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Mineralogy of the Ash Mountain Sn-bearing skarn, Tuya Range, northern British Columbia, Canada

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Rok publikování 2017
Druh Článek v odborném periodiku
Časopis / Zdroj Canadian Mineralogist
Fakulta / Pracoviště MU

Přírodovědecká fakulta

Obor Geologie a mineralogie
Klíčová slova skarn; tin; malayaite; andradite; Parallel Creek batholith; A-type granite; British Columbia
Popis The Ash Mountain Sn-bearing skarn, located in the Tuya Range of the Cassiar Mountains in northern British Columbia, was investigated in order to provide the first modern, comprehensive characterization of its mineralogy and zoning and to identify the main skarn-forming processes. The Ash Mountain skarn is unusual with respect to other Sn-bearing skarns because the main Sn-bearing minerals are malayaite and andradite (with 2.33 wt.% SnO2), and no cassiterite has been found to date. The associated intrusive body-the Parallel Creek granite-is a highly fractionated, felsic, A-type, biotite granite that was generated in a within-plate setting. The biotite in the granite is Al-rich annite with elevated Ti (up to 2.77 wt.% TiO2), F (up to 2.04 wt.% F), and Cl (up to 0.33 wt.% Cl); annite in an associated aplite dike contains up to 0.47 wt.% Cl. High F and Cl in annite indicate a high amount of fluxing components and could be used as an indicator of mineralized granites. The Ash Mountain skarn is an oxidized, calcic tin skarn that was formed through a sequence of metasomatic events that resulted in the crystallization of two distinct skarn zones: a proximal andradite skarn and a distal grossular-diopside-vesuvianite skarn. The paragenetic sequence of the skarn was determined to be: (1) Al + Si metasomatism of dolomite-bearing limestone to a grossular-diopside-vesuvianite skarn, (2) overprinting of the grossular-diopside-vesuvianite skarn by a Sn-bearing andradite skarn due to Fe metasomatism, and (3) remobilization of Sn in the andradite skarn by a reducing hydrothermal fluid, to crystallize malayaite. The near endmember composition of the malayaite suggests that this latest stage of skarn formation occurred at low temperatures (ca., 450 degrees C). The absence of cassiterite can be attributed to prevailing basic conditions during hydrothermal alteration.
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