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The Pusangguo skarn is a newly discovered Cu-Pb-Zn deposit in the Gangdese metallogenic belt, Tibet. In order to constrain the age of the deposit and the source of hydrothermal fluids, various types of titanite and coexisting minerals in the Pusangguo deposit were studied. The titanite occurring interstitially in fresh granodiorite is magmatic and characterized by high REE, Y, Mn, and Lu/Hf ratios, and high crystallization temperatures (700 to 750 °C). The titanite growing with, or included in, diopside in the prograde endoskarn, or occurring with epidote, calcite, and quartz in the retrograde exoskarn, is hydrothermal titanite characterized by low REE, Y, Mn, and Lu/Hf ratios. The titanite in the retrograde exoskarn typically contains a REE-enriched early core characterized by a negative Eu anomaly, and an overgrowth REE-depleted rim with a positive Eu anomaly. The secondary-ion mass spectrometry U-Pb dating of titanite drilled from thin sections of retrograde exoskarn shows intercept ages of 14.91 ± 0.31 Ma, which are consistent with the granodiorite age (14.63 ± 0.30 Ma), indicating coeval emplacement of granodiorite and skarn mineralization at ~ 14.7 Ma. In addition, in situ epidote and calcite Sr isotopes and titanite Nd isotopes, all analyzed in the same retrograde exoskarn thin section, show similar Sr-Nd isotopic compositions to magmatic plagioclase and granodiorite (whole rock), indicating that the retrograde hydrothermal fluids were directly derived from, or had the same origin as, the granodiorite.

Apatite is an excellent tracer of petrogenetic processes as it can incorporate a large range of elements that are sensitive to melt evolution (LREE-MREE, Sr, Pb, Mn, halogens, Nd isotopes). Recent advances in the understanding of trace element concentrations and isotope ratios in apatite provide a novel tool to investigate magmatic petrogenesis and sediment provenance. Recent experimental work has better characterized trace element partition coefficients for apatite, which are sensitive to changes in magma composition (e.g., SiO2 and the aluminum saturation index value). The chemistry of apatites from granitoids has been suggested to reflect the composition of the host magma and yield information about petrogenetic processes that are invisible at the whole-rock scale (mixing, in situ crystal fractionation, metasomatism). Nd isotopes in apatite can now be analyzed by LA-MC-ICP-MS to constrain mantle and crustal contributions to the source(s) of the studied magma. These recent advances highlight exciting new horizons to understand igneous processes using accessory minerals. In this contribution, we use a compilation of recent data to show that apatite in the matrix and as inclusions within zircon and titanite is useful for providing insights into the nature and petrogenesis of the parental magma. Trace element modeling from in situ analyses of apatite and titanite can reliably estimate the original magma composition, using appropriate partition coefficients and careful imaging. This provides a new way to look at magmatic petrogenesis that have been overprinted by metamorphic processes. It also provides the rationale for new investigations of sedimentary provenance using detrital accessory minerals, and could provide a powerful new window into early Earth processes if applied to Archean or Hadean samples.

The Caojiaba tungsten deposit (19.03 Mt@ 0.37 wt% WO3) is hosted by skarn along the contact between clastic and carbonate rocks in the Xiangzhong Metallogenic Province of southern China. The deposit is characterized by an early prograde skarn containing low andraditic garnet (Ad0.7–21.9) and hedenbergitic pyroxene (Hd52.9–77.3) overprinted by a retrograde biotite–chlorite assemblage and then by quartz–scheelite veins, similar to well-studied reduced tungsten skarns worldwide. Scheelite has low MoO3 (0.01–0.16 wt%), and ore commonly contains up to 1.5 ppm Au and up to 0.33 wt% Sb. Sensitive high-resolution ion microprobe (SHRIMP) U–Pb analyses of hydrothermal titanite coexisting with scheelite in three skarn ore samples provide ages between 206 ± 5 Ma and 196 ± 3 Ma (2σ). Our new ages demonstrate that the tungsten mineralization took place at Caojiaba between 206 and 196 Ma, overlapping the 228–201 Ma emplacement age of granitic rocks in the Xiangzhong Metallogenic Province. Mineralogical and geochronological evidence collectively indicates that Caojiaba is a distal reduced W skarn deposit. The 226–196 Ma granite-related W mineralization recognized throughout the province has a possible link with the widespread Sb–Au mineralization in the region.

Dongguashan is one of the largest porphyry-skarn Cu-Au deposits in eastern China and titanite is found in the ore system. Five types of both magmatic and hydrothermal titanites are distinguished, based on their textural and chemical characteristics. Types 1 and 2 titanites are magmatic in origin whereas types 3, 4, and 5 are hydrothermal. Magmatic titanites are wedge-shaped and display concentric and sector zoning, whereas hydrothermal titanites show a wide range of textures that vary with different alteration stages. REE, Sn, Mo, and Cu are enriched in magmatic titanites (types 1 and 2). In contrast, vanadium and HFSE are enriched in hydrothermal titanites, especially in type 4 titanite from the propylitic alteration zone. Magmatic titanite (type 1) coexists with magnetite and K-feldspar and crystallized in oxidized and H2O-rich magma at 730–760 °C. Type 2 titanite contains ilmenite inclusions reflecting changes in the fO2 of the magma chamber, possibly caused by input of mafic magma. The mobility and enrichment of HFSE and association with fluorapatite reflect the F-rich composition of the magmatic-hydrothermal fluid at Dongguashan. The relationship between titanite textures and chemistry indicates that titanite can serve as a recorder of magmatic-hydrothermal processes in porphyry copper systems. U-Pb dating of type 4 titanite from the propylitic alteration zone and type 5 titanite from skarn yielded ages of 139.0 ± 2.6 Ma and 137.0 ± 2.0 Ma, respectively, indicating that it formed synchronously with the associated quartz monzodiorite.

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.

Major, minor, and trace element abundances in titanite crystals from four granitic plutons in southern Yidun arc, SW China, have been determined using electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry. The selected plutons are the Cretaceous Xiuwacu (CXWC) pluton, with quartz vein-type Mo mineralization (economic-Mo), the Tongchanggou (TCG) pluton, with porphyry-type Mo mineralization (economic-Mo), the Triassic Pulang (PL) pluton, with porphyry-type Cu mineralization (subeconomic-Mo), and the Triassic Xiuwacu (TXWC) pluton, without any Mo mineralization (Mo-barren). Our study reveals that the chemical compositions of titanite crystals from these plutons such as REE, Sr, Ga, δEu, δCe, Fe2O3/Al2O3, halogens, and Mo can be used to track magma compositions, oxidation states, metal fertility, and crystallization history. The data from this study also show that titanite crystals from these plutons with different potential of Mo mineralization have similar Mo contents and exhibit an irregular variation between Mo and Sr abundances (indicating non-Mo enrichment in the residual melt during the progressive crystallization) for some Mo-mineralized plutons. Our new observations support the recent hypothesis that high initial Mo contents in magma and the enrichment of Mo in residual melts formed by fractional crystallization are not the only requirements to form a granite-related Mo ore deposit. Efficient extraction of the residual melts, possibly facilitated by high concentrations of magmatic F is also critical to the ore formation. Evidence for high-F concentration in felsic magma, which facilitates melt and fluid separation and economic Mo mineralization during magma evolution, may be traced by the presence of F-rich titanite crystals in the two Mo-mineralized granite plutons (CXWC and TCG). These new findings from this study confirm that titanite is indeed a good petrogenetic and metallogenic indicator. However, in light of the limited contribution of metal fertility to Mo mineralization, we suggest that titanite Mo concentrations should be used along with other crucial proxies, such as titanite F contents and Fe2O3/Al2O3 ratios to better evaluate the Mo-mineralized potential of granites.

Metamorphic chronology or petrochronology has steadily evolved over several decades through ever improving analytical techniques and more complete understanding of the geochemical and petrologic evolution of metamorphosing rocks. Here, the principal methods by which we link metamorphic temperatures (T) and ages (t) are reviewed, focusing primarily on accessory minerals. Methods discussed include textural correlation, inversion of diffusion profiles, chemical correlation, and combined chronologic and thermometric microanalysis. Each method demonstrates remarkable power in elucidating petrologic and tectonic processes, as examples from several orogens illustrate, but limitations must also be acknowledged and help define future research directions. Correlation methods are conceptually simple, but can be relatively non-specific regarding pressure-temperature conditions of formation. A new consideration of errors indicates that modeling of chronologic diffusion gradients provides relatively precise constraints on cooling rates, whereas models of chemical diffusion gradients can lead to large (factor of 2 or more) cooling rate uncertainties. Although arguably the best method currently in use, simultaneous T-t measurements are currently limited to zircon, titanite, and rutile. Directions for future improvement include investigation of diffusion profiles for numerous trace element-mineral systems using now-routine depth profiling. New trace element models will help improve chemical correlation methods. The determination of inclusion entrapment P-T conditions based on Raman spectroscopic measurement of inclusion pressures (\"thermoba-Raman-try\") may well revolutionize textural correlation methods.

The Triassic collision between the Yangtze and North China blocks resulted in the formation of ultrahigh-pressure metamorphic rocks along the Dabie-Sulu orogenic belt, the development of the Tan-Lu fault zone, and the establishment of a crustal-scale décollement within the Lower Yangtze foreland fold-thrust zone. The ductile fabrics exposed in the Zhangbaling-Feidong Complex of the southern Tan-Lu fault zone record the strain that accumulated during that collision. Herein, field observations and structural analysis of high-strain rocks (i.e. microstructures and quartz crystallographic preferred orientations) from the eastern Feidong Complex are combined with estimates of deformation P-T conditions to reveal that top-to-SSW subhorizontal, amphibolite-facies (600 and 700°C, 4.0-6.6 Kbar) ductile fabrics overprint the Paleo-Proterozoic Feidong Complex. U-Pb geochronology on zircon rims and syntectonic titanite indicates that the overprinting deformation occurred in the Middle Triassic (ca. 246-242 Ma). Reinterpretation of reflection seismic profiles across the Tan-Lu fault zone and Lower Yangtze foreland fold-and-thrust zone identifies a large, subhorizontal décollement beneath the sedimentary cover that appears to have influenced the formation of fold-thrust structures in the Lower Yangtze foreland. These new observations and geochronological results are consistent with a transpressional tectonic model wherein the Early-Middle Triassic northward indentation of the Yangtze block into the North China block drove deformation within the southern Tan-Lu fault zone.