Quartz Monzodiorite Research Articles

Crust-mantle geodynamic origin of ~2.7 Ga granitoid diversification in the Jiaobei terrane, North China Craton

The crust-mantle geodynamic origin of global late Archean granitoid diversification remains enigmatic. A series of early Neoarchean diversified granitoids were newly identified in the Jiaobei terrane of the North China Craton, including ~2749–2739 Ma Na-rich quartz dioritic, tonalitic, and trondhjemitic (DTTG) gneisses, and ~2718–2701 Ma K-rich quartz monzodioritic, granodioritic, and monzogranitic gneisses.The quartz dioritic and TTG gneisses commonly show transitional field relationships. They have low K2O/Na2O (0.19–0.59), and are characterized by decreasing MgO, FeOT, TiO2, P2O5, and CaO, changing Eu anomalies from negative to positive, and more fractionated REEs, with increasing SiO2. Both the quartz dioritic and TTG gneisses possess depleted zircon εHf(t2) values (+1.4 to + 7.0). Through quantitative petrogenetic modeling, a fractional crystallization model is invoked, i.e., the quartz dioritic gneisses were derived from partial melting of a depleted mantle source metasomatized by slab-derived melts, whereas TTG gneisses (a low silica and a high silica group) formed by different degrees of fractionation from the quartz dioritic magmas, with inferred liquidus minerals of hornblende, clinopyroxene, plagioclase, and apatite. In comparison, the K-rich granitoids show higher K2O/Na2O (0.69–2.87), with some containing euhedral muscovites. The quartz monzodioritic and granodioritic gneisses have higher MgO and Mg#, but lower Fe* (FeOT/(FeOT + MgO)) than the monzogranitic gneisses. The zircon εHf(t2) values (-0.5 to + 5.6) are lower than those of DTTG gneisses. It is suggested that these K-rich granitoids formed by partial melting of either a metasomatized mantle source (with recycled sediments) or metasedimentary rocks at diverse crustal levels.Early Neoarchean crust-mantle interactions of the Jiaobei terrane are reconstructed, including (1) earlier slab-mantle wedge interactions under a continental marginal arc, forming quartz dioritic and the derivative tonalitic and trondhjemitic rocks; (2) ongoing convergence led to high relief of the arc mountain, facilitating erosion and reworking/recycling of sediments; and (3) partial melting of coupled crust-mantle system following accretion between the above arc system and regional ~2.9 Ga or older continental nucleus generated different K-rich granitoids. It is emphasized that the construction and erosion of thickened arcs are prone to the formation of both high pressure TTGs and K-rich granitoids, leading to the late Archean granitoid diversification globally.

Late Palaeozoic–Early Mesozoic southward subduction of the Mongol–Okhotsk oceanic slab: geochronological, geochemical, and Hf isotopic evidence from intrusive rocks in the Erguna Massif (NE China)

ABSTRACT This study presents new zircon LA-ICP-MS U–Pb ages, zircon Hf isotopes, and whole-rock geochemical compositions for Late Palaeozoic–Early Mesozoic intrusive rocks from the Erguna Massif, Northeast China. Zircon U–Pb dating results indicate that the intrusive rocks were emplaced during the Late Permian–Middle Triassic (ca. 256–234 Ma) and Late Triassic (ca. 210 Ma) in the western and eastern parts of the Erguna Massif, respectively. The Late Permian gabbros and quartz monzodiorites display enrichment in Rb and K, but are depleted in Nb, Ta, and Ti. Their εHf(t) values (+5.1 to +9.1 and −0.2 to +3.7, respectively) and one-stage Hf model ages (TDM1 = 544–704 Ma and 764–889 Ma, respectively) indicate that they might be derived from the reworking of the Neoproterozoic lithospheric mantle that was metasomatised by subduction-related fluids. The Late Permian–Early Middle Triassic quartz monzonites, monzogranites, and syenogranites display variable enrichment of rare earth elements (REEs) and large ion lithophile elements (LILEs). They have εHf(t) values varying from −5.7 to +2.7 with two-stage Hf model ages (TDM2) of 1.09–1.69 Ga, implying that they possibly originated from the Mesoproterozoic continental crust. The Late Triassic syenogranites show geochemical signatures of A2-type granites with various enrichment in LILEs and LREEs and depletion in Nb, Ta, and Ti. Combined with regional geological evidence, we conclude that Late Permian to Late Triassic igneous rocks on both sides of the Mongol–Okhotsk suture belt record an active continental margin environment associated with the ongoing bidirectional subduction of the Mongol–Okhotsk Ocean. The eastern Erguna Massif and Xing’an Massif were likely located in a back-arc setting at least since ca. 216 Ma, with long-term southward subduction of the Mongol–Okhotsk oceanic slab spanning from the Late Permian–Early Jurassic.

Geochronology, geochemistry, and Hf isotopic compositions of Triassic igneous rocks in the easternmost segment of the East Kunlun Orogenic Belt, NW China: implications for magmatism and tectonic evolution

ABSTRACT The voluminous Triassic igneous rocks in the East Kunlun Orogenic Belt (EKOB) are important for investigations of the tectonic evolution of the Paleo-Tethys Ocean. This study focused on the geochronology and petrogenesis of igneous rocks in the Elashan area with the aim of constraining the regional tectonic evolution. The 238 Ma syenogranites are characterized by high SiO2 contents and marked depletions in Sr and Eu. We conclude that they are highly fractionated I-type granites derived from partial melting of Mesoproterozoic lower crust with significant fractional crystallization. Comparing with contemporaneous granites and mafic rocks, the 236 Ma quartz monzodiorites have moderate MgO (1.5–1.6 wt.%) and SiO2 (61.0–61.9 wt.%) contents and εHf(t) values (–1.2 to +1.9). They were probably generated by the mixing of Mesoproterozoic lower-crust-derived and enriched lithospheric mantle-derived melts. The 230 Ma appinites have high MgO contents (3.8–6.1 wt.%) and enriched Hf isotopic compositions, and were likely derived from partial melting of lithospheric mantle that had been metasomatized by subduction fluids. We infer that these rocks were emplaced in syn-collisional slab break-off and the later initial post-collisional extensional setting between the BayanHar-Songpan Ganze and East Kunlun terranes. The basement composition, magmatism, and tectonic evolution of the Elashan area are similar to those of the eastern EKOB.

Geochemistry of sulfide minerals from skarn Cu (Au) deposits in the Fenghuangshan ore field, Tongling, eastern China: Insights into ore-forming process

In situ elemental compositions of sulfide minerals have been widely applied to trace ore-forming processes of magmatic-hydrothermal ore systems, yet the application of elemental compositions of the sulfide minerals in skarn ore deposits is still restricted by the lack of understanding of their behaviors during the skarn formation processes. In this study, in situ (LA-ICP-MS and EPMA) elemental compositions of medium- to coarse-grained euhedral pyrite and xenomorphic granular chalcopyrite are investigated for the Fenghuangshan and Baoshantao skarn Cu (Au) deposits in the Tongling region, eastern China. The results show that the studied pyrite samples have relatively consistent trace element composition characteristics, while the chalcopyrite studied displays high Zn, Ag and Pb contents, and relatively high Bi content. Au, Ag, Cu, Pb, Bi, Sb and Tl are mainly of lattice bound appearance in the pyrite structure. The Au, Ag, Sb, Pb and Bi are mainly incorporated into the chalcopyrite structure as coupled substitutions. Low Au (mainly < 0.1 ppm), Se (<3 ppm) and As (<100 ppm) contents, and high Co/Ni (mainly >1) and Se/Tl (mainly >10) ratios of the pyrite studied, and high Sn (>10 ppm) and low Tl (<1 ppm) contents of the chalcopyrite imply a high temperature, high oxygen fugacity and acidic pH magmatic-hydrothermal fluid for the Tongling skarn Cu (Au) mineralization. High Zn and Bi contents in the pyrite and chalcopyrite studied, and low Co/Ni ratios (<0.1) of the pyrite from quartz monzodiorite probably indicate a sedimentary component from subducted slab contribution to the magmatic-hydrothermal system.

Short wavelength infrared (SWIR) spectroscopy of phyllosilicate minerals from the Tonglushan Cu-Au-Fe deposit, Eastern China: New exploration indicators for concealed skarn orebodies

The Middle–Lower Yangtze River Metallogenic Belt (MLYRB) is one of the most important Cu–Au–Fe–Mo skarn–porphyry metallogenic belts in Eastern China. After several decades of mining, the shallow-level mineral resources have been gradually exhausted, which call for new exploration tools for concealed orebodies. The Tonglushan Cu–Au–Fe skarn deposit (86.3 Mt @ 1.66% Cu, 0.94 g/t Au and 39.4% Fe) is located in the western MLYRB. Skarn alteration/mineralization are mainly hosted in the contact zone between Cretaceous (~141 Ma) quartz monzodiorite (and its porphyry) and the Lower Triassic carbonate rocks. Based on the mineral assemblages and their macro/microscopic textural relationships, the Tonglushan Cu–Au–Fe mineralization/alteration can be divided into five stages: pre-ore (S1: skarn–potassic alteration), Fe ore (S2: retrograde alteration and Fe-oxides), Cu–Au ore (S3: quartz–sulfides), carbonate alteration (S4) and supergene alteration (S5). Apart from the major skarn and retrograde alteration and carbonate minerals, abundant fine-grained phyllosilicate minerals, including chlorite, white mica (illite, muscovite and phengite), smectite (montmorillonite and saponite) and kandite (kaolinite, dickite and halloysite) group minerals have been identified at Tonglushan by SWIR spectrometry. Integrating petrographic observations and SWIR spectral analysis, four alteration zones (with distinct phyllosilicate assemblages) have been distinguished from the intrusion outward: (I) ore-barren quartz monzodiorite and its porphyry (montmorillonite–illite–chlorite), (II) endoskarn close to the skarn–hydrothermal mineralization center (montmorillonite–illite–chlorite–kaolinite–dickite), (III) skarn–hydrothermal mineralization center (saponite–chlorite), and (IV) the external contact zone in (dolomitic) marble (montmorillonite–chlorite ± kaolinite ± dickite).For the Tonglushan altered rock samples, SWIR spectrometry has identified wavelength shifts in the Fe–OH, Al–OH and sub-Al–OH absorption features of chlorite, white mica–montmorillonite and kandite, respectively. Chlorite Fe–OH absorption occurs at longer wavelengths (>2,250 nm), white mica–montmorillonite Al–OH absorption occurs at unusually long (>2,212 nm) and short (<2,202 nm) wavelengths, and kandite sub-Al–OH absorption occurs at longer wavelengths (>2,170 nm) in strongly-altered skarn proximal samples. Moreover, the presence of kaolinite, dickite, saponite, actinolite, phlogopite and/or chlorite–quartz–sulfides veins in these samples can be used as new vectors to explore deep-level mineralization centers at Tonglushan. The distribution of various kinds of phyllosilicate alteration minerals at Tonglushan, especially the white mica and kandites (with higher crystallinity) in the deep contact zones, indicates that the neutral to acidic hydrothermal fluids may have been generated with the precipitation of Fe-oxides and sulfides. This study also highlights the potential of SWIR spectroscopy of phyllosilicate minerals for exploring concealed skarn orebodies in the MLYRB.

Multiple generations of titanites and their geochemical characteristics record the magmatic-hydrothermal processes and timing of the Dongguashan porphyry-skarn Cu-Au system, Tongling district, Eastern China

Dongguashan is one of the largest porphyry-skarn Cu-Au deposits in eastern China and titanite is found in the ore system. Five types of both magmatic and hydrothermal titanites are distinguished, based on their textural and chemical characteristics. Types 1 and 2 titanites are magmatic in origin whereas types 3, 4, and 5 are hydrothermal. Magmatic titanites are wedge-shaped and display concentric and sector zoning, whereas hydrothermal titanites show a wide range of textures that vary with different alteration stages. REE, Sn, Mo, and Cu are enriched in magmatic titanites (types 1 and 2). In contrast, vanadium and HFSE are enriched in hydrothermal titanites, especially in type 4 titanite from the propylitic alteration zone. Magmatic titanite (type 1) coexists with magnetite and K-feldspar and crystallized in oxidized and H2O-rich magma at 730–760 °C. Type 2 titanite contains ilmenite inclusions reflecting changes in the fO2 of the magma chamber, possibly caused by input of mafic magma. The mobility and enrichment of HFSE and association with fluorapatite reflect the F-rich composition of the magmatic-hydrothermal fluid at Dongguashan. The relationship between titanite textures and chemistry indicates that titanite can serve as a recorder of magmatic-hydrothermal processes in porphyry copper systems. U-Pb dating of type 4 titanite from the propylitic alteration zone and type 5 titanite from skarn yielded ages of 139.0 ± 2.6 Ma and 137.0 ± 2.0 Ma, respectively, indicating that it formed synchronously with the associated quartz monzodiorite.

Slab roll-back and crustal growth in the Eastern Junggar terrane, NW China: evidence from Carboniferous A-type granitoids and adakitic rocks

ABSTRACT Revealing the formation mechanism of granitic plutons is vital for understanding crustal growth of Earth. Here, we present an integrated study of geochronological, elemental, whole rock Nd and zircon Hf isotopic data for a granitic pluton system that formed in the Eastern Junggar, NW China. Zircon U–Pb dating suggests the seven granitic plutons were emplaced at 356–312 Ma. The monzogranites have high alkaline and Zr contents, and high Ga/Al and TFe2O3/MgO ratios, which are geochemically similar to A-type granitoids. They display positive ɛNd(t) (+4.3 to +5.4) and ɛHf(t) (+7.6 to +12.4) values, and young Nd and Hf model ages, suggesting a lower arc crust source. The quartz monzodiorites have high Sr, low Y and Yb contents, yielding relatively high Sr/Y ratios that are similar to modern adakites. These rocks also have high positive ɛNd(t) (+7.6 to +8.0) and ɛHf(t) (+13.9 to +15.5) values, and young Nd and Hf model ages, indicating a subducted oceanic crustal source. In combination with data from other plutons in this area, we suggest that they were likely generated by roll-back of the subducted Junggar oceanic slab, which resulted in back-arc extension, asthenosphere upwelling, and partial melting of oceanic crust and lower arc crust.

Petrogenesis of late Mesozoic granitoids from the southern segment of the Tan–Lu Fault, eastern China: implications for the tectonic affinity of the Zhangbaling Uplift

ABSTRACT Late Mesozoic magmatic rocks of the Zhangbaling Uplift (ZBU) in eastern China, which comprises the northern Zhangbaling area and the southern Feidong area, can provide insights into the deep crustal processes and tectonic affinity of the massif. These rocks are dominated by granitoids with formation ages of 132–120 Ma and a peak at 129 Ma. The Shankouling dyke (120.4 ± 1.1 Ma) and the Zhuyuanzhang quartz monzodiorite (129.0 ± 2.2 Ma) crop out sporadically in the Feidong area. These rocks show adakitic signatures of high Al2O3 and Sr contents, high Sr/Y, (La/Yb)N, and (Dy/Yb)N ratios, and low Y and YbN contents. They have enriched (87Sr/86Sr)i ratios, negative εNd(t) and εHf(t) values, and unradiogenic Pb isotopic compositions that resemble those of coeval high Sr/Y granitoids in the Dabie Orogen. These ZBU rocks can be divided into two groups: low-Mg granitoids with more enriched Sr–Nd isotopic signatures and low Mg# values (<50), and high-Mg granitoids with weakly enriched Sr–Nd isotopic signatures and high Mg# values (mostly >50). Combining their geochemical features with previous results of experimental melts, we conclude that the low-Mg granitoids were derived from fluid-absent partial melting of in situ thickened lower continental crust, resulted from Triassic continental subduction and collision in this area, whereas the high-Mg granitoids were derived from delaminated eclogitic lower crust followed by interaction with mantle peridotites during magma ascent. Isotopic compositions show that these granitoids could have been derived from ancient crust of the Yangtze Block via re-melting of Neoarchean and Paleoproterozoic lower continental crust. The great depth of the Tan–Lu Fault Zone enabled delamination of the thickened eclogitic mountain root beneath the ZBU, which resulted in the formation and emplacement of the high-Mg rocks, followed by uplift of the Zhangbaling massif associated with rollback of the subducting Paleo-Pacific (Izanagi) Plate.

The use of lithogeochemistry in delineating hydrothermal fluid pathways and vectoring towards gold mineralization in the Malartic district, Québec

The world-class, oxidized intrusion-related Canadian Malartic gold deposit, with reserves estimated at 5.56 Moz Au grading 1.10 g/t Au, and a total geological endowment of 16.3 Moz Au, is one of the largest gold deposits in the Archean Superior Province of Canada. The gold mineralization is hosted predominantly by Pontiac Group metasedimentary rocks, Piché Group metavolcanic rocks, and quartz monzodiorite to granodiorite porphyritic intrusions. The ore takes the form of a low-grade envelope of disseminated pyrite (0.35 to 1 g/t Au) grading inwards into higher grade (>1 g/t Au) stockwork and breccia zones. Hydrothermal alteration in the metasedimentary rocks is zonally distributed around the fluid pathways. Proximal alteration is characterized by a microcline±albite-quartz replacement-type assemblage, with lesser phlogopite, calcite±Fe-dolomite, pyrite and rutile. The distal alteration assemblage comprises biotite, microcline±albite, phengite, quartz, calcite, pyrite and rutile.In this study, we assess the magnitude and distribution of fluid-rock interaction in the metasedimentary rocks of the Malartic district. The metaturbidites are separated into four lithotypes based on grain-size to reduce the effects of primary depositional processes on mass change calculations. Despite the variability in protolith composition, the metasedimentary rocks define a geochemically consistent, cogenetic sequence. The results of the mass transfer calculations indicate progressive gains in CO2, S, K2O and LOI, as well as Au, Te, W, Ag, As, Be, Sb, Bi, Mo and Pb, from background, to distal and proximal alteration zones (relative to the least-altered samples). Molar element ratio analysis (alkali/aluminum) indicates an increase in alkali metasomatism (K and Na) adjacent to the main hydrothermal fluid pathways, which is manifested by the progressive stabilization of microcline and albite at the expense of oligoclase, biotite and white mica.Ore-associated pathfinder elements delineate broad enrichment patterns around the deposit, and are used to understand hydrothermal fluid circulation in the Malartic district. A statistical approach based on a comparison of the mass change results with the background composition provides robust constraints on the magnitude and extent of the lithogeochemical haloes. Generally, the alteration forms envelopes that extend along the S2 fabric, with the largest lithogeochemical anomalies (e.g., Au, W, Te and Ag) reaching up to 10 km in length, and 2 km in width. The results of this study demonstrate that whole-rock lithogeochemistry can provide a valuable tool with which to define vectors toward gold mineralization in a regional exploration context.

Chapter 9 Continental magmatic arc and siliciclastic sedimentation in the far-field part of a 1.7 Ga accretionary orogen

Abstract Trachyandesitic to trachybasaltic lavas, interlayered siliciclastic sedimentary rocks and subaerial ignimbrites with a rhyolitic to trachydacitic composition lie unconformably above metamorphic rocks in west-central Sweden. These volcanic rocks erupted at 1711 + 7/−6 to 1691 ± 5 Ma and belong to a high-K, calc-alkaline to shoshonitic suite deposited in a continental arc setting. Positive ɛ Nd values and Nb/Yb ratios in the trachyandesitic to trachybasaltic rocks indicate an enriched mantle source. Coeval, 1710 ± 11 to 1681 ± 16 Ma plutonic and subvolcanic rocks are mainly granitic or quartz syenitic in composition. Subordinate components include quartz monzonite, quartz monzodiorite and monzogabbro or gabbro. ɛ Nd values in the range −1.0 to + 1.1 overlap with those in the inferred 1.9–1.8 Ga source rocks. All these rocks belong to the youngest phase of the lithodemic unit referred to as the Transscandinavian Igneous Belt. This magmatic province extends in a roughly NNW direction for at least 900 km, variably deformed and metamorphosed equivalents occurring inside and beneath younger orogenic belts to the south (Sveconorwegian) and north (Caledonian). The part of the province in west-central Sweden addressed here represents a far-field and shallow crustal component in this 1.7 Ga accretionary orogenic system.

Settlement conditions of magma (s) forming Jurassic plutonic rocks in the Gümüşhane (Eastern Pontides, Turkey)

In this study, the petrography, mineral chemistry and crystallization conditions were reported for the Alemdar and Isikdere plutons located in limited areas in the south of the Eastern Pontides. These plutons, which trend mostly in NE-SW directions, were emplaced by cutting the Early- Middle Carboniferous-aged Gumushane Granitoid and Early-Middle Jurassic Şenkoy formation. Petrographically, the studied plutons are compositionally fine to medium grained quartz-diorite, quartz monzodiorite and tonalite. The rocks in the plutons have granular, poikilitic, monzonitic, graphic and rare porphyritic textures with consist of plagioclase, (An05-92), hornblende (Mg# = 0.52- 0.81), biotite (Mg# = 0.32-0.67), orthoclase, quartz and Fe-Ti oxide. According to thermobarometric calculations, plutons have crystallization temperatures, pressures and oxygen fugacity values ranging from 541°C to 938°C, 0.1 to 4.4 kbar, and -23 to-12, respectively. The estimated water content calculated from amphibole is between 4.4 to 7.8%. It can be concluded that the studied plutons were emplaced at mid to shallow crustal depths (~4-15 km).

Genesis of Late Cretaceous intra-oceanic arc intrusions in the Pertek area of Tunceli Province, eastern Turkey, and implications for the geodynamic evolution of the southern Neo-Tethys: Results of zircon U–Pb geochronology and geochemical and Sr–Nd isotopic analyses

The plutonic units of the Elazığ magmatic complex crop out in the Pertek area of Tunceli Province (eastern Turkey) in the Southeast Anatolian Orogenic Belt (SAOB). Three stages of plutonic activity can be recognised on the basis of order of formation and geochemistry: (1) a first stage of gabbro, diorite, tonalite and quartz diorite; (2) a second stage of granite, granodiorite and quartz monzodiorite; and (3) a third stage of quartz monzonite and monzodiorite. Geochemical analyses show that the intrusive rocks are metaluminous I-types that vary in composition from tholeiitic to shoshonitic. The first- and second-stage intrusive rocks formed in an intra-oceanic arc setting, and the third-stage shoshonitic intrusive rocks formed in a collision setting. In this paper, we present the results of zircon U–Pb dating and geochemical and Sr–Nd isotopic analyses. The zircon U–Pb dating indicates emplacement of these rocks between 80.6 ± 0.9 and 77.2 ± 1.1 Ma (Late Cretaceous). Primitive mantle-normalised trace element concentrations show enrichments in large ion lithophile elements (LILEs) and light rare earth elements (LREEs). The values of 87Sr/86Sr(i) range from 0.70575 to 0.70748, 143Nd/144Nd(i) from 0.512453 to 0.512876, and εNd(i) from −1.7 to +6.7. Our results shed new light on the possible sources and evolution of the magmas during the northward subduction of the oceanic plate of the southern branch of the Neo-Tethys during the Late Cretaceous.

Hydrothermal Alteration Mineralogy and Geochemistry of the Archean World-Class Canadian Malartic Disseminated-Stockwork Gold Deposit, Southern Abitibi Greenstone Belt, Quebec, Canada

AbstractThe Canadian Malartic stockwork-disseminated gold deposit is an Archean world-class deposit located in the southern Abitibi greenstone belt. It contains over 332.8 tonnes (t; 10.7 Moz) of Au at a grade of 0.97 ppm, in addition to 160 t (5.14 Moz) of past production (1935–1981). Although the deposit is partly situated within the Larder Lake-Cadillac fault zone, most of the ore occurs up to ~1.5 km to the south of the fault zone. The main hosts of the mineralized zones are greenschist facies turbiditic graywacke and mudstone of the Pontiac Group (~2685–2682 Ma) and predominantly subalkaline ~2678 Ma porphyritic quartz monzodiorite and granodiorite. These intrusions were emplaced during an episode of clastic sedimentation and alkaline to subalkaline magmatism known as the Timiskaming assemblage (&lt;2680–2670 Ma in the southern Abitibi). The orebodies define two main mineralized trends, which are oriented subparallel to the NW-striking S2 cleavage and the E-striking, S-dipping Sladen fault zone. This syn- to post-D2 ductile-brittle to brittle Sladen fault zone is mineralized for more than 3 km along strike.The ore mainly consists of disseminated pyrite in stockworks and replacement zones, with subordinate auriferous quartz veins and breccia. Gold is associated with pyrite and traces of tellurides defining an Au-Te-W ± Ag-Bi-Mo-Pb signature. The orebodies are zoned outward, and most of the higher-grade (&gt;1 ppm Au) ore was deposited as a result of iron sulfidation from silicates and oxides and Na-K metasomatism in carbonatized rocks. The alteration footprint comprises a proximal alteration envelope (K- or Na-feldspar-dolomite-calcite-pyrite ± phlogopite). This proximal alteration zone transitions to an outer shell of altered rocks (biotite-calcite-phengitic white mica), which hosts sub-ppm gold grades and reflects decreasing carbonatization, sulfidation, and aNa+/aH+ or aK+/aH+ of the ore fluid.Gold mineralization, with an inferred age of ~2664 Ma (Re-Os molybdenite), was contemporaneous with syn- to late-D2 peak metamorphism in the Pontiac Group; it postdates sedimentation of the Timiskaming assemblage along the Larder Lake-Cadillac fault zone (~2680–2669 Ma) and crystallization of the quartz monzodiorite. These chronological relationships agree with a model of CO2-rich auriferous fluid generation in amphibolite facies rocks of the Pontiac Group and gold deposition in syn- to late-D2 structures in the upper greenschist to amphibolite facies. The variable geometry, rheology, and composition of the various intrusive and sedimentary rocks have provided strain heterogeneities and chemical gradients for the formation of structural and chemical traps that host the gold. The Canadian Malartic deposit corresponds to a mesozonal stockwork-disseminated replacement-type deposit formed within an orogenic setting. The predominance of disseminated replacement ore over fault-fill and extensional quartz-carbonate vein systems suggests that the mineralized fracture networks remained relatively permeable and that fluids circulated at a near-constant hydraulic gradient during the main phase of auriferous hydrothermal alteration.

Origin and evolution of hydrothermal fluids in the Marshoun epithermal Pb–Zn–Cu (Ag) deposit, Tarom-Hashtjin metallogenic belt, NW Iran

The Marshoun epithermal Pb–Zn–Cu (Ag) deposit is located in the Tarom–Hashtjin metallogenic belt (THMB), northwest Iran. The epithermal base metal veins are mainly hosted in Eocene volcanic and volcaniclastic rocks of the Karaj Formation, and late Eocene pyroxene quartz monzodiorite. The mineralization process can be divided into five stages: (1) quartz-chalcopyrite-pyrite veins and breccias, (2) quartz (calcite)-sphalerite-galena ± chalcopyrite ± pyrite veins and breccias, (3) barren post-ore quartz veinlets, (4) barren post-ore calcite veinlets, and (5) supergene mineral assemblages. The primary metallic minerals are pyrite, chalcopyrite, sphalerite, and galena; gangue minerals are mainly quartz, calcite, sericite, and chlorite. The main wall-rock alteration is silicification, intermediate argillic, carbonate, and propylitic alteration. Microthermometric measurements of primary LV fluid inclusion assemblages in quartz and sphalerite indicate that the veins were mainly formed at temperatures between 173 and 285 °C from fluids with salinities between 3.4 and 6.3 wt% NaCl equiv. Coexisting LV, VL, and V inclusions in quartz and sphalerite provide evidence for boiling in ore-stage breccia and veins. Additionally, the occurrence of bladed calcite as well as plumose and colloform/crustiform banded quartz in the ore zones and the presence of hydrothermal breccias are consistent with boiling. Obtained oxygen and sulfur isotope compositions (δ18Owater = +9.2‰ to +1.5‰; δ34SH2S = –10.0‰ to –5.7‰) indicate there was a major contribution from a magmatic component to metallogenesis. The fluid inclusion and stable isotope data indicate that fluid boiling and mixing facilitated hydrothermal alteration and mineralization at Marshoun. The Marshoun deposit is interpreted as an intermediate-sulfidation style of epithermal mineralization. Our data suggest that the epithermal mineralization in the THMB are related to late Eocene (ca. 36–37 Ma) shallow magmatic–hydrothermal activity. The altered Eocene volcanic-subvolcanic rocks, particularly at the intersection of subvolcanic rocks with faults were the most favorable locus for exploration targeting of epithermal ores at THMB.

Geochemical characteristics and origin of the Neoproterozoic high-K calc-alkaline granitoids in the northern part of Mandara hills, northeastern Nigeria

The high-K calc-alkaline granitoids in the northern part of the Mandara Hills are part of the well-exposed post-collisional plutons in northeastern Nigeria. The calc-alkaline rock association consists of quartz monzodiorite, hornblende biotite granite, biotite granites and aplite which intruded the older basement consisting mainly of low-lying migmatitic gneisses and amphibolites during the Neoproterozoic Pan-African Orogeny. Petrological and geochemical studies have revealed the presence of hornblende, iron oxide, and metaluminous to slightly peraluminous characteristics in the granitoids which is typical of I-type granite. The granitoids are also depleted in some high field strength elements (e.g. Nb and Ta) as well as Ti. Plots of Mg# versus SiO2 indicate that the granite was derived from partial melting of crustal sources. Lithospheric delamination at the waning stage of the Pan-African Orogeny possibly triggered upwelling of hot mafic magma from the mantle which underplated the lower crust. This, in turn, caused partial melting and magma generation at the lower to middle-crustal level. However, the peculiar geochemical characteristics of the quartz monzodiorite especially the enrichment in compatible elements such as MgO, Cr, and Ni, as well as LILE element (e.g. K, Ce, Cs, Ba, and Sr), signify that the rock formed from an enriched upper mantle source. The emplacement of high-K granites in the Madara Hill, therefore, marked an important episode of crustal reworking during the Neoproterozoic. However, further isotopic work is needed to confirm this model.

Early cretaceous igneous activities in the north flank of the North China Craton: the Shouwangfen complex example

ABSTRACT The Early Cretaceous igneous complexes in the north flank of the North China Craton (NCC) provide a window to investigate the Mesozoic magmatism in the NCC. Here we report the precise timing of Early Cretaceous magmatism and magma petrogenesis of the different rock types in the north flank of the NCC based on petrology, mineral chemistry, geochemistry, zircon geochronology and Sr-Nd isotopes. Zircon U-Pb dating reveals that the Shouwangfen complex was crystallized at 130–128 Ma. The rocks display enrichment in large ion lithophile elements (LILE) and LREE, and depletion in high field strength elements (HFSE) and HREE, with relatively high Sr/Y and La/Yb values, typical of subduction-related magmatic rocks. The mafic microgranular enclaves show typical igneous textures, acicular apatites, sieve-texture of plagioclase phenocrysts and overgrowth of amphibole around the pyroxene, corresponding to magma mixing and mingling and thermal exchange. The quartz monzonites display normal zoning of the plagioclase, low and homogeneous εNd(t) values and linear co-variations in two-component diagrams. The quartz monzodiorites are characterized by high and homogeneous εNd(t) values. Petrologic feature and geochemical data suggest that the quartz monzonites represent lower crustal magma with minor contribution of enriched melt of the sub-continental lithospheric mantle (SCLM), followed by fractional crystallization. The mafic microgranular enclaves were sourced from enriched SCLM, followed by mixing and mingling with the host quartz monzonitic magma. The quartz monzodiorites are mainly SCLM-derived and subsequently mixed with lower crust melts. The high water contents (≥3%) of these Early Cretaceous igneous complexes suggests a hydrous SCLM beneath the NCC. The Early Cretaceous igneous complexes formed within an extensional tectonic setting which were related to the retreat and dehydration of the paleo-Pacific slab. The hydration of the lithosphere induced extensive crust-mantle interaction and large-scale water-rich magmatism, leading to lithospheric thinning in the NCC during the Mesozoic.

Geochronology and geochemistry of the intrusive suite associated with the Khatsavch porphyry Cu-Au (Mo) deposit, South Mongolia

The Khatsavch porphyry Cu-Au (Mo) deposit is located in the Gurvansayhan island arc terrane of South Mongolia, approximately 45 km southwest of the Oyu Tolgoi Cu-Au district, one of the largest porphyry-type Cu-Au deposits in the world. The mineralization of the Khatsavch deposit is spatially and temporally associated with the second stage of the Baga Khachig intrusive complex, which intruded the Early Devonian Ekhiin Gol formation and is overlain by Quaternary sediments. Based on geological relationships, the age of the intrusive complex has been determined as Carboniferous; however, the precise age remains to be constrained.Here we present new geochronological, mineralogical, and geochemical data for the intrusive event that facilitated the formation of the Khatsavch deposit. Laser ablation ICP-MS analysis of U-Pb isotopes in zircons yields an age of 366 ± 6.4 Ma, which is within the uncertainty of ages of the granitoids that host the Oyu Tolgoi deposits (∼372 Ma and ∼366 Ma). Mineralogically, the granitoids of the Khatsavch and Oyu Tolgoi porphyry deposits are quartz monzonites, quartz monzodiorites, and granodiorites. Disseminated Cu-Au (Mo) mineralization occurs in quartz veins as well as in the granitoids of the Khatsavch deposit and is dominated by chalcopyrite, pyrite, molybdenite, and rare gold. Geochemically, rocks from the Khatsavch deposit are I-type granitoids with high K calc-alkaline affinity emplaced in a volcanogenic arc setting. Chondrite-normalized bulk rock rare earth element data show listric patterns similar to that of the Oyu Tolgoi, which is interpreted to reflect amphibole fractionation in arc settings. Granitoids from both deposits display smoothly decreasing Y, Yb, and Sr concentrations with differentiation, and increasing Sr/Y and La/Yb ratios with decreasing Y and Yb, which are consistent with hornblende, titanite, and plagioclase fractionation. Moreover, these granitoids are enriched in LILE, Pb, and U and depleted in Ta, Nb, and Ti. Based on the mineralogical and geochemical similarities of the Khatsavch and Oyu Tolgoi deposits, and their spatial and temporal proximity, it is argued that both ore systems are associated with the same magma source and that undiscovered deposits derived from this source may exist. Therefore, we suggest that the Gurvansayhan island arc terrane is an excellent exploration target well beyond the existing deposits.

Zircon U-Pb geochronology, geochemistry, Sr-Nd isotopic compositions, and tectonomagmatic implications of Nay (NE Iran) postcollisional intrusives in the Sabzevar zone

The mafic to felsic intrusive rocks of Nay (IRN) are located in the northeast of the central Iranian block. In this study, we present new major and trace element geochemistry, U-Pb zircon ages, and Sr-Nd isotopic data to discuss the origin of the IRN postcollisional units. The oldest units in the Nay area belong to Paleocene?early Eocene volcanic and pyroclastic series including basalt-andesite, latite, dacite, and tuff. These series are crosscut by subvolcanic and granitoid rocks with lithological composition varying from quartz gabbro to K-feldspar granite. The youngest igneous activity is represented by quartz monzodiorite dikes. Hornblende-biotite quartz monzonite from Nay granitoids was dated at 40 Ma (zircon U-Pb). The IRN rocks are metaluminous to peraluminous with high-K calc-alkaline and shoshonitic affinities. They display enrichment in light REEs [(La/Yb)N = 3.79?8.71] and LILEs (such as Ba, Th, Rb, U, and K), with depletion in HFSEs (such as Nb, Zr, Y, and Ti). All rocks have negative Eu anomalies [(Eu/Eu*)N = 0.17?0.88] and relatively flat heavy REE patterns [(Gd/Yb)N = 1.12?1.69]. Granitoids have initial 87Sr/86Sr values from 0.7053 to 0.7061 and ?Nd values from ?1.65 to ?0.02 calculated at 40 Ma. The geochemical composition of IRN rocks along with the low ISr and positive ?Nd values and mantle model ages of 0.6?0.8 Ga indicate that two end-members, enriched mantle and a continental crust, were involved in the magma generation. We argue that the Eocene IRN magmatism occurred as a postcollisional product by asthenospheric upwelling owing to the convective removal of the lithosphere during an extensional collapse of the central Iranian block.

Early Ordovician alkali-ultramafic Zhilandy complex (Central Kazakhstan): structure and age of formation

U–Pb geochronological study of amphibole-bearing quartz monzodiorites of the alkali-ultramafic Zhilandy complex in Central Kazakhstan, whose formation is deduced at the Early Ordovician era (479 ± 3 Ma). The obtained data indicate three stages of intra-plate magmatism in the western part of the Central Asian Orogenic Belt: Late Neoproterozoic stage of alkali syenites of the Karsakpay complex intrusion, Early Cambrian stage of ultramafic-gabbroid plutons of the Ulutau complex formation, and Late Cambrian–Early Ordovician stage of formation of the Zhilandy complex and Krasnomay complex intrusions.

The extension of the Transscandinavian Igneous Belt into the Baltic Sea region

Geological investigations of the Precambrian crystalline basement in the Baltic Sea region have been performed on five samples from drill cores or percussion drill fragments collected from 0.2 to 2.5 km depths. The samples were analyzed for geochemistry and dated with the U-Pb zircon methods using SIMS or LA-ICP-MS techniques. A coarse-grained K-feldspar-bearing granitoid at Frigsarve, southern Gotland, has an age of 1845 ± 4 Ma, and can be correlated with the TIB 0 generation of the Transscandinavian Igneous Belt (TIB). The U-Pb age of a quartz monzodiorite at Böda Hamn, northern Öland, was determined to 1799 ± 4 Ma, while a quartz monzonite at Valsnäs, central Öland, yielded 1788 ± 5 Ma; both rocks showing geochemical affinities to the TIB. The Böda Hamn quartz monzodiorite is correlated with the TIB 1a generation while the Valsnäs quartz monzonite is correlated with the TIB 1b generation. The U-Pb ages of granodiorites in the E7-1 and D1-1 drill holes offshore Latvia and Lithuania are 1764 ± 7 Ma and 1744 ± 7 Ma, respectively. Both rocks can be correlated with orthogneisses of the Blekinge Province in southern Sweden as well as orthogneisses in northern Poland.A review of previous correlations of the Precambrian crust in the Baltic Sea region suggests that five crustal units, formed in accretionary environments in the time period from 1.90 to 1.75 Ga, extend from the Fennoscandian Shield in SE Sweden into the Baltic Sea region. The northern part of the Baltic Sea region is dominated by the 1.90–1.87 Ga Svecofennian units continuing into the Precambrian basement beneath Estonia and Latvia. The oldest generation of the Transscandinavian Igneous Belt (TIB 0) can be followed from Askersund in south-central Sweden, via southern Gotland to northwestern Lithuania. The TIB 1 comprises three subunits (TIB 1a–c) which dominate the southwestern parts of the East European Craton from the Svecofennian Domain to the Tornqvist zone.