Geology of the Esterbrook Area, Converse and Albany Counties, Wyoming

The Esterbrook area lies within the Laramie Range in Converse and Albany Counties, Wyoming. Exposures include Precambrian metamorphic and igneous rocks, the Tertiary White River formation, and Quaternary alluvium. Hornblende schist and mica-quartz schist comprise the Precambrian metamorphic rocks. Foliation planes of these rocks trend northeast and dip steeply to the southeast. Metamorphic rocks of younger age probably lie to the southeast. A distinctive, Precambrian silicic pluton of biotite-leucogranite with marginal zones of muscovite-leucogranite and alaskite passively intrudes the metamorphic rocks, generally parallel to the foliation trends. Numerous granite pegmatites show a zonal distribution around the pluton and appear to be genetically related to it. Dikes of gabbro and basalt follow major structural trends in the metamorphic and igneous rocks. Pyrrhotite, galena, quartz-pyrite, and beryl-bearing mineral deposits are present in the metamorphic and igneous bodies. The deposits occur as fissure fillings and possible replacement bodies. The crystalline rocks and their associated mineral deposits have been re-exhumed by the erosion of the Tertiary White River formation which gently laps onto the Laramie core. Quaternary alluvium lies in the mountain stream beds. The area is in a stage of late youth --Abstract, page ii