Feltville Copper mine, Glenside Park (Feltville), Watchung Reservation, Union County, New Jersey, USAi

Regional Level Types
Feltville Copper mine	Mine
Glenside Park (Feltville)	Park
Watchung Reservation	Conservation Reserve
Union County	County
New Jersey	State
USA	Country

Located across the Blue Brook ravine and a few hundred yards east from the abandoned village of Feltville.

Most of the copper concentrations associated with the Orange Mountain (First Watchung) Basalt (OMB) are localized in hydrothermally altered sediments immediately beneath the basalt and in fissure veins within the basalt. This group includes the American mine, the Chimney Rock mine and others. The Feltville Copper mine is one of several small copper prospects located in scoracious rubble at the very top of the OMB and/or in the immediately overlying carbonaceous sediments of the basal Feltville formation. The local occurrences of copper minerals at the top of the OMB is presumably due to two factors: (1) the presence of a fracture or fracture network transecting the OMB that had a high enough hydraulic conductivity to allow oxidized copper-bearing fluids to pass quickly enough through the basalt so as to arrive at the base of the Feltville formation with a portion of its copper load still in solution and (2) the presence of gray to black carbonaceous detrital and calcareous sediments in the lower Feltville.

All the copper mineral concentrations associated with the OMB are variations on red bed type copper depositing systems (There's a huge literature on this). Copper (and silver) is soluble in oxidized saline fluids, the sort of fluids one would expect constituted the formation water in the thousands of feet of red Passaic formation sediments that underlie the OMB. Red bed type copper mineral deposition occurs where migrating oxidized brines encounter a more reduced chemical environment. The reduction mechanism associated with the OMB was relatively sluggish and so, locally, oxidized fluids reached the top of the basalt. There the fluids encountered a sharply more reduced environment. It is also likely that the formation waters of the Feltville were significantly less saline than those originating from the Passaic red beds. The marked redox change and the probable dilution of salinity were very effective mechanisms to wring out much of the remaining copper that had managed to transit the OMB.

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