Comment
Author: Admin | 2025-04-28
Simplified - High School Level ExplanationThe Sterling and Franklin deposits are fabulously rich in zinc (more than 20%) by weight, and also in iron and manganese. Both deposits are quite large: the Sterling mine in Ogdensburg produced more than 11 million tons of zinc ore, and that at Franklin twice as much. More than 365 different mineral species have been found in these two mines, placing the Franklin-Ogdensburg area in the top five most mineralogically complex localities on Earth.Zinc has been used since the 10th century BC, primarily for making brass, a copper-zinc alloy. Today, it has many uses including, plating steel to prevent corrosion (galvanizing), and manufacturing batteries, paint and other consumer products. Mining of our local zinc deposits began sometime before 1739, but exactly when and by whom is no longer known. However, because none of the three principal ore minerals (franklinite, willemite, and zincite) were as yet known to science, they had no way of understanding the nature of these deposits. Since then the number of scientific publications related in some way to these mines has grown to more than 1,000. Yet, despite more than 200 years of scientific inquiry, only recently has a consensus emerged on their origin.The zinc minerals at Franklin and Ogdensburg are wholly encased in a geologic unit called the Franklin Marble, which underlies much of the Wallkill River valley between Sparta, New Jersey on the southwest and Warwick, New York on the northeast and is about 1.3 billion years old. These unique deposits are exceptionally rich in zinc and no similar deposits have been found anywhere else on Earth.It is now generally accepted that the ore deposits at Franklin and Sterling Hill originated as hot, metal-rich fluids that were discharged onto the floor of a shallow sea about 1.3 billion years ago. The sea floor at that time was covered by white calcium carbonate muds, similar in many respects to the Bahama Banks today. In the illustration below, we see, in cross section, an oceanic plate at right colliding with a continental plate at left, which created fractures in the rock. Because oceanic crust is significantly denser than continental crust, the result of such a collision is that the continental plate overrides the oceanic plate, which then dives or “subducts” beneath the continental plate. Partial melting of the oceanic plate as it descends beneath the continental plate gives rise to a chain of volcanoes, which form from different kinds of magma (melted rock). When the magma reaches the surface through the fracture zones, it is called lava, which, depending on the minerals can range in color from black basalt (mafic) to very light granite (felsic). Mafic magma is rich in iron and magnesium and denser than felsic magma, which is rich in silica and aluminum. Hot, metal-rich fluids (hydrothermal fluids in the illustration) also ascended and erupted onto the sea floor, and formed layers of metal-rich muds. This was the situation about 1.3 billion years ago, when the carbonate muds and the
Add Comment