Abstract

The Coeur d'Alene district of Idaho is a world-class, silver-base metal district with production exceeding 1.0 billion troy ounces of silver. Despite the prolific production history, little is known about the structural controls of ore deposition or the style of deformation which accompanied metallization. The role of strike-slip faulting has been emphasized by past workers as an important structural control of the mineralization. Structural data from the Sunshine mine show that the main sense of movement of structures during ore deposition was along a steep southwesterly line during a dip-slip tectonic-metamorphic event. Kinematic indicators suggest mainly reverse motion during deformation and synchronous mineralization. Siderite-quartz veins variously oriented in the Sunshine mineralized zone intersect in a common line that plunges steeply to the southwest parallel to slickenlines. Tetrahedrite-rich ore shoots within the siderite-quartz veins also plunge southwest regardless of vein orientation. The dip-slip fabrics associated with the mineralizing event cut the Big Creek anticline, yet evidence shows that preexisting fold fabrics were reactivated during metallization.

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