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Lead-isotopic compositions of diverse igneous rocks and ore deposits from southwestern New Mexico and their implications for early Proterozoic crustal evolution in the western United States.

Geological Society of America Bulletin

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Abstract

Basement rocks in this area are 1750 m.y. old and extend northward through Colorado to Utah. Galena data show that the fraction of older sialic lead in these rocks increases toward the the Archaean craton in Wyoming. The crust apparently developed southward from Wyoming in stages at 2400 m.y. ago or before, 2100 m.y. ago and 1750 m.y. ago. The Laramide alkali to calc-alkaline rocks and their associated porphyry Cu and massive replacement deposits have similar 206Pb/204Pb ratios and are the least radiogenic in the region; their 206Pb/204Pb ratios are all <18.0. Mid-Tertiary rhyolitic rocks and their associated near-source, vein-type deposits have higher such ratios, i.e. 206Pb/204Pb > 18.0. Pb isotopes in this region offer some criteria for prospecting purposes. The 206Pb/204Pb values for the larger ore deposits related to Laramide activity are all <18.0, particularly for the larger ones. Within the mid- Tertiary group, the same criteria apply - i.e. the largest deposits have the lowest 206Pb/204Pb ratios. -L.C.H.

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Lead-isotopic compositions of diverse igneous rocks and ore deposits from southwestern New Mexico and their implications for early Proterozoic crustal evolution in the western United States.
Series title:
Geological Society of America Bulletin
Volume
94
Issue:
1
Year Published:
1983
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geological Society of America Bulletin
First page:
43
Last page:
57