A HIGH RESOLUTION GEOLOGIC MAP OF THE STERLING HILL MINE

Sterling Hill Mine is a historic zinc and iron mine located in Ogdensburg, NJ; and is part of the western New Jersey Highlands. The deposit has been mined since colonial times. From its beginnings to its closure in 1986, it yielded over 11 million tons of zinc ore. Ore minerals include primarily zincite, franklinite and willemite. The primary structural feature of the deposit is an overturned synform plunging steeply to the northeast at approximately 45 degrees. The Sterling ore body has been interpreted as a sedimentary-exhalative deposit, dating to the Mesoproterozoic (~1.1 GA). It consists of a complexly folded and faulted tabular orebody hosted by white graphitic marble, known as the Franklin Marble.The current study has been made possible by recent removal of great quantities of soil and fill that originally covered a large portion of the rock sequence. A complex assemblage of silicates and marbles stratigraphically below the ore, and near the nose of the fold has been unearthed. No fewer than three distinct marble units have been identified one consisting of dark gray calcite with microinclusions of copper, sulfur and lead; another containing orange to pink calcite enriched in REEs in addition to elevated levels of manganese, and a third in close proximity to the ore, stained red-brown with high concentrations of manganese. Three silicate units have also been identified. The first of these is a calcium-silicate layer in contact with the marble-hosted ore; a biotite rich gneiss with magnetite and minor apatite; and an amphibolite gneiss with large (2-3 cm) apatite crystals. Finally, there are several “biotite pods” located along a similar stratigraphic horizon, each containing large quantities of massive biotite and hornblende. A major goal of this project was to create a high-resolution geologic map of the exposures of the Sterling Hill Mine, since one does not yet exist. An RTK (Real Time Kinematic) GPS receiver was used for the survey, with accuracy generally of an inch or less, without the need for post-processing. Maps were created using ArcGIS software.