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The term "hydrothermal activity" simply means that hot fluids flowed through the rock and left some evidence that they did. Yellowstone National Park (photo on the right, Dr. D. 1983) is an example of hot fluids flowing through rock. Obviously geysers are not part of the current Herkimer mining district at present. The question is "did hot fluids flow through the Herkimer host rock in the past"?
If hot fluids did flow through the rock then some evidence would be left behind, if it hasn't been erased by the actions of weather or man. On this web page is presented such possible evidence. It is expected that, with the help of those in the field, additional samples and photos will be added to this evidence.
If hot fluids moved through the Herkimer district then these fluids would have left "signs" in the rock. The most obvious of these signs is highly altered rock, rock that has been changed by the hot fluids. Is there evidence of this in the Herkimer mining district?
Photo 1: Very bleached white rock, almost like pumice and nicked named that by some miners. The is a 3 foot wide boulder moved during heavy equipment work at DA, 2009.
Photos 2 and 3: The edge of a vug with a rounded phase 1 calcite (from TCR, 2010). You can see the leaching texture at the arrow where many holes can be seen. A close up of this testure is seen in photo 3.
Photo 4: In some instances the leaching of the rock is so intense that there is no rock left behind, just a skeleton of quartz. Imagine the material in photo 3 with all of the brownish red rock gone. Sample from TCR, donated by the mine owners, 2010.
Photo 5: This shows the intense leaching that is often seen with the baby floater druze phase. Note how "crumbly" the rock looks just left of the label. See also the baby floater page.
Is there evidence of a form of quartz in the Herkimer district that we have seen elsewhere in New York associated with hydrothermal activity (Ellenville, NY see photo below right)?
Below left is a photo of needle druze (blue arrow) over the common pyramidal druze (white arrow). Note the etching (or hydrothermal leaching) of the earlier quartz. The pyramidal quartz does not look like much other than a bunch of grey blobs. The sharp brilliant faces are mostly absent (see the druze page for unaltered druze photos).
In Illion NY, just a few miles west of Herkimer, is an area that has the remains of travertine like material - as seen in the photo below. Photos to the right and left are from active hot springs in Yellowstone.
W. David Hoisington, Ph.D.
Laboratory Evidence
The paper above is an important piece of research that indicates mineralization episodes occurred before and after the Herkimer diamonds. This is similar to the field evidence in the Herkimer deposits (see minerals link at the top of the page). In addition the researchers suggest that the Herkimer diamonds and the the formation of anthraxolite are linked to later fluids with a temperature at about 200 degrees C. Given the variation in the intensity of host rock alteration that is observed in the field, it could be that the temperature (and or the chemistry) of the fluids varied across the district.
Needle Druze Evidence
Travertine Evidence
Heavily Altered Rock Evidence
Aug., 2011
