Contrasting Siliceous Replacement Mineralization, East-Central Nevada
Mark D. Barton, Eric Seedorff, Robert P. Ilchik, Gregory Ghidotti, 1997. "Contrasting Siliceous Replacement Mineralization, East-Central Nevada", Carlin-Type Gold Deposits Field Conference, Peter Vikre, Tommy B. Thompson, Keith Bettles, Odin Christensen, Ron Parratt
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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