About This Item

Share This Item

The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 69 (1985)

Issue: 4. (April)

First Page: 680

Last Page: 680

Title: Tin Creek Zinc, Lead, and Silver Skarn Prospects, Farewell Mineral Belt, Alaska: ABSTRACT

Author(s): David J. Szumigala

Article Type: Meeting abstract

Abstract:

Several zinc, lead, silver, and copper skarn and replacement bodies occur in a 500 km2 area near Farewell, in the McGrath quadrangle, Alaska. Detailed examination of the skarns in upper Tin Creek, one of the major mineralized areas, indicates ore and gangue zoning, which inversely follows dike density.

Host rocks for skarns are mid-Paleozoic sedimentary rocks that are contact-metamorphosed, folded, faulted, and overlain and intruded by Tertiary igneous rocks. Skarns in the Tin Creek area are small (up to 3 m wide), discontinuous bodies of exoskarn found along dike contacts and as endoskarn in the dikes. Skarn also forms mantos in marble and irregular bodies along thrust and high-angle faults. Semimassive to massive sulfide mantos are present in calc-silicate hornfels. Many dikes do not have skarn along their contacts while others have skarn along only one margin, indicating that dikes and faults are only structural conduits for later metasomatic fluids.

Sulfide distribution and deposition are intimately associated with calc-silicate metasomatism. The skarn prospects are areally zoned, with garnet - (Ad12-100) and chalcopyrite-dominant skarns proximal and pyroxene-(Hd15-86) and sphalerite-dominant skarns distal to the center of most intense dike swarms. Sphalerite is preferentially associated with pyroxene, while chalcopyrite is preferentially associated with garnet. Metamorphic garnet and pyroxene are devoid of sulfides and have the lowest iron compositions. Early metasomatic garnet and pyroxene are generally richer in iron and are accompanied by minor sphalerite + chalcopyrite. Late metasomatic (main-stage) garnet and pyroxene contain the highest iron contents for these minerals and are extensively replaced by phalerite + chalcopyrite. Main-stage skarns are locally retrograded to amphibole or epidote + quartz. These calc-silicates may be replaced by sphalerite + chalcopyrite, with galena locally abundant as veins in pyroxene-dominant skarns.

Zinc, lead, and silver ore potential at Tin Creek exists at distances greater than 2 km from the dike swarm center. Zinc, lead, and silver ore is preferentially associated with pyroxene-dominant skarns formed during the main stage of metasomatism.

End_of_Article - Last_Page 680------------

Copyright 1997 American Association of Petroleum Geologists