Structure and bulk composition of the Tin Mountain pegmatite, Black Hills, South Dakota

Construction of structure contour and isopach maps has yielded a rather simple and orderly interpretation of the structure and has led to calculations of the tonnage of each of the internal units and of the bulk composition of the pegmatite. The outcropping part of the pegmatite trends S 75° E for 90 m and then connects with an arm of the pegmatite that plunges gently N-NW for approximately another 90 m. An albite-quartz-muscovite wall zone completely surrounds four inner units. Though these four inner units are termed zones, in accordance with standard practice, differentiation is more in a vertical direction than in a concentric arrangement. The upper two of these units are perthite rich.