Friday, May 6, 2005
Copper mine keeps its secrets
Until a week before his presentation, sponsored by the Carlisle Historical Society, Mariano was still looking for the holy grail — a sample of copper ore native to Carlisle. Then, just in time, a large boulder presented itself at the Concord Street home of Arthur and Ginny Mills. "I ran into a big boulder loaded with copper," he told the audience with some excitement. Upon investigation, it has chalcopyrite, bornite, azurite, and malachite, all confirmed by Mariano in a lab in Burlington. He brought a chunk of the "Discovery Rock" to the library and also showed slides of a cross-section, clearly displaying all its mineral components.
Still, this was not a "eureka" moment for Mariano, since major questions about mining copper here remain unanswered. Significantly, geologic literature is silent on the subject, except for an entry in the U.S. Geologic Survey that reports, in part: "Copper ore was mined at a mine located one mile south of Carlisle in Middlesex County." Open pits and an underground shaft extending 220 feet deep are cited, but "no production data is available." Despite exhaustive searches by professional geologists, mineralogists and petrologists, this is the one single piece of information coming from a scientific source. And, Mariano points out, no data exists on the nature of the Carlisle rocks or the mineralogy.
Mariano wonders what mid-nineteenth-century mineworkers did with the water found 220 feet below the surface. "How on earth in those days were they able to go down even 40 feet and handle the water problem with no electricity?" At the suggestion that steam power was used, Mariano replies, "That's no simple task. It would be incredible. That's what makes [the mine] so interesting."
Modestly acknowledging that he "knows something about copper" having worked for Kennicott Copper, the biggest producers of copper in the world, and other international corporations, Mariano has identified thousands of samples of rock in Carlisle and in remote corners of the globe. He showed slides of copper carbonate, a secondary copper mineral from the alteration of a copper iron sulphite called bornite, and described the characteristics of the diverse minerals within a rock sample.
Mariano believes that in the early days in Carlisle, there must have been extensive exposures of secondary copper mineralization that allowed people to see the copper without access to any of today's scientific equipment. One slide shows some metamorphic rocks adjacent to a covered pit: "These rocks don't show one indication of copper mineralization. None whatsoever," he asserts.
Another slide displays a sample of native copper (pure copper ore) from upper Michigan. It is not a rich copper color, but dull brown. "It doesn't exist too often in nature, but in some places it does," says Mariano.
A voice came from the audience: "Tony, there's a specimen here you've got to see. It's from our back yard." A woman came forth, holding two rocks, each the size of a small hand with many fingers extended. Mariano seemed surprised. "That looks like native copper. Where did you get that?" "Nathan Lane," came the answer." Mariano replied, "Yeah, but that came from somewhere else. That's beautiful." He pointed out that, "If this came from town, it's incredible. Something like this would have been described even then and there's nothing." The owner of the copper appeared crestfallen. Mariano compared the finding of these copper specimens in Carlisle to the hypothetical collapse of his workshop with its enormous collection of minerals, some of which would then find their way into native soil.
Although all the mine shafts and pits in town were long ago covered, one can easily be located. George Cogswell bought the Samuel Heald House at 698 Concord Street in 1965, when the shafts on his property were still open. Fearing for the safety of his small children, he stuffed a cast-iron bathtub down the largest shaft and covered others. Recently, Cogswell and Mariano toured the property and, with a metal detector, were able to locate the shaft with the bathtub.
Mariano's fascinating slide talk covered more than Carlisle's copper — he discussed the three types of rock found in town (igneous, sedimentary and metamorphic), and showed a map of local outcroppings and drumlins. He described gneissic rock with its signature banding, and pointed out a large boulder of this type in front of Town Hall. An audience member asked Mariano whether frequent lightning strikes in the copper mine area could be related to the presence of copper. "I don't think there's anything to substantiate that copper mineralization is responsible for lightning strikes," he answered. "You'd need to have a continuum of a conducting material," and he put to rest that theory.
However, it is clear that the elusive copper mine will continue to perplex Mariano until more of its secrets are revealed.
© 2005 The Carlisle Mosquito