EXAMINATION OF MICRO-SCALE SULFIDE DISTRIBUTION FOR THE GOLD MINERALIZATION IN THE LAPPBERGET DEPOSIT, GARPENBERG MINE, SWEDEN: TOWARDS A GEOMETALLURGICAL APPROACH

Sammanfattning: Ore characterization studies are of great importance to the mining industry, especially when dealing with precious metals by-products. It is a way towards increasing mining efficiency. The Swedish Boliden’s Zn–Pb–Ag–(Cu–Au) Lappberget Deposit is the main ore body at the Garpenberg Mine producing concentrates of zinc, lead, copper, and a gravity concentrate of silver and gold, which accounts for a significant revenue for the mine. Garpenberg Mine is an ancient and traditional mining site in Sweden, nonetheless the Lappberget deposit is a relatively recent discovery and there are still on-going studies on this ore body. More recently detailed ore investigations have been carried out on the sulfides and silver mineralization in different geological domains within the Lappberget deposit. In this context, the present work is focused on investigating the gold mineralization of the deposit, aiming to study the occurrence and distribution of gold minerals, characterize the gold in the ore and how its characteristics affect gold recoveries during its processing. To achieve these goals, different investigative methods were applied on drill core samples of the footwall disseminated to semi-massive mineralization (FWD), and on samples from the gravity concentrator at Boliden’s processing plant. The techniques applied were optical microscopy, scanning electron microscopy, energy dispersive x-ray spectrometry, electron probe microanalysis, laser ablation inductively couple plasma mass spectrometry, and bulk chemical analysis. The main findings pointed electrum as the main gold mineral, occurring with a strong sulfide association, in a variety of textures and grain sizes. The study also identified the occurrence of Au-Bi alloy, not previously described in literature of the Garpenberg region. The potential of invisible gold in the sulfide carriers was also a subject of investigation, as well as the evaluation of the characteristics of the samples from the gravity concentrator.