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Evidence for hot, Cenozoic sulfide mineralization in the Central Appalachians of PA
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Searching for pyrite and quartz veins in the overturned Juniata formation, D. Gold on the rocks, A. Sicree, R. Mathur and L. Mutti conference near the car. |
In the spring of 2003 the Pennsylvania Department of Transportation
uncovered pyrite rich veins that cross cut Late Ordovician and Early Silurian
age rocks during the construction of a corridor for route I99 near State College,
Pennsylvania. Exposure of the sulfide rich rock to the atmosphere led to a serious
acid rock drainage issue for local citizens of the State College area. The presence
of the sulfide minerals is not surprising because several studies have identified
and described Pb-Zn occurrences in these rocks of the Valley and Ridge. The
concentration of sulfide minerals in the rock (up to 5%) and widespread occurrence
of the sulfide mineralization was not expected.
Our students have used the SEM and X-ray diffractometer to characterize the
minerals present in the outcrop. Along with the mineralogical identification,
fluid inclusions from the quartz veins have been analyzed. Re-Os isotope have
been used to resolve the age of the pyrite. Our preliminary results indicate
the mineralization occurred 35Ma, much younger than anticipated. Also surprising
are the 'hot' (greater than 350 degrees centigrade) fluid inclusions results
associated with mineralization. Students continue to study this deposit and
similar local sulfide deposits using these techniques. The images provided show
unique 'whiskered' and needled pyrite along with the outcrops where samples
were obtained.
A. Zirakpavar and R. Mathur collecting pyrite for Re-Os isotope dating.
SEM image of the pyrite present, notice the cubes, plates and whiskered habit of the pyrite.