Abstract

The Moina skarn deposit, with its associated Sn-W-F veins and greisen, occurs at the margin of the Dolcoath leucogranite. The skarn occurs as a thick horizontal plate approximately one km in its longest dimension and up to 100 m thick and is separated from the granite's upper near-horizontal contact by approximately 200 m of the Moina sandstone. The necessary plumbing system for access of mineralizing fluids is probably a series of east-west-trending tension fractures, now Sn-W quartz veins, associated with a major northwest-southeast-trending fault known as the Bismuth Creek fault. Emplacement of the granite was at shallow depths (<3 km?).The skarn unit section consists of: (a) a granular garnet-pyroxene-vesuvianite-fluorite skarn; (b) the main skarn ("wrigglite") consisting of fluorite-magnetite-vesuvianite (cassiterite-scheelite-adularia) and having a characteristic fine-grained, rhythmic, finely layered contorted structure; (c) a granular, pale green pyroxene skarn which occurs as thin units (<5 cm) within and near the base of unit (b) above; (d) a wollastonite-rich skarn (>80 vol % wollastonite); and (e) a granular garnet-pyroxene-vesuvianite-fluorite skarn overlying the other units. Unit (e) is relatively enriched in boron ([asymp] 600 ppm).The skarn unit carries up to 25 weight percent F; 0.6 percent Sn, 0.5 percent W, 0.2 percent Be, 27.5 percent Zn, and 4.5 ppm Au. Sn, Be, and Fe values increase toward the upper part of the skarn sequence whereas Zn, Cu, and Mo values are erratic. Secondary Zn-Cu-In-Cd-Au sulfide-amphibole alteration of the primary F-Sn-Be oxide skarn is related to the Bismuth Creek fault. When the primary wrigglite skarn is altered, Sn is largely lost from that part of the skarn.

First Page Preview

First page PDF preview
You do not currently have access to this article.