Tales of the Devil: Origin of the Rowe Schist

The earth movements that affected the Appalachian Mountains after the Taconic Orogeny   USGS

During the late Cambrian and early Ordovician a series of turbidite flows came down the continental slope of the North American craton.  This was the origin of the Roweschist formation.  Turbidites are also good sources of gold ore.  There are several examples of this kind of formation worldwide with the Witwatersrand of South Africa being the most notable.  Much of the gold ore from Timmins, ON is another example as are many of the deposits of the world.  To date the Witwatersrand has produced around 40% of the entire world’s gold supply in the past 40 years.  The gold mines found here are some of the deepest in the world that now are approaching 13,000 feet deep.

Earth movements associated with the Taconic Orogeny during the late Ordovician caused this layer of turbidite to be shoved to its present location close to the Iapetus Suture zone that locally in Connecticut and New York is called Cameron’s Line under differing names it reaches to the mountains of western Norway.  It is truly one of the largest suture zones on earth.  By definition a suture zone is also a subduction zone where rocks of oceanic origin are forced under the continental margin.  Cameron’s Line is about two miles west of the Rowe schist the formation that underlies the property belonging to the finder of the Whodunit Mine.

According to the USGS the following illustration graphically explains the Taconic Orogeny an Alpino type orogeny, a long narrow belt of mountains that formed the Taconic mountain range.  This is the orogeny that initiated the first of several mountain building events that occurred in the Northern Appalachians.  This is the orogeny that had the greatest effect on the Litchfield site.

The site itself is composed of a series of turbidite flows that flowed down the continental slope into a back arc basin behind the island arc.  This was composed of the sand and mud component illustrated in the first of the illustrations shown of the below diagram.  The Hoosac Schist on the landward side of Cameron’s line is represented by the portion marked sand.  The continental crust is represented by the Precambrian rock north and west of the site on the landward side of Cameron’s Line. 

Cameron’s Line is where the Hoosac schist and the portion marked sediment meet in a long suture line that extends from Staten Island, NY that was broken in half after the Atlantic Ocean opened during the Mesozoic and after passing through Ireland, Scotland eventually ends in the mountains of northern Norway.

When the Taconic Orogeny ended the mountains that rivaled the Himalayas in height were completely eroded away to a flat plain we know as a peneplain.  There were small mountain building events that occurred during the Silurian that although they affected the local area were so small as to be hardly noticed.  The next big event that affected the eastern seaboard occurred during the Devonian called the Acadian Orogeny.

The Acadian Orogeny produced a different type of mountain range that was much broader then the Taconic Orogeny that to geologists is a Hercyanian type orogeny that was caused when Europe sideswiped the North American Continent.  It was during this event that the Rowe schist was intruded with molten magma causing it to become a type of rock called granofels.  This action caused many secondary minerals to be deposited in the schist ilmenite being the most prominent.  The event also caused further deformation to the Rowe schist.

At the end of this orogeny the Rowe schist has stayed above sea level unlike at the end of the Taconic orogeny as the rocks were eroded smooth the ocean came back to cover the land with ocean water.

Land affected by the Acadian Orogeny.  The original path of Cameron's Line is depicted in red. 

For the most part the only Orogenies that affected the local area were the Taconic, the Silurian (?) and the Devonian.  The later Orogenies affected the lands to the south and east.

Gold Producing Metallogenic Provinces and Epochs (MPE)

There are many metallogenic provinces and epochs (MPE) that can be traced through the formations of various rocks including those particular places and times when gold was deposited. There are at least eight of these episodes that can be found in the Appalachian Mountains of southern Québec. These MPE's can range all the way from the Grenville orogeny that occurred around 1.2 million years ago, and can be traced to different types of orogenies and mineralization to the end of the Permian era. 

A map of selected worldwide ore deposits of metals.
By KVDP

The different MPE's can be directly related to specific orogeny like the Grenvillian or any other orogenic event that has happened in the history of the world. An MPE can be found anywhere on the face of the earth. That means you had better know the geological history of the area where you are prospecting, and remember that some orogenic events left more gold behind them than others.

MPE's are usually associated with a suture zone where one tectonic plate has collided with another. In the case of an oceanic plate colliding with the continental plate the oceanic plate is subducted beneath the continental plate, and about 20 km inside account metal plate there should be a line of granitic intrusions.

The subduction zone acts as a giant heat engine melting the material that has been dragged downward by subduction causing it to become heated to the point the material is melted.  The subducted material is also saturated with water that lowers the melting point of the material, and supplies the water that at depths of kilometers beneath the surface of the earth becomes super heated water that is capable of dissolving many minerals that when they reach the right environment through the action of the superheated hydrothermal fluid are deposited as ore.

A subduction zone.
By A.J. Stern

Searching around in the area that has been intruded one is apt to find gold in the aura of contact metamorphism that is associated with the granitic intrusions. In this case gold is often associated with scheelite, an ore of tungsten in the form of tungsten carbonate. This occurrence is often found where the granite has intruded through an older layer of carbonate rocks such as limestone or dolomite where it forms a skarn..

On the oceanic side of the subduction zone are found many metal sulfide deposits where this whole deposits are usually found in small amounts, but there can also be some really huge deposits of sulfide that are formed this way. These are the result of sulfide deposits that are laid down by black smokers found on spreading centers located on the bottom of the ocean. These deposits are laid down very much like plums in a pudding at the scattered across the bottom of the ocean.

A black smoker at a spreading center at the bottom of the ocean. NOAA

As these deposits are carried away from the spreading center by the action of more magma being injected they cover the ocean bottom with spots where they are eventually subducted beneath a continental plate where they are often reactivated to form secondary mineral deposits sometimes in quantities large enough to form ore deposits.

MPE's are where ore deposits are typically found, and in many cases are considered to be the primary source of mineralization, and they eventually break down to form detrital mineral deposits.