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State Route 9 - Ellis Street and State Route 72 interchanges (State Route 72 roadcut), New Britain, Hartford Co., Connecticut, USA

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The history of highway construction and designation in this area is confusing and specimens can be labelled differently depending on when they were collected. In 1979, when the New Britain expressway section from Interstate 84, passed the planned Interstate 291 interchange, to state Route 15 was completed, it was designated as state Route 72 and many early specimens carry this label. In 1986, the planned Interstate 291 (north of Route 72) was completed but it was redesignated as state Route 9 (most specimens labelled "Route 9, New Britain" come from this section) along with the section of state Route 72 south of their intersection. The expressway section west of the interchange remains designated as state Route 72, though the renamed section contains the bulk of the mineralized road cuts. Based on modern nomenclature, these are at the Route 9 and Ellis Street interchange area, and at the Route 9 and Route 72 interchange area, which cover about 1 mile of expressway.

Mineralization is hosted primarily by NE-SW trending fault veins cutting basalt and sedimentary rocks and by gas cavities in the basalt. Gray (1982) provides a description of the Columbus Street vein that is relevant to the State Route 9 locality, although not all the same minerals are reported for both localities:

Basalt bordering the vein is silicified and bleached to a light gray color. This type of alteration is typical of the N45°W [actually N45°E according to Hubert et al (1992)] faults in the New Britain area irrespective of the presence of the carbonate-quartz-barite veins.

Vein filling was accomplished initially by the deposition of quartz, calcite, and ferroan dolomite in open spaces along the active fault zone. Movement continued throughout this phase frequently brecciating previously deposited vein material. After faulting ceased barite which occurs in plumose crystal groups up to 20 cm long, filled the open space in the center of the vein and cemented the carbonate-quartz breccias. The ferroan dolomite of the carbonate zone is oxidized to a dark red-brown color at the boundary of the barite zone. Cavities between barite crystals are filled by small amounts of drusy quartz, ferroan dolomite, and aragonite.

Sphalerite, chalcopyrite, galena, and minor amounts of barite, chalcocite, covellite, and tennantite fill open spaces and replace carbonates within the quartz-carbonate zones. Sphalerite was the first sulfide deposited. Galena and chalcopyrite followed later.

Vitreous black carbonaceous spheres, 1 to 5 mm in diameter, occur throughout the vein but are most abundant along the boundary of the quartz-carbonate and barite zones. Presumably these spheres were droplets of oil suspended in the hydrothermal fluids which became accidentally trapped during the deposition of the vein minerals.


Miller (circa 1986), Hubert et al (1992) and Scovil (2008) provide additional descriptions. Hubert gives an age of 180 million years ago for the mineralization. The host rocks are about 206 million years old.

Mineral List



35 entries listed. 30 valid minerals.

The above list contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

Gray, Norman H. (1982): Copper Occurrences In The Hartford Basin Of Northern Connecticut. In Guidebook for Fieldtrips in Connecticut and South Central Massachusetts, New England Intercollegiate Geological Conference, 74th Annual Meeting, Connecticut Department Of Environmental Protection Guidebook No. 5: 195-211.

Miller, F. W. (circa 1986), Hydrothermal Quartz and Barite Veins in the Basalt of New Britain, Connecticut. Harvard University Mineralogical Musum Association.

Hubert, John F., Paul E. Feshbach-Meriney and Michael A. Smith. (1992). The Triassic-Jurassic Hartford Rift Basin, Connecticut and Massachusetts: Evolution, Sandstone Diagenesis, and Hydrocarbon History. AAPG Bulletin: 76(11).

Scovil, Jeffrey. (2008): Minerals of the Ellis Street Extension Road Cut, Route 72, New Britain, Connecticut. Rocks & Minerals: 83(2): 152-160.

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