Lead isotope evidence for the formation of epithermal gold quartz veins in the Chortis Block, Nicaragua
| Autor: | D. Krstic, K. Sundblad, G. L. Cumming |
|---|---|
| Rok vydání: | 1991 |
| Předmět: | |
| Zdroj: | Economic Geology. 86:944-959 |
| ISSN: | 1554-0774 0361-0128 |
| Popis: | Lead isotope compositions are reported here for auriferous quartz veins of Nicaragua and for some of their possible source rocks. The veins are hosted by a belt of Cenozoic continental margin basalts and basaltic andesites, which were formed as a result of the subduction of oceanic crust belonging to the Cocos plate under pre-Mesozoic sialic crust of the Caribbean plate. Volcanic rocks in northeastern Nicaragua show the most evolved lead isotope composition, indicating a strong influence from the pre-Cenozoic basement. In contrast, no basement influence can be detected in the volcanic rocks in central and western Nicaragua. The isotopic composition of the volcanic rocks in Nicaragua is thus a function of two ultimate sources: ocean floor basalts and pre-Mesozoic continental crust.Three groups of gold-bearing quartz veins have been distinguished in Nicaragua based on base metal content, structural trends, and lead isotope composition. Polymetallic veins in the Atlantic Coast group of northeastern Nicaragua contain up to several percent base metals and show relatively radiogenic lead isotope compositions. This isotopic signature indicates metal derivation from a Cenozoic volcanic (or intrusive) source with significant contamination of old sialic crust. Veins in the Highland group of central Nicaragua show similar northeast-trending structures but much lower base metal contents. They have low radiogenic lead isotope compositions indicating a Cenozoic volcanic source with insignificant contamination of old sialic crust. Veins belonging to the Nicaraguan Depression group of northwestern Nicaragua have very low base metal contents and show a wide range of lead isotope ratios that probably reflects lead from two types of Cenozoic volcanic rocks, as well as pre-Mesozoic (>400 Ma) basement rocks. Veins belonging to this group are structurally controlled by a major northwest-southeast-trending half graben (the Nicaraguan depression), which may constitute a surficial expression of the southwestern limit of the pre-Mesozoic basement. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|