. Transactions. produce precipitation. Sufficient pyrite in the limestone waslacking to precipitate zinc and lead as sulphides from their oxi-dized salts; but zinc sulphide as blende was present in places 704 LEAD- AND ZINC-DEPOSITS VIRGINIA-TENNESSEE REGION. in sufficient quantity to have precipitated the lead salts as sul-phide, had the conditions been favorable to the subsequentdownward circulating waters. (3) The conditions favorable tothe conversion of sulphates into the carbonates and silicates ofzinc, formed from the oxidation of the original sulphide. Thisfollows, in part at least, fro
. Transactions. produce precipitation. Sufficient pyrite in the limestone waslacking to precipitate zinc and lead as sulphides from their oxi-dized salts; but zinc sulphide as blende was present in places 704 LEAD- AND ZINC-DEPOSITS VIRGINIA-TENNESSEE REGION. in sufficient quantity to have precipitated the lead salts as sul-phide, had the conditions been favorable to the subsequentdownward circulating waters. (3) The conditions favorable tothe conversion of sulphates into the carbonates and silicates ofzinc, formed from the oxidation of the original sulphide. Thisfollows, in part at least, from the statement made in (1); and,as stated elsewhere, the concentration of the oxidized zinc-oresnear and along the irregular weathered surface of the lime-stone in the bottom portions of the residual Ccilcit©Sphalerite |^>\^-J-^ Limestone, and ^l\l<\ fragments | | Dolomite Fig. 13.—Brecctated Limestone Cemented with Calcite and Mines, Near New Market, Tenn. X. Relation of the Ores to Geologic Structure. As already pointed out, the lead- and zinc-district of theGreat Valley region of Virginia-Tennessee is one of intensedeformation—folding, faulting and brecciation. Moreover, thelocalization and concentration of the ores follow closely thesestructural lines. Mineralization has not taken place throughall parts of the breccia-zones, which follow the faulted anti-clines; but only along some of the zones, in places and atirregular intervals, have the ores accumulated. Wherever the LEAD- AND ZINC-DEPOSITS VIRGINIA-TENNESSEE REGION. 705 ores have been found they have been noted in some part of ananticlinal fold in or near a faulted breccia-zone. The ores are,accordingly, of the breccia-type, as is shown in Figs. 13,14,15,16, 17 and 18. At Austinville, Va., and
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