Cornwall Mines (Cornwall Iron Mine), Cornwall Borough (Cornwall), Lebanon County, Pennsylvania, USAi

Regional Level Types
Cornwall Mines (Cornwall Iron Mine)	Group ofMines
Cornwall Borough (Cornwall)	Borough
Lebanon County	County
Pennsylvania	State
USA	Country

Originally, a series of three open pit mines (Big Hill, Middle Hill, Grassy Hill) with underground openings, located at Cornwall, near Lebanon. Started in 1732 and owned by the Cornwall Ore Banks Company (1864) and later, the Bethlehem Steel Company.

Lapham (1973, including Plate 22) notes that in the 20th century, 2 major deposits were being worked: the western by the open pit and underground No. 3 mine, and the eastern by the No. 4 mine. Much of the operation came to an abrupt halt in June 1972 when floods from Hurricane Agnes flooded the underground mines. Neither underground operation was reopened.

Smith et al. (1988) note that more copper-, cobalt-, and possibly gold-rich ore with substantial by-product iron was actively pursued from the eastern end of the open pit until June 30, 1973. The smaller, footwall orebody beneath the eastern end of the open pit was never mined, but may contain as much as 0.006 ounce (0.23 g)/ton Au. The orebodies consisted of replacement of contact metamorphic skarn by slightly later copper and iron-bearing hydrothermal fluids. The ore-bearing fluids may have been derived in part from the Triassic, York Haven Diabase, which forms the footwall to the larger orebodies (Rose et al. 1985). Certainly, the diabase served for the heat engine.

Smith et al. (1988) report that the total ore production known is 106,000,000 tons of recovered ore with an apparent grade of 0.4 % copper. From 1908 to 1973, the period for which records could be found, 67,000 ounces (2.53 t) of gold were recovered and 443,000 ounces (16.75 t) silver. Recovered pyrite concentrates contained 1.1 % Co and 0.1 % Ni. This is the type "Cornwall Type" iron ore deposit.

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