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Corporate Drive construction site, Long Hill, Trumbull, Fairfield Co., Connecticut, USA

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Location is approximate, estimate based on other nearby localities.
 
Latitude & Longitude (WGS84): 41° North , 73° West (est.)
Margin of Error:~2km
Locality type:Construction Site
Köppen climate type:Cfa : Humid subtropical climate


A large construction site on Corporate Drive. Blasting took place in 2011-2012 exposing a contact between rusty The Straits Schist above its so-called basal member (marble and amphibolite with accessory scheelite). Rocks are moderately faulted and hydrothermal mineralization occurred along fault surfaces.

Fluids mineralizing faults were highly enriched in fluorine and likely low temperature, producing two separate kinds of mineralization.

The most significant for mineral collecting is the emplacement of several cross-cutting, subvertical veins (to approx. 0.75 m in width) of fluorite (variety chlorophane) and quartz, and with distinct marginal zones consisting of sharp, euhedral albite crystals, muscovite (not margarite, based on Raman spectroscopy), marialite (based on Raman spectroscopy), and phlogopite where the contacting amphibolite has been metasomatized. These crystals reach up to 4cm and are white with distinctive steep terminations as well as occasional pyrite lamellae. Raman spectroscopy shows these crystals are albite variety oligoclase, the typical composition for metamorphic albite in Connecticut. These crystals are easily chiseled out of a mixture of quartz and fluorite and make for aesthetic specimens albeit their lack of color! Surprisingly, topaz is generally lacking, unlike other similar veins in the area, including those exposed uphill and to the south across the street, see http://www.mindat.org/loc-217040.html, where it is abundant. The texture of the vein material grades from coarse to fine and porcellaneous in some areas and often the topaz has been highly altered to a mixture of muscovite and margarite(?). The chlorophane, present in large cleavable masses, is colorless to smoky and unless protected from daylight immediately upon its exposure loses its SW UV fluorescence.

As found in the surrounding area, the amphibolite (which hosts mostly sub-cm, scattered grains of scheelite) has been altered, with abundant clinozoisite, marialite, clinoclore, and quartz. It also contains zones and anhedral crystals of green albite variety oligoclase. Hydrothermal activity deposited pyrite and pyrrhotite in this unit, the marble, and the fluorite-quartz veins. Lamellae of pyrite and red-orange fluorescing calcite are present in thin fractures in all of these units. Although the scheelite is predominantly restricted to the amphibolite, tiny grains were detected by fluorescence along and proximal to small faults in the marble as well, apparently mobilized by the associated hydrothermal activity.

NOTE: Please respect the primary areas of collecting interest at this locality. I am avidly researching the genesis of fluorite veins here. I require assistance in performing spatially resolved XRF analysis of plagioclase feldspars as well as delta O analysis of the veins and country rock. If anyone can help with this project, please message me (Jeremy A. Zolan.)


Mineral List


16 valid minerals.

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References

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Field observations made by Jeremy A. Zolan

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