Simultaneous Partition Experiment of Divalent Metal Ions between Sphalerite and 1 mol/L (Ni, Mg, Co, Fe, Mn)Cl2 Aqueous Solution under Supercritical Conditions

A simultaneous partition experiment of divalent metal ions was performed between sphalerite and 1 mol/L (Ni, Mg, Co, Fe, Mn)Cl2 aqueous solution under supercritical hydrothermal conditions of 500–800 °C and 100 MPa. The bulk partition coefficient that was defined by KPB(ZnS) = (xMeS/xZnS)/(mMeaq/mZnaq) followed the order of Zn ≑ Co ≑ Ni > Fe > Mn > Mg at all temperatures. In the partition coefficient versus ionic radius (PC–IR) diagrams with the logarithmic value of the bulk partition coefficient (log KPB(ZnS)) on the vertical axis, and the ionic radius of the six-fold coordinated site on the horizontal axis, Ni shows a positive partition anomaly, and the other elements were almost on the PC–IR curve. Based on the PC–IR curve, the optimum ionic radius for sphalerite existed where the ionic radius was slightly larger than Zn (~0.76 Å). A Ni positive partition anomaly may result from its large electronegativity.

A re-evaluation of the palaeoclimatic significance of phosphorus variability in speleothems revealed by high-resolution synchrotron micro XRF mapping

The distribution of phosphorous (P) in one modern and two Early Pliocene speleothems formed in low-lying, Christmas Island and the coastal Nullarbor caves wet settings in Australia is here investigated by microscopy and ultra-high resolution chemical mapping. Monitoring data in the modern setting suggest that co-precipitation of P with calcite occurs when the drip rate decreases, the aquifer is progressively drained and microbial mats possibly aid in the formation of concentrating phosphates. A bulk partition coefficient is proposed, which indicates that the P enrichment in the speleothem could be accounted for by inorganic processes. Our interpretation of the hydrological significance of P incorporation in wet, tropical speleothems is then used to interpret P peaks associated with micritic and stromatolithic layers in the two Early Pliocene stalagmites from the Nullarbor. From these observations it is speculated that dry periods may have interrupted the wet climate regime at ca. 4 Myr ago, hinting at a possible early onset of the Pleistocene climate mode.