Sleeper Rhyolite Gold Ore (above: field of view ~10.5 cm across; below: ~4.0 cm across) - here's some stunning Sleeper Rhyolite gold ore from the Sleeper Mine in northern Nevada, USA.  When tilted in the light, the native gold shines spectacularly.  This high-grade gold ore sample is an auriferous brecciated quartz-adularia rhyolite (some consider this rock to be latite).  Adularia is a low-temperature polymorph of KAlSi3O8 (orthoclase feldspar and microcline feldspar are more familiar polymorphs of potassium aluminosilicate).

The native gold here occurs in colloform bands, partially replaces breccia clasts, and is also disseminated in the matrix.  Published research on the Sleeper Rhyolite has indicated that these rocks represent an ancient epithermal gold deposit (hot springs gold deposit), formed by volcanism during extensional Basin & Range tectonics.

Age - the Sleeper Rhyolite dates to 16.3-16.5 million years (latest Early Miocene), and the gold mineralization dates to about 14.3-15.8 million years (during the early Middle Miocene).

Locality - Sleeper Open-Pit Mine (section 21, T40N, R35E), eastern side of Sod House Road, south of Rt. 140, northwestern margin of the Slumbering Hills, eastern margin of Desert Valley, northwest of the town of Winnemucca, central Humboldt County, northern Nevada, USA (41 20' 24" North, 118 2' 58" West). 

Sleeper Rhyolite Gold Ore



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