Mining is currently occurring at Wharf’s Deep Portland Pit and we anticipate resuming mining at the Golden Reward pit in the summer of 2016. Wharf’s conventional open pit mining and processing techniques utilize trucks, loader and crushing equipment before transferring the material to a heap leaching facility and activated carbon columns to recover gold. A third-party refiner further completes the processing.
View the latest Technical Report for the Wharf mine.
Geology and Exploration Potential
Wharf is located four miles west of Lead, South Dakota, in the northern Black Hills region. This forested area is the easternmost uplift of the Laramide orogeny, having risen from the surrounding plains approximately 50 million years ago. The elongate dome is about 60 miles in width by 120 miles in length. It consists of a core of Precambrian metamorphic and igneous rocks, flanked by exposures of Paleozoic through Mesozoic sedimentary rocks, and is intruded by a trend of Tertiary igneous bodies in the northern Black Hills. These intrusions have uplifted and exposed older rocks in the Lead window near the Wharf mine.
Wharf is located in the Bald Mountain mining district. The mined units are the Cambrian Deadwood Formation and Tertiary porphyritic trachyte sills. Manto-like deposits of disseminated gold in the lower sandstone of the Deadwood Formation are the highest-grade ore. Gold is also concentrated along near-vertical fractures in the remainder of the Deadwood. Much of the ore mined is porphyry, which is mineralized within pervasive fracture zones. Overlying rocks present in the mine area are the Ordovician Winnipeg and Whitewood, Devonian Englewood, and Mississippian Pahasapa Formations.
Tertiary igneous intrusions of varying composition are present in the area, but the mineralized and most voluminous rocks are Tertiary trachyte porphyry, which typically form sills 30 to 50 meters thick. Dikes and sills of late phonolite, often showing argillic alteration, are also common but are unmineralized.
The sedimentary units are nearly flat-lying and dip gently away from the Lead window. Minor faults present are rare and mineralized fracture zones trend toward a large igneous intrusion in the area.