Magmatic-hydrothermal Activity Research Articles

Garnet geochronology, major and trace element geochemistry of the Huanggangliang Fe-Sn polymetallic deposit, NE China

Cu-Fe (Au), W-Sn (Mo), Pb-Zn (Ag) and other element assemblages are common in many skarn deposits, but examples of Fe and Sn coexistence in nature are relatively rare. The Huanggangliang deposit in the southern Great Xing'an Range is the largest Fe-Sn polymetallic deposit in northern China, and there are five main mining areas (SK Ⅰ–SK Ⅴ) distributed along a SW–NE trend. SK Ⅰ and SK Ⅲ are the two larger mining areas in the Huanggangliang deposit, and their mineral assemblages and wall-rocks are significantly different: cassiterite and metal sulfides are duncommon in SK Ⅰ (andesite), while they are widely distributed in SK Ⅲ (marble). Garnet is widely distributed in SK Ⅰ and SK Ⅲ mining areas, and provides a good opportunity to explore the mechanism of Fe-Sn assemblage differentiation. Three types of garnet are distinguishable (Grt 1, Grt 2 and Grt 3) based on their mineral associations, textures and locations, and they mainly belong to the andradite-grossular solid solution series. The LA–ICP–MS U-Pb ages of the garnets from SK Ⅰ and SK Ⅲ are 136.0 ± 1.2 Ma (n = 25, MSWD = 1.9) and 136.2 ± 2.6 Ma (n = 37, MSWD = 1.8), respectively, suggesting that magmatic-hydrothermal activity in these two mining areas began at the same time. Grt 1 (located deep in SK Ⅰ and SK Ⅲ) and Grt 2 (located shallowly in SK Ⅰ) are mainly andradite, while Grt 3 (located shallowly in SK Ⅲ) is mainly grossular. They are all enriched in high field strength elements (HFSEs) and depleted in large ion lithophile elements (LILEs), and their REE patterns are enriched in light rare earth elements (LREEs) and depleted in heavy rare earth elements (HREEs). However, Grt Ⅰ-1a and 1b (deep garnets in SK Ⅰ) exhibit obvious positive Eu anomalies, while the other garnet types exhibit negative or no obvious Eu anomalies. Additionally, Grt 3 has high contents of V, Sn, U, Th, Zn and Y, and low contents of W and Mo. This pattern implies that the garnets in deep SK Ⅰ may have formed under oxidizing conditions with high temperatures, high oxygen fugacity (fO2) and weak acidity, while the garnets in shallow SK Ⅲ formed under reducing conditions with moderate temperatures, moderate fO2 and near-neutral pH. The garnets in shallow SK Ⅰ and deep SK Ⅲ may have formed under weak oxidation–reduction conditions at moderate to high temperatures, moderate fO2 and weakly acidic to neutral pH conditions. Our newly reported field geological, mineralogical, and geochemical data from garnet suggest that the ore-forming fluids of the Huanggangliang were magmatic-hydrothermal fluids mixed with slightly acidic external fluids, chloride complexes may have been the main transport ligands of REEs. The metallogenic environment may be an important factor leading to the difference of mineral assemblages in the Huanggangliang deposit.

Geological features of the Zn-Pb prospect in the Bou-Izourane district (Morocco)

The Zn-Pb mineralization in the Bou-Izourane district, located in the High Atlas Mountains of Morocco, contains estimated reserves of 40 200 tons of ore with an average grade of 20% Zn and 3.5% Pb. It is developed on N–S to NNW–SSE-trending faults that cut Liassic carbonate marl deposits. The paragenetic mineral sequence consists of galena, sphalerite and late-stage calcite. Oxidation phases of galena into cerussite and sphalerite into smithsonite are common in the Bou-Izourane ore, linked to the infiltration of meteoric waters and the oxidation of these sulphides. The Zn-Pb mineralization runs parallel to the fluorite veins associated with the igneous rocks of Tamazeght, but no petrographic or field relationship has been demonstrated between these two mineralizations (i.e., Zn-Pb and fluorite). The distribution of rare earth elements and yttrium (REY) in the Zn-Pb mineralization of Bou-Izourane shows a notable similarity with the Mississippi Valley Type (MVT) mineralization of the Central High Atlas of Morocco, although the concentrations more closely resemble those of REY in fluorite linked to the magmatic-hydrothermal activity of Tamazeght. However, the analysis of their distribution in post-fluorite calcite and post-Zn-Pb calcite reveals a strong concordance, suggesting that these two calcites are associated with the same phase and have a common origin. The classification of the Zn-Pb prospect in Bou-Izourane remains controversial, fluctuating between an MVT-type mineralization, similar to most Zn-Pb mineralizations in the Central High Atlas of Morocco, and a mineralization linked to the magmatic-hydrothermal activity of Tamazeght, which could provide heat and metallogenic material. Characterizing the Zn-Pb ore of Bou-Izourane is crucial for the future exploration of zinc and lead deposits in the High Atlas of Morocco and could advance the development of Zn-Pb mining in the region, from artisanal exploitation to professional mining

Linking beryllium enrichment to crystal-melt separation in granitic magmatic systems: Insights from high-silica granites in the southern Great Xing’an Range, NE China

High-silica granites are significant carriers of highly incompatible elements and are closely associated with mineralization of the rare metal beryllium. Thus, understanding their origin and evolution is of paramount importance for comprehending the evolution of the continental crust and enrichment processes of beryllium. This study presents zircon U-Pb ages, whole-rock major and trace element compositions, and Nd-Hf-O isotopic data for Early Cretaceous high-silica granite porphyries, monazite U-Pb ages and Nd isotopic data for beryllium-rich quartz veins, and whole-rock and apatite Nd isotopic data for Permian tuffs in the Dongshanwan W-Mo-Be deposit in the southern Great Xing’an Range, northeastern China. Our aim is to elucidate the link between mineralization and magmatism and to further our insight into the processes of crystal-melt separation and the mechanisms driving beryllium enrichment in granitic magmatic systems. Zircon U-Pb dating of the high-silica granite porphyry yields a weighted mean 206Pb/238U age of 141 ± 1 Ma, which is consistent with the age of hydrothermal monazite (ca. 140 Ma) from the beryllium-rich quartz veins. Hydrothermal monazite from the intra-granite porphyry quartz vein has positive εNd(t) values (+0.76 to +1.63) that overlap broadly with whole-rock Nd isotopic compositions of the host granite porphyry [εNd(t) = +1.24 to +1.61]. These characteristics indicate that the Dongshanwan beryllium mineralization was temporally and genetically associated with magmatic-hydrothermal activity of the Dongshanwan high-silica granite porphyries. Our systematic studies suggest that both the Dongshanwan high-silica granite porphyries and coeval Be-barren high-silica granites in the study area are high-K calc-alkaline I-type granites. They originated from a shared magmatic system and formed by the partial melting of a predominantly juvenile medium- to high-K basaltic crustal source, with a minor addition of old crustal components. Rayleigh fractionation modeling indicates that the granitic magma underwent a two-stage crystal-melt separation process. During the first stage, the fractional crystallization of a large proportion of plagioclase, in which beryllium is compatible, not only effectively inhibited beryllium enrichment in the differentiated melt, but also removed a large amount of Ca. During the second stage, minerals in which beryllium is incompatible dominated the fractionating assemblage owing to the low Ca contents in the magma, resulting in a surge in beryllium concentration in the differentiated melt. Our findings reveal that beryllium cannot be appreciably enriched in calc-alkaline granitic magmatic systems until plagioclase fractionation has substantially removed Ca from the system.

Age and petrogenesis of ore–forming volcanic–subvolcanic rocks in the Yidonglinchang Au deposit, Lesser Xing’an Range: Implications for late Mesozoic Au mineralization in NE China

The age and petrogenesis of volcanic–subvolcanic rocks associated with Au mineralization of the recently discovered Yidonglinchang Au deposit in the Lesser Xing’an Range provide insights into late Mesozoic Au metallogenesis in NE China. In this paper, we report zircon U–Pb chronological and Hf isotopic, whole–rock geochemical, and Sr–Nd isotopic data of the andesite porphyry and quartz diorite porphyry from the Yidonglinchang Au deposit. Zircon U–Pb dating shows that the andesite porphyry and quartz diorite porphyry associated with Au mineralization were formed at 101 and 99–97 Ma, respectively, suggestive of an early Late Cretaceous Au mineralization event in the Lesser Xing’an Range. Whole–rock geochemical data reveal that they have low SiO2 contents (59.87–61.48 % and 55.91–63.22 %, respectively) and high Mg# values (41.5–55.4 and 43.2–61.3, respectively). In addition, these rocks are enriched in large–ion lithophile elements (e.g., K, Rb, and Ba) and depleted in high–field–strength elements (e.g., Nb, Ta, P, Ti, Zr, and Hf). The rocks have slightly negative to positive zircon εHf(t) values (−2.3 to 5.7) and negative whole–rock εNd(t) values (−3.3 to −2.9), indicating a metasomatized mantle source with some contamination by crustal materials. Combined with regional magmatic and metallogenic characteristics, we conclude that the Au mineralization at Yidonglinchang formed as a result of early Late Cretaceous magmatic–hydrothermal activities. Previously obtained data show that the orogenic Au deposits in the northern NE China formed mainly during the Early Cretaceous, earlier than the late Early Cretaceous to Late Cretaceous epithermal Au deposits in the eastern NE China. The formation of the late Mesozoic Au mineralization in the northern and eastern NE China was likely controlled by distinct tectonic settings. During the late Early to early Late Cretaceous, the rollback of Paleo–Pacific oceanic slab beneath eastern NE China generated an extensional setting that led to large–scale magmatism and associated Au mineralization.

U–Pb Dating, Gemology, and Chemical Composition of Apatite from Dara-e-Pech, Afghanistan

Minerals of the apatite group commonly occur in granite pegmatites, and their ability to incorporate a wide range of trace elements makes them a good indicator of magma composition and magmatic–hydrothermal processes. Gem-quality purple apatite crystals from the Dara-e-Pech pegmatite field in Afghanistan have rarely been reported. Here, we investigated apatite crystals originated from this locality, using gemological testing, chemical analysis, and in situ U–Pb dating, with the purpose of identifying their origin, the constraints on the magma source in which the apatite crystals were formed, and the timing of the magmatic–hydrothermal activity. Our findings demonstrate that the purple apatite crystals were impure fluorapatite, characterized by heavy rare-earth element (HREE) enrichment, intermediate Eu anomalies, and non-CHARAC Y/Ho ratios. The results showed that these apatite crystals yielded a lower intercept age of 135.8 ± 6.9 Ma. We proposed that the pegmatitic apatite samples formed in a transitional magmatic–hydrothermal pegmatitic system with moderate fO2 in the Early Cretaceous (~135 Ma). Our study helps to constrain the magmatic–hydrothermal activities of the little-known Dara-e-Pech pegmatite field.

Mineralogical constraints on pegmatite genesis and rare metal mineralization in the Mufushan batholith, South China

Pegmatites are commonly associated with or strongly influenced by the crystallization of magmatic volatile phases (MVP) as ascending magmas undergo differentiation. The mechanism of fractional crystallization, liquid immiscibility, and water–rock interactions that influence the rare metals concentration in pegmatites are still unclear. We analyzed the mineralogy (incl. monazite, garnet, zircon, and muscovite) from pegmatites to unravel the timing and magmatic-hydrothermal processes for the giant Renli-Chuanziyuan pegmatite Li-Nb-Ta mineralization in the Mufushan region (South China). Five types of pegmatites have been identified at Mufushan, i.e., those containing mainly orthoclase (O-pegmatite), microcline (M-pegmatite), albite-orthoclase (AO-pegmatite), microcline-albite (MA-pegmatite), and spodumene-albite (S-pegmatite).Monazites from the Renli high-Th Li-mica pegmatite exhibit magmatic affinity. The ∼140 Ma age of monazite U-Pb suggests a temporal relationship between the Li-rich pegmatite and its muscovite granite host. Garnet from these pegmatites is magmatic and belongs to the almandine-spessartite series, and contains feldspar and apatite inclusions. Continuous fractional crystallization likely controlled the pegmatite development, as the garnet spessartite content increases with distance from the Mufushan batholith. Garnet in the spodumene-albite pegmatites has very low REE content, and it represents a late stage of crystallization related to magmatic-hydrothermal fluids. Compositional variation in muscovite from all of the pegmatites is negligible. The K/Rb ratio (a proxy for the degree of fractionation) increases gradually from the O- to S-pegmatite, whilst the muscovite F content correlates positively with the degree of magma fractionation. The transformation of muscovite to lepidolite in pegmatites can occur through magmatic-hydrothermal crystallization or metasomatism. Zircon in pegmatites generally occurs as metasomatic remnants, with uneven zoning shown in cathodoluminescence (CL) images. Hydrothermal zircon U-Pb ages are concentrated in the 140–134 Ma range, consistent with the garnet leucogranite ages. This suggests that pegamtites and the garnet leucogranite were formed in the same magmatic-hydrothermal activity. The accumulated MVP and incompatible elements may have migrated from deeper, more crystal-rich zones under medium degree of fractionation. The MVP may contain abundant dissolved melt components as single-phase hydrous silicate liquids, forming typical quartz-/feldspar-dominated pegmatite and the diversity of rare-metal deposits.

Deeply Derived Magma Controlling the Polymetallic Mineralization at Shuikoushan, South China: Constraints from Mineral U–Pb Dating and Whole-Rock Geochemistry

Various magmatic–hydrothermal activities have resulted in different styles of polymetallic mineralization in South China. Shuikoushan is a large Fe-Cu-Pb-Zn-Au-Ag orefield situated in fold-and-thrust belts within the South China Block. Two types of granodiorite have been identified in recent drilling work. The early-stage, coarse-grained granodiorite has developed magnetite-bearing skarns in the deep level. The late-stage, fine-grained granodiorite is associated with garnet-hematite–magnetite–pyrite–sphalerite–chalcopyrite-bearing skarns in its contact zone. Away from the garnet-bearing skarn are calcite–quartz–pyrite–sphalerite–galena veinlets in faulted breccia. Fieldwork has identified iron mineralization in both skarns, whereas copper mineralization was only discovered in the garnet-bearing skarns. Lead, zinc, gold, and silver mineralization were observed in the garnet-bearing skarns and faulted breccia. Zircon U–Pb analyses suggested the emplacement of two granodiorite at 167.8 ± 0.8 Ma (MSWD = 1.1, N = 31) and 163.6 ± 0.7 Ma (MSWD = 1.3, N = 32). Apatite and garnet U–Pb dating further indicated the magnetite-bearing skarns of 166.2 ± 1.9 Ma (MSWD = 4.5, N = 27), the hematite–magnetite–sulfide-bearing skarns of 158.6 ± 2.8 Ma (MSWD = 1.3, N = 34), and the calcite–quartz–sulfide veinlets of 159.5 ± 5.2 Ma (MSWD = 1.7, N = 24). The time–space relationship between the two intrusions and hydrothermal activities suggests that the fine-grained granodiorite is responsible for polymetallic mineralization. Whole-rock geochemistry analyses demonstrated the enrichment of LILEs and the depletion of Nb and Ta in two granodiorites, with a slight enrichment in LREEs and flat HREE patterns. These granodiorite bodies therefore belong to high-K calc-alkaline magma generated via the crust’s partial melting. The fine-grained granodiorite generally has a lower HREE and higher Dy/Yb, Sr/Y ratios than coarse-grained granodiorite, corresponding to the source of magma in garnet stable lower crust. The residual garnet keeps ferric iron in melts, leaving the fine-granodiorite more oxidized for copper and gold concentration. Through these analyses and our drilling work, a continuous skarn–hydrothermal–epithermal system has been identified for Cu-Pb-Zn-Au-Ag targeting in Shuikoushan.

Textural, trace element, and sulfur isotope analyses of pyrite from the Yindongpo deposit, East Qinling Orogen: Implications for gold mineralization

The Yindongpo deposit is a large-scale gold deposit with complicate mineralization types in East Qinling Orogen, triggering the debate on its ore genesis. Here we conduct textural, in situ trace elements and sulfur isotope analyses of pyrite to elucidate the genesis of gold mineralization in the Yindongpo deposit. Three types of pyrite were identified according to their occurrences in different hydrothermal veins. Py-Ⅰ mainly formed in the host rock, parallel to the foliation of the schist, occurring as crystal nodules with blurred boundary. Py-Ⅱ principally occur in the quartz-pyrite veins crosscutting the stratum. It is characterized by the pervasive occurrence of sulfide and silicate inclusions, which suggest phase separation (fluid boiling) took place during its formation. Py-Ⅲ commonly precipitate within quartz-dolomite-pyrite veins crosscutting or overprinting former quartz-pyrite veins, commonly associated with coarse-grained sulfides and native gold/electrum. All pyrite types exhibit a superimposed history. The Co, Ni, As characteristics and δ34S data show that from Py-Ⅰ, through Py-Ⅱ, to Py-Ⅲ, the portion of magmatic-hydrothermal fluid is increasing. Gold is tightly associated with base metal sulfides (galena, sphalerite, chalcopyrite), filling the voids, cracks, or margins of Py-Ⅰ, Py-Ⅱ, and Py-Ⅲ. The trace element bounded in the lattice of base metal sulfides include: (1) Cd for sphalerite, (2) Ag, Sb for galena, (3) Ag for tetrahedrite. Combined with previous studies, we conclude that the magmatic-hydrothermal activities at Early Cretaceous formed the major gold mineralization in the Yindongpo deposit.

Magmatic controls on Pb-Zn and W-Sn metallogenic variations in the Nanling Metallogenic Belt, South China: Difference in sources, oxygen fugacity and differentiation degree

The Nanling Metallogenic Belt (NMB) in South China contains huge amounts of Middle to Late Jurassic granitoid-related polymetallic Pb-Zn and W-Sn deposits. Whether there is a link between granitoid genesis and mineral species and what specific factors control the metallogenic specialization remained unclear. Herein, we presented a systematic investigation on the Dafang Pb-Zn ore-causative intrusion, and then placed it into the compiled comprehensive dataset of the NMB ore-hosting granitoids aiming to reveal the magmatic control on the Pb-Zn and W-Sn metallogenic variations in South China. Our results illustrate that the Dafang granitoid is potassic, alkaline (Na2O + K2O: 5.84 % to 7.87 wt%) and meta-luminous (A/CNK: 0.75 to 1.01), with middle SiO2 content (60.59–65.15 wt%), displaying an analogous nature of I-type granitoids. Trace elements of all samples are characterized by a significant enrichment in LREEs, Pb, and K, and a strong depletion of HREEs, HFSEs as well as Ba. Further zircon U-Pb dating yields a concordant age of 157.0 ± 0.8 Ma (MSWD = 1.1), consisting with the Jurassic magmatic-hydrothermal activities in the NMB. Their negative εHf(t) values (−6.7 to −10.2) and two-stage Hf model ages (1.6 to 1.7 Ga) suggest that the Dafang granitoid intrusion was generated from the partial melting of a Paleoproterozoic middle-lower crust. By comparing the Dafang with other NMB ore-causative granitoids in the comprehensive dataset, we investigated two types of ore-causative granitoids, i.e., the Pb-Zn- and W-Sn-mineralized granitoids, with distinct magmatic source, redox state and evolution degree. The Pb-Zn-bearing granitoids predominantly generated from amphibolite with a high oxygen fugacity (Ce4+/Ce3+: average 104.8, n = 55) and low differentiation degree (Rb/Sr: average 0.8, n = 60; Nb/Ta: average 12.5, n = 62). In contrast, the W-Sn metallogenic granitoids originated from metasedimentary rocks with a relatively lower oxygen fugacity (Ce4+/Ce3+: average 46.7, n = 258) and higher differentiation degree (Rb/Sr: average 59.0, n = 139; Nb/Ta: average 5.3, n = 156). Collectively, we conclude the Pb-Zn and W-Sn metallogenic variations in the NMB (South China) are jointly determined by magmatic sources, oxygen fugacity and differentiation degree.

Applications of trace element and isotope geochemistry in revealing origin and evolution of thermal spring water and ore deposit

Geochemistry is normally referred to as the study of Earth’s chemistry by exploring properties of materials and natural processes from deep beneath the Earth’s surface to the upper atmosphere, demonstrating the natural phenomena nowadays and discovering the history of nature. This study describes a subtopic of geochemistry: inorganic isotopes and trace elements, and discusses the application of the isotopes and trace elements in studies of geothermal spring water and ore deposit. The study of water samples in Hengjing, China was accomplished with the help of gas isotope analysis. The carbon isotope ratios and gas compositions indicate that the thermal waters are mostly sourced from meteoric and mantle sources in this area. The He isotope could evolute from mantle fluid, and CO2 is a product of the carbonate decomposition of rocks at high temperatures. The other study, conducted on the Zhaoxian ore deposit, revealed the origin and processes of formation of the different compositions of the ore. The magmatic-hydrothermal activity in this tectonically active area contributes much to the mineralization process of the ore, as shown by the analysis of trace elements of pyrite. The fluid inclusion He-Ar isotope shows that the ore was characterized by crust-mantle mixing with a little participation of meteoric water.

The origin and ore-forming processes of the Qixiashan Pb–Zn–Ag deposit, South China: Constraints from LA–ICP–MS analysis of pyrite and sphalerite

The Qixiashan Pb–Zn–Ag deposit, located in the Nanjing–Zhenjiang area of the Middle–Lower Yangtze Metallogenic Belt (MLYB), is one of the largest PbZn deposits in Eastern China. The middle Carboniferous carbonates of the Huanglong Formation are the main host rocks of orebodies. Whether this deposit is associated with magmatic activity or sedimentary exhalative deposit is still debated due to the poor constraints on the origin of the ore materials and metallogenic processes. To address this, we analyzed the compositions of pyrite and sphalerite from different mineralization stages and depths, and the distributions of minor and trace elements within the pyrite and sphalerite crystals, using in situ laser ablation–inductively coupled plasma–mass spectrometer and scanning electron microscope analyses. Four hydrothermal stages can be identified: the pre-ore pyrite stage (stage I); Pb–Zn–Py stage (stage II); Pb–Zn–Ag stage (stage III); and carbonate stage (stage IV). The sphalerite in the deposit is typically enriched in Fe, Mn, In, and Sn, and depleted in Ge and Cd. These results are characteristic of magmatic hydrothermal activity and indicate the mineralization was related to late Yanshanian magmatic activity. The Co and Ni contents of pyrite, and the Fe, In, and Sn contents of sphalerite decrease from the early to late stages, suggesting that the temperature of the hydrothermal fluid decreased continuously. Variations in the Se content of pyrite suggest that the fO2 increased from stage I to stage II, then decreased during stage III. Detailed SEM and elemental maps show that stage-II sphalerite (Sph-1) and pyrite (Py-2) are oscillatory zoned, which we interpret to reflect pressure fluctuations and repeated local fluid phase separation during stage II. We also infer from the zoning and subsequent formation of Py-3 that magmatic hydrothermal activity increased from stage I to II, then decreased from stage II to III. In addition, changes in the In, Sn, and Fe contents of sphalerite can be useful indicators of the upward migration of ore-forming fluid and can help during prospecting for related deep magmatic rocks.

Genesis of the Meng’entaolegai Ag–Pb–Zn polymetallic deposit, inner Mongolia, Northeastern China

The large-scale Meng’entaolegai Ag–Pb–Zn polymetallic deposit is located in the Great Hinggan Range metallogenic belt, northeastern China. To better understand the formation of the Meng’entaolegai deposit, we present in situ S isotope data, zircon U–Pb isotope data, sulfide Rb–Sr data, and molybdenite Re–Os data for the units associated with the deposit and surrounding regions. In situ analyses show that the δ34S values of the sulfides (galena, sphalerite, and pyrite) vary from + 2.4‰ to + 6.6‰ (mean = +4.7‰, n = 60). The data herein confirm that the sulfur was mainly derived from a magmatic source. Zircon U–Pb dating of the medium- to coarse-grained monzogranite, plagiogranite, and fine-grained monzogranite from the Duerji batholiths and granodiorite and monzogranite from the Meng’entaolegai deposit yield weighted mean ages of 244.3 ± 1.7, 243.0 ± 2.1, 151.8 ± 1.5, 232.6 ± 2.2, and 223.1 ± 2.3 Ma, respectively. The Meng’entaolegai deposit yields a molybdenite Re–Os age of 229.5 ± 1.5 Ma, but sulfide Rb–Sr dating yields an isochron age of 147.2 ± 2.3 Ma. These new age data have revealed that the Meng’entaolegai polymetallic deposit formed during two mineralization episodes: an early episode at 230 Ma and a second episode at 147 Ma. The Late Triassic hydrothermal activity and weakly Mo mineralization formed in an extensional setting after the final closure of the Palaeo-Asian Ocean. The Late Jurassic hydrothermal activity and Ag–Pb–Zn mineralization formed in an extensional environment related to the Mongol–Okhotsk Ocean, but these exposed granitic rocks are unlikely to be related to the Ag–Pb–Zn mineralization, suggesting that more research is needed on the magmatic hydrothermal activity within the study area.

The geochronology of pegmatites in the Jiajika lithium deposit, western Sichuan, China: Implications for multi-stage magmatic-hydrothermal events in the Songpan-Ganze rare metal metallogenic belt

The Songpan-Ganze orogenic belt is a large-scale rare metal metallogenic belt in western China. Several large-scale granitic pegmatite-type lithium deposits are located in the Songpan-Ganze orogenic belt, which include the Jiajika Li deposit, one of the largest pegmatite-type Li deposits in China. The geochronological constraints of pegmatites and granite in Jiajika are still inadequate for revealing the relationships between mineralization and tectonothermal events. In this study, we performed columbite-group minerals (CGM) and cassiterite U–Pb dating on seven different pegmatite veins with different occurrences and deformation styles in the Jiajika deposit. These pegmatites yield CGM U–Pb ages of 213 to 208 Ma and cassiterite U–Pb ages of 199 to 192 Ma, regardless of their occurrences and deformation. Columbite-group minerals exhibit low Ta# (=Ta/(Ta + Nb)) cores and high Ta# rims, which were formed during the magmatic stage and the hydrothermal stage, respectively. The appearance of cassitertite is closely related with greisenization. Therefore, the CGM U–Pb ages, which were obtained from the low Ta# cores of CGM, are interpreted as magmatic crystallization age, while the cassiterite ages reflect another younger stage of magmatic-hydrothermal event. According to field observation, we consider that the occurrences and deformation of pegmatite veins are controlled by the development of various fracture systems formed during the ascent of the granitic pluton. Our results suggest long-lasting multi-stage magmatic-hydrothermal events in the Jiajika region. Geochronological data of other rare metal deposits located in the Songpan-Ganze orogenic belt and the Western Kunlun orogenic belt are comparable with those of the Jiajika Li ore deposit, indicating that the entire Songpan-Ganze rare metal metallogenic belt experienced long-lasting and multiple magmatic and fluid activities. The overlaps of the geochronological results of granites and pegmatites in the Songpan-Ganze rare metal metallogenic belt suggest that regional magmatism is closely related to Li mineralization. The enrichment of Li in the Songpan-Ganze rare metal metallogenic belt is possibly related to its unique geodynamic setting and the long duration of magmatic-hydrothermal activities.

Boron-bearing skarn-magnetite mineralization of the Mingbulak ore field, Eastern Uzbekistan

Spatial distribution of skarn-magnetite deposits in the Tien Shan region is closely related to gabbroid magmatism that accompanies wide fault zones bordering the South Tien Shan folded system from the north and south and extending as a latitudinal belt towards the Middle and Southwestern Tien Shan.Studies fulfilled during recent decades in the Karzhantau Ridge area have quite clearly demonstrated its gold-copper-bismuth metallogenic specialization with the leading role of gold. The most promising position is characteristic of the Aktash group ore occurrences (Aktam-I, Aktam-II, and Yuzhnoe).Within the studied Mingbulak area of Karzhantau, the most widely distributed are mineral occurrences of iron ore, lead and zinc, gold, and copper, and less developed boron-bearing, tungsten, and fluorite ones. Most of the mineral occurrences in the area formed as a result of magmatic-hydrothermal activity and are confined to fault zones characterized by long duration and complexity of the formation. The mineralization is usually localized in the crush zones and feathering fractures of the faults. The skarn type includes ore occurrences of iron, a metal that is currently strongly deficient for mining enterprises in the Tashkent region.

Development mechanism of metamorphic fractured reservoirs in the Bozhong area, Bohai Bay Basin: Implications from tectonic and magmatic hydrothermal activities

The BZ19-6 condensate gas field is the largest metamorphic gas field of the Bohai Bay Basin in China and contains typical fractured reservoirs within the inner parts of an Archean metamorphic buried hill. However, the mechanisms driving its creation and evolution are not well explored. Based on core and sidewall samples, thin sections, X-ray diffraction (XRD) analysis, U–Pb age dating, fluid inclusions, and imaging logging and seismic data, the lithologies, mineral contents and reservoir characteristics of the inner parts of a metamorphic buried hill were evaluated and then the main factors controlling the fractured reservoir were further explored in the Bozhong area. The results show that the lithology mainly includes granitic gneiss, cataclastic rocks and Mesozoic intrusions, among which the granitic gneiss is widely distributed and contains a large number of light-colored minerals. The reservoir spaces are mainly composed of tectonic fractures (TFs), cleavage fractures (CFs), introduced fractures (IFs) and dissolved pores (DPs). Numerous tectonic fractures provide the main reservoir spaces and can be divided into two groups, namely those with nearly WE- and NS-oriented strikes, which are closely related to the stress fields produced by Indosinian and Yanshan movements, respectively. IFs and DPs were developed by magmatic activities, which occurred during the Mesozoic, while magmatic hydrothermal fluid had an obvious negative impact on reservoir quality, resulting in fracture fillings with minerals such as ankerite and calcite. In this study area, reservoir spaces underwent various changes, from creation to development and from filling to dissolution. Finally, we proposed an integrated reservoir model to describe the distribution and evolution of high-quality reservoirs. This study explores the formation mechanisms of fractured reservoirs within metamorphic rocks and makes practical contributions to oil and gas exploration of buried hills.

Origin of Banded Iron Formations: Links with Paleoclimate, Paleoenvironment, and Major Geological Processes

Banded iron-formations (BIFs) are marine chemical sedimentary rocks composed of siliceous and ferric materials, usually with typical thin layers or sheet structures. BIFs not only record a wealth of information about the state and evolution of the lithosphere, atmosphere, hydrosphere, and biosphere but also host the majority of the economic iron resources in the world. Here, we summarize the types, mineralogical, and geochemical characteristics of BIFs; analyze their formation conditions, their oxidative mechanism, and the absence causes of BIFs; and elucidate the associations between BIFs and major atmospheric oxidation events (Paleoproterozoic great oxidation event (2.4~2.1 Ga) and Neoproterozoic oxidation event (0.8~0.55 Ga)). BIFs are intimately associated with enhanced submarine magmatic–hydrothermal activities. Finally, it is concluded that the deposition and demise of BIFs are closely related to major geological events, and these major geological events interact with each other, jointly constraining the evolution of the atmospheric and marine environment and of geo-biological and geodynamic processes.

Geological constraints on volcanic-fluid pathways at the Maruyamasawa-Fumarolic-Geothermal-Area, and its relation to the present magmatic-hydrothermal activity in Zao Volcano, Tohoku, Japan

A field survey based on outcrop and hand-dug trench observations was conducted in the Maruyamasawa-Fumarolic-Geothermal-Area (MFG) of the Zao Volcano. Powder X-ray diffraction and microscopic analyses of samples collected from the MFG provide new possible links between underground magmatic–hydrothermal activity and fumaroles in the volcanic system. The MFG is a fumarolic area (solfatara) with evidence of intense geothermal activity, such as hot and cold springs, fumaroles precipitating native sulfur, and ongoing fumarolic alteration. The MFG occurs on a talus slope that mainly comprises detritus from Late Cretaceous granitoids mixed with blocks of the ca. 1 Ma Robanomimiiwa Pyrocalstics (Rmp). The Rmp is well exposed on a cliff behind the talus slope, and it unconformably overlies the granitoids with a NW-striking, SW-dipping contact. The southwestward extension of the Rmp-granitoids unconformity is projected laying approximately 500 m below the Okama crater, which is 800–1000 masl. The mineral assemblages of the MFG altered rocks are mainly 1) cristobalite + native sulfur ± pyrite, 2) cristobalite + quartz + alunite + kaolin-group minerals + smectite, and 3) quartz-only (intensely silicified) rocks. These mineral associations indicate a typical shallow acidic environment between steam-heated and fumarolic alteration zones. Three sandy layers (Layers 1 to 3 from bottom to top) are recognized in the hand-dug trench: Layer 1 is brown, poorly sorted and well-consolidated, Layer 2 is pale gray to gray and moderately sorted, and Layer 3 is pale gray and poorly sorted. The 14C dating of a paleosol underlying Layer 3 constrains the deposition event to around 437 ± 20 yrBP (2σ: 1429–1470). The presence of gray basaltic andesite (Rmp), granitic fragments (granitoids), and altered rocks (MFG constituent) in these layers suggests detrital remobilization from the MFG talus slope by rainfall (snowmelt) that emplaced thin lahar deposits. Furthermore, the detrital cristobalite and alunite in the L1-L3 matrix are minerals of fumarolic origin contained in the MFG altered rocks. These results indicate that the fumarolic activity and alteration of the MFG occurred before the deposition of these layers.Based on this information, we propose the following model for the MFG activity: (1) The Rmp-granitoids unconformity behaves as an open pathway for ascending volcanic fluids and controls the MFG geothermal features. (2) The MFG was formed over 600 years ago, probably during early Okama crater activity at the 1200s CE. (3) Volcanic fluids have ascended through the unconformity over the last several hundred years. Therefore, careful monitoring of the MFG is crucial for detecting surface anomalies that could indicate imminent eruptions of the Zao Volcano.

Geochronology, geochemistry and Hf isotopic compositions of late Silurian granodiorites in the Shaolang River metallogenic belt: Implications for magmatism and tectonic evolution

The Shaolang River metallogenic belt in Inner Mongolia is one of the main lead‐zinc polymetallic belt on the northern margin of the North China Plate. The granodiorites, which are closely coexisting with lead‐zinc veins in deposit, are extensively developed. Previous geochronological research results show that the dikes and veins in the metallogenic belt belong to the products of magmatic hydrothermal activity in the middle Yanshanian, so the genesis of the metallogenic belt deposit is generally considered to be a hydrothermal vein type deposit related to sub‐volcanic dikes. We obtained zircon LA‐ICP‐MS U–Pb ages and Hf isotopic compositions of granodiorites, which are widely distributed in the deposit and were considered to be closely connected with the genesis of the deposits. The zircon U–Pb ages are 419.4 ± 1.4 Ma and 424.5 ± 4.1 Ma for the granodiorites, respectively, and they formed in the late Silurian. The geological and geochemical data indicate that the granodiorites are consistent with the geochemical characteristics of typical adakite. All εHf(t) values of the granodiorites are minus, on the zircon Hf isotope age diagram, εHf(t) are below the evolution curve of chondrite. The two‐stage model ages (tDM2) are 2.45 ~ 2.79 Ga and 1.87 ~ 2.29 Ga, respectively, showing rock‐forming materials mainly derived from the Paleoproterozoic and earlier crustal partial melting, and there may have been mantle‐derived magma underplating of the lower crust. Combining with the previous regional research, it is concluded that the granodiorites were formed during the extinction of the island arc under the background of subduction of the Paleo‐Asian Ocean and North China Craton. Because of the 125 ~ 170 Ma metallogenic age, we concluded that the granodiorites in the ore areas have no obvious relationship with the deposit genesis. However, it provided the advantageous space for the formation of the lead‐zinc veins, it can be regarded as an important prospecting indicator in metallogenic belt.

Polyphase deformation of the Youjiang fold-and-thrust belt during the Mesozoic: Implications for the tectonic transition of the South China block

The South China block (SCB) experienced the tectonic transition from the Paleo-Tethys to the Paleo-Pacific tectonic domains during the Mesozoic, but the transition process is hotly debated. The Youjiang fold-and-thrust belt (YFTB), in the interior of the Youjiang Basin in the southwestern SCB, is located in a junction of these two tectonic domains and thus witnessed their tectonic evolution. It also separates the northern thin-skinned structures from the southern thick-skinned structures in the basin. Therefore, the YFTB is an intriguing window into the Mesozoic evolution in the southwestern SCB and the Mesozoic tectonic transition of the SCB. In this study, we conduct structural analysis at the middle of the YFTB and discuss the Mesozoic tectonic transition of the SCB. Four phases of deformation are identified in the YFTB during the Mesozoic. The first phase of deformation (D1) is characterized by a series of conjugate joints, NW–SE trending thrust faults and folds resulting from NE–SW shortening that was related to the collision between the SCB and Indochina block. The second phase of deformation (D2) is manifested by the pre-existing NW–SE striking thrust faults transformed to normal faults and the Late Triassic mafic magmatism. Our structural observations, combined with previous geochronological data for mafic dykes, suggest the study area experienced post-orogenic extension in the Late Triassic. The third phase of deformation (D3), accompanied with the westward subduction of the Paleo-Pacific oceanic plate, is represented by a series of conjugate joints and NE–SW-striking faults formed by NW–SE compression. As a result of the continuous subduction of the Paleo-Pacific plate and its subsequent slab rollback, the fourth phase of deformation (D4) is featured with normal faults, magmatic-hydrothermal activities, and regional mineralization, which are associated with the nearly E–W extension setting. Our study results indicate that, in the Early Mesozoic, the Youjiang Basin was dominated by the Paleo-Tethys domain and then transitioned to the Paleo-Pacific domain. Together with the magmatic lull between the Triassic and the Early-Middle Jurassic identified in the SCB, we propose that the tectonic transition process manifested in the YFTB more likely initiated in the Early Jurassic.

Key stage and model of hydrocarbon accumulation of Ordovician reservoir in Gucheng area, Tarim Basin, China

The heterogeneity of deep carbonate reservoirs is strong, it is significant for exploration and development to clarify the key stages of oil and gas accumulation. Taking the Ordovician in the Gucheng area of Tarim Basin as an example, this paper systematically investigated the key stage and model of hydrocarbon accumulation using the data of the cores, thin sections, cathode luminescence tests, laser ablation U-Pb isotope geochronometry, bitumen reflectance, and fluid inclusion tests, and seismic interpretation. (1) The Tarim Basin mainly develops three sets of effective source rocks, namely the Cambrian Yuertusi Formation, Cambrian Moheershan Formation, and Mid-Lower Ordovician Heituwa Formation, which are concentrated in the slope-basin facies of eastern Tarim Basin. (2) The Gucheng area is located in a favorable paleo-structural position. The pathway system composed of vertical faults and lateral unconformities occurs in the paleo-uplift, which is critical for hydrocarbon migration and accumulation. (3) The laser in-situ U-Pb dating, distribution and genesis of reservoir bitumen, burial-thermal maturation history, and the homogenization temperature of fluid inclusions suggest that the multi-stage tectonic thermal events of the Caledonian and Hercynian stages result in key adjustment and modification to deep hydrocarbon accumulation. Due to magmatic hydrothermal activities, the Caledonian primary oil reservoir massively evolved into oil-cracking gas reservoirs and residual paleo-oil reservoirs. (4) The paleo tectonic-fluid effect plays an important factor controlling the development of the Ordovician reservoirs. The evolution of the hydrocarbon accumulation in Gucheng area can be divided into three stages, namely formation of primary oil and gas reservoirs, oil-cracking gas reservoirs, and adjustment, destruction and reforming of gas reservoirs. To sum up, the western and northern parts of the paleo-uplift with favorable source-reservoir-cap rock assemblage and less effects of hydrothermal activities are the favorable zones for hydrocarbon exploration in the Gucheng area, the Tarim Basin.