The Appalachian Copper Belt. The Appalachian states contain a number of copper deposits in schist distributed from Maine to Alabama, but few of them are of commercial importance. Some were formerly important producers in the 1800s. This belt extends from Alabama on the south in a northeasterly direction to Newfoundland on the north. The richest deposits occur in Tennessee, Vermont and Newfoundland. The mine with the largest past production in the belt is at Ducktown, Tennessee. The copper ore occurs as true fissure veins in the crystalline schists. It consists chiefly of chalcopyrite in pyrrhotite and pyrite with a little quartz and is the richest where the pyrrhotite is the most abundant. According to H. Hies this district was one of the earliest producers of copper in the United States. The operations were commenced as early as 1850. The ores resulting from secondary enrichment were soon worked out and it was not until 1890 that the underlying low-grade sulfides were successfully worked. Since that time the mine has been a steady producer.
At Gold Hill, North Carolina, chalcopyrite occurs in true fissure veins found along sheeted planes in the metamorphics. Pyrite is associated with the copper ore. The Gossan Lead of southwestern Virginia and the copper deposits of Ore Knob, North Carolina, also belong to this type. At the former the ore is a mixture of pyrrhotite with subordinate chalcopyrite, and admixed quartz and schists. The vein fills a fault fracture between sericite schists, which contains mica, calcite, quartz, and actinolite, replaced by the later pyrrhotite and chalcopyrite. The copper content is low, viz., .75 per cent, and hence the ore is used for acid making, but the residue is available for copper. At Virgilina, Virginia, the ore is bornite with a little chalcopyrite and pyrite. It occurs in true fissure veins filled with quartz and sulfides. The veins conform to the banding of the mica schists. Replacements of the wall rock are rare. In Green County, Virginia, segregations of native copper, together with the oxides, cuprite and tenorite, and the carbonates, malachite and azurite, occur along sheared zones in the altered rocks of Algonkian age. In Pennsylvania, New Jersey and Connecticut, deposits of native copper are found along the contact of diabase and the intruded sandstones. The mines in these states have never been large producers.
The four copper mines worked from time to time in Vermont are the Ely mine in Vershire; the Corinth mine in Corinth; the Elizabeth mine and the Strafford mine in Strafford, Vermont. These are all in Orange County, and are now idle owing in part to the depletion of the available ore bodies and in part to the distance from railroad. The chief ore in each was chalcopyrite associated with pyrrhotite and pyrite. The copper ore is in saddle shaped bodies in the Vershire schists and in chimneys at the contact of the granite with the Vershire schists. The schists and the associated limestones are of Ordovician age. Tourmalines and garnets are abundant.
At the Ely mine in Vershire, Vermont, the chalcopyrite is associated with tourmaline. Like the rest, the ore occurs in saddle shaped bodies along the folds in the Vershire schists or in long chimneys at the contact of the intrusive granite with the Vershire schists. Pyrite and pyrrhotite are the common associated sulfides. The granite was the parent home of the copper and the chalcopyrite was deposited under hydrothermal conditions. This mine was known and worked before copper was discovered in the Lake Superior region. In the earlier days with 16 per cent, copper ore the mine was capable of producing 10,000,000 Ib. of copper per annum, but in the latter years of operation much of the ore did not exceeded 3 per cent, copper, which was then considered low grade ore.
All the copper ores of the Appalachian belt are somewhat auriferous. The early attempts to work the ores for both the gold and the copper content resulted in failure. The Vermont ores averaged about $2 per ton in gold. The Newfoundland ores are higher in their gold content. Much of that ore assays from 1/10th to 3/10ths of an ounce in gold. Some of the veins on the eastern coast of Newfoundland are true fissure veins traversing sandstones and conglomerates. Intrusive diabase appears to be the origin of the copper ore. Chalcopyrite and pyrite are the chief minerals. Chalcopyrite occurs in considerable quantity at Capleton, Province of Quebec, in a sheared amygdaloid. The mine has been a steady producer for a number of years.
Ducktown, Tennessee. The mineral deposits of Ducktown are in the southeast corner of Tennessee, near the North Carolina line, and extend southward into Georgia. They were first worked in the late 1840s. Besides large amounts of copper they have produced 1,500,000 tons of iron ore and a relatively small amount of silver and gold. They yield at present, in addition to the metals, over 1,000 tons of sulfuric acid daily. The ore now worked carries less than 2 per cent copper. Here we have steeply dipping lenses replacing calcareous beds in folded and faulted schists. It is heavy iron sulfide ore, principally pyrrhotite, pyrite, and chalcopyrite. The prevailing rocks of the district 1 are sandy schists and graywackes, with which are interbedded mica schists that have the shapes and character of closely folded sedimentary beds. The ores are somewhat metamorphosed and the gangue minerals bent. The dominant series is the metamorphosed product of Cambrian sedimentary beds. The schists are cut by dikes of gabbro, which are not so highly metamorphosed by pressure as the sedimentary beds. The schistosity and the bedding of the sedimentary rocks strike nearly everywhere northeast, and the prevailing dip is southeast. These rocks have been folded into sharp folds, many of them isoclines. Many of the folds were broken along the crests of anticlines and pass into strike faults that nearly everywhere dip southeast.
The ore bodies are replacements of limestone lenses which without much doubt were originally deposited at a single stratigraphic horizon. Anticlines and faulted anticlines, which are characteristic of this region, are shown also in the ore zone. The ores themselves are somewhat metamorphosed by dynamic processes, and the gangue minerals are bent, but at most places they do not exhibit a well-defined schistosity. The primary ore consists of pyrrhotite, pyrite, chalcopyrite, sphalerite, bornite, specular hematite, magnetite, actinolite, calcite, tremolite, quartz, pyroxene, garnet, zoisite, chlorite, micas, graphite, sphene and feldspars, a combination representing deep-seated conditions and limestone replacement. The deposits are not in contact with igneous rocks but are near intruding gabbro, and intruding granites are found a few miles away.
The gossan extends from the surface to a maximum depth of 100 feet. It carries 40 to 50 per cent, of iron, generally less than 12 per cent, of silica and alumina, and 0.3 to 0.7 per cent, of copper. The minerals are hydrous iron oxides, quartz, jasper, and kaolin, with a little cuprite, native copper, and sulfur. Below the gossan iron ores is a zone of rich copper ores, consisting of chalcocite and other copper minerals in a gangue of sulfates, quartz, and decomposed silicates. Under the higher portions of the outcrops of the lodes the top of this zone is about 100 feet below the surface, but the depth decreases down the slopes, and where the lodes are crossed by running streams the secondary copper ores are exposed at the surface. The zone is from 3 to 8 feet thick. The secondary minerals include chalcanthite, chalcocite, chalcopyrite, cuprite, gypsum, and iron sulfate. Much of thissecondary ore carries from 20 to 30 per cent, of copper.
In 1914 the ores yielded 28.7 pounds of blister copper per ton, or 1.435 per cent, with an average value of 9 cents in gold and silver per ton of ore. Some of the copper is marketed without electrolytic refining. The massive ore requiring little timber in mining, together with cheap fuel and labor costs, have made it possible to work these low-grade ores at a profit. Pyritic smelting is employed, and large sulfuric acid plants have been erected to utilize the sulfur driven off from the ores in roasting.
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