Apatite Texture Research Articles

Tracing fluid exsolution and hydrothermal alteration signature of the Mufushan Nb–Ta–(Li–Be–Cs) deposit, South China: an apatite perspective

The appearance of hydrous magmas and the following separation of volatile-rich fluids through hydrothermal alteration are intricately linked to the formation of granitic rare-metal deposits, the principal source of worldwide Li, Be, Nb, Ta and Cs production. The lack of mineralogical information from the developing magmatic–hydrothermal system has, however, prevented a thorough comprehension of these processes. Apatite occurs as an accessory mineral in the metasedimentary (schist)–magmatic (muscovite monzogranite)–pegmatite (ore-free or ore-bearing pegmatite) rocks in the Mufushan Complex (MFSC) rare-metal ore field of northeastern Hunan, South China, potentially providing insights into Nb–Ta–(Li–Be–Cs) mineralization. To demonstrate that apatite can potentially record the magmatic–hydrothermal evolution of metasedimentary–magmatic–pegmatite systems, this study presents a combined textural and geochemical study of apatite from the MFSC granitic pegmatite-type rare-metal mineralization. The MFSC apatite textures and compositions have changed since it first crystallized (i.e. post-crystallization alteration). Apatite from the schist shows a homogeneous rim or homogeneous textures with cracks or inclusions (S-ap1) and a patchy core (S-ap2), indicative of a magmatic–hydrothermal origin. Apatite from the muscovite monzogranite (G-ap) displays altered and distinctive core–rim textures, with visible voids, mineral inclusions and cracks, suggestive of overprinting of early magmatism texture by hydrothermal fluid. However, compared with S-ap1, S-ap2 and G-ap, the pegmatite apatite shows more complicated textures; that is, P-ap1 (homogeneous bright and dark areas) and P-ap2 (replacement texture involving alteration rim, growth zonation, patchy and complex zoning patterns). P-ap1 underwent early magmatism and weaker post-hydrothermal overprinting, and P-ap2 reflects a magmatic–hydrothermal product. S-ap1 and S-ap2 yield lower intercept ages of 130.6 ± 1.8 and 128.4 ± 3.8 Ma, respectively, which are consistent with the transitional age of the magmatic–hydrothermal metallogenic environment in northeastern Hunan. G-ap and P-ap1 yield older ages of 136.3 ± 2.8 and 141.3 ± 6.7 Ma, respectively, which correspond to the age of magmatic early stage (Nb–Ta)-mineralization within uncertainty in northeastern Hunan. The Sr isotopic composition of apatite provides evidence for the provenance of the MFSC batholith in the rare-metal metallogenesis of the Lengjiaxi Group. Therefore, we hypothesize that apatite in granitic rare-metal deposits within metasedimentary–magmatic–pegmatite systems might be employed as a viable proxy to explore the textures and geochemical fingerprints of fluid exsolution and hydrothermal alteration. Supplementary material: Analytical techniques and the results for apatite grains in this investigation are available at https://doi.org/10.6084/m9.figshare.c.7038699

Apatite texture and composition in the Tonglushan porphyry-related skarn system, eastern China: Implications for mineral exploration

The composition of ‘indicator’ minerals is thought to provide a guide to the potential of magmatic arc systems to form porphyry Cu deposits, but whether this is also the case for endoskarn- and exoskarn-dominated systems remains unclear, despite their importance as a source of Cu, Fe and Au. In a first step to address this, we compare the texture, cathodoluminescence (CL) colour and composition of apatite between relatively fresh quartz monzodiorite (QMD) and porphyry-type-, endoskarn- and Fe-(Cu)-mineralised exoskarn components of the Tonglushan porphyry-skarn system of the Daye ore district, China. In the relatively fresh QMD, apatite luminesces yellow-green due to elevated Mn contents. However, where affected by potassic-sodic alteration, it shows green–blue CL thought to reflect partial removal of Mn and an associated increase in REE. Apatite in the endoskarn is more pervasively replaced and veined, and shows mid-blue luminescence due to relatively low Mn, Mg and Cl. The exoskarns contain apatite with variable grain shapes and navy blue-violet or bright to dark blue CL colours, caused by low Mn and elevated Ce, and with only small patches of pale yellow-green CL. Apatite is near absent in the limestone wall rocks and xenoliths and, therefore, where present in the exoskarns is interpreted to have precipitated from the same fluids as the Fe-(Cu) mineralization.Apatite CL colour and chemistry is indicative of the different styles of alteration and mineralisation in the Tonglushan system and provides insights into the composition of skarn-forming fluids. Our results offer a potentially effective method for utilising apatite as a porphyry and skarn deposit indicator mineral in a range of exploration materials including regolith and stream sediments.

Apatite texture and trace element chemistry of carbonatite-related REE deposits in China: Implications for petrogenesis

Apatite is a ubiquitous mineral in carbonatites, and incorporates a variety of trace elements including rare earth elements (REEs). In this study, the textural and chemical variations of apatite were examined in order to trace the magmatic and hydrothermal petrogenesis of three carbonatite-related REE deposits: Shaxiongdong, Miaoya, and Bayan Obo. Various apatite textures were revealed by cathodoluminescence and back-scattered electron imaging. Magmatic apatite, which occurs predominantly in samples from Shaxiongdong, is euhedral, and commonly shows oscillatory or growth zonation with a yellow–green luminescent core and a violet luminescent rim. Euhedral to subhedral metasomatic apatite from Miaoya and Bayan Obo has a turbid texture, with the majority of grains associated with exsolved monazite. Hydrothermal apatite from Bayan Obo, typically occurring as aggregates in close association with fluorite and barite, is anhedral, with green or light violet luminescence.The different apatite textures are characterised by distinct trace element compositions. Magmatic apatite contains the highest concentrations of Mn (avg. 457 ppm) and Sr (avg. 18,285 ppm) and is characterised by a steeply inclined REE chondrite-normalised pattern. Metasomatic apatite, which has undergone in situ dissolution–reprecipitation, contains lower Mn (avg. 272 ppm) and Sr (avg. 9945 ppm) concentrations. It is characterised by highly variable REE trends with an La/SmN ratio varying from 0.13 to 5.61, and lower average La/YbN, La/SmN, and Sr/Y ratios (46, 2.2, and 18, respectively) than magmatic apatite. Hydrothermal apatite that was precipitated from a fluid is characterised by convex upward chondrite-normalised REE distributions with the lowest La/YbN, La/SmN, and Sr/Y ratios (13, 0.69, and 5.8, respectively). The average concentrations of Mn and Sr in this apatite are 270 and 6610 ppm, respectively. There are no Eu anomalies (Eu/Eu* = 0.97) in the chondrite-normalised REE plots for any of the analysed apatite samples. The combined textural and compositional variations of apatite in the three deposits reflect diverse magmatic and hydrothermal processes, including: 1) mineral fractionation contributing to core–rim zoning within the Shaxiongdong magmatic apatite; 2) dissolution–reprecipitation inducing monazite precipitation in Miaoya and Bayan Obo metasomatic apatite; and 3) coprecipitation with fluorite and barite from fluids generating the Bayan Obo hydrothermal apatite.A compilation of published apatite compositions from other rock types demonstrates that trace element compositions of apatite can be used to differentiate crystallisation environments and differentiate apatite from other rock types. Apatite from carbonatite has high Sr, REEs, La/YbN, Th/U, and Sr/Y, and no Eu anomaly, compared with apatite from igneous silicate rocks (except ultramafic rocks), and iron-oxide copper gold (IOCG) or iron-oxide apatite (IOA) deposits.

Apatite Texture, Composition, and O-Sr-Nd Isotope Signatures Record Magmatic and Hydrothermal Fluid Characteristics at the Black Mountain Porphyry Deposit, Philippines

AbstractThe trace elemental and isotopic signatures in apatite can be modified during hydrothermal alteration. This study investigates the suitability of apatite as an indicator of the source, chemistry, and evolution of magma and hydrothermal fluids. In situ textural, elemental, and O-Sr-Nd isotope analyses were performed on apatite in thin sections, from fresh and propylitically altered pre- and synmineralized dioritic porphyries from the Black Mountain porphyry Cu deposit in the Philippines.All studied apatite crystals have similar subhedral to euhedral shapes and are homogeneous in the grayscale in backscattered electron images. In cathodoluminescence images, the apatite in fresh and altered rocks displays yellow to yellow-green and green to brown luminescence, respectively. Apatite in fresh rocks has a higher Cl and Mn content, and lower Fe, Mg, Sr, Pb, and calculated XOH-apatite, compared to apatite in altered rocks. The content of F, rare earth elements (REEs), Y, U, Th, and Zr, and the Sr-Nd isotope signatures of apatite from fresh and altered rocks are similar in all apatite grains (87Sr/86Sr = 0.7034–0.7042 vs. 0.7032–0.7043, εNd(t) = 5.3–8.0 vs. 5.1–8.4). The X-ray maps and elemental and oxygen isotope signatures across individual apatite crystals are typically homogeneous in apatite from both fresh and altered rocks. The distinct luminescence colors, coupled with distinct mobile element compositions (Cl, OH, Mn, Mg, Fe, Sr, Pb), indicate modification of primary magmatic apatite during interaction with hydrothermal fluids. The similarities in Sr isotope ratios (87Sr/86Sr = 0.7032–0.7043) but slight differences in O isotope signatures (δ18O = 6.0 ± 0.3‰ vs. 6.6 ± 0.3‰) in apatite from fresh and altered rocks are consistent with the magma and hydrothermal fluids having the same source and suggest significant phase separation in the hydrothermal fluids given that 18O preferentially fractionates into the residual liquid relative to 16O during phase separation. The similarity of immobile element (REE, Y, U, Th, and Zr) contents in both populations of apatite, consistency of textures and Nd isotope compositions, and absence of obvious dissolution-reprecipitation features all suggest that altered apatite retains some magmatic characteristics. The apatite in fresh rocks has oxygen isotope compositions similar to that of zircons from the same sample (δ18O = 5.9 ± 0.3‰), indicating little to no oxygen isotope fractionation between zircon and apatite and that apatite can be a good proxy for the oxygen isotope composition of the magma. Based on the Cl contents of the magmatic and replacement apatite, and assuming their equilibrium with high-temperature magma fluid and replacement hydrothermal fluid, respectively, the calculated Cl content of the early magmatic fluid and the later replacement fluid can be estimated to be 6.4 to 15.1 wt % and ~0.25 ± 0.03 wt %, respectively. This indicates a depletion of Cl from the early high-temperature fluid to the replacement fluid, consistent with phase separation.This study demonstrates that cathodoluminescence, elemental compositions (such as Cl, Mn, Mg, Fe, Sr, Pb) and Sr-O isotope signatures in apatite can be modified during hydrothermal alteration, whereas other components (REE, Y, U, Th, and Zr) and the Nd isotope composition are preserved. These features can be used to constrain the origin, chemistry, and evolution of the primary magma and ore-forming hydrothermal fluids.

Trace Elements in Apatite as Genetic Indicators of the Evate Apatite-Magnetite Deposit, NE Mozambique

The Evate deposit is a Neoproterozoic (~590 Ma) magnetite-apatite-carbonate body emplaced parallel to foliation of the Monapo granulite complex in NE Mozambique. A complicated history of the deposit is recorded in apatite textures visualized in cathodoluminescence (CL) images. In spite of different solid and fluid inclusions, mineral assemblages, and the CL textures, electron probe microanalyses indicate relatively consistent apatite compositions corresponding to fluorapatite (XF = 0.51–0.73, XOH = 0.21–0.47, XCl = 0.02–0.06) with limited belovite- and cesanite-type substitutions. Laser ablation inductively coupled plasma mass spectrometric analyses show that apatites from unaltered magnetite-forsterite-spinel ores are depleted in Y, REE, Ba, and Sr compared to apatites from carbonate-anhydrite ores. Hydrothermally overprinted apatites with complex patchy domain CL textures are enriched in Y-REE in greenish-grey zones, Fe-U-Th in blue zones, and Mn-Sr-Ba in brown domains. Observed CL-emissions in the Evate apatites result from very subtle variations in REE, Mn, and U contents controlled by the variability of redox conditions. The decreased Th:U ratio in the hydrothermally overprinted apatites reflects the oxidation and partial removal of U4+ from the apatite structure during the interaction with oxidizing aqueous fluids capable of transporting U6+. Flat, LREE (La-Sm)-enriched chondrite-normalized patterns with Eu/Eu* = 0.7–1.4 and Ce/Ce* = 0.9–1.5, together with concentrations of diagnostic trace elements (Sr, Mn, Y, REE) are consistent with apatites from magmatic carbonatites and phoscorites. This study corroborates that the Evate deposit is a post-collisional orogenic carbonatite genetically linked with mafic plutonic rocks intruding the Monapo granulite complex after granulite-facies metamorphism, and later overprinted by intensive hydrothermalism. The Evate apatite is peculiar in retaining its pristine magmatic signature despite the extensive hydrothermal-metasomatic alteration accompanied by dissolution-reprecipitation.

Zircon and apatite as tools to monitor the evolution of fractionated I-type granites from the central Great Xing’an Range, NE China

It is widely accepted that granitic melts can be highly evolved, however, the effective records of this process are usually obscure, especially for the exsolution and evolution of volatiles. We present a comprehensive investigation on zircon and apatite from less to highly fractionated granites from the central Xing’an Range, NE China, in order to reveal the mineral records for the evolution processes of granitic melt. Petrographic, whole-rock and mineralogical geochemical investigations indicate that the three granites are co-magmatic and experienced different degrees of fractionation. The variations of zircon morphology, textures and geochemical compositions reflect the progressive evolution of granitic melts from volatile-undersaturated to oversaturated conditions. The significantly decreased Raman spectra intensities imply that the zircon crystals experienced increased radiation damages and hydrothermal alteration during the fractionation of granitic magma. Correspondingly, apatite textures transform from fluid-inclusion-free to fluid-inclusion-rich stage with increasing F/Cl ratios during the magmatic evolution, implying that the segregation of isolated fluid phase in the fractionating magma. Accordingly, we conclude that the textural and compositional evolution of zircon and apatite can be regarded as efficient tools for recording granitic magma evolution.

Halogens, trace element concentrations, and Sr-Nd isotopes in apatite from iron oxide-apatite (IOA) deposits in the Chilean iron belt: Evidence for magmatic and hydrothermal stages of mineralization

Abstract The ratio of the halogens F and Cl in apatite is highly sensitive to changes in the composition of an evolving silicate melt or aqueous fluid. For this reason apatite chemistry is widely used as a monitor of halogen behavior in magmatic-hydrothermal systems. Apatite is an ubiquitous mineral in iron oxide – apatite (IOA) mineral deposits, where P and volatiles such as F, Cl, H2O and S play a major role in ore genesis. In this study, we present a combination of textural, micro-analytical and isotopic data for apatite from three Andean IOA deposits (Carmen, Fresia and Mariela) of Early Cretaceous age from the Coastal Cordillera of northern Chile. Apatite textures and compositions show evidence of post-crystallization alteration. Apatite is predominantly zoned with respect to Cl and F, showing a decoupled geochemical behavior between these two elements. Overall, four types of apatite or domains were identified in the analyzed grains based on the XCl-apatite/XF-apatite and XCl-apatite/XOH-apatite ratios determined using the atomic proportions of F, Cl and OH. F-apatite is characterized by a XCl-apatite/XF-apatite 25 and a XCl-apatite/XOH-apatite > 4.5 and up to 3000; Cl-OH-F-apatite has a XCl-apatite/XF-apatite = 0.15–8 and a XCl-apatite/XOH-apatite = 0.25–5.45; and Cl-OH-apatite shows a XCl-apatite/XF-apatite = 8–75 and a XCl-apatite/XOH-apatite = 0.5–3. Carmen apatite is mostly F-apatite, but shows Cl-OH compositions restricted to rims and fractures, whereas apatite from Mariela is dominantly Cl-apatite and Cl-OH-apatite. Apatite from Fresia have variable compositions between Cl-OH-F, Cl-OH- and Cl-apatite, where Cl- and Cl-OH-apatites are characterized by an enrichment of S, Na, Sr and Fe relative to F-apatite. Most notably, S and Na correlate with Cl. In Carmen and Fresia, Cl-OH-apatite is slightly depleted in LREEs, Th and U, a finding consistent with micro-textural evidence of metasomatic processes including coupled dissolution-reprecipitation and formation of secondary monazite and xenotime inclusions. In contrast, apatite from Mariela exhibits no depletion in LREEs and displays a homogeneous distribution of Th and U between the different apatite types, with no monazite and xenotime inclusions. The textural types of apatite identified in this study, coupled with the halogen and trace element composition of apatite, are consistent with modification of primary, F-apatite by interaction with hydrothermal fluids, which led to the formation of Cl-OH-apatite and Cl-apatite. In addition, the initial 87Sr/86Sr ratios and eNd values of apatite (0.7038 to 0.7050 and −0.3 to +6.5, respectively), calculated considering a 130 Ma age, are consistent with a magmatic origin for the primary F-apatite with minimal or no crustal contribution. Thus, textural, geochemical, and isotopic results of apatite support a magmatic-hydrothermal origin for these Andean IOA deposits with variable degrees of metasomatic overprint as evidenced by the formation of Cl-OH and Cl-apatite.

Observation of Apatite Formation on Titanium Plate and Bone Surfaces in Electric Stimulation

Apatite formation due to mineralization has important implications in the biological function of hard tissues. The mechanical properties of mineralized tissues such as teeth enamel, dentin, and bone depend strongly on the apatite structure in the tissue. The control of both volume fraction and apatite texture is important in determining the structural characteristics. It is also important to create an apatite layer on the surface of implanted materials to improve biocompatibility between the surface and the tissues. In this study, apatite deposition and formation on Ti plates and bone surfaces were studied by means of electric stimulation conducted in apatite-neutralizing solution. Apatite particles were deposited not only on the Ti plate surfaces but also on the bone, combined with Ti wires wrapped under DC loading. Apatite crystal growth was observed on the samples during electric stimulation.

Hydrothermal Alteration Revealed by Apatite Luminescence and Chemistry: A Potential Indicator Mineral for Exploring Covered Porphyry Copper Deposits

Apatite is a common resistate mineral occurring in a range of host rocks and ore-related hydrothermal alteration assemblages. Apatite in several porphyry copper deposits in British Columbia has a unique set of physical and compositional characteristics that can be used to evaluate the chemical conditions of magmas that formed the causative intrusions or associated hydrothermal alteration. Apatite under visible light and SEM shows no notable variations between unaltered and altered varieties but cathodoluminescence reveals significant differences. Apatite in unaltered rocks displays yellow, yellow-brown, and brown luminescence, whereas in K silicate-altered rocks apatite displays a characteristic green luminescence. The green-luminescent apatite replaces yellow- or brown-luminescent apatite and locally overgrows it. Apatite occurring with muscovite (i.e., phyllic)-altered rocks displays characteristic gray luminescence. The chemistry of apatite, as determined by electron microprobe and laser ICP-MS analyses, directly reflects its alteration and luminescence. The unaltered yellow-luminescent apatite has high concentrations of Mn (0.3–0.5 wt % MnO) and a high Mn/Fe ratio (>1), whereas the brown-luminescent apatite has low Mn, but higher concentrations of S and REE + Y. The green K silicate alteration-related luminescence is caused by lower Mn/Fe ratios (ca. 1) along with depletions of other trace elements such as Cl, S, and Na. Gray-luminescent apatite occurring with muscovite-altered rocks results from significant Mn loss ( The correlation between apatite texture, luminescence, and chemical composition with the type and intensity of porphyry alteration offers a potentially fast and effective method to utilize it as an indicator for porphyry mineralization in a range of exploration materials including soils, regoliths, and heavy mineral concentrates from glacial and fluvial materials.

Magmatic Apatite: A Powerful, Yet Deceptive, Mineral

Apatite may be a minor constituent in magmatic rocks but it is a powerful research tool because it is ubiquitous and it incorporates magmatic water, halogens, S, C, and trace elements including Sr, U, Th, and the rare earth elements. Recent advances in experimental and analytical methodologies allow geologists to analyze apatite textures and compositions in great detail. This information improves understanding of the behavior of volatiles and trace elements both in terrestrial igneous melts and their related fluids and in extraterrestrial bodies, such as the Moon and Mars. With more research, the petrological power of apatite can only increase with respect to understanding eruptive, pluton-building, and mineralizing magmatic systems.

Rare earth elements in apatite as a monitor of magmatic and metasomatic processes: The Ilímaussaq complex, South Greenland

Textural and compositional variations of apatite from the plutonic Ilímaussaq complex in South Greenland and its surrounding country rocks track magmatic and metasomatic processes. Detailed back-scattered electron (BSE) imaging reveals various types of apatite textures including (i) growth zonation (concentric, oscillatory as well as sector zonation) formed during magmatic differentiation, (ii) resorption and overgrowth textures due to fluid/melt induced metasomatic overprint of precursor apatite and (iii) replacement textures indicating the destabilization of apatite in favor of monazite.In the least evolved rocks of the Ilímaussaq complex, apatite incorporates rare earth elements and Y (REY) mainly via the coupled substitution Ca2++P5+=REY3++Si4+. In the more evolved peralkaline rocks and in metasomatically overprinted rocks, however, the coupled substitution 2 Ca2+=REY3++Na+ becomes increasingly relevant, and apatite incorporates successively more LREE compared to HREE as shown by increasing (La/Gd)N and (Gd/Yb)N ratios. Similarly, at the contact between the Ilímaussaq rocks and the granitic country rocks, the metasomatic effect of the emplacement of the Ilímaussaq melts is preserved in partly resorbed precursor apatite, which is overgrown by REY-enriched apatite with higher (La/Gd)N and (Gd/Yb)N ratios compared to apatite from granites more distant from the contact.This study shows, that apatite textures and compositions are suitable to track both primary magmatic and later fluid-present metasomatic processes. The incorporation of REY in apatite is not only dependent on the amount of REY present but also depends largely on Na activity in the apatite-precipitating melts and fluids.

Texture analyses of Sauropod dinosaur bones from Tendaguru

The apatite texture of fossil Brachiosaurus brancai and Barosaurus africanus sauropod bones from the excavation site at Tendaguru, Tanzania, was characterized by neutron diffraction pole figures. The results obtained reveal predominantly 〈0 0 0 1〉-fibre textures of the apatite; the fibre direction coincides with the longitudinal direction of the long bones of the skeletons. Neutron pole figures further indicate that other texture types may also be present. Texture strength is similar to dinosaur tendons and contemporary turkey tendon studied by others. Variations of texture strength across the bone wall cross-sections are not significantly large.