Ash Mountain, Tuya Range, Atlin Mining Division, British Columbia, Canadai

Regional Level Types
Ash Mountain	Mountain
Tuya Range	Mountain Range
Atlin Mining Division	Division
British Columbia	Province
Canada	Country

On Ash Mountain in the Cassiar Mountains of northern British Columbia, discontinuous skarn lenses occur in limestones within folded, faulted and metamorphosed argillites and quartzites of the Carboniferous Oblique Creek Formation, intruded by granites of the Late Cretaceous Parallel Creek Batholith. Disseminated scheelite occurs in various skarns, with grab sample assays running to 0.15 per cent WO3 (Assessment Report 8196).

Scribner, Groat and Cempirek (2017 Canadian Mineralogist) says: The Ash Mountain Sn-bearing skarn, located in the Tuya Range of the Cassiar Mountains in northern British Columbia (59°17′50′′N, 130°31′04′′W), 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, where the latter formed in the first stage of metasomatic reaction and was later overprinted by an oxidized, Fe,Sn-enriched fluid that formed the andradite 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, less rich in Mg and Fe, to crystallize malayaite. The near endmember composition of the malayaite (maximum of 4.3% titanite component) suggests that this latest stage of skarn formation occurred at low temperatures (ca. <450 °C). The absence of cassiterite can be attributed to prevailing basic conditions during hydrothermal alteration.

Other Databases

Link to British Columbia Minfile:	104O 021

Other Regions, Features and Areas containing this locality

References