Geology of the New York City Region

19. The Franklin and Ogdensburg Mineral Resource Area

The region around Franklin and Ogdensburg in Sussex County is one of the most famous mineral and mining districts in North America. The bedrock has yielded more than 330 different mineral species, more than any other mineral locality on Earth! Many minerals are known only from this area. Its wealth of zinc ore is responsible for the nickname "The Fluorescent Mineral Capitol of the World." The two destinations for day trips are the Franklin Mineral Museum and the Sterling Zinc Mine. Both sites include museums with displays of fluorescent minerals and mining equipment, including displays documenting the history of mining development of the area. The Franklin Mineral Museum (Figure 43) provides access for rock collecting in the Buckwheat dump, a great pile of rock tailings from the abandoned open pit and underground mines in the vicinity. The Sterling Mine offers underground mine tours which examine the methods used and the history of the mine. It also includes a look at the "Rainbow Room," a mine passage which intersects a vein of unmined zinc minerals that are illuminated briefly with ultraviolet light on every tour. Both sites are open to the public from late spring until early fall. Both also charge a moderate admission fee. Figure 44 is a map showing the location of mines in relation to the bedrock geology of the mining district.

Figure 43. The Franklin Mineral Museum.
Figure 44. Map of the Franklin mineral district (after Paleche, 1974).

The zinc and iron deposits occur as mineralized zones within the Proterozoic age Franklin Marble. The marble crops out in a long, narrow belt (about 5 miles long and a half mile wide). The marble belt is complexly folded. The major ore veins occur on both sides of plunging synclines within the marble. The marble belt is bounded on the north by granitic gneiss of Proterozoic age that crops out throughout a band of hills along the western border of the highlands. In this region the hills are called Hamburg Mountains on the northern side of the Reading Prong extending from around Sparta, New Jersey northward into New York. The south side of the Franklin Marble belt is a northeast trending graben of Cambrian age Hardyston Quartzite overlain by limestones of the Ordovician Kittatinny Group.

The primary zinc minerals in the area are willemite, franklinite, and zincite. Willemite, a zinc silicate and a primary ore mineral in Franklin area mines, fluoresces an intense bright green under ultraviolet light (see Figure 45). The host rock for the ore bodies is typically a fluorescent variety of calcite that fluoresces bright orange-red under ultraviolet light. Samples of these minerals are the showcase pieces in fluorescent mineral displays in museums around the world.

Figure 45. The common minerals of the Franklin mineral district, under white light (a) and under short-wave ultraviolet light (B) -- minerals are: franklinite (black), willemnite (green), and calcite (red).

The mining district has a long and rich history; highlights are as follows. The earliest reports of this area suggest that ores of iron and zinc were being mined before 1750. The early Dutch miners thought the reddish-brown ore was a form of copper. The first large operation was the Ogden Mine which opened in 1772 and supplied a charcoal furnace in Sparta. The "Lord Stirling Pits" also opened in 1772, and was named by the developer, Lord Stirling (William Alexander, a Major General in Washington's Continental Army). Lord Stirling's mining ventures failed because, like the Dutch miners, he attempted to extract copper and iron from the zinc ores.

Ogdensburg owes its name to the town Patriarch, William Ogden, who settled the valley; he and his wife had 22 children in the process. One of his daughters married Dr. Samuel Fowler, the owner of Mine Hill which includes the Franklin ore body, and eventually, the Sterling Hill Mine. Fowler was also unsuccessful in capitalizing on his mining investments because he was unable to adequately separate the different metals within the ore. His one success was to develop a zinc oxide-based paint to substitute for lead-based paint. This was the first practical use of the zinc products, and in retrospect probably saved the health of thousands, if not many millions of people!

From the early 1800s through the Civil War the most important product of the mines was iron (magnetite ore). Just before the Civil War practical uses for alloys of zinc were discovered, and the zinc industry began to prosper. After a series of legal battles, the mining district was united under the New Jersey Zinc Company. Full development of large capacity mining operations of the Sterling Mine and Mine Hill began in 1897. Thomas Edison invested $3.5 million in an iron mining and milling project, but his efforts were largely unsuccessful due to competition with the development of large iron deposits in Minnesota. A mill began operation in 1900 capable of processing 1500 tons of ore daily. Production rates from all area mines were fairly steady until mining ceased in the 1980s. The Franklin area mines remained in the top ten producing zinc districts through most of the twentieth century. The high maintenance costs, the exhaustion of the large ore veins, plus the dramatic drop in the price of zinc resulted in the end of mining operations in 1986.

The ore deposits at Sterling Hill were mined to a depth over 2,700 feet (well below sea level). During the history of mining many fissures were encountered causing serious flooding problems. Pumping the groundwater out was a constant expense of operating the mines. Once the pumps were shut off water eventually filled the underground mines to near surface level.

Return to the Highlands Province Main Page.
Continue to the next page. Return to Main Page
The URL is:
Last modified: 3/11/2019