Gold Occurrences in Pennsylvania

Pennsylvania has a long and rich tradition of mining especially for anthracite and bituminous coal as well as iron. What is not generally known however is the state is also produced a considerable amount of gold. It has a well-trained workforce of miners many of whom have a tendency to be prospectors. Because of this some iron miners down around Cornwall have actually produced more than 61,000 ounces of gold while they were mining the magnetite iron ore. Aside from the mine at Cornwall another mine that reportedly produced gold from magnetite was the Grace mine in Morgantown.

There were a series of three openings to the iron deposit in Cornwall located at Big Hill, Middle Hill and Grassy Hill that were originally owned by the Cornwall Ore Banks Co., but were eventually owned by Bethlehem Steel who eventually closed the mines in 1979.  This deposit of magnetite was produced by the replacement of limestone by hydrothermal activity during the Jurassic from a diabase intrusive, so in effect the deposit is a skarn.

The eastern part of the state is covered with crystalline rocks producing potential gold lodes as well as placer gold. This gold weathers out of the crystalline rocks and is collected in the rivers and streams of eastern Pennsylvania. This is not the only source of gold however, in the northern part of the state the last glacier left placer gold in the terminal moraines found in Pennsylvania.

There are several streams producing placer gold that came in Lancaster and York Counties in glaciers that have advanced into the state during the past million years. Any of these glaciers were capable of bringing gold down from Canada where one of the richest gold belts the world the Abitibi is found in Québec and Ontario. According to some geologists there have been as many as 24 episodes of glaciation that have affected the northern part of the United States in the past 2.5 million years.

Although the eastern part of the state is mostly covered with crystalline rocks that produce gold as lode gold that weathers out so it becomes placer gold that collects in the rivers and streams found in eastern Pennsylvania.

One of the places where gold has been found is along the Susquehanna River where it has been found as both nuggets and flakes of gold. Generally Wyoming County has been a good place to look for gold as well as in the surrounding counties.  In York County  placer gold is associated with the deposits of diabase that make up the tops of many ridges. The action of weathering releases the gold from bedrock allowing it to migrate downhill into the streams and rivers in the area.

During the Civil War the great battle at Gettysburg was fought on some of these diabase ridges with names like Little Round Top or Cemetery Ridge. There is no doubt that the rivers and streams around the Gettysburg Battle Site undoubtedly contain gold. 

The best way to find out where the gold is in Pennsylvania is to research old newspapers and town histories.  The state only keeps track of commercial mining operations and not that of individual prospectors. Old newspapers are often the source of stories about where one of the local citizens has found gold in their town.

Helpful Links:

Gold Pennsylvania prospecting, http://www.e-goldprospecting.com/html/gold_pennsylvania_prospecting.html

Eastern Gold, http://doccopper.tripod.com/gold/easternAu.html

Jeri Jones http://www.jonesgeo.com/home.htm

http://home.epix.net/~prospect/index101.html

There are several gold prospecting clubs that are active in Pennsylvania that can supply more information about Pennsylvania gold.

Our thanks to Stephen Shanks of the Pennsylvania Geological Survey for additional information.

Gold in quartz veins

Gold is often found associated with milky hydrothermal quartz that is called “bull quartz. Although gold has many other associations with base metals this is its association with iron pyrite (fool’s gold). Gold is found with many other metals and ores. One common association is with iron ore where it is often found in association with granular magnetite. This is a common occurrence in places like Nova Scotia and the Cornwall, Pennsylvania iron mines.

The common way gold in quartz is found is when hydrothermal water with both gold and quartz percolate up through the fissures in bedrock that is hot enough to hold both minerals dissolved in solution. Both minerals drop out of solution when the water cools. Quartz falls out of the solution first. The speed of the dissolution can be judged by the size of the quartz crystals. Basically, the larger the crystals the slower the hot fluids cooled. Gold is one of the last minerals that to come out solution. Gold is one of the last minerals the last minerals to be deposited out of solution.

There are several other minerals that are likely to fall out of the solution first, quartz is only the first of many. Other common minerals that are apt to be deposited ahead of gold are galena lead sulfide, sphalarite zinc sulfide and bornite a sulfide of copper and iron that is called peacock ore. Gold is usually found as an encrustation on other minerals that form in the spaces in the quartz matrix. Quartz containing gold is called by miner’s “bull quartz” a milky quartz having the crystal faces obscured in the body of the rock.

They are there none-the-less you just can’t see them with the naked eye however, they can be seen by using an X-ray Diffraction Spectrometer. These are usually called “Powder Cameras” by the geologists that use them. They work by mixing the powdered mineral with caladium, a mixture of acetone and nitrocellulose. They are then formed into small rods containing the powdered mineral that are placed in the X-ray beam. By photographing these rods with a special X-ray camera using a photographic plate that shows the resulting diffraction patterns of each mineral. Every mineral has a distinctive diffraction pattern that is used to identify it just like fingerprints.

Gold can be found in just about any rock, sometimes in specks that are too small to be seen with a conventional microscope. They are only seen with an electron microscope. These deposits are diffused into the rock and weren’t discovered until the 1970s. These deposits hold enough gold as tiny specks to be economically viable.

One such mine is the Carlin mine operated by Newmont Mining in northern Nevada. Another mine is one the author tried to get control of in Mexico years ago where the gold was diffused through marble as equally tiny specks. We discovered the deposit had the potential of producing several billion dollars worth of gold, except the owners were not willing to sell the property.

References:

Gold Reef Mining, Wikipedia, http://en.wikipedia.org/wiki/Quartz_reef_mining

Igneous Geology of the Carlin Trend, Michael W. Ressel, et al, Geoscience World, http://econgeol.geoscienceworld.org/cgi/content/abstract/101/2/347

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