (1978); as location 1 by Cobb (1972; MF-424); and as location SE24 by Nokleberg and others (1987).
Geology: The following description is summarized from Brew and others (1978). The Margerie prospect is a porphyry copper deposit. Disseminated chalcopyrite, pyrite, pyrrhotite, and powellite-scheelite occur in a massive porphyritic, Tertiary quartz monzodiorite stock and associated dikes. The stock contains a porphyritic quartz monzonite core. A prominent joint set that trends N50E and dips steeply to the northwest cuts across the stock and extends into the surrounding Permian section of hornfelsed marine volcanic and sedimentary rocks. Porphyritic monzodiorite dikes up to 50 feet thick and quartz-sulfide veins up to 1.7 feet thick occupy the joint set. The dikes extend into the country rock but the veins do not. The veins, which are less important than disseminated mineralization, contain quartz, chalcopyrite, arsenopyrite, sphalerite, pyrite, pyrrhotite, powellite-scheelite, and molybdenite. Disseminated sulfide mineralization, primarily chalcopyrite, pyrite, pyrrhotite, and some powellite-scheelite, is largely confined to the stock and dikes. Where dikes extend into the surrounding marine sedimentary rocks, they contain much less disseminated sulfides. The joint system may have acted as the conduit for sulfide mineralization that replaced mafic minerals in the intrusive rocks. Plagioclase has been subjected to slight to moderate sericitization and K-spar alteration and biotite has been moderately chloritized. Limited investigation of the marine sedimentary rock section northeast of the stock did not reveal significant mineralization. However, the Permian marine volcanic and sedimentary rocks to the southwest of the stock contained various iron-stained zones, fault and fracture fillings of quartz and sulfides, and lenses of massive pyrite, pyrrhotite, and chalcopyrite. The Margerie prospect is within the Tarr Inlet suture zone, which forms the western boundary of the Geike province of Brew and others (1978). Based on the age of the host stock and dikes, the mineralization is Tertiary.
Workings: Brew and others (1978) cite the following sequence of activity at the Margerie prospect. The prospect was discovered by Leo Mark Anthony in 1960 and 6 claims were staked that year. Investigations were made by E. M. MacKevett of the USGS in 1966, George Moerlein in 1968 and the U.S. Bureau of Mines in 1975 and 1976. A Masters thesis by M. A. Parke was in preparation in 1978.
Age: Tertiary (Brew and others, 1978).
Alteration: Plagioclase has been subjected to moderate sericitization and K-spar alteration, and biotite has been moderately chloritized (Brew and others, 1978).
Reserves: As part of the mineral resources study of the Glacier Bay National Monument by Brew and others (1978), the U.S. Bureau of Mines estimated the deposit to contain 160 million tons of inferred resource that contain 0.2% copper, 0.008 ounces of gold per ton, 0.13 ounces of silver per ton, and 0.01% tungsten.

Commodities (Major) - Ag, Au, Cu, W; (Minor) - Mo, Zn
Development Status: None
Deposit Model: Copper porphyry with associated veins, pods, and disseminations (Cox and Singer

Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.

Mineral List

11 valid minerals.