THE GENESIS OF THE HOPEWELL BARITE ORE DEPOSIT IN RELATION TO THE LATE-JURASSIC EXTENSIONAL TECTONIC ACVITY, NEWARK BASIN

The hopewell barite mine, located in the Newark basin, is hosted in the Jurassic diabase. Barite occurs mainly along the NE-SW trending faults that are roughly parallel to the regional hopewell fault.

The δ³⁴S_SO4 values of barite range from +17.1 and +17.3‰, which fall within that of the Triassic-Jurassic seawater sulfates (13 - 20‰). The δ¹⁸O_SO4 values of barite (+15.1 to +15.5‰) also fall within the Triassic-Jurassic seawater (13 - 17‰). Although, the S-O isotopic signature of barite is similar to that of the Triassic-Jurassic seawater, the latter is not the source of sulfur for barite. Sulfur of barite did not derive from the magma because the sulfur isotopic composition of barite does not fall into the range of igneous rocks (-1.0 to +4.0‰). Therefore, sulfate derived from the dissolution of sulfates carried by streams to the lake. These dissolved sulfates were trapped within the sediments.

During the Late Triassic-Jurasssic extensional tectonic activity, a deep-seated, barium-rich fluid migrated from deep parts of the basin towards the borders through major faults (e.g. Hopewell fault). At the site of deposition, the barium-rich hot fluid mixed with a shallow, cooler, sulfate-rich fluid leading to the precipitation of barite in the intensely fractured diabase.