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State Route 9 & Ellis Street interchange (State Route 72 roadcut), New Britain, Hartford Co., Connecticut, USA
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State Route 9 & Ellis Street interchange, New Britain, Hartford Co., Connecticut, USA

Photo: 2002 John H. Betts
Latitude: 41°39'24"N
Longitude: 72°46'10"W
Mineralization is hosted primarily by fault veins cutting basalt and sedimentary rocks and by gas cavities in the basalt. Gray (1982) provides a description of the nearby, similar Columbus Street vein that is relevant to the State Route 9 (formerly State Route 72) 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.

Hubert et al (1992) and Scovil (2008) provide additional descriptions of similar vein sites nearby and this site, respectively. Hubert gives an age of 180 million years ago for the mineralization.

Mineral List

Covellite ?
var: Amethyst

19 entries listed. 18 valid minerals.

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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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