September Geology and GSA Today media ...(ccurs as inclusions in high- and low-alu...)

Date:8/22/2008

ccurs as inclusions in high- and low-aluminum amphibole and pyroxene, and indicates that sulfate-saturated magmas spanned a period of six million years at Yanacocha, Peru. Magmatic anhydrite from Yanacocha and other sites is characterized by light rare earth element-enriched patterns and elevated strontium contents distinct from magmatic-hydrothermal anhydrite. Petrologic arguments suggest that the hydrous and oxidized Yanacocha magmas contained more than approximately 1000 ppm sulfur, both dissolved in the melt and as a separate sulfate phase, which is sufficient to provide all the sulfur for the genetically related giant sulfur-rich Yanacocha epithermal gold deposits. High-aluminum amphiboles contain unusual anhydrite with wormy and amoeboidal textures, which are tentatively interpreted to represent trapping of an immiscible CaSO4-water melt, together with sulfur-rich apatite at a temperature of ~950 degrees Celsius and a water pressure greater than 3 kbar. Chambefort et al. claim that such unusually sulfate-rich magmas may be required to produce sulfur-rich magmatic-hydrothermal mineral deposits.

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Particle size separation and evidence for pedogenesis in samples from the Chinese Loess Plateau spanning the past 22 m.y.

Frank Oldfield et al., Dept. of Geography, University of Liverpool, Liverpool L69 7ZT, UK. Pages 727-730.

The deep accumulations of wind-blown silt (loess) that form the Loess Plateau of China provide a record of past climate changes spanning the past 22 million years. They therefore comprise one of the longest continuous terrestrial archives of environmental change anywhere in the world. The record is encoded in alternating bands of loess blown from the dry lands of the continental interior and buried soils formed during periods when warmer, moister climatic conditions prevailed. Decoding the signatures of past changes involves a mix of techniques, including particle-size analysis and magnetic measurements.
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Contact: Christa Stratton cstratton@geosociety.org 303-357-1093 Geological Society of America Source:Eurekalert

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