<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Albert H. Hofstra</dc:contributor>
  <dc:creator>Andrew H. Manning</dc:creator>
  <dc:date>2017</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;The He, Ne, and Ar isotopic composition of fluid inclusions in ore and gangue minerals were analyzed to determine the source of volatiles in the high-grade Goldfield and Tonopah epithermal Au-Ag deposits in southwestern Nevada, USA. Ar and Ne are mainly atmospheric, whereas He has only a minor atmospheric component. Corrected&amp;nbsp;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;He/&lt;/span&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;span&gt;He ratios (with atmospheric He removed) range widely from 0.05 to 35.8 times the air&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;He/&lt;/span&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;span&gt;He ratio (R&lt;/span&gt;&lt;sub&gt;A&lt;/sub&gt;&lt;span&gt;), with a median of 1.43 R&lt;/span&gt;&lt;sub&gt;A&lt;/sub&gt;&lt;span&gt;. Forty-one percent of measured&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;He/&lt;/span&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;span&gt;He ratios are ≥4 R&lt;/span&gt;&lt;sub&gt;A&lt;/sub&gt;&lt;span&gt;, corresponding to ≥50% mantle He assuming a mantle ratio of 8 R&lt;/span&gt;&lt;sub&gt;A&lt;/sub&gt;&lt;span&gt;. These results suggest that mafic magmas were part of the magmatic-hydrothermal system underlying Goldfield and Tonopah, and that associated mantle-sourced volatiles may have played a role in ore formation. The three highest corrected&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;He/&lt;/span&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;span&gt;He ratios of 17.0, 23.7, and 35.8 R&lt;/span&gt;&lt;sub&gt;A&lt;/sub&gt;&lt;span&gt;indicate a primitive mantle He source and are the highest yet reported for any epithermal-porphyry system and for the Cascades arc region. Compiled&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;He/&lt;/span&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;span&gt;He measurements from epithermal-porphyry systems in subduction-related magmatic arcs around the world (n&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span&gt;=&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span&gt;209) display a statistically significant correlation between&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;He/&lt;/span&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;span&gt;He and Au-Ag grade. The correlation suggests that conditions which promote higher fluid inclusion&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;/span&gt;&lt;sup&gt;3&lt;/sup&gt;&lt;span&gt;He/&lt;/span&gt;&lt;sup&gt;4&lt;/sup&gt;&lt;span&gt;He ratios (abundance of mantle volatiles and focused upward volatile transport) have some relation to conditions that promote higher Au-Ag grades (focused flow of metal-bearing fluids and efficient chemical traps). Results of this and previous investigations of He isotopes in epithermal-porphyry systems are consistent with the hypothesis posed in recent studies that mafic magmas serve an important function in the formation of these deposits.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/j.oregeorev.2017.06.023</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>Noble gas data from Goldfield and Tonopah epithermal Au-Ag deposits, ancestral Cascades Arc, USA: Evidence for a primitive mantle volatile source</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>