Apparent constriction fracture flow: A suggested mechanism for fault and vein formation, with examples from the Coeur D'Alene district, Idaho
- Univ. of Idaho, Moscow, ID (United States). Dept. of Geology and Geological Engineering
- Sunshine Precious Metals, Inc., Kellogg, ID (United States)
Reverse and normal faults with widely varied attitudes in the Coeur d'Alene district show variable mineralization and a dominant trend of N55W; they dip steeply south and intersect in an axially symmetric array. Post-fault veins of widely varied attitude in the Sunshine mine dip steeply south and intersect in an axially symmetric array also, but have a dominant trend of N90E. Some veins show reverse slip and others normal slip, both syn-mineral. Both intersection sets plunge steeply SSW, paralleled by syn-mineral mullions, grooving and slickenlines. The faults and veins cross earlier fabrics. Quartzite and argillite of the Belt Supergroup, which host the Sunshine mine deposits, generally dip steeper than the veins. Siderite gangue occurs in veins both in quartzite and in argillite. Veins split locally, and siderite remains continuous through splits. Relics of crustified siderite are preserved in places. Apparent constriction fracture flow is postulated to generate the axially symmetric faults and veins. The two fracture events, although close in time, were separated by counterclockwise rotation of the dominant shear plane. Both fracture arrays formed during inhomogeneous, semi-ductile slip parallel to their lines of intersection, resulting in synchronous normal and reverse slip in different places. This is modeled by slip in an inclined stack of oval rods, along their length. Siderite was deposited by filling in shallower-dipping vein segments in quartzite created during reverse slip along refracted shears, as well as in steeper-dipping vein segments in argillite created during normal slip along refracted shears.
- OSTI ID:
- 5769610
- Report Number(s):
- CONF-921058-; CODEN: GAAPBC
- Journal Information:
- Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
- Country of Publication:
- United States
- Language:
- English
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