Hale-Walker prospects, Collins Hill, Portland, Middlesex Co., Connecticut, USA
|Latitude & Longitude (WGS84):||41° 35' 7'' North , 72° 35' 17'' West|
|Latitude & Longitude (decimal):||41.58528,-72.58806|
|Köppen climate type:||Dfa : Hot-summer humid continental climate|
Two small prospects in narrow granitic pegmatite dike best known for its aquamarine. Minerals such as good epidote in quartz veins from the surrounding metamorphics are also included. According to Cameron et al (1954):
"The pegmatite...crops out on land owned jointly by Charles F. Walker, R. F. D., Portland, and Harry L. Walker, R. F. D., Glastonbury. It may extend eastward beneath overburden to land owned by Clifford Hale, R. F. D., Portland. In 1932 two small cuts were opened on the Walker property by the Eureka Flint & Spar Co., Portland, and were worked for 3 or 4 months for feldspar. According to Mr. William Wilkes, superintendent, about 70 tons of no. 1 feldspar was recovered. Both quarries have since been idle. The upper opencut is 25 feet long, 9 feet wide, and 1 to 10 feet deep. The lower opencut is 38 feet long, 10 feet wide, and 5 to 18 feet deep. Both pits are free of water and probably contain little backfill. The prospect was mapped by E. N. Cameron and V. E. Shainin in May 1943."
The pegmatite is a tabular body at least 180 feet long and 6 to 8 feet thick. It ranges in strike from N. 79° W. to east and dips 63° to 74° SW. The dike is sharply discordant to the enclosing granite-gneiss (Monson gneiss), whose foliation strikes N. 20° W. and dips westward at moderate to steep angles. The contact between the Monson gneiss and the Bolton schist lies 60 feet west of the westernmost exposure of the pegmatite. The pegmatite does not seem to extend across the contact.
The dike, a disseminated type of beryl deposit, consists chiefly of quartz and perthite. It has a border zone and a core. The border zone is ½ to 1 inch thick and is composed of fine-grained quartz, plagioclase and tourmaline. The core consists of medium- to coarse-grained quartz and perthite with subordinate amounts of plagioclase, muscovite, and accessory beryl, tourmaline, columbite-tantalite and monazite. Monazite is rare.
Most of the beryl occurs in the core, either with small anhedral crystals of perthite scattered in a matrix of coarse quartz, plagioclase and accessory tourmaline, or with fine-grained quartz, plagioclase, and accessory tourmaline.
The beryl is green to blue-green and occurs in crystals 0.2 to 2 inches long and 0.1 to 2 inches in diameter, but most of the crystals are very small.
19 valid minerals. 2 erroneous literature entries.
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
|Late Ordovician - Middle Ordovician|
443.8 - 470 Ma
|Collins Hill Formation|
Age: Ordovician (443.8 - 470 Ma)
Stratigraphic Name: Collins Hill Formation
Description: ( = Partridge Formation of New Hampshire) - Gray, rusty-weathering, medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, muscovite, biotite, and garnet, and commonly staurolite, kyanite, or sillimanite, generally graphitic, interlayered with fine-grained two-mica gneiss, especially to the west, and with calc-silicate and amphibolite layers, also rare quartz-spessartine (coticule) layers.
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.