Physical Sciences and Mathematics Commons^™

Geology And Petrology Of The Lake Ann Stock And Associated Rocks, Eric William James

WWU Graduate School Collection

The Lake Ann stock is a two pyroxene quartz monzodiorite to granodiorite epizonal intrusive emplaced into the Shuksan thrust fault in the latest Pliocene. It is similar to other Late Tertiary Cascade intrusives in mineralogy, texture, chemistry, and setting. These similarities are attributable to near surface emplacement, quick cooling and magmatic arc setting. Epizonal emplacement is indicated by fine, equigranular textures, granophyre, late stage alteration, late miarolitic dikes, plagioclase resorbed by alkali feldspar, and low pressure contact metamorphic assemblages. Temperature of emplacement was between 600°C and 925°C; pressure was less than 2 kb. Chemistry of individual samples and variation diagrams …

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 …