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Saindak is one of the typical porphyry Cu deposits (PCDs) in the Chagai magmatic arc in Pakistan. Ore-forming porphyries at Saindak PCD are mainly composed of tonalite. Here, we use geochemistry of apatite enclosed in plagioclase phenocrysts from the ore-forming tonalite to constrain the releasing and recharging processes of S and Cl in the underlying parental magma chamber during PCD mineralization. Although apatite inclusions have homogeneous intra-grain S and Cl compositions, there is significant inter-grain S and Cl variations in apatite inclusions located from core to rim in the hosting plagioclase. Such inter-grain S and Cl variation in apatites are coupled with the core-to-rim trends of An, FeO and Mg contents of the hosting plagioclase phenocryst. It indicates that the Saindak PCD likely formed by episodic injection of primitive magmas during the growth of an underlying magma chamber, rather than by one major injection or by addition of mafic melt derived from different source region. Each primitive melt injection introduced essential ore-forming materials such as S and Cl, which were rapidly and effectively released to the coexisting fluids, causing mineralization. Once primitive melt injection stops, signaling the end of growth of underlying magma chamber, mineralization will cease quickly although the hydrothermal system can still survive for a long time. However, the later released fluids are relatively depleted in ore-forming materials, and thus have lower capability to generate mineralization. Accordingly, predominant porphyry-type mineralizations occurred during the growth rather than waning stage of a magmatic system. [ABSTRACT FROM AUTHOR]

In addition to well-known subduction processes, the collision of two continents also generates abundant ore deposits, as in the case of the Tibetan Plateau, which is the youngest and most spectacular collisional belt on Earth. During the building history of the Gangdese magmatic belt, several magmatic flare-up events developed, however, significant magmatic-hydrothermal lead–zinc mineralization dominantly accompanied the magmatism during the syncollisional period (~ 65–41 Ma). Based on integrated geochemical and isotopic data, we provide insights into the genesis and evolution of syncollisional magmas, and their implications for significant magmatic-hydrothermal lead–zinc mineralization. The Sr–Nd isotopic compositions of most syncollisional igneous rocks ( 87 Sr/ 86 Sr = 0.7034–0.7123; ε Nd(t) = − 9.0 to + 1.8) indicate a mixing origin between mantle-derived basaltic magmas and ancient crustal melts, and fractional crystallization is a fundamental mechanism by which syncollisional magmas evolve towards intermediate to silicic compositions. Most lead–zinc mineralization-related plutons are high silica (76.14% wt.% SiO 2 on average), high oxygen fugacity (average ΔFMQ + 2.5) granites with highly evolved chemical signatures [average Eu n /Eu n * = 0.33, high Rb/Sr (average = 3.9)], and they represent the final products from primary magmas. Due to the contribution of ancient crustal melts to the genesis of mineralization-related parent magmas, the spatial distribution of Pb–Zn deposits within the northern Gangdese magmatic belt is controlled by the lithospheric architecture. In compressional environments, magmas have low evacuation efficiency and long magma chamber lifespan, which is favorable for basaltic parents evolved to high silica granites through sufficient fractional crystallization. This scenario contributes to our understanding of the significant magmatic-hydrothermal lead–zinc mineralization that occurred in the syncollisional period. [ABSTRACT FROM AUTHOR]

[Display omitted] • The Yare complex as well as granite units in the Mayum, Pujue, Nanmuqie, and Qiagong areas in the Gangdese magmatic arc were emplaced in Miocene. • The barren adakitic porphyries in Gangdese magmatic arc were derived from ancient crustal sources with little contributions from mantle-derived material. • The history of continuous and relatively complex magmatism prior to emplacement are important factors that discriminate between fertile and barren magmatism. Numerous Miocene porphyry deposits related to adakites have been identified in the eastern Gangdese magmatic arc (east of 87°E), but few of these type of deposits have been found in the western part (west of 87°E), even contemporaneous adakitic porphyries were exposed in the western part. A little research has been undertaken on barren adakitic porphyries in the Gangdese magmatic arc, and the key controls on the metallogenic differences remains unclear. This study presents new whole–rock geochemical, Sr–Nd isotopic, zircon U–Pb and Hf isotopic data for barren adakitic rocks of the Yare complex as well as barren porphyritic and adakitic units in the Mayum, Pujue, Nanmuqie, and Qiagong areas. These data are compared with data for fertile adakitic porphyries, providing insights into the origin and evolution of barren and fertile adakitic magmatism as well as the conditions associated with the porphyry mineralization. The barren adakitic porphyries were formed at 18.03–13.29 Ma. These intrusions have higher (87Sr/86Sr) i ratios (0.708752–0.709785) and lower Ɛ Nd (t) values (−8.4 to −6.5) and zircon Ɛ Hf (t) values (−13.81 to 3.23) than the fertile adakitic porphyries, suggesting the former were derived from ancient crustal sources with a little contributions from mantle-derived material. The fertile adakitic porphyries were formed as a result of partial melting of juvenile lower crust (such as Cu–Mo deposits) and with mixing of material from middle-upper crust (such as Mo–(Cu)–Pb–Zn deposits). The fertile adakitic porphyries also contain more water than the barren adakitic porphyries. Other important factors that discriminate between fertile and barren adakitic magmatism include the involvement of parental magma chambers as well as a history of continuous and relatively complex magmatism prior to emplacement. [ABSTRACT FROM AUTHOR]

The article reports on geological study of Pb-Zn deposits located in Narusonghuo, China. Topics discussed include several Pb-Zn mineralization formed by various physical processes chloritization, silicification and carbonation, found in the region, associated with quartz syenite porphyry, geochemical analysis on the same and role of Neo Tethys oceanic crust and wedge mantle in formation of Narusongduo porphyry magma, with characteristic chemical geology.

Early Cretaceous high-Mg adakitic rocks from central Eastern China provide important insights into the thinning mechanism of the over-thickened lithosphere in the Yangtze Block (YB) as well as the North China Block (NCB). The Tanlu fault (TLF), located between the North China and Yangtze Blocks, and has been considered as a prominent pathway of magmas and fluids that resulted in lithosphere thinning of the YB during the Mesozoic–Cenozoic. Here we report the petrology, whole-rock geochemistry, zircon U–Pb geochronology, in situ Hf isotopes, and whole-rock Sr–Nd–Pb isotopes of four high-Mg adakitic intrusions along the TLF in northeastern Langdai. These adakitic intrusions consist of monzodiorite, quartz monzonite porphyry, and quartz monzodiorite. Zircon LA-MC-ICPMS analyses of five samples yield weighted mean 206 Pb/ 238 U ages of 127.58 ± 0.80, 126.90 ± 0.81, 120.71 ± 0.64, 122.75 ± 0.57, and 129.2 ± 1.1 Ma, indicating their emplacement during the Early Cretaceous. The intrusions have intermediate SiO 2 (53.18–65.48 wt%) and high potassium (K 2 O = 3.07–3.95 wt%; Na 2 O/K 2 O = 1.02–1.26) and are classified as shoshonitic to high-K calc-alkaline series. They are characterized by high MgO (1.80–7.35 wt%), Mg # (50–65), Sr (591–1183 ppm), Ni (20.3–143.0 ppm), and Cr (51.40–390.0 ppm) contents, high (La/Yb) N (11.60–28.33) and Sr/Y (27.9–113.5) ratios, and low Y (7.79–22.4 ppm) and Yb (0.60–2.01 ppm) contents, comparable with high-Mg adakites. The samples are enriched in light rare earth elements but depleted in heavy rare earth elements and high field strength elements with slightly negative to positive Eu anomalies ( δ Eu = 0.81–1.30), resembling the features of high-Mg adakitic rocks. Their whole-rock ε Nd( t ) = −16.2 to −15.0, initial ( 87 Sr/ 86 Sr) i = 0.7060–0.7074, low radiogenic Pb ( 206 Pb/ 204 Pb( t ) = 16.208–16.509, 207 Pb/ 204 Pb( t ) = 15.331–15.410, and 208 Pb/ 204 Pb( t ) = 36.551–36.992), and zircon ε Hf( t ) = −36.6 to −16.6 suggest magma derivation from a continental crustal source. The geochemical and isotopic features, in combination with existing geological data, suggest that the intrusions are high-Mg adakites and, by comparison with contemporaneous intrusions in Eastern China, were likely to have been formed by partial melting of over-thickened basaltic lower crust following the delamination of eclogitic lithosphere during the Late Jurassic to Early Cretaceous. It is possible that the TLF played a key role in lithospheric delamination and thinning and in the generation of the high-Mg adakitic rocks. [ABSTRACT FROM AUTHOR]