Ahles Mine (Osmun-Robeson Mine; Pequest), Oxford Furnace, Oxford Township, Warren County, New Jersey, USAi

Regional Level Types
Ahles Mine (Osmun-Robeson Mine; Pequest)	Mine
Oxford Furnace	- not defined -
Oxford Township	Township
Warren County	County
New Jersey	State
USA	Country

A Fe occurrence/mine located about 1 mile North of Oxford Furnace near Oxford. Features a shaft started 1901 to a depth of 168 feet. Two additional shafts added 1902 + 760 feet of drifts. Slope to 200 foot level sunk in 1907; 1,800 foot drift to No. 1 shaft in 1908. #3 shaft to 250 foot level.

The Ahles mine was the largest of a group of manganiferous iron deposits found in the Grenville age marble near Oxford. The group included the Little, Riddle, Queen, Osmun and Raub mines in addition to the Ahles. The Ahles mine was probably the last significant iron mine in New Jersey to be started from scratch. Shaft sinking began in 1901. Neither the Ahles nor any of the other of these ore deposits was described in adequate detail while they were in operation although the Ahles was still operating when Bayley (1910) wrote “Iron Mines and Mining in New Jersey”.

The ore of all the mines in this group was deeply weathered and consisted of magnetite and “ocherous” limonite. The ore had to be washed and in some cased the limonite was sold for paint pigment. The magnetite contained significant manganese as did the limonite where it occurred as concentrations of black oxide(s).

Less is known about the unweathered ore. Bayley describes dump material from the Little mine as being marble containing varying concentrations of magnetite. As the carbonate weathered away it left a voluminous residue of limonite and Mn oxide. The ore of the Ahles mine was locally “cherty” and “gashed”. Samples of this material, seen by this author, consisted of anhedral magnetite grains in dense, yellowish brown, fine-grained quartzite. This material contained numerous small, angular cavities lined with very finely crystalline quartz and partially filled with botryoidal manganese oxide. Analysis of an egg sized grab sample showed that it contained approximately 14% MnO.

The Ahles mine is very near the southern margin of the area underlain by marble. The country rock is a very siliceous marble. On the south, footwall, side of the orebody the rock grades into gneiss within a short distance. In the other mines, located more distant from the contact with gneiss, the orebodies are, in many cases, described by Bayley as being between “walls of ferruginous clay” or “compact sandstone”.

The Raub mine was similar to the other mines in the local area underlain by marble except that it was located near the northern limit of the marble and the western end of the orebody contained some sphalerite. A short distance west of the Raub mine some exploratory digging for zinc was done. In the 1930’s sphalerite and galena were reported from the Edison marble quarry, which by that time had swallowed the area of the zinc prospect.

The iron ores of the Ahles mine and other mines in the nearby area appear to be stratiform, synsedimentary features that were originally composed of manganiferous iron oxides and carbonates with local concentrations of silica. Once metamorphosed the ores were manganiferous magnetite in iron-manganese rich carbonate gangue. These ores were deeply weathered with accumulations of clay and siliceous residues at their margins.

The relationship of the sphalerite and galena to the iron ores and the marble is not known. This author is unaware of any existing outcrop or preserved samples. It may be that the lead/zinc and iron are coeval. Examples of this sort are known in the Grenville of Quebec. This author believes that it is more likely that the lead/zinc is a Paleozoic (Permian?) fracture filling, part of a widespread hydrothermal overprint on the entire region.

Other Regions, Features and Areas containing this locality

References