Quartz Diorite Research Articles

The Aksug Porphyry Cu–Mo Ore-Magmatic System (Northeastern Tuva): Sources and Formation of Ore-Bearing Magma

Abstract ––Two stages are recognized in the evolution of the Aksug ore-magmatic system (OMS): (1) formation of the Aksug granitoid pluton and (2) emplacement of small ore-bearing intrusions. Intrusive bodies of the two stages are composed of rocks of the same type and bear copper mineralization: poor dispersed and large-scale veinlet-disseminated, respectively. The pluton and small intrusions are formed by gabbroid and granitoid rocks, with similar petrogeochemical characteristics of igneous rocks of the same type. The plutonic gabbroic association includes gabbro, gabbrodiorites, and pyroxene–amphibole diorites/quartz diorites. The small subvolcanic gabbroic intrusions are gabbrodiorite and diorite porphyrites. The trace element patterns of the gabbroids are similar to those of igneous rocks in subduction zones. The gabbroids are characterized by isotope parameters εNd(500) = +6.1 to +7.2 and (87Sr/86Sr)500 = 0.7022–0.7030 and model age TNd(DM) = 0.85–0.74 Ga. As follows from the geochemical parameters, the depleted mantle metasomatized by subduction fluids was the source of basaltic magma. The plutonic granitoid association includes tonalites, plagiogranites, and amphibole diorites/quartz diorites; the small subvolcanic granitoid intrusions are tonalite porphyry and quartz diorite porphyrites. The trace element patterns and Nd and Sr isotope compositions of the granitoids are much similar to those of the gabbroids. According to the geochemical parameters, tonalitic and plagiogranitic magmas formed through the melting of juvenile mafic crust, and dioritic magma resulted from the mixing of basaltic and tonalitic/plagiogranitic magmas. In the course of the OMS formation, metals and volatiles were introduced by basaltic and granitoid magmas from the metasomatized mantle and juvenile mafic crust. The compression setting during the pluton formation hampered the separation of ore-bearing fluids, which led to poor dispersed mineralization. The extension setting during the emplacement of small intrusions favored the intense separation of ore-bearing fluids. The interaction of magma and fluids of the small intrusions with rocks of the pluton was accompanied by the removal of metals from the latter and their involvement in the ore-forming process. This increased the ore potential of the magmatic system and favored the formation of rich mineralization at the final stage of its evolution.

Ore-hosting igneous rocks in the Xiahe–Hezuo district, West Qinling orogen, China, and their relationships with gold mineralization

• The Gulangdi Formation in West Qinling orogen (WQO) was formed prior to Triassic. • Gold-bearing igneous rocks in WQO were crystallized prior to gold mineralization . • Gold-bearing igneous rocks were generated by subduction of the Mian–Lue Ocean. • The Mian–Lue Ocean started the subduction process since ca. 251 Ma. • The gold metallogeny in WQO postdates regional magmatism by 40 to 20 m.y. The Xiahe–Hezuo district in the West Qinling orogen hosts a large number of gold deposits, most of which are spatially associated with igneous rocks. However, the nature and origin of these igneous rocks and their possible relation with gold mineralization remain poorly understood. In this study, the ore-hosting igneous rocks from the Zaozigou, Yidi’nan, and Gangcha gold deposits are selected to perform geochronological and geochemical analyses, aiming to clarify their petrogenesis and their role in gold mineralization. The quartz diorite porphyry from the Zaozigou gold deposit, the quartz diorite from the Yidi’nan gold deposit, and the andesite from the Gangcha gold deposit yield LA-ICP-MS zircon U-Pb ages of 250 ± 2, 251 ± 1, and 247 ± 1 Ma, respectively, representing the earliest Triassic magmatic rocks in the West Qinling orogen. The quartz diorite porphyry and quartz diorite display relatively high ( 87 Sr/ 86 Sr) i ratios (0.707188–0.710693), negative ε Nd (t) (−11.7 to −6.2) and zircon ε Hf (t) values (−13.0 to −1.6), and ancient two-stage Nd and Hf model ages (2073–1357 Ma), indicating they were generated by partial melting of ancient crustal materials. The andesite exhibits slightly positive ε Nd (t) values (0.8–1.8) and negative ε Hf (t) values (−20.6 to −2.2), indicating it was derived by partial melting of a metasomatized lithospheric mantle with significant crustal contamination. All of these igneous rocks show enrichments in large ion lithophile and light rare earth elements, depletions in high field strength elements, and high Mg # values (>50), indicating their generation in a subduction-related magmatic arc. These imply that the northward subduction of the Mian–Lue Ocean beneath the West Qinling orogen may had already started since the earliest Triassic. The geological and geochronological evidences suggest these igneous rocks were not genetically associated with the ore-forming process, and they merely provided the space for gold deposition.

Co-Ni-arsenide mineralisation in the Bou Azzer district (Anti-Atlas, Morocco): Genetic model and tectonic implications

The two main types of mineralisation in the Co-Ni-As Bou Azzer district, i.e., “contact” mineralisation” and “cross-cutting” structures have been re-defined based on new field, structural, textural and mineralogical observations. The main orebodies consist of elongated lenses of massive Ni-Co-Fe arsenide minerals. These lenses occur in a core of carbonate or siliceous gangue and are almost exclusively located along the contact between serpentinite and a quartz diorite intrusion. Vein system, cross-cutting the different lithologies, is ore-bearing only along segments in contact with the serpentinite and/or the massive mineralisation. The two orebody types share a rather similar mineralisation history, starting with a Ni-rich arsenide stage (mainly expressed within the massive mineralisation), followed by a massive Co-arsenide stage recognised in both mineralisation styles, and ending with Fe-rich arsenide and base metal sulphide stages. Detailed field observations, microstructural, tectonic, textural and mineralogical analyses led us to propose a genetic model for the Bou Azzer ore district in which massive mineralisation was formed by alteration and transformation of previously formed breccia levels composed of serpentinite (transformed to gangue) and magnetite/spinel (transformed to Co-Ni arsenide minerals) fragments. Inversely, a tectono-hydrothermal event controlled by a NE-oriented transtension generated the vein system, associated certainly with partial remobilisation and reconcentration of metals from the massive mineralisation because veins are principally mineralised when crossing massive orebodies. We discuss a possible temporal continuum between the two mineralisation styles: massive mineralisation, coeval with serpentinisation (serpentine neoformation), is related to the transformation of brecciated lenses, and vein mineralisation is formed as an infill of large fractures during transtensive tectonics. This model has significant tectonic implications, because serpentinite breccia lenses, favourable high-permeability environment for the massive mineralisation formation, can be compared to ophicalcic rocks developed in a context of mantle exhumation by detachment. Two types of textures can be differentiated within the massive mineralisation: i) Brecciated Massive Mineralisation, developed in the core of ophicalcic levels, and ii) Laminated Massive Mineralisation, supposed to form within ancient mylonitic serpentinite levels corresponding to intensive deformation zones. Although the geodynamic significance will not be addressed in this article, we propose and discuss an alternative model in which the presence of exhumed mantle rocks allows the formation of specific massive arsenide deposits.

Assessment of radon radiological hazards in some ophiolite rocks, North Eastern Desert, Egypt

The natural stones are commonly used as interior and exterior building material. The accessory minerals of some rocks can generate a high amount of radon in the atmosphere. Ophiolitic rocks including serpentinites, metagabbros, gabbros metabasalts, metabasaltic-andesites, meta-andesites, Dokhan andesites, dacites, rhyolites, quartz diorites, tonalites, granodiorites, monzogranites and syenogranites. From the Eastern Desert of Egypt were analyzed for radon. The annual effective dose values of all studied rocks are higher than the world average due to the high radon content in the samples. The studied rocks are not recommended to be used as construction material.

The role of porphyry-related skarns in the Chating porphyry copper and gold deposit, eastern China

The Chating deposit is a porphyry copper deposit in the Middle Lower Yangtze River Valley Metallogenic Belt, with skarns found in both the carbonate wall rock and in carbonate xenoliths in the intrusions. Detailed drill hole logging identified endoskarn and exoskarn in Chating, mainly distributed inside the ore–bearing quartz diorite porphyry instead of at the contact with the country rock. The skarns at Chating are unmineralized unless overprinted by porphyry related copper mineralization. Garnet in the Chating skarns can be divided into several types based on their occurrence and whether they were overprinted by porphyry mineralization. The garnets from the ore–bearing (G1a), barren endoskarn (G1b) and proximal ore–bearing exoskarn (G2a) are LREE-enriched, HREE–depleted with positive Eu anomalies whereas garnets from the barren massive exoskarn (G2b) are LREE-enriched with flat HREE and negative Eu anomalies. The G3 garnets are from marbleized skarn distal to the ore-bearing quartz diorite porphyry and consist of Al-rich and Fe-rich andradite; the Al–rich G3 garnets are LREE-depleted and HREE-enriched whereas the Fe-rich G3 garnets are LREE-enriched and HREE-depleted, both have negative Eu anomalies. The physicochemical conditions and composition of skarn-forming fluids controlled the REE, Eu, U and Y distribution in the garnets. The similarities of the REE patterns to those of magmatic–derived fluids suggests a dominantly magmatic fluid formed the endoskarn and proximal exoskarn. Fluid–rock interaction and addition of external fluids diluted the fluid that formed the exoskarn, decreasing the Cl and metal contents, resulting in lower REE contents and negative Eu anomalies in G2b and G3 garnets. The δ34S data for anhydrite from potassic alteration, sericite alteration, endoskarn and exoskarn range from 3.51‰ to 10.92‰, consistent with a dominantly magmatic fluid source. The δ34S for the anhydrite from the skarns ranges from 3.51‰ to 8.74‰, which combined with the absence of coeval sulfides, suggests a very high oxygen fugacity for the skarn-forming fluids. The small-scale skarns in Chating contain more anhydrite than garnet and consequently did not act as ground preparation as they do in typical skarn deposits. We propose that the anhydrite-rich exoskarn and the small scale of the endoskarn, combined with the high oxygen fugacity and low Cl content in the skarn-forming fluids resulted in the barren skarns of the Chating deposit.

Multi-stage infiltration of Na- and K-rich fluids from pegmatites at mid-crustal depths as revealed by feldspar replacement textures

In volcanic zones, geophysical observations have identified the presence of deep-seated fluids around intrusions in the mid-crust. However, the fluid compositions and mechanisms of fluid migration at high temperatures in the crust are still poorly understood. In this study, we investigated plagioclase alteration in mafic schists (clinopyroxene [Cpx] schist, hornblende [Hbl] schist, and actinolite [Act] schist) at the contact with a quartz diorite intrusion on Kinkasan Island, NE Japan. The quartz diorite consists of hornblende and plagioclase, and crystallized at 670–760 °C and 0.30–0.45 GPa. The quartz diorite contains abundant pegmatitic veins, which consist of plagioclase at their margins and K-feldspar + quartz ± garnet in their centers. Some pegmatitic veins cut the schistosity of the metamorphic rocks. In the metamorphic rocks, two stages of fluid-mediated alteration during cooling were recognized. The first stage of fluid infiltration (Stage I) was characterized by the formation of a reaction zone around pegmatitic dikes in the Cpx schists. The Cpx was altered to hornblende (Hbl) and Ca-plagioclase (An83–95) was altered to Na-plagioclase (An36–67). The replacement proceeded along the grain boundaries of plagioclase and clinopyroxene. The second stage (Stage II) resulted in the formation of K-feldspar veins and replacement of plagioclase (An35–57) by K-feldspar (An0Ab1Or99) and albite (An2Ab95Or3–An12Ab87Or1) in the Act and Hbl schists, and the latter were probably derived from the Cpx schists. Assuming the pressure was the same as the crystallization of the quartz diorite intrusion, the alteration temperatures were estimated as 690–730 °C for Stage I and 400–570 °C for Stage II. Mass balance considerations with assumptions of the volume conservation during the replacements of plagioclase and clinopyroxene/amphibole grains indicate the Cpx schists gained Na and H2O and lost Ca in Stage I, and the Act schists gained K and Si and lost Al and Ca at almost constant Na in Stage II. This indicates that the fluid composition changed from Na- to K-rich during cooling. During the Stage II alteration, when ~45% of the plagioclase grains were altered, significant nano- to micro-scale pores were generated in plagioclase, which produced a porosity of ~3.0%–3.5% in the plagioclase and increased the whole-rock porosity by 1.3% ± 0.2%. These pores are now isolated, irregularly shaped, and occur preferentially along the replacement front, suggesting that the pores migrated during or after replacement. The altered zone in plagioclase developed from trans-granular microcracks rather than grain boundaries. Our results suggest that infiltration of K-rich fluids could be self-promoting, with such fluids forming their own pathways via dissolution and precipitation processes during plagioclase replacement. Given that plagioclase is the dominant mineral in various rock types in the mid-crust, reaction-induced porosity networks in plagioclase could be the dominant fluid pathway at mid-crustal depths. The nature of this porosity and fluid migration are potentially controlled by temperature and/or the composition of the fluids.

Association between exposure to different stone aggregates from asphalt and blood coagulability: A human exposure chamber study.

A large fraction of particulate matter (PM), especially PM10, concentrations are due to non-exhaust emissions, such as road abrasion and wear on tires and brake pads. Concentrating on road abrasion, we aimed to investigate blood coagulability in healthy adults after exposure to two types of stone materials commonly used in asphalt on Norwegian roads. This study followed a randomized, double-blind, cross-over study design. Using an exposure chamber, 24 healthy young volunteers were exposed to aggregates of two different types of rocks and placebo dust: quartz diorite, rhomb porphyry, and lactose (placebo dust). Each exposure session lasted for 4 hours (h), and blood samples were collected before exposure (baseline), 4h post-exposure, and 24h post-exposure to analyse potential changes in the von Willebrand factor (vWF) as well as of fibrinogen, d-dimer, leukocytes, and thrombocytes. The dust concentration in the exposure chamber was measured with real-time instruments and gravimetric samples of total dust, respirable dust, PM10, PM2.5, and ultrafine particles (UFP). The results were analysed using a linear mixed-effect model. Leukocyte blood counts increased post-exposure for all exposure materials; however, none of the increases were statistically significant. The concentration of fibrinogen increased after exposure to quartz diorite, while it decreased after exposures to rhomb porphyry and lactose. Type of material was a statistically significant explanatory variable for the concentration of fibrinogen, with the most significant increase occurring 24h post-exposure to quartz diorite. After exposure to the three materials, vWF decreased. For the thrombocytes, an increase in blood count was observed 24h post-exposure to quartz diorite and rhomb porphyry, with a modest (p=0.09) positive association for quartz diorite. Although the results are limited, we conclude that the different effects observed post-exposure to quartz diorite support considering potential health effects when choosing materials in the production of asphalt.

Geochronology, geochemistry and mineral chemistry of Malayer–Boroujerd–Shazand pegmatite dikes, Sanandaj–Sirjan zone, NW Iran

Pegmatite dikes in the Malayer–Boroujerd–Shazand magmatic complex, located in the Sanandaj-Sirjan zone of the Zagros orogen, are hosted in both granitoid rocks and their contact and regional metamorphic aureoles. In this study, we report the geochronology, geochemistry and mineral chemistry of these pegmatite dikes. The granitoid rocks in the Malayer–Boroujerd–Shazand magmatic suites are mainly monzogranite, quartz diorite, granodiorite and quartz monzonite characterized by metaluminous to peraluminous I-type compositions of the calc-alkaline series and display the geochemical characteristics of volcanic arc granites related to an active continental margin. The pegmatite dikes mainly consist of quartz, feldspar (albite and orthoclase), tourmaline, muscovite and less common biotite and garnet. The tourmaline content in the igneous-hosted pegmatite dikes is higher than those of metamorphic rocks, whereas the muscovite content is lower in the igneous-hosted pegmatite dikes. The K/Rb ratio and the Rb content of pegmatite dikes and their minerals (K-feldspar and muscovite) indicate that they are less evolved. Pegmatite dikes display a typical calc-alkaline affinity of I-type granites and are classified as peraluminous Lithium-Caesium-Tantalum (LCT) family (barren sub-type) to muscovite class. The tourmaline is a schorl-foitite type, which is common in the early crystallization stage of less evolved pegmatites. U–Pb zircon dating of the Boroujerd and Shazand pegmatite dikes yield weighted mean 206Pb/238U ages of 160.2 ± 1.8 and 121.8 ± 1.5 Ma, respectively. In contrast, U–Pb zircon dating of the Malayer pegmatite dike gives a mean 206Pb/238U age of 43.2 ± 1.5 Ma. Our new geochronological data indicate that the first group of pegmatite dikes (older pegmatite dikes) in the Boroujerd district (160.2 ± 1.8 Ma) shows an overlap with the main and first magmatic episode in the Sanandaj–Sirjan zone during Jurassic times, simultaneous with the Middle Cimmerian Orogenic phase, and formed during the subduction initiation. The second group of pegmatite dikes in the Shazand district (121.8 ± 1.5 Ma) formed in the Early Cretaceous and shows a temporal overlap with previously reported ages (ca. 130–114 Ma) during the early Alpine tectonic movements (Late Cimmerian Orogenic phase). Finally, the younger group of pegmatite dikes in the Malayer district (43.2 ± 1.5 Ma) formed in the Eocene overlapping with previously reported ages (ca. 34–52 Ma) which is equivalent to the Laramian phase. These data reveal that the magmatism in the Malayer–Boroujerd–Shazand magmatic complex started in the Early-Middle Jurassic resembling adjacent areas in the Sanandaj–Sirjan zone (e.g., Hamedan region) by melting of crustal protoliths in a subduction tectonic setting. The second and third groups of pegmatite dikes formed during the late subduction to syn-collisional process, respectively. These pegmatite generation marked the subduction initiation to syn-collisional span in the region. The zircon geochemistry (negative Ce anomalies and positive Eu anomalies) is indicative of the relatively oxidized conditions of the parent magma and shows characteristics of continental crust zircon.

Structural controls on the localization of the mineralized Copper Cliff embayment and the Copper Cliff Offset dyke, Sudbury Igneous Complex, Canada

The Main Mass of the Sudbury Igneous Complex (SIC) is a 1.5–5 km thick, layered sheet of impact melt rocks, intensely studied because of the magmatic Ni-Cu-PGE sulfide deposits associated with the base of the Main Mass and connected dykes, known as the Sublayer and Offset dykes, respectively. The mode of emplacement of the mineralized Offset dykes that connect to the Main Mass through morphologic crater-floor irregularities (embayments) and the style of post-cratering deformation that affected the Offset dykes is not fully understood. This field-based study of the Copper Cliff Embayment (CCE) and Offset (CCO) dyke contributes to unraveling the mode of melt emplacement and the role of pre-impact faults in the deformation of the southern SIC. Field relationships indicate that the CCO dyke formed before the CCE and Sublayer were chemically fully evolved. Respective melts were injected into footwall rocks weakened by pre-impact deformation and cratering as a protracted event, with barren quartz diorite (QD) emplaced prior to mineralized, inclusion-bearing quartz diorite (IQD). Massive sulfide ore bodies appear to have formed late in the evolution of the dyke and physical separation (decoupling) of silicate magma and sulfide melt is required. NW-SE-shortening folded and faulted the strata hosting the CCO dyke and deformation was facilitated through re-activated E-W-striking, pre-impact faults. Restoring the initial geometry of the dyke and embayment, using 3D modelling and field constraints, helped to refine total slip estimates along major faults and confirmed that melts migrated gravitationally downward into the CCO dyke.

Petrography, geochemistry and tectonic setting of adakitic bodies in the Tighanab area and their relationship with iron skarn mineralization (southeast of Sarbisheh-east of Iran)

Petrography, geochemistry and tectonic setting of adakitic bodies in the Tighanab area and their relationship with iron skarn mineralization (southeast of Sarbisheh-east of Iran)

Petrogenesis of the Late Triassic Biluoxueshan granitic pluton, SW China: Implications for the tectonic evolution of the Paleo-Tethys Sanjiang Orogen

The Sanjiang Orogen is important for us to better understand the tectonic evolution of the Paleo-Tethys Ocean. However, the petrogenesis and tectonic setting of the Late Triassic igneous rocks in the central part of the orogen are poorly understood. In this study, we present new whole-rock elemental and isotopic compositions for the Biluoxueshan Pluton, which consists of quartz diorite, granodiorite, and alkali-feldspar granite. Zircon U-Pb dating yields crystallisation ages of 231 ± 1 Ma for the quartz diorite, 227 ± 1 Ma for the granodiorite, and 227 ± 2, 224 ± 2, 222 ± 1, and 217 ± 3 Ma for alkali-feldspar granites, indicating a prolonged emplacement of the pluton. Quartz diorites are metaluminous, high-potassium calc-alkaline, and magnesian in composition. Granodiorites are characterized by peraluminous composition and the existence of normative-corundum, resembling S-type granite. They have negative zircon εHf(t) values (−13 to −10.8) and old Hf crustal model ages (2060–1920 Ma), indicating a Paleoproterozoic crustal source. Alkali-feldspar granites are metaluminous to weakly peraluminous, have higher SiO2 content, FeOT/MgO ratio and differentiation index (DI) than other samples, and pronouncedly negative Eu anomalies, which are characteristics of highly fractionated granites. They have narrow εHf(t) values of −2.7 to +2.6 with corresponding Hf crustal model ages of 1410–1060 Ma, indicating a Mesoproterozoic juvenile crustal source modified by mantle-derived magma. By combining previous and the new data, we proposed a new tectonic evolution model of a Late Triassic northward scissor-like post-collisional extension during ca. 235–223 Ma in the Changning-Menglian Suture Zone.

Geochronological and geochemical constraints on the genesis of the Tieshan complex in the Edong district, Eastern China with implications for Fe and Cu skarn mineralization

Fe and Cu skarn deposits constitute the most important skarn type worldwide, whereas the controlling factors that lead to the difference in metal associations remain not well known. The Fe- and Cu-hosting Tieshan complex in the Edong district provides a good opportunity for comparative study on the genetic differences between Fe and Cu skarn deposits. In this study, integrated studies of geochronology, geochemistry and Sr-Nd-Hf isotope compositions were conducted on the complex. LA-ICP-MS zircon U-Pb dating results show that the Tieshan complex was emplaced in the time interval of 135 ± 3 to 144 ± 1 Ma. Multiphase rocks from the complex can be broadly subdivided into two suites. The Fe-Cu-related suite, which consists of diopside diorite, quartz diorite, quartz diorite porphyrite and porphyritic granodiorite, possesses low SiO2 (53.5–67.1 wt.%), K2O (2.44–3.53 wt.%) and Rb (45−83 ppm) contents, but high Sr (1132−2684 ppm), Ba (1073−1656 ppm) contents and negligible Eu anomalies, with very high Sr/Y (>90) ratios, similar to typical high Ba-Sr granitoids. The rock suite has initial 87Sr/86Sr values of 0.70648 to 0.70737, εNd(t) values of −12.3 to −8.2 and εHf(t) values of −16 to −7, comparable to values of the Early Cretaceous mafic rocks in the Edong district and adjacent areas, indicating that it might be largely derived from an enriched lithospheric mantle source, along with minor involvement of lower-crustal components. By contrast, the Fe-related suite, which is composed of quartz diorite, quartz diorite porphyrite and granodiorite porphyry, is characterized by relatively high SiO2 (63.0–71.0 wt.%) and K2O contents (3.36–5.53 wt.%), and a wide range of Sr (158−1135 ppm), Ba (762−1366 ppm) contents and Sr/Y (11–99) ratios. In combination with the presence of abundant inherited zircon grains, the lower εNd(t) (−12.4 to −9.3) and εHf(t) (−25 to −15) values indicate a greater degree of lower-crustal contribution for the Fe-related suite. In addition, the calculated zircon Ce (Ce/Ce* and Ce4+/Ce3+) and Eu (Eu/Eu*) anomalies suggest that the Fe-Cu-related suite has much higher oxygen fugacity (fO2) than the Fe-related suite. This study highlights fO2 and fractionation degree of magma as useful indicators for differentiating Fe and Cu skarn mineralization.

Geochronological Framework of Paleoproterozoic Intrusive Rocks and Its Constraints on Tectonic Evolution of the Liao-Ji Belt, Sino-Korean Craton

The Liao-Ji belt (LJB) is one of the Paleoproterozoic tectonic belts located in the North China Craton. A large number of Paleoproterozoic meta-volcanic-sedimentary rock and intrusive rocks are preserved in the LJB, which provide reliable carriers for the study of the Paleoproterozoic tectonic evolution of the North China Craton. The Paleoproterozoic intrusive rock in the LJB can be divided into the following seven types: syenogranite, quartz diorite, porphyry granite, migmatitic granite, syenite, metamorphic plutonic rock, and granitic pegmatite and metagabbro (metamorphic diabase). Zircon U-Pb dating of 15 samples from intrusive rocks was carried out in this study. The chronology framework of the Paleoproterozoic intrusive rock in the LJB was established, and the magmatism of intrusive rocks can be divided into three stages: 2 200 to 2 110, 2 010 to 1 937, 1 900 to 1 820 Ma. The chronological framework supported the evolution model of subduction accretionary arc-continent collision in the LJB effectively. Combined with previous geochemical work, it was a passive continental margin environment at approximately 2 200 Ma, and then transformed into and active continental margin. The bimodal intrusive rocks between 2 180 and 2 150 Ma indicated a back-arc tension environment which lasted until approximately 2 110 Ma with a large number of basic intrusive rocks. And then the back-arc basin began to contract and the magmatic activities were reduced, with only a small number of intrusive rock activities occurring at approximately 2 040, 2 010 and 1 937 Ma. After the orogenic activities, there was a post-orogenic extension stage from 1 900 to 1 820 Ma. Magmatic activities caused by the environmental extension started to occur more frequently and subsequently resulted in the large-scale intrusive rocks in eastern Liaoning.

Multiphase intrusion at the giant Pulang porphyry Cu-Au deposit in western Yunnan (Southwestern China): comparison between ore-causative and barren intrusions

Porphyry Cu-Au deposits (PCDs) have commonly multiphase porphyry intrusions, yet only one (or a few) of the intrusive phase is/are ore-causative. Understanding the criteria to form ore-causative porphyry is important for both ore deposit research and PCD exploration. At the giant Pulang PCD in western Yunnan, there are three generations of porphyries, i.e., (from oldest to youngest) the quartz diorite porphyry (QDP), quartz monzonite porphyry (QMP) and granite porphyry (GP), and only the QMP has major mineralization. Based on ore deposit geology, and zircon U–Pb–Hf–O isotope systematics, we suggested that the QMP is spatially and temporally ore-related. Oxygen fugacity of the QMP and GP magmas is estimated to be higher than that of the QDP. In addition, Hf–O isotope compositions of the QMP and GP are close to those of the average mantle. We suggested that with the continuous Late Triassic subduction of the Garze–Litang ocean basin, the subducted-slab dehydration and the addition of mantle-wedge materials to the ore-forming magmas increased gradually. The younger magmas (e.g., QMP and GP) are thus more oxidized, and have higher water and ore-material contents, giving them higher ore-forming potential. The reason maybe that the late GP is barren may be due to the depletion of ore-forming materials by the main-stage mineralization during the QMP intrusion.

Ore genesis of Qingyunshan Cu-Au deposit in the Dehua-Youxi area of Fujian Province, southeastern China: Constraints from U-Pb and Re-Os geochronology, fluid inclusions, and H-O-S-Pb isotope data

The Qingyunshan Cu-Au deposit, located in the Dehua-Youxi area (Fujian Province, southeastern China), is a vein-type deposit that occurs along fractured zones in the Late Jurassic volcanic-sedimentary rocks and Early Silurian intrusions. Three mineral paragenetic stages are identified, including the pyrite-quartz veins (stage I), polymetallic sulfide-quartz-calcite veins (stage II), and calcite (±siderite)-chalcedony-comb quartz veins (stage III). The stage II is the main mineralization stage, dominated by pyrite, chalcopyrite, and galena as well as two generations of Fe-poor sphalerite with average Fe content of 0.84 wt% in the early sub-stage and 0.31 wt% in the late sub-stage. Fluid inclusion studies indicate that the stage I has a temperature of 220–240 °C and salinity of 3.00–3.50 wt% NaCleq., whereas the stage II has lower temperature (140–160 °C), but similarly low salinity (2.50–3.00 wt% NaCleq.), suggesting it is an intermediate-low temperature epithermal deposit. Hydrogen and oxygen isotope data indicate the fluids of stage I has a δD value of −72.5 to −69.5‰ and δ18Ow value of −2.96 to −0.46‰, whereas the stage II fluids show similar or slightly higher δD value (−68.0 to −66.5‰), but significantly lower δ18Ow value from −6.96 to −6.26‰, which suggest meteoric water predominated in the ore-forming fluid and shows an increasing trend from stage I to II. The δ34S values of sulfide minerals are between −3.7 and −2.3‰, consistent with a major magmatic sulfur source. The lead isotope data show a relatively narrow range with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of 18.392–18.513, 15.642–15.758, and 38.497–39.043, respectively. These Pb-isotope data are similar to those of the Late Jurassic intrusions, but quite different from those of the surrounding rocks of Early Silurian quartz diorite. Pyrite from the ores yielded a Re-Os isochron age of 158.1 ± 9.3 Ma, which is similar to the zircon U-Pb age (162.0 ± 1.0 Ma) of the host dacite crystal tuff in the Nanyuan Formation. Therefore, we concluded that the Late Jurassic magmatic activity (ca. 160 Ma) has a genetic relation with formation of the Qingyunshan vein-type Cu-Au deposit, for which the ore metals were mainly derived from the magma, but ore-forming fluids evolved from a mixing of magmatic fluids and meteoric water with the later playing a major role in the main stage of ore formation.

Geochronology, geochemistry, and Sr-Nd-Pb-Hf isotopes of the late Paleozoic Dongshuigou composite pluton in the Dunhuang Block, southernmost Central Asian Orogen: Petrogenesis and implications for crustal growth

Late Paleozoic granitoid rocks hold critical information regarding continental crustal growth and evolution of the Dunhuang Block at the southernmost margin of the Central Asian Orogenic Belt (CAOB). Here, we report new zircon U-Pb ages and Hf isotope data, as well as whole-rock geochemistry and Sr-Nd-Pb isotopic compositions for Devonian granitoid rocks and dacite porphyry in the Dongshuigou area of the Dunhuang Block, NW China. Petrographic investigation suggests that the Dongshuigou composite pluton, mainly consisting of quartz diorite, granodiorite, and biotite granite, was emplaced in the middle Devonian (ca. 390–380 Ma), whereas the dacite porphyry intruded into the granodiorite in the late Devonian (ca. 367 ± 4 Ma). The quartz diorite and granodiorite are similarly sodic, middle-K calc-alkaline, high Mg# (48.5–49.8) and Cr-Ni contents, enriched in LREE and LIIE (e.g., Rb, Ba, and P), and depleted in HFSE (e.g., Na and Ta), indicative of typically arc-like geochemical signatures. The quartz diorite has positive εNd(t) (+0.38), variable εHf(t) values (+3.12 to +10.7), juvenile Nd (1.04 Ga), and Hf model ages of 0.83 to 1.15 Ga. In comparison, the granodiorite displays negative εNd(t) values (−0.73) closed to the chondrite line, positive εHf(t) values (+3.75 to +8.36), juvenile Nd (1.12 Ga), and Hf model ages of 0.83 to 1.12 Ga. Both plutonic rocks show low initial Pb isotopes similar to those of typical lower crust-derived rocks. Our data indicate that the diorites and granodiorites were derived from partial melting of the juvenile lower crust with addition of minor mantle materials. The high-K, calc-alkaline dacite porphyry exhibits relatively high SiO2 and K2O contents, moderate Mg# (45.2–46.2) values, enrichment in Rb, U, Pb, and K, depletion in Nb, Ta, and Ti, and low Sr and Y abundance. These geochemical characteristics are similar to those of lower crust-derived arc-related rocks, including the development of abundant inherited zircons, implying that the dacite porphyry was likely generated by a mixed source of the mafic lower crust and minor metasomatized mantle materials. The biotite granites are characterized by high Sr contents (481–542 ppm) and Sr/Y ratios (76.0–98.4), low Y (5.37–6.51 ppm) and Yb (0.50–0.56 ppm) contents, and high Mg# values (55–56) and Cr-Ni contents, showing geochemical affinities of adakitic rocks. They have positive εNd(t) (+2.97 to +3.00), variable εHf(t) values (−6.05 to +12.4; mostly >0) with Nd and average Hf model ages of 0.82 Ga and 0.92 Ga, respectively. The biotite granites exhibit low initial 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 18.336–18.339, 15.622–15.622, and 38.478–39.510, respectively, indicating that some subduction-related materials, such as mature arc primitive or ocean island volcanic rocks could have been added to the magma source. The biotite granites were likely derived from partial melting of subducted oceanic crust, which was modified by interactions with mantle wedge, with the addition of minor Mesoproterozoic materials during magma ascent. By synthesizing with the regional geology, we suggest that the middle Devonian granitoids and the late Devonian dacite porphyry in the Dongshuigou are arc/subduction-related rocks that formed in a continental arc setting. Taken together, Devonian arc-related magmatic events in the Dunhuang Block indicate significant crustal growth that was accompanied with minor reworking of ancient lower crust.

Petrogenesis of the Early Cretaceous adakitic intrusive rocks in Chuzhou and Guandian, Anhui Province: Constraints from zircon U-Pb geochronology and Sr-Nd-Hf isotopic compositions

本文以华北陆块东部早白垩世滁州闪长玢岩和管店石英闪长岩为研究对象，报道了新的全岩地球化学（主量元素、微量元素以及Sr-Nd同位素）以及锆石U-Pb年代学和Hf同位素的综合研究结果，进而约束其岩石成因和构造意义。滁州闪长玢岩中锆石发育振荡环带，管店石英闪长岩中锆石具条痕状吸收的特点，它们均为岩浆成因。锆石LA-ICP-MS U-Pb定年结果显示，滁州和管店闪长质锆石年龄分别为128±1Ma和130±2Ma，表明二者均形成于早白垩世。地球化学特征显示，滁州和管店闪长质岩石具有类似的主量元素和微量元素组成，整体具中等的SiO₂含量（58.55%~60.12%）和富MgO（4.43%~5.10%，Mg^#=57~61）的特征，Na₂O/K₂O比值为1.20~1.47，属于高钾钙碱性系列岩石；富集轻稀土元素和大离子亲石元素（如Rb、Ba），亏损重稀土元素和高场强元素（如Nb、Ta、Zr、Hf），并具不同程度的Eu负异常（δEu=0.85~0.93）。它们具高的Sr（575×10^-6~1035×10^-6）和低的Y含量（10.2×10^-6~15.3×10^-6）以及高的Sr/Y比值（57~69），属于埃达克质岩石。此外，滁州和管店闪长质岩石具有类似的Sr-Nd以及锆石Hf同位素的特征，滁州闪长玢岩的⁸⁷Sr/⁸⁶Sr初始比值介于0.7061~0.7066之间，ε_Nd（t）值为-17.7~-16.9，锆石ε_Hf（t）值变化于-23.1~-19.1之间，而管店石英闪长岩的⁸⁷Sr/⁸⁶Sr初始比值为0.7046~0.7059，ε_Nd（t）值为-18.7~-15.8，锆石ε_Hf（t）值为-25.6~-20.0。综合上述，滁州和管店闪长质岩石均属于高镁埃达克质岩石，起源于拆沉的加厚下地壳部分熔融的熔体与地幔橄榄岩反应的产物，形成于早白垩世华北东部陆块拆沉作用下的伸展背景。;This paper reports new geochemical data involving whole-rock major, trace and Sr-Nd isotopic compositions, and zircon U-Pb ages with Hf isotopic data for the Chuzhou dioritic porphyry and Guandian quartz diorite in the Early Cretaceous, with the purpose of constraining their petrogenesis and tectonic significance. Zircons in the dioritic porphyry display typical oscillatory zoning and in quartz diorite show clear striped absorption in cathodoluminescence images, both of which have magmatic origin. LA-ICP-MS zircon U-Pb dating yield age of 128±1Ma in dioritic porphyry and 130±2Ma in quartz diorite respectively, indicating that they were both emplaced during the Early Cretaceous. The dioritic rocks show intermediate SiO₂ (58.55%~60.12%) and high MgO contents (4.43%~5.10%, Mg^#=57~61) with Na₂O/K₂O=1.20~1.47, which are classified as high-K cala-alkaline series. In addition, they are enriched in LREE and LILE (e.g., Rb and Ba), depleted in HREE and HFSE (e.g., Nb, Ta, Zr and Hf) with negative Eu anomalies (δEu=0.85~0.93), and exhibit high Sr (575×10^-6~1035×10^-6) and low Y contents (10.2×10^-6~15.3×10^-6) with significantly high Sr/Y ratios (57~69), being typical of adakitic rocks. Moreover, the Chuzhou dioritic porphyry has uniform (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7061~0.7066, ε_Nd(t) values of -17.7~-16.9, and ε_Hf(t) values of -23.1~-19.1, and Guandian quartz diorite has similar (⁸⁷Sr/⁸⁶Sr)_i ratios of 0.7046~0.7059 and variable ε_Nd(t) (-18.7~-15.8) and ε_Hf(t) (-25.6~-20.0) values. As a consequence, the adakitic intrusive rocks in Chuzhou and Guandian are derived from the partial melting of delaminated lower crust in contamination with mantle peridotite, and we supposed that the rocks are formed in an extension setting during the Early Cretaceous delamination in eastern North China Block.

GEOCHRONOLOGY OF CRYSTALLINE ROCKS OF THE SHUMYLIV SECTION OF THE SOUTH BUG RIVER VALLEY (HAISYN BLOCK)

The Haisyn complex rocks (sobites (Shcherbakov, 2005)), consisting of diorite-like rocks and amphibolites, which biotite granites develop, is outcroping near the village of Shumyliv along the South Bug river and in an abandoned open pit mine (on South of Shumyliv). The rocks are characterized by high magnetization according to magnetic survey results. A linear magnetic anomaly extends in the north-east direction (NE 69º) with a distance of more than 35 km. Entin et al. (2019) proposed that this magnetic anomaly is caused by a dyke with a felsic or intermediate composition. The internal structure of accessory zircon crystals from quartz diorite and granite were studied. In both types of rocks, zircon crystals are complex and consist of three different generations. The first generation consists of fractured nuclei of light pink color, which apparently grew in rims of zircon of the 2nd and/or 3rd generation. Zircon of the second generation is light pink in color. It forms rims around the first generation of zircon, but also occasionally occurs the interior core areas of crystals. Third generation zircon forms rims around the first two generation zircons, or growth episodes. As usually, the heads of crystals have a light brown to brown color. The age of formation of monazite in the granite and titanite in the quartz diorite was determined by the uranium-lead isotope method. The two endogenous geological processes have ages of 2049 ± 6 million years and 2005±2 million years, respectively.

The geology of the Clifden district, Connemara Co. Galway, Ireland and present understanding of Connemara geology

The Clifden district, illustrated with an accompanying new detailed 1:12,500 geological map and fold trace map, includes most of the stratigraphy of the Connemara Dalradian and is used to summarise present understanding of the older geological history of Connemara in the light of new structural work and recent age determinations. The Grampian metamorphism peaked with sillimanite formation during and after the late D2 syntectonic intrusions of metagabbros at 475–470Ma and the formation of the major D2 Derryclare fold which was then repeatedly folded by numerous major D3 folds synchronous with the injection in the south of the 467Ma Quartz diorite gneiss suite, maintaining the high-grade metamorphism. Late D3 saw the general initiation of cooling and uplift, the latter pronounced in eastern Connemara above and around the subterranean gathering of the Oughterard Granite magma, plus movement on the late D3 Renvyle-Bofin slide, generating an area of lower pressure metamorphism with cordierite and andalusite not found in the Clifden area.

The geology of the Clifden district, Connemara Co. Galway, Ireland and present understanding of Connemara geology

The Clifden district, illustrated with an accompanying new detailed 1:12,500 geological map and fold trace map, includes most of the stratigraphy of the Connemara Dalradian and is used to summarise present understanding of the older geological history of Connemara in the light of new structural work and recent age determinations. The Grampian metamorphism peaked with sillimanite formation during and after the late D2 syntectonic intrusions of metagabbros at 475–470Ma and the formation of the major D2 Derryclare fold which was then repeatedly folded by numerous major D3 folds synchronous with the injection in the south of the 467Ma Quartz diorite gneiss suite, maintaining the high-grade metamorphism. Late D3 saw the general initiation of cooling and uplift, the latter pronounced in eastern Connemara above and around the subterranean gathering of the Oughterard Granite magma, plus movement on the late D3 Renvyle-Bofin slide, generating an area of lower pressure metamorphism with cordierite and andalusite not found in the Clifden area.