Petrogenesis and metallogenic implications for the Machang, Huangdaoshan, and Tuncang plutons in eastern Anhui: an integrated age, petrologic, and geochemical study

<p>The Tuncang–Chuzhou–Machang area (eastern Anhui province) is geologically located in the intersection between the Yangtze block and the Qinling–Dabie orogenic belt. Many Mesozoic plutons outcrop in this district that are Cu–Au prospective but inadequately studied. We report new LA-ICP-MS zircon U–Pb ages, petrologic, and whole rock geochemical data for three representative plutons at Machang, Huangdaoshan, and Tuncang. New dating results suggest that all the Machang (129.3 ± 1.6 Ma), Huangdaoshan (129 ± 1.7 Ma), and Tuncang (130.8 ± 1.9 Ma) plutons were emplaced in the Early Cretaceous, slightly older than other plutons in neighbourhood of the Zhangbaling uplift. The three plutons contain typical low-Mg adakitic affinities, in which the rocks contain SiO₂ >56%, Al₂O₃ ≥15%, Mg# <53, elevated Sr, Ba, Cr, Ni, Sr/Y, and La/Yb, low Y and Yb and no discernible Eu anomaly. Their petrogenesis may have been related to the delamination and partial melting of the lower crust, which is different from the Chuzhou pluton, which was interpreted to have formed by partial melting of the subducted slabs. We suggest that this petrogenetic difference may explain why the pluton at Chuzhou is Cu–Au fertile, whereas those at Machang, Huangdaoshan, and Tuncang are largely barren. It is proposed that adakitic plutons formed by partial melting of the subducted slabs have high metallogenetic potentiality in the area.</p

Petrogenesis and timing of emplacement of porphyritic monzonite, dolerite, and basalt associated with the Kuoerzhenkuola Au deposit, Western Junggar, NW China: implications for early Carboniferous tectonic setting and Cu–Au mineralization prospectivity

<p>The Kuoerzhenkuola epithermal Au deposit is located in the northern part of the West Junggar region of NW China and is underlain by a recently discovered porphyritic monzonite intrusion that contains Cu–Au mineralization. Zircon LA-ICP-MS U–Pb dating of this intrusion yielded an age of 350 ± 4.7 Ma. The porphyritic monzonite is calc-alkaline and is characterized by high concentrations of Sr (583–892 ppm), significant depletions in the heavy rare earth elements (HREE; e.g. Yb = 0.96–2.57 ppm) and Y (10.4–23.3 ppm), and primitive mantle-normalized multi-element variation diagram patterns with positive Sr and Ba and negative Nb and Ti anomalies, all of which indicate that this intrusion is compositionally similar to adakites elsewhere. The composition of the porphyritic monzonite is indicative of the derivation from magmas generated by the melting of young subducted slab material. The area also contains Nb-enriched basalts that are enriched in sodium (Na₂O/K₂O = 1.20–3.90) and have higher Nb, Zr, TiO₂, and P₂O₅ concentrations and Nb/La and Nb/U ratios than typical arc basalts. The juxtaposition of adakitic rocks, Nb-enriched basalts, and dolerites in this region suggests that the oceanic crust of the expansive oceans within the West Junggar underwent early Carboniferous subduction. Magnetite is widespread throughout the Kuoerzhenkuola Au deposit, as evidenced by the volcanic breccias cemented by late hydrothermal magnetite and pyrite. In addition, the zoned potassic, quartz-sericite alteration, and propylitic and kaolin alteration in the deeper parts of the porphyritic monzonite are similar to those found in porphyry Cu–Au deposits. These findings, coupled with the mineralogy and geochemistry of the alteration associated with the Kuoerzhenkuola Au deposit, suggest that the mineralization in this area is not purely epithermal, with the geology and geochemistry of the porphyritic monzonite in this area suggesting that a porphyry Cu–Au deposit is probably located beneath the Kuoerzhenkuola Au deposit.</p

Genesis of late carboniferous granitoid intrusions in the Dayinsu area, West Junggar, Northwest China: evidence of an arc setting for the western CAOB

<p>The Dayinsu area is located in the northern part of the West Junggar district near the border between China and Kazakhstan and is an important component of the Central Asian Orogenic Belt (CAOB). The Dayinsu area hosts numerous granitoid plutons in Devonian–Carboniferous volcano–sedimentary strata. The older Laodayinsu and Kubei (345–330 Ma) plutons are located in the west with the younger Bayimuzha and Qianfeng (330–325 Ma) plutons in the east. The whole-rock SiO₂ contents of the four granitoid plutons range from 52.22 to 68.42 wt.% and total alkaline contents (K₂O + Na₂O) range from 4.94 to 9.16 wt.%. The granites are enriched in large ion lithophile elements and light rare earth elements with depletions in Nb, Ta, Ce, Pr, P, and Ti. The plutons are metaluminous with I-type signatures. The geochemistry of the intrusions suggests that they formed in a subduction zone setting, and subsequently underwent fractional crystallization during emplacement, with higher degrees of fractionation in the eastern sector than in the west. Similarities in the geochronology and geochemical characteristics of the granitoid plutons in Dayinsu to those in the Tabei district (west to Dayinsu area) suggest that both districts are part of the Carboniferous Tarbagatay Mountain intrusive event. The early Carboniferous (345–324 Ma) granitoid intrusions in the Tarbagatay Mountain likely formed in an island arc subduction setting during the evolution of the CAOB.</p

High-Precision Measurements of ⁴⁴Ca/⁴⁰Ca Using Multiple-Collector Inductively Coupled Plasma Mass Spectrometry without Collision-Cell Technology

Herein, we present a new method for determining the Ca isotopic composition of geological samples. To eliminate matrix elements from Ca, a column chromatography method was developed using a N,N,N′N′ tetraoctyl-1,5-diglycolamide (TODGA) resin. The Ca isotopic compositions were measured by a multiple collector inductively coupled plasma mass spectrometry (MC-ICP-MS) without collision cell equipment, especially that direct measurement to 44Ca/40Ca can be achieved. To mitigate the interference from 40Ar during 40Ca measurement, the cold plasma technique was used to suppress the Ar+ generation, resulting in a background Ar+ intensity of <300 mV, in contrast to the conventional hot plasma conditions, which typically yield thousands of volts for Ar+ intensities. Given the potential for a concentration mismatch between the sample and bracketed standard solutions to cause an intensive shift in measured Ca isotopic compositions, a correction for the [Ca] match is needed. To avoid matrix effects arising from residue matrix elements, it is crucial to limit the concentrations below 1% of Ca for most matrix elements (including Al, Mg, K, Na, and Sr) and below 1‰ for Fe. Notably, the tolerance of residue Sr is effectively improved compared to measurements with CC-MC-ICP-MS and traditional Hot-plasma-SSB-MC-ICP-MS methods with the conventional hot plasma technique, thereby lowering the complexity of column chemistry. The measured δ44/40Ca, δ44/42Ca, and ε40Ca values for eight reference materials agree well with previously reported values within analytical uncertainties. This method demonstrates long-term precision is better than 0.10‰ (two standard deviations) for both δ values (i.e., δ44/40Ca and δ44/42Ca). We anticipate that the proposed method will benefit the growth of the Ca isotope data set and foster an increase in the application of Ca isotope in Earth science studies