UIS Commission on Karst Hydrogeology and Speleogenesis
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Karstbase Bibliography Database

Dublyansky, Yuri; Spötl, Christoph
DE WAELE, JO; FORTI, PAOLO; NASEDDU, ANGELO
The late miocene mineralized hypogene karst at bare mountain, southern nevada, usa
IL CARSO IPOGENICO MINERALIZZATO DEL TARDO MIOCENE DEL BARE MOUNTAIN, NEVADA DEL SUD, USA
Mine Caves/ Grotte di Miniera
Bologna
2013
0
28
229
230

Bare Mountain is an isolated complex of mountain peaks Southeast of the town of Beatty in southern Nevada. This small mountain range is located between the alluvial basins of Crater Flat to the East and the northern Amargosa Desert to the Southwest. The range is built of a folded and complexly faulted, generally northward-dipping sequence of weakly to moderately metamorphosed upper Proterozoic and Paleozoic marine rocks. Along the eastern and northern margins of Bare Mountain there are four clusters of Ag-Hg-fluorite deposits from which pipe-like breccia bodies have been reported in the literature. One of these deposits, the Diamond Queen Mine (aka Goldspar Mine; 36°50.4’ N, 116°38.3’ W) was prospected for gold and mined for fluorspar. The age of the mineralization is younger than 12.9±0.4 Ma (according to K/Ar dates of replacement adularia). During our visit in 2010 we observed solutional cavities in the open-pit works of the mine carved in the dolomite of the Cambrian Nopah Formation. The cavities have dimensions of a few meters to tens of meters. Their inner surfaces are smooth and barren. The morphology of the cavities strongly suggests dissolution under phreatic conditions. Cavities are filled with buff-colored clay material containing bands of black to dark-violet to yellow- green to colorless fluorite. Fluid inclusions in the Diamond Queen fluorite yielded homogenization temperatures of ca. 130°C. We measured the δD of the fluid inclusion water in this fluorite and compared them to δD values measured in scalenohedral calcite from the Sterling Mine (Au) located 1.5 km to the north. Isotopic values are remarkably similar: δD = -100±2 ‰ (n = 6). Despite the fact that the analyzed water was derived from hypogene, hydrothermal minerals these isotopic values bear a paleoclimatological significance. This is because according to the currently accepted model, the Au-Hg-fluorite deposits at Bare Mountain owe their existence to the circulation of meteoric water triggered by emplacement of the silicic magma chamber under the Timber Mountain-Oasis Valley caldera some 15 km to the north. The Late Miocene meteoric- hydrothermal water is isotopically similar to the modern-day precipitation (-106 to -92 ‰). Between ca. 1.5 and 2.5 Ma the δD values of meteoric water in the area were substantially less negative (-70 to -50 ‰) and then gradually decreased to modern values. Knowledge regarding hypogene karst associated with the epithermal ore deposits in Nevada is limited. In north-central Nevada, post-ore hypogene dissolution, brecciation and mineralization occurred at some of the Carlin Trend deposits at ca. 2 Ma. In contrast, hypogene karst was a preore process at Diamond Queen; it has played a role in creating the ore-bearing structure.

SOUTHERN NEVADA; USA; isotopes;
978-88-89897-09-6
Dublyansky, Yuri; Spötl, Christoph , 2013, The late miocene mineralized hypogene karst at bare mountain, southern nevada, usa , 0 , 229 - 230