R. R. Reid, S. W. Caddey, and J. W. Rankin
Primary refraction control of ore shoots, with examples from the Coeur d'Alene District, Idaho
Economic Geology and the Bulletin of the Society of Economic Geologists (October 1975), 70(6):1050-1061

Abstract:
Newly developed procedures combining established principles of structural geology can lead to well-defined mineral exploration targets in bedded rocks related either to fault movements during ore deposition or to postore fault movements. Where faults cut bedded rocks at acute angles, the axes of potential ore shoots lie parallel to the intersection of the layering with the fault surfaces. Occurrence of openings favorable to ore deposition depends on fault deflection by refraction in the layering combined with favorable fault movement. The net-slip direction may be interpreted from extension joint orientation or by other means, and predictions can be made as to the location and orientation of ore shoots. Ore shoots also occur in extension fractures.Shear fractures entering relatively competent layers are deflected (refracted) toward the normal to the bedding interface about an axis defined by the line of intersection of the bedding with the shear fractures. The angle of deflection is governed by the angle of incidence and the refractive index of the more competent layer. Maximum refraction occurs where the intermediate principal stress (Sigma ₂ ) lies parallel to the layering. If the maximum principal stress (Sigma ₁ ) is perpendicular to the layering, shear angles become smaller where the faults pass from less competent into more competent layers. If Sigma ₁ is parallel to the layering, the angles become larger in more competent layers than in less competent layers. For other stress orientations, refraction effects are smaller, except that no refraction occurs where Sigma ₂ is perpendicular to the layers.