Shaft 7, Delaware Aqueduct, Town of Fishkill, Dutchess County, New York, USAi

Regional Level Types
Shaft 7	- not defined -
Delaware Aqueduct	- not defined -
Town of Fishkill	Township
Dutchess County	County
New York	State
USA	Country

Shaft 7 is located at the northern edge of a range of highlands, underlain by Precambrian rocks, mostly granulite facies gneisses, known as the Hudson Highlands, a subdivision of the more regional Reading Prong. It is not the locality of the minerals credited to it but one of several entry points for construction of the New York City water system's Delaware Aqueduct. From Shaft 7 the North Tunnel extended northwestward toward Newburgh, NY and the South Tunnel was driven southeastward toward Shaft 8. These tunnels met similar headings being driven from other entry points.

The Delaware Aqueduct was constructed before the widespread use of tunnel boring machines. Drilling and blasting made the rock much more accessible. The principal mineralogical source is Zodak (1941). It should be noted that survey station designations scattered through the text, for example 1887+54, are keyed not to the shaft but to the beginning of the project at the Rondout Reservoir.

The most interesting mineral discovered in that section of the aqueduct excavated through Shaft 7 is an axinite group species, probably axinite-(Fe). It was found with calcite in vuggy fractures in pegmatite. Zodac (1941) visited the South Tunnel in mid-April, 1940 when it had been driven approximately 4000 feet southeast from the shaft. Near the end of September the heading had advanced to a little more than 7100 feet. Assuming specimen material was recovered as the tunnel advanced the axinite locality is estimated to be approximately 5000 feet southeast of Shaft 7, beneath the area near Van Wyck Lake Road and the Fresh Air Fund's Sharpe Reservation camp. Rocks exposed at the surface in this area include the Cambrian Poughquag quartzite and the Wappinger dolomite but neither of these younger formations extends deep enough to have been intersected by the tunnel.

The information in Zodak (1941) suggests that the the axinite locality was no more than a couple hundred feet beneath the contact with Paleozoic quartzite and dolomite. Fractures were numerous and the Timp Pass fault, a regional thrust fault, is nearby. Precambrian rocks in the general area included thin bands of impure marble and skarn. Beyond these generalities the details of the geologic relationships between lithologies, fractures and fluid flux are not decernable.

Other Regions, Features and Areas containing this locality

References