Geologic description
The SM occurrence is in the Hayes Glacier unit of Devonian to Mississippian age (Nokleberg and others, 1992) and consists of a folded exposure of 7 feet of massive sulfides exposed on a nunatak. At least four distinct types of massive sulfide mineralization are found in glacial debris below the nunatak. These include: (1) banded pyrite-sphalerite-galena(-chalcopyrite), (2) massive pyrite, (3) massive pyrrhotite with minor chalcopyrite and pyrite, and (4) banded pyrite and sphalerite in a matrix of black graphitic siltstone. The abundance of each of these types of mineralization suggests that a substantial deposit may be present under the glacial ice. Isoclinal folding is prominent in outcrop. The massive sulfides occur at the contact between a pyritic and sericitic, felsic metavolcanic layer and a black graphitic siltstone. This contact appears to be repeated in several locations on the nunatak (R.A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1978). Average metal values of the massive sulfide were 0.26 percent copper, 0.27 percent lead, 2.97 percent zinc, 0.62 ounce of silver per ton, and 0.05 ounce of gold per ton (R.A. Blakestad and others, unpublished Resource Associates of Alaska Inc. report, 1978). The Hayes Glacier rocks that host the SM occurrence consists of fine-grained phyllitic schists and mylonite derived from sedimentary and volcanic protoliths. The rocks locally display intense structural deformation due to their proximity to the Denali Fault. The rocks are metamorphosed to lower greenschist facies and are less metamorphosed than Jarvis Belt rocks to the northeast (Nokleberg and others, 1992). The basal part of the unit consists of mafic to intermediate composition metavolcanic rocks overlain by interbedded felsic metavolcanic units and extensive pelitic and graphitic metasedimentary rocks (Dashevsky and others, 2003). |
