Complex ores, in this instance, a polymetallic base metal ore with additional precious and penalty elements, pose particularly tough challenges for successful production forecasts. Plant performance and recoveries for complex ores are more difficult to predict due to the larger number of variables that must be considered, tracked, and characterized during the multi-stage separation process.

The focus of this study is to evaluate the mineralogical and textural controls that affect the variability in the flotation performance of a complex and variable ore. The research is based on a case study of the polymetallic Lappberget Zn-Pb-Ag-(Cu-Au) massive sulfide deposit at the Garpenberg Mine in Sweden. The mine is currently operated by Boliden Mineral AB and produces four different concentrates: zinc, lead, copper, and agravimetric concentrate targeted for gold and silver.

Geometallurgical characterization was conducted to understand the variability within the Lappberget deposit and to quantify the impact of geology (e.g., host rocks, mineralogy, and texture) on the metallurgical response and metal recovery processes. The approach undertaken is divided into five stages: (1) geological characterization, (2) ore classification, (3) geometallurgical testing, (4) development of prediction models, and (5) geometallurgical domaining. The first two stages aim at characterizing the geological characteristics of the ore and understanding its variability, whereas the latter three stages aim to describe and quantify the variability in the flotation performance of the ore and determine how it relates to its geological characteristics.

For the geological characterization, qualitative and quantitative mineralogical and textural investigations were undertaken for the different sulfides present in the deposit, mainly sphalerite, pyrite, galena, and chalcopyrite. Results from this study revealed the mineralogical, textural, and chemical variations of these sulfides within the deposit. This heterogeneity reflects the complex ore-forming conditions and the polyphase history of tectono-metamorphic processes that have affected the deposit. Three sphalerite types and four pyrite types were identified based on their distinct mineral chemistry, trace element signatures, texture, and host rock associations.

Based on the geological characteristics of the Lappberget deposit, ten geological domains were established to provide a framework for understanding the variability in flotation performance within the deposit. Batch flotation tests were conducted for samples from each geological domain. Quantified mineralogical characterization of the flotation products from the batch flotation tests was undertaken using automated mineralogy complemented by electron microprobe analysis. Results from the deportment study of the silver-rich ore type revealed a variety of complexly intergrown silver-bearing minerals: mainly native silver, allargentum, and freibergite. A strong association between silver and antimony was also observed. The results of the sphalerite deportment study indicate that in terms of ore mineral characteristics, physical factors, such as grain size and liberation, have a more significant effect on sphalerite flotation than the presence of elevated iron and manganese in the sphalerite crystal structure. The high variability in the feed grade of the different ore types identified in the Lappberget deposit reflects the heterogeneity of the ore and, consequently, the variable flotation performance.