1 Geophysics/Tectonophysics/Seismology (Posters)

A GEOPHYSICAL INVESTIGATION OF BENSON MINES, STAR LAKE, N.Y

Paper number: 1-5
Program: Technical Sessions

Authors

Abstract

In 1950, Benson Mines at Star lake, New York was the largest open pit magnetite iron ore mine in the world. In 1978, Benson Mines was closed causing 470 people to lose their jobs and a whole community was lost. Local school enrollment decreased from 1400 students to 625 and many teachers lost their jobs and the local hospital lost nurses and doctors. Since the closing of the mine in 1978, the mine has filled with water to a depth of 300 feet. A permanent seismic station (STLK) was installed within 10000 feet of the mine and portable seismographs were deployed periodically to detect induced seismicity at the mine. No significant induced seismicity has been detected as occurred in the Mineville area in the eastern Adirondacks.

Last summer, fifty-three gravity and magnetic measurements were made at 528 feet intervals around the 5.0 mile perimeter of the mine. This research was initiated as an undergraduate research project to determine if any significant amounts of magnetite remained in the mine. A magnetic survey conducted at Ameba Pit (now a lake) in the area of highest grade ore revealed a 3000 gamma magnetic high with a steep magnetic gradient indicating a shallow source. Two north-south magnetic and gravity traverses were conducted along the eastern and western sides of the open pit mine. The magnetic profiles indicate magnetic anomalies as large as 12000 to 16000 gammas. The gravity anomalies were as high as 75 gravity units and correlate well with the magnetic anomalies. These anomalies indicate significant amounts of magnetite are present in the subsurface and steep magnetic gradients indicate it is at a shallow depth.