Quartz Diorite Intrusions Research Articles

Blueschist emplacement in the Sepik Headwaters region, Papua New Guinea: field relations, petrology, isotopic dating and tectonic setting

The Tau Blueschist in the headwaters of the Sepik River in north-central New Guinea occurs in an allochthonous east–west lens (55 × 8 km) known as the Tau body. The well-foliated Tau mafic schists contain abundant blue amphibole with some intimately associated pelitic–calcareous–graphitic metasediments. Within the Tau body, the metamorphic grade increases towards the north, from lawsonite rocks to epidote blueschists. Pumpellyitic lawsonitic metabasites are known only from river float. Isolated occurrences of coarsely crystalline mafic tectonic blocks (knockers) occur within and just north of the Tau body and comprise a complete spectrum from epidote blueschist to eclogite that includes amphibolite. The blueschists occur within the upper Mesozoic to Eocene Salumei Formation of prehnite–pumpellyite to low-greenschist facies grade. The Salumei Formation comprises a tectonic mixture of Upper Cretaceous mostly pelitic sediments derived from the Australian continent to the south and Eocene ophiolite fragments and arc-related volcanogenic rocks from the north. The region is dominated by west-to-northwest-trending folds, observed in most outcrops, and high-angle faults. The mesoscopic structures and steep dips of bedding and foliation in pre-Oligocene rocks suggest regional-scale isoclinal folding. Regionally, the Frieda and Fiak-Leonard Schultze faults separate the Salumei Formation (and Tau body) to the south from amphibolite and greenschist grade Ambunti Metamorphic rocks to the north; both may have the same protolith. The Ambunti Metamorphics, the Oligocene diorites intruding them and the Tau blueschists all rapidly cooled from ∼500 °C in the late Oligocene (ca 27–23 Ma). The Ambunti Metamorphics and Oligocene diorites are unconformably overlain by unmetamorphosed middle Miocene Wogamush Formation. Subsequent quartz diorite intrusions into the southernmost Ambunti and Salumei Formation metamorphics and the lower Wogamush Formation volcanics was part of the middle Miocene (ca 15 Ma) Maramuni Arc. We propose that the Sepik Terrane was separated from New Guinea in the Late Jurassic by a narrow backarc basin that was starved of sediment until the Late Cretaceous when the Salumei delta prograded across it. Paleogene subduction dipping northwards beneath the Sepik Terrane led to late Eocene to early Oligocene suturing to the New Guinea margin and partial exhumation of an accretionary wedge including the Tau Blueschist and serpentinised mantle slivers. Late Oligocene extension and diorite intrusion were associated with rapid cooling and exhumation of the metamorphic rocks. Subduction flipped and the middle Miocene Maramuni Arc and Wogamush Formation were emplaced followed by collisional tectonism with the Melanesian Arc. This placed the margin into compression and created the modern orogen.

Petrogenesis and high-precision U-Pb zircon geochronology of the Howley Islands intrusions, Central Newfoundland Appalachians: Hydrous magmatism of Emsian age (ca. 400 Ma) along a multi-million-ounce orogenic gold belt

The Howley Islands intrusions consist of three coarse-grained amphibole-phlogopite/biotite quartz gabbro dykes and one medium-grained amphibole-biotite quartz diorite body that cut rocks of the Exploits Subzone in central Newfoundland along strike from the multi-million-ounce Valentine gold deposits. The petrogeneses and ages of these rocks were investigated to better constrain the process evolution of the orogenic gold belt that extends for more than 200 km across central Newfoundland.The quartz gabbro dykes are composed of magnesio-ferri-hornblende-cummingtonite-phlogopite/biotite macrocrysts mantled by plagioclase (labradorite to oligoclase)-quartz coronas. The gabbros are LILE- and LREE-enriched, transitional arc-like rocks that formed from a different melt source and parental magma than the quartz diorite body. The quartz diorite is plagioclase-rich (50 modal % andesine), contains only trace cummingtonite, lacks phlogopite, and preserves rare diopside overgrown by magnesio-ferri-hornblende. This intrusion is more alkaline and OIB-like than the quartz gabbros and exhibits the influence of a deeper, more enriched mantle component, although both melts variably interacted with deep lithosphere. The quartz gabbro dykes and quartz diorite body may represent melts of the lower lithosphere and upper asthenosphere, respectively.The abundance of coarse- to medium-grained amphibole and phlogopite/biotite in the samples is consistent with crystallization of hydrous magmas and rapid, water-enhanced crystal growth, with cooling paths recorded by chemically zoned grains of magnesio-ferri-hornblende and plagioclase. One quartz gabbro displays reverse core to rim chemical zoning of plagioclase from andesine to labradorite, which may reflect decreasing pressure during magma ascent and crystallization, magma mixing of evolved and more primitive magmas, and/or fluctuations in H2O content. The presence of cummingtonite suggests crystallization at relatively low temperatures in shallow, low-pressure, upper crustal magma chambers. The quartz gabbros may represent melts equivalent to the nearby Howley Islands gabbro body, whereas the quartz diorite may represent a plagioclase cumulate along the margin of another melt chamber.U-Pb CA-ID-TIMS zircon geochronology yielded ages of ca. 400.3 Ma for the gabbro dykes and 399.9 Ma for the quartz diorite intrusion, within the ca. 410–377 Ma age range for mineralization of the nearby Valentine gold deposits. The ca. 400 Ma intrusions, when considered in conjunction with regional models, reflect melting and hydrous magmatism in the mantle wedge above a retreating Avalonian slab that was dehydrating during the Acadian orogenic cycle. The coincidence of Pridoli (ca. 422 Ma) to Emsian (ca. 400 Ma) bimodal magmatism and orogenic gold mineralization in central Newfoundland reflects more than twenty million years of high geothermal gradients and fluid flow, which when combined with structural focusing along faults, was apparently optimal for the formation of orogenic gold deposits of significant economic potential.

Rapid switch in geodynamic setting revealed by episodic granitoid magmatism in the Lynn Lake greenstone belt of Paleoproterozoic Trans-Hudson Orogen, Manitoba, Canada

Bedrock geological mapping indicates that diverse granitoid intrusions occur closely in space and time in the Paleoproterozoic Lynn Lake greenstone belt of the Trans-Hudson Orogen, Manitoba, Canada. These intrusions display distinct geochemical characteristics of I-type, A-type and adakite-like granitoids as revealed by their respective alkalinity, alumina saturation state, and trace element concentrations and ratios. The ca. 1879 Ma I-type granitoid pluton intruded the 1892 to 1884 Ma supracrustal package of volcanic, volcaniclastic and minor sedimentary rocks that constitute the greenstone belt, which was cut by 1873 Ma A-type granite and then by 1854 Ma adakite-like quartz diorite intrusions. Why the geochemical affinities of these granitoids change so rapidly (within ∼25 Myr) in orogenic belts, however, is not as well understood. Here we propose using SmNd isotope data and trace element modeling that the compositional variety of the granitoid intrusions likely reflects the mineral assemblages of their source rocks rather than magmatic fractionation. They may have been formed by partial melting of the disparate sources at different depths to respond to the change in tectonic regimes. The timing of the granitoid intrusions tracks a rapid geodynamic transition from subduction to intra-arc extension and to slab break-off due to terrane accretion and collision. This records a crucial piece of history in geodynamic evolution of the Trans-Hudson Orogen, which to date has been overlooked largely in many other orogens.

Multiple mineralization events at Paleozoic Sanchakou porphyry Cu deposit, Xinjiang: New insights from geology, geochronology, fluid inclusions, and H-O-C isotopes

The Sanchakou Cu deposit is located in the eastern section of the Dananhu arc belt in Eastern Tianshan, Xinjiang, and recorded multiple magmatic-mineralization events. The porphyry-style mineralization period produced disseminated, sulfide-dominant veined, and patchy sulfides containing chalcopyrite ± bornite ± carrolite ± molybdenite (Mol-1), which was associated with magnetite ± biotite ± chlorite ± sericite alteration in a suite of quartz diorite intrusions. The overprinting mineralization period contributed to minor Cu and Mo mineralization, featured by later disseminated molybdenite (Mol-2), chalcopyrite, and widespread low-temperature (<280 °C) vein-type stellerite assemblages. Two distinct geological ages of molybdenite (including Mol-1 and Mol-2) from Sanchakou have been determined in this study. The old 187Re/187Os isochron age for euhedral Mol-1 represents the timing of original porphyry-style mineralization (386 ± 16 Ma), in agreement with LA-ICP-MS zircon U-Pb age of dark diorite dykes (390 ± 11 Ma). The young 187Re/187Os age for fine-grained Mol-2 is interpreted to be a maximum age of sulfide formation or remobilization (364 ± 15 Ma), most likely associated with the emplacement of Late Devonian gneissic granite intrusions. Fluid inclusion microthermometry, mineralogy, and physicochemical calculations for the porphyry-type mineralization period (including four stages) at Sanchakou suggest that earlier magmatic fluids have evolved from high T (310–460 °C), high logfO2 (−22 to − 26), and alkaline condition during stage I to low T, low logfO2 (−34), and acidic condition during stage II. The decrease of oxygen fugacity caused by abundant deposition of magnetite in stage I produced large-scale Cu and Mo precipitation. Stage II to IV fluids have gradually decreasing temperatures and salinities, due to involvement of meteoric water that also facilitates the ore deposition. This result is consistent with the evolution of O isotope compositions of the fluids (δ18Ofluids = − 9.3 to 4.3), further implying the significance of fluid mixing instead of fluid boiling that caused ore deposition. Locally high-grade copper concentrations at Sanchakou are likely attributed to the overprinting modification event on the original ore bodies. All of these observations indicate that the Paleozoic Sanchakou ore-forming system is similar to other deformed porphyry Cu systems in the Central Asian orogenic belt (CAOB) and worldwide. The Cu mineralization and modification event at Sanchakou is coincident with the second peak productivity in CAOB. We further suggest that the Paleozoic diorite complex and stellerite alteration can be as a significant exploration target for porphyry-style Cu mineralization in the Eastern Tianshan.

Development of Open Transport of Aqueous Fluid from Pegmatite Revealed by Trace Elements in Garnet

We investigated the fluid flow and elemental transport from a granitic body to the middle crust by determining the trace element compositions of garnet in pegmatites related to a quartz diorite intrusion and metamorphic rocks on Kinkasan Island, northeast Japan. Garnet in the pegmatites and biotite schists is characterized by spessartine– (Sps–) almandine- (Alm-) rich compositions of Sps14–69Alm22–70Prp2–14Grs1–13 and Sps16–30Alm54–66Prp9–16Grs3–6, respectively. A garnetite pod in the metamorphic unit has grossular- (Grs-) rich compositions (Sps1–4Alm8–11Prp0.1–0.4Grs80–87Adr3–4). The peak temperature ( T ) and pressure ( P ) conditions of the biotite schist during contact metamorphism were 600–650°C and 0.27–0.41 GPa, respectively. The primary fluid inclusions in quartz crystals within the pegmatites hosted by the quartz diorite and hosted by the metamorphic rocks have a wide range of homogenization temperatures (200–380°C). These correspond to the trapping temperature of 500–700°C, assuming a salinity of 4 wt.% NaClequivalent at pressure of the crystallization of the quartz diorite. Chondrite-normalized rare earth element (REE) patterns of garnets in the pegmatites in the quartz diorite and metamorphic unit are generally characterized by enrichment of heavy REEs and negative Eu anomalies with the REE contents in the schists which are systematically lower than in the pegmatites. However, garnet in the biotite schists close to the pegmatites has similar REE contents to garnet in the adjacent pegmatites. These geochemical features suggest that garnet in the biotite schists grew in response to fluid infiltration from the pegmatites. Besides, the Grs-rich garnet in the garnetite pod and its host quartz schist have flat heavy REE patterns and no Eu anomalies, which probably reflect a metasomatic process related to plagioclase replacement that produced Ca-Al-rich fluids. Our results suggest that the infiltration of pegmatitic fluids enhances elemental transport and metamorphic reactions in the middle crust.

Lithological Control of Stream Chemistry in the Luquillo Mountains, Puerto Rico

Meteoric waters move along pathways in the subsurface that differ as a function of lithology because of the effects of chemical and physical weathering. To explore how this affects stream chemistry, we investigated watersheds around an igneous intrusion in the Luquillo Mountains (Puerto Rico). We analyzed streams on 1) unmetamorphosed country rock (volcaniclastic sedimentary strata, VC) surrounding an igneous intrusion, 2) the quartz-diorite intrusion (QD), and 3) the metamorphosed aureole rock (hornfels-facies volcaniclastics, HF). These lithologies differ physically and chemically but weather under the same tropical rain forest conditions. The sedimentary VC lithology is pervasively fractured while the massive QD and HF lithologies are relatively unfractured. However, the QD fractures during weathering to produce spheroidally-weathered corestones surrounded by cm-thick rindlets of increasingly weathered rock. Meteoric waters flow pervasively through the network of already-fractured VC rock and the spheroidally weathered rindlets on the QD, but only access a limited fraction of the HF, explaining why streams draining HF are the most dilute in the mountains. This results in various thicknesses of regolith from thick (VC) to moderate (QD) to thin or nonexistent (HF). The pervasive fractures allow groundwater to flow deeply through the VC and then return to the mainstem river (Río Mameyes) at lower elevations. These “rock waters” drive concentrations of rock-derived solutes (silica, base cations, sulfate, phosphate) higher in the lower reaches of the stream. Water also flows through weathering-induced fractures on the QD at high elevations where rindletted corestones are present in stacks, and this water flux dissolves plagioclase and hornblende and oxidizes biotite. This “QD rock water” is not generated at lower elevations in the Río Icacos watershed, where stacks of corestones are absent, and contributions to stream solutes derive from weathering of feldspar- and hornblende-depleted saprolite. The stream chemistry in the QD-dominated watershed (Río Icacos) thus varies from concentrated QD-rock water at channel heads below steep ridgelines toward more diluted “saprolite water” downstream. These observations emphasize the importance of lithology and fracture patterns in dictating water flowpaths, stream chemistry, and regolith development in headwater catchments.

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.

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.

Petrogenesis of Ordovician granitoids in Western Kunlun, NW Tibetan Plateau: Insights into the evolution of the Proto-Tethys Ocean

Abstract Granitoid rocks are universal in continental crust and are of special significance in understanding tectonic settings. This paper presents detailed zircon U-Pb dating, Hf isotope, whole-rock geochemistry, and Sr-Nd-Pb isotope analyses, and mineralogy of two Ordovician granitoid intrusions and one quartz diorite intrusion in Western Kunlun, NW Tibetan Plateau. The Yutian Complex is composed of diverse rock suites, including monzogabbros, quartz monzodiorites, monzogranites, and monzodioritic enclaves. These suites have similar rock formation ages (447–440 Ma) and minerals, e.g., amphibole grains from different suites belonging to pargasite. Moreover, they exhibit geochemical similarities, such as broadly parallel trace-element patterns characterized by enrichments in light rare earth elements and large ion lithophile elements, and depletions in high field strength elements, which are typical features of arc rocks. Furthermore, the studied samples display homogeneous zircon Hf values, e.g., εHf(t) = −1 to −3, and whole-rock isotopic compositions, e.g., εNd(t) = −4 to −6. Thus, they were most likely derived from a mantle wedge enriched by subducted sediments and fluids, which then evolved into different suites through fractional crystallization of hornblende and plagioclase. The ca. 440 Ma North Yutian quartz diorite intrusion, with an average of εHf(t) value of −6, was a product of the partial melting of mafic lower crust through slightly fractional crystallization of hornblende. In contrast, the ca. 470 Ma Aqiang granodiorite intrusion has εHf(t) values varying from −5 and −2, but it has heterogeneous petrological and geochemical features. It is considered to be a product of the partial melting of the overriding mantle wedge modified by fluids derived from the subducted Proto-Tethys slab and some mixed crustal materials. The Aqiang samples belong to the slightly fractionated I-type series, but they have variable alumina saturation index (ASI = molar Al2O3/[CaO – 3.33 × P2O5 + Na2O + K2O]) values (0.74–1.03) due to variable peraluminous biotite contents. The different suites in the Yutian Complex display low ASI values (&amp;lt;1) controlled by sources and fractional crystallization. The Yutian Complex and the North Yutian intrusion were emplaced during the southward subduction of the Proto-Tethys oceanic lithosphere, and the Aqiang intrusion was emplaced in response to the northward subduction.

Primary magmatic biotite in granitoid intrusions associated with Late Mesozoic Jinchanggouliang-Erdaogou lode gold deposits, North China Craton: Linkage to gold mineralization

The Late Mesozoic Jinchanggouliang and Erdaogou lode gold deposits in the central segment of the northern North China Craton are mainly hosted in Late Archaean metamorphic rocks of the Jianping Formation and Jurassic volcanic-sedimentary rocks. These deposits are spatially and temporally associated with a series of I-type granitoid intrusions: i.e., the 128–136 Ma Duimiangou granodiorite complex with a massive margin and a porphyritic center at Jinchanggouliang, the 161.4 ± 1.1 Ma Loushang quartz diorite intrusion and numerous syenite porphyry dykes (160.9 ± 1.0 Ma) at Erdaogou, and the ~ 227–217 Ma Xitaizi monzogranite batholith. Compositions of primary magmatic biotite in these granitoid intrusions have been used to investigate the nature of granitoid magmas and the evolution of magmatic processes and to identify possible linkages between gold mineralization and granitoid magmatism. All primary magmatic biotite grains are Mg-rich in composition (XMg = Mg/(Mg + Fe) = 0.41–0.69). The Cl contents of biotite (0.09–0.42 wt%) in the Loushang quartz diorite and the Duimiangou massive granodiorite correlate negatively with XMg and are consistent with the “Mg-Cl avoidance” rule. The Cl contents of biotite (0.01–0.14 wt%) in the Duimiangou porphyritic granodiorite, syenite porphyry and Xitaizi monzogranite, on the other hand, remain relatively constant and may be affected by multiple variables such as Cl-rich fluids and subtle changes in temperature. Halogen fugacity of the parental magma calculated from biotite shows that the Duimiangou granodiorite complex at Jinchanggouliang and syenite porphyry dykes at Erdaogou have the log(fHF/fHCl) ranges of −0.71 to −0.27 and −2.16 to −1.08, respectively, and have similar log(fH2O)/(fHCl) values from 3.53 to 4.23. Oxygen fugacities (logfO2) calculated from biotite equilibria for the Duimiangou granodiorite complex and syenite porphyry dykes are −13.7 to −7.2, straddling on the nickel-nickel oxide and hematite-magnetite buffers. The Xitaizi monzogranite and the Loushang quartz diorite have lower log(fO2) values from −14.9 to −12.4, between the nickel-nickel oxide and hematite-magnetite buffers. The Duimiangou granodiorite complex and syenite porphyry dykes with high oxygen fugacities are similar to oxidized magmas associated with porphyry Cu-Mo-Au deposits. These results suggest that multiple episodes of I-type granitoid magmas in the study area were rich in Cl and high in oxygen fugacity, especially those associated with the Duimiangou granodiorite complex and syenite porphyry dykes. The I-type melts represented by the Duimiangou granodiorite complex and syenite porphyry dykes as well as their related Cl-rich, oxidizing fluids were likely efficient in dissolving, transporting and precipitating gold for the formation of the Jinchanggouliang and Erdaogou lode gold deposits.

Geochemical discrimination of intrusions in the Choran Cu[sbnd]Au deposit, Iran, using silicate chemistry

The Choran CuAu deposit is located 70 km of Bardsir in the southern part of Urumieh-Dokhtar magmatic belt (UDMB). In this area, mineralization is associated with Oligocene –Miocene quartz diorite and granodiorite intrusions emplaced within Eocene volcanic–pyroclastic – sedimentary sequences. Main hydrothermal alterations in the Choran region include sodic-potassic and potassic as well as phyllic, alunite and kaolinite which extended mostly in the granodiorite. Mineralizations at the Choran deposit involve pyrite, arsenopyrite, chalcopyrite, chalcocite, covellite and sphalerite. The composition of the plagioclase in the granodiorite and quartz diorite rocks ranges from albite (66.8 to 48.7) and (64.8 to 51.4) respectively. Also, Al/(Ca + Na + K) ratios of plagioclase in granodiorite samples (average; 1.50) are higher than that of quartz diorite intrusions (average; 1.33) which is analogous to those reported previously for mineralized porphyry systems. All studied primary and re-equilibrated biotites are collectively clustered in the Mg-biotite field. However, based on the log (XMg/XFe) versus log (XF/XOH) of biotite, granodiorite units are associated with I-type moderately crustal contaminated (I-MC) suite, whereas quartz diorite biotites represent I-type weakly crustal contaminated (I-WC) character. Comparison of biotite halogen contents indicates that F and Cl values increase from quartz diorite to granodiorite intrusions. Importantly, biotite thermometry of granodiorite and quartz diorite samples indicate temperatures of <400 °C (quartz diorite; average 340 °C, granodiorite; average 379 °C) which are overlapped with temperature of sulfide mineralization in the porphyry systems (<400 °C). Totally, through assessing the key factors of mineralization using silicate chemistry, it is proved that granodiorite units have higher potential to form porphyry-style sulfide mineralization in the Choran deposit.

Tracking fluid sources for skarn formation using scapolite geochemistry: an example from the Jinshandian iron skarn deposit, Eastern China

Scapolite occurs as the major halogen-bearing phase at all paragenetic stages of skarn formation and mineralization in the Jinshandian iron skarn deposit, Eastern China. Here we integrate geochemical characteristics of scapolite with in situ B and Sr isotopes of associated tourmaline and fluorapatite, respectively, to trace the sources and evolution of the fluids responsible for mineralization in this deposit. Pre-ore stage I scapolite has molar Cl/Br ratios ranging from ~ 920 to 2200, which, together with the boron isotope composition of pre-ore stage I tourmaline, are consistent with formation from magmatic fluids from the Jinshandian intrusion. In contrast, scapolite in syn- and post-ore stages (II and III) has significantly higher Cl/Br ratios (2900–6200) that are outside the range of magmatic fluids but are consistent with involvement of fluids derived from the halite-bearing evaporite horizons that lie within regionally extensive sedimentary country rocks. The influx of sedimentary-derived fluids is also consistent with 87Sr/86Sr of syn-ore stages II fluorapatite (0.7098–0.7109), which are significantly higher than those of the skarn-related quartz diorite intrusions (0.7058–0.7061) but approach the isotopic compositions of the Middle Triassic evaporites and other continental sedimentary country rocks. These data indicate that evaporite-sourced fluids were involved in iron ore formation at the Jinshandian deposit and may be important for the formations of other iron ore deposits. Our findings also show that scapolite halogen geochemistry in combination with other fluid tracers, such as B and Sr isotopes, can be extremely useful for identifying the origins and evolution of fluids in magmatic-hydrothermal systems.

Genesis of the Angeer Yinwula Pb–Zn deposit, Inner Mongolia, China: constraints from fluid inclusions, C–H–O–S–Pb isotope systematics, and zircon U–Pb geochronology

The Angeer Yinwula Pb–Zn deposit of Inner Mongolia, China, is located in the Erlianhot–Dongwuqi metallogenic belt, which is considered to be the eastern part of the Central Asian Orogenic Belt. We used the ore geology, fluid inclusion, isotopes, and zircon U–Pb geochronology to elucidate the genesis and tectonic setting of the deposit. The deposit belongs to the moderate-temperature hydrothermal-vein type, and most of the ore bodies occurred in the quartz diorite intrusions and silty slate country rocks of the Devonian Angeer Yinwula Group. Fluid inclusion petrography and microthermometry results show that the inclusions that developed in the different mineralization stages changed from the LV type (vapor-rich two-phase) + S type (daughter-mineral-bearing three-phase) + VL type (liquid-rich two-phase) to the VL type + LV type and eventually evolved into the VL type, and the ore-forming fluids changed from a moderate-temperature and moderate- to high-salinity, boiling fluid system to a low-temperature and low-salinity H2O–NaCl system. The isotope (C, H, O, S) characteristics suggest that the ore-forming fluids were derived from a magmatic source, and the lead was derived from a deep-seated mantle-derived magma and also included some crustal material. The LA–ICP–MS zircon U–Pb age of the quartz diorite is 152.0 ± 1.5 Ma, which is the best estimate for the age of mineralization of the deposit. Overall, we suggest that the deposit formed in a Late Jurassic Paleo-Pacific Plate subduction setting, although this hypothesis needs to be further tested by conducting computational simulations in the field of emerging computational geosciences.

The petrogenesis of early Paleozoic high-Ba–Sr intrusions in the North Qinling terrane, China, and tectonic implications

High-Ba–Sr (HiBaSr) intrusions provide important insights into early Paleozoic magmatism and tectonic evolution of the Qinling orogenic belt, China. Here, new zircon U–Pb ages, whole-rock major and trace element data, and Sr–Nd–Hf isotopic compositions are presented for three HiBaSr dioritic intrusions (Yangjiazhuang and Tangzang quartz diorite intrusions and Honghuapu diorite intrusion) in the North Qinling terrane. The Yangjiazhuang quartz diorites and Honghuapu diorites are high-K calc-alkalic to shoshonitic rocks, whereas the Tangzang quartz diorites are Na-rich calc-alkalic rocks. LA–ICP–MS zircon U–Pb dating indicates that the K-rich dioritic intrusions were formed at 439–438 Ma, and the Na-rich intrusion at 429–425 Ma. Rocks of the three intrusions are metaluminous to weakly peraluminous, and are characterized by high Ba and Sr contents of 792–3050 and 579–1385 ppm, respectively, with obvious enrichment in LILEs (e.g., Rb, Ba, Th, and U) and depletion in HFSEs (e.g., Nb, Ta, and Ti). They exhibit relatively uniform Sr and Nd isotopic compositions with (87Sr/86Sr)i ratios of 0.7032–0.7059, εNd(t) values of −0.65 to −2.78, and two-stage Nd model ages (TDM2) of 1.23–1.39 Ga, indicative of an enriched mantle source. The K-rich intrusions exhibit minor Nd–Hf isotopic decoupling (ΔεHf(t) = 2.93–5.01) and have low Nb/U ratios (2.11–3.01) and Mg numbers (48.5–52.1), suggesting that the Yangjiazhuang quartz diorites and Honghuapu diorites were formed through fractional crystallization of partial melts of enriched mantle metasomatized by terrigenous-sediment-derived fluids. The Na-rich Tangzang quartz diorites exhibit distinct ΔεHf(t) values (5.72–9.35) and elemental contents (e.g., high Na2O and Nb), and highly variable Rb/Y, Nb/Y, Th/Zr, and Nb/Zr ratios, indicating that they formed through crustal assimilation and fractional crystallization of partial melts of enriched mantle previously fertilized by terrigenous sediment-derived fluids and slab melts. Petrogenetic models for the HiBaSr dioritic rocks and Late Ordovician–Silurian igneous rocks of the western North Qinling terrane indicate that the K-rich HiBaSr intrusions formed in a slab subduction setting, whereas the Na-rich intrusion was controlled by slab break-off after continental collision. Together with granulite-facies metamorphism in the region, the emplacement of the HiBaSr dioritic rocks indicates that the closure of the Shangdan Ocean and initial collision between the North China Craton and Yangtze Block occurred at ca 433 Ma, with subsequent slab break-off triggering extensive Silurian magmatism at ca 430–402 Ma.

The formation and trace elements of garnet in the skarn zone from the Xinqiao Cu-S-Fe-Au deposit, Tongling ore district, Anhui Province, Eastern China

Xinqiao is a large copper-gold deposit and consists of two major mineralization types: stratabound and skarn. The skarn occurs along the contact between a quartz diorite intrusion and Carboniferous-Triassic limestone. Xinqiao has a strongly developed skarn zone, including endoskarn and exoskarn; the exoskarn is divided into proximal and distal exoskarn. We present systematic major, trace and rare earth element (REE) concentrations for garnets from the skarn zone, discuss the factors controlling the incorporation of trace elements into the garnets, and constrain the formation and evolution of the garnet from skarn zone in Xinqiao deposit. Grossular (Adr20–44Grs56–80) mostly occurs in endoskarn and has typical HREE-enriched and LREE-depleted patterns, with small Eu anomalies and low ∑REE. Garnets from the exoskarn show complex textures and chemical compositions. The composition of garnets range from Al-rich andradite (Adr63–81Grs19–47) to andradite (Adr67–98Grs2–33). Garnet in endoskarn has typical HREE-enriched and LREE-depleted patterns. Al-rich andradite in proximal skarn has small Eu anomalies and moderate ∑REE. Andradite from distal exoskarn shows strong positive Eu anomalies and has variable ∑REE. The U, Y, Fe and Al relationship with ∑REE shows that two mechanisms controlled incorporation of REE into the garnets: crystal chemistry (substitution and interstitial solid solution) mainly controlled in the endoskarn garnet (grossular) and the proximal exoskarn (Al-rich andradite), and fluid and rock chemistry (surface adsorption and occlusion) controlled REEs in the distal exoskarn. Furthermore, Al has a negative relationship with ∑REE indicating that REE3+ did not follow a coupled, YAG-type substitution into the garnets. Variations in textures and trace and rare earth elements of garnets suggest that the garnets in the endoskarn formed by slow crystal growth at low W/R ratios and near-neutral pH in a closed system during periods of diffusive metasomatism. The garnets in the exoskarn formed rapidly from externally derived fluids during advective metasomatism, and adsorption had a major control on the REE patterns in distal exoskarn. With the end of water-rock reaction, the contents of REE decreased in the hydrothermal fluid, and the system became nearly closed.

Geology and Isotope Geochemistry of the Wainaulo Cu-Au Porphyry Deposit, Namosi District, Fiji

The late Miocene, calc-alkalic, Wainaulo Cu-Au porphyry deposit of the Namosi district, Fiji, hosts distinct styles of alteration and mineralization that overlapped to produce a substantial porphyry Cu-Au resource. The early stages produced medium-grade Cu, low-grade Au and concentric calc-potassic to propylitic alteration that is zoned around the early-stage diorite intrusions. Discrete zones of high-grade Cu and Au and calc-sodic alteration were then superimposed during the intrusion of the main-stage quartz diorites and the formation of quartz-sulfide and epidote-sulfide veins. As the magmatic-hydrothermal system waned, lower Cu and Au grades, with a weaker intensity of calc-sodic alteration and lower density of veins, were produced coincident with emplacement of subsequent quartz diorite intrusions. Late-stage anhydrite-pyrite veins and chlorite-illite alteration overprinted the quartz diorite intrusive complex. The final hydrothermal event consisted of argillic alteration that was concentrated in and around steeply dipping, ENE-trending shears. These structures appear to have controlled the emplacement of the quartz diorite complex and distribution of high-grade Cu-Au mineralization, suggesting they were active during the pre- and synmineralization stages. Stable and radiogenic isotopic data provide evidence for direct seawater contributions to the magmatichydrothermal system. Measured δ34Ssulfide (–5.0 to 3.8‰) and δ34Ssulfate (9.0–16.8‰) values are consistent with a predominantly magmatic source, whereas an elevated bulk sulfur composition (6.7‰) suggests mixing with an isotopically heavy fluid (e.g., seawater). Estimates of δDfluid derived from epidote (–9.1 to 11.3‰) and δ18Ofluid from epidote and anhydrite (–0.2 to 4.7‰) approach that of Vienna standard mean ocean water, and the initial Sr isotope ratios of epidote (0.70364–0.70378) suggest a component of seawater Sr ranging from 3.2 to 5.8%. These results are consistent with the inferred submarine paleogeographic setting and may explain the abundance of albite- and epidote-rich alteration assemblages at Wainaulo.

Early Jurassic adakitic rocks in the southern Lhasa sub-terrane, southern Tibet: petrogenesis and geodynamic implications

AbstractCretaceous–Miocene adakitic rocks in the southern Lhasa sub-terrane have been intensively investigated, while possible Early Jurassic adakitic rocks in this area have been largely neglected. Petrological and geochemical studies revealed adakitic affinities of an Early Jurassic quartz diorite intrusion with mafic enclaves and three tonalite bodies from the Jiacha area in the southern Lhasa sub-terrane. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating suggests crystallization ages of 199–179 Ma for these rocks. Both quartz diorites and tonalites have typical adakitic geochemical characteristics such as high Al2O3 (15.14–18.22 wt.%) and Sr (363–530 ppm) contents, low Y (4.46–15.9 ppm) and Yb (0.51–1.74 ppm) contents and high Sr/Y ratios of 27–106. The adakitic quartz diorites are further characterized by high MgO (2.63–3.46 wt.%), Mg# (48–54) and εHf(t) (6.6–13.4) values, which were probably produced by partial melting of a subducted oceanic slab with a mantle contribution. The adakitic tonalites have very low abundances of compatible elements and relatively low εHf(t) values (3.5–10.3), and are interpreted to have formed by partial melting of Neoproterozoic mafic lower crust. Upwelling asthenosphere, triggered by rollback of the subducting Bangong–Nujiang (Meso-Tethys) oceanic plate, provided the necessary heat for slab and lower crust melting, resulting in the geochemical diversity of the coexisting felsic intrusive rocks. Contrary to other models, this study further demonstrates that the Bangong–Nujiang oceanic plate was subducted southward beneath the Lhasa terrane during the Early Jurassic.

The Nuevo Chaquiro Cu-Au-(Mo) Porphyry Deposit, Middle Cauca Belt, Colombia: Geology, Alteration, Mineralization

Nuevo Chaquiro is a newly discovered blind porphyry Cu-Au-(Mo) deposit located in the Middle Cauca belt, Colombia, approximately 60 km south-southeast of Medellin. The most recent resource estimate was stated as 566 M tonnes (t) averaging 0.64% Cu, 0.31 g/t Au, 4.34 g/t Ag, and 127 ppm Mo. The geology of Nuevo Chaquiro consists of a Miocene volcanic sequence of andesitic tuffs, agglomerates, and flows (Combia Formation) intruded by small stocks and dikes of diorite and quartz diorite also of Miocene age. Sparsely occurring outcrops at Nuevo Chaquiro consist of a 1.2 × 0.8 km zone of pervasive sericitic alteration with locally well developed quartz-Fe oxide stockworks. The sericitic alteration grades downward into sericite-chlorite alteration and then predominantly potassic (biotite-magnetite) alteration at depths of 250 to 400 m. Calcic-potassic alteration, containing actinolite and epidote, occurs at greater depths. A high-grade sheeted vein complex occurs immediately adjacent to the upper contact of an Early quartz diorite intrusion. Quartz veinlet density in this area reaches up to 80% quartz by volume, accompanied by up to 5 vol % chalcopyrite. Later Intermineral porphyries created a second orebody slightly to the west but contiguous with the Early orebody. Here Cu-Au-Mo mineralization in an inverted bowl shape is associated with potassic alteration that manifests itself as secondary flooding of the tuff wall rock matrix by hydrothermal biotite, accompanied by disseminations and hair veinlets of chalcopyrite, magnetite, pyrite, and molybdenite. The porphyry system is also accompanied by intermediate-sulfidation carbonate–quartz-base metal veins, typically with sericitic alteration selvages, which occur on the upper western flank of the deposit. At Nuevo Chaquiro, multiple intrusions of Early and Intermineral porphyry contain calcic-potassic and potassic alteration, with a later overprint by sericite-chlorite alteration centered on intrusion apexes. The amount of sericite-chlorite overprinting varies with each intrusion. Collectively, these intrusions are all overprinted by a single, later sercitic (phyllic) alteration event that is superimposed as a broad cap upon the entire system. There is a consistent paragenesis for the alteration/mineralization associated with each intrusion, suggesting a relatively stable underlying shallow magma chamber that fluxed geochemically similar pulses of magmatic/hydrothermal fluid with each porphyry. In many aspects, Nuevo Chaquiro is a “typical” Au-rich porphyry copper system. However, the contrast between the mineralization styles between the Early and Intermineral orebodies as well the timing differences in copper deposition suggest that differences in porphyry mineralization styles also occur at Nuevo Chaquiro.

Neoarchaean quartz diorites in the Jiefangyingzi area, Central Asian Orogenic Belt: geological and tectonic significance

Quartz diorite intrusions in the Jiefangyingzi area associated with deformed Palaeozoic rocks of the Palaeozoic Bainaimiao arc magmatic belt on the northern margin of the North China Craton (NCC) were studied to determine their age, chemical composition, and isotopic characteristics. U–Pb dating of magmatic zircons indicates that the quartz diorites formed in Neoarchaean time between 2502.6 ± 9.1 Ma and 2551 ± 7.3 Ma. The quartz diorites have high Al2O3 and low K2O contents, A/CNK = 0.75–0.97, and belong to the low-K tholeiitic series. The quartz diorites are enriched in light rare earth elements (LREEs) with high (La/Yb)N ratios and exhibit weak positive or no Eu anomalies, characteristics of high-alumina tonalite–trondhjemite–granodiorite (TTG) igneous rocks. Zircon εHf(t) value for the quartz diorites ranges from +1.6 to +8.7, and the two-stage Hf-depleted mantle model age (TDM) ranges from 2705 to 2744 Ma, suggesting that the quartz diorite was derived from melting juvenile Neoarchaean crust formed from partial melting of the mantle at 2.7 Ga. Amphibolite xenoliths have low REE concentrations and are moderately depleted in LREE with (La/Yb)N ratios of 0.46–1.09. The trace element characteristics of the amphibolites are consistent with a mid-ocean-ridge basalt (MORB)-like protolith. This is the first time that Archaean rocks have been identified in the Bainaimiao arc magmatic belt and the age and nature of Jiefangyingzi quartz diorites suggest that they belonged to the NCC. The Early Palaeozoic Bainaimiao arc thus appears to represent an Andean-type continental arc on the northern margin of the NCC.

Geochemistry and fluid characteristics of the Dalli porphyry Cu–Au deposit, Central Iran

The Miocene Dalli porphyry Cu–Au deposit in the central part of Urumieh–Dokhtar magmatic arc is the first reported Au-rich porphyry Cu deposit in the Zagros orogenic belt. The Cu–Au mineralization is mainly hosted in diorite and quartz diorite intrusions, presenting as numerous veinlets in the altered wall rocks, with potassic, phyllic, and propylitic alteration developed. Based on the mineral assemblages and crosscutting relations of veinlets, hydrothermal mineralization–alteration occurred in at least three stages, characterized by veinlets of (1) Qtz+Kfs+Mag±Ccp, (2) Qtz+Py+Ccp±Bn±Cv±Cc and, (3) Qtz+Chl+Bt. The ore-bearing intrusions exhibit typical geochemical characteristics of subduction zone magmas, including LREE fractionated pattern, strong enrichment in LILE (Cs, Rb, Ba, Pb, and U), and depletion of HFSE, with marked negative Ti and Nb anomalies. The adakite-like ore-hosting porphyry intrusions are characterized by a systematic gradual decreasing and increasing of Y and Eu/Eu∗ with increasing SiO2 content, respectively. Moreover, they exhibit a significant increasing trend of Sr/Y with decreasing of Y, which indicates progressive hornblende fractionation and suppression of plagioclase fractionation during the evolution toward high water content of parental magma. A relatively flat HREE pattern with low Dyn/Ybn and Nb/Ta values may represent that amphibole played a more important role than garnet in the generation of the adakitic melts in the thickened lower crust. Based on the phase assemblages confirmed by detailed laser Raman spectroscopy analyses and proportion of solid, liquid, and gaseous components, five types of fluid inclusions were recognized, which are categorized as; (1) liquid-rich two phase (liquidH2O+vaporH2O) (IIA), (2) vapor-rich two phase (vaporH2O/CO2+liquidH2O) (IIB), (3) high saline simple fluids (IIIA; liquidH2O+vaporH2O+Hl), (4) high saline opaque mineral-bearing fluids (IIIB; liquidH2O+vaporH2O+Hl+Hem+Ccp+Py) and (5) multi-phase type (IIIAB; liquidH2O+vaporH2O+Hl+Anh+Hem+Mag+Ccp). In early stage veins, the homogenization temperature of multiphase inclusions as high as 620°C, with corresponding salinities of up to 75wt.% NaCl equivalent represent the initial ore-forming fluids. From early to late stage veins, the gradual decrease of homogenization temperature of saline inclusions (IIIAB, IIIA, and IIIB) from 620 to 340°C (corresponding salinities of 75–35wt.% NaCl equivalent) may reflect fluid boiling and mixing of the early magmatic fluids with circulating groundwater. The common association of hematite and anhydrite daughter phases with the most primitive inclusions (IIIAB) in early-stage veins and the lack of CO2-bearing inclusions in the middle to late stage veins reveal CO2 content and oxygen fugacity of the fluids was significantly decreased from early to main stage of sulfide mineralization (second generation of veins). It seems that magnetite crystallization and CO2-escape have a decisive role in oversaturation of S2− and subsequent rapid and large-scale precipitation of sulfides in second generation of veins at the Dalli deposit.