scholarly journals T-P-fO2 conditions of sulfide saturation in magmatic enclaves and their host lavas

Lithos ◽  
2021 ◽  
pp. 106313
Author(s):  
Ariadni Georgatou ◽  
Massimo Chiaradia ◽  
Kalin Kouzmanov
2020 ◽  
Author(s):  
Ariadni Afroditi Georgatou ◽  
Massimo Chiaradia

<p>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.</p><p>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).</p><p>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(<sup>o</sup>C) (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.</p><p> </p><p><em>Chang and Audétat 2018, J.Petrol. 59(10):1869-1898</em></p><p><em>Chen et al., 2019, Earth Planet.Sci.Lett. 531, 115971</em></p><p><em>Du et al., 2014, Geosci.Front. 5,237-248</em></p><p><em>Georgatou et al., 2019, Lithos 296-299,580-599</em></p><p><em>Georgatou and Chiaradia, 2020, Solid Earth 11(1):1-21</em></p><p><em>Keith et al., 2017, Chem.Geol. 451:67–77</em></p><p><em>Ridolfi et al., 2010, Contrib.Mineral.Petrol. 160,45-66</em></p><p><em>Mutch et al., 2016, Contrib.Mineral.Petrol. 171,85</em></p>


2015 ◽  
Vol 160 ◽  
pp. 100-116 ◽  
Author(s):  
Marc-Antoine Fortin ◽  
Jacqueline Riddle ◽  
Yann Desjardins-Langlais ◽  
Don R. Baker

2015 ◽  
Vol 109 (5) ◽  
pp. 577-596 ◽  
Author(s):  
Shuo Chen ◽  
Yaoling Niu ◽  
Wenli Sun ◽  
Yu Zhang ◽  
Jiyong Li ◽  
...  

2021 ◽  
Author(s):  
Hongda Hao ◽  
Ian H. Campbell ◽  
David R. Cooke ◽  
Eizo Nakamura ◽  
Chie Sakaguchi

Abstract New geochronological and geochemical data for the barren and ore-associated suites from the Northparkes porphyry Cu-Au deposits, Australia, have implications for magma fertility. The Goonumbla and Wombin Volcanics and intrusions are barren in the Northparkes area. A sample from Wombin suite yielded a zircon U-Pb age of 433.8 ± 3.1 Ma, whereas the ore-associated porphyries yielded ages between 441.8 ± 3.7 and 436.3 ± 4.5 Ma. The bulk of the mineralization at Northparkes is associated with a K-feldspar-phyric quartz monzonite porphyry (K-QMP), which gave U-Pb zircon ages of 441.8 ± 3.7 and 441.1 ± 2.5 Ma. Whole-rock Sr-Nd isotope compositions of the Goonumbla, Wombin, and ore-associated suites are similar, with (87Sr/86Sr)i = 0.704112 to 0.704424 and εNd = 5.6 to 6.9, which is typical of primitive intraoceanic island arcs, and their Pb isotope values lie within the MORB array. Most of the zircons from the Wombin and ore-associated suites have arc mantle-like O-Hf isotope compositions, with δ18O values that vary from 6.13 to 4.95, and εHf(t) from 11.5 to 6. These results suggest that the Goonumbla, Wombin, and ore-associated suites originated from typical arc mantle. The magmas that produced the Goonumbla and Wombin suites were dominated by plagioclase-pyroxene fractionation, and the Wombin suite has a low oxidation state with ΔFMQ between ~0 and 1.5. They were relatively reduced and dry. This combination resulted in early sulfide saturation, probably without reaching fluid saturation. Trace element modeling shows that plagioclase-amphibole dominated the later stages of fractionation of the ore-associated suite, implying that it had a higher water content than the barren suites. It was also more oxidized (ΔFMQ from ~0 to 4). The result was late sulfide saturation, which was followed shortly thereafter by voluminous fluid release. As a consequence, the ore-forming fluid effectively transferred Cu and Au from the magma to the site of hydrothermal ore deposition. We suggest that the higher water content and oxidation state of the ore-associated suite was due to the deep underlying magma chamber, which was recharged by many more pulses of magma than the chamber that underlay the barren suites. This is more effective in raising the concentration of incompatible water and ferric iron in the residual melt than straight fractional crystallization. High oxygen fugacities and water contents played a significant role in determining the timing of sulfide and fluid saturation, respectively, and as a result, they had a critical influence on magma fertility.


Geology ◽  
2020 ◽  
Vol 48 (5) ◽  
pp. 519-524 ◽  
Author(s):  
Jingguo Du ◽  
Andreas Audétat

Abstract Ore-forming magmas are commonly considered to have been unusually metal rich. Because Cu and Au are strongly chalcophile, early sulfide saturation has been regarded as detrimental to porphyry Cu-Au mineralization. Here we demonstrate, based on amphibole-rich cumulate xenoliths and amphibole megacrysts from the Tongling porphyry(-skarn) Cu-Au mining district in southeastern China, that this view is not necessarily correct. Age data combined with petrological and geochemical evidence suggest that the mineralizing magmas at Tongling underwent significant fractional crystallization of amphibole, clinopyroxene, and magmatic sulfides in the middle to lower crust. The fact that the silicate melts nevertheless were able to produce substantial porphyry(-skarn) Cu-Au deposits implies that the formation of metal-rich cumulates at depth was not detrimental to their fertility. On the contrary, the common association of porphyry Cu (Au, Mo) deposits with high-Sr/Y magmas suggests that amphibole fractionation at depth even promotes the mineralization potential, despite the likely loss of metals.


2021 ◽  
Vol 559 ◽  
pp. 119913
Author(s):  
Kang Liu ◽  
Li Zhang ◽  
Xuan Guo ◽  
Huaiwei Ni

Sign in / Sign up

Export Citation Format

Share Document