Hydrothermal Apatite Research Articles

PRECISE AGE CONSTRAINTS FOR THE WOXI Au-Sb-W DEPOSIT, SOUTH CHINA

AbstractAccurately resolving the timing of formation of Au-Sb-W deposits hosted in metasedimentary rocks has been the aim of extensive research but has also led to controversy. In this study, we present high-precision laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb dating of hydrothermal apatite and wolframite from the Woxi Au-Sb-W deposit, South China. Veins are dominated by quartz, native gold, auriferous pyrite, arsenopyrite, stibnite, scheelite, wolframite, and apatite. Wolframite grains yield U-Pb ages of 144.8 ± 1.5 Ma (2s) and 140.3 ± 1.4 Ma, which overlap with apatite ages of 148.7 ± 2.4 to 144.1 ± 2.7 Ma. Collectively, the new data confirm the Woxi deposit is solely Late Jurassic-Early Cretaceous in age, despite previous dates using other isotopic systems that were as old as Silurian. Our compilation of geologic characteristics, tectonic setting, and geochronology of Au-Sb-W deposits from the western part of the Jiangnan belt shows there were two episodes of Au-Sb-W metallogenesis. These events in the Late Triassic and Late Jurassic-Early Cretaceous related to an extensional setting following Triassic intracontinental orogeny and to Late Jurassic-Early Cretaceous extension associated with Izanagi plate rollback, respectively.

In situ elemental and Sr-Nd isotopic compositions of hydrothermal apatite from the Shazhou U deposit in the Xiangshan complex: Implications for the origins of ore-forming fluids of volcanic related U deposits in South China

• In situ Sr-Nd isotopes of apatite are effective in tracing origins of ore forming fluids in the Shazhou U deposit. • The reducing U-poor fluid was derived from mantle-derived magma which formed the mafic dikes in wall rocks. • The oxidizing U-rich fluid originated from percolation of meteoric water in the adjacent red-bed basins. • The Late Cretaceous mafic magmatism and red-bed basins are two key factors controlling U mineralization in South China. The origin of ore-forming fluids of volcanic related U deposits remains controversial. This study reports in situ elemental and Sr-Nd isotopic compositions of apatite associated with U mineralization from the Shazhou volcanic related U deposit in South China, which provides a new perspective to constrain the origin and evolution of its ore-forming fluids. Hydrothermal apatites from the hematized rocks and U-mineralized rocks show distinct textures and chemical features, indicating two types of fluids involved in the U mineralization process. The hematitization fluid was oxidizing and enriched in U and Cl. A reducing fluid with lower Cl/F and U was introduced and mixed with the oxidizing hematitization fluid to cause U precipitation. Apatite from the hematized rocks has a lower 87 Sr/ 86 Sr (0.709246–0.714383) than that of apatite in U ore veins (0.710383–0.719318). The εNd(t) of apatite in the hematized rocks is from −7.6 to −9.4, whereas apatite in U ore veins has higher εNd(t) ranging from −1.2 to −8.4, close to that of mafic dikes intruded into the volcanic rocks. In situ Sr-Nd isotopes of apatite indicate the oxidizing fluid originated from the red-bed basins, whilst the origin of the reducing fluid was related to the mantle-derived mafic dikes. The reducing fluid has experienced assimilation by the metamorphic basement rocks to gain higher radiogenic strontium. This study demonstrates that in situ elemental and Sr-Nd isotopic compositions of apatite are effective in identifying different ore-forming hydrothermal fluids and constraining their origins and chemical evolution.

Late Permian orogenic gold mineralization at Haoyaoerhudong, northern China: Constraints from hydrothermal titanite and apatite chemistry

The giant Haoyaoerhudong gold deposit is located on the north margin of the North China Craton. This deposit takes the form of lenticular orebodies hosted by the Mesoproterozoic carbonaceous schist, phyllite, and slate. Gold-related hydrothermal alteration types recognized at Haoyaoerhudong are silicification, sulfidation, biotitization, and graphitization. In addition, titanite and apatite were recorded in hydrothermal system. There are four types of hydrothermal apatite, namely, rounded Ap-S in altered schist, fractured Ap-V1 in quartz–biotite–sulfide veins, anhedral Ap-V2 in quartz–sulfide stringers, and Ap-V3 with abundant fluid inclusions in quartz–sulfide veinlets. As for different titanite types, Ttn-S is found to replace ilmenite in altered schist. Clustered Ttn-V1 is associated with graphite and gold in quartz–biotite–sulfide veins. Anhedral Ttn-V2 generally coexists with pyrrhotite and chalcopyrite in quartz–sulfide stringers. Euhedral Ttn-V3 is intergrown with Ap-V3 in quartz–sulfide veinlets. A U–Pb age of 255.6 ± 2.5 Ma (MSWD = 4.2, n = 27) was obtained for Ttn-V3 via in situ U–Pb analyses, which is younger than the nearby biotite granite (272.9 ± 1.5 Ma MSWD = 2.1, N = 25). The Haoyaoerhudong deposit can therefore be considered the product of a postmagmatic mineralization event at around 256 Ma. Apatite and titanite trace elements are robust tools for tracking fluid pathways in orogenic gold deposits. The enrichment of Mn, Fe, Y, and rare earth elements (REE) is observed in Ap-S but is progressively depleted from Ap-V1 through Ap-V2 to Ap-V3. There are also higher concentrations of Mn, Fe, Mo, Bi, Nb, Ta, Zr, Hf, and REE for Ttn-S than other titanites. Nevertheless, the K, Ba, Sr, and V concentrations are enriched in Ttn-V3, similar to the enrichment of Sr in Ap-V3. The apatite and titanite compositions measured here indicate the low salinity but Sr and alkali metals -enriched ore-forming fluids, typical for orogenic gold systems. Systematic geochemical variations in Eu, Mn, and V concentrations may imply that the ore-forming fluids were slightly oxidized compared to altered schist. The interaction between the carbonaceous schist and hydrothermal fluids would have led to CO2 consumption and apatite, titanite, and graphite formation. We further concluded that Sn vs. Mo, V vs. Th/U, and Zr + Hf vs. Th/U diagrams help to distinguish hydrothermal titanite in orogenic gold deposits from those in porphyry, skarn, and iron oxide–copper–gold deposits.

In situ apatite U-Pb dating for the ophiolite-hosted Nianzha orogenic gold deposit, Southern Tibet

Mineralization age dating is essential for understanding orogenic-type gold metallogeny, but suitable minerals for dating are not always available. Apatite can incorporate considerable amount of U and Th, making it a potential U-Pb geochronometer to study hydrothermal alteration and mineralization processes. The newly-discovered Nianzha is a large orogenic Au deposit (∼25 t @ 3.08 g/t Au) and located in the contact fault zone between ultramafic rocks and diorite in the Renbu tectonic mélange of southern Tibet. Two different types of apatite were identified in the Nianzha gold deposit: type I magmatic apatite hosted in diorite and syenite, and intergrown with other magmatic minerals; type II hydrothermal apatite hosted in mineralized diorite. These apatite grains are coarse euhedral granular and closely associated with auriferous sulfides (e.g., pyrite, chalcopyrite, galena). Type I apatite is F- and SO3-rich, whereas type II apatite is distinct from type I apatite by its significantly higher Cl, Mn, rare earth elements (REE), U, Th, and As contents, indicative of a hydrothermal origin. Thus, formation age of type II apatite reflects the timing of gold mineralization. Two type I magmatic apatite samples yielded similar discordia U-Pb ages of 80.35 ± 1.56 Ma (MSWD = 1.3; n = 86) and 79.53 ± 1.27 Ma (MSWD = 0.91; n = 72), respectively, whilst type II hydrothermal apatite yielded a discordia age of 44.60 ± 1.45 Ma (MSWD = 1.2; n = 64). The gold mineralization age is consistent with that of nearby orogenic gold deposits (e.g., Mayum, Bangbu, Zhemulang, and Juqu) in the region. Therefore, we suggest that hydrothermal apatite U-Pb dating can effectively constrain the timing of orogenic Au mineralization events.

Fluid-rock interaction and fluid mixing in the large Furong tin deposit, South China: New insights from tourmaline and apatite chemistry and in situ B-Nd-Sr isotope composition

AbstractThe Furong tin deposit (South China) is genetically associated with the multiphase Qitianling batholith that consists of main-phase and minor, but more fractionated, late-phase granites. Several tourmaline and apatite generations are distinguished. Tourmaline (Tur) variants comprise pre-ore Tur-1 as disseminations and nodules in the late-phase granite, pre- to syn-ore Tur-2 as replacements in nodules and as veins crosscutting the late-phase granite and nodules, syn-ore Tur-3 in tin greisens, pre- to syn-ore Tur-4 as veins in the altered main-phase granite, and syn-ore Tur-5 from tin skarns in a distinct Ca-rich environment. Apatite (Ap) generations include accessory Ap-G in the main-phase granite, and Ap-I to Ap-III from three stages related to skarn-type mineralization (garnet-diopside stage-I, pargasite-phlogopite-cassiterite stage-II, and sulfide-rich stage-III). Textural and compositional features suggest that all tourmaline variants are hydrothermal in origin with alkali and schorl to foitite composition and minor extensions to calcic and X-site vacant tourmaline groups, whereas all apatite generations belong to fluorapatite with Ap-G crystallizing from the magma and Ap-I to Ap-III being hydrothermal in origin. The narrow range of tourmaline δ11B values (–14.8 to –10.4‰) suggests a single magmatic boron source in the ore-forming fluids. The similar rare earth element patterns and εNd(t) values (–8.2 to –5.9 for Ap-G and –8.0 to –7.3 for Ap-I) between magmatic and hydrothermal apatite indicate that the skarn-forming fluids are dominantly derived from granites. The 87Sr/86Sr ratios of Ap-I to Ap-III (0.70733–0.70795) are similar to the carbonate wall rocks, but distinctly different from the more radiogenic granites, indicating Sr exchange with carbonate rocks. Integrating previous H-O isotopic data, the tourmaline and apatite elemental and B-Sr-Nd isotope results suggest that the greisen-type ore formed by interaction of B-, Na-, Li-, Zn-, and Sn-rich magmatic fluids with the late-phase granite in a closed and reduced feldspar-destructive environment, whereas the tin skarns resulted from mixing of magmatic fluids with meteoric water and interaction with the carbonate wall rocks in an open system where oxygen fugacity changed from reduced to oxidized conditions. During fluid-rock interactions and fluid mixing, considerable Ca, Mg, V, Ni, and Sr from the host rocks were introduced into the ore system. Coupled hydrothermal minerals such as tourmaline and apatite have great potential to fingerprint the nature, source, and evolution of fluids in granite-related ore systems.

Ore fluid origin recorded by apatite chemistry: A case study on altered dolerite from the Badu Carlin-type gold deposit, Youjiang basin, SW China

The Paleozoic-Mesozoic Youjiang sedimentary basin in SW China is developed on a Lower Paleozoic low-grade metamorphic basement, and contains dozens of Carlin-type gold deposits with a total Au reserve of over 900 metric tonnes (t). Although most of these deposits are hosted in sedimentary rocks, ∼70% of the gold (∼24.5 t) in the Badu deposit is hosted in altered OIB-type dolerite. To date, the ore-fluid source of Carlin-type gold deposits in the basin is highly debated, hampering the formulation of genetic models. Here, for the first time, we present ore-related apatite chemical and Sr isotope compositions from the altered dolerite at Badu to provide new insight into the ore-fluid source of this key gold province.Petrography studies distinguished three apatite generations (Ap1 to Ap3): Pre-ore Ap1 is needle-shaped or fine-grained (<20 μm), and occurs mainly in the unmineralized dolerite; Main-ore Ap2 is euhedral-subhedral coarse-grained (>100 μm) and spatially associated with auriferous pyrite and arsenopyrite in the mineralized dolerite; Late-ore Ap3 is also euhedral-subhedral coarse-grained (>100 μm), and hosted in quartz ± ankerite veins crosscutting the mineralized dolerite. Geochemically, Ap1 contains relatively high Cl (∼0.134 wt%), MnO (∼0.038 wt%), MgO (∼0.155 wt%), and SiO2 (∼0.285 wt%) contents, whereas Ap2 and Ap3 have relatively high SrO contents (∼0.448 and ∼0.45 wt%, respectively). This geochemical difference can be used to distinguish magmatic from hydrothermal apatite at Badu. Ap2 has similar chemistry to Ap3 except for the higher SO3 contents (up to ∼0.318 wt%), and they both have similarly higher 87Sr/86Sr ratios (0.709489–0.711787) than those of the unmineralized dolerite (0.706295–0.706323) and the sedimentary ore host in the basin, but similar to the Lower Cambrian basement rocks (0.70909–0.82733). This similarity indicates that the ore-forming fluids were dominantly sourced from the basinal basement or from deep magmatic fluids with radiogenic Sr addition from the basement rocks. The ore-forming fluids may also have leached MREEs from the sulfate-rich basement rocks, leading to the observed MREE enrichments in Ap2 and Ap3. Our study highlights that the basement material contribution is critical for the Carlin-type gold mineralization in the Youjiang basin.

Use of high-U hydrothermal apatite containing excess 206Pb to constrain the age of uranium mineralization at the Coles Hill deposit, Virginia, USA

High-U hydrothermal apatite with complex UPb systematics is closely spatially associated with mineralization at the Coles Hill deposit, the largest unmined uranium deposit known in the United States. The deposit is hosted in metasomatized rocks of the 450- to 430-Ma-old Martinsville Intrusive Complex in south-central Virginia. Direct dating of metamict uranium-ore minerals, mostly coffinite, is not possible due to open-system radon loss. Instead, UPb isotopes in cogenetic apatite were investigated as a means of evaluating the age of mineralization. Here we report in situ electron probe microanalyses (EPMA) of coffinite, isotope-dilution thermal-ionization mass spectrometry (ID-TIMS) UPb data for mineralized whole rock samples, and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) UPb isotope data for apatite in both unmineralized and U-mineralized host rocks.Massive deficits in radiogenic Pb preclude reliable UPb “chemical ages” calculated from EPMA data obtained from coffinite. In contrast, LA-ICPMS data for secondary apatite in unmineralized rocks indicate low-U concentrations (100–102 ppm), “normal” (consistent with models of terrestrial Pb isotopic evolution) initial Pb isotope compositions, and UPb age estimates of ~330 Ma, which is consistent with dates previously proposed for the regional Paleozoic shear zone that hosts the deposit. Ore-stage apatite associated with coffinite has high-U concentrations (typically 102–103 ppm but up to 2.4 wt% U) and large excesses of 206Pb (207Pb/206Pb < 0.01) unsupported by in situ U decay. Data show that initial Pb had variable isotopic compositions including both “normal” Pb derived from host rocks and 206Pb-enriched Pb introduced by secondary metasomatic fluids. Evaluation of the complex evolution and mixing of Pb sources has broader implications for UPb dating of hydrothermal apatite.Excess 206Pb in apatite is derived from decay products of 222Rn lost from coffinite and mobilized by Na-, P-, and U-enriched metasomatic fluids during the main mineralizing event at ~230 Ma. Ore-stage alteration did not uniformly reset the UPb systematics in host rocks precluding a well-constrained whole-rock isochron age. However, whole-rock isotope data imply U mobility at ~200–220 Ma and support a Triassic age for the final stages of mineralization. Results also indicate that apatite with up to several weight percent uranium is able to retain U and its decay products for hundreds of millions of years; an important consideration when assessing this mineral as a potential matrix for long-term storage of radioactive waste.

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.

Early Paleozoic Orogenic Gold Deposit in the Cathaysia Block, China: A first example from the Shuangqishan Deposit

The Shuangqishan gold deposit (>20t gold) is located in a hitherto poorly-documented gold province in the southeastern Cathaysia Block, South China. It is hosted by Neoproterozoic amphibolite-facies metamorphic rocks and consists of quartz-sulfide veins with distinct alteration haloes. Three stages of hydrothermal activity have been identified, and gold is mainly associated with veins of Stage II (quartz-pyrite±chalcopyrite). Gold occurs both as refractory gold hosted by pyrite and free gold enclosed in, or filling, microfractures of pyrite and quartz. U-Pb isotope dating of hydrothermal apatite from the Substage IIa veins yielded an age of 436.8 ± 7.6 Ma. The ore fluid was of carbonic-aqueous composition and low oxygen fugacity. Total homogenization temperatures in Substage IIa and IIb range from 270° to 310°C and 250° to 295°C, respectively. Variable CO2/H2O ratios indicate fluid unmixing under fluctuating pressures. Stage I quartz veins show evidence of ductile deformation and have δ18Ofluid and δD values of 10.3 to 11.2‰ and −67to −66‰, respectively, consistent with a metamorphic fluid. Stage II veins have slightly higher δ18O values of 10.9 to 13.7‰, with calculated δ18Ofluid values of 4.8 to 8.0‰. The 3He/4He ratios of pyrite are elevated (0.06–0.23 Ra) relative to crustal He reservoirs (<0.01 Ra). Fluid inclusions in quartz yielded δ13CCO2values of −23.0to −11.4‰ (V-PDB), reflecting variable contributions of organic carbon. The sulfide δ34SV-CDT values range from −4.7to −1.0‰, consistent with a deep-seated sulfur source. The Pb isotope compositions of pyrite (206Pb/204Pb=17.141–17.871, 207Pb/204Pb=15.484–15.570) are more radiogenic than those of unaltered host rocks. All available data demonstrate that the Shuangqishan deposit is the first report orogenic gold deposit formed during the late Wuyi-Yunkai intracontinental orogeny in the Cathaysia Block.

Constraints on scheelite genesis at the Dabaoshan stratabound polymetallic deposit, South China

Abstract The genesis of the Dabaoshan stratabound base metal deposit has remained in dispute since its discovery. Scheelite is commonly present in both the Cu-S orebody and adjacent porphyry-style Mo-W mineralization and can provide insights into the hydrothermal history. In the stratabound Cu-S orebodies, there are three stages of mineralization: early-stage, Cu-(W), and late-stage. Two types of scheelite (here referred to as SchA and SchB) are identified in the Cu-(W) mineralization stage. SchA is anhedral and disseminated in massive sulfide ores. It coexists with chalcopyrite and replaces the preexisting arsenic-bearing pyrite. SchA exhibits chaotic cathodoluminescent (CL) textures and contains abundant mineral inclusions, including pyrite, chalcopyrite, arsenopyrite, uraninite, and minor REE-bearing minerals. Chemically, SchA displays middle REE (MREE)-enriched patterns with negative Eu anomalies. SchB occurs in veins crosscutting the stratabound orebodies and shows patchy textures in CL images. Based on CL texture, SchB is subdivided into SchB1 and SchB2. SchB1 is CL-dark and occasionally shows oscillatory zoning, whereas SchB2 is CL-bright and relatively homogeneous. Chemically, SchB1 has a high-U content (mean = 552 ppm) and REE patterns varying from MREE-enriched to MREE-depleted. In contrast, SchB2 is depleted in U (mean = 2.5 ppm) and has MREE-enriched patterns. Compared with SchB, SchA is significantly enriched in Ba. Scheelite in the stratabound orebodies has similar Y/Ho ratios and trace-element characteristics as Sch3 in the Dabaoshan porphyry system. In situ U-Pb dating of hydrothermal apatite, collected from the Sch3-bearing veins in the footwall of stratabound orebodies, yielded a mineralization age of 160.8 ± 1.1 Ma. Zircon from the Dabaoshan granite porphyry yielded a U-Pb age of 161.8 ± 1.0 Ma. These two ages are consistent within uncertainty, suggesting that the ore-forming fluid responsible for tungsten mineralization in the stratabound orebodies was derived from the porphyry system. When fluid emanating from the deep porphyry system encountered the overlying Lower Qiziqiao Formation and stratabound orebodies, replacement reactions resulted in dramatic variations in physiochemical conditions (e.g., decrease in fO2, increase in Ca/Fe, As, Ba). During this process, U6+ was reduced to U4+, and As and Ba were leached out of the preexisting pyrite and host rock. Fluid-rock interactions triggered a rapid discharge of fluids, forming SchA with chaotic CL textures and abundant inclusions, but uniform REE patterns. SchB (characterized by patches with different chemical characteristics) may have been formed from repeated injection of ascending fluids into fractures crosscutting the preexisting massive sulfide ores. We propose that Jurassic porphyry Mo-W mineralization contributed to tungsten mineralization in the stratabound orebodies. Considering that Cu and W mineralization are genetically related, not only in the footwall but also in the stratabound orebodies, we infer that Cu in the stratabound orebodies was locally sourced from the Jurassic porphyry mineralization.

Hydrothermal fluid characteristics and implications of the Makou IOA deposit in Luzong Basin, eastern China

A large number of iron oxide–apatite (IOA) deposits occur in the Middle and Lower Yangtze River metallogenic belt (MLYB), eastern China. Proterozoic phosphorus-rich strata are also widely exposed in this belt, providing a good opportunity to research the relationship between phosphorus-rich layers and IOA deposits. The Makou IOA deposit is located in the central part of the volcanic Luzong Basin. The ore body is developed in the contact zone between gabbro-diorite and Cretaceous trachyandesite, and it is the only IOA deposit in the basin that spatially associated with a dioritic intrusion. The main hydrothermal alteration minerals are albite, diopside, apatite, chlorite, and carbonate. In this study, we employed SHRIMP SI to analyse in situ O isotope ratios of magmatic and hydrothermal apatite and in situ S isotope ratios of pyrite from the Makou deposit. Additionally, LA-ICP-MS was used for trace element analysis. The results show that the sulfur in the pyrite of the Makou deposit comes from different sulfur phases (e.g. H2S and SO2) in the hydrothermal fluid, and ΣS34total is similar to that of magmatic sulfur, indicating that the hydrothermal fluid was weakly affected by evaporite, which is substantially different from other IOA/skarn iron deposits in the MLYB. Both analysed apatite samples are classified as fluorapatite, in which the δ18Oap of the Makou magmatic/hydrothermal apatite is similar to that of the initial mantle (3.7–5.5‰) and much lower than that of the Susong sedimentary-metasomatic apatite (13.7–14.2‰). The LREE/HREE ratio increase from magmatic to hydrothermal apatite, whereas the Sr/Y decreases, indicating that the hydrothermal fluid metasomatised the dioritic intrusive rock, resulting in a large amount of albite crystallisation and release Fe from pyroxene and biotite to hydrothermal fluid, indicates that Fe-rich fluid in IOA deposit could be formed by albitization of the consolidated intrusive rock. By combining this finding with the oxygen isotope data, we propose that the mineralization of the Makou deposit was mainly controlled by a magmatic-hydrothermal process. The low CO2 and SO42− contents in the volcanic rock are a key factor leading to apatite precipitation. The addition of a phosphorus-rich layer or evaporites is not necessary for the formation of IOA-type deposits in the MLYB.

Apatite at Niutoushan U–Pb–Zn deposit in Xiangshan ore field: A tracer for hydrothermal fluid

The volcanic‐hosted Xiangshan uranium ore field is the largest uranium deposit in Jiangxi Province, South China. In this ore field, Pb–Zn mineralization has been discovered beneath the uranium orebodies at Niutoushan‐Heyuanbei area. Apatite is a ubiquitous accessory mineral in the volcanic rocks, as well as the U and Pb–Zn alteration–mineralization zones. Six main types of apatite, which show the evolution of volcanic magma and hydrothermal fluids, have been observed on the basis of textures, associated mineral assemblages, chemical compositions (halogen, MnO, FeO, and SO3, etc.), and mineral inclusions. For magmatic primary apatite, porphyritic lava‐hosted P‐Apa and P‐Apb have higher F/Cl ratios and lower contents of MnO and FeO than rhyodacite‐hosted R‐Ap. For hydrothermal apatite, U‐Ap1‐a, U‐Ap1‐b, and S‐Ap1 are recognized as hydrothermal‐affected apatite, while U‐Ap2 and S‐Ap2 as apatite precipitating from hydrothermal fluid. U‐Ap1‐a and U‐Ap1‐b, hosted in the green‐stained alteration zone, are characterized by highly heterogeneous BSE imaging and contain monazite and ThSiO4 inclusions. Such apatites record the remobilization and reprecipitation of rare earth elements (REEs), Th and U by a relatively high‐temperature, F‐ and CO2‐enriched but Na‐depleted fluid at the early REE‐phase stage. U‐Ap2 occurring in pitchblende–fluorite dominated ore sample, is featured with negligible Cl, variable F and relatively higher Ti contents. It records a new hydrothermal pulse of relatively low temperature, oxidized, highly Ca‐, Ti‐, and F‐enriched but Cl‐depleted which probably conduces to leaching and transporting significant amounts of uranium. S‐Ap1 and S‐Ap2 hosted within the sericite–quartz–carbonate alteration halo on both sides of Pb–Zn–Fe sulphide veinlets, have relatively high Cl and variable F content. This apatite records reduced, Cl‐, Ca‐enriched, magmatic‐derived fluid events. Combined with previous researches, the apatite data suggest that U and Pb–Zn mineralization may form from two spatially and temporally distinct hydrothermal systems. Thus, apatite can fingerprint multi‐stage hydrothermal fluids and be treated as a useful tool for mineral exploration.

Working up an Apatite: Enigmatic Mesoarchean Hydrothermal Cu-Co-Au Mineralization in the Pilbara Craton

Abstract Globally, significant examples of hydrothermal Cu-Co mineralization are rare within Archean greenstone belts, especially relative to the endowment of these terranes with other world-class hydrothermal ore deposits, particularly Au deposits. Using U-Pb geochronology of hydrothermal apatite, this study provides the first absolute age constraints on the timing of mineralization for the Carlow Castle Cu-Co-Au deposit. Carlow Castle is a complex, shear zone-hosted, veined Cu-Co-Au mineral system situated within the Paleo-Mesoarchean Roebourne greenstone belt of the Pilbara craton of northwestern Western Australia. Although U-Pb geochronology of this deposit is challenging due to low levels of radiogenic Pb in synmineralization apatite, mineralization is best estimated at 2957 ± 67 Ma (n = 61). Additionally, analysis of alteration phases associated with Carlow Castle mineralization suggests that it is dominated by a propylitic assemblage that is characteristic of alkaline fluid chemistry and peak temperatures &amp;gt;300°C. Within proximal portions of the northwest Pilbara craton, the period of Carlow Castle’s formation constrained here is associated with significant base-metal volcanogenic massive sulfide mineralization and magmatic activity related to back-arc rifting. This rifting and associated magmatic activity are the most likely source of Carlow Castle’s unique Cu-Co-Au mineralization. Carlow Castle’s Mesoarchean mineralization age makes it among the oldest discovered Cu-Co-Au deposits globally, and unique in the broader context of hydrothermal Cu-Co-Au deposits. Globally, hydrothermal Cu-Co mineralization occurs almost exclusively as Proterozoic and Phanerozoic stratiform sediment-hosted Cu-Co deposits due to the necessity of meteorically derived oxidized ore fluids in their formation. This research therefore has implications for exploration for atypical Cu-Co deposits and Cu-Co metallogenesis through recognition of comparably uncommon magmatic-hydrothermal Cu-Co-Au ore-forming processes and, consequently, the potential for analogous Cu-Co-Au mineralization in other Archean greenstone belts.

Mineralogical constraints on Nb–REE mineralization of the Zhujiayuan Nb (−REE) deposit in the North Daba Mountain, South Qinling, China

The trachyte‐hosted Zhujiayuan deposit is located in the North Daba Mountain of South Qinling, China. In this deposit, the presence of different stages and genetic types of biotite, apatite, and rutile make it an excellent locality to constrain the mineralization process of Nb–REE in the alkaline igneous rock. In this study, supported by electron probe microanalyzer (EPMA), chemical analyses of biotite, apatite, rutile, columbite‐group minerals, fersmite, monazite, and aeschynite‐group minerals were presented. Three types of biotite were identified, including magmatic (Bt‐1), reequilibrated (Bt‐2), and hydrothermal biotite (Bt‐3). Apatite can be divided into two types: magmatic (Ap‐1) and hydrothermal apatite (Ap‐2). Rutile can also be divided into two types: magmatic (Rt‐1) and hydrothermal rutile (Rt‐2). Rt‐1 and Ap‐1 contain average 1.44 wt% Nb2O5 and 4.14 wt% LRE2O3, respectively, indicating that certain concentrations of Nb and REE were incorporated into the rutile and apatite, respectively, during the magmatic crystallization process. The distributions of the columbite‐group, fersmite, monazite, and aeschynite‐group minerals, as well as the compositional characteristics of monazite, indicate the important role of hydrothermal metasomatism during Nb–REE mineralization. The compositional characteristics of Bt‐2 indicate relatively high F and Cl fugacities in the hydrothermal fluid. Bt‐2 and Bt‐3 both have higher Nb2O5 content than Bt‐1, indicating a higher Nb content in the fluid. The source of fluidic Nb likely derived from the metasomatism of magmatic rutile. The REE content decreased from Ap‐1 to Ap‐2, possibly due to a dissolution–reprecipitation process. The compositional changes from Bt‐1 to Bt‐3 and Ap‐1 to Ap‐2 also revealed a decrease in temperature, increase in oxygen fugacity, and increase in Ca content from the magmatic to the hydrothermal system. We speculate that rutile and apatite may have originally formed from an Nb–REE‐rich alkaline‐silicate melt derived from the metasomatized mantle, which led to the initial Nb–REE enrichment. Subsequent hydrothermal alteration by hydrothermal fluids rich in F and Cl, accompanied by changes in the above physical and chemical conditions and fluid composition, caused a relatively limited and localized remobilization of Nb–REE into the fractures and vesicles in the trachyte.

Early orogenic gold mineralization event in the West Qinling related to closure of the Paleo-Tethys Ocean – Constraints from the Ludousou gold deposit, central China

The West Qinling Orogen experienced a complex orogenic history and developed related orogenic gold deposits. Most known orogenic gold deposits in West Qinling are hosted by brittle to ductile shear zones and mainly formed during 220–190 Ma. The Ludousou gold deposit, located in the northwesternmost segment of West Qinling, has breccia gold ores controlled by E-W, NE-, NW-, and N-S trending faults, and is hosted by tuff and quartz diorite porphyry. Uranium-Pb zircon investigations indicate that tuff and quartz diorite porphyry were emplaced at 252.9 ± 4.1 Ma and 247.0 ± 2.2 Ma. Magmatic apatites from the same quartz diorite porphyry crystallized at 243.5 ± 4.8 Ma indicating a rapid cooling history. Hydrothermal sericite coexisting with gold-bearing pyrite and arsenopyrite from mineralized quartz diorite porphyry provided 40Ar/39Ar plateau and inverse isochron ages of 235.68 ± 0.29 Ma and 235.61 ± 0.41 Ma. Hydrothermal apatite separated from the same mineralized quartz diorite porphyry yielded concordant U-Pb age of 235.7 ± 4.9 Ma. Such data bracketed that the Ludousou gold mineralization event occurred at ca. 236 Ma postdating the 252–247 Ma magmatism by approximately 8–11 million years. Combined present field observations and geochronological data with sulfur isotopic and fluid inclusion investigations in literatures, we therefore propose that ore-forming fluids may not be derived from ore-hosting tuff and quartz diorite porphyry, and such rapid cooled host-rocks might even provide little heat source during ore formation. The Ludousou gold deposit is best classified as an orogenic gold deposit, and probably can extend the orogenic gold mineralization event in the West Qinling related to closure of the Paleo-Tethys Ocean tracing back to ca. 236 Ma.

The polyphase evolution of a late Variscan W/Au deposit (Salau, French Pyrenees): insights from REE and U/Pb LA-ICP-MS analyses

The Salau deposit, located in the Axial Zone of the French Pyrenees, is the most important tungsten deposit ever mined in France.Two types of mineralization, both closely associated with a granodiorite intrusion, are distinguished. The first is a fine-grainedscheelite skarn related to contact metamorphic and metasomatism between the intrusion and the adjacent carbonate rocks. Thesecond type is represented by massive sulfides accompanied by coarse-grained scheelite, apatite, and electrum. This synkinematicmineralization is found enclosed within the skarn ore but occurs also within the granodiorite stock along majorductile–brittle shear zones. REE contents of scheelite and apatite from the two types of mineralization show differences suggestingthat the two types derived from two different fluids. U/Pb dating on zircon, apatite and scheelite illustrates that magmaticzircon and apatite formed at 295 ± 2 Ma during emplacement and cooling of the granodiorite intrusion. These are cogenetic to thefine-grained scheelite skarn. Hydrothermal apatite frommassive sulfide ores yields a younger age of 289 ± 2 Ma, whereas closelyassociated coarse-grained scheelite yields a consistent although less precise age of 284 ± 11 Ma. These results suggest that the latemassive sulfide ore with abundant coarse-grained scheelite and electrum is related to the emplacement of an underlying, moreevolved intrusion, accompanied during its ascent by the development of steeply dipping reverse-dextral shear zones

Metallogeny of the Zoujiashan uranium deposit in the Mesozoic Xiangshan volcanic-intrusive complex, southeast China: Insights from chemical compositions of hydrothermal apatite and metal elements of individual fluid inclusions

The Zoujiashan U deposit in the Mesozoic Xiangshan volcanic-intrusive complex is one of the largest volcanic-related type U deposits in China. Chemical composition of hydrothermal apatite and metal contents in individual fluid inclusions of quartz and fluorite are investigated in order to understand the precipitation mechanism of U and to further constrain the origin of U and ore-forming fluids of the Zoujiashan deposit. Illitization, hematitization, and U mineralization successively occurred within rhyolite and porphyritic lava. Three types of hydrothermal apatite are identified. Apatite Type 1 (Ap1) and apatite Type 2 (Ap2) are both euhedral-subhedral crystals found in hematitization zone, while only Ap2 shows evident irregular chemical zoning along its rims. Apatite Type 3 (Ap3) occurs as anhedral aggregates closely associated with U-minerals in U ore veins, implying synchronous precipitation of Ap3 and U ores. Comparable chemical compositions of Ap1 and cores of Ap2, including similar high Cl content, indicate both of them were precipitated from a Cl-rich fluid that induced hematitization. The elevated F contents of Ap3 and rims of Ap2 implies that a F-rich fluid was involved and altered Ap2 during the main stage of U deposition. Ap1 and cores of Ap2 have lower Mn contents than Ap3 and rims of Ap2, indicating an oxidized character for the Cl-rich fluid and a reducing character for the F-rich fluid.Metal contents of fluid inclusions in fluorite and quartz occurring in U ores suggest that two end-members of fluids, including a U-rich and a U-poor, were involved in the main stage of U mineralization. Mixing between these two fluids led to the deposition of U- and Th-minerals through oxidation-reduction reactions and destabilization of Th-F complexes, respectively. The U-rich fluid is depleted in Th and Sr compared with the U-poor fluid. Based on comparison of chemical compositions of apatite and fluid inclusions, we suggest that the Cl-rich fluid precipitating Ap1 and Ap2 corresponds to the U-rich end-member fluid, while the F-rich fluid precipitating Ap3 represents a mixture between the two end-members. The high U (12.7–58.5 ppm) in the U-rich end-member fluid is in agreement with a relatively high oxygen fugacity and a surface-derived origin. The U-poor end-member fluid has lower Rb/Cs than the U-rich end-member and the unaltered host rocks, indicating the U-poor fluid was derived from a mantle wedge that experienced addition of Cs by fluids generated from the devolatilization of the subducted paleo-Pacific slab.

Hydrothermal apatite SIMS Th[sbnd]Pb dating: Constraints on the timing of low-temperature hydrothermal Au deposits in Nibao, SW China

Precise geochronology is a crucial tool for understanding the genesis of low-temperature hydrothermal mineral deposits, but datable minerals are not always available; e.g., mineralization within sedimentary rocks, such as Carlin-type or Carlin-like Au deposits. Here, we demonstrate that hydrothermal apatite associated with Au from the large Nibao deposit in the Yunnan–Guizhou–Guangxi region of South China can be dated to yield the age of Au mineralization. Nibao is a Carlin-like deposit hosted in a Permian carbonate-bearing pyroclastic breccia. The auriferous minerals are predominantly zoned pyrite containing As-, Cu-, and Au-rich rims. Euhedral and subhedral apatite forms a mosaic texture and is intergrown with hydrothermal quartz, sericite, and zoned auriferous pyrite, indicating that the apatite is of hydrothermal origin and was coeval with Au mineralization. Unlike sedimentary and igneous apatite, hydrothermal apatite is relatively depleted in LREEs, enriched in MREEs, and slightly depleted in Eu. Hydrothermal apatite also has high Th/U ratios, negligible U concentrations, and very low concentrations of common Pb. This makes the apatite a potential candidate for ThPb dating. Our SIMS ThPb analyses yield a weighted mean 232Th/208Pb age of 141 ± 3 Ma (N = 23, MSWD = 2.2) for apatite coeval with auriferous pyrite, and this is the best estimate of the timing of Au mineralization. Hydrothermal apatite is also present in similar deposits in the Golden Triangle of South China. Therefore, ThPb dating of hydrothermal apatite potentially allows for the accurate dating of low-temperature hydrothermal deposits in China and worldwide.

Numerical Modeling of REE Fractionation Patterns in Fluorapatite from the Olympic Dam Deposit (South Australia)

Trace element signatures in apatite are used to study hydrothermal processes due to the ability of this mineral to chemically record and preserve the impact of individual hydrothermal events. Interpretation of rare earth element (REE)-signatures in hydrothermal apatite can be complex due to not only evolving fO2, fS2 and fluid composition, but also to variety of different REE-complexes (Cl-, F-, P-, SO4, CO3, oxide, OH− etc.) in hydrothermal fluid, and the significant differences in solubility and stability that these complexes exhibit. This contribution applies numerical modeling to evolving REE-signatures in apatite within the Olympic Dam iron-oxide-copper-gold deposit, South Australia with the aim of constraining fluid evolution. The REE-signatures of three unique types of apatite from hydrothermal assemblages that crystallized under partially constrained conditions have been numerically modeled, and the partitioning coefficients between apatite and fluid calculated in each case. Results of these calculations replicate the measured data well and show a transition from early light rare earth element (LREE)- to later middle rare earth element (MREE)-enriched apatite, which can be achieved by an evolution in the proportions of different REE-complexes. Modeling also efficiently explains the switch from REE-signatures with negative to positive Eu-anomalies. REE transport in hydrothermal fluids at Olympic Dam is attributed to REE–chloride complexes, thus explaining both the LREE-enriched character of the deposit and the relatively LREE-depleted nature of later generations of apatite. REE deposition may, however, have been induced by a weakening of REE–Cl activity and subsequent REE complexation with fluoride species. The conspicuous positive Eu-anomalies displayed by later apatite with are attributed to crystallization from high pH fluids characterized by the presence of Eu3+ species.

The Wirrda Well and Acropolis prospects, Gawler Craton, South Australia: Insights into evolving fluid conditions through apatite chemistry

The Wirrda Well and Acropolis prospects are located ~25km SSE and SW, respectively, from the giant Olympic Dam Cu-U-Au-Ag deposit within the Olympic Cu-Au Province of South Australia. Mineralisation in the two prospects displays a temporal and spatial zonation characteristic of other IOCG-type deposits and prospects within the province, including Olympic Dam, in which an early high-temperature, magnetite-dominant mineralisation is transitional to a hematite-dominant mineralisation style, accompanied by subordinate and often localised carbonate alteration. Both prospects contain conspicuous hydrothermal apatite which is characteristic in terms of host assemblage and geochemical signature. Chondrite-normalised rare earth element (REE) fractionation patterns for apatite depict the evolution of hydrothermal fluids during ore formation. An early generation of apatite is abundant within magnetite-dominant mineralisation in both prospects, and displays a characteristic light-REE enriched fractionation trend. Overprinting of this initial high-temperature assemblage results in the loss of REE and Y (REY), as well as Cl, along fractures within this apatite, as well as the formation of new generations of apatite that are also depleted in these elements. The transition from early reduced, to later oxidised assemblages within both prospects is accompanied by an evolution of the REY signature of apatite in which LREE-enriched patters with negative Eu-anomalies are replaced by convex middle-REE (MREE)-enriched patterns, positive Eu-anomalies and the development of a conspicuous negative Y-anomaly. Comparable trends are recognised elsewhere within the district and are interpreted as the hallmark of productive mineralised IOCG ore systems. The evolution of chondrite-normalised REY patterns can be explained in terms of changes in fluid parameters, speciation of REY in ore-forming fluids, and the capacity of REY to precipitate and partition into apatite in ways that contrast with those expected by simple consideration of crystal structure. Results are concordant with modelling of REY-speciation, which show that, under hydrothermal conditions typical of IOCG mineralisation, a decrease in salinity, pH and temperature is associated with hematite-sericite alteration sufficient to produce MREE-enriched apatite. These data offer encouragement for the use of apatite geochemistry in mineral exploration within the Olympic Cu-Au Province, and potentially in analogous terranes elsewhere, given the clear association between MREE-enriched apatite and often well-mineralised, hematite-dominant domains within these large IOCG systems.