Chemistry, mineralogy and crystallization conditions of porphyry Mo-forming magmas at Urad-Henderson and Silver Creek, Colorado, USA

37Citations
Citations of this article
18Readers
Mendeley users who have this article in their library.

Abstract

The metal content, volatile content and crystallization conditions of ore-related rhyolite samples from the Climax-type porphyry Mo deposits at Urad-Henderson and Silver Creek (Rico) were reconstructed based on the composition of melt inclusions, mineral inclusions, and titanium-inquartz thermobarometry. Additional melt inclusion data were obtained from contemporaneous mafic dikes. Crystallized melt inclusions were either directly analyzed by laser ablation inductively coupled plasma mass spectrometry, or re-homogenized and then analyzed by electron microprobe. Inter-mineralization rhyolite melts at Urad-Henderson were highly evolved (four times more fractionated than average granite of the continental crust), contained 10-15ppm Mo, 6-7 wt % H2O and 0·5-0·7wt % F, and record crystallization conditions of 730-770°C, 1-3 kbar and an oxygen fugacity about two log units above the fayalite-magnetite-quartz buffer (FMQ+2). Melts from two presumably syn-mineralization rhyolite dikes at Silver Creek were slightly less evolved and contained 3-5ppm Mo, 7-8 wt % H2O and ~0·3wt % F, and record crystallization conditions of 780-800°C, 2-5 kbar. Both datasets are characterized by distinctly lower fluorine contents but higher temperatures and higher water contents than corresponding values reported for ore-related rhyolites at Climax. Calculated melt viscosities (log η=3·5-4·9 Pa s) are lower than those of average granitic melts at the same temperature, which may have facilitated crystal-melt segregation and thus accumulation of large volumes of fractionated, crystal-poor melts in shallow magma chambers, a process that seems to be critical for the formation of Climax-type porphyry Mo deposits.

Cite

CITATION STYLE

APA

Zhang, D., & Audétat, A. (2017). Chemistry, mineralogy and crystallization conditions of porphyry Mo-forming magmas at Urad-Henderson and Silver Creek, Colorado, USA. Journal of Petrology, 58(2), 277–296. https://doi.org/10.1093/petrology/egx016

Register to see more suggestions

Mendeley helps you to discover research relevant for your work.

Already have an account?

Save time finding and organizing research with Mendeley

Sign up for free