Granitic Intrusions Research Articles

Magmatic to hydrothermal evolution of the Gaogangshan Mo deposit, NE China: Mineralogical insights from quartz

Integrated study on cathodoluminescence (CL) textures and compositions of quartz is proven to be an effective way to reconstruct the ore-forming conditions and processes of porphyry system under subduction tectonic setting. However, little relevant research has been conducted on collision-type porphyry deposits. The Gaogangshan deposit in the northern Lesser Xing'an Range, NE China, consists of typical collision-type porphyry Mo mineralization related to Permo-Triassic granitic intrusions. Ore-forming process is recorded by multiple generations of quartz, including pre-ore stage quartz with unidirectional solidification texture (UST), early ore-stage quartz-molybdenite veins with K-feldspar alteration halos (Q1), late ore-stage quartz-sulfides veins with sericite alteration (Q2), and post-ore stage quartz veins (Q3) associated with calcite and fluorite. Cathodoluminescent textures, trace elements and fluid inclusions in quartz reveal physicochemical conditions, evolution of ore fluids and the Mo mineralization process. The UST quartz and Q1 veins are dominated by CL-bright homogenous and/or granular mosaic textures, containing more Ti concentrations (average = 35–42 ppm) than Q2 and Q3 veins. The molybdenite-bearing Q2 veins are dominated by CL-gray granular and zonal textures, displaying less CL intensity and lower Ti concentrations (average = 16 ppm) than early-stage quartz. The Q3 veins have the lowest CL-intensity and the lowest Ti concentrations (average = 2.5 ppm) among all quartz types. Three types of inclusions are identified in above quartz samples, including liquid–vapor aqueous inclusions, CO2-bearing liquid–vapor aqueous inclusions and halite-bearing multiphase aqueous inclusions. The ore-forming fluids in ore-stage Q1 and Q2 veins are dominated by large salinity variation (2.3–38.9 wt% NaCl equiv.), CO2-bearing (4.2–8.9 mol%) two-phase aqueous inclusions with vapor volumetric proportions of 30–65%. Intersections of fluid inclusion isochores with Ti-in-quartz isopleths yield quartz formation conditions of ∼2.2 kbar at ∼640℃ for UST quartz, ∼1.25 kbar at ∼510℃ for Q1, ∼1.0 kbar at ∼440℃ for Q2, and ∼0.37 kbar at ∼220℃ for Q3. The Gaogangshan porphyry Mo deposit formed at depths of 3.8 to 4.7 km.

Mineralogy and in situ S and Pb isotope characteristics of ore minerals from polymetallic mineralization in the Gierczyn-Przecznica area, SW Poland

Chlorite-mica-quartz schist in the Gierczyn-Przecznica area in SW Poland contains polymetallic ores which were the source of tin and cobalt in the past. This mineralogical study revealed the presence of silver-bearing minerals including members of the tetrahedrite (Ag <3 apfu) and freibergite series (3 < Ag < 8 apfu), galena (0.26–1.48 wt.% Ag), and a phase with the chemical composition of Te-rich canfieldite Ag8Sn(S,Te)6. In Przecznica Sn-sulphides are represented by stannite while cobaltite is the most abundant host for cobalt, followed by Co-bearing arsenopyrite. Glaucodot, ullmannite and members of the löllingite-rammelsbergite solid-solution series (Fe,Ni,Co)As2 also contain cobalt but are scarce in the samples. An exposure in the “Psi Grzbiet” area is characterized by the presence of Ag, Ni, Sb and Te minerals accompanied by very small amounts of As-bearing phases (represented by arsenopyrite) while the mineralogical composition in the Przecznica area is characterized by an abundance of As phases and a lack of Sb minerals. Sulphur isotopes of sulphides from Przecznica are heavier than in most deposits related to the Karkonosze Granite intrusion, while their Pb isotope signature in galena suggests an Early Paleozoic pre-Variscan affinity rather than a Variscan one.

Mineralizations of Nb–Ta–Li and rare-earth elements in the Jiabusi rare-metal deposit, Inner Mongolia, China: Constraints from monazite, cassiterite, and bastnasite U–Pb geochronology and geochemistry

The Jiabusi Nb–Ta–Li deposit is a medium-sized rare-metal deposit discovered in central Inner Mongolia in recent years, and it is accompanied by Rb-Cs-REEs mineralization. Its magmatic and metallogenetic ages, magmatic source attributes, and mechanisms of magmatic evolution and related mineralization are not known. To identify these characteristics, with multi-stage granitic intrusions of the Jiabusi deposit as study objects, investigations relating to petrography, lithogeochemistry, monazite–cassiterite–hydrothermal bastnasite LA-ICP-MS U–Pb geochronology, and Nd isotopes were systematically conducted. The following results were obtained: The LA-ICP-MS monazite U–Pb ages of the metallogenetic Li-mica albite granite and granitic pegmatite are 148±7 and 141±2 Ma and 141±3, 137±2, 136±3, and 132±2 Ma, respectively; the cassiterite U–Pb ages of the Ta–Rb ore bodies are 148±2 and 146±1 Ma; and the bastnasite U–Pb age of the magmatic hydrothermal fluid is 116±1 Ma. These ages indicate that there were two episodes of granitic magmatism and related rare (rare-earth) metal mineralization in the Jiabusi area during the Yanshanian period (Jurassic–Cretaceous). Geochemical analysis results reveal that the barren biotite granite is characterized by high SiO2 (75.89 wt%) and high alkali (Na2O + K2O = 8.48 wt%) and a relatively high FeOT/(MgO + FeOT) value (0.92) and a relatively high Zr + Nb + Ce + Y content (393×10−6), whereas Al2O3 (12.35 wt%), CaO (0.51 wt%), and MgO (0.13 wt%) contents are all relatively low. These results indicate that the biotite granite is A-type granite, with characteristics similar to those of A1-type granite. The Li-mica albite granite is characterized by high F (0.95%-2.76%) and strongly peraluminous nature (A/CNK = 1.26–2.34). Meanwhile, it is strongly enriched in Cs, Li, Rb, Nb, and Ta but extremely depleted in Ba, Sr, P, Ti, Zr, and light REEs, with quite a strong negative Eu anomaly (δEu <0.01), an evident lanthanide tetrad effect (TE1,3 = 1.36–1.44), and Zr/Hf (3.0–4.0) and Nb/Ta (0.5–1.0) ratios deviating from those of a normal magmatic system. X-ray fluorescence and electron probe microanalysis surface scanning imaging analysis revealed the activity of F-REE-rich hydrothermal fluid and related REE mineralization in the uppermost part of altered granites. These features indicate that the metallogenetic ore bodies underwent higher degrees of magmatic fractionation and F-rich fluid–present melt–hydrothermal interaction. The Li-mica albite granite and multi-stage granitic pegmatite have consistent Nd isotope characteristics (εNd(t) = −3.4 to −3.9) and relatively concentrated two-stage model ages (TDM,2 = 1174–1247 Ma), suggesting that they are quite likely syngeneic multi-stage products with different degrees of fractional crystallization. Through comprehensive analysis of the results in this study and from previous research, the Yanshanian (Jurassic–Cretaceous) granite in the Jiabusi area is inferred to quite likely have originated from the partial melting of the ancient lower crust caused by lithospheric thinning and asthenospheric upwelling along the northern margin of the North China Craton, and it is revealed that a large amount of juvenile crustal materials had contributed to this process.

Apatite records metamorphic and hydrothermal fluid evolution at the large Shuangqishan orogenic gold deposit, SE China

Orogenic gold deposits are currently the world’s major source of Au, but uncertainty exists in the timing of mineralization relative to the ages of host rocks, metamorphism, and magmatism. Consequently, the origin and detailed evolution of ore-forming fluids have long been elusive. Apatite occurs widespread in various types of mineral deposits and can provide valuable information on ore genesis. Here, we present textural, high-precision in situ U-Pb geochronological, trace elements, and Sr isotope data for metamorphic and hydrothermal apatite in the Shuangqishan gold deposit in southeastern China. These data, together with U-Pb dates of metavolcanic host rocks, granitic and mafic intrusive rocks, allow us to precisely constrain the timing of mineralization and reconstruct the history of the ore-forming fluids there. The apatite crystals within metamorphic and auriferous quartz veins can be grouped into three generations according to cathodoluminescence imaging and trace element concentrations: Ap1 precipitated in the pre-mineralization metamorphic stage, whereas Ap2 and Ap3 formed in the auriferous hydrothermal stage. Metamorphic Ap1 displays a negative Eu anomaly, indicating a predominance of Eu2+ and crystallization under relatively reduced conditions. On the other hand, syn-gold hydrothermal Ap2 and Ap3 have marked positive Eu anomalies. Radiometric ages for metamorphic Ap1 are at ca. 461 Ma, whereas hydrothermal Ap2 and xenotime from auriferous quartz gave U-Pb ages of 425 ± 15 Ma and 416 ± 15 Ma, interpreted as the time of gold mineralization. Emplacement ages determined by U-Pb zircon data are 439 ± 2 Ma for granitic intrusion and 427 ± 2 Ma for a mafic dike in the mining district. Mineralization, therefore, postdates the metamorphism of local host rocks and granitic magmatism by ∼35 ± 24 m.y. and ∼14 ± 17 m.y., respectively. The synchronism of gold genesis and mafic magmatism provides additional evidence for a mantle derivation of the ore-forming fluids. The highly radiogenic 87Sr/86Sr ratios obtained for Ap1 (0.7178−0.7302) are consistent with its precipitation from a metamorphic fluid. Higher Sr concentrations (Ap2 = 1228−2884 ppm, Ap3 = 2325−3169 ppm) and positive Eu anomalies (Eu/Eu*: Ap2 = 1.03−2.84, Ap3 = 2.00−4.30) but lower and variable 87Sr/86Sr ratios in hydrothermal Ap2 (0.7100−0.7165) and Ap3 (0.7086−0.7116) are mainly ascribed to extensive fluid-wall rock exchange of Sr during mineralization. It is therefore suggested that fluid-rock reaction played a vital role in the observed positive Eu anomalies of hydrothermal apatite. Our study highlights the usefulness of apatite as a novel and robust geochronological, geochemical, and isotopic indicator of complex mineralization processes in hydrothermal gold deposits.

Reactivation of metal-fertilized lower continental crust: Origin of intrusion-related Asiha gold deposit in Eastern Kunlun orogenic Belt, China

Gold deposits in the East Kunlun Orogen Belt (EKOB) are generally identified as orogenic gold deposits. However, recently, a new magmatic-hydrothermal model has been proposed to explain the genesis of these deposits that show intimate spatial and temporal relationships with abundant Triassic granitic intrusions, implying an intrusion-related gold system. The petrogenesis of these granites and their relation to gold mineralization are still unclear, owing to the lack of direct evidence of the connection between gold mineralization and granitic rocks. The gold-bearing Asiha intrusions (GBAI) from the Gouli area of the eastern segment of the EKOB are not only contemporary and located with mineralization but also have abnormally high gold content and sulfide accessory mineral. The GBAI are mainly composed of quartz diorite and granite porphyry. An integrated investigation involving mineral composition, zircon U-Pb dating and Hf isotopes, whole-rock elemental (including Au) and Sr-Nd-Pb isotopic geochemistry of the GBAI, as well as the in-situ Pb isotopic geochemistry of pyrites from the Asiha gold deposit, was conducted to constrain magmatic sources and petrogenesis of the GBAI, and gold mineralization mechanism. Zircon U-Pb dating reveals that the Asiha quartz diorite was formed at 230 Ma. The mineralized granite porphyries with high SiO2 contents (71.7–74.3 wt%) are peraluminous high-K calc-alkalic rocks, while the unmineralized quartz diorite with low SiO2 contents (58.1–60.0 wt%) are metaluminous high-K calc-alkalic rocks. Both rocks are potassic, strongly enriched in LILEs and LREEs with high LILE/HFSE ratios, depleted in Nb, Ta, Ba and Sr, and have weakly negative Eu anomalies and high zircon saturation temperature. Petrographic and geochemical features suggest that the quartz diorite is typical of I-type, while the granite porphyry is highly fractionated I-type granite. Their variable concentrations of major and trace elements are due to fractional crystallization of plagioclase, hornblende, and accessory minerals (apatite, zircon and monazite). Notably, the Asiha intrusions all contain high Au contents (Au = 0.02–0.05 ppm) compared to the primitive mantle estimated from chondrite values (0.88 ppb), indicating the existence of gold enrichment. All these granites are characterized by limited ranges of initial 87Sr/86Sr (0.7087–0.7133), εNd(t) (−6.0 to −5.0), 206Pb/204Pb (18.1–19.0),207Pb/204Pb (15.6–15.7), and 208Pb/204Pb (38.2–38.9), as well as zircon εHf(t) with values of −4.4 to −1.7. Their lead isotopes are consistent with that of pyrite in the ores (206Pb/204Pb = 18.41–18.45, 207Pb/204Pb = 15.61–15.65, 208Pb/204Pb = 38.47–38.56). Based on our results, we suggest that the GBAI were originally generated by partially melting of a previously Au-fertilized juvenile lower crust, which had been formed by metasomatized SCLM-derived alkaline basaltic underplating, and underwent AFC processes during emplacement. Subsequently, the post-magmatic fluids concentrated and precipitated Au to form the Au-bearing quartz veins.

Insights into the evolution of the southeastern Dom Feliciano Belt and its connection to the Pan-African Orogeny based on new U-Pb and Lu-Hf zircon data

The Neoproterozoic supracrustal units of the Dom Feliciano Belt in southern Brazil and eastern Uruguay provide a record of the tectonic evolution of the Brasiliano/Pan-African cycle in terms of sedimentation, deformation, and metamorphism during the western Gondwana supercontinent assembly. From the northern Punta del Este Terrane (Jaguarão Domain) and neighboring Herval Complex were acquired new LA-ICPMS U-Pb and Lu-Hf zircon data from significant samples of metasedimentary rocks and intrusive granites. The central units of the domain are the Arroio Telho and Arroio Grande metasedimentary complexes, which have detrital zircon data ranging in age from 3.2 to 0.7 Ga, with prominent age peaks at 2.2–1.7 Ga, 1.5–1.0 Ga, and 1.0–0.7 Ga. The Herval Complex samples revealed a similar provenance of detrital zircon ages, with two main intervals of 1.5–1.1 Ga and 1.0–0.7 Ga, and also minor Paleoproterozoic (2.0–1.7 Ga) and Archean (2.8–2.4 Ga) ages. The maximum depositional age of the supracrustal complexes is constrained to age populations between 700 and 650 Ma. The mylonitic intrusive peraluminous granites yielded crystallization ages of ca. ∼570 Ma. The Neoproterozoic metamorphic zircon overgrowths range from 680 to 570 Ma. The Lu-Hf data from the meso- to Paleoproterozoic zircons have εHf(t) values ranging from −10 to +10, with the dominance of slightly positive results, and Hf(t) model ages from Paleoproterozoic to Archean. The εHf(t) values in Neoproterozoic zircons are dominantly negative (−15 to +5) with meso- to Paleoproterozoic Hf(t) model ages. These results demonstrate that sedimentary deposition ceased and underwent metamorphism during the development of the Cryogenian/Ediacaran arc-related magmatism of the Dom Feliciano belt. Given the scarcity of Mesoproterozoic rocks in the Mantiqueira Province and nearby cratonic areas, the obtained data suggest that these detrital populations originated in southwestern African rocks. The Congo/Kalahari cratons (Africa) are the most likely source area for Paleoproterozoic and Archean detrital zircons. The geological context and isotopic results of the investigated supracrustal complexes point to a prior extensional tectonic setting during the Tonian (∼800 Ma), with regional deformation and metamorphism linked with the Dom Feliciano Belt accretionary and collisional stages (660–570 Ma).

Petrogenesis and Tectonic Implications of the Cryogenian I-Type Granodiorites from Gabgaba Terrane (NE Sudan)

The widely distributed granitic intrusions in the Nubian Shield can provide comprehensive data for understanding its crustal evolution. We present new bulk-rock geochemistry and isotopic (zircon U-Pb and Lu-Hf) data from the Haweit granodiorites in the Gabgaba Terrane (NE Sudan). The dated zircons presented a 206Pb/238U Concordia age of 718.5 ± 2.2 Ma, indicating that they crystallized during the Cryogenian. The granodiorites contain both biotite and amphibole as the main mafic constituents. The samples exhibit metaluminous (A/CNK = 0.84–0.94) and calc-alkaline signatures. Their mineralogical composition and remarkable low P2O5, Zr, Ce, and Nb concentrations confirm that they belong to I-type granites. They exhibit subduction-related magma geochemical characters such as enrichment in LILEs and LREEs and depletion in HFSEs and HREEs, with a low (La/Yb)N ratio (3.0–5.9) and apparent negative Nb anomaly. The positive Hf(t) values (+7.34 to +11.21) and young crustal model age (TDMC = 734–985 Ma) indicates a juvenile composition of the granodiorites. The data suggest that the Haweit granodiorites may have formed from partially melting a juvenile low-K mafic source. During subduction, the ascending asthenosphere melts might heat and partially melt the pre-existing lower crust mafic materials to generate the Haweit granodiorites in the middle segment of the Nubian Shield.

Late Paleozoic and early Mesozoic granitoids in the northwestern Bureya Massif, Central Asian Orogenic Belt: Timing and tectonic significance

ABSTRACT The Bureya Massif is an important massif in the eastern Central Asian Orogenic Belt (CAOB), and contains voluminous late Palaeozoic–early Mesozoic granitoids that are ideal for investigating the tectonic evolution of the eastern CAOB. Here we report whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for several granite intrusions in the northwestern Bureya Massif, with the aim of constraining the timing of magmatism and late Palaeozoic–early Mesozoic tectonism in the eastern CAOB. The zircon U–Pb dating results indicate that granitoids with ages of 306 ± 4, 243 ± 3, 191 ± 2, and 189 ± 4 Ma occur in the Bureya Massif. These, and previously published data, reveal that at least four stages of magmatism occurred in the northwestern part of the massif: ~306 Ma, ~243 Ma, 219–212 Ma, and ~201-189 Ma. The late Carboniferous (306 ± 4 Ma) gneissic monzogranites have an S and A-type granite affinity, and were derived with significant contribution of the mantle component in a syn- to post-collisional setting between the Bureya and Xing’an massifs. The Middle Triassic (243 ± 3 Ma) porphyritic I-type monzogranites, Early Jurassic (191 ± 2 Ma) porphyritic S-type syenogranites, and Early Jurassic (189 ± 4 Ma) gneissic S-type monzogranites have a supra-subduction zone geochemical signature. These granitoids formed in an active continental margin setting associated with southward subduction of the Mongol–Okhotsk oceanic plate.

A newly recorded Cryogenian-Ediacaran Dokhan Volcanic caldera with resurgent uplift in the Arabian-Nubian Shield, southwest Safaga, Egypt

The late Neoproterozoic Dokhan Volcanics (DV) of the Egyptian Eastern Desert (northern Arabian-Nubian Shield), were investigated at Gebel Nuqara, near the boundary between the Northern and Central Eastern Deserts. In particular, the nature of the peculiar circular and annular regional structures at Nuqara, were targeted for study. This included exploring the relationships of DV and intrusive units to each other and to regional dikes and faults. The central part of the Nuqara DV exposures consists of two volcanic units: 1) “Older DV” (intermediate varieties, dominantly andesites; 659 ± 16 Ma), with associated arc granitoids (663.2 ± 8.4 Ma), followed by andesite dikes (636.9 ± 7.2 Ma); and 2) “Younger DV” (acidic varieties; 602.3 ± 4.4 Ma for rhyolites, and 589.4 ± 6.1 Ma for rhyolite porphyry). This central area of DV units is enclosed within an annular intrusion of granite. The geochemical data for the Nuqara DV reveal intermediate low-silica adakitic (basaltic-andesite and andesite) and acidic high-silica adakitic (rhyolite and rhyolite porphyry). Both adakite groups share a common geochemical trend, and show evidence for magma diversification via fractional crystallization. The Nuqara DV is identified as a caldera sequence, with resurgent uplift, based on a positive comparison of the volcanic morphology, lithology, structure and mechanism of DV eruptions in the study area with those of other resurgent calderas. The geodynamic setting, volcanic architecture, and geochemistry of the DV, as well as its in-situ zircon LA–ICP–MS estimated ages, allow recognition of a series of eruptive stages, leading to collapse to form the Nuqara caldera, followed by resurgent uplift of the caldera floor during intrusion of rhyolite porphyry domes. The resurgent caldera model assigns a greater significance for the rhyolite porphyry as the exposed top of a sub-volcanic magma chamber. Resurgence is viewed as resulting from increased pressure or volume changes in the magma reservoir. A consequence of resurgence was uplift and erosion of the previous collapse-related topography.

Generation of the Early Cretaceous granitoid in the Dazeshan region, Jiaodong Peninsula: Implications for the crustal reworking in the North China Craton

Lower crust-derived granitic rocks provide constraints on the crustal reworking process and consequently give hints on the destruction mechanism of the cratons. The North China Craton (NCC) underwent extensive crustal melting in the Mesozoic. This study investigated granitic intrusions in the Dazeshan region of the Jiaodong Peninsula. Whole-rock major and trace element analyses and zircon U-Pb ages coupled with Hf isotopes were used to reveal the crustal reworking processes. Zircons separated from the quartz porphyry, Linglong granite, rhyolite porphyry, and biotite granite showed weighted mean 206Pb-238U ages of 119.2 ± 1.0 Ma, 140.2 ± 1.0 Ma, 120.6 ± 0.5 Ma, and 119.9 ± 0.7 Ma, respectively. The quartz porphyry, rhyolite porphyry, and biotite granite had high silica contents (SiO2 = 74–77 wt.%) but low MgO, Co, and Ni concentrations. The calculated εHf(t) values for the rhyolite porphyry and the biotite granite ranged from −18.3 to −20.0 and −17.8 to −20.2, respectively. These geochemical features imply ancient crust sources. The quartz porphyry showed distinct primitive mantle-normalized rare earth element (REE) patterns and was characterized by lower ΣREE content and lack of pronounced negative Eu anomalies. Whole-rock and zircon Dy/Yb ratios showed no correlation with whole-rock Rb/Sr ratios and zircon Hf contents, reflecting limited effects of crystal fractionation. The Ba/La ratios were also high (&amp;gt;150), but the Sr/Y and La/Yb ratios were low (Sr/Y &amp;lt; 50; La/Yb &amp;lt; 15). These features likely indicate that the quartz porphyry was generated by water-fluxed melting without differentiation. The rhyolite porphyry and biotite granite shared many geochemical similarities, denoting a unified source. The high La/Yb (&amp;gt;30) but low Sr/Y (&amp;lt;20) ratios and apparent negative Eu anomalies indicated plagioclase fractionation. Decreased zircon Dy/Yb with increasing Hf concentrations reflected noticeable amphibole fractionation. These two suites had fairly low Ba/La ratios. These data together point toward an identical source: dehydration melting of a relatively thickened crust. These melts experienced crystal fractionation after extraction. We propose that the intrusions were generated by the underplating of water-rich mafic magma, which provided both fluid and heat and finally induced two kinds of melting.

Origin of the Amensif Zn-Cu (Pb-Ag-Au) distal skarn deposit (Western High Atlas, Morocco): Constraints from C-O-S isotopes

The Amensif Zn-Cu (Pb-Ag-Au) ore deposit is located in the northern part of the western High Atlas. The deposit hosts 1 million tons (Mt) of Zn-Cu-Pb metal reserves at 3% Zn, 2% Cu, and 1% Pb. The lenticular sulfide ores are structurally controlled open-space fillings (fractures, faults) in the Lower Cambrian carbonates. The mineralogical paragenetic sequence consists of andradite-quartz-epidote-dolomite-calcite-sphalerite-chalcopyrite-pyrite-galena with subordinate amounts of barite. The pre-ore stage and ore stage I dolomite samples have δ13CPDB and δ18OSMOW values in the range of −10.2 to −2.6‰ and 17.4–26.8‰, respectively. The lower δ18O value of these dolomites suggests oxygen isotope exchange between the ore-forming fluids and the carbonate host rock whereas negative δ13CPDB values reveal the interaction between these hydrothermal fluids and black shales. The δ34S values of sulfides ore (sphalerite, chalcopyrite, and pyrite) are high, ranging from 6.4 to 14.4‰. These S isotopic values reveal that sulfur derived from the mixture of magmatic sulfur and lower Cambrian carbonate-derived sulfur in almost equal proportions. Sulfide ores precipitated from the mixing between the magmatic-hydrothermal fluids exsolved from a hidden magma or the nearby Azegour granite of Permian age and an external cooler fluid of unknown origin. Fluid-rock interactions with the carbonate host rock contributed in the precipitation of the ore. Mineralogical and geological features allow us to ascribe the Amensif Zn-Cu (Pb-Ag-Au) polymetallic ore as a distal skarn system which is spatially associated with the lower Permian granite intrusion.

Granite Pluton at the Panasqueira Tungsten Deposit, Portugal: Genetic Implications as Revealed from New Geochemical Data

Core samples recovered from exploration boreholes and granite/greisen outcrops at the Panasqueira world-class tungsten deposit in central Portugal were subjected to chemical analyses and petrographic studies. We present a geochemical dataset and the trace element compositions of quartz and micas from a large part of the unexposed Panasqueira granitic pluton. Our data suggest that the hidden granite body is more complicated than previously believed. It consists of a flat cupola of porphyritic granite with only traces of mineralization at Rio and a steep stock of greisenized leucogranite surrounded by a swarm of flat quartz–muscovite veins rich in wolframite between Barroca Grande and Panasqueira. The contents of W (Sn, Nb, Ta) in muscovite markedly drop at a transition from the unmineralized greisen body to quartz veins. The W deposit was formed in three principal stages: (1) intrusion of porphyritic two-mica granite accompanied with local near-contact greisenization and uncommon quartz–wolframite veinlets; (2) intrusion of a more strongly fractionated leucogranite and formation of the cupola and apophyses; (3) circulation of hydrothermal fluids from deeper parts of the granite body into the cupola, greisenization, hydraulic fracturing and opening of flat structures in and outside the cupola and formation of ore veins.

Герхардтит и ликазит из родингитов Баженовского офиолитового комплекса (Средний Урал)

The results of studying nitrate mineralization in rodingites of the Bazhenovsk ophiolite complex located on the eastern slope of the Middle Urals are presented. Rodingites are metasomatic rocks of garnet-pyroxene composition that replace gabbroid and diorite dikes that cut across the Bazhenovsk ultramafic massif. Some apogabber and apodiorite rodingites have in turn been altered by hydrothermal fluids, probably generated by an underlying granite intrusion. Chalcocite is the main sulfide mineral in hydrothermally altered rodingites. It forms clusters of irregular shape, up to 1 cm in size. Visually, chalcocite is often covered with greenish and bluish films, which, upon detailed study, turned out to be an aggregate of chrysocolla, dolerophanite, langite, connellite, and mitscherlichite with the presence of nitrate mineralization. Copper nitrates are represented by gerhardtite and likasite, the latter mineral apparently developing after the former. For both minerals, the data of X-ray electron probe analysis and IR spectroscopy are given, and the morphology of their aggregates and individuals is also shown. In addition, X-ray diffraction data for gerhardtite are given, since it has a dimorphic analogue – rouaite. The formation of nitrate mineralization, in our opinion, is of natural origin, since mantle rocks are a source of nitrogen.

U-Pb detrital zircon geochronology of the Middle to Upper Jurassic strata in the Surat Basin: New insights into provenance, paleogeography, and source-sink processes in eastern Australia

New U-Pb detrital zircon ages from sandstones have been determined for the Walloon Coal Measures-Springbok Sandstone section of the Surat Basin. In the late Jurassic Surat Basin, there is a shift from relatively thick coal measures – the Walloon Coal Measures – consisting of laterally discontinuous coal-seam horizons intercalated with lithic sandstones and mudstones to an overlying coal-poor sandstone-dominated unit – the Springbok Sandstone – that is more laterally continuous. Across the basin, the contact between the two units varies from transitional to unconformable, and the sandstone becomes less lithic. The nature of the contact and the compositional variability of the sandstone across the basin have implications for predicting communication between gas production fields and potential aquifers in the Walloon Coal Measures and overlying Springbok Sandstone. This study tests whether detrital zircon age (LA-ICP-MS) populations from sandstones within these two units can identify provenance shifts and potential tectonic drivers for basin infill at this time. Detrital zircon ages of both units, informed by paleocurrent measurements showing a southerly flowing depositional system, suggest sediment was sourced from three distinct terranes: the Thomson Orogen in northeastern Queensland; Permian-Triassic granitic intrusions emplaced within the northeast New England Orogen during the Hunter-Bowen Orogeny accretion event; and an inferred but now eroded Jurassic magmatic-arc located along the eastern margin of Gondwana. Two major source-delivery systems, named here Western and Eastern Source systems, are recognized by distinct detrital zircon age populations in both formations in the northern Surat Basin. The Western Source of the Walloon Coal Measures delivered substantial Jurassic age zircons, with minor Pre-Cambrian input; the Eastern Source delivered substantial reworked Precambrian and lesser Jurassic zircons. In contrast, the Western Source of the Springbok Sandstone delivered substantial Jurassic and distinct Triassic zircons dated between ca 234 Ma and 224 Ma in the north-west, while the Eastern Source delivered more pronounced Pre-Cambrian input, with minor Jurassic and absent or minor age zircons in the northeast. Maximum depositional ages for the Springbok Sandstone are approximately 2 Ma younger in the northwestern than in the northeastern Surat Basin. The westward younging could be due to migration of the system and/or differential movement on the bounding faults.

How greisenization could trigger the formation of large vein-and-greisen Sn-W deposits: A numerical investigation applied to the Panasqueira deposit

The formation of large tin-tungsten (Sn-W) deposits around granitic intrusions requires the circulation of large volumes of fluids within permeable structures. Half of the world’s tungsten production originates from highly mineralized veins above granitic intrusions and from the altered part of the granite (the greisen), whose formation results from intense fluid-rock interactions. During greisenization processes, mineral reactions involve a decrease in the rock volume and thus an increase in porosity and permeability. To understand the complex fluid-rock interactions leading to the formation of large Sn-W ore deposits, we conducted numerical modeling accounting for magmatic fluid production and realistic permeability changes due to granite alteration and overpressure in the hosting rocks. The water/rock ratio is computed to constrain the rate of greisenization and therefore the porosity and permeability evolution laws. Four model results are presented: with and without fluid production exsolved from the granitic magma, and with and without dynamic reaction-enhanced permeability. The formation of greisen is reproduced, and greisen thickness reaches 200 m for the more sophisticated model. The interplay between greisenization and fluid production creates zones of overpressure above the granite that could localize the permeable structures such as the veins swarm observed at Panasqueira. Dynamic permeability promotes high fluid velocity and intense fluid-rock exchanges that could result in the formation of large ore deposits by enhancing mass transfer within and above granitic intrusions.

Strategies for Targeting in Undercover Terrains: Modeling Multi-Source Data in Apuí Region, SW Amazon Craton, Brazil

Exploring covered terrains is a challenge that requires the integration of multiple sources of knowledge, particularly in the initial stages of mineral exploration. The Apuí region, located in the Southwestern Amazon Craton, has a small and constant gold production, despite the deep cover and limited geological knowledge. The gold is mainly hosted in quartz veins and breccias that cut Paleoproterozoic volcano-sedimentary sequences. The occurrences have similar characteristics to magmatic–hydrothermal deposits, such as a lack of regional metamorphism and intense hydrothermalization. We undertook a multi-source prospective investigation on different scales using 2D and 3D techniques to translate the footprints of the mineral system into mappable criteria. Gold prospectivity maps for the Juma District and Guida Target were produced by integrating geological, geochemical, and geophysical datasets in knowledge-driven fuzzy systems. Regional airborne magnetization vector inversion (MVI) models were utilized. The correlation between the drill cores and the magnetic susceptibility models highlighted a potential surface for gold mineralization associated with the boundary between a granitic intrusion and volcano-sedimentary rocks. The prospectivity maps reduced the search area, and the regional susceptibility models allowed for the reconnaissance of structures and bodies that may be related to gold mineralization at depth. The results present new strategies for increasing discovery performance in the Southern Amazon Craton under cover.

Quantitative record of the Neoarchean water cycle from a 2.67 Ga magmatic-hydrothermal system, Fennoscandian Shield

Given the scarcity of reliable paleoclimate record, the surface temperatures of the first half of Earth’s history remain poorly constrained. Here we show how the climate-sensitive δ18O value of surface precipitation recorded in Archean igneous and hydrothermal formations can help to resolve the state of early Earth climate. The Keivy complex, Kola craton (Fennoscandian Shield), formed via the intrusion of granitic and mafic magmas in the shallow crust at 2.67 Ga, where circulation of meteoric water created a distinct archive of the contemporaneous water cycle. Using whole rock data, mineral separates, and in situ zircon δ18O measurements, we disentangle the reaction mechanisms between the shallow magma and local precipitation. Syn-emplacement hydrothermal alteration produced near-contact lithologies with δ18O values as low as –8‰ recorded in amphiboles, while igneous zircons from granites crystallized from melts with δ18O from +1‰ to +4.5‰. High-precision U-Pb geochronology constrains the granite intrusion at 2673.5 ± 0.3 Ma. Using the Δ17O approach, these rocks reveal that the precipitation had a δ18O value 18‰ lower than the hydrosphere, providing one of the earliest quantitative records of continental precipitation generally compatible with a cold climate at high latitudes.

Quantitative record of the Neoarchean water cycle from a 2.67 Ga magmatic-hydrothermal system, Fennoscandian Shield

Abstract Given the scarcity of reliable paleoclimate record, the surface temperatures of the first half of Earth’s history remain poorly constrained. Here we show how the climate-sensitive δ18O value of surface precipitation recorded in Archean igneous and hydrothermal formations can help to resolve the state of early Earth climate. The Keivy complex, Kola craton (Fennoscandian Shield), formed via the intrusion of granitic and mafic magmas in the shallow crust at 2.67 Ga, where circulation of meteoric water created a distinct archive of the contemporaneous water cycle. Using whole rock data, mineral separates, and in situ zircon δ18O measurements, we disentangle the reaction mechanisms between the shallow magma and local precipitation. Syn-emplacement hydrothermal alteration produced near-contact lithologies with δ18O values as low as −8‰ recorded in amphiboles, while igneous zircons from granites crystallized from melts with δ18O from +1‰ to +4.5‰. High-precision U-Pb geochronology constrains the granite intrusion at 2673.5 ± 0.3 Ma. Using the Δ17O approach, these rocks reveal that the precipitation had a δ18O value 18‰ lower than the hydrosphere, providing one of the earliest quantitative records of continental precipitation generally compatible with a cold climate at high latitudes.

Construction, Test and Application of a Tungsten Metallogene Named MGW11: Case Studies in China

Geochemical gene is a new promising concept proposed recently in the discrimination and traceability of geological materials and is also a useful tool to recognize geochemical anomalies in mineral exploration. Based on the lithogenes of LG01 and LG03, geological materials can be classified into nine types of LG_CR compositionally. With respect to geological materials with 11 types of LG_CR, in order to eliminate the lithological influence and to further narrow the prospecting target area, a tungsten metallogene named MGW11 is proposed for geochemical tungsten exploration after the tungsten metallogene MGW. Six weathering profiles of 11 types of LG_CR developed on granitic intrusions in different areas in China are selected to test the stable properties such as heredity and inheritance of MGW11 and MGW. The results indicate that MGW11 and MGW metallogenes illustrate stable properties during rock weathering regardless of weathering degrees, although gene variations of MGW11 and MGW are also observed during extreme weathering. Based on the regional geochemistry survey data in the Lianyang area in south China, where stream sediments are mostly 11 types of LG_CR compositionally, geochemical maps of mineralization similarities of MGW11 and MGW are contoured, and the anomaly areas are determined on the mineralization similarity value of ≥40%. Comparing the tungsten deposits and anomaly areas determined on MGW11 and MGW metallogenes spatially, a total of six polymetallic W deposits recognized in the study area are all located in the anomaly areas. Therefore, mineralization similarities of MGW11 and MGW can be viewed as useful integrated indices on geochemical tungsten exploration. In areas with 11 types of LG_CR compositionally, anomaly areas determined on the MGW11 are smaller than those on the MGW, which indicates that MGW11 is more efficient than MGW in targeting W deposits during tungsten prospecting because of the elimination of the lithological influence.

Класс Festuco-Brometea в Южном Зауралье (степная зона Челябинской области)

Класс Festuco-Brometea в Южном Зауралье (степная зона Челябинской области)