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In Bizmişen area, Middle Eocene (46.3–42.0 Ma) plutonic rocks (quartz diorite) were intruded into Triassic-Cretaceous limestones and Upper Cretaceous ophiolites and caused to skarn zones containing prograde (garnet, clinopyroxene) and retrograde (amphibole, epidote, calcite, magnetite, phlogopite, serpentinite and chlorite) minerals. Due to contact relationships of quartz diorites with both serpentinized ultramafic rocks and limestone blocks, the mineralogical associations represent calcic (grossular/andradite, amphibole, chlorite and epidote) as well as magnesian (diopside, serpentine, phlogopite, talc) skarns. During the skarnization process, garnet, diopside, epidote, scapolite and amphibole minerals developed in the endoskarn zone within quartz-diorite, and diopside, tremolite, serpentine, phlogopite, talc, Mg-chlorite and calcite minerals developed in the exoskarn zones in ophiolites (serpantinite and listwaenite) and limestones. Skarn and magmatic clinopyroxenes in serpentinized ultramafic hosted exoskarn zone have a compositional range of Wo 45-53 En 35-53 Fs 0 – 15 and Wo 24-51 En 38-76 Fs 0 – 11 , and classified as diopside and augite, respectively. The end members of garnets are Adr 46–54 Grs 43–50 Prp 1–2 Sps 1.1–5 in amphibole-epidote-calcite-garnet skarn in endoskarn zone, whereas Adr 40–93 Grs 4–57 Prp 0.2–2.3 Sps 0.9–2 in epidote-calcite-garnet skarn in exoskarn zone, and classified as andradite-rich grandite garnets. FeO, MnO and partially MgO contents gradually increase from the edges to the center in zoned garnet grains. Amphibole compositions represent to calcic (Ca >1 atoms per formula unit) group (pargasite) and indicate the high oxygen fugacity conditions which caused the increase in the rate of magnetite crystallization. Al 2 O 3 and FeO contents of epidotes range 23.68–27.63 and 9.10–14.45 wt%, respectively, correspond to composition of epidote and clinozoisite. The iron oxide contents (FeO, wt%) of magnetites change from 91.72 to 98.36 correspond to structural Fe3+ 1.88 – 1.97 and Fe2+ 0.91 – 1.0 values. The contents of Ti, divalent and trivalent metal cations correspond to ulvospinel-magnetite compositional line at the magnetite end-member. The mineral chemistry of skarn minerals shows similarities to those of most iron skarn deposits. Garnet U-Pb ages (46.95–45.63 Ma) are consistent with the cooling ages of the Bizmişen pluton. The prograde stage of skarn should be occurred syn -intrusion, whereas retrograde stage should be developed later than youngest garnet age (45.6 Ma) and before the oldest late stage argillic alteration (37.5 Ma). [ABSTRACT FROM AUTHOR]

The Poularies igneous complex is a Neoarchean (2728 Ma) intrusion composed of diorite, quartz diorite, hornblende tonalite, and biotite tonalite. It is was emplaced into the shallow crust of the Abitibi granite-greenstone belt during volcanic cycle 1 (2730–2725 Ma) and is contemporaneous with the eruption of mafic (Stoughton-Roquemaure Group) and silicic volcanic rocks (Hunter Mine Group). The petrogenetic relationship between the silicic rocks of the Poularies igneous complex is not constrained. In this study we test the petrological association between the different rock types of the Poularies complex using fractional crystallization modeling. Hydrous (H 2 O = 3 wt%) fractional crystallization modeling using a 'primitive' intermediate starting composition demonstrates that all rock types of the Poularies complex can be generated from a common parental magma in the upper crust (1 kbar) under mildly oxidizing conditions (ΔFMQ = 0). Moreover, it is demonstrated that the parental magma of the Poularies complex was likely derived by partial melting of mafic rocks from the Abitibi granite-greenstone belt. We conclude that the Poularies complex is representative of a magma chamber that generated the silicic lavas of the spatially associated Hunter Mine Group in a rifting or tensional plate stress environment. Our model may be applicable to other shallow syn -volcanic plutons of the Abitibi granite-greenstone belt. • The Poularies complex is a syn-volcanic pluton of the Abitibi greenstone belt. • FC modeling shows that all lithologies may be related to a common parental magma. • The parental magma was derived by partial melting of mafic crust. • The Poularies complex was a magma chamber that generated silicic volcanic rocks. [ABSTRACT FROM AUTHOR]

Recent studies have shown that multistage magmatic and metallogenic events in NE China were dominated by the Paleo-Asian Ocean tectonic regime and the Paleo-Pacific Ocean tectonic regime. However, outstanding questions remain on the petrogenesis and fertility of ore-causative magma in each metallogenic event. In this study, we report new geochronologic and geochemical data on ore-causative intrusions from the Tianbaoshan orefield in the east Jilin-Heilongjiang belt (EJHB), aiming to identify their petrogenesis, magma fertility, and their implications for the geodynamic evolution of the EJHB. Middle Permian Lishan ore-causative quartz monzodiorites with abundant mafic microgranular enclaves (MMEs) were emplaced at ca. 264.9 ± 2.6 Ma. Petrographic and geochemical characteristics (87Sr/86Sr (i) = 0.7049–0.7053, ε Nd (t) = 2.9–3.7, and ε Hf (t) = 4.7–11.7) indicate a juvenile crust source injected by a slab-metasomatized mantle component. The Early Jurassic Beishan monzogranites (ca. 192.5 ± 1.8 Ma) were generated by the partial melting of the juvenile underplating basaltic lower crust with subsequent fractional crystallization in response to their highly evolved geochemical features, combined with their depleted Sr-Nd-Hf isotopic signature (I Sr = 0.7032–0.7037, ε Nd (t) = 2.8–3.3, and ε Hf (t) = 7.2–12.2). Based on the zircon trace element geochemistry, we infer that the Middle Permian quartz monzodiorites had a high oxygen fugacity (Ce4+/Ce3+ = 40–216), potentially generating the Pb-Zn-Cu mineralization. Early Jurassic Beishan monzogranites had a lower magmatic oxygen fugacity (Ce4+/Ce3+ = 14–106), which may account for the Mo-dominated mineralization. A combination of this study and previous results corroborates that the Tianbaoshan orefield records the superposition of different tectonic regimes during metallogenesis. [Display omitted] • Uncovered the petrogenesis and fertility of ore-causative magmas in NE China's Tianbaoshan orefield. • Identified Middle Permian Lishan quartz diorites, revealing juvenile crust and mantle influences. • Characterized Early Jurassic Beishan monzogranites, indicating partial melting of basaltic crust. • Linked magmatic oxygen fugacity variations to distinct Pb-Zn-Cu and Mo mineralizations. • Demonstrated the influence of multiple tectonic regimes on the Tianbaoshan orefield's metallogenesis. [ABSTRACT FROM AUTHOR]

The Semail ophiolite located in the eastern part of the Arabian platform preserves remnants of ocean plate stratigraphy and related metamorphic sole. To understand the petro-tectonic evolution of a metamorphic sole during subduction to obduction processes, here we investigate the garnet metagabbros from the metamorphic sole and the tonalites which intruded the mantle section of the Khor Fakkan Block. We present results from petrology, geochemistry, zircon U-Pb, Hf and O isotope analyses and phase equilibria modeling. The garnet metagabbro samples have E-MORB-type enriched-mantle compositions with zircon dates of ca. 89–96 Ma, and positive εHf(t) values ranging from 5.6 to 10.0. The tonalite is peraluminous with those range of ca. 87–92 Ma, and a range of positive εHf(t) values of 5.1–10.0. The similarity in εHf values from both the garnet metagabbro and tonalite samples suggests a strong relevance to their mantle source, indicating the role of subducted material during their formation. In contrast, the δ18O(zircon) values show distinctly different values of high δ18O(zircon) of ~13–16‰ for the tonalite and ~ 5–8‰ for the metagabbro samples, reflecting variations in the role of surface-derived source materials. The phase equilibria modeling of the garnet metagabbro shows high-pressure amphibolite facies metamorphism that preceded the peak granulite facies metamorphism, followed by lower pressure hydration and decompression. This clockwise P-T path might reflect partial melting and differentiation of mantle wedge section above subducted slab. Our results provide insights into the complex processes within a supra-subduction zone, implying differences in degree of partial melting of the ocean plate stratigraphic sequences including recycled oceanic slab and surface-derived marine sediments that were subsequently interacted with hydrothermally altered mantle at a mantle wedge during subduction to obduction processes that formed the Semail ophiolite during the Upper Cretaceous. Unlabelled Image • Petro-tectonic evolution of the Semail ophiolite through multidisciplinary approach • Hf-O isotope compositions reflect the role of subducted supracrustal material in the mantle wedge. • Garnet metagabbros from the metamorphic sole complex processes within a supra-subduction zone during the Upper Cretaceous [ABSTRACT FROM AUTHOR]

We performed geological, geochronological, geochemical, and isotope-geochemical studies of igneous rocks of the Ust'- Ignok gabbrodiorite massif in the Urik-Iya graben of the Siberian craton and summarized the obtained and published data on early Proterozoic mafic igneous rocks in the South Siberian postcollisional magmatic belt. It has been established that the Ust'-Ignok massif is composed of rocks of the continuous series from biotite gabbro via gabbrodiorites and diorites to quartz diorites. U-Pb zircon dating of quartz diorites of the Ust'-Ignok massif yielded an age of 1836 ± 10 Ma, i.e., the massif rocks might have originated at the final stage of the formation of the South Siberian postcollisional magmatic belt. The rocks of the Ust'-Ignok massif are of normal and medium alkalinity. All igneous rocks from gabbro to quartz diorites show distinct negative anomalies of Nb-Ta and Ti in their multielement patterns, and their eNd(T) values vary from +0.3 to -0.9. The geochemical indicator ratios in the gabbroids point to insignificant contamination of their source with continental-crust material and to their formation through the melting of an enriched lithospheric-mantle source. Gabbrodiorites-quartz diorites of the Ust'-Ignok massif resulted, most likely, from the fractional crystallization of gabbroids. Analysis of the geochemical and isotope characteristics of mafic igneous rocks of the South Siberian postcollisional magmatic belt shows that most of them resulted from the melting of the subcontinental lithospheric mantle with suprasubductional geochemical features. This mantle might have formed during subduction processes preceding the formation of the Siberian craton. [ABSTRACT FROM AUTHOR]

We studied the mineralogical and geochemical features and formation conditions of productive mineral assemblages of the Tardan gold--sulfide--quartz deposit located in the endo-/exocontact zone of the Kopto--Bai-Syut gabbro-diorite--plagiogranite pluton of the Early Ordovician Tannu-Ola complex (O1tn). Postskarn mineralization of vein--dissemination type in skarns, quartz diorites, and carbonate rocks is limited by tectonic crushing zones and conjugated with beresitization and listwanitization of the ore-bearing rocks. Mineralogical and geochemical research has shown the formation of ultrahigh-fineness (986--952‰) and high-fineness (947--918‰) gold at the first productive gold--quartz--calcite substage, of high-fineness gold (918--904‰) → medium-fineness gold (896--809‰) → low-fineness gold (798--756‰) ± hessite Ag2Te ± volynskite AgBiTe2 at the second productive gold--telluride--sulfide--quartz--carbonate substage, and of medium-fineness gold (897--802‰) → low-fineness gold (799--717‰) → electrum (691--612‰) → mercurian electrum (471--451‰) ± hessite Ag2Te ± acanthite Ag2S ± matildite AgBiS2 at the third productive gold--sulfosalt--sulfide--quartz substage. High- and medium- fineness gold prevails in the ores, ultrahigh- and low-fineness gold is subordinate, and electrum and mercurian electrum are scarce. The fineness of native gold in the ores varies from 451 to 986‰, averaging 858‰. The productive mineral assemblages of the Tardan deposit formed from aqueous fluids containing Mg, Na, and K chlorides (salinity of 6.1--12.9 wt.% NaCl eq.), with a decrease in the mineral formation temperature from 380 to 150 ºC and variations in fO2, fS2, fSe2, and fTe2. [ABSTRACT FROM AUTHOR]

The Liudaowaizi Cu deposit is located in the east of Jilin Province and represents one of the few known Early Jurassic skarn Cu deposits in NE China. Here, we present new whole-rock major and trace element, zircon U–Pb and Hf isotopic data of quartz diorite exposed in the Liudaowaizi skarn Cu deposit. The quartz diorite belongs to the calc-alkaline series, is enriched in some of the large-ion lithophile elements (LILE; e.g., Rb, Ba, Th, and K) and is depleted in high-field-strength elements (HFSE; e.g., Ta, Nb, and Ti). LA-ICP-MS dating of zircons from the quartz diorite in the deposit yielded ages of 196 ± 1 Ma that are interpreted to be the emplacement age of this intrusion. Positive εHf values (6.6–11.6) and young T DM2 (490–813 Ma) of the quartz diorite indicate that the parent magma was derived from the partial melting of a juvenile lower crust, and magmatism and Cu mineralization were possibly related to the subduction of the Paleo-Pacific Plate. [ABSTRACT FROM AUTHOR]

P-T conditions, fluid regime and carbon isotope composition of graphite and fluid inclusions from garnet-sillimanite-bearing leucocratic tonalites, trondhjemites and granites associated with orthopyroxene-bearing granulite metapelites in the Southern Marginal Zone (SMZ) of the Limpopo Complex, South Africa, are presented in the paper. Re-integrated compositions of perthitic alkali feldspars and antiperthitic plagioclase, as well as P-T and T-X CO2 phase equilibria modeling using PERPLE_X software indicate that the granitoids began to crystallize at temperatures of 900–940 °C and pressures of 7–9 kbar, and were equilibrated with a fluid phase with X CO2  > 0.5–0.6 as is recorded in dense fluid inclusions in quartz. A small fraction of a saline fluid accumulated during cooling only. Average δ 13 C PDB values for graphite (−6.52 to −8.65‰) and fluid inclusions (−2.50 to −5.58‰) from the granitoids differ substantially from the values, which have been obtained in previous studies for graphite from the surrounding SMZ metapelites. Isotope data thus indicate that fluids associated with the granitoid magmas of the SMZ originated from a source unrelated to the host metapelites. In terms of the “heavy” isotope signatures of carbon, the granitoids might carry fluids, which have been produced during devolatilization of mafic rocks (amphibolites) interlayered with hydrothermal carbonate veins in the adjacent granite-greenstone successions of the Kaapvaal craton that have been buried underneath the SMZ granulites during their exhumation. The cratonic rock could serve as a source for the trondhjemite magmas intruding the SMZ granulites. In this scenario, the studied granitoids crystallized from these magmas variously contaminated by metapelitic material. Graphite precipitated via reduction of CO 2 -rich fluid as the result of dissolution of pyrrhotite-rich metapelites in the magmas. [ABSTRACT FROM AUTHOR]

The Vestfold Hills sector on the coastal fringe of the Princess Elizabeth Land forms part of an Archean to Paleoproterozoic aged cratonic nucleus of the East Antarctic Shield. A charnockite-granite association from the Mossel Gneiss Group in the northern region of the Vestfold Hills is investigated in this work to characterise the metamorphic-magmatic evolution of the area. Conventional thermometry and phase equilibria modelling indicate that the charnockite formed as a result of ultra-high temperature metamorphism at low-intermediate pressure (∼4 kbar). Phase equilibria modelling, reveals that the melt-integrated charnockite composition is a restitic product of a protolith of quartz diorite composition which underwent isobaric heating (peak temperature up to 960 °C) at 4 kbar pressure followed by anatexis. The anatexis of the quartz diorite protolith also resulted in the formation of the associated granitic melt. U–Th-Pb Total ages obtained from monazites of the granite integrated with CHIME ages extracted using the isochron method indicate an emplacement age of ∼2200 Ma and two younger events are recorded at ∼2000 Ma and ∼1700 Ma. The younger ages are ascribed to the resetting during the emplacement of younger basalt dykes that cross cut the charnockite-granite sequence. Vestfold Hills' geological correlations with Indian and Australian cratons are discussed considering this new data. [ABSTRACT FROM AUTHOR]

The Missanabie-Renabie gold district in the Wawa gold camp of the Archean Superior craton, Ontario, Canada, is characterized by laminated saccharoidal quartz veins within shear zones. Over 50 years, from 1941 to 1991, ∼1.1 million ounces of gold were produced from a number of these veins hosted by shear zones that overprint 2720.8 ± 1.4 Ma biotite tonalite of the Missinaibi Lake batholith. Because of their laminated nature and association with shear zones, the veins were interpreted as syn-orogenic fault-fill veins that formed during the migration of hydrothermal fluids along actively deforming shear zones. A structural study of well-exposed, mechanically stripped outcrops indicates that the veins were emplaced in brittle structures prior to the onset of regional ductile deformation and that they subsequently localized the formation of the shear zones in which they are hosted. The veins define isoclinal F1 folds and are overprinted by a regional S2 cleavage, L2 stretching lineation, and F2 folds. The shear zones hosting the veins formed as D3 sinistral-reverse shearing became localized in the mechanically weak alteration envelopes surrounding the veins. Syn-orogenic hydrothermal fluids locally infiltrated the shear zones during D3 and formed gold-barren veins of quartz ± epidote ± chlorite ± K-feldspar ± hematite associated with hematite-bearing alteration zones. Dextral reactivation of the shear zones during D4 produced Z-shaped drag folds, dextral shear bands, and NW-striking quartz tension gashes. Massive pyrite veins with an orientation similar to the quartz tension gashes were emplaced either during or subsequent to D4 and represent a second gold mineralization event. Other granitoid-hosted mines in the Wawa gold camp, such as the Magino deposit and those associated with the Jubilee stock, also comprise pre-orogenic auriferous quartz veins, suggesting that this style of mineralization defines a number of economic deposits in the camp. The Missanabie-Renabie gold district exemplifies how pre-orogenic veins acted as planar anisotropies that localized the development of shear zones, the channeling of successive pulses of syn- to post-orogenic hydrothermal fluids, and resulted in the formation of hybrid deposits comprising both pre- and syn-orogenic veins. Although the main gold mineralization event occurred prior to regional deformation, the hybrid deposits display characteristics that are typical of orogenic gold deposits. This study emphasizes that hybrid deposits are likely an underrecognized style of mineralization in Archean gold camps and contributes to an understanding of why multiple styles and ages of mineralization overlap spatially in the Superior craton and globally. [ABSTRACT FROM AUTHOR]

The Sabzevar ophiolites, located at the northern margin of the Central-East Iranian microcontinent (CEIM), are part of the Mesozoic-Paleogene Neotethyan suture zone developed along the Alpine-Himalayan convergence zone. These ophiolites consist mostly of oceanic lithospheric remnants, covered by early Campanian-late Maastrichtian volcano-sedimentary successions. A distinctive characteristic of the Sabzevar ophiolites is the occurrence of mafic dike swarms (gabbros, gabbronorites and diorites) with forearc-arc-tholeiitic geochemical signature, intruding the mantle section. Occurrence of orthopyroxene, development of pegmatitic texture, crystallization of clinopyroxene prior to plagioclase, and the presence of anorthite-rich plagioclase imply relatively high H 2 O content in the magmatic plumbing system. Rare plagiogranites (tonalite and trondhjemite compositions) show geochemical features compatible with a supra-subduction setting, whereas late (hornblende-bearing) gabbro dikes show a within-plate signature. The bimodal geochemical affinity (subduction vs. intraplate) is also attested by clinopyroxene compositions. The gabbroic, plagiogranitic and gabbronoritic samples yield Early Cretaceous SHRIMP zircon U-Pb ages of 96.7 ± 1, 98 ± 1 and 94 ± 1 Ma, respectively. A progression from tholeiitic MORB-like to more depleted high-Mg andesite and eventually alkaline affinities is here proposed, framing the magma evolution as generated in an evolving forearc setting that post-dated (of at least 9 Myr) the formation of the metamorphic sole during the infant stages of subduction of the Sabzevar Ocean. A scenario of far-field forced subduction initiation of the Sabzevar Ocean is proposed as consequence of propagation of the residual stresses transmitted from the Arabia-Eurasia convergence zone across the CEIM during Cretaceous times (Albian-Campanian). [ABSTRACT FROM AUTHOR]

Kajan subvolcanic rocks in the Urumieh–Dokhtar magmatic arc (UDMA), Central Iran, form a Late Miocene-Pliocene shallow-level intrusion. These subvolcanics correspond to a variety of intermediate and felsic rocks, comprising quartz diorite, quartz monzodiorite, tonalite and granite. These lithologies are medium-K calc-alkaline, with SiO 2 (wt.%) varying from 52% (wt.%) to 75 (wt.%). The major element chemical data also show that MgO, CaO, TiO 2 , P 2 O 5 , MnO, Al 2 O 3 and Fe 2 O 3 define linear trends with negative slopes against SiO 2 , whilst Na 2 O and K 2 O are positively correlated with silica. Contents of incompatible trace elements (e.g. Ba, Rb, Nb, La and Zr) become higher with increasing SiO 2 , whereas Sr shows an opposite behaviour. Chondrite-normalized multi-element patterns show enrichment in LILE relative to HFSE and troughs in Nb, P and Ti. These observations are typical of subduction related magmas that formed in an active continental margin. The Kajan rocks show a strong affinity with calc-alkaline arc magmas, confirmed by REE fractionation (La N /Yb N = 4.5–6.4) with moderate HREE fractionation (Sm N /Yb N = 1.08–1.57). The negative Eu anomaly (Eu/Eu* <1), the low to moderate Sr content (< 400 ppm) and the Dy/Yb values reflect plagioclase and hornblende (+- clinopyroxene) fractionation from a calc-alkaline melt Whole–rock Sr and Nd isotope analyses show that the 87 Sr/ 86 Sr initial ratios vary from 0.704432 to 0.705989, and the 143 Nd/ 144 Nd initial ratios go from 0.512722 to 0.512813. All the studied samples have similar Sr-Nd isotopes, indicating an origin from a similar source, with granite samples that has more radiogenic Sr and low radiogenic Nd isotopes, suggesting a minor interaction with upper crust during magma ascent. The Kajan subvolcanic rocks plot within the depleted mantle quadrant of the conventional Sr-Nd isotope diagram, a compositional region corresponding to mantle-derived igneous rocks. [ABSTRACT FROM AUTHOR]

The paper discusses a possible model of the ancient (Hadean-Archean) Earth’s geodynamic evolution. We believe that the early Earth was characterized by a stagnant lid regime and whole-mantle convection suggesting cells that convect through the whole mantle (from the core-mantle boundary to the lithosphere base). The lid tectonics was perturbed by asteroid-meteorite bombardments that destroyed the primary terrestrial partly granitoid crust. The destroyed crust together with the residual enriched mantle reservoirs sank into the lower mantle. In addition to the crust destruction, the bombardments led to emplacement of a huge proportion of basalt-komatiitic melts, which can be interpreted as mantle overturn events. In the Hadean, the Earth survived frequent large-scale asteroid-meteorite bombardments, which resulted in almost a complete destruction of the primary terrestrial crust. In the Early Archean, the Earth still experienced the same tectonic processes, as in the Hadean; however, meteorite impact was small-scale and the bombardments influenced only a limited area of a common, as it seems to us, subequatorial supercontinent. Those bombardments led to the sagduction of the Archean basalt-komatiiic terrestrial crust, which sank into the mantle, transforming into amphibolite-eclogite rocks giving rise to a tonalite-troondhjemite-granodiorite suite. As preserved in the zircon record, the formation of the Archean mantle-derived magmas occurred as pulses at 4.5, 4.2-4.3, 3.8-3.9, and 3.3-3.4 Ga. These peaks, most likely, correspond to the Hadean-Archean meteorite bombardments. There is evidence of formation of the subcontinental lithospheric mantle (SCLM) beneath the cratons between 3.3 and 3.5 Ga. This SCLM was markedly different from peridotites of modern ophiolites. However, the existence of ophiolitic peridotites indicates that modern style plate tectonic processes were in operation at that time, as we will discuss below. The transition from the early Earth (Hadean-Archean) tectonic style to the recent tectonics occurred between 3.4 (2.7?) and 2.0 Ga. [ABSTRACT FROM AUTHOR]

Abstract: Mesoarchean to Neoarchean orthogneisses (2.95–2.79Ga) in the Fiskenæsset region, southern West Greenland, are composed of an older suite of metamorphosed tonalites, trondhjemites, and granodiorites (TTGs), and a younger suite of high-K granites. The TTGs are characterized by high Al2O3 (14.2–18.6wt.%), Na2O (3.4–5.13wt.%), and Sr (205–777ppm), and low Y (0.7–17.4ppm) contents. On chondrite- and N-MORB-normalized trace element diagrams, the TTGs have the following geochemical characteristics: (1) highly fractionated REE patterns (La/Ybcn =14–664; La/Smcn =4.3–11.0; Gd/Ybcn =1.5–19.7); (2) strong positive anomalies of Sr (Sr/Sr*=1.0–15.9) and Pb (Pb/Pb*=1.4–34.9); and (3) large negative anomalies of Nb (Nb/Nb*=0.01–0.34) and Ti (Ti/Ti*=0.1–0.6). The geochemical characteristics of the TTGs and trace element modeling suggest that they were generated by partial melting of hydrous basalts (amphibolites) at the base of a thickened magmatic arc, leaving a rutile-bearing eclogite residue. Field observations suggest that spatially and temporarily associated tholeiitic basalts (now amphibolites) in the Fiskenæsset region might have been the sources of TTG melts. The high-K granites have steep REE patterns (La/Ybcn =3.8–506; La/Smcn =2.7–18.9; Gd/Ybcn =0.92–12.1) and display variably negative Eu anomalies (Eu/Eu*=0.37–0.96) and moderate Sr (84–539ppm) contents. Four outlier granite samples have variably positive Eu (Eu/Eu*=1.0–12) anomalies. Given that the granodiorites have higher K2O/Na2O than the tonalites and trondhjemites, it is suggested that the granites were derived from partial melting of the granodiorites. It is speculated that the dense eclogitic residues, left after TTG melt extraction, were foundered into the sub-arc mantle, leading to basaltic underplating beneath the lower rust. Melting of the granodiorites in response to the basaltic underplating resulted in the production of high-K granitic melts. Formation of the Fiskenæsset TTGs, the foundering of the eclogitic residues into the mantle, and the emplacement of the high-K granites led to the growth of Archean continental crust in the Fiskenæsset region. [Copyright &y& Elsevier]

Abstract: The structure, composition, and age of Vendian–Early Cambrian plagiogranitoid associations composing the Kshta and Taraskyr massifs of the Yenisei pluton in the Altai–North Sayan island-arc belt are considered. We have established that these associations formed within 550–520 Ma and differ in petrographic composition and sources. Two stages of island-arc plagiogranitoid magmatism are recognized: early (550–540 Ma, formation of plagiogranitoids of the Kshta (545 ± 8 Ma) and Taraskyr (545 ± 7 Ma) massifs) and late (525–520 Ma, formation of plagiogranitoids of the Maina complex of the Yenisei (524 ± 2 Ma) and Tabat plutons). By petrochemical composition and geochemical characteristics, the rocks of the Kshta massif are high-alumina plagiogranitoids similar to adakites. They might have been produced through the melting of metabasites compositionally similar to N-MORB in equilibrium with garnet-containing restite during the subduction of oceanic slab at ≥15 kbar. The rocks of the Taraskyr massif are low-alumina plagiogranites. They formed through the melting of metabasites located in the lower layers and(or) the basement of the island-arc system in equilibrium with plagioclase-containing restite at 3–8 kbar. The low-alumina plagiogranitoids of the Yenisei pluton melted out under the same conditions. Isotope-geochemical studies showed that the Vendian–Early Cambrian plagiogranitoids formed at the early stage are characterized by high positive ∑Nd(T) values (7.5–4.9), Late Riphean model Nd-age (TNd(DM) = 0.64–0.98 Ga), and Sr isotope ratio varying from 0.7040 to 0.7053. These data point to the juvenile parental melts of the rocks and the varying content of ancient crustal material in the magma generation zone. [Copyright &y& Elsevier]

Abstract: High-pressure (HP) granulites widely occur as enclaves within tonalite-trondhjemite-granodiorite (TTG) gneisses of the Early Precambrian metamorphic basement in the Shandong Peninsula, southeast part of the North China Craton (NCC). Based on cathodoluminescence (CL), laser Raman spectroscopy and in-situ U-Pb dating, we characterize the zircons from the HP granulites and group them into three main types: inherited (magmatic) zircon, HP metamorphic zircon and retrograde zircon. The inherited zircons with clear or weakly defined magmatic zoning contain inclusions of apatites, and 207Pb/206Pb ages of 2915–2890 Ma and 2763–2510 Ma, correlating with two magmatic events in the Archaean basement. The homogeneous HP metamorphic zircons contain index minerals of high-pressure metamorphism including garnet, clinopyroxene, plagioclase, quartz, rutile and apatite, and yield 207Pb/206Pb ages between 1900 and 1850 Ma, marking the timing of peak HP granulite facies metamorphism. The retrograde zircons contain inclusions of orthopyroxene, plagioclase, quartz, apatite and amphibole, and yield the youngest 207Pb/206Pb ages of 1840–1820 Ma among the three groups, which we correlate to the medium to low-pressure granulite facies retrograde metamorphism. The data presented in this study suggest subduction of Meso- and Neoarchean magmatic protoliths to lower crust depths where they were subjected to HP granulite facies metamorphism during Palaeoproterozoic (1900–1850 Ma). Subsequently, the HP granulites were exhumated to upper crust levels, and were overprinted by medium to low-pressure granulite and amphibolite facies retrograde event at ca. 1840–820 Ma. [Copyright &y& Elsevier]

Abstract: Within the Belomorian eclogite province, near Gridino Village, rocks of different compositions (tonalite-trondhjemite-granodioritic gneisses, granites, mafic and ultramafic rocks) were metamorphosed. The metamorphism included subsidence with increasing pressure and temperature, an eclogite stage, decompression in the granulitic facies, and a retrograde stage in the amphibolitic facies. We attempted to characterize the succession and to date igneous and metamorphic events in the evolution of the Gridino eclogite association. For this purpose, we conducted the following studies: U–Pb isotope dating of zircon (conventional and SHRIMP II methods) from gneisses, a mafic dike, and a high-pressure granitic leucosome; U–Pb dating of rutile from mafic dikes; 40Ar/39Ar dating of amphibole and mica; and Sm–Nd studies of rocks and minerals. The Sm–Nd model ages of felsic (2.9–3.1 Ga) and mafic (3.0–3.4 Ga) rocks from the Gridino eclogite association and individual magmatic zircon grains with an age of ca. 3.0 Ga indicate the Mesoarchean age of the metamorphic-rock protoliths. The most reliable result is the upper age bound of eclogitic metamorphism (2.71 Ga), which reflects the time of the posteclogitic decompression melting of eclogitized rocks under high-pressure retrograde granulitic metamorphism. The mafic dikes formed from 2.82 Ga to 2.72 Ga, most probably, at 2.82 Ga, in accordance with the crystallization age of magmatic zircon from metagabbro. Superimposed amphibolitic metamorphism and the “final” exhumation of metamorphic complexes at 2.0–1.9 Ga are associated with the later Svecofennian tectonometamorphic stage. Successive cooling of the metamorphic associations to 300 °C at 1.9–1.7 Ga is shown by U–Pb rutile dating and 40Ar/39Ar mica dating. [Copyright &y& Elsevier]

Abstract: According to the metallogenic theory by transmagmatic fluid (TMF), one magmatic intrusion is a channel of ore-bearing fluids, but not their source. Therefore, it is possible to use TMF’s ability for injection into and for escaping from the magmatic intrusion to evaluate its ore-forming potential. As the ore-bearing fluids cannot effectively inject into the magmatic intrusion when the magma fully crystallized, the cooling time and rates viscosity varied can be used to estimate the minimum critical thickness of the intrusion. One dimensional heat transfer model is used to determine the cooling time for three representative dikes of different composition (granite porphyry, quartz diorite and diabase) in the Shihu gold deposit. It also estimated the rates viscosity varied in these time interval. We took the thickness of dike at the intersection of the cooling time – thickness curve and the rates viscosity varied versus thickness curve as the minimum critical thickness. For the ore-bearing fluids effectively injecting into the magma, the minimum critical thicknesses for the three representative dikes are 33.45 m for granite porphyry, 8.22 m for quartz diorite and 1.02 m for diabase, indicating that ore-bearing dikes must be thicker than each value. These results are consistent with the occurrence of ore bodies, and thus they could be applied in practice. Based on the statistical relationship between the length and the width of dikes, these critical thicknesses are used to compute critical areas: 0.0003–0.0016 km2 for diabase, 0.014–0.068 km2 for quartz diorite and 0.011–0.034 km2 for granite porphyry. This implies that ore-bearing minor intrusions have varied areas corresponding to their composition. The numerical simulation has provided the theoretical threshold of exposed thickness and area of the ore-bearing intrusion. These values can be used to determine the ore-forming potentials of dikes. [Copyright &y& Elsevier]

Abstract: Geochemistry and U–Pb ages of leucosomes and tonalites in a high pressure granulite unit of the Dulan area have been determined to constrain the tectonothermal evolution related to collision and thickening of lower crust in the North Qaidam Mountains (NQD). Leucosomes and tonalites show a marked chemical resemblance to adakites: (1) high La/Yb and Sr/Y, and low Y and HREE; (2) high Al2O3 and low Mg# values with obvious positive Eu anomalies; and (3) slightly positive εNd(t) values. Zircon U–Pb analysis of leucosomes and tonalites yielded 206Pb/238U ages of 428–437Ma and 436–437Ma respectively, which constrain the emplacement ages of the adakitic rocks. Petrological, geochronological and geochemical characters indicate that the adakitic rocks may have been derived from partial melting of a thickened mafic lower crust (>50km), suggesting a dominating source regime of synchronous high-pressure mafic granulites. Contemporary magmatism in other units of the NQD shows evidence of a widespread tectonothermal event during early Silurian (420–450Ma) that includes metamorphism, magmatism and anatexis related to collision and thickening of lower crust. [Copyright &y& Elsevier]

Abstract: The Xutai and Lujiagou plutons, exposed in the Songshan–Jishan area in the southern margin of the North China Craton (NCC), are studied to constrain the tectonic regime of the NCC between 2.5 and 2.4Ga. The Xutai pluton (dated at 2509±33Ma) mainly consists of tonalite and monzogranite with a calc-alkaline affinity (Rittmann Index (δ)<3.3). Low 10,000Ga/Al (1.15 to 1.38) and zircon saturation temperature (T Zr =612 to 779°C) and a negative correlation between P2O5 and SiO2 classify them as I-type granite. Enriched LREE, low Y and Yb with high Sr/Y ratios are attributed to garnet in the residue, indicating a deep source for the pluton. Zircon grains have positive ε Hf(t) values (+4.6 to +9.4) with T DM C ages ranging from 2708 to 2435Ma (average of 2502Ma), close to the crystallization age of the pluton, indicative of a juvenile crust source. Negative Nb, Ta and Ti anomalies of the pluton and its intrusive contact relationship with older subduction-related amphibolites are supportive of an arc setting. The Lujiagou pluton (dated at 2399±24Ma) mainly consists of syenogranite with a calc-alkaline affinity (δ<3.3). High SiO2 (73.25 to 75.21wt.%) and K2O (5.38 to 8.03wt.%) and low P2O5 (0.01 to 0.04wt.%) indicate that the primitive magmas of the rocks have experienced fractionation. The rocks have 10,000Ga/Al (0.71 to 2.55) and T Zr (614 to 796°C) lower than those for A-type granite and negative correlation between P2O5 and SiO2, consistent with highly fractionated I-type character. Zircon ε Hf(t) values (−0.2 to +4.4) with T DM C from 2909 to 2652Ma are indicative of mantle-derived components, contaminated by older crust. However, the rocks have high SiO2, K2O and low Mg#, precluding their derivation from a juvenile source. Considering the LREE enriched nature, low Y, negative Eu anomalies and zircon Hf and whole rock Nd isotopic components identical to TTGs, we propose that the Lujiagou pluton inherited from preexisting Songshan TTGs, consistent with formation in an extensional setting. We thus propose that the Xutai and Lujiagou plutons record a tectonic transition from compressive to extensional setting in the southern margin of the NCC during 2.5 to 2.4Ga. [Copyright &y& Elsevier]

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Abstract: Rocks of the Late Cretaceous Dagbasi Pluton (88–83Ma), located in the eastern Pontides, include mafic microgranular enclaves (MMEs) ranging from a few centimetres to metres in size, and from ellipsoidal to ovoid in shape. The MMEs are composed of gabbroic diorite, diorite and tonalite, whereas the felsic host rocks comprise mainly tonalite, granodiorite and monzogranite based on both mineralogical and chemical compositions. MMEs are characterized by a fine-grained, equigranular and hypidiomorphic texture. The common texture of felsic host rocks is equigranular and also reveals some special types of microscopic textures, e.g., oscillatory-zoned plagioclase, poikilitic K-feldspar, small lath-shaped plagioclase in large plagioclase, blade-shaped biotite, acicular apatite, spike zones in plagioclase and spongy-cellular plagioclase textures and rounded plagioclase megacrysts in MMEs. Compositions of plagioclases (An33–An60), hornblendes (Mg#=0.77–1.0) and biotites (Mg#=0.61–0.63) of MMEs are slightly distinct or similar to those of host rocks (An12–57; hbl Mg#=0.63–1.0; Bi Mg#=0.50–0.69), which suggest partial to complete equilibration during mafic–felsic magma interactions. The felsic host rocks have SiO2 between 60 and 76wt% and display low to slightly medium-K tholeiitic to calc-alkaline and peraluminous to slightly metaluminous characteristics. Chondrite-normalized rare-earth element (REE) patterns are fractionated (Lacn/Lucn=1.5–7.3) with pronounced negative Eu anomalies (Eu/Eu*=0.46–1.1). Initial ε Nd(i) values vary between −3.1 and 1.6, initial 87Sr/86Sr values between 0.7056 and 0.7067. Compared with the host rocks, the MMEs are characterized by relatively high Mg-number of 22–52, low contents of SiO2 (53–63wt%), low ASI (0.7–1.1) and low to medium-K tholeiitic to calc-alkaline, metaluminous to peraluminous composition. Chondrite-normalized REE patterns are relatively flat [(La/Yb)cn=1.4–3.9; (Tb/Yb)cn=0.9–1.5] and show small negative Eu anomalies (Eu/Eu*=0.63–1.01). Isotope signatures of these rocks (87Sr/86Sr(i)=0.7054–0.7055; ε Nd(i)=–1.0 to 1.9) are largely similar to the host rocks. Gabbroic diorite enclaves have relatively low contents of SiO2, ASI; high Mg#, CaO, Al2O3, TiO2, P2O5, Sr and Nb concentrations compared to dioritic and tonalitic enclaves. The geochemical and isotopic similarities between the MMEs and their host rocks indicate that the enclaves are of mixed origin and are most probably formed by the interaction between the lower crust- and mantle-derived magmas. All the geochemical data suggest that a basic magma derived from an enriched subcontinental lithospheric mantle, interacted with a crustal melt that originated from dehydration melting of the mafic lower crust at deep crustal levels. The existence of compositional and textural disequilibrium and the nature of chemical and isotopic variation in these rock types indicate that magma mixing/mingling between an evolved mafic and a granitic magma was involved in their genesis. Microgranular enclaves are thus interpreted to be globules of a more mafic magma probably from an enriched lithospheric mantle source. Al-in-amphibole estimates the pluton emplacement at ca. 0.3–3.8kbar, and therefore, magma mixing and mingling must have occurred at 3.8kbar or below this level. [Copyright &y& Elsevier]

Abstract: Assembly of the supercontinent Columbia at about 1.85–1.90 Ga coincided with several events that affected the entire earth. The oldest worldwide network of orogenic belts formed at the same time. Although some granite–granodiorite (GG) suites had formed earlier, the GG suites became common in the 1.8–1.9 Ga orogenic belts. These suites succeeded the older tonalite–trondhjemite–granodiorite (TTG) suites, which were not produced after 1.8 Ga. Changes on the earth''s surface at 1.8–1.9 Ga include rapid increase in the concentration of oxygen in the atmosphere and oceans and probably the evolution of eukaryotes. All of these surface changes occurred as Columbia accreted, and the assembly of Columbia may have contributed to the drastic changes in the earth''s surface environment as well as to the evolution of primitive life forms. [Copyright &y& Elsevier]

Abstract: The tonalite-trondhjemite-granite (TTG) crust has been considered to be buoyant and hence impossible to be subducted into the deep mantle. However, recent studies on the juvenile arc in the western Pacific region indicate that immature island arcs subduct into the deep mantle in most cases, except in the case of parallel arc collision. Moreover, sediment trapped subduction and tectonic erosion are also common. This has important implications in evaluating the role of TTG crust in the deep mantle and probably on the bottom of the mantle. Because the TTG crust is enriched in K, U and Th, ca. 20 times more than that of CI chondrite, the accumulated TTG on the Core Mantle Boundary (CMB) would have played a critical role to initiate plumes or superplumes radiating from the thermal boundary layer, particularly after 2.0 Ga, related to the origin of superplume-supercontinent cycle. This is because selective subduction of oceanic lithosphere including sediment-trapped subduction, tectonic erosion and arc- and microcontinent-subduction proceeded under the supercontinent before the final amalgamation ca. 200-300 million years after the formation of the nuclei. We speculate the mechanism of superplume evolution through the subduction of TTG-crust and propose that this process might have played a dominant role in supercontinent breakup. [Copyright &y& Elsevier]

Abstract: The Sergipano Belt is the outcome of collision between the Pernambuco–Alagoas Massif and the São Francisco Craton during Neoproterozoic assembly of West Gondwana. Field relationships and U–Pb geochronology of granites intruded in garnet micaschists of the Macururé Domain are used to constrain the main collisional event (D2) in the belt. The granites are divided into two groups, the pre-collisional granites (pre- to early-D2) and the syn-collisional granites (syn- to tardi-D2), the latter were emplaced as sheets along the S2 axial plane foliation or they were collected at the hinge zones of F2 folds. A U–Pb SHRIMP zircon age of 628±12 Ma was obtained for the pre-collisional Camará tonalite. Two U–Pb TIMS titanite ages were obtained for the syn-collisional granites, 584±10 Ma for the Angico granite and 571±9 Ma for the Pedra Furada granite, and these ages are close to the garnet-whole rock Sm–Nd isochron of 570 Ma found for the peak of metamorphism in the Sergipano Belt. The ages of the Camará tonalite (628 Ma) and the Pedra Furada granite (571 Ma) mark respectively the maximum age for beginning of the D2 event and minimum age for the end in the Macururé Domain. Using these ages, the main Neoproterozoic D2 collisional event has been in operation in the Sergipano Belt for at least 57 million years. Correlation with coeval granitoids farther north in the Borborema Province indicate that while in the Sergipano Belt the syn-D2 granites (ca. 590–570 Ma) were emplaced under compression, in the Borborema Province they emplaced under extensional conditions related to regional strike-slip shear zones. These contrasting emplacement settings for contemporaneous Neoproterozoic granitoids are explained by a combination of continent–continent collision and extrusion tectonics. [Copyright &y& Elsevier]

Abstract: In the northwestern part of the Sharyzhalgai uplift of the Siberian craton (Bulun block), the earliest sialic crust (grey-gneiss complex) is composed of plagiogneisses, their migmatized varieties, and subordinate plagiogranitoids. The petrochemical, trace-element, and Sm-Nd isotope compositions of rocks were studied, and U-Pb dating of zircons (SHRIMP II) was performed. Plagiogneisses and plagiogranitoids of trondhjemite and, more seldom, tonalite compositions are predominant; their compositions are typical of rocks of Archean tonalite-trondhjemitegranodiorite (TTG) complexes (Al2O3 ≥ 15%, Mg# = 28–38, (La/Yb) n = 23–66, Sr/Y = 27–135, Eu/Eu⁎ = 0.7–1.1). Plagiogneisses of meta-andesite-rhyodacite association are subordinate (SiO2 = 59–69%, (La/Yb) n = 7–32, Sr/Y = 11–24, Eu/Eu⁎ = 0.5–0.7). Cathodoluminescent study of zircons revealed “magmatic cores” and metamorphic rims; most of the rims differ from the cores in U and Th contents and low or greatly varying Th/U ratios. In migmatized plagiogneisses of trondhjemite composition, two zircon generations of different morphologies have been recognized. The protoliths of the grey-gneiss complex rocks formed in the Paleoarchean as a result of two discrete magmatic events, at ∼3.3 and 3.25 Ga, and their metamorphism and migmatization took place at ∼3.2 Ga. The isotopic and geochemical features of rocks evidence that the primary melts were produced mainly through the melting of metabasic sources at different depths of the thickened crust. Plagiogneisses of trondhjemite composition apparently resulted from magma generation involving ancient sialic material. [Copyright &y& Elsevier]

Based on a compilation of published sources, rocks referred to as adakites show the following geochemical and isotopic characteristics: SiQ2 ≥56 wt percent, Al2O3 ≥15 wt percent, MgO normally <3 wt percent, Mg number ≈0.5, Sr ≥400 ppm, Y ≤18 ppm, Yb ≤1.9 ppm, Ni ≥20 ppm, Cr ≥30 ppm, Sr/Y ≥20, La/Yb ≥20, and 87Sr/86Sr ≤0.7045. Rocks with such compositions have been interpreted to be the products of hybridization of felsic partial melts from subducting oceanic crust with the peridotitic mantle wedge during ascent and are not primary magmas. High Mg andesites have been interpreted to be related to adakites by partial melting of asthenospheric peridotite contaminated by slab melts. The case for these petrogenetic models for adakites and high Mg andesites is best made in the Archean, when higher mantle geotherms resulted in subducting slabs potentially reaching partial melting temperatures at shallow depths before dehydration rendered the slab infusible. In the Phanerozoic these conditions were likely only met under certain special tectonic conditions, such as subduction of young (≤25-m.y.-old) oceanic crust. Key adakitic geochemical signatures, such as low Y and Yb concentrations and high Sr/Y and La/Yb ratios, can be generated in normal asthenosphere-derived tholeiitic to calc-alkaline are magmas by common upper plate crustal interaction and crystal fractionation processes and do not require slab melting. An assessment of several are volcanic suites from around the world shows that most adakite-like compositions are generated in this way mad do not reflect source processes. Similarly, rare adakite-like intrusive rocks associated with some porphyry Cu deposits are the evolved products of extensive crustal-level processing of calc-alkaline basalt-andesite-dacite-rhyolite series magmas. If slab melts contribute to such magmas, their geochemical signatures would have been obliterated or rendered ambiguous by subsequent extensive open-system processes. In Archean terranes, where adakitic and high Al tonalite-trondhjemite-granodiorite (TTG) magma series rocks are more common, porphyry Cu deposits are rare and, where found, are associated with normal calc-alkaline suites rather than adakites. The two different magma series are compositionally distinct in terms of several major and trace element parameters. Common upper plate magmatic processes such as melting-assimilation-storage-homogenization (MASH) and assimilation-fractional-crystallization (AFC) affecting normal are magmas can be demonstrated to explain the distinctive compositions of most adakite-like are rocks, including high Mg andesites and especially those rare examples associated with porphyry Cu deposits. In contrast, slab melting can in most cases neither be proved nor disproved mad is therefore unsatisfactory as a unique factor in porphyry Cu genesis. [ABSTRACT FROM AUTHOR]

Abstract: The Southern Prince Charles Mountains (SPCM) are mostly occupied by the Archaean Ruker Terrane. The Lambert Terrane crops out in the northeastern part of the SPCM. New geochemical and zircon U–Pb SHRIMP ages for felsic orthogneisses and granitoids from both terranes are presented. Orthogneisses from the Ruker and Lambert terranes differ significantly in their major and trace-element compositions. Those from the Ruker Terrane comprise two distinct groups: rare Y-depleted and abundant Y-undepleted. U–Pb isotopic data provide evidence for tonalite−trondhjemite emplacement at 3392±9 and 3377±9 Ma, pre-tectonic granite emplacement at 3182±9 Ma, metamorphism(?) at c. 3145 Ma, and thermal events at c. 1300(?) and 626±51 Ma. The Lambert Terrane orthogneisses probably originated in a continental magmatic arc. Zircon dating shows a very different geological history: pre-tectonic granitoid emplacement at 2423±18 Ma, metamorphism at 2065±23 Ma, and syn-tectonic granitoid emplacement at 528±6 Ma, syn-tectonic pegmatite emplacement at 495±18 Ma. The Lambert Terrane can be correlated with neither the Meso- to Neoproterozoic Beaver Terrane in the Northern PCM, which differs in isotopic composition, nor with the Archaean Ruker Terrane, which differs in both granitoid chemical composition and the timing of major geological events. It represents a Palaeoproterozoic orogen which experienced strong tectonic re-activation in Pan-African times. The Lambert Terrane has some geochronological features in common with the Mawson Block, which comprises south Australia and some areas in East Antarctica. [Copyright &y& Elsevier]

Paleoproterozoic Birimian Supergroup rocks of southwest Ghana host numerous mesothermal lode gold deposits, including the >38 million ounce (Moz) Ashanti deposit at Obuasi and other multimillion ounce deposits at Bogoso, Konongo, Prestea, Bibiani, and in the Yamfo-Sefwi region. Gold deposits of the Chirano district are localized along the Chirano lode horizon, a 9-km segment of the Chirano, and related shear zones on the southeast margin of the Sefwi-Bibiani belt. Economically significant mineralization at Chirano is largely hosted by altered tonalite intrusions. Weaker alteration and subparts per million gold grades extend into adjacent Birimian mafic igneous rocks and Tarkwaian Group sedimentary rocks. Pink albite alteration (albite-quartz-pyritehe-matite-rutile ± leucoxene-chalcopyrite ± gold) and later pale carbonate alteration (ankerite-sericite-quartzpyrite- hematite-gold (fineness 910-940)-Ag-Au-telluride) characterize the gold deposits of the Chirano district. Alteration assemblages and the Bi, Te, and Mo contents of the mineralized rocks at Chirano are more typical of lode gold deposits than orthomagmatic gold deposits. "Alteration assemblages at Chirano contrast with the graphite-carbonate-pyrite-arsenopyrite-pyrrhotite assemblages that dominate the lode gold deposits in southwest Ghana, which are hosted by graphitic shear zones and Birimian sedimentary rocks. Differences between alteration assemblages at Chirano and those in graphitic shear zones may reflect the different wall-rock assemblages with which the hydrothermal fluid equilibrated rather than different fluid sources. Mineralization in the Chirano district formed during a relatively late episode of small-displacement, brittle cataclasis on the Chirano lode horizon after reverse ductile shearing associated with regional-scale shortening. This structural history is similar to that documented at the larger Ashanti and Bogoso deposits on the opposite side of the Kumasi basin... [ABSTRACT FROM AUTHOR]

Recognition of geochemical anomalies is a pivotal assignment in exploration projects. This study aims to delineate different Au Cu geochemical anomalies using number-size (N-S) and concentration-area (C-A) multifractal models in the Siah Jangal area, SE Iran. In this research, lithogeochemical datasets were applied for the exploration of Au and Cu. A comparison between geochemical anomaly maps based on the N-S and C-A fractal models shows the N-S fractal modeling is a powerful tool for separation of weak elemental geochemical anomalies in all of sampling zones. Based on a comparison between the results of these two methods and field studies, the geochemical anomaly zones, defined by the N-S fractal model, are more accurate than those recognized by the C-A fractal model. The obtained results of the N-S and C-A fractal models have been interpreted with the extensive set of information including structural interpretation, geological and alteration data. Au and Cu mineralization in the Siah Jangal area are hosted mainly by Oligocene-Miocene sub-volcanic rocks, especially strongly altered porphyric quartz diorite, hornblende diorite and diorite. Moreover, the positive dependence between various alteration zones and high concentrations of Au and Cu proves that strongly anomalous areas are correlated with these alteration zones. High grade Au (> 1000 ppb) and Cu (>150 ppm) are associated with the altered sub-volcanic rocks in the northern, eastern, and SW parts of the study area. Therewith, the strong anomaly populations are mostly occurred within the fault and fracture systems in the study area. This is a promising signal because quartz-sulfide veins and veinlets are associated with such structures. [Display omitted] • Number-size and concentration-area fractal models were applied to identify Au Cu enrichment zones. • Main relevant geological features were identified by remote sensing and field study for validation of the results. • Fractal models' results were compared with geological features to study the robustness of the models. [ABSTRACT FROM AUTHOR]

• The Tieshan complex was emplaced at the time interval of 144 ± 1 to 135 ± 3Ma. • The Fe-Cu-related suite has geochemical signatures similar to typical high Ba-Sr granitoids. • Both the Fe-Cu related suite and Fe-related suite were primarily originated from the enriched lithospheric mantle. • The Fe-related suite has more contributions from continental crust compared with the Fe-Cu-related suite. • Oxygen fugacity and differentiation degree of magma are useful indicators for Fe and Cu skarn mineralization. Fe and Cu skarn deposits constitute the most important skarn type worldwide, whereas the controlling factors that lead to the difference in metal associations remain not well known. The Fe- and Cu-hosting Tieshan complex in the Edong district provides a good opportunity for comparative study on the genetic differences between Fe and Cu skarn deposits. In this study, integrated studies of geochronology, geochemistry and Sr-Nd-Hf isotope compositions were conducted on the complex. LA-ICP-MS zircon U-Pb dating results show that the Tieshan complex was emplaced in the time interval of 135 ± 3 to 144 ± 1 Ma. Multiphase rocks from the complex can be broadly subdivided into two suites. The Fe-Cu-related suite, which consists of diopside diorite, quartz diorite, quartz diorite porphyrite and porphyritic granodiorite, possesses low SiO 2 (53.5–67.1 wt.%), K 2 O (2.44–3.53 wt.%) and Rb (45−83 ppm) contents, but high Sr (1132−2684 ppm), Ba (1073−1656 ppm) contents and negligible Eu anomalies, with very high Sr/Y (>90) ratios, similar to typical high Ba-Sr granitoids. The rock suite has initial 87Sr/86Sr values of 0.70648 to 0.70737, ε Nd (t) values of −12.3 to −8.2 and ε Hf (t) values of −16 to −7, comparable to values of the Early Cretaceous mafic rocks in the Edong district and adjacent areas, indicating that it might be largely derived from an enriched lithospheric mantle source, along with minor involvement of lower-crustal components. By contrast, the Fe-related suite, which is composed of quartz diorite, quartz diorite porphyrite and granodiorite porphyry, is characterized by relatively high SiO 2 (63.0–71.0 wt.%) and K 2 O contents (3.36–5.53 wt.%), and a wide range of Sr (158−1135 ppm), Ba (762−1366 ppm) contents and Sr/Y (11–99) ratios. In combination with the presence of abundant inherited zircon grains, the lower ε Nd (t) (−12.4 to −9.3) and ε Hf (t) (−25 to −15) values indicate a greater degree of lower-crustal contribution for the Fe-related suite. In addition, the calculated zircon Ce (Ce/Ce* and Ce4+/Ce3+) and Eu (Eu/Eu*) anomalies suggest that the Fe-Cu-related suite has much higher oxygen fugacity (f O 2) than the Fe-related suite. This study highlights f O 2 and fractionation degree of magma as useful indicators for differentiating Fe and Cu skarn mineralization. [ABSTRACT FROM AUTHOR]