Chimney Rock Quarry (Houdaille Industries Quarry; The Bound Brook Quarry; Stavola Industries Quarry), Bridgewater Township, Somerset Co., New Jersey, USA
Latitude: 40°35'0"N
Longitude: 74°33'40"W
An Orange Mountain (First Watchung Mountain) basalt quarry, which began operations in the early 1900's. The quarry is currently owned by the Stavola group of Companies.
This quarry has produced world class specimens of native copper, chalcocite, natrolite and chalcopyrite. The chalcopyrite occurs as botryoidal masses up to 50 cm across from a single discovery that yielded at least 500 pounds of specimens. Many of these specimens are polished to bring out the golden color under the tarnish and they closely resemble the classic "blister ore" specimens from Cornwall, England. Although large masses of native copper (some weighing several hundred pounds) are known from here a single discovery in the late 1990's produced beautiful crystallized specimens. Some specimens have crystals to 4 cm across which are complex in symmetry and often associated with amethyst or chrysocolla. Although thousands of pounds of copper were found at that time only 20 or so specimens were truly world class with large crystals. The best of the chalcocites from this locality were also found at the same time as the copper crystals. The best specimens have dull, slightly etched crystals to 7 cm on matrix. These occurred in thin calcite veins with associated chrysocolla. Most of the finest chalcocites from this find were etched out of calcite however some had brilliant luster and occurred in pockets. A major natrolite discovery at this quarry yielded white translucent to transparent crystals to 17 cm long. These are the finest examples of the species from North America and although thousands of crystals were collected they are relatively rare on the market today. Some of the crystals were faceted and yielded flawless stones to over 10 carats.
(James Zigras, 2011.)
The Chimney Rock Quarry and the coincident Chimney Rock Copper Mine are located approximately 3000 feet NE of the intersection of US Route 22 and I-287, 1 mile SSW of Martinsville and 1.5-2 miles NW of Bound Brook, New Jersey.
The quarry is developed in the lower and middle portions of the Orange Mountain (First Watchung) basalt. In spite of an apparent exposure of over 350 feet of the basalt there is no amygdaloidal horizon that definitively marks the top of a flow unit. The only amygdaloidal horizon is exposed on the upper benches of the north side of the quarry, near the stratigraphic upper limit of the exposure. Unlike the amygdaloidal horizons normally found at the tops of flow units this one has limited lateral continuity. The nature of this amygdaloidal horizon is still unclear. The lack of a flow top suggests that there has been repetition of the stratigraphic section by faulting.
Most secondary minerals at Chimney Rock occur in veins. The basalt is cut by numerous fractures. Although brecciation associated with these fractures is often extensive displacements appear to be small in most cases. The bulk of the secondary vein filling is calcite or datolite. Veins containing abundant prehnite are much less common and tend to be limited to the stratigraphically upper parts of the exposure. Because of the abundance of calcite veins the Chimney Rock Quarry was long known for its calcite crystals. Locally, other minerals including quartz, opal, zeolite and copper minerals were also found in the veins. Two local but spectacular occurrences of large natrolite and analcime crystals have been recorded. Both were found in extensional portions of fractures. Neither was a steam explosion breccia, a spiracale, as has been suggested elsewhere.
The secondary minerals found in the fracture system do not occur randomly. They are found in a recognizable pattern that indicates deposition from a hydrothermal fluid, probably basin brine, that migrated upward out of the Passaic formation, into and through the basalt. In the literature the copper mineral assemblage and the prehnite(datolite)- zeolite mineral assemblage are usually treated as separate entities. It is important to recognize that the Chimney Rock Quarry has provided abundant evidence that these two mineral assemblages resulted from the same hydrothermal system and are parts of a single, more inclusive assemblage.
Amygdules, 2.5 to 6 inches in diameter, occur isolated and sparsely scattered through the basal meter of the flow. Most of the larger amygdules are subround, but pipe vugs are occasionally seen and are up to 2 inches across and 20 inches long. Alteration associated with these amygdules is very minor. The secondary minerals within these amygdules are generally limited to chalcedony/jasper, quartz, calcite, hematite and goethite. Goethite occurs as small, exquisite crystals and groups of crystals.
The Chimney Rock Quarry was excavated on top of the old Chimney Rock Copper Mine and has been known for its copper minerals for many years. Although the copper minerals occur in the veins that transect the basalt, most of the copper is found in the Passaic formation sediments immediately beneath the basalt. The Passaic Formation beds are mudstones ranging from thick bedded to laminated. Some beds are riddled with small cavities left by preexisting evaporite minerals, mainly gypsum and glauberite. Within approximately 1.5 feet of the overlying basalt the sediments have been darkened due to the recrystallization of hematite pigment to specularite. Chemical analysis (Woodward, 1944) do not indicate significant conversion to magnetite. This darkened rock, is widespread in areas where copper is abundant and has been referred to as “hornfels”. However, this alteration may be of hydrothermal origin since it is only associated with copper deposition. The true hornfels is probably no thicker than the approximately 2 inches seen at other exposures of the base of the Orange Mountain Basalt where copper minerals are not present.
In the darkened zone just beneath the basalt native copper, and very minor native silver, occurs in veinlets, approximately 0.1 inch in width and perpendicular to the basalt contact. The veinlets extend from the basalt/sediment contact downward for up to a foot, rarely more, and terminate abruptly. Within these veinlets copper appears to replace the sediment. The copper-bearing veinlets form a polygonal network, like shrinkage cracks but larger, perhaps 18 inches across. This may represent some sort of sediment dewatering structure.
Copper also occurs as a variety of irregular replacements within the thin, darkened zone. Some are localized by an identifiable feature, such as a bedding plane or a layer of root casts, but many are not.
The sediment surrounding virtually all native copper replacements is strikingly bleached. The bleaching, from dark maroon to tan, is due to the reduction of ferric iron and the partial leaching of ferrous iron (Woodward, 1944).
This copper deposit is of the “red bed” type. The principal difference between Chimney Rock and typical red bed copper deposits is that the chemical reducing agent appears to have been ferrous iron in the basalt rather than pyrite, carbonaceous matter or sulphate-reducing bacteria in a black shale. The Chimney Rock deposit is typical of all the copper deposits associated with the basal contact of the Orange Mountain basalt.
Chalcocite is also present in the zone of darkened sediments immediately beneath the basalt but deposited later than, and is subordinate to, native copper. Chalcocite deposition is limited to thin, crosscutting veins.
A number of secondary minerals are associated with the native copper and chalcocite. The most common of these are chrysocolla, malachite and cuprite.
In recent years a fault was exposed that contained a large mass of red sediment. This fault bounded mass of sediment was progressively exposed, beginning circa 1989 until about 2001 when it was finally leveled to the quarry floor. For several years it stood as a prominent monolith, known informally as “The Great Red Wall”. Copper mineralization occurred in veins, mostly in the heavily sheared outer margins of the sediment mass, and as replacements of the sediment. Although much more complex in detail there were many similarities between the occurrences of copper minerals in this fault bounded sediment and the sediments beneath the basalt.
NOTE: Trespassing at this locality results in arrest.
References
Manchester, J.G. (1931) The Minerals of New York City and its Environs. Bulletin of the New York Mineralogical Club, 1-168.
Woodward, H.P. (1944), Copper mines and mining in New Jersey: Department of Conservation and Economic Development, State of New Jersey, Bulletin 57.
Sinkankas, J. (1961), Natrolite from Houdaille Industries quarry, Bound Brook, Somerset County, N. J., American Mineralogist: 46: 1195 – 1197.
Sassen, R. (1978) Natrolite and Associated Secondary Minerals at the Chimney Rock Quarry, Bound Brook, New Jersey. Mineralogical Record, 9:25-31.
Speiser, R. (1978) A Quest for New Jersey Minerals: 14.
Tschernich, R. (1992) Zeolites of the World: 67.
Cummings, W. L. (1998), Geology of the Chimney Rock Copper Occurrence, A Deposit Typical of the Watchung Basalts, in Puffer, J. H. ed., The Economic Geology of Central New Jersey, Field Guide and Proceedings, Geological Association of New Jersey, Fifteenth Annual Meeting: 29 - 49.
Cummings, W. L. (2007), Unpublished data.
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