| A study of the Faro and Vangorda Zn-Pb-Ag ores and concentrator products was made by image analysis to evaluate the influence their mineralogical characteristics have on grade and recovery of lead, zinc, silver and gold. Drill-core and concentrator samples were characterized by mineral identification and modal analysis, and by determining ore mineral grain size distributions, precious metal content of the ore minerals, and ore mineral liberations and associations. The detailed behaviour in the concentrator of sphalerite and galena from each deposit was calculated by materials balance.;A technique for measuring ore mineral associations by the proportion of perimeter adjacent to other minerals was developed and tested. The technique allows the determination of mineral associations, preferred mineral associations, preferred mineral associations by grain size, preferred breakage and relative bond strengths between minerals. Sphalerite and galena are preferentially associated with pyrite in pyritic ores, with quartz in quartzose ores, and with barite in baritic ores. In quartzose ores a significant proportion of sphalerite and galena is disseminated as fine grains in the quartz matrix. In pyritic and baritic ores coarse-grained sphalerite and galena have a higher association with each other than their fine-grained counterparts. In those same ores fine-grained galena is more closely associated with pyrite than coarse-grained galena. In baritic Vangorda ore, an association of fine-grained sphalerite and galena with siderite is detected. These textures have implications for mineral beneficiation. There is strong evidence that preferred breakage takes place during grinding. Coarse-grained pyrite and barite break preferentially from sphalerite and galena, whereas sphalerite and galena have a slight tendency not to detach from each other. Medium-grained siderite detaches poorly from sphalerite and galena. It is interpreted that preferential breakage is due to differences in bond strength between sphalerite, galena and the other major minerals. A sequence for increasing bond strength between sphalerite and the other minerals is: Barite ;The major factors which reduce concentrate grades and metal recoveries due are presence of trace amounts of secondary minerals (covellite, digenite, chalcocite, bornite, goethite, secondary galena), as well as marcasite and pyrrhotite, the presence of a large amount of fine-grained galena, the associations of sphalerite and galena with siderite and each other and the mineralogical distribution of much of the silver in acanthite and the gold in gold-silver-alloy. |
