State Route 9 - Ellis Street and State Route 72 interchanges (State Route 72 roadcut), New Britain, Hartford Co., Connecticut, USA
|Latitude & Longitude (WGS84):||41° 39' 20'' North , 72° 46' 13'' West|
|Latitude & Longitude (decimal):||41.6555764877, -72.7702598359|
The history of highway construction and designation in this area is confusing and specimens can be labelled differently depending on when they were collected. Most collecting took place in 1974-5 when the state expressway section in New Britain, referred to then as Route 72, was being constructed and cut through numerous, heavily faulted low basalt ridges. As originally designated, the Route 72 expressway extended from state Route 15 (SE of New Britain), past the planned Interstate 291 interchange (which headed north), toward and past Interstate 84 (W side of New Britain). It was completed in 1979 and many early specimens labels refer to Route 72. 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 existing section of state Route 72 south of their intersection connecting to Route 15. The Route 72 expressway section west of the interchange with former I-291 remained designated as state Route 72. But the stretch of Route 72 renamed Route 9 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. Though many old labels are not locality specific, the geology and mineralogy are essentially the same throughout most of New Britain so the exact origin is somewhat academic.
Mineralization is hosted primarily by a myriad of 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:
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.
Januzzi (1976) provides an early mineral list. 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.
28 valid minerals.
This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.
Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org
174.1 - 201.3 Ma
Age: Early Jurassic (174.1 - 201.3 Ma)
Stratigraphic Name: Portland Arkose
Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. 
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.