MAGNETIC ANOMALY MAPPING AND SUBSURFACE MODELING OF HINCKLEY RESERVOIR, HINCKLEY, NY

A dam on West Canada creek at Hinckley, NY forms a ~10 sq km lake, Hinckley Reservoir. The lake overlies the western boundary of the Proterozoic Adirondack massif with Ordovician carbonate rocks of the Trenton , and the western end of the lake resides over Quaternary sand deposits. The Proterozoic rocks mostly consist of highly sheared granitic gneiss of the Piseco shear zone, however, less voluminous mafic layers have been mapped within the shear zone immediately to the east of the lake. Finally, Hinckley Reservoir and the West Canada Creek form an E-W lineament that was previously interpreted as the eastern extension of the Trenton fault (a fault that traces westward from Piseco Lake, through Hinckley, Trenton and the village of Holland Patent).

To better understand the complex geology beneath Hinckley Lake, a high-resolution magnetic survey was conducted to produce a magnetic anomaly map and model the subsurface. The field survey utilized a GPS linked, magnetic gradiometer, and an inflatable motor boat. The survey involved a zig-zag track followed by length-wise survey lines for a total distance of 67 km. More than 36000 data were collected at a rate of 5 readings per second and 1.7 m average spacing. The survey time was ~3.5 hours, and repeat readings were collected several times at the same location to correct for diurnal variation. The magnetic data was cleaned to remove incomplete reading due to instrument error and contour anomaly maps were generated. A magnetic anomaly of about 300 nT defines a pronounced magnetic lineament with a trend of 085. This magnetic lineament is parallel to the long axis of the lake and extends into West Canada creek. The north and south sides of the magnetic lineament show high and low anomalies respectively. This lineament most likely represents the trace of the Trenton fault, separating Proterozoic rocks with varied ferromagnesian mineral content. There is a low regional magnetic gradient (~100 nT) that crosses the entire lake and most likely represents the location of Paleozoic cover rocks that progressively thicken westward.