Transactions . ess through such minutefaults have often produced ore-bodies by replacement on either sideof the fissure. Fig. 31 shows a case from one of the mines of sili-ceous ore near Portland, South Dakota, where the offset causedby a small fault is preserved in the ore mass. In this case the H-ith Mr. Lindffrcjn and Mr. Bocker as to hclieve that the appear-ance of one mineral in the crystal form of another affords no proof of theaction of fiich a , unless the new and the old mineral contain somecommon element and indicate chemical change rather than solutionand subsequent m
Transactions . ess through such minutefaults have often produced ore-bodies by replacement on either sideof the fissure. Fig. 31 shows a case from one of the mines of sili-ceous ore near Portland, South Dakota, where the offset causedby a small fault is preserved in the ore mass. In this case the H-ith Mr. Lindffrcjn and Mr. Bocker as to hclieve that the appear-ance of one mineral in the crystal form of another affords no proof of theaction of fiich a , unless the new and the old mineral contain somecommon element and indicate chemical change rather than solutionand subsequent mechanical deposition. Replacement Ore Bodies—Irving ir ore is evidently introduced after the fault structure is developed,as it is not itself affected by the displacement. There is, futher-more, no break in the continuity of the ore mass which passesfrom one side to the other of the former fissure without interrup-tion. Fig. 32 shows the reverse condition where an ore-body isitself displaced along a Fig. 31.—Fault preserved in orc-body. Ore-body itself not faulted, andhence formed after faulting. Joints.—Joints or intersectin^]^ have frequently beenpreserved in ore masses. Such jointing is distinguished from fis-suring described in the previous paragraph by greater numberof the cracks, their occurrence at angles to each other and thegeneral absence of appreciable displacement along any singlecrack. They grade into a brecciated structure with the increasein the number of fractures but may be distinguished from it bythe fact that in intersecting joints or stock works the blocks ofrock between the fissures have not been appreciably moved fromtheir original position so that banding and other te.\tural pecu-liarities of the rock pass uninterruptedly across the boundingfissures from one fragment to another.
Size: 2301px × 1086px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., book, bookcentury1800, booksubjectmineralindustries, bookyear1895
