High Oxygen Fugacity Research Articles

Contrasting apatite geochemistry between ore-bearing and ore-barren intrusions of the giant Kalmakyr gold-rich porphyry Cu deposit, Tien Shan, Uzbekistan

The Kalmakyr deposit in Uzbekistan is one of the world’s largest gold-rich porphyry Cu deposits, and mineralization was proposed to be closely associated with the emplacement of the latest intrusive phases, that is, granodiorite porphyry. However, it is still unclear which features of these ore-bearing intrusions are crucial for the enormous metal enrichment and how they correlate with magmatic fertility. In this study, we address these questions by comparing the petrological and in situ major and trace element geochemistry of apatite for the ore-bearing and ore-barren intrusions. Magmatic apatite from the ore-bearing granodiorite porphyry has higher Eu/Eu* (0.50–0.58), Sr/Y (1.09–1.64), and La/Yb (36.19–53.42) ratios than the ore-barren quartz porphyry (0.01–0.02, 0.02–0.03, and 2.01–3.75, respectively) and monzonite (0.20–0.11, 0.36–1.12, and 19.71–56.32, respectively). Moreover, the ore-bearing granodioritic magma has higher S (average of 111 ppm) and Cl (average of 8602 ppm) contents than the magma of quartz porphyry (S contents average of 9 ppm; Cl contents average of 2652 ppm) and monzonite (S contents average of 9 ppm; Cl contents average of 8483 ppm). These features collectively suggest that the ore-bearing granodiorite porphyry has relatively high oxygen fugacity, H2O, Cl, and S contents compared to those from the ore-barren intrusions. By comparing our data with the published dataset from porphyry Cu–Mo and Mo-only deposits in the world, we suggest that the high Cl content and low F/Cl ratio in magmatic apatite might be an important indicator to prospect for gold-rich porphyry Cu deposits.

Geochronology and skarn mineralogy of the Akesayi Fe deposit in the Western Kunlun, Xinjiang: Implications for mineralization process

The Akesayi deposit, located in the eastern part of the Tianshuihai terrane of the Western Kunlun Orogenic Belt, Xinjiang, China, is a recently discovered medium-sized magnetite deposit containing approximately 51 million tons of ore with an average grade of 41 wt%. This deposit is hosted by skarns at the contact between monzonitic granite, diorite porphyry, and medium to low-grade metamorphic clastic rocks of the Permian Huangyangling Group. The ore types include banded, disseminated, and massive ores. The metallogenic process can be divided into prograde skarn, retrograde skarn, oxide, quartz-sulfide, and carbonate stages. The metallic minerals include magnetite and pyrite, and the gangue minerals include olivine, garnet, hedenbergite, hornblende, actinolite, biotite, cummingtonite, chlorite, quartz, and calcite. The zircon U–Pb dating of biotite adamellite intrusion and schist together constrains the formation age of the host rocks in the Akesayi Fe deposit to 217–272 Ma. Rb–Sr dating of eight garnet samples yields an isochron age of 12.41 ± 0.31 Ma, which is almost identical to the 12.56 ± 0.50 Ma age obtained via Sm–Nd dating of eight garnet samples. Furthermore, zircon U–Pb dating yields ages of 12.76 ± 0.12 Ma and 12.37 ± 0.18 Ma for diorite porphyry and monzonitic granite near the Fe orebodies, respectively. The initial Sr isotopes of garnet ((87Sr/87Sr)i = 0.710901) prove that the diorite porphyrite ((87Sr/87Sr)i = 0.709283) is related to skarn mineralization. Thus, the Akesayi deposit is a skarn-type iron ore related to the middle Miocene diorite porphyry. The mineral assemblage indicates the extensive development of manganese-skarn in the Akesayi mining area. The manganese content of host rocks of the deposit is low, and the source of manganese in the skarn may mainly come from the hydrothermal fluids associated with Miocene diorite porphyry emplacement. The compositional variations between the cores and rims of single garnet grains and different stages of tephroite indicate the concentration characteristics of the hydrothermal system, particularly manganese content, which evidently changed during hydrothermal activity. The endmembers of garnet and pyroxene suggest that the ore-forming environment transformed from a relatively reduced acidic environment to an alkali-rich, high-oxygen fugacity environment. The widely developed chlorine-rich amphiboles and biotite indicate that the hydrothermal fluids were rich in chlorine and may have been related to the diorite porphyrite intrusion near the ore bodies. The iron mineralization of the Akesayi deposit is analogous to the Gangdese Miocene porphyry–skarn polymetallic mineralization, which occurred during the Miocene in a post-collisional tectonic setting. Considering the series of Miocene intrusives discovered in West Kunlun, we propose that Miocene skarn Fe mineralization events occurred in West Kunlun, and that this area has great prospecting potential.

Two-stage, U-mineralization of A-type granites from the Huangmeijian complex, eastern China

Parts of A-type granites are closely related to some critical mineral resources. The study of origin and geochemical properties of those A-type granites are of great significance in revealing the metallogenic potential. The Early Cretaceous Huangmeijian (HMJ) complex is located in the Lower Yangtze River Belt (LYRB), eastern China, which is proposed to be associated with uranium deposits. Here, we present whole-rock major and trace elements, and zircon U–Pb geochronology to reveal the formation of the two-stage, uranium mineralization of A-type granites. The high Zr + Nb + Ce + Y concentrations (598−1181 ppm) and Ga/Al ratios (2.7−4.2) suggest an A-type geochemical affinity. On the ternary discriminant diagrams, they can be further divided into A1-type. In-situ LA-ICP-MS U–Pb dating on the zircon grains from the HMJ complex yielded weighted mean ages of 129.7 ± 1.6 Ma (quartz alkali feldspar syenite), 131.3 ± 1.0 Ma (quartz alkali feldspar syenite), and 118.7 ± 0.7 Ma (alkali feldspar granite), respectively. The former two age results are consistent within error, and similar to other A-type granites in the LYRB. The latter one is newly identified, and is obviously younger than most A-type granites developed in the LYRB. Geochemical data suggest that these A-type granites are formed under high temperature and low oxygen fugacity conditions in an extensional setting. The presence of huttonite favors for the hydrothermal event and the uranium mineralization. It is important to note that, compared to the ca. 130 Ma quartz alkali feldspar syenites, the ca. 118 Ma alkali feldspar granites have obviously higher U (21.3–79.2 ppm) and Th (81.2–104 ppm) concentrations, which are also higher than those of other A-type granites developed in the LYRB. Moreover, the U concentration is even higher than some uranium mineralized granites of South China. Thus, besides the previously reported ca. 130 Ma A-type granite, the ca. 118 Ma A-type granite is of great probability to be a main source of uranium for the formation of uranium deposits in the LYRB, eastern China.

Zircon constraints on gold enrichment in a high-silica porphyry, Yixingzhai region, north of the Trans-North China Orogen

The Hewan granite porphyry is a newly discovered, highly evolved Au deposit in north China. Two types magmatic zircon are found in the porphyry. Type I is CL-dark and only occurs in the core of some zircons. Type II is CL-bright and mantles Type I zircon or occurs as individual grains. The two Types are close in age, i.e. 138.0 ± 2.2 Ma for Type I and 135.9 ± 2.1 Ma for Type II. Type I zircon is enriched in Y, U, Th, Nb, Ta, P, REE, while Type II zircon is relatively depleted in these elements, which reflects a reverse in the magma evolution. Whole-rock geochemistry and the presence of xenocrystic zircons (2522 ± 18 Ma), combined with εHf(t) (−20.2 to −22.3) and δ18O (5.3 to 6.6 ‰) for Type I zircons, suggests that the Hewan granite porphyry was mainly derived from the melting of the surrounding older, country rock gneiss. The higher εHf(t) (−16.5 to −19.4) and lower δ18O (5.0 to 6.0‰) of Type II zircon indicates that Type II zircon formed during infiltration of a later fluid. This later fluid also had a higher oxygen fugacity (Ce/Ce* Z = 248 to 3663) and a higher H2O activity. We propose that the Hewan granite porphyry originated from the shallow melting of regional gneisses due to heat from underplating mafic magmas related to a subduction event. Type I zircons, which formed during this event where later mantled or totally replaced by Type II zircon due to an influx of Cl-, S-, and Au-bearing fluids from these crystallizing underplating mafic magmas. The high F and pH in this shallow magma promoted decoupling of AuCl− in the upwelling fluids, which allowed for the deposition of elemental Au.

Trace Element Composition of Molybdenite: Deposit Type Discrimination and Limitations

Molybdenite is a common sulfide hosting many trace elements. Trace elements in molybdenite from individual deposits have been widely used to constrain the source and conditions of ore-forming fluids. However, the relationship between the trace element composition of molybdenite and deposit types has not been well investigated from a large dataset. Here, simple statistics and partial least squares–discriminant analysis (PLS-DA) were used to determine whether different types of deposits can be distinguished by trace elements in molybdenite and what factors control the variations in trace element composition based on published laser ablation ICP–MS data. Molybdenite from porphyry deposits is separated from that from quartz veins, greisen Sn–W, granite vein Mo, and granodiorite Mo deposits. The former is characterized by relatively high Re, Cu, Ag, Se, Pb, Bi, and Te contents, whereas the latter has higher Ni, Co, Sn, Sb and W contents. Molybdenite from the quartz vein Au ± W deposits (Au-dominated), and porphyry Cu–Au–Mo (moderate Au) are separated from other deposits without gold due to positive correlations with Au, Sb, Te, Pb, and Bi for the former. Assemblages of Au–Sb–Te–Pb–Bi in molybdenite are thus useful to discriminate as to whether deposits contain gold and the degree of gold mineralization. Higher oxygen fugacity is responsible for the relative enrichment of W in molybdenite from greisen Sn–W deposits, whereas lower oxygen fugacity results in the relative enrichment of Re in molybdenite from porphyry Cu ± Mo ± Au and Mo ± Cu ± Au deposits. There are some limitations to using molybdenite as an indicator mineral because of the complex occurrences of elements in molybdenite, large compositional variations within a specific deposit type, and an imbalanced dataset. To develop molybdenite as an indicator mineral tool, further work should be carried out to overcome these limitations. This study provides an attempt to classify deposit types using molybdenite trace elements and has important implications for ore genesis research and mineral exploration.

Petrogenesis and metallogenesis of the Qieganbulake carbonatite-related phosphate deposit associated with the mafic–ultramafic–carbonatite complex in the Kuluketage block, northeastern Tarim Craton

AbstractThe Qieganbulake deposit associated with a mafic–ultramafic–carbonatite complex in the Kuluketage block is not only the world’s second-largest vermiculite deposit, but also a medium-size carbonatite-related phosphate deposit. Field observations, radiometric dating results and Sr–Nd–Hf isotopes reveal that the parental magmas of the carbonatite and mafic–ultramafic rocks are cogenetic and formed synchronously at c. 810 Ma. Geochemical characteristics and Sr–Nd–Hf–S isotopes ((87Sr/86Sr)i = 0.70581–0.70710; ϵNd(t) = −0.20 to −11.80; ϵHf(t) = −7.5 to −10.3; δ34S = +0.7 ‰ to +3.0 ‰ (some sulfides with high δ34S values (+3.2 to +6.6) were formed by late hydrothermal sulfur)), in combination with mineral compositions and previous research, strongly indicate that the Qieganbulake mafic–ultramafic–carbonatite complex formed via extensive crystal fractionation/cumulation and liquid immiscibility of a carbonated tholeiitic magma, possibly derived from partial melting of an enriched subcontinental lithospheric mantle previously modified by slab-released fluids and sediment input in a continental rift setting. The coupled enriched Sr–Nd isotopic signatures, in combination with previous research, suggest that the enriched subcontinental lithospheric mantle could have been metasomatized by asthenospheric mantle melts to different degrees. The Qieganbulake carbonatite-related phosphate ores were the products of normal fractional crystallization/cumulation of P–Fe3+ complex enriched carbonatite magma in high oxygen fugacity conditions, which was generated by liquid immiscibility of CO2–Fe–Ti–P-rich residual magma undergoing high differentiation.

Petrogenesis and geochronology of the bronze fox porphyry Cu-Au deposit: Implications for the geodynamic evolution of the Gurvansaykhan Island arc, southern Mongolia

ABSTRACT A diversity of Devonian-Carboniferous volcanic arcs and granitoid intrusions are exposed in the Gurvansaykhan arc terrane of southern Mongolia. Several giant porphyry Cu-Au-Mo deposits are associated with intrusions within these arcs. The Bronze Fox deposit located in the central part of the Gurvansaykhan arc terrane is an example of a potentially economic deposit with affinity of adakite-like granitoid porphyry (i.e. 428 Mt grading 0.26% to 0.30% Cu for up to 2,437 Mlb of copper and 0.84 Moz gold). The genesis and magmatic evolution of the causative rocks of the Bronze Fox porphyry Cu-Au hosting rocks are poorly understood, and different models are still under debate. In the current study, we present new field observations and petrographic, geochemical, and geochronological data to describe the magmatic evolution and geodynamic settings. In addition, the mineral chemical data are reported from some selected rock-forming minerals to identify crystallization conditions of the studied rock suites by employing geothermobarometric methods. Zircon chronological data reveal the emplaced age at 331 ± 3.4 Ma for the volcanic lava, followed by mineralized granodiorite and monzodiorite with intruded ages of 326.5 ± 3.4 Ma and 326.5 ± 2.7 Ma, respectively. The studied intrusive and extrusive rocks are high-K-alkaline and metaluminous, characterized by high Mg#. They are enriched in large ion lithophile elements (Sr and Ba) and light rare earth elements (LREEs) and depleted in high field strength elements (Nb, Ta, and Ti) and heavy rare earth elements (HREEs). The highly mineralized granodiorite intrusion yields zircon crystallization temperatures ranging from 631.8 to 779.4°C, and the monzodiorite intrusion, which contains relatively low-grade mineralization, has a wider range (599.0 to 803.4°C). The formation pressures of the former range from 0.5 to 0.2 kbar, which is equivalent to a depth of 1.38 km based on amphibole geochemical calculations. The results of mineral chemistry indicate that the unmineralized diorite unit was formed under medium pressure (~50 MPa) and high temperature (~750°C) at depths of 6.8 to 7.5 km. Similarities in geochemistry and petrographic features suggest that the igneous rocks probably originated from a similar magma source (i.e. from the melting of ancient oceanic crust and sediments) but experienced different degrees of partial melting or mixing with lower juvenile crust melts. The estimated fO2 values obtained by amphibole chemistry in the granodiorite and quartz diorite of the Bronze Fox copper-gold mineralization range from −13.0 to −11.8 and −13.2 to −10.8, respectively, confirming that these igneous rocks probably crystallized under relatively oxidized conditions above the nickel-nickel oxide (NNO) buffer. Such results yield an overall range between NNO +2.6 and NNO +1.4, which are characterized by high oxygen fugacities and high Ce4+/Ce3+ ratios that reflect oxidizing magma, thus indicating quite promising potential for porphyry Cu-Au mineralization in the region. Based on the findings of this work, we suggest a new tectonic model of arc magmatism that is a response to the subduction of the Paleo-Asian Ocean in the early Carboniferous period.

Neoproterozoic lithospheric extension related to break-up of the Rodinia supercontinent: Constraints from a newly-identified granite porphyry in southeastern Yunnan, China

Although the southeastern Yunnan region preserves an important record of the evolution of the South China block (SCB), its Precambrian geology is not well understood due to poor exposure. The newly-discovered Laojunshan granite porphyry (LNGP) is the only Precambrian unmetamorphosed granitoid unit exposed in the southwestern SCB. Here, we present integrated studies of the LNGP including whole-rock major and trace-element geochemistry and Nd isotopes, together with zircon U-Pb chronology and Lu-Hf isotopes by LA-ICP-MS. Zircon U-Pb dating results for two granite porphyry dykes yielded ages of 811.2 ± 7.0 Ma and 830.3 ± 5.2 Ma. The studied samples have high total alkalis (6.46–9.68 wt%), SiO2 (69.44–75.6 wt%), P2O5 (0.11–0.33 wt%) and Al2O3 (10.44–14.39 wt%) but low CaO (0.09–1.29 wt%) contents; these characteristics together with high Al saturation indices (1.1–1.7), indicate the LNGP is of strongly peraluminous S-type granite affinity. The LNGP is characterized by Rb-Th-U-K enrichments and Ba-Sr-Nb-Ti-Ta depletions, and right-sloping REE patterns with obvious negative Eu anomalies (Eu/Eu* = 0.2–0.4). Major and trace elements show good correlations with SiO2. Diagrams of Th vs Th/Nd, La vs La/Sm and Zr vs Zr/Sm indicate that fractional crystallization was an important process in the genesis of the LNGP. The Ba vs Eu, Sr vs Eu and Ba vs Sr correlations and high Rb/Sr (8.2–74) and Ca/Sr (12–614) ratios demonstrate that magmatic evolution involved extensive fractionation of plagioclase and K-feldspar. The initial zircon Hf isotopic composition of the porphyry varies widely (εHf(t) = −10.1 to +6.7), with corresponding two-stage Hf model ages of 1291–2331 Ma; whereas whole-rock Nd isotopes are relatively uniform (εNd(t) = −5.8 to −4.6), with two-stage Nd model ages of 1886–2130 Ma. The variable zircon Hf isotopic compositions suggest a heterogenous source for the LNGP, containing juvenile components (with higher εHf(t) values) and ancient reworked crustal materials (with lower εHf(t) values). Geochemical data, including Rb/Sr, Rb/Ba, Al2O3/(MgO + Fe2O3T), CaO/(MgO + Fe2O3T) and (Na2O + K2O)/(Fe2O3T + MgO + TiO2) ratios and (Na2O + K2O + Fe2O3T + MgO + TiO2) content suggests a meta-pelite/greywacke source. Early arc-continent or continent–continent collision may produce mixtures of juvenile sediments formed by erosion of with ancient crustal materials that were strongly folded and deeply buried in the studied area. The LNGP has medium to high magmatic temperatures (761–875 °C) and low oxygen fugacity (ΔFMQ −5.4 to ΔFMQ −2.8). The LNGP was emplaced at middle-upper crustal levels (pressure < 5kbar) in an extensional setting analogous to granitoid associated with the Neoproterozoic age rift-related Nanhua and Kangdian magmatic belts that bound the periphery of the Yangtze block. These belts are interpreted to be the result of the break-up of the Rodinia supercontinent during the period 850 to 700 Ma. We similarly interpret the emplacement of the LNGP, which occurred within an extensional setting, to be a response to the break-up of the Rodinia supercontinent.

Serpentinization and its implications for ultramafic-hosted sulfide mineralization: A case study at the Tianzuo hydrothermal field, 63.5°E, Southwest Indian Ridge

Reaction of ultramafic rocks with seawater and subsequent serpentinization has been considered one of the most important factors controlling the formation of ultramafic-hosted seafloor massive sulfide (UM-SMS) deposits. However, the mineralization processes responsible for these deposits remain poorly understood, in particular because they are less abundant as compared with their basaltic counterparts. In this work, serpentinites with different alteration grades collected at the Tianzuo hydrothermal field (THF), Southwest Indian Ridge, were studied. Mineralogical and chemical analyses were performed in the secondary opaque minerals resulting from serpentinization to understand the role of this process during the formation of UM-SMS deposits. Our results show that these opaque minerals mainly consist of magnetite, hematite, pentlandite, and minor pyrite, suggestive of high but varying oxygen and sulfur fugacities. The hematite is characterized by an enrichment in Mg, Si, Ni, and Co as compared with magnetite. Pentlandite associated with hematite has elevated and consistent Ni contents as compared with that associated with magnetite. These results indicate that breakdown and decomposition of primary silicate and sulfide minerals during serpentinization has controlled the sources of ore-forming materials. Concentrations of Te are variable and show a positive correlation with Ni in pentlandite associated with magnetite or hematite, suggesting that gabbroic intrusions provided additional material to the hydrothermal system. Oxidation and sulfidation conditions are ideal for the formation of trisulfur ion S3− in THF, which can significantly improve the capability of hydrothermal fluids for leaching ore-forming metals from the wall rocks, promoting the formation of THF. In addition of reduced systems, hydrothermal fluids with high oxygen and sulfur fugacities triggered by extensive seawater infiltration can most likely also develop in ultramafic-hosted systems. These results suggest that the areas with well-developed fractures are promising candidates for further exploration of UM-SMS deposits along mid-oceanic ridges.

Age and compositions of garnet in a magnesian skarn Au-Cu deposit, Tibet, implications for ore-fluid evolution

Compared to calcareous skarn Au-Cu deposits, magnesian skarn (Mg-skarn) Au-Cu deposits are scarce; hence the early evolution of the ore-fluids to late mineralization for the kinds of deposits has been inadequately investigated. Located at the southern margin of the Bangong-Nujiang metallogenic belt, the Galale Au-Cu deposit contains 32.59 tonnes of gold (average grade 2.04 g/t) and 105,600 tonnes of copper (average grade 0.66 %). The orebodies are hosted in an Mg-skarn with associated minerals, including olivine, pyroxene, garnet, and serpentine, which developed in the contact zone between the granodiorite and dolomite of the Jiega Formation. However, the genetic relationship between the Mg-skarn, granodioritic magma, and Au-Cu mineralization remains unclear. The contribution of early stage ore-forming fluids to late Au-Cu mineralization is still vague. In this study, we present the major and trace element compositions, and U–Pb isotope data for garnets obtained from the Galale deposit. We used the data to define the timing, nature, and evolution of early ore-forming fluid and described the genesis of the deposit. The color, at macro- and micro-scales, and chemical composition of the garnets can be used to divide them into two categories, namely early Al-rich Grt-I type garnets, and late stage Fe-rich Grt-II type garnets. In practice, Grt-I (And29.5∼56.1Gro41.3∼68.0Pra1.6∼2.8) and Grt-II (And96.7∼99.9Gro0∼2.7Pra0.1∼0.7) are grossular-andradite solid solution system garnets. Based on the chondrite-normalized REE patterns, Grt-I can be further divided into two sub-classes: Grt-I-1 domain in the core, enriched in HREEs and U, and Grt-I-2 material in the rim, relatively depleted in HREEs. Grt-II is enriched in LREEs and depleted in HREEs. Eu anomalies are slightly negative for the Grt-I-1 domain, weakly positive for the Grt-I-2 domain, and strongly negative for the Grt-II type garnets. The variations in texture and composition in garnets indicated that the formation of Grt-I garnets occurred during diffusive metasomatism in a relatively closed system, in a moderately oxidized ore-forming fluid setting. The formation of Grt-II occurred in a strongly oxidized setting during advective metasomatism in an open system. The enrichment of REE and U in Grt-I garnets was mainly controlled by a “menzerite” type substitution mechanism, partially explaining the strong positive correlation between Mg and REE concentrations. In the Grt-II type garnets, enrichment may also have been co-controlled by coupling substitution and adsorption. In situ U–Pb dating of garnet shows that Grt-I-1 and Grt-I-2 material has isotopic ages of 92 ± 2 Ma (2σ, MSWD = 0.85) and 91 ± 2 Ma (2σ, MSWD = 0.96), respectively. The results were consistent with the previous ages obtained from the granodiorite and Molybdenite using Re–Os isotopic dating within error. This indicates that magma, skarn alteration, and mineralization were spatially and temporally related. In addition, it indicates that the Galale deposit is a typical Mg-skarn Au-Cu deposit. In the earliest stages of deposit development, ore-forming fluids with a high oxygen fugacity (fO2) have inherited their characteristics from the magma. The crystallization of many magnetites during the oxide stage has decreased oxygen fugacity in the metallogenetic system. This has resulted in a relatively low fO2 fluid for Au-Cu precipitation. The study demonstrates that the ore-fluid fO2 plays a vital role in metal migration, hence Au-Cu mineralization in Mg-skarn deposits.

Source Lithology and Magmatic Processes Recorded in the Mineral of Basalts from the Parece Vela Basin

AbstractSince the Early Cenozoic, the Philippine Sea Plate (PSP) has undergone a complex tectonic evolution. During this period the Parece Vela Basin (PVB) was formed by seafloor spreading in the back‐arc region of the proto‐Izu‐Bonin‐Mariana (IBM) arc. However, until now, studies of the geological, geophysical, and tectonic evolution of the PVB have been rare. In this study, we obtained in situ trace element and major element compositions of minerals in basalts collected from two sites in the southern part of the PVB. The results reveal that the basalts from site CJ09‐63 were likely formed via ∼10% partial melting of spinel‐garnet lherzolite, while the basalts from site CJ09‐64 were likely formed via 15%–25% partial melting of garnet lherzolite. The order of mineral crystallization for the basalts from site CJ09‐64 was olivine, spinel, clinopyroxene, and plagioclase, while the plagioclase in the basalts from site CJ09‐63 crystallized earlier than the clinopyroxene. Using a plagioclase‐liquid hygrometer and an olivine‐liquid oxybarometer, we determined that the basalts in this study have high H2O contents and oxygen fugacities, suggesting that the magma source of the Parece Vela basalts was affected by subduction components, which is consistent with the trace element composition of whole rock.

Petrogenesis and Metallogenic Evolution of Leucogranites from the Paleoproterozoic Malanjkhand Granitoids, Central India

Abstract The Birsa and Devgaon leucogranites represent contemporaneous episodes of highly fractionated felsic magmatism associated with the Paleoproterozoic Malanjkhand granitoids in the Bastar craton, Central India. Major element oxides geochemistry reveals that two leucogranites are strictly granite in composition and both show calc-alkaline affinity. Geochemical discrimination diagrams inferred that these leucogranites shows affinity towards I-type magma with metaluminous characters. Geochemical classification inferred that the Birsa leucogranite preferred to be magnesian whereas Devgaon leucogranite designated to be ferroan type. Geothermobarometry estimation suggested that 1.2-4.5 kbar pressure and 750°-830°C temperature conditions at the shallow depth of the continental crust is responsible for the emplacement of leucogranites. Crystallization evolution of feldspar in the leucogranite provided evidences of late stage felsic magmatism in the Malanjkhand pluton. Molybdenum enrichment in the leucogranite possibly due to crystal fractionation under high oxygen fugacity conditions inherited from the magma chamber in the continental crust. Anomalous high concentration of Mo in the Devgaon leucogranite is contributed from episodic hydrothermal system with poor supply of sulphur. Occurrences of molybdenite in the Devgaon leucogranite provides high exploration potential to investigates granite molybdenite system in the Bastar craton.

Titanite geochemistry and its indicators for Cu-mineralized magmas: Insight from three dioritic intrusions in the Tongling area of the Lower Yangtze River metallogenic belt

Titanite has been regarded as a potential petrogenetic and metallogenic indicator owing to its stability and enrichment of trace elements. To verify the availability of geochemical titanite proxies in the Cu-mineralized magma system and to reveal magmatic constraints on Cu mineralization related to magmatic hydrothermal fluid, in situ major and trace element abundances and Nd isotopes of igneous titanite were determined for three Mesozoic diorite intrusions in the Tongling ore district of eastern China. The investigated intrusions were the Tongguanshan, Fenghuangshan, and Hucun intrusions, all of which host porphyry-skarn Cu deposits. Our study shows that the titanite δEu value and Fe/Al ratio, rather than the δCe and Ga content, are more effective indicators of the magma oxidation state in all three intrusions. Based on the titanite δEu value and Fe/Al ratio, the causative magma of the Fenghuangshan intrusion (titanite δEu = 0.50 ± 0.08; Fe/Al = 0.21 ± 0.07) was identified as being less oxidized than those of the Tongguanshan (titanite δEu = 0.64 ± 0.09; Fe/Al = 0.93 ± 0.15) and Hucun (titanite δEu = 0.80 ± 0.03; Fe/Al = 0.91 ± 0.04) intrusions. This result was consistent with the zircon Ce4+/Ce3+ ratio. Moreover, owing to the limited effect of fluid exsolution and fractional crystallization on the F content of the investigated titanite, the higher titanite F content of the Fenghuangshan intrusion (titanite F = 0.40 ± 0.09 wt%) implies that the parental magma of this intrusion is more F-enriched than those of the Hucun (titanite F = 0.17 ± 0.09 wt%) and Tongguanshan (titanite F = 0.10 ± 0.07 wt%) intrusions; however, titanites from all three Cu-mineralized intrusions had similar or lower F content than those from intrusions without Cu mineralization. The above findings indicate that magmas with high oxygen fugacity have relatively high potential for porphyry-skarn Cu mineralization, while the high enrichment of F is not necessary for Cu mineralization. Additionally, we found that titanite εNd(t) values can inherit whole-rock εNd(t) values and thus can be used to investigate petrogenesis. This study confirms that titanite geochemistry is an efficient petrogenetic and metallogenic indicator for Cu-mineralized magma systems when the prerequisites are met.

Metallogenesis of Porphyry Copper Deposit Indicated by In Situ Zircon U-Pb-Hf-O and Apatite Sr Isotopes

The origin of the Dexing porphyry Cu deposit is hotly debated. Zircon and apatite are important accessory minerals that record key information of mineralization processes. SHRIMP zircon U-Pb analyses of granodiorite porphyries yield ages of 168.9 ± 1.2 Ma, 168.0 ± 1.0 Ma, and 172.8 ± 1.3 Ma, whereas zircons in the volcanic rocks of the Shuangqiaoshan Group have Neoproterozoic ages of 830 ± 7 Ma, 829 ± 8 Ma, and 899 ± 12 Ma. The porphyry displays zircon in situ δ18O of mantle values (5.5 ± 0.2‰), low apatite 87Sr/86Sr ratios (0.7058 ± 0.0005), and high εHf values (5.1 ± 1.5), which are consistent with mantle-derived magmatic rocks. Apatite from the porphyries has relatively high total rare earth elements (REEs) and negative Eu anomalies, with relatively high Cl and As contents. These features are distinctly different from apatite in the Shuangqiaoshan Group, which shows lower total REE, Cl, and As contents but higher F content and positive Eu anomalies. Zircon in porphyries yields a relative high oxygen fugacity of ∆FMQ + 1.5 based on zircon Ce4+/Ce3+. Apatite in porphyries also shows high oxygen fugacity based on its SO3 and Mn compositions, reaching ∆FMQ + 2, which is different from that of the lower continental crust in general, but similar to subduction-related magmas. In contrast, the oxygen fugacity of the Shuangqiaoshan Group is much lower, suggesting a different origin for its wall rock. Therefore, the Dexing porphyries were not derived from the lower crust but derived from partial melting of the subducting Paleo-Pacific plate.

Reconstruction of smelting conditions during 16th‐ to 18th‐century copper ore processing in the Kielce region (Old Polish Industrial District) based on slags from Miedziana Góra, Poland

AbstractThis study presents the first reconstruction of the smelting conditions in 16th‐ to 18th‐century smelters from Miedziana Góra (Holy Cross Mountains, Poland). Based on geochemical (inductively coupled plasma mass spectrometry/emission spectrometry, X‐ray fluorescence) and mineralogical analysis (X‐ray diffractometry, scanning electron microscopy, electron probe micro‐analysis) of historical slags, their chemical/phase composition and the basic smelting parameters (temperature, melt viscosity, and oxygen fugacity) were determined. Due to the differences in chemical and phase composition, slags from different smelting stages have been distinguished: hypocrystalline slags (MG6) from speiss/matte production and glassy (MG1–MG5) from matte conversion. In glassy slags, pyroxenes, quartz/cristobalite grains, and aggregates composed of metallic Cu and PbO are dispersed in the glass. Hypocrystalline slags are composed of wollastonites, anorthites, and metallic Cu. The temperature range at which the slags were formed was from ~1100°C (solidus temperature) to 1150–1200°C (liquidus temperature). The silicate melt's viscosity was from log η = 1.19 to 4.42 Pa s (at 1100–1200°C). The higher viscosity of MG1–MG5 slags indicates that, unlike MG6 slags, they were not formed during gravity separation. Information about the phase composition made it possible to determine the oxygen fugacity in the range of log fO2 = −4 to −12 atm. High oxygen fugacity indicates the oxidizing nature of the smelting process.

Early Jurassic high-temperature granites along eastern Bangong-Nujiang suture in Tibet and its geodynamic implications

The varying geochemical compositions of granites are generally considered as the proxy record of different geodynamic processes. The granites collected in the Kaqiong microblock along the eastern Bangong-Nujiang suture in Tibet show A-type granite affinity, but do not strictly follow the definition of A-type granite in some aspects. Zircon U Pb dating shows that the Kaqiong granite pluton was emplaced in the Early Jurassic (186–176 Ma), bracketing in the timing of the lithospheric and asthenospheric mantle-derived magmatism (197–175 Ma) in the Kaqiong microblock. These granites are metaluminous to peraluminous and high-K calc-alkaline to shoshonitic rocks. They have high contents of alkalis (K 2 O + Na 2 O), high field strength elements (e.g., Zr, Nb), and rare earth elements (except Eu), with high magmatic temperatures; these features are typical of A-type granite. However, these granites show slightly lower 10,000 × Ga/Al ratios of 2.3–3.0 and lower FeO tot /(FeO tot + MgO) values of 0.58–0.68 than the typical A-type granite. Their whole-rock Sr Nd isotopic compositions ( I Sr = 0.72996–0.73481, ε Nd (t) = −12.4 to −10.8, T DM C = ~1.9 Ga) and zircon Hf isotopic compositions (ε Hf (t) = −18.9 to −6.1, T DM2 = ~2.0 Ga) indicate that they mainly originated from pre-existing crustal materials. We suggest that the Kaqiong granites were produced by protracted partial melting of the basement rocks at relatively high temperature and high oxygen fugacity conditions. The Early Jurassic high-temperature granites were formed due to a significant mantle heat addition into the crust in an extensional continental arc, caused by the rollback of the subducted Bangong-Nujiang Tethyan oceanic slab. The study is an example of how high-temperature granites could shed light on the geodynamic processes. • Geochronology, geochemistry, and Sr-Nd-Hf isotope compositions of the Kaqiong granites • The Kaqiong granites are the high-temperature granites. • The Kaqiong granites formed in an extensional continental arc • The type of granites provides insight into the geodynamic processes of a subducting slab.

A spectral approach on mineralogy and geochemistry of garnet skarns in Arc-Type granitoids

Garnets that common constituent of skarn type iron deposits are wide ranges of chemical compositions, and they are also important as a semi-gemstone mineral. This study has been investigated garnets and inclusions of its formed in contacts of Pertek granitoid and Keban marble by using a combination of multiple techniques including Raman spectrum, electron microprobe, petrography and LA-ICP-MS. The main mineral assemblage observed in the skarn formation is diopside, garnet, quartz, magnetite, calcite and pyrite. The garnets are in size between 1 and 7 cm and have reddish, greenish and light–dark brown colour. The compositions of the garnets are mainly grossular-andradite, andradite-grossular, less grossular and andradite. Increased porosity and horizontal flow of hydrothermal fluids during metasomatism resulted in the formation of garnets of different sizes. Raman spectroscopy studies on garnets show to be that the idiomorphic and semi-idiomorphic garnets are predominantly grosular, andradite and uvarovite in the core. Raman spectroscopy studies on garnets showed to have predominantly grossular, andradite and uvarovite composition in the core of the idiomorphic and semi-idiomorphic garnets. As for the rare earth element (REE) analysis and distribution model, the chondrite-normalized REE patterns of all garnets in the study area have similar trends and generally in the right-slopping shape depleted in HREE and enriched in LREE, mostly controlled by adsorption. High Fe2O3, CaO and MgO contents may cause to high mobility during skarn formation associated with contact metamorphism and cation exchange via hydrothermal fluids (eg uvarovite in the core). All garnets have generally positive Ce and positive Eu anomalies. These results suggest that the garnets in the studya area formed in conditions showing increase in pH and high oxygen fugacity or decrease in temperature in the source of the hydrothermal fluids.

Chronology and geochemical composition of cassiterite and zircon from the Maodeng Sn-Cu deposit, Northeastern China: Implications for magmatic-hydrothermal evolution and ore-forming process

Primary tin deposits usually contain little or no copper due to the distinct geochemistry of Sn and Cu. However, examples of copper-rich tin deposits in many tin provinces around the world are also well known. The genesis of copper-rich tin deposits remains controversial. The Maodeng Sn-Cu polymetallic, a typical Cu-rich Sn deposit in the southern Great Xing’an Range (SGXR) Northeast China, offers an excellent opportunity to reveal the genesis of coupled copper-tin deposits. The ore mineralization is associated with the granite porphyry, complement phase of the Alubaogeshan complex, which emplaced into the volcanic rocks of the Lower Permian Dashizhai Formation. Herein, we report new zircon and cassiterite U-Pb ages and their trace elements compositions, with the aim of constraining the metallogenic chronology framework, and clarifying the indicative effects of the ore-forming fluids on mineralization in different ore-forming stages, and thus establishing the genetic model for the Sn-Cu deposit. LA-ICP-MS U-Pb dating of zircon from the granite porphyry yields a weighted mean U-Pb age of 134.6 ± 0.4 Ma, which consistent to the zircon U-Pb age (ca. 138 Ma) of porphyry monzogranite (main phase of the Alubaogeshan complex) and cassiterite U-Pb ages (137–140 Ma), suggesting an Early Cretaceous Sn-Cu mineralization under the Paleo-Pacific plate slab roll-back setting. Granite porphyry displays more evolved characterisrics, with higher SiO2 contents (71.5 ∼ 77.4 wt%), Rb/Sr ratios (3.39 ∼ 10.33) and lower Nb/Ta ratios (10.86 ∼ 13.06) compared to those of porphyry monzogranite (SiO2 contents of 70.4 ∼ 72.1 wt%; Rb/Sr and Nb/Ta ratios of 1.03 ∼ 1.72 and 13.34 ∼ 15.83, respectively). This is further supported by the trace elements contents of zircons from granite porphyry and porphyry monzogranite, because the former has a stronger Eu anomaly, higher Hf concentrations, lower Zr/Hf and Th/U ratios than the latter. Our new data, integrated with previously published geochemical data, suggest that the granites associated with Cu-rich Sn deposits are characterized by higher oxygen fugacity, lower differential degree and aluminum saturation index (ASI) than those of Sn-W deposits. This could also use to address the Sn-Cu deposits usually have relatively small Sn mineralization potential. The trace elements of the cassiterites are characterized by high Fe (up to 3358 ppm), Ti (up to 1894 ppm) and abnormal high In (∼2500 ppm) concentrations, but low Nb, Ta contents. From early to late stage, the W and U contents and Nb/Ta and Zr/Hf ratios are increased, reveal that the ore-forming process experienced the cooling, increasing volatile contents and fluid-rock reaction. Finally, a new metallogenic model was established, which highlight oxidized Cu-rich fluids exsolved from the upwelling mantle magma would add to the reduced, Sn-rich magma chambers. This contribution indicate that, the Cu and Sn metals come from the mantle magma and crustal granitic magma, respectively, and that Cu-rich Sn deposits are more likely a product of spatial coupling.

Origin of moderately volatile element depletion on differentiated bodies: Insights from the evaporation of indium from silicate melts

In comparison with the Sun and CI chondrites, moderately volatile elements (MVEs) are depleted in terrestrial planets and other small, rocky differentiated bodies in the inner solar system. The abundances of most MVEs in the bulk silicate Earth (BSE) fall on a trend that defines a near log-linear decrease with their 50% nebular condensation temperature (Tc50). This temperature scale has traditionally been used to infer elemental volatility during planetary formation and accretion, however, indium (In) deviates from this correlation. Despite being a siderophile element that could have been depleted by core formation, In is overabundant for its calculated Tc50 in the BSE, as well as in the silicate portions of other small bodies (e.g., Moon and Vesta). This overabundance of In indicates that Tc50, calculated under nebular conditions, may not be applicable to planetary evaporation that occurs at much higher oxygen fugacity (fO2) and pressure than nominal nebular conditions. Here, we conduct a series of evaporation experiments for basaltic melts to quantify the volatility of In under conditions relevant to planetary evaporation. Our results show that, when using the evaporation temperature (Te1, refers to the temperature at which 1% of element i has evaporated from liquid to gas phase under equilibrium) as the volatility scale, the abundances of volatile elements, including In, of the Moon and Vesta display a progressive depletion with increasing volatility (decreasing Te1). This smooth depletion pattern contrasts with the overabundance of In shown on the Tc50 scale, suggesting that volatile depletion on small bodies occurred under non-nebular environment instead of during nebular condensation. On the other hand, the volatile element composition of the BSE (including In) could be explained by integrating (i) early accreted precursor materials of the proto-Earth that underwent volatile loss under conditions more oxidizing than those of the solar nebula with (ii) late added volatile-rich materials.

Ferri-taramite, a new member of the amphibole supergroup, from the Jakobsberg Mn–Fe deposit, Värmland, Sweden

Abstract. Ferri-taramite (IMA CNMNC 2021-046), ideally ANaB(CaNa)C(Mg3Fe23+)(Si6Al2)O22W(OH)2, occurs in skarn from the Jakobsberg manganese mine, Värmland, Sweden. Associated minerals are celsian, phlogopite, aegirine-augite, andradite, hancockite, melanotekite, microcline (var. hyalophane), calcite, baryte, prehnite, macedonite and oxyplumboroméite. Conditions of formation, close to peak metamorphism (at circa 650 ∘C and 0.4 GPa), include silica undersaturation, a slightly peralkaline character and relatively high oxygen fugacities. Ferri-taramite forms poikiloblastic crystals up to 5 mm and is dark brownish black with a yellowish grey streak. The amphibole is brittle with an uneven to splintery fracture. Cleavage parallel to {110} is good. Hardness (Mohs) is ∼ 6, and Dcalc=3.227(5) g cm−3. Holotype ferri-taramite has the experimental unit formula A(Na0.79K0.16Pb0.01)Σ0.96B(Ca1.26Na0.72Mn0.022+)Σ2C(Mg2.66Mn0.582+Fe0.162+Zn0.02Fe1.263+ Al0.26Ti0.06)Σ5.00T(Al1.86Si6.14)Σ8O22W(OH)2, based on chemical analyses (EDS, laser-ablation ICP-MS) and spectroscopic (Mössbauer, infrared) and single-crystal X-ray diffraction data. The mineral is optically biaxial (–), with α=1.670(5), β=1.680(5) and γ=1.685(5) in white light and 2Vmeas=70(10)∘ and 2Vcalc=70.2∘. Ferri-taramite is distinctly pleochroic in transmitted light, with X pale yellow, Y dark brown, Z yellowish brown and absorption Y&gt;Z&gt;X. The eight strongest reflections in the X-ray powder pattern (d values (in Å), Irel, hkl) are 8.44, 60, 110; 3.392, 25, 131; 3.281, 39, 240; 3.140, 100, 310; 2.816, 45, 330; 2.7104, 38, 151; 1.3654, 26, 461; and 1.4451, 33, 6‾61. Refined unit-cell parameters from single-crystal diffraction data are a=9.89596(13), b=18.015(2), c=5.32164(7) Å, β=105.003(13)∘ and V=916.38(2) Å3 for Z=2. Refinement of the crystal structure yielded R=2.26 % for 2722 reflections with Io&gt;2σ(I). The Mn2+ and Fe2+ ions show preference for the M1 and M3 octahedrally coordinated sites, whereas Fe3+ is strongly ordered at M2. The A-group cations, K and Na, are split over two subsites, A(m) and A(2), respectively.