The sulphide horizon ranges up to 40 feet thick and contains elevated concentrations of pyrite, pyrrhotite, chalcopyrite and molybdenite. Another interesting aspect of the ore deposit worked by the Edison mine is a sulphide-rich horizon. The most dramatic icon of these parallel bands is the Horseshoe cut with its 2 narrow, parallel cuts separated by a mass barren material. Ore at the Edison mine was extracted from 2 parallel bands of magnetite-rich gneiss, each approximately 40-50 feet thick and 50-75 feet apart. However, recent evidence (Puffer and Gorring, Canadian Journal of Earth Science 42(10): 1735–1748 (2005)) suggests that the K-spar gneiss that hosts the Edison mine ore may be a meta rhyolite. Although K-spar gneiss is a fairly common lithology in the northwestern highlands most has been interpreted as meta arkose. The typical grade of this ore was 12 – 14% Fe. The magnetite-rich bands are concordant with the foliation of the gneiss indicating that it is a premetamorphic feature. Magnetite was contained in a potassium feldspar gneiss. The Edison mine exploits a type of ore that is unlike that of most of the great many iron mines that dotted the Reading Prong highlands of New Jersey as well as adjacent New York and Pennsylvania. Because there was a railroad spur to the site it became a tourist destination because it combined the scenery of the hills and forest with the industrial progress that was so highly valued in that era. Because it was remote from the established towns, by the standards of the time, it included housing for the workers and was the first populated place in the area with electricity and electric lights. The Edison mine was a large industrial enterprise even by today’s standards. The Edison mine workings were superimposed on some of the older mines, mainly the Ogden and Roberts. ![]() The most extensive tract of ore with an adequate grade for the project became the site of the Edison townsite, the mill and the two major ore producing quarries. The small mines were opened on local, relatively high grade areas, within an extensive area of low grade magnetite-bearing rock. The mine site was chosen after an extensive dip needle (sort of a crude magnetometer) survey of zone that contained numerous small iron mines and exploration trenches. ![]() The idea was to mine relatively low grade iron ore, cheaply from surface open pits, concentrate the magnetite and form it into briquette heavy enough to be blast furnace feed. Edison invested approximately $2 million of his own funds and another million of investor money. The Edison Mine was developed in the 1890’s by Thomas Edison. ![]() This mine incorporated several of the earlier Ogden group mines. Here he applied his inventions to concentrate magnetite into briquette but almost went bankrupt when the Mesabee Range deposits were discovered in the mid-west. Edison was a respected inventor of mining technology, including beneficiation machines. This mine was owned by the New Jersey and Pennsylvania Concentrating Co., an enterprise of Thomas Alva Edison. A former Fe mine in magnetite ore located 2 to 3 miles SE of Ogdensburg in Sparta Township.
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