Mineralogical Controls on the Recovery of Antimony in Base-Metal Flotation – Outlining the Framework of a Geometallurgical Model for the Rockliden VHMS Deposit, Sweden

The results presented in this thesis are a case study on the polymetallic Zn–Cu volcanic-hosted massive sulphide (VHMS) deposit at Rockliden. The Rockliden mineralisation is located in north-central Sweden, about 150 km south of the Skellefte district. Exploration at Rockliden started in the 1980’s despite the relative remote location of the deposit from processing facilities in the Skellefte ore district. During the first exploration period, flotation tests wereconducted which indicated that the locally high Sb grade in the mineralisation would increase the Sb content of the Cu–Pb concentrate and lower its quality at the smelter. In 2007 exploration was resumed at the Rockliden site andmassive sulphide mineralisation was found to extend toward the depth. The average Sb grade in the mineralisation decreases with depth; it is approximately 0.13 wt% above 400m below surface and only 0.06 wt% Sb below 400m. The focus of this PhD study was to evaluate mineralogical controls on the distribution of Sb minerals in base-metal flotation, which influences the Sb grade and hence the quality of the Cu–Pb concentrates. Modelling the Sb grade of the Cu–Pb concentrates is expected to be helpful in flowsheet design, e.g. for decision making on when to usehydrometallurgical treatment to reduce the Sb grade of this product prior to submission to the smelter. The first part of the study was to characterise the massive sulphides and the immediate host rocks with special reference to Sb mineralogy. The mineralogy and mineral associations were documented by optical and scanning electron microscopy (SEM). Micro-analytical tools (such as wavelength-dispersive X-ray spectroscopy at an electron probe microanalyser) were used to study the mineralogical distribution of major, minor and trace elements (e.g., Zn, Cu, Fe, Sb). Sphalerite and chalcopyrite are the main base-metal minerals in the massive sulphides. Antimony (Sb) is a minor to trace element bound in different minerals. The Sb mineralogy is complex; the most common Sb-bearing phases include gudmundite and Cu- and Pb-bearing Sb sulphosalts; tetrahedrite, bournonite, and meneghinite. Furthermore, the Sb minerals were found to occur partly locked with base-metal sulphides and gangue in flotation products from initial flotation tests. Mineralogical parameters such as grain size, degree of liberation and locking (mineral association in particles) were outlined as potential controls on the distribution of the Sb minerals. The second part of this study was to quantify mineralogical parameters influencing the distribution of the Sbminerals in a laboratory flotation test. For this purpose composites blended from drill core samples were collected and tested, and the flotation products were analysed with MLA measurement. The measurements were massbalancedby a particle tracking technique and the impact of the mineralogical parameters controlling the Sb distribution was evaluated. The laboratory flotation test showed that Cu- and Pb-bearing Sb sulphosalts show different flotation behaviour than gudmundite and that locking of gudmundite with Cu- and Pb-bearing minerals influences its distribution. Further, chemical, bulk mineralogical and particle information was used to build Sb distribution models based on a first-order kinetic process using HSC Chemistry Sim software. Chemical assays alone were insufficient to simulate the Sb grades of flotation products, since they do not distinguish between the various Sb minerals. The simulation indicated that a model using bulk mineralogy (e.g. collected by Scanning Electron Microscopy based measurements) would be sufficient for estimating the Sb recovery and grade of the Cu–Pb concentrate in the exploration or scoping stage of the Rockliden deposit The following components are required for a complete particle-based geometallurgical model of Rockliden: a process-adapted geological model, a particle-breakage model, and a unit process model. Implementing full particle information in the HSC Chemistry Sim software would improve the flotation model for Sb distribution, i.e. unit process model. Further, suggestions on building a process-adapted geological model and a particle breakage modelare given based on the demands of a corresponding flotation model. The potential of the particle-based approach to provide a holistic view on the deposit by connecting ore geology, mineral processing and process metallurgy aspects of the Rockliden deposit was shown in this study.Godkänd; 2016; 20160205 (frimin); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Friederike Elisabeth Minz Ämne: Malmgeologi/Ore Geology Avhandling: Mineralogical Controls on the Recovery of Antimony in Base-Metal Flotation Outlining the Framework of a Geometallurgical Model for the Rockliden VHMS Deposit, Sweden Opponent: Dr Julie Hunt, Minerals Engineering, Materials and Environment (GeMMe) Department, University of Liege, Belgium. Ordförande: Biträdande professor Christina Wanhainen, Avd för geovetenskap och miljöteknik, Institutionen för samhällsbyggnad och naturresurser, Luleå tekniska universitet. Tid: Fredag 8 april 2016, kl 10.00 Plats: F341, Luleå tekniska universite