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The Assam-Meghalaya Gneissic Complex (AMGC) of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism. The present study is concerned with the first appraisal of intermediate magmatism (diorite, monzonite, and monzodiorite) found in the Borjuri Pluton of Mikir Massif, which is the eastern extension of AMGC. The diorites are strongly metaluminous and exhibit enriched LREE ([La/Yb]N = 1.63–7.37) with respect to HREE ([Gd/Yb]N = 1.95–2.27). The studied rocks do not show any mineralogical or textural indication of metamorphism. Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting. The lower Mg# (33.49–38.69), low Cr (below detection limit), and Ni (27–41 ppm) contents along with elemental ratios such as Rb/Sr (0.32–0.95), La/Nb (0.49–4.21), and Nb/Ce (0.11–0.64) suggest a crustal source for the diorites. Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials. The P–T conditions of diorite emplacement (7.4 kbar, 688 °C) were calculated using the amphibole-plagioclase geothermobarometer. Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime. The Borjuri Pluton is in close proximity with the Kathalguri Pluton, which has been reported as a product of Pan-African magmatism. In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites, we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism.

The Jiajika granitic- and pegmatite-type lithium deposit, which is in the Songpan-Garze Orogenic Belt in western Sichuan Province, China, is the largest in Asia. Previous studies have examined the geochemistry and mineralogy of pegmatites and their parental source rocks to determine the genesis of the deposit. However, the evolution of magmatic-hydrothermal fluids has received limited attention. We analyzed He–Ar–H–O isotopes to decipher the ore-fluid nature and identify the contribution of fluids to mineralization in the late stage of crystallization differentiation. In the Jiajika ore field, two-mica granites, pegmatites (including common pegmatites and spodumene pegmatites), metasandstones, and schists are the dominant rock types exposed. Common pegmatites derived from early differentiation of the two-mica granitic magmas before they evolved into spodumene pegmatites during the late stage of the magmatic evolution. Common pegmatites have 3He/4He ratios that vary from 0.18 to 4.68 Ra (mean 1.62 Ra), and their 40Ar/36Ar ratios range from 426.70 to 1408.06 (mean 761.81); spodumene pegmatites have 3He/4He ratios that vary from 0.18 to 2.66 Ra (mean 0.87 Ra) and their 40Ar/36Ar ratios range from 402.13 to 1907.34 (mean 801.65). These data indicate that the hydrothermal fluids were shown a mixture of crust- and mantle-derived materials, and the proportion of crust-derived materials in spodumene pegmatites increases significantly in the late stage of the magmatic evolution. The δ18OH2O–VSMOW values of common pegmatites range from 6.2‰ to 10.9‰, with a mean value of 8.6‰, and δDV–SMOW values vary from − 110‰ to − 72‰, with a mean of − 85‰. The δ18OH2O–VSMOW values of spodumene pegmatites range from 5.3‰ to 13.2‰, with a mean of 9.1‰, and δDV–SMOW values vary from − 115‰ to − 77‰, with a mean of − 91‰. These data suggest that the ore-forming fluids came from primary magmatic water gradually mixing with more meteoric water in the late stage of the magmatic evolution. Based on the He–Ar–H–O and other existing data, we propose that the ore-forming metals are mainly derived from the upper continental crust with a minor contribution from the mantle, and the fluid exsolution and addition of meteoric water during the formation of pegmatite contributed to the formation of the Jiajika superlarge lithium deposit.

Hydrothermal alteration with bleaching of host rocks is the most important prospecting indicator for gold deposits in the Jiangnan Orogen Belt. The alteration has been identified as pre-ore carbonate (siderite)-sericitization and the Fe of siderite in the alteration zone is derived from the host rocks rather than fluids. In addition, such alteration decreases in intensity and width with depth and gold mineralization also occur in the non-bleached rocks, casting doubt on the reliability of the prospecting indicator. Detailed petrographic work and SEM analysis on the Wangu deposit indicate that there are two types of siderites, i.e., Sd1 and Sd2. Among them, Sd1 grains are relatively small and distributed along the planes of unaltered host rocks, while Sd2 grains, only occurring in the altered slates, are commonly larger. Both types of siderites were altered by auriferous fluids, producing porous cores and minerals such as pyrite, quartz, and ankerite. Compared with unaltered parts, the altered parts have lower Fe, but higher U, Pb, and REE. In addition, Sd1 and Sd2 are similar in Mn, Na, V, and Sr concentrations but different in Fe and Mg. The occurrence and geochemical compositions of both siderites indicate that Sd1 could be transformed into Sd2 by pre-mineralization alteration through dissolution-reprecipitation. Chlorite is another important Fe-bearing mineral in the host rocks, and EPMA analysis suggests that it is ripidolite with relatively high Fe contents. Consequently, chlorite can also provide Fe to form the pre-ore carbonate(siderite)-sericitization. Geochemical modeling demonstrates that both ripidolite and siderite can result in sulfidation and therefore gold precipitation. As a result, this study demonstrates that pre-ore alteration with characterized bleaching is not a prerequisite for gold mineralization despite of its prominent features. Due to the presence of Fe-bearing Sd1 and chlorite, gold mineralization could still occur through sulfidation in the unaltered rocks.

The Sandaowanzi gold deposit is an extremely Au-rich deposit in the Northern Great Hinggan Range in recent years. Zircon U–Pb geochronology, Hf isotope analysis, and the geochemistry of andesites of the Longjiang Formation from the Sandaowanzi gold deposit were used to investigate the origin, magmatic evolution as well as mineralization and tectonic setting of the Early Cretaceous epithermal gold deposits in the northern Great Hinggan Range area. Zircon U–Pb dating reveals an emplacement age of 123.4 ± 0.3 Ma, indicating that the andesites of the Sandaowanzi gold deposit was formed during the Early Cretaceous. The andesites are enriched in light rare earth elements relative to heavy rare earth elements and have weak negative Eu anomalies (δEu = 0.76–0.90). The rocks are also enriched in large-ion lithophile elements, such as Rb, Ba, Th, U, and K, and depleted in the high-field-strength elements, such as Nb, Ta, and P. These characteristics are typical of volcanic rocks related to subduction. Igneous zircons from the andesite samples have relatively homogeneous Hf isotope ratios, 176Hf/177Hf values of 0.282343–0.282502, εHf(t) values of − 12.58 to − 6.95, and two-stage model ages (TDM2) of 1743–1431 Ma. The characteristics of the andesites of the Longjiang Formation are consistent with derivation from partial melting of enriched mantle wedge metasomatized by subducted-slab-derived fluids. These rocks formed in an extensional environment associated with the closure of the Mongol–Okhotsk Ocean and subduction of the Paleo-Pacific Plate. Mineralization occurred towards the end of volcanism, and the magmatic activity and mineralization are products of the same geodynamic setting.

Geodynamic mechanism responsible for the generation of Silurian granitoids and the tectonic evolution of the Qilian orogenic belt remains controversial. In this study, we report the results of zircon U–Pb age, and systematic whole-rock geochemical data for the Haoquangou and Liujiaxia granitoids within the North Qilian orogenic belt and the Qilian Block, respectively, to constrain their petrogenesis, and the Silurian tectonic evolution of the Qilian orogenic belt. Zircon U–Pb ages indicate that the Haoquangou and Liujiaxia intrusions were emplaced at 423 ± 3 Ma and 432 ± 4 Ma, respectively. The Haoquangou granodiorites are calc-alkaline, while the Liujiaxia granites belong to the high-K calc-alkaline series. Both are peraluminous in composition and have relatively depleted Nd isotopic [εNd(t) = (− 3.9 – + 0.6)] characteristics compared with regional basement rocks, implying their derivation from a juvenile lower crust. They show adakitic geochemical characteristics and were generated by partial melting of thickened lower continental crust. Post-collisional extensional regime related to lithospheric delamination was the most likely geodynamic mechanism for the generation of the Haoquangou granodiorite, while the Liujiaxia granites were generated in a compressive setting during continental collision between the Qaidam and Qilian blocks.

The Yangla Cu deposit is the largest ore deposit in the Jinshajiang polymetallic metallogenic belt, northwest Yunnan, China. There is no consensus on the genesis of the ore deposit owing to the limited studies on the chemical compositions of sulfides. This study used an electron probe micro-analyzer to constrain the chemical compositions of pyrite, chalcopyrite, molybdenite, and sphalerite in the porphyry Cu ore of the Yangla Cu deposit and compared them with the chemical compositions of sulfides in the skarn Cu ore. The trace element contents and their occurrences were used to estimate the metallogenic temperature and infer the genesis of the Yangla deposit. The results show that the sulfides in the porphyry Cu ores have variations of ore element concentrations relative to their theoretical values. Pyrite is depleted in S but elevated in Fe; chalcopyrite is depleted in Cu, Fe, and S; and molybdenite and sphalerite are enriched in S whilst depleted in Mo and Zn. The concentrations of the main metallogenic elements Cu, Fe, Mo, Zn, and S in the porphyry are generally lower than those in skarn, suggesting that the porphyry ore was formed in a moderate to moderate-high temperature metallogenic environment. The formation time may also be slightly later than that of the skarn Cu ore. Elements such as As, Co, Cu, Pb, Zn, Mo, Cd, and Ni mainly exist as isomorphic replacements and mineral inclusions in the sulfides of both porphyry and skarn Cu ores. The trace element features of sulfides in the two ore bodies show that the Yangla Cu deposit may be a composite super imposed ore deposit, and its formation has undergone the process of exhalative-sedimentary to skarn-porphyry mineralization.

The Temté basement in North Cameroon is crosscut by dyke swarms with N 20°–40° trending, including dykes 15–30 m wide, up to 3 km-long. Representative rocks exhibit intersertal to sub-ophitic textures. Electron microprobe analyses identified diopside, augite, pargasite, biotite, Ti-magnetite, plagioclase, and sanidine. Whole-rock ICP-MS and ICP-AES chemical analyses showed compositions of basaltic andesite, basaltic trachyandesite and trachyandesite in composition. Igneous differentiation was likely governed by fractional crystallization associated with limited fluid metasomatism. Some lavas could have been moderately contaminated by crustal materials during feeding of local cracks through turbulent magma flows. Discrimination geochemical diagrams and immobile trace and REE element ratios show that the mantle source of Temté dolerites was a deep phlogopite-bearing EMII mantle component and has undergone moderate to high partial melting rate. Correlations of fieldwork and analytical data with previous results evidence the Temté dolerite dyke swarms as fingerprints of crustal extension accompanying regional uplift in an active continental margin when early rifting led to the formation of the Poli marginal basin.

This study focuses on the hydrochemical characteristics of 47 water samples collected from thermal and cold springs that emerge from the Hammam Righa geothermal field, located in north-central Algeria. The aquifer that feeds these springs is mainly situated in the deeply fractured Jurassic limestone and dolomite of the Zaccar Mount. Measured discharge temperatures of the cold waters range from 16.0 to 26.5 °C and the hot waters from 32.1 to 68.2 °C. All waters exhibited a near-neutral pH of 6.0–7.6. The thermal waters had a high total dissolved solids (TDS) content of up to 2527 mg/l, while the TDS for cold waters was 659.0–852.0 mg/l. Chemical analyses suggest that two main types of water exist: hot waters in the upflow area of the Ca–Na–SO4 type (Hammam Righa) and cold waters in the recharge zone of the Ca–Na–HCO3 type (Zaccar Mount). Reservoir temperatures were estimated using silica geothermometers and fluid/mineral equilibria at 78, 92, and 95 °C for HR4, HR2, and HR1, respectively. Stable isotopic analyses of the δ18O and δD composition of the waters suggest that the thermal waters of Hammam Righa are of meteoric origin. We conclude that meteoric recharge infiltrates through the fractured dolomitic limestones of the Zaccar Mount and is conductively heated at a depth of 2.1–2.2 km. The hot waters then interact at depth with Triassic evaporites located in the hydrothermal conduit (fault), giving rise to the Ca–Na–SO4 water type. As they ascend to the surface, the thermal waters mix with shallower Mg-rich groundwater, resulting in waters that plot in the immature water field in the Na–K–Mg diagram. The mixing trend between cold groundwaters from the recharge zone area (Zaccar Mount) and hot waters in the upflow area (Hammam Righa) is apparent via a chloride-enthalpy diagram that shows a mixing ratio of 22.6 < R < 29.2 %. We summarize these results with a geothermal conceptual model of the Hammam Righa geothermal field.