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Horn Mountain Occurrence, Willow Creek District, Matanuska-Susitna Borough, Alaska, USA

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Horn Mountains are probably the largest known high-grade mordenite deposit in North America.
Location: On southeast flank of Horn Mountain, 2,000 ft north of headwaters of Wood Creek. The occurrence extends along the flank, northeast of the point given. Accurate within 2,000 ft. Locality 71 of MacKevett and Holloway (1977).
Geology: Zeolite-bearing tuff beds formed by burial diagenesis and low-grade regional metamorphism of Early Jurassic tuffaceous rocks of the Talkeetna Formation. Zeolites are at least 30 meters thick extending for 14 kilometers and composed of 50 percent commercial grade mordenite. Heulandite occurs in thin, tabular crystals and laumontite is present in smaller amounts. Mordenite is an alteration product of volcanic sandstones and replacement of glassy shards of vitric tuffs (Hawkins, 1973). During the time of formation, the zeolite-bearing rock was subjected to a maximum temperature of 200 degrees Celsius and fluid pressures of 0.5 to 3 kilobars. This is equivalent to 1 to 10 kilometers burial depth (Hawkins, 1976).
Workings: Surface mapping and sampling.
Age: Early Jurassic or younger; the zeolited tuff beds are part of the Early Jurassic tuffaceous rocks of the Talkeetna Formation.
Alteration: Mordenite is an alteration product of volcanic sandstones and replacement of glassy shards of vitric tuffs (Hawkins, 1973).

Commodities (Major) - Zeolites
Development Status: None
Deposit Model: Burial diagenesis and low-grade regional metamorphism of tuffaceous rocks (Hawk

Mineral List



3 entries listed. 2 valid minerals.

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References

Cobb, E.H., 1979, Summary of references to mineral occurrences (other than mineral fuels and construction materials in the Anchorage quadrangle, Alaska: U.S. Geological Survey Open-File Report 79-1095, 184 p. Hawkins, D.B., 1973, Sedimentary zeolite deposits of the upper Matanuska Valley, Alaska: Alaska Division of Geological and Geophysical Surveys Special Report 6, 17 p., 1 sheet, scale 1:63,360. Hawkins, D.B., 1976, Mordenite deposits and zeolite zonation in the Horn Mountains area, South-central Alaska: Alaska Division of Geological and Geophysical Surveys Special Report 9, 9 p., 2 sheets, scale 1:21,000. Hawkins, D.B., 1976, Commercial-grade mordenite deposits of the Horn Mountains, southcentral Alaska: Alaska Division of Geological and Geophysical Surveys Special Report 11, 11 p., 1 sheet, scale 1:15,840. MacKevett, E.M., Jr., and Holloway, C.D., 1977, Map showing metalliferous and selected non-metalliferous mineral deposits in the eastern part of southern Alaska: U.S. Geological Survey Open-File Report 77-169-A, 99 p., 1 sheet, scale 1:1,000,000.

 
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