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Redox-controlled olivine-sulfide equilibration of the Shitoukengde Ni–Cu deposit in Qinghai-Tibet Plateau and its implications.
- Source :
-
Mineralium Deposita . Mar2024, Vol. 59 Issue 3, p577-599. 23p. - Publication Year :
- 2024
-
Abstract
- Olivine (Fo80-88) from the Shitoukengde deposit exhibits low levels of Ca, Cr, and Al (< 220 ppm) and varying Ni content. The low Ca-Cr-Al contents in olivine and subsolidus temperatures (600–900 °C) indicated by olivine-spinel thermometers align with subsolidus equilibria, emphasizing substantial postcumulus modifications. Therefore, the postcumulus effect must be considered when applying olivine-spinel oxybarometers to intrusive rocks. Back-calculating the spinel Fe–Mg contents to magmatic temperature, the estimated oxidation fugacity (fO2) range between FQM − 1.5 and FQM − 3.0, approximately 0.5 to 1.5 ΔFQM more reduced compared to those calculated from the raw spinel composition. Moreover, the fO2 aligns with results obtained from the olivine-sulfide pair (FMQ − 3.0 to FMQ 0). The considerably reducing state and wide oxidation variation are consistent with the graphite occurrence within the reduced intervals and the systematic fO2 indicated by olivine V/Sc ratios. Combined with the wide olivine Ni range (200–1500 ppm) and the restricted Ni tenor in coexisting sulfides, those findings imply that the olivine-sulfide interaction was predominantly controlled by fO2. Diffusion modeling at magmatic temperatures reveals that the core-level Fe–Ni re-equilibration after crystallization requires hundreds of years. The homogeneous olivine composition suggests that re-equilibrium has been achieved in Shitoukengde. However, in fast cooling systems, olivine may record the status approaching olivine-sulfide equilibration, leading to extensive intragrain Ni variation (up to 1000 ppm). This study highlights that extreme Ni depletion in olivine from sulfide-bearing rocks is a sign of reducing conditions. Strongly Ni-rich olivine, such as those in the Kevitsa deposit, could result from interaction with high-Ni tenor sulfides at oxidizing conditions. [ABSTRACT FROM AUTHOR]
- Subjects :
- *OLIVINE
*COOLING systems
*OXIDATION states
*SPINEL
*FUGACITY
Subjects
Details
- Language :
- English
- ISSN :
- 00264598
- Volume :
- 59
- Issue :
- 3
- Database :
- Academic Search Index
- Journal :
- Mineralium Deposita
- Publication Type :
- Academic Journal
- Accession number :
- 175389179
- Full Text :
- https://doi.org/10.1007/s00126-023-01215-6