Mineral Geochemistry Research Articles

Distribution of tellurium, selenium, cobalt and gold in sulfide minerals: A case study of the Jiguanzui porphyry-skarn Au-Cu deposit, eastern China

The Jiguanzui deposit is a representative porphyry-skarn Au-Cu deposit in the Mid-Lower Yangtze River metallogenic belt, Eastern China, characterized by significant critical metal (Te, Se, Co) association. Previous study focused on the Te and Se distribution in the ores and pyrite minerals on deposit scale, this study present trace element geochemistry of various sulfide minerals (chalcopyrite, bornite, sphalerite, molybdenite) through LA-ICP-MS analysis, aiming to reveal the distribution of Te, Se, Co, and Au among sulfide minerals in this deposit. Except molybdenite, which host high concentrations of Te and Se, pyrite and chalcopyrite generally have higher Te contents than bornite and sphalerite, whereas bornite and chalcopyrite exhibited relatively high Se concentrations. Cobalt and Au are dominantly hosted in the pyrite and chalcopyrite, respectively, although the highest Au concentration up to 14 ppm was analyzed in pyrite. Principal component analysis of trace element contents and time-resolved LA-ICP-MS signal depth profiles indicate that Te occurred as Te-Ag minerals and mineral inclusions within the sulfides, whereas Se and Co are incorporated into the lattices of sulfide minerals. Principal component analysis of trace element contents in various sulfides exhibit intimate Pb-Bi-(Cu)-Au associations, suggesting that Au is present as tiny mineral inclusions coexisting with either Cu-Bi sulfosalts or Pb sulfides or sulfosalts. This case study also highlights that Te and Se hosted in pyrite are not recoverable with current recycling technologies.

The cobalt and nickel enrichment in base metal sulfides from the Xiarihamu Cu-Ni-Co deposit, China: Constrained by in-situ mineral geochemistry of sulfides

Rapidly growing demand for cobalt and nickel in rechargeable battery industry promotes research on metallogenic theory of magmatic Cu-Ni-Co sulfide deposits. Xiarihamu Cu-Ni-Co deposit, one of the lately discovered Co-rich magmatic sulfide deposits in China, is typical of distribution in orogenic belts, rather than in divergent tectonic settings as many deposits of the same type. In-situ elemental and sulfur isotopic analyses of base metal sulfides (BMS; pyrrhotite, pentlandite, and chalcopyrite) from Xiarihamu were conducted in this study. The strongly negative correlation between Fe and Co + Ni reveals the major occurrence of Co and Ni as isomorphism states in pentlandite and pyrrhotite. The δ34S values of pentlandite and pyrrhotite generally increase with Co contents and Co/Ni ratios, indicating that the Co enrichment within BMS accompanied with enhanced contamination of crustal sulfur. Zinc, Cd, Sb, and Te are significantly and preferentially fractionated into intermediate sulfide solution (ISS) from which chalcopyrite exsolved. The Se contents and Se/S ratios of pentlandite and pyrrhotite in lherzolite/harzburgite are much higher than those of BMS from gabbro, which has systematically higher δ34S values. Combined with the partially overlapped Sb/Se and As/Se ratios of BMS from lherzolite and gabbro, as well as similar calculated R factors of ore-hosting peridotite and gabbro, it is proposed that the studied Xiarihamu gabbro was crystallized from a separate pulse of Co-Ni-enriched, Se-depleted and intensively contaminated mafic parent magma, rather than evolved from ultramafic magma through crystallization fractionation. The lack of olivine and spinel in gabbro also promoted more Co and Ni into sulfide liquid. Based on Se/Te ratios, the pentlandite and pyrrhotite from drill core XH1E01S was originated from sulfide liquid, which suffered higher degree of crystallization fractionation of monosulfide solution (MSS). While pentlandite and pyrrhotite that crystallized from less evolved parent sulfide liquid bear less cobalt, such as those collected from drill core XH1109. This study strengthens the potential importance of crustal contamination and crystallization fractionation of MSS from sulfide liquid during Co enrichment within BMS (pentlandite and pyrrhotite).

Evaluation of Granite Fertility Utilizing Porphyry Indicator Minerals (Zircon, Apatite, and Titanite) and Geochemical Data: A Case Study from an Emerging Metallogenic Province in the Taimyr Peninsula, Siberian High Arctic

The Taimyr Peninsula in the Russian High Arctic comprises a late Paleozoic-early Mesozoic collisional belt where several porphyry-type mineralization occurrences were identified during the last decade, making this area a potential exploration target for Cu-Mo deposits. In order to further evaluate the metallogenic potential of the poorly outcropped northeastern part of Taimyr, samples from seven granitoid intrusions were investigated in this study aimed to evaluate the granite fertility based on petrography, geochemistry, and composition of porphyry indicator minerals (zircon, apatite, and titanite). The studied intrusions represent small to moderate-sized bodies (40–800 km2) composed of biotite (±amphibole) quartz monzonites, granodiorites, granites, and biotite leucogranites that formed in the course of late Paleozoic-early Mesozoic tectono-magmatic events at the Siberian margins. The late Carboniferous Tessemsky massif represents suprasubduction granitoid series, while the Pekinskiy, Shirokinskiy, Dorozhinskiy, Kristifensenskiy, and Yuzhno-Lodochnikovskiy massifs are correlated with the early Triassic Siberian Traps LIP. The rocks of intrusions comprise a relatively uniform geochemically, predominantly magnesian, slightly peraluminous, calc-alkaline high-K amphibole-bearing I-type granitoid series with adakitic affinity, where Triassic plume-related granitoids inherit geochemical signatures of Carboniferous supra-subduction granitoids, and all rock types are marked by enrichment in LILE and negative Ta, Nb, and Ti anomalies. It is suggested that the adakitic geochemical characteristics of the Taimyr granites are a result of derivation from a relatively homogeneous mafic lower crustal source that formed at the stage of Carboniferous continental subduction and continued to produce granitic melts in the course of the early Mesozoic magmatic evolution. Whole rock geochemistry and composition of porphyry mineral indicators (zircon, apatite, and titanite) indicate that the Taimyr granites crystallized from oxidized water-saturated magmas at moderate temperatures, with the majority of samples showing characteristics typical for porphyry-fertile granites worldwide (fO2 = ΔFMQ +1 to +3 with zircon Eu/Eu* > 0.4 and apatite SO3 > 0.2 wt.%). Data from Dorozhinskiy, Kristifensenskiy, Pekinskiy, and Tessemskiy intrusions fully match geochemical criteria for porphyry-fertile granitoids, and these massifs are considered the most prospective for Cu-Mo mineralization. Granites from Shirokinskiy and Yuzhno-Lodochnikovskiy intrusions only partially match compositional constraints for fertile melts and can be considered as second-tier exploration targets. Finally, available data for the Simsovsky massif preclude its classification as a porphyry-fertile body. These conclusions are in line with previously developed exploration criteria for the northeastern Taimyr, showing that geochemical indicators of granite-fertility can be used on a regional scale in parallel with other exploration methods.

Discrimination of two diverse fluid evolutions from the Nanyangtian scheelite deposit, southeastern Yunnan: Evidences from fluid inclusions and mineral geochemistry

The Nanyangtian scheelite deposit is located in the Nanwenhe-Song Chay dome (NSCD), southeastern Yunnan. This deposit has undergone four metallogenic stages and is characterized by several kilometers of bedded scheelite-bearing skarn (NYT-II stage), feldspar-bearing quartz veins (NYT-III stage), and sulfides (NYT-IV stage) in the Neoproterozoic schist and gneiss, all of which exhibit similar fold deformations. Throughout the stages, Th and salinity of fluids gradually decrease, weakly and positively correlating, representing a slow cooling process. NYT-I fluids (F-, H2O-rich and high T, p), as indicated by the plagioclase within feldspar-bearing quartz veins, may have directly evolved from a highly fractional residual melt or a salt-rich aqueous melt, signifying the magmatic-hydrothermal transition. From NYT-II to NYT-III fluids, a wider variation of δ18OH2O (−2.4 ∼ 5.1 ‰) to a narrow range of δ18OH2O (2.8 ∼ 5.1 ‰), and a narrow δ34S range (5.18 ‰ ∼ 8.62 ‰) also indicates that fluids may evolve from the relatively oxidized granitic magma. Furthermore, NYT-I fluids could extend throughout the entire fluid evolution, culminating in two diverse paths: one is a much purer magmatic water towards the NYT-III and NYT-IV fluids, and the other is a more meteoric water-dominated towards the NYT-II fluids. A lower water/rock ratio (W/R) existed in the NYT-II stage, leading to the formation of moderately oxidized Tungsten (W)-skarns and scheelites through the NYT-I salt-rich aqueous melts or their reactions with wall rocks in a stable environment. W/R ratios increased in the NYT-III stage, resulting in the formation of NYT-III feldspar-bearing quartz veins with CO2 generation and alkalinity enhancement. As oxidation diminished, fluids gradually evolved into the NYT-IV fluids, forming sulfides.

Constraints of upper crust magmatic processes on the formation of Saindak porphyry Cu deposit: Insights from mineral geochemistry

Upper crustal magmatic processes play a crucial role in linking the magmatic and hydrothermal systems of porphyry deposits, ultimately controlling the generation of ore-forming fluids. Understanding these processes within a magma chamber is essential for deciphering the formation of porphyry deposits. The Saindak deposit, a large porphyry Cu system in the western Chagai belt, features coeval ore-forming and barren magma pulses, providing key insights into the characterization of porphyry systems. In this study, detailed petrographic observations and geochemical analyses of amphibole, plagioclase, and apatite were conducted to unravel the magmatic evolution at Saindak. Based on textural relationships and crystallization sequences, three distinct populations of amphibole in the ore-forming magma were identified. These amphiboles record the entire fractional crystallization process of magma that initially emplaced at a depth of ∼5 km to the connected magma system at ∼2 km. The study of amphibole and apatite reveals that the fertile magma underwent large-scale fluid exsolution in an open system. The simultaneous and rapid depletion of Cu, Cl, S, and H2O in the magma indicates that Cl and S were highly partitioned into the exsolved fluid phase. These elements formed complexes, which effectively concentrated metals in the fluid. Conversely, the barren magma was characterized by either low metal content or limited fluid exsolution within the magma chamber. Overall, we reconstruct the upper crustal magmatic processes at Saindak and conclude that efficient extraction of Cu through fluid exsolution is the key to porphyry deposit formation.

Mineralogy and geochemistry of gold and copper mineralization, Sultan Anouch, Malayer, West Iran

Mineralogy and geochemistry of gold and copper mineralization, Sultan Anouch, Malayer, West Iran

A hybrid framework for Detection of Multivariate porphyry Cu Signatures and Anomaly Enhancement: Incorporation of SFA, GMPI, and Grey Wolf Optimization

Geochemical data from stream sediment are commonly employed for regional scale mineral exploration, as they can be utilized to detect geochemical anomalies associated with mineralization processes. However, recognizing efficient multielement geochemical signatures related to target mineralization using stream sediment geochemical data can be challenging due to the intricate nature of mineralization events. To achieve this goal, this article proposes a combination of statistics, logistic functions and machine learning techniques. Initially, the staged factor analysis (SFA) approach was applied to the data to determine the geochemical footprints associated with porphyry copper mineralization in the Varzaghan area. Subsequently, the geochemical mineralization probability index (GMPI) was utilized to facilitate appropriate separation, more precise identification, and the transfer of data into a fuzzy space. By using a combination of SFA and GMPI, it was feasible to enhance the detection of geochemical halos and concealed anomalies. Ultimately, the output of these two approaches was subjected to an improved clustering technique known as GWO-K-means to detect geochemical anomalies. The findings indicated that there is a strong relationship between known mineral occurrences (KMOs) and the identified anomalous areas. The success rate curve demonstrated that the optimized model outperformed the K-means model, proposing that optimization can boost the accuracy in identifying geochemical targets. Overall, the outcomes of this study can be beneficial for proper planning of future exploration activities.

Mechanisms of Co enrichment in the Zhubu Ni–Co–PGE deposit in the Emeishan LIP, SW China: Constraints from mineral geochemistry and Fe–S isotopes of sulfides

The Zhubu Ni–Co–PGE sulfide deposit in the Permian Emeishan Large Igneous Province (LIP), SW China is hosted by a mafic–ultramafic intrusion that comprises two morphologically distinct ore-forming spaces: a central, layered sequence that represents a magma chamber surrounded by a marginal sub-vertical conduit zone. The marginal conduit zone contains significant Ni–Co–PGE sulfide mineralization, suggesting that high volumes of sulfide-bearing silicate melt flowed through the magma conduit system. Determining the hosts of Co is key to understanding the Co enrichment process in the Zhubu deposit, as well as in the Emeishan LIP as a whole. We assess this here using the geochemistry and Fe–S isotope compositions of sulfides in the Zhubu deposit. Cobalt is mainly concentrated in pentlandite sulfide in the websterite, with Co contents increasing in the order pyrrhotite < chalcopyrite < pyrite < pentlandite < violarite; the abundance of violarite, however, is notably lower than that of the other sulfides. The Co contents of pentlandite, pyrite, and chalcopyrite are negatively correlated with their Ni and Fe contents, suggesting that Co substitutes isomorphically for Ni and Fe in the sulfide structure. The δ56Fe values of sulfides increase in the order pyrrhotite < chalcopyrite < pentlandite < pyrite resulted from kinetic fractionation of Fe isotopes. The δ56Fe values of pentlandite and chalcopyrite in lherzolite are higher than those in websterite, implying that lherzolite and websterite formed in compositionally distinct magmas, Fe isotope compositions become heavier with crystal fractionation. The δ34S values of sulfides increase in the order pyrrhotite < pentlandite < chalcopyrite < pyrite, similar to the fractionation sequence of sulfide melts, suggesting that externally derived S was added to the magma and contributed to its sulfide saturation. The Co contents of chalcopyrite and pyrite vary positively with δ56Fe values, and negatively with δ34S values, indicating that the addition of externally derived S and resulting sulfide segregation were critical to Co enrichment.

Footwall refrigeration versus footwall hydration: Reassessing steep thermal gradients below detachment faults with in situ SIMS oxygen isotope analysis

The extensional detachment systems of metamorphic core complexes (MCC) have the potential to facilitate significant fluid movement between Earth's surface and the warm, ductile middle crust. One long-standing and influential detachment fault-fluid interaction model called the “footwall refrigeration hypothesis” (Morrison and Anderson, 1998) postulates that cool meteoric fluids circulating downward along a detachment can facilitate large-scale heat loss at depth before rocks are exhumed by faulting. Stable isotopes of oxygen and hydrogen have long been recognized as potentially useful tracers of surface-to-depth fluid flow in core complexes; however, typical sampling methods and the competing effects between temperature and fluid composition have made oxygen isotope signatures of meteoric fluid infiltration difficult to detect and/or interpret in the rock record.Here, we use in situ δ18O measurements by secondary ion mass spectrometry (SIMS) to address the rock record of meteoric fluid interactions and temperature variation within the Whipple Mountains MCC footwall beneath the Whipple detachment fault (WDF). The micro-scale sampling of SIMS (10 µm diameter x 1–2 µm deep pits) allows investigation of isotope variability as a function of mineral geochemistry and microstructure and enables more accurate interpretation of the causes of isotope variability. In the Whipple footwall mylonites, quartz and epidote show grain-to-grain oxygen-isotope variability within samples and as a function of distance from the main detachment. Approaching the WDF, both quartz and epidote show increasing spread toward low δ18O values. The lowest SIMS-measured δ18O epidote values require exchange with a low δ18O, meteoric fluid at high temperature. However, SIMS data also reveal that meteoric fluid-rock interactions were spatially heterogeneous at the scale of individual grains, resulting in local preservation of metamorphic quartz-epidote oxygen isotope equilibrium unaffected by infiltrating meteoric fluid. Within preserved metamorphic domains at all investigated structural levels of the WDF footwall, quartz and epidote δ18O values are tightly clustered and yield similar fractionations (∆18Oqz-ep). For samples from the longest footwall traverse, these ∆18Oqz-ep values are 4.0 ± 0.4‰, consistent with δ18O equilibrium at 521+43/-37 °C. We conclude that there is no evidence of a large paleo-thermal gradient associated with the Whipple Detachment Fault (i.e., no evidence for footwall refrigeration).

Occurrence and enrichment of cobalt and nickel in the Yindongshan ultramafic–mafic intrusion-hosted iron deposit, western Hubei Province, China

The Yindongshan iron deposit in western Hubei Province of China is hosted within Ordovician ultramafic–mafic intrusions. Recent field geological surveys have detected cobalt (Co) and nickel (Ni) enrichment within the Yindongshan clinopyroxenite, suggesting good potential for subeconomic Co-Ni mineralization. This study investigated the occurrence modes and enrichment processes of Co and Ni in the Yindongshan deposit through field geology and in situ analysis of the rock texture, geochronology, and geochemistry of sulfides, Fe-Ti oxides, and silicate minerals. The Yindongshan clinopyroxenites were emplaced at 440.2 ± 7.2 Ma via titanite LA-ICP-MS U-Pb dating, and underwent extensive post-magmatic metamorphism at 401.2 ± 8.6 Ma via apatite U-Pb dating. This metamorphism led to the widespread formation of amphibole via the replacement of clinopyroxene. Subsequently, hydrothermal epidote-albite veins, calcite-pyrite veins, and later actinolite veins developed. Pyrites from both clinopyroxenites and calcite veins show limited δ34S variations from −5.4 ‰ to −1.2 ‰, suggesting a magmatic sulfur source. Late-vein actinolites display geochemical characteristics distinct from those of amphiboles, indicating possible involvement of external fluids. LA–ICP–MS trace element results reveal a general increase in Co and Ni contents from silicate minerals and Fe-Ti oxides to pyrite and from earlier-crystallized coarse-grained clinopyroxenite to later medium- to fine-grained clinopyroxenite. The highest Co and Ni contents observed in pyrite from coarse-grained clinopyroxenite suggest their preferential incorporation into early sulfide minerals and then progressively depleted through magmatic evolution such as fractional crystallization. The positive correlation between Co and Ni with Fe in pyrite, along with the consistent parallel time-resolved LA–ICP–MS depth profiles among different mineral phases, indicates that isomorphic substitution occurred in pyrite. In silicate minerals, the Co and Ni contents increase from pyroxene, amphibole, to actinolite, with almost no Co or Ni present in epidote. The elevated Co and Ni contents in metamorphic amphiboles are attributed to their remobilization from magmatic pyrite to newly formed amphiboles. During the late hydrothermal phase, external fluids might transport additional Co and Ni, contributing to higher concentrations in late actinolite veins. In general, Co and Ni in the Yindongshan iron deposit are primarily hosted in sulfide minerals and can be remobilized during regional metamorphism and metasomatism. Thus, magmatic iron or iron–titanium oxide deposits hosted by mafic–ultramafic intrusions with sulfide mineralization may serve as promising targets for further Co-Ni exploration.

Linking beryllium mineralization to fluid-rock reactions: A case study of the Madumeng quartz vein-type beryllium mineralization in the Southern Great Xing'an Range, Northeast China

The Southern Great Xing'an Range (SGXR) in Northeast China is a significant polymetallic mineralization belt. Although several beryllium (Be) deposits have been reported in the SGXR, the timing and mechanisms of Be mineralization are poorly understood. To determine the mechanisms of newly-discovered Be mineralization in the Madumeng area, we carried out monazite–zircon–apatite U–Pb dating, whole-rock and mineral geochemical, and monazite Nd isotopic analyses of the beryl-bearing quartz veins and host Late Permian–Early Triassic granite. Monazite from the beryl-bearing quartz veins yielded U–Pb ages of 138–137 Ma, and the host granite yielded zircon and apatite U–Pb ages of 251 ± 1 and 256 ± 27 Ma, which indicate that the Madumeng Be mineralization formed later than the host granite. Monazite in the beryl-bearing veins has similar εNd(t) values (−1.31 to +4.27) to those of Early Cretaceous highly fractionated granite related to Be mineralization in the SGXR, which suggests the ore-forming material was derived from exsolved fluids associated with Early Cretaceous, deep-seated, highly fractionated granites. Fluid-rock reactions had a key role in generating the Madumeng Be mineralization, and the intensity of these reactions was recorded by the whole-rock and mineral geochemistry. The alteration during fluid-rock reactions increased the pH and Ca contents of the fluids. Mica and beryl record the release of Ca and Fe from the granite into the fluid. The released Ca2+ ions combined with F− ions in the fluid, leading to instability of Be–F complexes and subsequent precipitation of beryl. Our findings indicate that the Early Cretaceous was an important period of Be mineralization in the SGXR and highlight the contribution of fluid-rock reactions to Be precipitation in quartz vein-type Be mineralization.

Formation of Large to Giant Porphyry Mo Deposits: Constraints From Whole-Rock and In Situ Mineral Geochemistry of Causative Magmatic Rocks in the Tongbai-Hong’an-Dabie Orogens, Central China

Formation of Large to Giant Porphyry Mo Deposits: Constraints From Whole-Rock and In Situ Mineral Geochemistry of Causative Magmatic Rocks in the Tongbai-Hong’an-Dabie Orogens, Central China

Petrogenetic evolution of the Jalapa del Marqués pluton: Miocene arc magmatism in southern Mexico and its tectonic implications

Arc-related plutonic rocks in southern Mexico occur along the Pacific coast in the Sierra Madre del Sur (SMS) igneous province. These rocks record the migration of the Caribbean–North America–Farallon/Cocos junction towards the east between the Late Cretaceous and Miocene. However, little is known about the petrogenesis of igneous rocks that were emplaced during the latest expressions of magmatism in the SMS (i.e., early–middle Miocene). Based on fieldwork, petrography, whole-rock and mineral geochemistry, thermobarometric calculations, and zircon UPb dating, we document the petrogenetic evolution of the Jalapa del Marqués pluton and adjoining intrusions, which are the youngest so far dated in the SMS and are located ∼150 km inland from the present-day trench. This subduction-related magmatic complex consists of granites, granodiorites, diorites, dacite porphyries, and intermediate-to-felsic dikes, whose geochemical features suggest early evolutionary processes driven by fractionation of amphibole ± clinopyroxene (moderate–high pressures) or plagioclase (low pressures). Pulses of evolved magmas were episodically injected into upper-crustal reservoirs (7–14 km) over ∼9 Myr, starting at 22.14 ± 0.65 Ma (2σ)—earlier than previously thought (∼15.7 Ma)—and producing subsequent pulses at 19.45 ± 0.36 Ma, from 16.36 ± 0.37 to 15.8 ± 0.34 Ma, and from 13.9 ± 0.5 to 13.3 ± 0.2 Ma. These ages correlate with the onset and early stages of volcanic centers in the Trans-Mexican Volcanic Belt (TMVB), some of which were located up to 500 km landward from the present-day trench. The large difference in the distance-to-trench between coeval magmatism in the Jalapa del Marqués pluton and the TMVB, indicates a variation in the subduction angle between two segments of the Farallon/Cocos Plate that were likely separated by a slab-tear. The eastward migration of this slab-tear (along with the triple junction) terminated the magmatic activity in the SMS by switching the locus of magmatism to the TMVB. This probably occurred shortly after the studied magmatic complex was assembled.

Genesis of high-Al chromitites from Xiaosuihe peridotite (Central Jilin Province, NE China): Implication for initial subduction of the Paleo-Asian ocean

This study presents whole-rock major- and trace-element data of serpentinites and mineral geochemistry of chromite/spinel from both serpentinites and associated podiform chromitites from the Xiaosuihe region in central Jilin Province, NE China, aimed to elucidate the genesis of serpentinites and podiform chromitites. The serpentinites exhibit low Al2O3/SiO2 ratios (0.01–0.02) and high Mg# (0.90–0.91), indicating their derivation from the fore-arc mantle wedge and protolith as harzburgite. Chromitite ores with semi-massive to disseminated textures occur as small pods. The chromite/spinel (Chr) present in both the podiform chromitite and serpentinite can be categorized into four distinct microstructural groups: (1) partially altered chromite, characterized by high-Al primary cores (Cr# = 0.44–0.49), surrounded by high-Cr porous rims; (2) porous chromite, featuring abundant pores enriched in Cr and Fe and depleted in Mg and Al, filled with chlorite; (3) zoned chromite consisting of high-Al cores surrounded by non-porous rims of Cr-magnetite (Cr-mag); and (4) homogeneous chromite, which is non-porous ferritchromite (Fe-Chr). The high-Al primary cores of the partly altered chromite are depleted in Cr but enriched in Mg, exhibiting MORB-like tholeiitic affinities. In contrast, the altered Chr displays low Mg# [Mg/(Mg + Fe2+)] along with elevated Cr# [Cr/(Cr + Al)] and Fe# [Fe3+/(Cr + Al + Fe3+)] values. Based on the above results, the high-Al cores of chromite within the chromitite originally formed through melt/fluid-rock interaction within the forearc mantle wedge. During the exhumation and post-magmatic processes, the reaction between high-Al Chr and olivine resulted in chlorite formation alongside secondary Chr enriched in Fe2+ and Cr content. Subsequently, the infiltration of hydrous fluid led to the development of Fe3+-rich Chr or Cr-mag along grain boundaries or fractures within the original chromite during the retrograde process. The Xiaosuihe serpentinized harzburgites, along with associated chromitites, represent the composition of peridotite in the forearc mantle wedge that could have formed during the initial subduction of an oceanic island arc abutting the northern North China Craton during the Cambrian. Subsequently, these rocks underwent retrograde metamorphism from amphibolite (eclogite) to greenschist facies during their exhumation.

Occurrence and geochemistry of altered radioactive accessory minerals as sources of radionuclide in Mesozoic granite aquifers (Korea)

Accessory minerals in granitic rocks are unlikely significant radionuclide contributions to groundwater due to their remarkable durability. However, accessory minerals incorporating U and Th may suffer structural damages due to the radioactivity and become highly susceptible to alteration. This study investigates geochemistry coupled with textural analysis of the U–Th bearing accessory minerals using a field emission scanning electron microscope and an electron probe micro-analyzer. Altered zircons with numerous open structures related to the radioactive decay show higher contents of U and Th and low analytical totals. Some thorites show high contents of U and non-formula elements due to the hydrothermal alteration in the metamicted thorite. The cerianite including U occurs as micro-veinlet in fracture with trace of Fe and Mn oxides, which indicates secondary phase formation from the decomposed accessory minerals in an oxidizing environment. Some accessory minerals with the high content of U and Th have been found in Mesozoic granite terrain in South Korea, where high concentration levels of radionuclide in groundwater were also reported. The leaching of U may be more likely when the accessory minerals are highly metamicted or altered as found in our samples. The altered zircon and thorite of the study area could be major carriers of radioelement in Mesozoic granitic aquifers where the occurrence of soluble U-minerals has not been reported.

Mineral Geochemistry of Apatite in the Jiama Porphyry‐Skarn Deposit, Tibet and its Geological Significance

AbstractThe Jiama deposit, a significant porphyry‐skarn‐type copper polymetallic deposit located within the Gangdese metallogenic belt in Tibet, China, exemplifies a typical porphyry metallogenic system. However, the mineral chemistry of its accessory minerals remains under‐examined, posing challenges for resource assessment and ore prospecting. Utilizing electron microprobe analysis and LA‐ICP‐MS analysis, this study investigated the geochemical characteristics of apatite in ore‐bearing granite and monzogranite porphyries, as well as granodiorite, quartz diorite, and dark diorite porphyries in the deposit. It also delved into the diagenetic and metallogenic information from these geochemical signatures. Key findings include: (1) The SiO2 content, rare earth element (REE) contents, and REE partition coefficients of apatite indicate that the dark diorite porphyry possibly does not share a cogenetic magma source with the other four types of porphyries; (2) the volatile F and Cl contents in apatite, along with their ratio, indicate the Jiama deposit, formed in a collisional setting, demonstrates lower Cl/F ratios in apatite than the same type of deposits formed in a subduction environment; (3) compared to non‐ore‐bearing rock bodies in other deposits formed in a collisional setting, apatite in the Jiama deposit exhibits lower Ce and Ga contents. This might indicate that rock bodies in the Jiama deposit have higher oxygen fugacity. Nevertheless, the marginal variation in oxygen fugacity between ore‐bearing and non‐ore‐bearing rock bodies within the deposit suggests oxygen fugacity may not serve as the decisive factor in the ore‐hosting potential of rock bodies in the Jiama deposit.

Diagenetic Impact on High-Pressure High-Temperature Reservoirs in Deep-Water Submarine Fan Sandstone of Qiongdongnan Basin, South China Sea

The diagenetic evolution of sandstone is very complicated under the conditions of high temperatures and pressures in deep-water, deep-buried regimes, which have great influence on reservoir quality. This study investigates the typical reservoir target of Neogene deep-water, submarine-fan sandstones under high-temperature, high-pressure regimes in the Qiongdongnan Basin, South China Sea. Utilizing a thin section, scanning electron microscope (SEM), mineral geochemistry combined with burial history evolution, complex diagenetic events, and main controlling factors of the sandstone in the Neogene Meishan Formation were determined. The results show that the evolution of sandstone reservoirs is initially controlled by depositional framework compositions and subsequently modified by eogenetic and mesogenetic alterations during progressive burial. Eogenetic alterations mainly include the following: (1) mechanical compaction; (2) dissolution of feldspar; (3) low-Fe calcite cementation. Mesogenetic events were identified as the following: (1) dissolution of feldspar; (2) ferroan calcite and ankerite formation; (3) precipitation of quartz and clay mineral. Mechanical compaction is greatly influenced by the original depositional framework composition, and sandstone samples enriched in high contents of detrital clay matrix always experienced extensive mechanical compaction. Different phases of carbonate cement during different diagenetic regimes lead to continuous destruction on reservoir porosity. The dissolution of unstable feldspar minerals during eogenetic and mesogenetic environments leads to the development of secondary porosities and would enhance the quality of the reservoir. Overpressure formation is pervasively developed owing to early disequilibrium compaction and subsequent natural gas charging. Only well-sorted sandstones with low contents of detrital clay matrix could resist early mechanical compaction, lead to ample residual original porosities, and then undergo extensive mineral dissolution to generate sufficient secondary porosities. Subsequently, these porosities would be effectively protected by overpressure formation. Poor-sorted sandstones with high contents of detrital clay matrix would experience strong mechanical compaction and extensive destruction of original porosities. Thus, these sandstones are difficult to have significant dissolution and are unable to be effectively protected by overpressure formation. Therefore, the interplay between the original framework composition and the corresponding diagenetic pathways coupled with overpressure formation would result in strong reservoir heterogeneity for the deep-buried sandstones during progressive burial.

Subduction erosion revealed by exhumed lower arc crustal rocks in an accretionary complex, northeastern China

Abstract Subduction erosion at convergent margins is a leading mechanism for the destruction (recycling and reworking) of continental crust. But because of the lack of direct evidence, it is not straightforward to identify erosive events and their intensities in fossil subduction zones. The Heilongjiang accretionary complex in northeastern China was formed during the early Mesozoic subduction of the Paleo-Pacific Ocean. We investigated amphibolites from this accretionary complex, whose protoliths (based on whole-rock trace elements and Sr-Nd-Hf isotopes) were mafic continental arc magmatic rocks (255–249 Ma; zircon core U-Pb ages) from the upper plate. Phase equilibria modeling constrained by mineral geochemistry indicates that the amphibolites and their wall rocks were first heated to low granulite facies (750–800 °C, ~7 kbar) at 251–244 Ma (zircon rim U-Pb ages) and then cooled to ~700 °C with increasing pressure (8–9 kbar) before 213–187 Ma (titanite and apatite U-Pb ages). To explain the occurrence of the lower arc crustal lithologies in the accretionary complex and their metamorphic history, we propose that the subducting plate strongly eroded the forearc crust, allowing the plate interface to advance landward and scrape the amphibolites and wall rocks formed under the old arc, which finally were exhumed along the subduction channel and became components of the complex. The case study exemplifies direct petrological evidence of strong subduction erosion occurring in an ancient orogen, thus implying that consumption of the entire forearc crust could occur within only ~50 m.y.

Geology and Geochemistry of Lead-Zinc Mineralization in Ameri, Southeastern Nigeria

The Geology and geochemistry of Lead-Zinc Mineralization has been carried out in parts of Ameri, South eastern Nigeria. The study area was mapped and lithological units and structural features were identified and studied. A total of twenty-seven (27) samples from five (5) wells (AMR 014, AMR 036, AMR 038, AMR 048, and AMR 049) of the study area were collected, prepared and subjected to geochemical analysis for both major and trace elements using EDX3600B X-ray fluorescence spectrometer. The analytical data were statistically computed using principal component factor analysis PCFA, statical package for social science SPSS, descriptive statistics DS, correlation matrix CM and were also adopted for various geochemical plots using Excel Microsoft office, geochemical data kid GCD Kid and Suffer software for geological map digitization, to determine the geochemical characteristics of the Lead-Zinc ore, the host rock and the environment of formation. The geology of the study area is strategically part of the Lower Benue Trough of Nigeria, it is made up of shale intruded by several small to medium sized mesocratic – melanocratic, phaneritic intrusives which are alkaline in nature with a slight variation in their mineralogical and textural characteristics. Structurally, the fractured zones or veins marked along the Enyigba and Ameka lodes could also be responsible for the mineralization of the Ameri Lead-Zinc. The Lead-Zinc in Ameri is associated with other gangue minerals such as marcasite, pyrite, quartz veins, carbonate materials, chalcopyrite, siderites, sphalerites and it shows that the Lead-Zinc mineralization in the study area is hosted by shales, which are probably parts of the slightly deformed cretaceous sedimentary rocks made up of essentially Albian shales and subordinate siltstones. Values of lead within this shear zone ranges from 0.06% - 64.58%, 0.02% - 64.35%, 0.01% –0.14%, 0.03% - 0.11% for AMR 036, AMR 038, AMR 048, AMR 049 respectively, while Zn ranges in value from; 0.09% - 53.98%, 0.08% - 1.11%, 0.19% - 58.64%, 0.08% - 56.11%. The value of lead and zinc within the hanging wall are 0.06% and 0.08%, 0.03% and 0.06%, 0.04% and 0.12%, 0.04% and 0.13% for AMR 036, AMR 038, AMR 048, AMR 049 respectively. Paleo-redox condition of Low Cu/Zn ratios from 0.001-0324, 0.001 – 0.307, 0.075-0.424, 0.001-0.309 and 0.001-0.321 for AMR 014, AMR 036, AMR 038, AMR 048, AMR 049 indicate more oxidizing conditions. This is confirmed by the Ni/Co ratio of 0.00-58.50, 0.00- 43.625, 0.00- 35.333, 0.00-1.704, 0.211- 1.472 for AMR 014, AMR 036, AMR 038, AMR 048, AMR 049 respectively mostly below the ratio indicated to be oxidic with little anoxic environmental affinity. The total Alkalis versus Silica plot from the intrusaive revealed their basic to ultrabasic nature, as the bivariate plots of the analyzed samples shows positive and /or strong relationship between the trace elements in the Ameri lodes and their respective certified concentration values which is also an indicator that the elements are probably from same hydrothermal source with the Lead-Zinc of the study area.

Characterization of Arroyo Verde Epithermal Deposit: Paragenesis, Mineral Geochemistry, Geochronology and Fluid Inclusions in Lower Chon Aike Volcanism, Argentina

Characterization of Arroyo Verde Epithermal Deposit: Paragenesis, Mineral Geochemistry, Geochronology and Fluid Inclusions in Lower Chon Aike Volcanism, Argentina