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R. A. Ayuso

Publications and source records attributed to R. A. Ayuso.

26 records · Page 2Linked to original sources
USGS1991

Rock chemistry and fluid inclusion studies as exploration tools for ore deposits in the Sila batholith, southern Italy

The Sila batholith is the focus of an extensive petrogenetic research program, which includes an assessment of its potential to host granite-related ore deposits. Univariate and multivariate statistical techniques were applied to major- and minor-element rock geochemical data. The analysis indicates that the highest potential for mineralization occurs in corundum-normative, peraluminous, unfoliated, relatively late-stage plutons. The plutons are enriched in Rb, Nb, Ta and U, but depleted in Fe, Mg and Sr. The K/Rb, Ba/Rb, Rb/Sr and Rb 3 /Ba·Sr·K indices and high R -factor scores of Si-K-Rb are typical of mineralized granitic rocks. A reconnaissance fluid inclusion study indicates that the sub-solidus rock was infiltrated by solutions of widely different temperatures (50–416°C) and variable salinities (0 to ∼26 wt.% NaCl equivalent). The higher-temperature solutions probably represent granite or magmatic-related Hercynian fluids, whereas the lower-temperature fluids may be either Hercynian or Alpine in age. Fluids with characteristics typical of mineralized “porphyry” systems have not been recognized.

Journal of Geochemical Exploration↗
USGS1986

Lead-isotopic evidence for distinct source of granite and for distinct basement in the northern Appalachians, Maine

Lead-isotopic compositions of feldspars in plutons of the coastal lithotectonic block (Avalonian basement), central Maine (Merrimack) synclinorium, and Connecticut Valley-Gaspé synclinorium in northern Maine (Granville basement) indicate the presence of three fundamentally different sources of Devonian granitic rocks in Maine. Plutons in the coastal lithotectonic block have the most radiogenic values ( 206 Pb/ 204 Pb: 18.25–19.25; 207 Pb/ 204 Pb: 15.59–15.67; 208 Pb/ 204 Pb: 38.00–38.60); plutons in northern Maine are the least radiogenic ( 206 Pb/ 204 Pb: 18.00–18.50; 207 Pb/ 204 Pb: 15.51–15.55; and 208 Pb/ 204 Pb: 37.80–38.38). Intermediate lead-isotope values characterize the plutons in central Maine ( 206 Pb/ 204 Pb: 18.20–18.40; 207 Pb/ 204 Pb: 15.56–15.60; and 208 Pb/ 204 Pb: 38.00–38.30). All plutons show relatively radiogenic lead values for their ages and suggest the imprint of continental crustal sources especially in the coastal block and in central Maine. Plutons from the Connecticut Valley–Gaspé synclinorium allow for a more significant isotopic input from the subcontinental mantle. The three distinct lead-isotope groups probably identify plutons formed in different crustal fragments in a continental collisional environment that were juxtaposed after emplacement of the granites.

Geology↗
USGS1984

Comparative geochronology in the reversely zoned plutons of the Bottle Lake Complex, Maine: U-Pb on zircons and Rb-Sr on whole rocks

The Bottle Lake Complex is a composite granitic batholith emplaced into Cambrian to Lower Devonian metasedimentary rocks. Both plutons (Whitney Cove and Passadumkeag River) are very coarse grained hornblende and biotite-bearing granites showing petrographic and geochemical reverse zonation. Two linear whole rock Rb/Sr isochrons on xenolith-free Whitney Cove and Passadumkeag River samples indicate ages of 379??5 m.y. and 381??4 m.y., respectively, in close agreement with published K-Ar ages for biotite from Whitney Cove of 377 m.y. and 379 m.y., and for hornblende 40Ar/39Ar determinations from Passadumkeag River which indicate an age of 378??4 m.y. The initial Sr isotopic ratio for Whitney Cove is 0.70553 and for Passadumkeag River is 0.70414. A whole-rock isochron on a suite of xenoliths from the Passadumkeag River granite indicates a whole rock Rb-Sr age of 496??14 m.y., with an initial Sr isotopic ratio of 0.70262. Two types of zircon exhibiting wide petrographic diversity are evident in variable proportions throughout the batholith. One of these types is preferentially found in a mafic xenolith and it is widely dispersed in the host granites forming discrete grains and probably as inclusions in the other type of zircon. U-Pb analyses of zircons give concordia intercept ages of 399??8 m.y. for Whitney Cove, 388??6 m.y. for Passadumkeag River, 415 m.y. for a mafic xenolith in Passadumkeag River, and 396??32 for combined Whitney Cove and Passadumkeag River granite. The zircons show a spread of up to 20 m.y. in the 207Pb/206Pb ages. Omitting the finest zircon fraction in the Passadumkeag River results in a concordia intercept age of 381??3 m.y., in better agreement with the whole-rock Rb-Sr and mineral K-Ar ages. For the Whitney Cove pluton, exclusion of the finest fraction does not bring the zircon age into agreement with the Rb-Sr data. Age estimates by the whole rock Rb-Sr, mineral K-Ar and Ar-Ar methods suggest that the crystallization age of the plutons is about 380 m.y., slightly younger than the U-Pb zircon intercept ages. A possible reason for this discrepancy is that the zircons contain inherited lead. Thus, zircon U-Pb ages might represent a mixture of newly developed zircon and older inherited zircon, whereas the Rb-Sr whole rock age (380 m.y.) reflects the time of crystallization, and the argon ages result from rapid cooling after emplacement. ?? 1984 Springer-Verlag.

Contributions to Mineralogy and Petrology↗
USGS1984

Manganese-rich red tourmaline from the Fowler talc belt, New York.

Red uvite containing up to 4.34 wt.% MnO is found in the Arnold talc mine near Fowler, New York, USA. Microprobe analyses give a composition of 51% uvite in the uvite-dravite series. Associated minerals in this manganiferous metamorphic assemblage (possibly an evaporite) are manganese-rich tremolite (hexagonite) braunite and quartz.-R.A.G.

Canadian Mineralogist↗
USGS1983

Mineral resource potential map of the Lye Brook Wilderness, Bennington and Windham counties, Vermont

The Lye Brook Wilderness contains no significant mineral deposits. Although the Cheshire Quartzite is a potential source of low-grade silica sand and crops out in a large area within the wilderness, its degree of induration and relative inaccessibility make its use prohibitive. No major concentation of base metals exist within the Precambrian rocks, although they contain the highest metal concentrations within the wilderness. Uranium mineralization is not extensive in the Precambrian rocks, despite the occurrence of significant deposits nearby.

Vermont↗