US Silver - Exploration Targeting

Exploration Targeting

Historic exploration at the Galena and Coeur mines was carried out by following the “trend” of the veins with drifting and diamond drilling. This method was successful but it is believed that it did not allow for recognition of the larger picture of the geologic interplay of faults, veins, and stratigraphy. One obvious effect of the trend based exploration was that the underground workings at the Galena mine were developed in NW-SE direction from the central shafts. The directional development has caused large prospective areas of the Galena and Coeur mines to remain unexplored. One such area is the hanging wall of the Polaris fault. The single largest and most productive vein in the Galena and Coeur mines is the Galena’s Silver vein which has produced over 25 million ounces of silver and is located in the hanging wall of the Polaris fault. The trend based exploration caused the workings to be developed in northwesterly trend because of numerous secondary ore vein bearing veins in the footwall of the silver vein. This development direction caused the workings to cross into the footwall of the Polaris leaving the entire hanging wall of the Polaris fault virtually unexplored for about 4 miles (6.4 km) from the eastern side of the Galena to the boundary with the Sunshine Mine.

Structural control on vein mineralization has long been recognized in the Coeur d’Alene District. However, using these observations in developing predictive exploration models has proven difficult. With the advent of 3-D modeling software the integration of structure, stratigraphy and geochemistry into a three-dimensional model for use in exploration has been facilitated and is being carried out at Coeur Silver Valley.

The basis of the current structural work at the Galena is that the emplacement of the vein arrays is structurally controlled. There are secondary controls imposed by stratigraphy and geochemistry but structure is considered the most dominant because the movement of fluid required for vein and mineral precipitation requires the presence of active structures. A geometric model of the Coeur-Galena was constructed in Datamine Studio software, which has allowed for examination of the faults and veins and their relationships to one another.