The sulfide enclave cargo: Insights into magmatic-hydrothermal ore systems

The study of magmatic enclaves can provide a vertical understanding of the variable levels at which magmatic differentiation occurs, allowing us to quantify the conditions under which processes like sulfide saturation take place. Recent studies have confirmed the importance of lower crustal hornblende-rich enclaves (Chang and Audétat, 2018) and deep pyroxene-rich cumulates, as fertile sources in post-subduction and collisional settings, by sequestrating most of the Cu extracted from the mantle (Chen et al., 2019). Moreover, studies of sulfides in the host rock (Keith et al., 2017, Georgatou et al., 2018, 2020) and in enclaves (Du et al., 2014; Georgatou et al., 2018) have shown that sulfide saturation appears to be a multi-stage process starting with Fe,Ni-rich sulfides, switching to Ni-poor, Cu-rich sulfides and finally to only Cu-rich sulfides. Bracketing the P-T range in which sulfide saturation occurs relative to the sulfide occurrence and composition for diverse geodynamic settings in both mineralised and barren systems would permit us to assess the effect of sulfide saturation on the mineralization potential of the ascending residual melt.

Here, we investigate sulfide-bearing magmatic enclaves from: (i) the Miocene volcano-plutonic complexes of Konya (hosting the Doganbey Cu-Mo-W porphyry and Inlice Au-epithermal) and Usak (hosting the Kisladag giant Au-porphyry), in Western Turkey (post-subduction settings), (ii) the Kula Plio-Quaternary volcano, in the Usak basin, also in Turkey (intraplate OIB-like signature volcano in post-subduction setting). We compare results from the above areas with those of previously studied enclaves (Georgatou et al., 2018) and of new enclaves of the Quaternary Ecuadorian volcanic arc, hosting, among others, the Cascabel Cu-Au Miocene porphyry deposits (subduction setting).

Our results confirm previous conclusions (Georgatou et al., 2018) that mafic enclaves and cumulates carry a greater amount of sulfides compared to the more felsic host rock and that sulfides are generally Cu-poorer compared to the ones found in the host rock. Preliminary thermobarometry data on sulfide bearing amphibole cores found in the host rock yield P(GPa)/T(^oC) (Ridolfi et al., 2010) of 0.39-0.53/1060-1093 for Kula, 0.46-0.11/1015-819 for Konya, 0.20-0.33/917-969 for Usak and 0.2-0.38/902-987 for Ecuador. Estimates on amphibole occuring in hornblende-rich enclaves of Kula and Ecuador indicate P/T values of 0.22-0.57/988-1097 and 0.24-0.4/900-1013, respectively. Crossrefencing with Mutch et al., 2016 shows similar temperatures but significantly higher pressures, indicating for the case of Kula 0.69-0.83 GPa in the host rock and 0.53-0.86 GPa in the enclaves. These data suggest widespread sulfide saturation occurring at mid- to upper crustal depths with the highest P-T values corresponding to the onset of early Fe,Ni-rich sulfide saturation. Future investigation of sulfide-rich enclaves found in other areas and crossreferencing with multiple thermobarometers will further constrain the P-T conditions for later stages of sulfide saturation.

 

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