<p>Quartz-sulfide hydrothermal vein in quartz monzonite from the Cretaceous of Montana, USA. (~5.4 cm across along the base)
</p><p>This rock is from Butte, Montana, known as the “Richest Hill on Earth”.  The mineralized rocks at Butte have produced gold, silver, copper, molybdenum, manganese, and other metals.  Mineralization is hosted in the Butte Quartz Monzonite, a large Late Cretaceous igneous pluton.  These rocks have been intruded &amp; altered by hydrothermal veins containing valuable metallic minerals - principally copper sulfides.  Copper mineralization has been dated to 62-66 million years ago, during the latest Maastrichtian Stage (latest Cretaceous) and Danian Stage (Early Paleocene).
</p><p>This quartz monzonite sample has a hydrothermal vein running across it.  The vein has quartz (= gray) and weathered copper sulfides (= bluish &amp; black).
</p><p>Geologic unit: Butte Quartz Monzonite (a.k.a. Butte Pluton), Boulder Batholith, mid-Campanian Stage, late Late Cretaceous, 76.3 Ma
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Locality: loose piece from rubble pile next to a large tailings pond, above the Continental Pit, town of Butte, Silver Bow County, southwestern Montana, USA
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/47445767@N05">James St. John</a>
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<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/jsjgeology/30588174684/">Quartz-sulfide hydrothermal vein in quartz monzonite (Butte Quartz Monzonite, Late Cretaceous; Continental Pit, Butte, Montana, USA)</a>