@article{KorgesJungeBorgetal.2021, author = {Korges, Maximilian and Junge, Malte and Borg, Gregor and Oberth{\"u}r, Thomas}, title = {Supergene mobilization and redistribution of platinum-group elements in the Merensky Reef, eastern Bushveld Complex, South Africa}, series = {The Canadian mineralogist}, volume = {59}, journal = {The Canadian mineralogist}, number = {6}, publisher = {Mineralogical Association of Canada}, address = {Ottawa}, issn = {1499-1276}, doi = {10.3749/canmin.2100023}, pages = {1381 -- 1396}, year = {2021}, abstract = {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 elementbismuthotellurides 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.}, language = {en} } @phdthesis{Korges2019, author = {Korges, Maximilian}, title = {Constraining the hydrology of intrusion-related ore deposits with fluid inclusions and numerical modeling}, doi = {10.25932/publishup-43484}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-434843}, school = {Universit{\"a}t Potsdam}, pages = {VIII, 99}, year = {2019}, abstract = {Magmatic-hydrothermal fluids are responsible for numerous mineralization types, including porphyry copper and granite related tin-tungsten (Sn-W) deposits. Ore formation is dependent on various factors, including, the pressure and temperature regime of the intrusions, the chemical composition of the magma and hydrothermal fluids, and fluid rock interaction during the ascent. Fluid inclusions have potential to provide direct information on the temperature, salinity, pressure and chemical composition of fluids responsible for ore formation. Numerical modeling allows the parametrization of pluton features that cannot be analyzed directly via geological observations. Microthermometry of fluid inclusions from the Zinnwald Sn-W deposit, Erzgebirge, Germany / Czech Republic, provide evidence that the greisen mineralization is associated with a low salinity (2-10 wt.\% NaCl eq.) fluid with homogenization temperatures between 350°C and 400°C. Quartzes from numerous veins are host to inclusions with the same temperatures and salinities, whereas cassiterite- and wolframite-hosted assemblages with slightly lower temperatures (around 350°C) and higher salinities (ca. 15 wt. NaCl eq.). Further, rare quartz samples contained boiling assemblages consisting of coexisting brine and vapor phases. The formation of ore minerals within the greisen is driven by invasive fluid-rock interaction, resulting in the loss of complexing agents (Cl-) leading to precipitation of cassiterite. The fluid inclusion record in the veins suggests boiling as the main reason for cassiterite and wolframite mineralization. Ore and coexisting gangue minerals hosted different types of fluid inclusions where the beginning boiling processes are solely preserved by the ore minerals emphasizing the importance of microthermometry in ore minerals. Further, the study indicates that boiling as a precipitation mechanism can only occur in mineralization related to shallow intrusions whereas deeper plutons prevent the fluid from boiling and can therefore form tungsten mineralization in the distal regions. The tin mineralization in the H{\"a}mmerlein deposit, Erzgebirge, Germany, occurs within a skarn horizon and the underlying schist. Cassiterite within the skarn contains highly saline (30-50 wt\% NaCl eq.) fluid inclusions, with homogenization temperatures up to 500°C, whereas cassiterites from the schist and additional greisen samples contain inclusions of lower salinity (~5 wt\% NaCl eq.) and temperature (between 350 and 400°C). Inclusions in the gangue minerals (quartz, fluorite) preserve homogenization temperatures below 350°C and sphalerite showed the lowest homogenization temperatures (ca. 200°C) whereby all minerals (cassiterite from schist and greisen, gangue minerals and sphalerite) show similar salinity ranges (2-5 wt\% NaCl eq.). Similar trace element contents and linear trends in the chemistry of the inclusions suggest a common source fluid. The inclusion record in the H{\"a}mmerlein deposit documents an early exsolution of hot brines from the underlying granite which is responsible for the mineralization hosted by the skarn. Cassiterites in schist and greisen are mainly forming due to fluid-rock interaction at lower temperatures. The low temperature inclusions documented in the sphalerite mineralization as well as their generally low trace element composition in comparison to the other minerals suggests that their formation was induced by mixing with meteoric fluids. Numerical simulations of magma chambers and overlying copper distribution document the importance of incremental growth by sills. We analyzed the cooling behavior at variable injection intervals as well as sill thicknesses. The models suggest that magma accumulation requires volumetric injection rates of at least 4 x 10-4 km³/y. These injection rates are further needed to form a stable magmatic-hydrothermal fluid plume above the magma chamber to ensure a constant copper precipitation and enrichment within a confined location in order to form high-grade ore shells within a narrow geological timeframe between 50 and 100 kyrs as suggested for porphyry copper deposits. The highest copper enrichment can be found in regions with steep temperature gradients, typical of regions where the magmatic-hydrothermal fluid meets the cooler ambient fluids.}, language = {en} }