Sulphide Pyrrhotite Sphalerite

Depending on the composition of disseminated and medium-coarse-grained ore, they can be divided into two basic groups sulphides and chloritic tourmaline ores. In the sulphide ore, the minerals are represented by pyrite, pyrrhotite, arsenopyrite, chalcopyrite, galena and stannin. Less common are sphalerite and bismuth. 

Several minerals have been identified in polished thin sections of various rock types including massive sulphide, gossan, intermediate crystal-lapilli tuff, and felsic ash tuff (Fig. 2). These minerals include apatite, monazite, zircon, allanite, titanite, xenotime, magnetite, cassiterite, cobaltite-gersdorffite, rutile, ilmenite, goethite, sphalerite, galena, arsenopyrite, chalcopyrite, pyrite, and pyrrhotite. These minerals range in size from 20 pm to 250 pm and represent potential Indicator minerals. 

VMS mineralisation at Big Lake consists of stringer-textured to semi-massive pyrrhotite, chalcopyrite, and sphalerite, in decreasing order of abundance, at up to 80% sulphides by volume over a few metres. Best-mineralised intervals contain 6 % Cu and 2 % Zn weighted over five to ten metres, with significant enrichment in Au, Ag, and other metals. 

The VMS sulphides define a broadly conformable sheet 5-50 m below the base of the BLUC. This synformal surface of mineralisation generally coincides with the transition from ultramafic cumulates and strongly foliated metavolcanic rocks to an underlying sequence of metavolcanic rocks and interflow metawacke and metasiltstone rocks (Fig. 2). Sphalerite-pyrrhotite mineralisation in hydrothermal veins was also observed within the BLUC several km west of this study area. 

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