Tin (Sn) and tungsten (W) mineralization are often associated with each other in relation to highly evolved granites, but economical ore grades are restricted to rare global occurrences and mineralization styles are highly variable, indicating different mechanisms for ore formation. The Sn-W Zinnwald deposit in the Erzgebirge (Germany/Czech Republic) in the roof zone of a Variscan Li-F granite hosts two contrasting styles of mineralization: 1) cassiterite (Sn) in greisen bodies and 2) cassiterite and wolframite (W) in predominantly sub-horizontal quartz-rich veins. The relative timing and causes for ore formation remain elusive. Studies of fluid inclusion assemblages in wolframite, cassiterite and quartz samples from greisen and veins by conventional and infrared microthermometry and LA-ICP-MS analyses have revealed compelling evidence that all elements required for the formation of the Zinnwald Sn-W deposit were contained in a single parental magmatic-hydrothermal fluid that underwent two main processes: 1) fluid-rock interaction during Sn-greisen formation and 2) depressurization and vapor loss leading to ore precipitation in quartz-Sn-W veins. The results also show that fluid inclusion assemblages in ore minerals can document fluid processes that are absent in the fluid inclusion record of gangue minerals. The study further highlights the role of phase separation in the formation of W-rich Sn-deposits and indicates that W-deposits in distal parts of evolved granites may be restricted to fluids derived from deeper-seated plutons.

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Near-surface supergene ores of the Merensky Reef in the Bushveld Complex, South Africa, contain economic grades of platinum-group elements, however, these are currently uneconomic due to low recovery rates. This is the first study that investigates the variation in platinum-group elements in pristine and supergene samples of the Merensky Reef from five drill cores from the eastern Bushveld. The samples from the Richmond and Twickenham farms show different degrees of weathering. The whole-rock platinum-group element distribution was studied by inductively coupled plasma-mass spectrometry and the platinum-group minerals were investigated by reflected-light microscopy, scanning electron microscopy, and electron microprobe analysis. In pristine (“fresh”) Merensky Reef samples, platinum-group elements occur mainly as discrete platinum-group minerals, such as platinum-group element-sulfides (cooperite–braggite) and laurite as well as subordinate platinum-group element-bismuthotellurides and platinum-group element-arsenides, and also in solid solution in sulfides (especially Pd in pentlandite). During weathering, Pd and S were removed, resulting in a platinum-group mineral mineralogy in the supergene Merensky Reef that mainly consists of relict platinum-group minerals, Pt-Fe alloys, and Pt-oxides/hydroxides. Additional proportions of platinum-group elements are hosted by Fe-hydroxides and secondary hydrosilicates (e.g., serpentine group minerals and chlorite). In supergene ores, only low recovery rates (ca. 40%) are achieved due to the polymodal and complex platinum-group element distribution. To achieve higher recovery rates for the platinum-group elements, hydrometallurgical or pyrometallurgical processing of the bulk ore would be required, which is not economically viable with existing technology.