ORIGIN AND GEOCHEMISTRY OF THE MESOPROTEROZOIC FRANKLIN MARBLE, NEW JERSEY

The Mesoproterozoic Franklin Marble, found in New Jersey, is the host rock of many ore deposits including Zinc (Zn), Iron (Fe), and Manganese (Mn). The Franklin Marble originated from the metamorphism of a shallow marine limestone within a hypersaline setting.

Oxygen (δ¹⁸O) and carbon (δ¹³C) isotopes revealed that the Franklin marble was formed in a subduction zone of a tectonically controlled environment that resulted in the metamorphism of carbonate-bearing rocks. The value of δ¹⁸O (20.14 ‰ SMOW) signifies its origin in a closed back-arc basin. The value of δ¹³C (- 0.5 ‰ VPDB) strongly supports the organic source of carbon in marine environment.

Chemical analysis using FUS – ICP indicates that the Franklin Marble is the host rock of metals and rare earth elements (REE) including Ba (45 ppm), Sr (649 ppm), Y (11 ppm), Sc (6 ppm), Zr (5 ppm), and V (15 ppm). The high concentration of Sr along with the presence of REE strongly support the hydrothermal activities of the magmatic intrusion in a shallow marine setting. Consequently, the Franklin marble was altered from the pre-existing limestones by the presence of these hydrothermal fluids and tectonic activities.

This study concludes that the formation of Franklin Marble has passed through stages of deposition of the carbonate facies in a shallow marine environment, infiltration of magmatic hydrothermal fluids through the pre-existing pore spaces and fractures in the sea floor, and subsequent tectonic events during the Grenville Orogeny that resulted in the formation of medium pressure to high temperature Franklin marble in the New Jersey Highland.