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The Xiaoxi'nancha porphyry Au-Cu deposit is located in Yanbian, Jilin Province, NE China. Gold-Cu mineralization is mainly associated with chlorite-sericite alteration. The 40Ar/39Ar age of pre-mineralization hydrothermal biotite in potassic alteration defines a relatively well-defined cluster at ~ 111 Ma to 114 Ma with a total fusion age of 112.0 ± 0.3 Ma. In-situ secondary-ion mass spectrometry U-Pb dating of hydrothermal titanite occurring with chalcopyrite yielded an intercept age of 109.0 ± 2.4 Ma. The similarity between the biotite and titanite formation ages suggests a mineralization age of ~ 110 Ma. Chlorite, quartz and apatite coexist in equilibrium and are closely related to mineralization. The Al-in-chlorite geothermometer indicates a formation temperature of 236–351℃ (mean 309℃), and the quartz-apatite pair yielded an average formation temperature of 306℃. The in-situ δ34S compositions of sulfide have restricted and slightly positive values (pyrite 2.3 to 3.9‰, chalcopyrite 1.6 to 3.8‰ and molybdenite 2.3 to 3.7‰). The fluid δ18O values, calculated assuming quartz-fluid equilibrium, vary from 2.4 to 5.5‰ (average = 4.0‰). Therefore, the ore-forming hydrothermal fluids were of moderate-temperature with predominantly magmatic characteristics. Apatite exhibits distinct variations in structure and composition, and slight variations in oxygen isotopic composition. The areas in apatite with dark BSE textures are characterized by lower δ18O values, Cl contents and temperatures and higher F contents, consistent with the result of water–rock interaction rather than mixing with meteoric water. The water–rock interaction and its resulting cooling, can reduce the metal solubility, likely triggering mineralization at Xiaoxi'nancha. [ABSTRACT FROM AUTHOR]

The origin of propylitic fluids in intermediate sulfidation mineralization has not been investigated in detail. Here, we present an extensive petrographic, geochemical, and isotopic (O-H-Sr) study of propylitic epidote, chlorite, and calcite from the Zhengguang intermediate sulfidation epithermal Au-Zn deposit, NE China. Propylitic minerals can be divided into three main types based on their different textural occurrences, namely interstitial cement of clasts of hydrothermal breccia, replacement of primary plagioclase or hornblende, and vein infill of cracks, with late, minor calcite as amygdules in vesicles of andesite representing a fourth textural occurrence. The H-O isotope compositions and mass balance calculations suggest that most propylitic epidote records a dominant (> 50%) contribution of magmatic fluids. The decrease of the average δ18 O H 2 O values equilibrated with different types of epidote (cement 6.8 ± 0.7‰, replacement 5.1 ± 1.1‰, vein 4.5 ± 1.4‰, 1 SD), and the decreasing content of high-temperature elements (e.g., Cu-Mo) from cement, through replacement to vein epidote and chlorite, collectively indicates a decreasing role of magmatic fluids. Replacement epidote and chlorite are enriched in Sr-Mn-Y-Sb, whereas replacement epidote and calcite record similar (87Sr/86Sr)i values to the andesitic host rock, suggesting that replacement minerals inherit certain elements from plagioclase and hornblende, and the Sr isotope signature of the wall rocks. We highlight that propylitic alteration in epithermal deposits can involve significant proportions of magmatic fluids and texturally different alteration mineral types should be considered when using mineral isotopic or chemical compositions to track fluid sources or to vector towards the location of intrusive centers. [ABSTRACT FROM AUTHOR]

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]

This study investigates apatite and anhydrite inclusions in zircon from ore-forming intrusions in the Duolong porphyry Cu-Au deposit, central Tibet (Fig. 2 Geological characteristics (a) and cross sections (b, c) of the Duolong porphyry Cu-Au deposit, central Tibet, showing sample locations (Li et al. [21], [25]) The Duolong magmatic complex evolved from diorite to granodiorite porphyry and quartz diorite porphyry, the hosts of Cu-Au mineralization (Fig. Apatite inclusions ( I n i = 98) in zircon from the granodiorite porphyry and quartz diorite porphyry have F contents of 1.14-2.99 wt%, Cl of 0.16-2.51 wt%, and SO SB 3 sb of 0.04-1.38 wt%, with minor SiO SB 2 sb (0.05-1.39 wt%), MnO (0.12-0.93 wt%), Na SB 2 sb O (0-0.28 wt%), and FeO (0.01-0.64 wt%; Supplementary Table 1). Apatite and anhydrite were randomly enclosed by zircon crystals, which were later hosted in ore-forming porphyries One apatite inclusion coexisting with an anhydrite inclusion in a single zircon grain contains 0.69 wt% SO SB 3 sb with a low I X i SB F sb / I X i SB Cl sb ratio of ~ 1.2 (Fig. [Extracted from the article]

Oxygen fugacity is a key parameter in controlling the petrogenesis of mafic-ultramafic rocks and their associated sulfide mineralization, especially in convergent settings. This study uses new and previously published experimental data on olivine-sulfide pairs to reparameterize an expression for oxygen barometry using the distribution coefficient KDFeNi for Fe-Ni exchange between olivine and sulfide. We derive a new expression, ΔQFM = (9.775 + 0.416 ∙ CNi − KDFeNi)/4.308, where ΔQFM denotes divergence from the fayalite-magnetite-quartz buffer. The revised oxygen barometry has been applied to the Permian magmatic Ni-Cu deposits in the Central Asian Orogenic Belt, NW China. The Ni-Cu deposits in the East Tianshan—North Tianshan, Central Tianshan, and Beishan—are considered as a single mineral system, whereas the spatially separated deposits in the East Junggar are considered as a separate system. The deposit of the East Tianshan group exhibits a large range of oxygen fugacity (QFM − 2 to ~QFM + 1) and Ni tenor (metal concentration in pure sulfide, ~ 5 to 16 wt%). The Poyi and Huangshannan deposits contain high-Ni tenor sulfides, varying from 12 to 16 wt%. The relatively high Fo values (> 85 mol%) and Ni contents (> 2000 ppm) in olivine of these deposits indicate that the high-Ni tenor sulfides were segregated from less differentiated high-Ni magmas that also had relatively high oxygen fugacity (~QFM + 1). The remaining Ni-Cu deposits in the East Tianshan—the Huangshandong, Huangshanxi, Hulu, Tulaergen, Tudun, and Xiangshanzhong deposits—have intermediate Ni tenors (5-8 wt%). These sulfides correspond to intermediate Fo values (80-84 mol%) and Ni contents (700-1400 ppm) in the coexisting olivine, illustrating that they were segregated from magmas with lower Ni contents thought to be the result of a large amount (15-20%) of olivine fractionation at depth. These magmas are more reduced (− 2 < ΔQFM < + 0.3) than the less evolved magmas (~QFM + 1). It is shown that the ΔQFM value calculated for the deposits in East Tianshan decreases with decreasing Fo value, indicating that the host magmas became gradually reduced during evolution, which can be explained by primarily oxidizing magma progressively assimilating crustal material containing reducing agents, such as carbon. The Kalatongke deposit in the East Junggar belt, with the lowest Ni tenors in sulfides (3-5 wt%) and low Fo values in olivine (< 78 mol%), was derived from relatively oxidizing magmas (~QFM + 1) that had experienced significant olivine plus clinopyroxene and plagioclase fractionation at depth. We propose that the variation in oxygen fugacity and Ni tenor in the Permian Ni-Cu deposits in the Central Asian Orogenic Belt is the result of gradual contamination and a variable degree of fractional crystallization. [ABSTRACT FROM AUTHOR]

The Huangshandong Ni-Cu deposit is the largest magmatic sulfide deposit discovered to date in the Central Asian Orogenic Belt in northern Xinjiang, western China. The host intrusion is a 274-Ma composite mafic-ultramafic intrusion consisting of four separate intrusive units: a large layered gabbroic sequence (phase I), a sheet-like ultramafic body (phase II), a dyke-like gabbronorite body (phase III), and an irregular ultramafic unit (phase IV). Important sulfide mineralization is present in the last three intrusive units, predominantly as disseminated and net-textured sulfides (pyrrhotite, pentlandite, and chalcopyrite). The Huangshandong mafic-ultramafic intrusive rocks are characterized by arc-like geochemical signatures such as low Ca content in olivine and negative Nb-Ta anomalies in whole rocks. This, together with a post-subduction setting for the East Tianshan in the Permian, suggests that the source mantle was modified previously by slab-derived fluids in the Carboniferous. The mantle-derived magma was ponded in a staging chamber in the lower part of the newly formed arc crust. The first batch of magma to arrive at Huangshandong was most fractionated and depleted in Ni, crystallizing Fe-rich and Ni-depleted olivine (Fo, <300 ppm Ni). The second batch of magma was more primitive, crystallizing more primitive olivine (Fo). The third batch of magma was also highly fractionated and depleted in Ni, crystallizing Fe-rich and Ni-depleted olivine (Fo, ~600 ppm Ni). The final batch of magma became more primitive again, crystallizing the most primitive olivine (Fo). The occurrence of rounded sulfide inclusions in olivine primocrysts in the Huangshandong ultramafic rocks indicates that immiscible sulfide liquid droplets were present during olivine crystallization. The Ni tenors of disseminated sulfide ores in the gabbronorite dyke vary mainly between 5 and 8 wt%, which are too high to have been produced by the parental magma of the dyke. The Ni, Cu, and platinum-group elements (PGE) tenors of disseminated sulfide ores in the dyke (phase III) and the ultramafic sheet (phase II) are remarkably similar. These observations, together with the sequence of magma emplacement, suggest that the sulfide liquids entrapped in the magma of the dyke formed at depth by a previous pulse of more primitive magma. The estimated parental magma for the most primitive lherzolites in the Huangshandong intrusion contains 10 wt% MgO. Modeling shows that sulfide saturation in the parental magma of the Huangshandong lherzolites could have resulted from fractional crystallization. Significant PGE depletions relative to Ni and Cu in the disseminated sulfide ores of the Huangshandong deposit may be due to sulfide retention in the source mantle. [ABSTRACT FROM AUTHOR]