GARNET LEDGE GARNET SCHIST
A famous collecting locality having abundant garnets
is Garnet Ledge, just south of the Stikine River mouth, near the town of
Wrangell, in southeastern Alaska, USA.
Many thousands of deep red, gemmy almandine garnets
have been collected from Garnet Ledge for over a century. The land at
Garnet Ledge was given to the Boy Scouts in the early 1960s, and ever since,
only the children of Wrangell may collect garnets there for free.
Garnet Ledge Geology - Almandine garnets occur in grayish-colored schists
containing a mixture of sillimanite, muscovite, biotite, staurolite, chlorite,
plagioclase, graphite, and ilmenite. Before metamorphism, the precursor
rocks were Late Jurassic-Early Cretaceous fine-grained siliciclastic
sedimentary rocks. These were cooked by contact metamorphism during
intrusion of a quartz diorite pluton of the Admiralty-Revillagigedo Plutonic
Belt (Alaskan Coast Plutonic Complex) during the early Late Cretaceous (at
89-92 million years). The garnets appear to have formed over a one
million year interval, from 89 to 90 million years ago. The Garnet Ledge
locality is a small, 1.3 square kilometer fragment of roof pendant over the
quartz diorite pluton. Summarized from information in Stowell et al.
(2001).
Location
- Garnet Ledge, adjacent to mouth of Garnet Creek, coastal exposure along the
southeastern side of the mouth of the Stikine River, just south of Point
Rothsay, just northwest of Garnet Mountain, ~12 km north of Wrangell, southeast
of Petersburg, southeastern Alaska, USA (about 56¡ 34Õ 17Ó North, 132¡ 21Õ 54Ó
West).
Garnet schist (5.5 cm across) from the Cretaceous of Garnet Ledge, Alaska.