GROUND MAGNETIC SURVEYS OVER AEROMAGNETIC ANOMALIES IN THE ADIRONDACKS

An aeromagnetic survey of 6100 square miles in the Adirondack Mountains was made in 1945. The survey was undertaken to guide a program of exploration for magnetite. Magnetic maps were published to aid in the long-range geologic studies in the area. The interpretation of the magnetic maps is that most of the magnetic highs are produced by minor amounts of disseminated magnetite occurring as an accessory mineral in the bedrock.

Ground magnetic traverses were conducted with a proton precession magnetometer over some of the prominent aeromagnetic anomalies that were considered most likely to indicate ore deposits. Total field magnetic measurements were made over the Twin Lakes aeromagnetic anomaly near Star Lake, the Brand Pinacle aeromagnetic anomaly and the Potsdam Quadrangle magnetic anomaly.

The magnetic traverse across the Potsdam Quadrangle revealed a magnetic high of 1500 gammas. The source of this anomaly is in the Precambrian which in this area is covered by Potsdam sandstone and the Theresa Fm. The anomaly is probably due to a granitic gneiss in the Precambrian but would be of little interest as a magnetite source.

A magnetic traverse over the Brand Pinacle aeromagnetic anomaly on the Loon Lake aeromagnetic map indicates a 12000 gamma anomaly. Anomalies of this magnitude are rare and a reasonable interpretation is a shallow local magnetite concentration in a granite gneiss host rock.

The most interesting anomaly is located at Star Lake in the Twin Lakes area. Several magnetic traverses were conducted across the Twin Lakes anomaly to reveal a 13000 gamma anomaly. This anomaly located near the closed Benson Mines magnetite mine is probably the most promising as a source of magnetite.