LA-ICP-MS determination of gold in Bi-chalcogenides from four deposits in the Fennoscandian Shield

Abstract

Gold concentrations in Bi-chalcogenides (tellurobismuthite and laitakarite) from four deposits in the Fennoscandian Shield have been determined by LA-ICP-MS. Both minerals contain gold above background levels, with tellurobismuthite from Orivesi (Kutamejärvi), Finland, with concentrations between 1 and more than 300 ppm. The concentrations of gold vary over two orders of magnitude within individual analysed patches. The gold signal in the majority of individual LA-ICP-MS profiles is irregular. Laitakarite from Orijärvi (Finland) contains lesser concentrations (up to 10 ppm). Tellurobismuthite in two Sveconorwegian orogenic gold occurrences differ markedly; 798 and 2,472 ppm in Glava (Sweden) and <1 ppm at Moberg (Norway). The present dataset shows that Bi-chalcogenides may, in some cases, be considered as gold carriers, and can contain gold at similar levels as pyrite. Measured concentrations in tellurobismuthite are, with the exception of Glava, lower than those obtained in published experimental work on that mineral. This is interpreted as due to the formation of discrete sub-􀈝m sized inclusions of gold within the Bi-minerals during post-depositional overprinting. The influence of metamorphism is clearly an important factor in determining the distribution of gold within Bi-chalcogenides.