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Contrasting Siliceous Replacement Mineralization, East-Central Nevada

By
Mark D. Barton
Mark D. Barton
Center for Mineral Resources, Department of Geociences, University of ArizonaTucson, AZ 85721
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Eric Seedorff
Eric Seedorff
BHP Copper Company9275 N. Shannon Road, Tucson, AZ 85741;
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Robert P. Ilchik
Robert P. Ilchik
Center for Mineral Resources, Department of Geociences, University of ArizonaTucson, AZ 85721P.O. Box 41690, Tucson, AZ 85171.
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Gregory Ghidotti
Gregory Ghidotti
Center for Mineral Resources, Department of Geociences, University of ArizonaTucson, AZ 85721
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Published:
January 01, 1997

Abstract

Fine-grained siliceous replacement of carbonate-bearing rocks (‘jasperoid’) occurs in most mineral districts in east -central Nevada. In many of these occurrences, jasperoid contains Au and(or) Ag and little or no base metals, although concentrations and ratios range markedly. Here we compare and contrast these systems based on the geological and geochemical characteristics of the siliceous rocks and, where present, associated igneous and other types of hydrothennally altered rocks. At issue are both the broad patterns of regional metallogeny and specific links between Carlin-type mineralization and other geologic phenomena. These results are based on our own work and published data.

Broadly, two end-members are distinguished: (1) silicification as an intermediate- to late-stage part of complex alteration associated with igneous centers, and (2) jasperoids lacking other associated alteration and having few or no associated igneous rocks. Within this region, siliceous replacements are found with nearly all metallic(± magmatic) suites. The principal types are summarized in Table 1 and localities with selected characteristics are shown in Figure 1.

Igneous-related systems have well-developed time-space patterns of high-temperature proximal alteration overprinted and surrounded by lower temperature alteration assemblages. Jasperoids and other siliceous bodies are prominent in the latter suite, showing considerable differences in their mineralogical, geochemical, and textural characteristics. Pronounced zoning occurs over distances of a few hundred meters to no more than a few kilometers. These systems also exhibit strong correlations between style and composition of alteration, the composition of the igneous rocks, and associated metals (Fig. 1 ). Igneous-related systems show a pronounced

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Contents

Society of Economic Geologists Guidebook Series

Carlin-Type Gold Deposits Field Conference

Peter Vikre
Peter Vikre
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Tommy B. Thompson
Tommy B. Thompson
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Keith Bettles
Keith Bettles
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Odin Christensen
Odin Christensen
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Ron Parratt
Ron Parratt
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Society of Economic Geologists
Volume
28
ISBN electronic:
9781934969816
Publication date:
January 01, 1997

GeoRef

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