Geology and ore deposits in the Reid Inlet area, Glacier Bay, Alaska

Rossman, D

A Au-bearing area of about 7 1/2 sq. mi. near the head of Glacier Bay between Reid and Lamplugh glaciers was first discovered by Joseph Ibach in 1924. The dominant rock type in the area is granodiorite, which is intruded into bedded rocks that may be of Paleozoic age. The bedded rocks consist of conglomerate, limestone, and black graphitic schist. A light-colored quartz diorite younger than the granodiorite crops out S. of the mapped area. Most of the ore deposits are found in fissure-type quartz veins in both the granodiorite and the older bedded rocks. The mineralizing solutions that brought in the Au have altered the country rock for as much as a few tens of feet on each side of the fissures. Locally this altered rock is Au-bearing, but in the places sampled the Au content was found to be too low for mining to be profitable. Most of the quartz veins are lenticular, both horizontally and vertically, and the Au tends to be concentrated in discrete spots along the veins. These factors cause the ore to be spotty and its location to be unpredictable, and has led to the concept that at many places the ore does not continue below the surface. Geologically, however, there appears to be no reason to believe that Au mineralization is confined to surface outcrop. The Leroy and Rainbow properties are the only two within the mapped area that have yielded significant quantities of Au, but the veins on the Highland Chief and probably the Rambler claims appear to be of sufficient size and grade to be potential ore producers. The Leroy mine is the largest in the area. The ore body consisted of a fissure-type quartz vein with an average width of 2 to 3 ft. and a length of about 60 ft., but in 1954 all the ore in the main vein had been mined out above the main working level. Probably several hundred tons of ore was mined and milled from the Rainbow vein. The results of an investigation of a mineralized area near Lituya Bay are included in this report. The mineralized material consists of hydrothermally altered rock found in volcanic rocks believed to be of Mesozoic age. The Au content of the observed altered rock is too low for profitable mining, but spots may be discovered in which the Au concentration is sufficiently high to be of economic significance.

Geology and ore deposits in the Reid Inlet area, Glacier Bay, Alaska

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