Geology and ore deposits in the Reid Inlet area, Glacier Bay, Alaska, with added notes on a mineralized zone near Lituya Bay

Abstract

A gold-bearing area of about 7 1/2 square miles, first discovered by Mr. Joseph Ibach in 1924, exists near the head of Glacier Bay between Reid and Lamplugh glaciers. 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 south of the mapped area. Most of the ore deposits are found in fissure type quartz veins. These occur in both the granodiorite and in the older bedded rocks. The mineralizing solutions which brought in the gold have altered the country rock for as much as a few tens of feet to each side of the fissures. Locally, this altered rock is gold-bearing, but in the places sampled the gold content was found to be too low to permit profitable mining. Most of the quartz veins tend to be lenticular, both horizontally and vertically, and the gold tends to be concentrated in discrete spots along the veins. These factors tend to make the ore spotty and its location unpredictable. This has given rise to the concept that the ore in the area has a tendency not to continue below the surface. Geologically there appears to be no reason to believe that gold mineralization is confined to surface outcrop. The Leroy and Rainbow properties are the only two that have yielded significant quantities of gold within the mapped area, 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 averaging between 2 and 3 feet in width with a length of about 60 feet, but in 1954, all of the ore in the main vein had been mined out above the main working level. Ore probably amounting to several hundreds of tons was mined and milled from the Rainbow vein. The results of an investigation of a mineralized area near Lituya Bay is included in this report. The mineralized material consists of hydrothermally altered rock found in volcanic rocks believed to be of Mesozoic age. The gold content is too low to permit profitable mining, although it is possible that undiscovered spots exist in which the gold concentration is sufficiently high to be of economic significance.