Biotite Geochemistry Research Articles

Two-stage mineralization of the Jinkeng Sn-Cu deposit in Eastern Guangdong, Southeast China: Response to magmatic activities and tectonic transformation

The Jinkeng Sn-Cu polymetallic deposit in South China consists of two different types of orebodies: 1) NE-striking skarn- and vein-type Cu-Pb-Zn-Sn orebodies in volcanic rocks suffering subsequent ductile shear deformation, and 2) NW-striking quartz-cassiterite-sulfide veins filled in the faults at the porphyritic granodiorite outward from the fine-grained granite which does not exhibit deformation. The relationships among Sn-Cu polymetallic mineralization, regional magmatism, and deformation metamorphism are still controversial. To address it, the geochronological, whole-rock and mineral geochemical research along with the detailed field investigation were conducted in this study. Our zircon U-Pb dating results show that the volcanic rocks formed at 158–162 Ma, earlier than the porphyritic granodiorite which yields the emplacement age of 146–147 Ma. In-situ LA-ICP-MS U-Pb dating of cassiterite from the deformed skarn ores indicates the early-stage mineralization occurred at 146 ∼ 148 Ma, which is similar to the emplacement age of the porphyritic granodiorite, but earlier than the formation of quartz-cassiterite-sulfide veins and the fine-grained granite (141∼144 Ma). Further, the whole-rock and biotite geochemistry, and zircon Hf isotope compositions suggest that the porphyritic granodiorite exhibits a lower degree of magma differentiation, higher oxygen fugacity, higher Cl and lower F contents than the fine-grained granite. The porphyritic granodiorite might provide the most Cu-Pb-Zn budget accompanied by minor Sn for early-stage mineralization. Overall, our study suggests that the Jinkeng Sn-Cu polymetallic deposit formed in two scenarios where the early dominated Cu-Pb-Zn and minor Sn mineralization related to the emplacement of the porphyritic granodiorite is superimposed by the late vein-type Sn-dominated mineralization related to the emplacement of the fine-grained granite. The two isolated mineralizing events (∼147 Ma and ∼141 Ma, respectively) in Jinkeng were probably responded to the regional magmatic activities triggered by the tectonic transformation where two extensional tectonic events were separated by a short contractional event (147–144 Ma).

Geochemistry of biotite and its formation conditions in Hararan granitoid

Geochemistry of biotite and its formation conditions in Hararan granitoid

Biotite Geochemistry and Its Implication for the Difference in Mineralization in the Xiongcun Porphyry Cu–Au Ore District, Tibet

The Xiongcun Cu–Au ore district is in the southern middle Gangdese Metallogenic Belt, Tibet, and formed during Neo-Tethyan oceanic subduction. The Xiongcun ore district mainly comprises two deposits, the No. I and No. II deposits, which were formed by two individual mineralization events according to deposit geology and Re–Os isotopic dating of molybdenite. The No. I deposit is similar to a reduced porphyry copper–gold deposit, given the widespread occurrence of primary and/or hydrothermal pyrrhotite and common CH4-rich and rare N2-rich fluid inclusions. The No. II deposit, similar to classic oxidized porphyry copper–gold deposits, contains highly oxidized minerals, including magnetite, anhydrite, and hematite. The halogen chemistry of the ore-forming fluid from the No. I and No. II deposits is still unclear. Biotite geochemistry with halogen contents was used to investigate the differences in ore-forming fluid between the No. I and No. II deposits. Hydrothermal biotite from the No. I deposit, usually intergrown with sphalerite, is Mg-rich and classified as phlogopite and Mg-biotite, and hydrothermal biotite from the No. II deposit is classified as Mg-biotite. Hydrothermal biotite from the No. I deposit has significantly higher SiO2, MnO, MgO, F, Li, Sc, Zn, Rb, Tl, and Pb contents and lower Al2O3, FeOtot, Cl, Ba, Cr, V, Co, Ni, Y, Sr, Zr, Th, and Cu contents than the biotite from the No. II deposit. Hydrothermal biotites from the No. I and No. II deposits yield temperatures ranging from 230 °C to 593 °C and 212 °C to 306 °C, respectively. The calculated oxygen fugacity and fugacity ratios indicate that the hydrothermal fluid of the No. I deposit has a higher F content, oxygen fugacity, and log(fHF/fHCl) value and a lower log(fH2O/fHF) value than the hydrothermal fluid from the No. II deposit. The biotite geochemistry shows that the No. I and No. II deposits formed from different hydrothermal fluids. The hydrothermal fluid of the No. I deposit was mixed with meteoric waters containing organic matter, resulting in a decrease in oxygen fugacity and more efficient precipitation of gold. The No. I and No. II deposits were formed by a Cl-rich hydrothermal system conducive to transporting Cu and Au. The decreasing Cl, oxygen fugacity, and temperature may be the key factors in Cu and Au precipitation. Biotite geochemistry allows a more detailed evaluation of the halogen chemistry of hydrothermal fluids and their evolution within porphyry Cu systems.

Petrology and biotite geochemistry of Mengku granitoids in the Changning-Menglian suture zone, southwest China: Insights into magma evolution and Sn mineralization

The Changning-Menglian suture zone (CMSZ) is one of the major Sn metallogenic zones related to Triassic granitoids. However, the genetic relationship between magmatic petrogenesis and metallogeny is not well-constrained. Highly evolved granitoids are an important type of granitic rocks, given their close relationship with Sn mineralization. Here we provide monazite U-Pb data and comprehensive major-trace element (including halogen) data for biotites from the Mengku granitoids, to constrain their magma evolution and link to regional Sn metallogeny. Our U-Pb dating on monazite from the highly evolved granitoids yielded weighted mean age of 223.6 ± 1.4 Ma (n = 20, MSWD = 1.3). The new geochronologic results, coupled with recently reported ages from the Lincang batholith, suggest that most of the Lincang granitoids formed within a relatively consistent period at ca. 230–215 Ma. Geochemically, these Triassic granitoids can be divided into three groups. Group 1 granitoids display low Al2O3, P2O5, FeOT + MgO, Eu, Sr and Zr contents with high differentiation index (DI = 88–94) and A/CNK (1.07–1.17), consistent with the features of highly evolved granites. In contrast, Group 2 monzogranites and Group 3 dioritic enclaves have higher TiO2, P2O5, FeOT + MgO, Eu, Sr and Zr contents, comparable to I-type granites. All magmatic biotite grains are Mg-rich in composition (XMg = 0.44–0.60). A positive correlation between F and MnO contents in biotites from Mengku granitoids indicate that more evolved Group 1 magmas underwent fractional crystallization. The most evolved magmas (Group 1) have relatively low log(fH2O/fHF) values (4.34–5.05) and high log(fHF/fHCl) values (4.85–5.39), suggesting lower Cl contents and higher F contents than other magmas. Oxygen fugacities (logfO2) calculated from biotite equilibria for the Mengku granitoids are –22.2 to −17.7, straddling on the NNO and QFM buffers. Low log(fO2) values and positive correlation between Sn and log(fHF/fHCl) suggest that relatively reduced condition, highly evolved and F-rich granitic magmas are conducive to Sn mineralization in the CMSZ.

Genetic relationship between the two-period magmatism and tungsten mineralization in the Yangchuling deposit, Jiangxi Province: Evidence from biotite geochemistry

阳储岭斑岩型W-Mo矿床位于江南造山带中部，是华南地区最早发现的斑岩型钨钼矿床。已探明WO₃资源储量6.13万吨（平均品位0.2%），Mo资源储量1.69万吨（平均品位0.03%~0.06%），其成矿作用与中生代花岗质岩浆活动密切相关。区内发育早期花岗闪长岩和晚期二长花岗斑岩，钨矿体以细脉状和浸染状产于二长花岗斑岩体内，而花岗闪长岩内未见矿化。两期岩浆活动与钨成矿的关系尚不明确，制约其含矿差异性的因素尚不清楚。本文以花岗闪长岩和二长花岗斑岩中的黑云母为研究对象，对比研究两类岩浆结晶分异程度、氧逸度、岩浆流体卤素浓度，探讨其对钨成矿的制约。黑云母主量元素分析结果显示，阳储岭两类岩浆岩均为壳源，但显著不同于S型花岗岩的Mg/（Fe+Mg）和Al^Ⅵ值，指示其具有Ⅰ型花岗岩的特征。黑云母的微量元素信息显示，相对于花岗闪长岩中的黑云母（类型一），二长花岗斑岩中的黑云母（类型二）显示低的K/Rb、Nb/Ta比值，高的Rb、Cs、Nb和Ta含量，表明其分异程度较花岗闪长岩更高，更有利于钨的富集。两类黑云母所指示的岩浆氧逸度均在NNO缓冲线附近，表明其母岩浆均为还原性岩浆，但二长花岗斑岩显示出更为还原的特征，还原环境有利于钨矿的形成。类型二黑云母比类型一黑云母具有低的Ⅳ（F）但高的Ⅳ（F/Cl）值，表明其F富集程度更高。通过黑云母计算出对应岩浆流体的log（<i>f</i>H₂O/<i>f</i>HF）^fluid、log（<i>f</i>H₂O/<i>f</i>HCl）^fluid、log（<i>f</i>HF/<i>f</i>HCl）^fluid值。结果表明类型二具有比类型一更低的log（<i>f</i>H₂O/<i>f</i>HF）^fluid、log（<i>f</i>H₂O/<i>f</i>HCl）^fluid值，显示二长花岗斑岩流体中更加富含HF和HCl。而类型二高的log（<i>f</i>HF/<i>f</i>HCl）^fluid值，显示出其更高的HF/HCl比值，对应了更高的结晶分异程度。阳储岭晚期二长花岗斑岩与早期花岗闪长岩为同一岩浆房分离结晶作用的产物，矿化存在于二长花岗斑岩顶部，岩浆结晶分异过程中，挥发性组分F、Cl和成矿元素W、Mo从体积更大的花岗闪长质岩浆聚集到小体积的二长花岗质岩浆中，形成具有经济价值的W-Mo矿体。研究结果表明，黑云母可有效示踪花岗质岩浆性质和岩浆结晶分异程度，并可作为矿产勘查的有利标志。

The origin of uranium deposits related to the Huangmeijian A-type granite from the Lu-Zong volcanic basin, South China: Constraints from zircon U-Pb geochronology and mineral chemistry

Although most of granite-related uranium deposits in South China are spatially and genetically associated with S-type granites, few are related to A-type granites. In this study, we present whole-rock major and trace elements, zircon U-Pb geochronology, and mineral chemistry data for the Huangmeijiang A-type granite in the Lu-Zong volcanic basin (South China) to investigate the origin of uranium deposits related to this pluton. The uranium ore bodies mainly occur within the Jurassic Luoling formation close to the Huangmeijian pluton. Whole-rock and biotite geochemistry indicates that the F-rich alkaline magmas with relatively high fO2 prompted the partitioning of U into the fluids released from the Huangmeijian pluton with an affinity of A-type granites, which would set the stage for the later concentration of the U into the Jurassic Luoling formation. Thorite, zircon, apatite, and bastnäsite are the dominant accessory minerals that host U in this pluton. Backscattered electron (BSE) images suggest that some zircon and thorite grains can be divided into the unaltered domains and altered domains. The textural features are interpreted as a later hydrothermal event superimposed on the magmatic zircon and thorite. In situ LA-ICP-MS U-Pb dating on the unaltered domains and altered domains of zircon grains yielded weighted mean ages of 127.8 ± 1.0 Ma and 65.7 ± 5.3 Ma, respectively. The former age represents the emplacement age of the Huangmeijian pluton, and the latter one overlaps the timing of a uranium mineralization event (∼66.6 Ma) in this area. The altered domains of thorite and high-(U + Th) zircon grains have lower U contents than those of the unaltered domains, indicating that uranium was mobilized from thorite and zircon during fluid infiltration, which might be the main source of uranium for the ∼ 66.6 Ma uranium mineralization. Our study suggests that the Huangmeijian pluton was the primary source of uranium for the formation of uranium deposits in this area.

Biotite geochemistry and its implication on the temporal and spatial difference of Cu and Mo mineralization at the Xiaokele porphyry Cu-Mo deposit, NE China

The Late Jurassic large Xiaokele porphyry Cu-Mo deposit is newly discovered in the northern Great Xing’an Range, NE China. Both Cu and Mo mineralizations have occurred in the potassic stage and are present in the potassic zone, but only Mo (Cu negligible) mineralization has been developed in the phyllic stage and is present in the phyllic zone. The cause for such temporal and spatial difference of Cu and Mo mineralization at Xiaokele remains unclear. In this study, biotite major element compositions were studied to reveal the magmatic-hydrothermal processes, and the temporal and spatial difference of Cu and Mo mineralization at Xiaokele. Biotite geochemical data show that the magmatic biotites (Bi-I), and the potassic-stage (Bi-II) and phyllic-stage (Bi-III) hydrothermal biotite are Mg-biotites, and that mineralization at Xiaokele occurred under 52–86 MPa (equivalent to 1.95–3.32 km depth). Calculated oxygen fugacity of Bi-I, Bi-II, and Bi-III biotites are all above nickel-nickel oxide (NNO) oxygen buffer, suggesting that these biotites were formed under oxidizing conditions. The decreasing Cl and largely constant F content from Bi-I, Bi-II to Bi-III result in an increasing trend of IV(F/Cl), indicating different elemental behavior between F and Cl during the magmatic-hydrothermal fluid evolution. Given that Cl content is a key Cu-transporting ligand in porphyry type mineral systems, the decreasing Cl content in Bi-III indicates lower Cu transporting capacity in the phyllic stage, resulting in the negligible Cu mineralization in the phyllic zone. Since F is important for Mo transport in hydrothermal systems, we conclude that the constant F content reflects stable Mo transporting capacity in the fluids, resulting in significant Mo mineralization in both the potassic and phyllic zones. Our results show that biotite geochemistry can be used to explain the temporal and spatial distribution of Cu and Mo mineralization in porphyry Cu-Mo systems.

Petrogenesis of a calc-alkaline lamprophyre (minette) from Thanewasna, Western Bastar Craton, Central India: insights from mineral, bulk rock and in-situ trace element geochemistry

Abstract The lamproites and kimberlites are well known from the Eastern Bastar Craton, Central India. However, a Proterozoic lamprophyre dyke is discussed here, from the Western Bastar Craton (WBC). The field geology, petrographic, mineralogical and whole-rock and in-situ trace element geochemistry of biotite are described to understand the petrogenesis and lithospheric evolution in the WBC. The Thanewasna lamprophyre (TL) is undeformed and unmetamorphosed, intruded into c. 2.5 Ga charnockite and metagabbro but closely associated with c. 1.62 Ga undeformed Mul granite. The TL has a characteristic porphyritic texture, dominated by phenocrysts of biotite, microphenocryst of amphibole, clinopyroxene and a groundmass controlled by feldspar. Mineral chemistry of biotite and amphibole suggest a calc-alkaline (CAL) type, and pyroxene chemistry reveals an orogenic setting. The TL is characterized by high SiO 2 and low TiO 2, MgO, Ni and Cr, consistent with its subcontinental lithospheric origin. The presence of crustal xenolith and ocelli texture followed by observed variations in Th/Yb, Hf/Sm, La/Nb, Ta/La, Nb/Yb, Ba/Nb indicate substantial crustal contamination. Whole-rock and in-situ biotite analysis by laser ablation inductively coupled plasma mass spectrometry show low concentrations of Ni (30–50 ppm) and Cr (70–150 ppm), pointing to the parental magma evolved nature. Enrichment in H 2 O, reflected in magmatic mica dominance, combined with high large ion lithophile element, Th/Yb ratios, and striking negative Nb–Ta anomalies in trace element patterns, is consistent with a source that was metasomatized by hydrous fluids corresponding to those generated by subduction-related processes. Significant Zr–Hf and Ti anomalies in the primitive mantle normalized multi-element plots and the rare earth element pattern of the TL, similar to the global CAL average trend, including Eastern Dharwar Craton lamprophyres. Our findings provide substantial petrological and geochemical constraints on petrogenesis and geodynamics. However, the geodynamic trigger that generated CAL magmatism and its role in Cu–Au metallogeny in the WBC, Central India, is presently indistinct in the absence of isotopic studies. Nevertheless, the lamprophyre dyke is emplaced close to the Cu–(Au) deposit at Thanewasna.

Whole-rock and biotite geochemistry of granites from the Miao’ershan batholith, South China: Implications for the sources of granite-hosted uranium ores

Granite-hosted uranium deposits are the most important types of uranium deposits in South China, but the metal sources of these deposits are still poorly constrained. The Miao’ershan batholith (South China) is a natural laboratory to address this issue, as well as to highlight the use of biotite composition as an indicator for the petrogenesis and uranium fertility of granites. Here, we present whole-rock and biotite geochemical data for U-bearing (Zhangjia and Douzhashan) and barren (Xiangcaoping and Paleozoic) granites of the Miao’ershan batholith. Contents of Li, Be, Mn, Sn, In, Nb, Ta, Ga, W, and U in the studied biotites increase from barren to U-bearing granites, while Mg, Ni, Co, V, and Rb display the opposite trend, which may indicate higher degrees of fractionation of the U-bearing granites. An Fe/(Fe + Mg) ratio of 0.65 in biotite appears to be an efficient threshold to discriminate between U-bearing and barren granites. New ternary discrimination diagrams are introduced, based on Li–V × 20–Mn and Sn–Co × 5–Nb, respectively, to aid the recognition of the U-bearing and barren granites. The relatively high whole-rock U concentrations (8.0–38.6 ppm) and low whole-rock ratios of Th/U (0.5–3.2) and REE/U (2.1–13.5) of the Zhangjia and Douzhashan granites favored the crystallization of uraninite. The samples experiencing fluid-wallrock interaction from the Zhangjia granite are characterized by low whole-rock U concentrations of 3.0 to 4.2 ppm and high Th/U ratios of 8.2 to 10.1, suggesting that a significant part of the U has been leached out by oxidizing meteoric waters. This confirms that the granite represents the primary source of U at the Zhangjia uranium deposit.

Using magmatic biotite chemistry to differentiate barren and mineralized Silurian–Devonian granitoids of New Brunswick, Canada

The geochemistry of biotite crystals from thirty fertile and barren Silurian–Devonian granitoids of New Brunswick, Canada, was studied in situ using electron microprobe and laser ablation inductively coupled plasma-mass spectrometry to investigate the suitability of biotite geochemistry as a diagnostic fertility index among these intrusions. The Fe2+/(Fe2+ + Mg2+) ratio of biotite varies as a function of intrusion metal affinity, increasing from Cu–Mo-related (mean of 0.56 ± 0.12), to Mo-related (mean of 0.69 ± 0.06) to Sn–W-related (mean of 0.77 ± 0.16), with barren granitoids lying between Cu–Mo and Mo types (mean of 0.66 ± 0.06). The results show a distinctive geochemical contrast between mineralized and barren samples. Compatible elements (Ti, Mg, Co, Ni, V, Cr, Ba, and Sr) decrease from barren to Cu–Mo, Mo, and Sn–W granitoids, whereas incompatible elements (Mn, Zn, Sn, W, Rb, Cs, and Li) show the opposite trend. These two trends might indicate higher degree of fractionation indicated by biotite chemistry in Sn–W-related granites. Furthermore, barren intrusions have the lowest water content (1–3 wt.% H2O), whereas Sn–W and Cu–Mo-related intrusions have between 3 and 6 wt.% H2O. Mo-bearing intrusions have a limited range of H2O contents (4–4.5 wt.%). A high degree of halogen enrichment related to degree of fractional crystallization results in enrichment of incompatible elements in the magmas associated with Sn–W mineralization and is reflected by the geochemical characteristics of biotite from these systems. New metallogenic classifications are introduced using ternary V–Na–Li (ppm) and Sn + W (ppm) versus Ga (ppm) to differentiate barren and mineralized granitic systems in New Brunswick.

Biotite geochemistry deciphers magma evolution of Sn-bearing granite, southern Myanmar

Hydrothermal Sn ± W deposits are commonly formed by ore-forming fluids that exsolved from water-saturated granitic magmas. However, the timing of fluid exsolution and its influence on volatiles and ore-forming elements still remain confused. For this purpose, geochemical and OH isotopic compositions of biotite from Late Cretaceous-Eocene granitic intrusions in the Sibumasu terrane (southern Myanmar) are presented. MnO content of biotite is a well negative correlation with the amount of biotite and whole-rock (La/Yb)N ratio, indicating that it could be a good index of granitic magma differentiation. Cl content of biotite from Paleocene granite shows an increased first and subsequently decreased trend with increasing MnO content (0.71–2.36 wt%), suggesting Cl enrichment by magma evolution and depletion by late-stage fluid exsolution. Fluid exsolution is also supported reduced Li contents of biotite and OH isotopic compositions of residual magmatic water equilibrated with high-MnO biotite (δ18O = 7.0 to 8.8‰ and δD = −114 to −93.5‰). All studied biotite grains from Late Cretaceous granite have low Cl contents (0.01–0.11 wt%), decreased Li with increasing MnO contents, and residual magmatic water-like OH isotopic values (δ18O = 6.9‰ and δD = −105‰), indicating that their host granitic melts had undergone fluid exsolution. Importantly, a positive correlation between Sn and MnO contents in biotite suggests that magma differentiation is a dominant process for Sn enrichment. No depletion of Sn by fluid exsolution likely caused by low salinity fluids exsolved from Cl-poor granitic melts, which were estimated by low Cl contents of biotite (<0.2 wt%). The reduced Nb and Ta contents in high-MnO biotite possibly resulted by fractionation of Nb/Ta-bearing minerals during late-stage magma evolution. Moreover, ore-forming fluids equilibrated with hydrothermal muscovite from Sn-bearing quartz veins have consistent OH isotopic compositions (δ18O = 6.8–7.0‰ and δD = −61.9 to −90.2‰) with magmatic water, suggesting that ore-forming fluids probably exsolved from more evolved granitic melts with strong Sn and F enrichment.

Genesis of Chating Cu-Au deposit in the Middle-Lower Yangtze River Metallogenic Belt, Eastern China: Implications from magnetite and biotite geochemistry

Porphyry deposits developed in intracontinental settings have some geological characteristics that differ from those developed in arc-related continental margins. The Chating deposit is a newly discovered Cu-Au deposit in the Middle-Lower Yangtze River Metallogenic Belt (MLYB), eastern China. We carried out detailed petrographic observations and major and trace element analyses of different types of magnetite and biotite from the host quartz diorite porphyry and different alteration zones in Chating to elucidate the genesis of Chating deposit.Alteration types in Chating include skarn, sodic-calcic, potassic and phyllic, and copper mineralization is closely associated with potassic alteration of quartz diorite porphyry. The different types of magnetite and biotite at Chating show distinctive geochemical characteristics. Higher Ti and Al in magmatic magnetites and biotites compared to the hydrothermal minerals indicate higher temperature and pressure in the quartz diorite porphyry. Higher V in magmatic magnetites and lower XMg in magmatic biotites indicate higher fO2. Similar mineral geochemistry from typical worldwide porphyry deposits, for example, Al2O3, TiO2, FeOT, MgO, Na2O, IV(F) and IV(Cl) contents in biotite, and Ni/Cr, Ti, Al, Sn and Ga in magnetite, indicate a predominately magmatic fluid source. Differences in Si, Ca, Co/Ni, Mg, and Mn in different types of magnetite, and MnO, CaO, SiO2 differences in two types of biotite from typical porphyry copper deposits show the influence of external fluids. Moreover, high IV(F) values and low IV(Cl) values in biotites demonstrate that the magmatic-hydrothermal system in Chating was enriched in Cl and lacked F, consistent with the importance of Cl in the transport of Cu. Based on different discrimination diagrams for magnetite, such as Ni/Cr versus Ti, Ni/(Cr + Mn) versus Ti + V, and Al + Mn versus Ti + V, and the geochemical similarities of biotite from Chating and other porphyry deposits, combined with the similarity of alteration assemblages, we conclude that Chating has porphyry Cu-Au affinities, but the hydrothermal system was affected by external fluids, in contrast to more typical subduction-related porphyry deposits.

Petrogenesis of Triassic granite from the Jintan pluton in Central Jiangxi Province, South China: implication for uranium enrichment

Numerous Triassic biotite granites and two-mica granites crop out in the interior of South China, and some of them possess high U contents, which have been regarded as the sources for later hydrothermal mineralization. Their petrogenesis is therefore crucial for constraining the possible origins of the U enrichment. Here we report new LA-ICPMS zircon UPb ages, mineral geochemistry of biotite and muscovite, whole rock geochemical results and SrNd and zircon Hf isotope data from the Jintan pluton in Central Jiangxi Province, South China. LA-ICPMS zircon UPb dating indicates that both biotite granite (BG) and two-mica granite (TMG) in the Jintan pluton crystallized at ~220 Ma. The TMG have higher U contents (7.85 to 48.90 ppm, average18.44 ppm) than theBG (4.99 to 17.72 ppm, average 8.64 ppm). Both BG and TMG show negative whole-rock εNd(t)and zircon εHf(t)values and contain some inherited zircons. The TMG are strongly peraluminous (A/CNK = 1.13–1.33), contain abundant primary muscovite, and display S-type affinity on plots of Yvs Rb and Th vs Rb, suggesting that they are S-type granites. The BG also display S-type granite affinities on plots of Yvs Rb and Th vs Rb. The suites display similar SrNd isotope compositions (BG initial 87Sr/86Sr values = 0.711389 to 0.714225 and εNd(t) = −9.91 to −9.16, TMG initial 87Sr/86Sr values = 0.711832 and εNd(t) = −10.02) and are spatially associated, suggesting that the BG should also be classified as S-type granites. The TMG have higher zircon εHf(t)values (−6.4 to −1.1) than the BG (−8.7 to −3.7), indicating the TMG and BG might be derived from similar sediments but possibly with some distinct characteristics in their sources. The BG exhibit linear covariations in chemical compositions with relatively high total REE and light REE contents and MgO contents, while the TMG displays broader compositional variations but with relatively low total REE, light REE and MgO contents. Biotite geochemistry indicates the TMG formed in a more reduced magmatic system than the BG. The temperatures estimated by zircon saturation thermometry indicate the BG had distinctly higher magmatic temperatures than the TMG. The TMG display relatively high Al2O3/TiO2 ratios and low CaO/Na2O ratios than the BG but have higher Sr/Y and La/Yb ratios. The geochemical and petrological data suggest the BG were derived from clay-poor psammite sources at deeper levels with higher temperatures and higher oxygen fugacity, and underwent an extensive fractional crystallization, while the TMG was derived from clay-rich pelitic sources at higher levels and lower temperatures and oxygen fugacity with only limited fractional crystallization. We conclude that the combination of U-rich sources, physical-chemical conditions such as low partial melting temperature or low degrees of partial melting, a reduced environment and low REE and LREE contents of magmas controlled the U enrichment in TMG.

Redox Condition, Nature and Tectono-magmatic Environment of Granitoids and Granite gneisses from the Karbi Anglong Hills, Northeast India: Constraints from Magnetic Susceptibility and Biotite Geochemistry

ABSTRACT The Karbi Anglong hills (erstwhile Mikir hills) in northeast India are detached and separated from the Meghalaya plateau by a NW-SE trending Kopili rift. The Karbi Anglong hills granitoids (KAHG) and its granite gneissic variants belong to Cambrian plutons formed during Pan-African orogenic cycle, which commonly intrude the basement granite gneisses and Shillong Group metasediments. The KAHG can be broadly classified into three major granitoid facies viz., coarse grained porphyritic granitoid, medium grained massive non-porphyritic granitoid, and granite gneiss, which share a common mineral assemblage of plagioclase-K-feldspar-quartz-biotite±hornblende-apatite-titanite-zircon-magnetite but differ greatly in mineral proportion and texture. Modal mineralogy of KAHG, granite gneiss and basement granite gneiss largely represents monzogranite and syenogranite. The magnetic susceptibility (MS) of the KAHG, granite gneiss and basement granite gneiss varies widely between 0.11×10−3 and 43.144×10−3 SI units, corresponding to ilmenite series (&amp;lt;3×10−3 SI; reduced type) and magnetite series (&amp;gt;3×10−3 SI; oxidized type) of granitoids respectively. The observed MS variations are most likely intrinsic to heterogeneous source regions, modal variations of orthomagnetic and ferromagnetic minerals, and tectonothermal and deformational processes that acted upon these rocks. The primary and re-equilibrated compositions of biotites from the KAHG, granite gneiss and basement granite gneiss suggest calc-alkaline, metaluminous (I-type) nature of felsic host magma formed in a subduction or post-collisional to peraluminous (S-type) host magma originated in syn-collisional tectonic settings, which were evolved and stabilized between FMQ and NNO buffers typically corresponding to reducing and oxidising magma environments respectively.

Zircon U-Pb geochronology and geochemistry of granites in the Zhuguangshan complex, South China: Implications for uranium mineralization

The Zhuguangshan complex, composed of Caledonian, Indosinian, and Yanshanian granites, and Cretaceous mafic dykes, is one of the most important granite-hosted uranium producers in South China. Here we present LA-ICP-MS zircon U-Pb and hornblende 40Ar/39Ar geochronology and whole-rock and biotite geochemistry for the granites in this complex to evaluate the magmatism and its constraints on uranium mineralization. Samples collected from the Fuxi, Youdong, Longhuashan, Chikeng, Qiling, and Sanjiangkou intrusions yield zircon weighted 206Pb/238U ages of 426.7 ± 5.4 Ma, 226.4 ± 3.5 Ma, 225.0 ± 2.7 Ma, 152.2 ± 3.0 Ma, 153.9 ± 2.1 Ma, and 155.2 ± 2.1 Ma, respectively. A new Ar-Ar dating of the hornblende of the diabase from the Changjiang uranium ore field yields a plateau age of 145.1 ± 1.5 Ma. These results coupled with published geochronological data indicate that six major magmatic events occurred in the study area at 420−435 Ma, 225−240 Ma, 150−165 Ma, ~140 Ma, ~105 Ma, and ~90 Ma. Both U-bearing and barren granites occur in this complex, and they display differences in whole-rock and biotite geochemistry. The barren granites show higher Al2O3, CaO, TFMM, Rb, Zr, Ba, SI, Mg#, (La/Yb)N, and Eu/Eu*, but lower SiO2, ALK, Rb, DI, Rb/Sr, and TiO2/MgO than those of the U-bearing granites. Biotites in the U-bearing granites are close to the Fe-rich siderophyllite-annite end member with Fe/(Fe + Mg) ratios higher than 0.66, whereas those in the barren granites are relatively close to the Mg-rich eastonite-phlogopite end member with Fe/(Fe + Mg) ratios <0.66. The U-bearing granites were mainly derived from the partial melting of pelitic sedimentary source, whereas the psammitic source generated the barren granites. In addition, the barren granites show higher TFMM, Ba, and Eu/Eu* but lower SiO2, Rb/Sr and Al2O3/TiO2 ratios with higher zircon saturation temperatures relative to the U-bearing granites. These results indicate that the geochemical compositions of the U-bearing and barren granites are dictated not only by the compositions of source rocks but also the physicochemical conditions of partial melting. Our study suggests that these two factors are also the major factors that control uranium ore potential of the granites in the Zhuguangshan complex. The geochemical variations of U-bearing and barren granites can serve as a potential detector for granite-hosted uranium deposits.

Geochemistry of biotite from charnockitoids in the granite-forming series (Nimnyr Block of the Aldan Shield)

The geochemical evolution of biotite (Bt) from garnet-bearing associations in the granite-forming series of the Nimnyr Block (Aldan Shield) is considered. The series includes the primary rock (gneiss or basic rock), autochthonous enderbite- or charnockite-gneiss (Lc1), migmatitic leucosome (Lc2, Lc4), and paraautochthonous charnockite (Lc3-ch1) and (Lc5-ch2 → grn). Bt in each series is characterized by an individual, significant difference in the concentrations of Ti, V, Cr; rarely Al, Fe, Mg, and Rb; and very rarely La, Ce, Nd, and Gd. The uniform trend of evolution of Bt compositions in the series was established for Al, KAl, (K + Na)/Al, rarely for Mg, Ti, and К. In contrast to the series with ch2, Bt becomes enriched in LREEs from autochthonous Lc1 to allochthonous Lc2 and Lc3. The different compositional variations of Bt in relation some minor elements is explained by the different composition of the material, which underwent melting, temperature variations (from 820 to 750°C), and changes in pH of the mineral-forming medium.

Implications of Late Cretaceous U–Pb zircon ages of granitic intrusions cutting ophiolitic and volcanogenic rocks for the assembly of the Tauride allochthon in SE Anatolia (Helete area, Kahramanmaraş Region, SE Turkey)

An assemblage of NE–SW-trending, imbricate thrust slices (c. 26 km E–W long × 6.3 km N–S) of granitic rocks, basic-felsic volcanogenic rocks (Helete volcanics), ophiolitic rocks (Meydan ophiolite) and melange (Meydan melange) is exposed near the Tauride thrust front in SE Anatolia. The volcanogenic rocks were previously assumed to be Eocene because of associated Nummulitic limestones. However, ion probe U–Pb dating of zircons extracted from the intrusive granitic rocks yielded ages of 92.9 ± 2.2–83.1 ± 1.5 Ma (Cenomanian–Campanian). The Helete volcanic unit and the overlying Meydan ophiolitic rocks both are intruded by granitic rocks of similar age and composition. Structurally underlying ophiolite-related melange includes similar-aged, but fragmented granitic intrusions. Major, trace element and rare earth element analyses coupled with electron microprobe analysis of the granitic rocks show that they are metaluminus to peraluminus and calc-alkaline in composition. A magmatic arc setting is inferred from a combination of tectonomagmatic discrimination, ocean ridge granite-normalized multi-element patterns and biotite geochemistry. Sr–Nd–Pb isotope data further suggest that the granitoid rocks were derived from variably mixed mantle and crustal sources. Granitic rocks cutting the intrusive rocks are inferred to have crystallized at ~5–16 km depth. The volcanogenic rocks and granitic rocks originated in a supra-subduction zone setting that was widely developed throughout SE Anatolia. Initial tectonic assembly took place during the Late Cretaceous probably related to northward subduction and accretion beneath the Tauride continent (Keban and Malatya platforms). Initial tectonic assembly was followed by exhumation and then transgression by shelf-depth Nummulitic limestones during Mid-Eocene, as documented in several key outcrops. Final emplacement onto the Arabian continental margin took place during the Early Miocene.

Petrogenesis of Triassic granites from the Nanling Range in South China: Implications for geochemical diversity in granites

Abstract A combined study of whole-rock major-trace elements and Sr–Nd isotopes, zircon U–Pb ages, Hf and O isotopes as well as biotite geochemistry was carried out for Triassic granite intrusions from the Nanling Range in South China. The results provide insights into the effects of source composition and melting conditions on the geochemical diversity of granites. The granites of interest are peraluminous, and contain primary muscovite and tourmaline. They are characterized by high zircon δ18O values of > 9.0‰, high initial 87Sr/86Sr values of ~ 0.7200, and homogeneous eNd(t) values of − 11.3 to − 9.8, as well as variable zircon eHf(t) values of − 12.2 to − 5.8. Biotite geochemistry is similar to that of common peraluminous granites. An integrated interpretation of these petrological, mineralogical and geochemical data indicates that these granites were derived from partial melting of metasedimentary rocks under variable physicochemical conditions. The differences in whole-rock and biotite geochemistry between the intrusions are ascribed to the variable effects of source heterogeneity and melting temperature. The Luxi intrusion exhibits higher contents of MgO, FeOT, TiO2 and CaO than common melts derived from metasedimentary rocks, tight variations in major-trace elements and homogeneous Sr–Nd isotopic compositions, and homogeneous biotite composition with high Mg# [= Mg / (Mg + Fe) in molar] and lower whole-rock A/CNK values [= Al2O3 / (CaO + Na2O + K2O) in molar]. These can be explained by originating from a relatively mafic metasedimentary source. On the other hand, the geochemical diversity of granites can be caused by the difference in melting temperature in addition to the source heterogeneity. This is suggested by the Xiazhuang and Fucheng intrusions which exhibit similar range of SiO2. Nevertheless, the Fucheng intrusion is ferroan, and high in TiO2, (Na2O + K2O)/CaO, TiO2/MgO, Ga/Al and Zr + Nb + Ce + Y, but low in CaO, MgO and Mg#. Most of its major elements and their ratios are similar to those of A-type granites that were generated from F-rich rocks at high temperatures, consistent with the enrichment of Fe and F in its biotite. Thus, partial melting of a metasedimentary restite at reduced conditions after previous melt extraction is suggested to produce the geochemical feature of A-type granites in the Fucheng intrusion. In contrast, partial melting of fertile metasedimentary rocks would produce normal S-type granites like the Xiazhuang intrusion, with its geochemical variations ascrible to source heterogeneity and differential melting. Therefore, the geochemical composition of granites is primarily dictated by the composition of source rocks in addition to the physicochemical conditions of partial melting.

Andean-type active margin formation in the eastern Taurides: Geochemical and geochronogical evidence from the Baskil granitoid (Elazığ, SE Turkey)

The Southeast Anatolian Orogen resulted from collision of the Afro-Arabian and the Eurasian plates following the Cretaceous to Miocene closure of the southern Neotethyan oceanic basin. In this orogenic belt, there are number of tectonomagmatic/stratigraphic units in the Kahramanmaraş–Malatya–Elazığ region that are important to understand the geological evolution of southeast Anatolia during the Late Cretaceous. These are (a) metamorphic massifs (i.e. Malatya–Keban platform), (b) ophiolites (i.e. Göksun, İspendere, Kömürhan), (c) ophiolite-related metamorphics (i.e. Berit metaophiolite) and (d) granitoids (i.e. Göksun, Doğanşehir and Baskil). The Baskil granitoid crops out to the northwest of Elazığ and is a large magmatic body (170 km 2) that intruded all of the above-mentioned units during Late Cretaceous time. The Baskil granitoid comprises both mafic and felsic plutonic/sub-plutonic rock associations. The felsic plutonic phase includes granite, granodiorite, tonalite and quartz monzonite whereas the felsic sub-plutonic phase is characterized by aplite, granophyre, granite porphyry and granodiorite porphyry. The granite and granodiorite contain mafic microgranular enclaves (MME). The mafic plutonic phase comprises gabbro, diorite, quartz diorite, whereas the mafic sub-plutonic phase is represented by diabase, microdiorite, quartz microdiorite, diorite porphyry, quartz diorite porphyry and dykes of orbicular gabbro dyke. Geochemically, the Baskil granitoid rocks have I-type, metaluminous-peraluminous calc-alkaline characteristics. The REE- and ocean ridge granite-normalized multi-element patterns and tectonomagmatic discrimination diagrams, together with biotite geochemistry suggest that the granitoids were formed in a volcanic arc setting. The 40Ar/ 39Ar geochronology of the granitoid rocks yielded biotite ages of 81.9 ± 0.7 Ma and 81.5 ± 0.8 Ma (95% confidence level). Coexisting hornblende, and hornblende from additional samples, yielded ages ranging from 84.0 ± 0.7 Ma to 81.5 ± 1.1 Ma. The ophiolites are believed to have formed in a suprasubduction zone tectonic setting, whereas the ophiolite-related metamorphic rocks formed either during the initiation of intraoceanic subduction or later-stage thrusting (∼ 90 Ma). These units were then thrust beneath the Malatya–Keban platform during the progressive closure of the southern Neotethys. This was followed by intrusion of the granitoids (85–82 Ma) along the Tauride active continental margin of the southern Neotethys.

Geochemistry of biotite, muscovite and tourmaline from Early Palaeozoic granitoids of Kinnaur district, Higher Himachal Himalaya

Geochemistry of biotite, muscovite and tourmaline from Early Palaeozoic granitoids of Kinnaur district, Higher Himachal Himalaya