<?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>N.B. Keevil</dc:contributor>
  <dc:contributor>C. Harrison</dc:contributor>
  <dc:creator>E.S. Larsen</dc:creator>
  <dc:date>1952</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;The&amp;nbsp;&lt;/span&gt;age&lt;span&gt;&amp;nbsp;of&amp;nbsp;&lt;/span&gt;igneous&lt;span&gt;&amp;nbsp;&lt;/span&gt;rocks&lt;span&gt;&amp;nbsp;is determinable by a&amp;nbsp;&lt;/span&gt;method&lt;span&gt;&amp;nbsp;based on the included&amp;nbsp;&lt;/span&gt;accessory&lt;span&gt;&amp;nbsp;&lt;/span&gt;minerals&lt;span&gt;. In the common&amp;nbsp;&lt;/span&gt;igneous&lt;span&gt;&amp;nbsp;&lt;/span&gt;rocks&lt;span&gt;, most of the lead is concentrated in the potassium&amp;nbsp;&lt;/span&gt;minerals&lt;span&gt;, and most of the radioactivity is in the zircon and other&amp;nbsp;&lt;/span&gt;accessory&lt;span&gt;&amp;nbsp;&lt;/span&gt;minerals&lt;span&gt;. The lead in the potassium&amp;nbsp;&lt;/span&gt;minerals&lt;span&gt;&amp;nbsp;is believed to be mostly primary lead; that in zircon is probably chiefly radiogenic lead. By separating the zircon of fresh&amp;nbsp;&lt;/span&gt;igneous&lt;span&gt;&amp;nbsp;&lt;/span&gt;rocks&lt;span&gt;,&amp;nbsp;&lt;/span&gt;determining&lt;span&gt;&amp;nbsp;the amount of lead with the spectrograph and the radioactivity by alpha counters, the&amp;nbsp;&lt;/span&gt;age&lt;span&gt;&amp;nbsp;of Paleozoic and Precambrian&amp;nbsp;&lt;/span&gt;rocks&lt;span&gt;&amp;nbsp;can be determined with an accuracy of approximately 90 per cent. Basalts and gabbros may contain too few&amp;nbsp;&lt;/span&gt;accessory&lt;span&gt;&amp;nbsp;&lt;/span&gt;minerals&lt;span&gt;&amp;nbsp;for satisfactory&amp;nbsp;&lt;/span&gt;age&lt;span&gt;&amp;nbsp;determination by this&amp;nbsp;&lt;/span&gt;method&lt;span&gt;. Zircon is the most satisfactory&amp;nbsp;&lt;/span&gt;mineral&lt;span&gt;&amp;nbsp;for this kind of determination. Apatite and sphene give high results and therefore must contain primary lead. Sphene gives erratic results.&amp;nbsp;&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1130/0016-7606(1952)63[1045:MFDTAO]2.0.CO;2</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Geological Society of America</dc:publisher>
  <dc:title>Method for determining the age of igneous rocks using the accessory minerals</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>