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

Emily D. Scribner, Lee A. Groat and Jan Cempirek
Mineralogy of the Ash Mountain Sn-bearing skarn, Tuya Range, northern British Columbia, Canada
The Canadian Mineralogist (March 2017) 55 (2): 333-347


The Ash Mountain Sn-bearing skarn, located in the Tuya Range of the Cassiar Mountains in northern British Columbia (59 degrees 17'50'N, 130 degrees 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.% SnO (sub 2) ), 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.% TiO (sub 2) ), 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 degrees C). The absence of cassiterite can be attributed to prevailing basic conditions during hydrothermal alteration.

ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 55
Serial Issue: 2
Title: Mineralogy of the Ash Mountain Sn-bearing skarn, Tuya Range, northern British Columbia, Canada
Affiliation: University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada
Pages: 333-347
Published: 201703
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 38
Accession Number: 2017-080791
Categories: Igneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 6 tables
N59°17'50" - N59°17'50", W130°31'04" - W130°31'04"
Secondary Affiliation: Masaryk University, CZE, Czech Republic
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201742
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