Geology, mineralogy and genesis of gold mineralization at Calliachar-Urlar Burn, Scotland

Abstract

At Calliachar Burn, 4 km from Aberfeldy, Scotland, 14 steeply dipping quartz-sulphide ± gold veins infill master joints that crosscut gently dipping metasediments and metabasics in the Pitlochry Schist Formation of the Upper Dalradian. Associated wallrock alteration consists of extreme bleaching with the development of sericite, chlorite and carbonate enrichment. Gold grades vary with mineralogy between the veins, ranging from high-grade quartz-galena-pyrite ± base-metal sulphides ± electrum to low-grade galena-chalcopyrite ± base-metal sulphides. Coarse-grained pyrite enclosing primary pyrrhotite ± chalcopyrite ± cubanite ± mackinawite and later chalcopyrite, galena and sphalerite inclusions is the main phase, accompanied by lesser amounts of zoned arsenopyrite. Pyrite is intergrown with, and replaced by, chalcopyrite and sphalerite, but mainly by galena, itself carrying small tetrahedrite-group mineral, hessite (Ag2Te), benleonardite (Ag8(Sb,As)Te2S3) and native tellurium inclusions. Gold is present as small,