The wolframite-bearing quartz and pegmatitic veins occupy steeply southwest-dipping, northwest-striking fractures in deuterically altered granite adjacent to the contact with Jurassic quartz porphyry which is the country rock in the Needle Hill mine area. Much of the wolframite occurs in massive form along vein margins; some, locally accompanied by molybdenite, is found as tabular prismatic crystals in vug linings. The mineralization is assumed to be genetically related to emplacement of the granite in late Cretaceous time.

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