Mineral Chemistry Of Biotite Research Articles

Geochemistry and origin of felsites and associated A-type granites at Wadi Atalla area, Central Eastern Desert, Egypt: Implication for genesis of Neoproterozoic post-collisional highly silicic melts

Alkaline volcanics (felsites) and A-type granites are spatially and temporally associated in the Wadi Atalla area, Central Eastern Desert, Egypt. These rocks represent final Neoproterozoic magmatic activity in the Northern Nubian Shield. Wadi Atalla felsites form NW-trending elongate mass consisting of silicic volcanics, which is intruded by A-type granites of Um Had and Um Effein plutons. Field relations indicate that both felsites and A-type granites were emplaced in a series of magmatic pulses. Felsites include tuffaceous, porphyritic and hypabyssal varieties, while A-type granites comprise syenogranite and alkali feldspar granite. Geochemically, they are highly silicic rocks and display a narrow range of SiO2. They have high-K alkaline nature with metaluminous to peraluminous character and were erupted in a post-collisional tectonic setting. Mineral chemistry of biotite supports the alkaline and A-type characters of the studied rocks. Atalla felsites and associated A-type granites show light REE enrichment relative to heavy REE [(La/Lu)n = 2.67–5.72] with pronounced negative Eu anomalies (Eu/Eu* = 0.15–0.52). Compositional similarities between Atalla felsites and A-type granites in the studied area suggest that the intrusive and extrusive events are broadly related. The systematic variation of major- and trace-element contents of the felsites and A-type granites indicates derivation from similar sources through partial melting of juvenile crustal rocks, followed by extensive fractional crystallization. The main fractionated phases are feldspars, with minor role of fractionation of amphibole, biotite, apatite and FeTi oxides. Multiple saturation calculations indicate water-saturated storage and final equilibration conditions for the felsites ranging from 788 °C at 90 MPa to 740 °C at 255 MPa. The parental magmas of the felsites and A-type granites were linked to lithospheric delamination and upwelling of asthenospheric mantle material. This process led to generation of mantle melts that supplied heat to melt the juvenile crust of the Arabian-Nubian Shield (ANS), along with crustal uplift recorded by intersecting strike-slip faults and shear zones. Atalla felsites represent a distinctive post-collisional alkaline volcanic phase in the Nubian Shield that has been emplaced in an extensional tectonic regime, during a phase of fracturing and crustal uplift, which followed the end of the Pan-African orogeny. This volcanic phase is younger than the Dokhan volcanics in the Eastern Desert and older than the typical Katherina volcanics in southern Sinai.

Mineral Chemistry of Biotite and Its Petrogenesis Implications in ca. 2.5 Ga Wangjiazhuang Granitic Pluton, North China Craton

Mineral Chemistry of Biotite and Its Petrogenesis Implications in ca. 2.5 Ga Wangjiazhuang Granitic Pluton, North China Craton

Mineral chemistry of biotite and hornblende from mesoproterozoic quartz syenite intrusions of the Cuddapah Intrusive Province, Eastern Dharwar Craton, India: implications for their source characterization

Mineral chemistry of biotite and hornblende from mesoproterozoic quartz syenite intrusions of the Cuddapah Intrusive Province, Eastern Dharwar Craton, India: implications for their source characterization

Geochronology, whole-rock geochemistry, Sr[sbnd]Nd isotopes, and biotite chemistry of the Deh-Bala intrusive rocks, Central Urumieh-Dokhtar Magmatic Arc (Iran): Implications for magmatic processes and copper mineralization

The Urumieh-Dokhtar Magmatic Arc (UDMA) of Iran hosts a variety of volcano-plutonic rocks of different composition and age formed by subduction of Neo-Tethyan Ocean beneath Eurasian supercontinent and the subsequent processes of post-subduction magmatism. This study focuses on mineral chemistry of biotite and amphibole, zircon UPb geochronology, whole-rock geochemistry, and SrNd isotopic geochemistry in the Deh-Bala granitoid, in an attempt to investigate the porphyry-epithermal mineralization potential. The Deh-Bala intrusions in the central part of the UDMA consist mainly of granodiorite and minor tonalite, with microgranular enclaves (MEs) of gabbrodiorite, diorite, and monzodiorite composition. In addition, the main ore minerals associated with more altered and mineralized varieties of these intrusions include chalcopyrite, covellite, malachite, and pyrite. The silicic, argillic, phyllic (sericitic), and propylitic facies of alteration occur in parts of the Deh-Bala area; these types of alteration, which are typically considered the most important predictors of porphyry copper‑gold and (or) epithermal precious metal mineralization.LA-ICP-MS UPb dating of zircons reveals that the pluton was emplaced during Middle-Eocene (ca. 39.0 Ma). The Deh-Bala granitoids (DBG) are calc-alkaline in composition (Na2O + K2O: 4.8–7.3 wt%) and display SiO2 contents from ∼53 to ∼67 wt%. They are enriched in light rare earth elements (LREEs) relative to heavy rare earth elements (HREEs), with marked Eu anomalies. They are also characterized by an enrichment in large-ion lithophile elements (LILEs, such as Rb, K, and U) and a depletion in high-field strength elements (HFSE, such Nb, Y, Ti, and Zr), displaying obviously depletions with Ba, P, and Sc. The DBG shows whole-rock initial 87Sr/86Sr ratios (ISr) of 0.7048–0.7061, εNd(t) values of −1.79 to +1.64, and Nd two-stage depleted mantle model ages (TDM2) from 747 to 1004 Ma. These isotopic data, combined with the geochemical signatures, indicate that the DBG originated through mixing of mafic and felsic end-members, the former was derived from melting of the lithospheric mantle, and the latter derived from partial melting of Neoproterozoic crustal materials in a continental-arc.Biotite compositions analysed by electron microprobe are consistent with the Deh-Bala magmas being oxidized and chlorine-rich, similar to worldwide porphyry copper‑gold systems formed in arc-related settings associated with convergent margin subduction zones. Such a chlorine-rich magmatic-hydrothermal system is known to be effective in scavenging copper and (or) gold from melt and its transfer to shallow levels.

Determination of physicochemical conditions and role of fluids in evolution of Geysour granitoid (eastern Gonabad), using biotite mineral chemistry

توده گرانیتوئیدی گیسور با سن کرتاسه پایینی از گرانودیوریت، آنکلاوهای میکروگرانولار مافیک و سیل میکروگرانیت تشکیل‌شده است. کانی‌های اصلی این سنگ‌ها عبارتند از پلاژیوکلاز، کوارتز، ارتوکلاز و بیوتیت. بیوتیت­های نمونه های گرانودیوریت و آنکلاوها در گروه I و گروه بیوتیت­ های آهن­ دار قرار دارند و بیوتیت­ های نمونه ­های میکروگرانیت در گروه I و گروه بیوتیت ­های منیزیم ­دار قرار می­ گیرند. دمای تشکیل بیوتیت ­ها در گرانودیوریت 653 تا 732 درجه سانتی‌گراد ، آنکلاو 631 تا 724 درجه سانتی‌گراد و در میکروگرانیت 689 تا 732 درجه سانتی‌گراد است. همچنین مقدار فشار متوسط برای گرانودیوریت و آنکلاو حدود Kbar 4 و میکروگرانیت Kbar 2 است. بیوتیت­ های توده گرانودیوریتی و آنکلاوها در بالای بافر NNO قرار دارند و بیوتیت ­های میکروگرانیت در زیر خط بافر NNO و در محدوده بافر QFM واقع می ­شوند. از آنجایی‌که توده گرانیتوئیدی گیسور از گرانیت ­های نوع I دما‌ پایین است، نم ی­توان از نمودارهای متمایز‌کننده محیط­ های زمین‌ساختی با استفاده از ترکیب بیوتیت ­ها استفاده‌ کرد. همه بیوتیت ­ها با روندهای خطی log(fHF/fHCl)، log(fH2O/fHCl) و log(fH2O/fHF) زاویه زیادی می­ سازند که بیانگر تغییر شرایط فوگاسیته و تغییر محتوای هالوژن سیال ­ها در اثر واکنش سنگ دیواره است. نسبت ­های فوگاسیته سیالات هیدروترمال نشان می­ دهند که سیالات هیدروترمال از نوع پتاسیک هستند؛ اما سیالات ماگمایی توده نفوذی گیسور به‌طور مشخصی متفاوت از سیالات پورفیری است.

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.

Study of biotite quartzdiorite rocks of NW Delijan by using biotite mineral chemistry

Study of biotite quartzdiorite rocks of NW Delijan by using biotite mineral chemistry

Biotite Mineral chemistry, an approach to petrogenesis of Saray volcano, Northwestern of Iran

آتشفشان سارای در حاشیه شرقی دریاچه ارومیه واقع شده است و یک کمپلکس آتشفشانی- نفوذی مرکب خاموش می‌باشد. این آتشفشان عمدتاً تناوبی از روانه‌های لئویسیتیتی و فوران‌های آذرآوری با ترکیب لئویسیتیتی می‌باشد. دایک‌های لئویسیت‌فنولیتی، لامپروفیری، تراکیتی، یک توده کوچک نفوذی سینیتی و چند دایک با ترکیب سینیتی سایر واحد‌های سنگی آتشفشان سارای را تشکیل می‌دهند. کانی بیوتیت در مینت‌ها، مونشیکیت‌ها، تراکیت‌ها و سینیت‌های آتشفشان سارای از کانی‌های اصلی محسوب می‌شود و جهت بررسی دقیق‌تر، به‌ویژه تشخیص شرایط ژنز آنها، از بیوتیت‌های موجود در این سنگ‌ها، آنالیز نقطه‌ای انجام گرفت. میکا-های دایک‌های مینتی و مونشیکیتی و سینیت‌ها ترکیب فلوگوپیتی داشته و میکای تراکیت‌ها همگی از نوع بیوتیت می‌باشند. اکثر بیوتیت‌های مورد مطالعه در محدوده بیوتیت‌های اولیه مجدداً متعادل‌شده قرار می‌گیرند. بررسی شیمی‌کانی آنها نشان می‌دهد که این مجموعه از یک ماگمای کالک‌آلکالن و در یک محیط کوهزایی تشکیل شده‌اند. عدد منیزیومی بیوتیت در لامپروفیرها اغلب بیش از 9/0، در سینیت‌ها اغلب بین 8/0 الی 9/0 و در تراکیت‌ها حدود 7/0 می‌باشد. فوگاسیته اکسیژن ماگما در حین تبلور اکثر بیوتیت‌ها حدود 9- تعیین می‌شود. با توجه به تفاوت ترکیب شیمیایی بیوتیت‌های نمونه‌های سینیتی و تراکیتی می‌توان گفت که به احتمال قوی بیش از یک و حتی بیش از دو مخزن تراکیتی- سینیتی مستقل از هم در آتشفشان سارای تشکیل شده‌اند.

Adakitic Paracale Granodiorite in southeastern Luzon, Philippines: A peek at a Proto-Philippine Sea Plate-related magmatic arc

This paper describes the geochemistry, petrogenesis and tectonic setting of a silicic pluton, the Paracale Granodiorite (PG), intruded into an ophiolitic suite in southeastern Luzon island, Philippines. Whole rock chemistry suggests that the PG samples are calc-alkaline and are characterized by light rare earth element (LREE)-enrichment and relatively weak heavy rare earth element (HREE)-depletion. They also show depletion in Nb, Ta, Zr and Ti and positive anomalies in K, Pb and Sr when normalized with the Primordial Mantle and normal-mid-ocean ridge basalt (N-MORB). The PG biotite mineral chemistry shows an affinity to calc-alkaline trends based on the FeOtot versus Al2O3, whereas in the MgO-Al2O3 plot, they exhibit transitional calc-alkaline to peraluminous characteristics. These information, along with a temperature >600 °C based on biotite chemistry, and hydrous setting for the generation of the PG suggest generation in a subduction-related setting. When plotted in the Y versus Sr/Y and YbN versus (La/Yb)N, the PG samples exhibit adakitic signature. Partial melting, fluid addition and sediment participation are discerned from the geochemistry. Melting, assimilation, storage and homogenization (MASH) with limited fractionation are the dominant mechanisms of formation. The PG could represent a Late Cretaceous to Paleogene magmatic arc generated during the subduction of the proto-Philippine Sea Plate.

Petrogenesis of granitic rocks in the Pingtan Island, Fujian Province: Constraints from zircon U-Pb dating, O-Hf isotopes and biotite mineral chemistry

Petrogenesis of granitic rocks in the Pingtan Island, Fujian Province: Constraints from zircon U-Pb dating, O-Hf isotopes and biotite mineral chemistry

Petrogenesis of granitic rocks in the Pingtan Island, Fujian Province: Constraints from zircon U-Pb dating, O-Hf isotopes and biotite mineral chemistry

东南沿海地区发育具有'等同位素组成'特征的晚中生代双峰式火成岩，其成因备受争论。本文选择了福建省平潭岛双峰式杂岩体中的花岗闪长岩、英云闪长岩与花岗岩开展了高精度锆石U-Pb定年、原位O-Hf同位素和黑云母矿物化学方面的研究，以探讨这些花岗质岩石的成因。分析结果显示，花岗闪长岩、英云闪长岩与花岗岩的锆石U-Pb年龄分别为116.8±1.0Ma、116.3±1.0Ma与117.4±1.0Ma，表明它们均侵位于早白垩世。这三类岩石也有较为相似的锆石O-Hf同位素组成。其中，锆石的δ18O分别变化为4.6%~5.3‰、4.8%~5.3‰及5.0%~5.6‰，与地幔的O同位素值基本一致。锆石的eHf（t）变化范围分别为+2.0~+7.1、+2.8~+6.5及+1.8~+5.6，相应的两阶段模式年龄tDM2分别为741~1046Ma、754~995Ma及815~1058Ma。锆石O-Hf同位素数据反映其熔融源区主要为相对较年轻的地壳物质，来自华夏地块古老基底的贡献较少。另外，黑云母矿物化学暗示这三类岩石具有Ⅰ型花岗岩的特征。但是，黑云母种属在不同岩性间存在差异，其中花岗闪长岩与英云闪长岩中的黑云母为镁质类型，花岗岩中的黑云母为铁质类型。从花岗闪长岩、英云闪长岩到花岗岩，黑云母的结晶温度和岩浆体系的氧逸度均逐渐降低，这与钙碱性岩浆分异演化的趋势基本一致。结合前人研究资料及区域地质演化历程，我们认为平潭岛杂岩体中的花岗质岩石形成于古太平洋俯冲背景，其熔融源区主要为新增生地壳物质。花岗质岩石内部岩性的差别主要是母岩浆经历不同程度分异演化的结果。我们的研究结果暗示壳幔岩浆混合在东南沿海早白垩世长英质岩石形成过程中所具有的作用可能较为有限。

Advances in Research of Mineral Chemistry of Magmatic and Hydrothermal Biotites

Biotite is an important hydrated ferromagnesian silicate mineral in igneous rocks and porphyry deposits. The determination of chemical compositions of biotite plays an important role in both igneous petrology and ore forming processes. This paper summarizes research results of magmatic and hydrothermal biotites exemplified by the Lakange porphyry Cu–Mo deposit and the Qulong porphyry Cu deposit in the Gangdese porphyry–skarn metallogenic belt, Tibet. Biotite mineral chemistry can provide critical insights into classification, geothermometer, geothermobarometry, oxygen fugacity, petrogenesis and tectonic setting, evaluating magmatic‐hydrothermal process by halogen and halogen fugacity ratios, and distinguishing between barren and mineralized rocks. Biotite provides the latest mineralogical evidence on metallogenic prognosis and prospecting evaluation for porphyry Cu polymetallic deposits or magmatic hydrothermal deposits.

Dissecting through the metallogenic potentials of Precambrian granitoids: case studies from the Bastar and Eastern Dharwar Cratons, India

Abstract The Malanjkhand granodiorite in the Bastar Craton hosts a major copper (+ molybdenum) deposit. It represents a Precambrian granite–ore system lacking in key morphological features of porphyry-type deposits but is comparable as a chemical package with a distinct mode of evolution of the magmatic-hydrothermal system. Mineral chemistry of biotite and apatite along with bulk geochemical data constrain critical parameters such as initial water and halogen contents of the magma. Evolution of the magmatic-hydrothermal fluid has been envisaged with available thermobarometric data. A quantitative ore genetic model in terms of efficiency of removal of metals and resultant mineralization in terms of quantity of metals has been attempted for the Malanjkhand deposit. The Eastern Dharwar Craton witnessed prolific granitic activities in multiple phases during the Late Archean and are spatially close to auriferous schist belts. Against a widely held view of a single metamorphogenic origin of metal and ore fluid, a granite–gold connection can be visualized for the auriferous schist belts of the Eastern Dharwar Craton through comparison of fluid characteristics in the granitoid and ore regimes and mineral chemical constraints. Although a quantitative genetic link between the granitoid and gold would need more data, a magmatic component of the ore fluid could be established based on the available information.

Evidence for magma–evaporite interactions during the emplacement of the Central Atlantic Magmatic Province (CAMP) in Brazil

Mafic sills of the Central Atlantic Magmatic Province (CAMP) in Brazil are temporally linked to the end-Triassic extinction (ETE), one of the largest mass extinctions of the Phanerozoic. The sills were emplaced into the volatile-rich sedimentary rocks of the Amazonas and Solimões basins in northern Brazil. Here we present a new geochemical study of 26 dolerite samples from 6 deep boreholes in the Brazilian basins, including whole-rock major and trace elements, whole-rock Sr–Nd isotopes and detailed biotite mineral chemistry. The bulk of the dolerites are characterized by phenocrysts of clinopyroxene and plagioclase in subophitic to intergranular textures, Fe–Ti oxides, and rare olivine and orthopyroxene. A different mineralogical assemblage (microphenocrysts of alkali-feldspar, quartz, biotite and apatite) is found in small independent domains, localized within the framework of coarser plagioclase and clinopyroxene laths. These fine-grained evolved domains crystallized in late-stage, evolved melt pockets in the interstitial spaces between earlier crystallized coarser grained crystals. The majority of the studied dolerites are generally evolved tholeiitic basalts and basaltic andesites with low TiO2 concentrations (<2.0 wt.%). Four samples have high TiO2 concentrations (>2.0 wt.%), and are found in the eastern part of the Amazonas Basin. Whole-rock major and trace element and Sr–Nd isotope geochemistry of both low- and high-Ti sills is similar to that of previously published CAMP rocks from the two magma types. Low-Ti sills show enriched isotopic signatures (143Nd/144Nd201Ma 0.51215 to 0.51244; 87Sr/86Sr201Ma 0.70568 to 0.70756), coupled with crustal-like characteristics in the incompatible element patters (e.g. depletion in Nb and Ta). Unaltered high-Ti samples show more depleted isotopic signatures (143Nd/144Nd201Ma 0.51260 to 0.51262; 87Sr/86Sr201Ma 0.70363 to 0.70398). Low-Ti dolerites from both the Amazonas and Solimões basins contain biotite with extremely high Cl concentrations (up to 4.7 wt.%). We show that there is a strong correlation between host-rock lithology and Cl concentrations in biotite from the dolerites, and interpret this to reflect large-scale crustal contamination of the low-Ti magmas by halite-rich evaporites. Our findings support the hypothesis that sill-evaporite interactions increased volatile release during the emplacement of CAMP. This strengthens the case for active involvement of this LIP in the end-Triassic crisis, and suggests that the sub-volcanic part of a LIP can be of major importance in driving climate change and mass extinctions.

A new find of calc-alkaline lamprophyres in Thanewasna area, Western Bastar Craton, India

Lamprophyre dykes within the granitoid and charnockite are reported for the first time from the Western Bastar Craton, Chandrapur district, Maharashtra. It shows porphyritic–panidiomorphic texture under a microscope, characterised by the predominance of biotite phenocrysts with less abundance of amphibole and clinopyroxene microphenocryst. The groundmass is composed more of K-feldspars over plagioclase, amphiboles, clinopyroxene, biotite, chlorite, apatite, sphene and magnetite. The mineral chemistry of biotite and magnesio-hornblende is indicative of minette variety of calc-alkaline lamprophyre (CAL), which is further supported by preliminary major oxides and trace element geochemistry. This unique association of CAL with granitoid provides an opportunity to study the spatio-temporal evolution of the lamprophyric magma in relation to the geodynamic perspective of the Bastar Craton.

Origin of the high-temperature Olserum-Djupedal REE-phosphate mineralisation, SE Sweden: A unique contact metamorphic-hydrothermal system

The Swedish part of the Fennoscandian Shield hosts a variety of rare earth element (REE) deposits, including magmatic to magmatic-hydrothermal types. This paper focuses on the origin of the Olserum-Djupedal REE-phosphate mineralisation located in the sparsely studied Västervik region, SE Sweden. Here, mineralisation occurs in three main areas, Olserum, Djupedal and Bersummen. Primary hydrothermal REE mineralisation formed at high temperatures (about 600 °C), leading to precipitation of monazite-(Ce), xenotime-(Y), fluorapatite and minor (Y,REE,U,Fe)-(Nb,Ta)-oxides in veins and vein zones dominated by biotite, amphibole, magnetite and quartz. The veins are hosted primarily by metasedimentary rocks present close to, or within, the contact aureole of a local 1.8 Ga ferroan alkali feldspar granite pluton, but also occur within in the chemically most primitive granite in the outermost part of that pluton. In the Djupedal area, REE-mineralised metasedimentary bodies are extensively migmatised, with migmatisation post-dating the main stage of mineralisation. In the Olserum and Bersummen areas, the REE-bearing veins are cross-cut by abundant pegmatitic to granitic dykes. The field relationships demonstrate a protracted magmatic evolution of the granitic pluton and a clear spatial and temporal relationship of the REE mineralisation to the granite.The major and trace element chemistry of ore-associated biotite and magnetite support genetic links between all mineralised areas. Biotite mineral chemistry data further demonstrate a distinct chemical trend from metasediment-hosted ore-associated biotite distal to the major contact of the granite to the biotite in the granite-hosted veins. This trend is characterised by a systematic decrease in Mg and Na and a coupled increase in Fe and Ti with proximity to the granite-hosted veins. The halogen compositions of ore-associated biotite indicate elevated contents of HCl and HF in the primary REE mineralising fluid. Calculated log(fHF/fHCl) values in the Olserum area suggest a constant ratio of about −1 at temperatures of 650–550 °C during the evolution of the primary hydrothermal system. In the Djupedal and Bersummen areas, the fluid locally equilibrated at lower log(fHF/fHCl) values down to −2. High Na contents in ore-associated biotite and amphibole, and the abundance of primary ore-associated biotite indicate a K- and Na-rich character of the primary REE mineralising fluid and suggest initial high-temperature K-Na metasomatism. With subsequent cooling of the system, the fluid evolved locally to more Ca-rich compositions as indicated by the presence of the Ca-rich minerals allanite-(Ce) and uvitic tourmaline and by the significant calcic alteration of monazite-(Ce). The later Ca-rich stages were probably coeval with low to medium-high temperature (200–500 °C) Na-Ca metasomatism variably affecting the granite and the wall rocks, producing distinct white quartz-plagioclase rocks.All observations and data lead us to discard the prevailing model that the REE mineralisation in the Olserum-Djupedal district represents assimilated and remobilised former heavy mineral-rich beds. Instead, we propose that the primary REE mineralisation formed by granite-derived fluids enriched in REE and P that were expelled early during the evolution of a local granitic pluton. The REE mineralisation developed primarily in the contact aureole of this granite and represents the product of a high temperature contact metamorphic-hydrothermal mineralising system. The REE mineralisation probably formed synchronously with K-Na and subsequent Na-Ca metasomatism affecting the granite and the wall rocks. The later Na-Ca metasomatic stage is probably related to a regional Na ± Ca metasomatic and associated U ± REE mineralising system operating concurrently with granitic magmatism at c. 1.8 Ga in the Västervik region. This highlights the potential for discovering hitherto unknown REE deposits and for the reappraisal of already known deposits in this part of the Fennoscandian Shield.

The origin of Late Ediacaran post-collisional granites near the Chad Lineament, Saharan Metacraton, South-Central Chad

The southern Saharan Metacraton is one of the least geologically constrained regions in the world as bedrock exposures are rare. To the west of Lake Fitri near the communities of Ngoura and Moyto in south-central Chad there are two granitic inliers that form a series of lenticular to ellipsoidal low laying hills. Very little is known about the Lake Fitri inliers and their regional correlation to larger massifs in Chad is undetermined. The granites yielded weighted-mean zircon 206Pb/238U ages of 554 ± 8 Ma and 546 ± 8 Ma indicating they were emplaced ~45 million years after the cessation of arc-related magmatism and the subsequent collision between the Congo-São Francisco Craton and the Saharan Metacraton. The rocks have distinct groupings of inherited zircons with ages of ~580 Ma and ~635 Ma suggesting they are at least in part derived by recycling of older crustal rocks. The biotite mineral chemistry, whole rock compositions and petrological modeling indicate the granites were derived by melting of crustal lithologies but the whole rock Nd isotopes (εNd(t) = +1.3–+2.9) are characteristic of a mantle source. The contrasting inheritance-rich nature of the granites with a juvenile Nd isotopic signature is likely due to mixing between magmas derived from juvenile (Neoproterozoic) arc-related crust and asthenospheric magmas. Asthenospheric upwelling was probably a response to post-orogenic lithospheric delamination related to fault movement along the Chad Lineament, a possible extension of the Tcholliré-Banyo shear zone that extended to the interior of the Saharan Metacraton. The implications are that lithospheric delamination may not have occurred immediately after collision but rather propagated along a narrow belt that extended well into the central regions of the Saharan Metacraton.

Oxygen fugacity, temperature and pressure estimation from mineral chemistry of the granodiorite porphyry from the Jilongshan Au-Cu deposit and the Baiguoshu prospecting area in SE Hubei Province: A guide for mineral exploration

The Jilongshan Au-Cu deposit is located in the Jiurui district of the Middle-Lower Yangtze River Metallogenic Belt in the south-eastern part of Hubei Province and close to the northern border of Jiangxi Province. This study focuses on mineral chemistry of biotite, amphibole and plagioclase in the ore-related granodiorite porphyry at the Jilongshan deposit and similar porphyry rock from the nearby Baiguoshu prospect, in an attempt to investigate the mineralization potential in the Baiguoshu area. The biotites from the Jilongshan and Baiguoshu granodiorite porphyries all belong to magnesian-biotite but the Jilongshan contains higher Mg. The calculation of Fe3+ and Fe2+ of the biotites indicated that the Jilongshan pluton shows higher oxygen fugacity that is favorable for Cu-Au mineralization, whereas the Baiguoshu pluton shows lower fO2. The Jilongshan amphiboles show higher Mg/(Mg+Fe) and lower Si which mainly belong to magnesiohornblende, whereas the Baiguoshu accommodates mainly the tschermakite. The plagioclases of the Jilongshan and Baiguoshu plutons show no compositional difference and both belong to andesine. The calculated temperatures and pressures by the coexisting amphibole-plagioclase pairs indicate that average crystallization temperature of the Jilongshan pluton is 624–736°C and the pressure is low at 0.5–0.9kbar, in contrast the Baiguoshu pluton shows higher temperature of 724–832°C and higher pressure of 3.2–6.3kbar. These data suggest that the Baiguoshu pluton has less mineralization potential than the Jilongshan pluton, therefore the Baiguoshu prospect shows less economic importance and further exploration should be carried out at depth in the Jilongshan area.

Petrochemistry and zircon U-Pb geochronology of granitic rocks in the Wang Nam Khiao area, Nakhon Ratchasima, Thailand: Implications for petrogenesis and tectonic setting

Carboniferous biotite granite, Late Permian hornblende granite, and Triassic biotite-hornblende granite, all of which belong to the Eastern Granite Belt, expose in the Wang Nam Khiao area, Nakhon Ratchasima, northeastern Thailand. The Carboniferous biotite granite is dominated by quartz, K-feldspar, plagioclase, and biotite. The Late Permian hornblende granite contains dominant assemblages of plagioclase, quartz, K-feldspar, hornblende, and minor amount of biotite, while the Triassic biotite-hornblende granite consists of quartz, plagioclase, K-feldspar with small amounts of biotite, and hornblende. The REE patterns with steep decrease from light to heavy REE together with the LILE (e.g. K, Sr) enrichment and depletion of some particular HFSE (e.g. Nb, Ti) indicate low degree of partial melting. Mineral chemistry of biotite and hornblende in the granites reflects crystallization from hydrous calc-alkaline arc-derived magmas possibly formed by subduction. Amphibole-plagioclase thermometry and Al-in-hornblende barometry indicate that the Late Permian hornblende granite and the Triassic biotite-hornblende granite may have equilibrated at 3.0–5.8kbar/700–820°C and 2.0–3.2kbar/600–750 °C, respectively, in the middle-upper crust (about 10–15km depth). Zircon U-Pb geochronology of the Carboniferous biotite granite, Late Permian hornblende granite and Triassic biotite-hornblende granite yielded intrusion ages of 314.6–284.9Ma, 253.4Ma, and 237.8Ma, respectively, which implies multiple episodes of arc-magmatism formed by Palaeo-Tethys subduction beneath Indochina Terrane during Late Carboniferous/Early Permian, Late Permian and Middle Triassic.

Geochemistry and geochronology of ore-bearing and barren intrusions in the Luanchuan ore fields of East Qinling metallogenic belt, China: Diverse tectonic evolution and implications for mineral exploration

The Luanchuan ore fields form part of the East Qinling metallogenic belt in central China. In this study, we compare two ore-bearing intrusions, the Shibaogou granitic pluton (SBG) and the Zhongyuku granitic pluton (ZYK), with the ore-barren Laojunshan intrusion (LJS) from the Luanchuan ore field. Geochemically, all the three intrusions are characterized by high-Si, high-K, and alkalis, together with moderate-ASI, exhibiting I-type granite features. The rocks, especially the ore-related plutons also show enrichment in LREEs. Mineral chemistry of biotite from the intrusions exhibits similar features of high Si and Mg, and low Al and Fe. Zircon grains from the ZYK intrusion yielded a U-Pb age of 149.6±2.4Ma. The zircon grains show εHf (t) values and two stage model ages (TDM2) in the range of −16.8 to −19.7 and 1998–2156Ma respectively. The biotite composition and Hf isotopic data indicate that the magma was derived by re-melting of deep crustal material with minor input of mantle components. We evaluate the results to understand the physico-chemical conditions, petrogenesis, and tectonic setting, and their implications for mineral exploration. The ore-bearing plutons show wide ranges of temperature and oxygen fugacity, favoring Mo-W mineralization. In addition, estimates on pressure and depth of emplacement suggest that lower solidification pressure in a decompressional setting contributed to the evolution of magmatic hydrothermal deposits. Our data suggest that the ZYK has the highest potential for Mo-W mineralization. The ore-bearing plutons of ZYK and SBG were formed in a transitional tectonic setting from compression to extension, with the large-scale metallogeny triggered by slab melts at ca. 145Ma. However, the ore-barren LJS batholith formed in an extension-related geodynamic setting at ∼115Ma. Our study shows that different tectonic settings and consequent physico-chemical conditions dictated the ore potential of the intrusions in the Luanchuan ore district.