Geology, alteration, and mineralization of the Kougarok Sn deposit

At the Kougarok deposit in mineralization occurs in association with a Cretaceous granite complex. The tin mineralization is hosted in both granite and pelitic schist country rock. The most significant concentrations of cassiterite occur in a late zinnwaldite granite body which cuts older granite phases of the intrusive complex. The body has a subhorizontal lower contact and an irregular upper contact which merges into higher level dikes and plugs. The intensity of hydrothermal alteration increases upward in the body; successive alteration as-semblages, in order of increasing destruction of igneous texture, consist of sericite-tourmaline, brown zinnwaldite-sericite, white zinnwaldite-sericite, and quartz + _ tourmaline greisen. In general, the grade of tin mineralization parallels the intensity of the alteration, ranging from less than 0.10 percent in the sericite-tourmaline zone to over 1.0 percent in the quartz + _ tour-maline greisen. Highly anomalous arsenic (greater than 1,000 ppm), anomalous lead (up to 1,500 ppm), and silver ( up to 30 ppm) are associated with tin grades greater than 1.0 percent. Tantalum and niobium, in tantalite-columbite, are also enriched (up to 900 ppm Ta and ap-proximately 600 ppm Nb) upward in the zinnwaldite granite but vary independently of tin