Reports
Copper, zinc, lead, iron, cobalt, and barite deposits in the Piedmont Upland of Maryland
1965, Heyl, A.V. and Pearre, N.C.
Bulletin 28
Abstract
Three copper districts—from west to east, respectively, the Linganore, Sykesviile, and Bare Hills-lie within the Piedmont upland of Maryland, which is 20 to 40 miles wide. Their aggregate output is not known, but incomplete production statistics indicate not less than 10,000 tons of metallic copper, worth more than 3 million dollars. Copper mining in Maryland began about 1750 and continued at intervals thereafter until 1918. Several of the early mines were large for their time.
In addition to copper, the Linganore district has produced zinc, lead, silver, and gold, and the Sykesviile district has produced iron. Cobalt is a constituent of the Sykesviile ores, but it has never been recovered commercially.
The bedrock of the Piedmont upland in Maryland increases in metamorphic grade eastward, from low-grade greenschist facies in the Linganore district to intermediate-grade amphibolite facies in the Bare Hills district. Similarly, the ore deposits grade from mesothermal in the Linganore district to hypothermal in the Bare Hills district.
The Linganore district, in Frederick and Carroll Counties, is in the western part of the Piedmont upland. The main primary minerals that have been of commercial value are bornite, chalcopyrite, chalcocite, argentiferous galena, sphalerite, and barite. Most of the minerals are in fine-grained replacement bodies and breccia ore bodies in marble, commonly near the contact between marble and metavolcanic rocks or phyllite. Where mineralized, the marble is brecciated and manganiferous. A few ore bodies are in veins.
The Sykesviile district, mostly in Carroll County extending into westernmost Baltimore County, is in the central part of the Piedmont upland in a transitional belt of schists and gneisses of both the greenschist and amphibolite facies. Some of the rocks show retrogressive metamorphism. The deposits are in veins, in faults, and in lenticular bodies of chlorite-amphibole schist. Chalcopyrite, bornite, magnetite, hematite, sphalerite, and carrollite are the main ore minerals. Quartz and actinolite are common gangue minerals.
The Bare Hills district in the northern suburbs of Baltimore is in the eastern part of the Piedmont upland. Lenticular veins of magnetite and chalcopyrite, with a little bornite, are in gneissic rocks of the amphibolite fades. Coarse-grained silicates such as hornblende, cummingtonite, and anthophyllite are gangue minerals in the veins and in adjacent wall rocks.
