Warwickite type locality, Amity, Town of Warwick, Orange Co., New York, USA

The minerals of the Amity-Edenville area occur almost exclusively in the Franklin Marble, a mid Protorozoic, granulite facies, calcite-rich metacarbonate. The Franklin Marble contains numerous horizons, often seen as isolated, elongated lenses but sometimes distributed in continuous trends. Some of these horizons are rich in aluminium and are characterized by corundum, spinel and brittle micas. Other, more limited, layers contain boron minerals or are rich in arsenopyrite.

The Amity-Edenville area hosts the most famous boron - bearing skarn in the Franklin Marble. As with many occurrences in the area it is limited in extent but unlike many similar localities, 19th century collectors did not strip it bare. The locality, number 26 of Kearns (1977), is in a thicket just off Newport Bridge Rd. approximately 2/3 mile east of Amity (intersection of N’p’t Br. and Price’s Switch Rd). The site is being encroached on by suburban McMansions. The locality was first noted by Shepard (1838) and so dates from the early period of mineralogical investigation of the area. Keep in mind that geology, as an organized science, was only about 50 years old (if one dates its beginning from Hutton’s presentation of “THEORY of the EARTH; or an INVESTIGATION of the Laws observable in the Composition, Dissolution, and Restoration of Land upon the Globe” in the spring of 1785). Geologists, of that era, were often seen as odd. In 1824 Sir Walter Scott wrote “St. Ronan’s Well” in which geologists are described as acting “like road makers run daft”.

A similar boron skarn, at Rudeville, NJ, was one of the mineral assemblages examined by Volkert, et al (2005). The age of that example coincided with a widespread hydrothermal recrystallization that was associated with an extended period, 1005 – 950 MA, of post orogenic pegmatite intrusion. Like the warwickite – bearing skarn near Amity, the Rudeville occurrence lacked gneissic texture. This is consistent with a post orogenic formation. One remaining question, noted by Volkert, et al (2005) is whether the boron and other componants of the skarn were introduced by the hydrothermal fluids or whether the skarn represents an original concentration in the marble that was later recrystallized.

Boron – bearing skarns have been found at a number of localities in the Franklin Marble since Kearns (1975) described fluoborite from Rudeville, NJ. In most of these the principal mineral has been fluoborite which is quite brightly fluoresent in short wave ultraviolet light making it easier to find. It is likely that small occurrences of boron – bearing skarn are not rare, especially ones like the Amity and Rudeville examples in which fluorborite is rare or absent making them difficult to recognize.

There is a voluminous literature concerning the Franklin Marble including recent papers that have led to a much tighter focus on the timing of geologic events, on the environment of deposition of the marble and on hydrothermal alteration/mineralization associated with post orogenic pegmatites.

References:

Kearns, L.E. 1977: The Mineralogy of the Franklin Marble, Orange County, New York. Ph.D thesis, Univ. of Delaware, Newark, Delaware.

Shepard, C. U., 1838, Notice of warwickite, a new mineral species: Amer. Jour. of Sci., ser. 1, v. 8, pg. 313-315.

Volkert, R. A., Zartman, R. E., and Moore, P. B., 2005. U-Pb zircon geochronology of Mesoproterozoic postorogenic rocks and implications for post-Ottawan magmatism and metallogensis, New Jersey Highlands and contiguous areas, USA. Precambrian Research, 139, 1 – 19.