Geologic descriptionThe following description of the Yellow Pup tungsten deposit is summarized from Robinson (1981). The rocks consist of a hornfelsed sequence of feldspar-quartz schist, biotite-muscovite-quartz schist, muscovite-quartz schist, calc-amphibolite, and marble. The tungsten-bearing beds occur in pelitic schists and quartzite that contain resorbed biotite and andalusite porphyroblasts that reflect hornfelsing caused by the intrusion of the nearby Gilmore Dome stock. The tungsten-bearing rocks are marble, calc-amphibolites, and siliceous calc-silicate rocks. These rocks form distinctive layers within a package of rocks dominated by barren mica schist, quartz schist, and quartzite. Two types of calc-amphibolites are present. The most common is epidote amphibolite, which has sporadic concentrations of scheelite and powellite. The other calc-amphibolite occurs in a 2-meter-thick layer in the main open cut and consists of hornblende, quartz, tremolite, muscovite, epidote clinozoisite, garnet, plagioclase, and chlorite. There may be as much as 10 percent scheelite in this amphibolite. In the mine, the mineralized zone is arched into a small, north-plunging, asymmetrical antiform that flattens to the south where it is truncated by a high-angle fault. Most mineralization appears to be within the eastern limb of the structure. Other scheelite occurrences are present in epidote-amphibolite layers in surface trenches; the size of these zones varies, but none appear to be as large or as high grade as the calc-amphibolite zone. |
