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The Petrology, Petrography, And Geochemistry Of The Black Jack Breccia Pipe, Silver Star Plutonic Complex, Skamania County, Washington, Robert H. Birk
The Petrology, Petrography, And Geochemistry Of The Black Jack Breccia Pipe, Silver Star Plutonic Complex, Skamania County, Washington, Robert H. Birk
WWU Graduate School Collection
Tourmaline-bearing breccia pipes are associated with late stage Tertiary porphyritic intrusive rocks in the Silver Star Plutonic Complex.
Whole-rock geochemical analysis of rocks from the complex show a silica vs. alumina/(K2O + Na2O + CaO) trend (Feiss, 1978) toward geochemical conditions favorable for porphyry copper-type mineralization. Copper present in diorite, quartz diorite, and quartz diorite porphyry rocks probably entered silicates, whereas copper formed porphyry copper-type mineralization in the more felsic granodiorite and granodiorite porphyry intrusions.
Optical, x-ray, and chemical analyses indicate two distinct populations of tourmaline present in the breccia pipes; an early "Hemlock Ridge-type" which …