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Preliminary geologic interpretation of aeromagnetic data in the Nixon Fork district, Alaska

January 1, 1969

An aeromagnetic map covering 480 square miles was compiled for the Nixon Fork district, which is located approximately 35 miles northeast of McGrath, Alaska. The survey was flown in search of concealed intrusive rocks which may have produced contact metamorphic deposits in limestone similar to the known lode deposits which have been the principal source of gold in the district.

The exposed quartz monzonite stocks with which the lode deposits are associated produce negative magnetic anomalies. Slight to moderately strong positive anomalies correlate with granitic intrusives in contact with Upper Cretaceous rocks in the Iditarod-Nixon Fork fault zone. No significant mineral deposits have been found in conjunction with these granitic bodies.

Positive anomalies, delineating buried intrusives, occur near the east and west boundaries of the mapped area. The nature of the westernmost intrusive is unknown.

An area of possible economic interest lies between Limestone Mountain and Whirlwind-Canyon Creeks in the eastern sector of the mapped area. An elliptical positive anomaly is superimposed on an elongate, slightly negative anomaly. This negative anomaly may represent an intrusive similar to the quartz monzonite with which the lode deposits are affiliated. The positive anomaly may be a near-vertical mafic dike intruded to within 50 feet of the surface of a limestone ridge. Limestone in the vicinity of the dike may be a favorable area for prospecting for lode deposits similar to the known gold-producing deposits of the district.

Publication Year 1969
Title Preliminary geologic interpretation of aeromagnetic data in the Nixon Fork district, Alaska
DOI 10.3133/ofr699
Authors Lennart A. Anderson, Bruce L. Reed, Gordon R. Johnson
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title Open-File Report
Series Number 69-9
Index ID ofr699
Record Source USGS Publications Warehouse