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de Quadros Telmo F. P. Koppe Jair C. Strieder Adelir J. Costa João Felipe C. L. 《Natural Resources Research》2003,12(1):57-65
A large number of mineral deposits are associated with hydrothermal processes, especially auriferous deposits. In such processes, studies on percolating fluids may indicate the presence of potash (K), among other elements. In this study, aerogammaspectrometric data-processing methodologies are evaluated, especially those methods based on the suppression of the primary contribution of potassium, the result of lithological and soil variations, and to environmental conditions. Resulting maps point out the contribution of hydrothermal K. This processing procedure was used because of the association of hydrothermal K and auriferous mineralizations according to the deposit model defined for the studied region. Intensity maps locate the areas with great influence of hydrothermal K. Data integration required to improve a change in the gammaspectrometric data processing in order to positively correlate hydrothermalised areas. Data integration could distinguish high and medium favorable targets for mineral exploration of lode-Au deposits in the studied region. 相似文献
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H.?Albert?GilgEmail author Giulio?Morteani Yuri?Kostitsyn Christine?Preinfalk Istvan?Gatter Adelir?J.?Strieder 《Mineralium Deposita》2003,38(8):1009-1025
In the Ametista do Sul area, Rio Grande do Sul, Brazil, amethyst-bearing geodes are hosted by a ~40- to 50-m-thick subhorizontal
high-Ti basaltic lava flow of the Lower Cretaceous Paraná Continental Flood Basalt Province. The typically spherical cap-shaped,
sometimes vertically elongated geodes display an outer rim of celadonite followed inwards by agate and colorless and finally
amethystine quartz. Calcite formed throughout the whole crystallization sequence, but most commonly as very late euhedral
crystals, sometimes with gypsum, in the central cavity. Fluid inclusions in colorless quartz and amethyst are predominantly
monophase and contain an aqueous liquid. Two-phase liquid–vapor inclusions are rare. Some with a consistent degree of fill
homogenize into the liquid between 95 and 98 °C. Ice-melting temperatures in the absence of a vapor phase between –4 and +4 °C
indicate low salinities. Chondrite-normalized REE patterns of calcites are highly variable and show generally no systematic
correlation with the paragenetic sequence. The oxygen isotope composition of calcites is very homogeneous (δ18OVSMOW=24.9±1.1‰, n=34) indicating crystallization temperatures of less than 100 °C. Carbon isotope values of calcites show a considerable variation
ranging from –18.7 to –2.9‰ (VPDB). The 87Sr/86Sr ratio of calcites varies between 0.706 and 0.708 and is more radiogenic than that of the host basalt (~0.705). The most
likely source of silica, calcium, carbon, and minor elements in the infill of the geodes is the highly reactive interstitial
glass of the host basalts leached by gas-poor aqueous solutions of meteoric origin ascending from the locally artesian Botucatú
aquifer system in the footwall of the volcanic sequence. The genesis of amethyst geodes in basalts at Ametista do Sul, Brazil,
is thus considered as a two-stage process with an early magmatic protogeode formation and a late, low temperature infill of
the cavity.
Editorial handling: A. Cheilletz 相似文献
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