The petrogenesis of the isolated pegmatites from granites is under debate. In the Chinese Altai, massive isolated pegmatites have been regarded as derivatives of granitic melts, which contradicts to ...the results of recent studies. In this work, the geology and mineralogy, as well as the zircon U-Pb chronology and Hf isotope geochemistry, of 10 Permian pegmatites are analyzed, and a comparative study of the Permian pegmatites and granites is conducted to reveal the petrogenesis of the Permian pegmatites in the Chinese Altai. The Permian pegmatites are concentrated in the Qiongkuer domain with a linear distribution and show structural control from regional anticlinoriums and connections to adjacent migmatites and luecogranite dykes. Their zircon U-Pb ages are 274–253 Ma, with the dominating age being late Permian. The pegmatites have three mineralization types including Li-Be-Ta-Nb ± Sn, Be-Nb-Ta ± REEs (rare earth elements) and REEs. The former two are comparable with the Triassic and Devonian-Carboniferous pegmatites in mineralization and Hf isotope composition, respectively, and the latter is unique in the Permian generation. The Permian pegmatites have comparable Hf isotope compositions with the juvenile and specific components in the Habahe Group, which indicates the dependency of mineralization on source from the heterogeneous Habahe Group metasedimentary rocks. The pegmatites also show decoupling spatial-temporal and differentiation-source correlations with the Permian granites, indicating no genetic relationship between them. Combining with the Permian high temperature metamorphism and previous tectonic-magmatic-metamorphic studies, we suggest that the Permian rare metal/earth pegmatites were likely generated by anatexis of the Habahe Group metasedimentary rocks under an extensional setting after the arc-arc collision between the Junggar arcs and the Chinese Altai.
•The Permian pegmatites in the Chinese Altai formed mainly during late Permian.•The pegmatites have three mineralization types including Li-Be-Ta-Nb ± Sn, Be-Nb-Ta ± REEs and REEs.•The mineralization types of the pegmatites show dependencies on source and partial meting degrees of source.•The pegmatites show decoupling spatial-temporal-differentiation-source correlations to the Permian granites.•The pegmatites were likely generated by anatexis of metasedimentary rocks after arc-arc collision.
Understanding the petrogenesis of rare‐metal pegmatites is important for understanding ore‐forming processes and their tectonic settings. In this study, we performed zircon U–Pb geochronological and ...Hf–O isotopic analyses of the Xiaokalasu, Dakalasu, and Yelaman pegmatites in the Chinese Altay orogen. These pegmatites have low εHf(t) values (−0.6 ~ +4.3), two‐stage model ages of 989 ~ 1,293 Ma, and high δ18O values (+6.52 ~ +11.31), indicating that they may have been derived from the anatexis of mature sedimentary rocks in the deep crust, with a small amount of mantle‐derived or juvenile material. Geochronological and Hf–O isotopic data for granitic intrusions in the Chinese Altay Mountains indicate that the εHf(t) values decreased from the Permian to the Triassic, which implies that two‐stage post‐collisional magmatism occurred in this region. During the Permian, the thin lower crust was cold; thus, magmatism likely originated in the deep crust close to the Moho surface and involved intense mantle–crust interactions. During the Triassic, asthenospheric upwelling provided heat to the lower crust, which increased the geothermal gradient and led to the anatexis of shallow crustal material.
Two‐stage post‐collisional magmatism model. (1) At the beginning of asthenosphere upwelling, the thinned lower crust would have been in a low‐temperature condition, and thus the magmatism might be originated at deep crust and close to the Moho surface. Because of the intensive mantle–crust interactions, more mantle materials have contributed into the initial magma. (2) The upwelling of asthenosphere kept providing heat into the lower crust, and, as a result, the geothermal gradient increased. These processes make the partial melting of shallower crust materials possible. If implemented, there could generate felsic melts without mantle material contribution.
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•The CMS classification is firstly applied to the pegmatitic rocks in the Chinese Altai.•The syn-orogenic rare metal pegmatites in the Chinese Altai are proved by zircon U-Pb ...dating.•The pegmatites and granites have a common source from immature crust source.•The syn-orogenic pegmatites originate from anatexis of metasediments under a forearc extensional setting.
Recently, an increasing number of anatetic pegmatites have been confirmed. In contrast to the granitic pegmatite, the anatetic pegmatite has no relation to granite. It is therefore necessary to reacquaint the origin and classification of pegmatitic rocks. As one of the largest pegmatite provinces, the Chinese Altai provides a natural laboratory for pegmatite study. To date, the type, age, source and tectonic setting of the syn-orogenic pegmatites in the Chinese Altai remain unclear. In this work, the CMS (Chemical composition-Mineral assemblage-Structural geology) classification is primarily applied on the pegmatitic rocks in the Chinese Altai. Five types’ pegmatitic rocks, including metapegmatite, pegmatoid, pegmatite, pseudopegmatite and granite pegmatite, are identified by their CMS features. In addition, the geology, mineralogy, zircon U-Pb ages and Hf isotopes of six pegmatites are presented in this work. The pegmatites, numbered JMHB02, QBL02, TLT01, ALJK01, AMLG01 and TMLT01, are dated at 394.8 ± 4.0 Ma, 402.6 ± 5.5 Ma, 385.9 ± 3.5 Ma, 368.0 ± 4.0 Ma, 358.3 ± 4.6 Ma and 333.0 ± 6.0 Ma, respectively, indicating that they were formed during the syn-orogenic stage of the Altai orogenic process. They are exposed in the Qiongkuer domain in the southern Chinese Altai, juxtaposed with the late- and/or post-orogenic pegmatites in the same pegmatite field. No parental granite can be confirmed for all these pegmatites. Comparatively, the synorogenic pegmatites are scarce, and have lower mineralization grades than the late- and postorogenic pegmatites. Zircon Hf isotopic compositions of the syn-orogenic pegmatites have positive ɛHf(t) values of +2.06–+8.28 and old TDM2 ages of 1,234–860 Ma and are consistent with those of most of the syn-orogenic I- and S-granites, which indicates that the pegmatites and granites have a common immature crustal source from the early Paleozoic metasedimentary rocks. Compared to the post-orogenic pegmatites in the Central Altai domain, the syn-orogenic pegmatites in this work have larger positive ɛHf(t) values and younger TDM2 ages, indicating that more juvenile components were involved in their magma sources. Combining this study with previous works, we suggest that the anatexis of metasediments induced by decompression and injection of heat energy and mantle-derived materials under a forearc extensional setting led to the formation of the syn-orogenic pegmatites in the Chinese Altai.
Granitic pegmatites and associated rare-metal deposits, unique features in the Altay orogen, are located in a key tectonic position of the southern Central Asian Orogenic Belt (CAOB) and document the ...tectonic evolution of the Paleo-Asian Ocean. The Kelumute No. 112 pegmatite, which intruded into the Jideke two-mica granites, hosts abundant rare-metal (e.g., Li, Be, Nb, Ta) ore deposits and ranks only second to the Koktokay No. 3 pegmatite in both size and reserves. To explore the evolution time limitation of magmatic, magmatic–hydrothermal and hydrothermal stages in the pegmatite magma system, the tectonic setting and the genetic relationship between pegmatites and granites, this study presents zircon UPb and Hf isotopic compositions of the Kelumute No. 112 pegmatite and the wall rocks (two-mica granite and biotite granite) as determined by LA-ICPMS and LA-MC-ICPMS. The weighted mean 206Pb/238U ages of the internal textural zones of the pegmatite, including zones I, II, III, V and VI, are 238.3±2.0Ma, 233.5±3.7Ma, 188.3±1.7Ma, 218.8±1.9Ma and 210.7±1.6Ma, respectively. Wall rocks of two-mica granite and biotite granite are dated at 445.6±4.3Ma and 455.6±5.4Ma, respectively. Zircons from the Kelumute No. 112 pegmatite have lower positive εHf(t) values (+0.03 to +2.35), with TDM model ages of 1112–1225Ma. Wall rocks show similar zircon εHf(t) values (−1.41 to +4.13) and TDM model ages (1172 to 1515Ma). However, three xenocrystic zircons from the granites are characterized by larger negative εHf(t) values (−5.85 to −9.83) and older TDM model ages (1839 to 2090Ma). Thus, the following conclusions can be drawn: 1) the Kelumute No. 112 pegmatite and its wall rocks (Jideke two-mica granite and biotite granite) have no genetic relationship, as indicated by the large gaps between their formation ages. However, they did originate from a common source composed of ancient crust and mantle-derived materials under two different tectonic settings; 2) the magmatic, magmatic–hydrothermal transition and hydrothermal stages of the No. 112 pegmatite magma lasted for ~5Ma, ~23Ma and ~22Ma, respectively; and 3) the No. 112 pegmatite magma was most likely formed in a post-collision tectonic setting, indicating that block amalgamation and collisional orogeny of the CAOB continued into the Triassic.
► The Kelumute No. 112 pegmatite and wall rocks originated from a common source without a genetic relationship. ► The durations of magmatic, magmatic–hydrothermal and hydrothermal stage of the No. 112 pegmatite were quantitated availably. ► Blocks amalgamation and collisional orogenesis of the CAOB still continued in the Triasssic.
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•The spatial–temporal and source-differentiation relationships between the Fanjingshan granite and pegmatite are proved.•The Fanjingshan granite and pegmatite could be sourced from ...the Taojinhe Formation.•The Neoproterozoic granitoids in the western JO have larger ore-forming potential than those in the eastern JO.•The multiple generations of rare metal ore deposits in South China have a common source from the Paleoproterozoic crust.•The western JO shows source inheritance from the Cathaysia Block.
Recent studies have demonstrated the Mesozoic explosive metallogeny of rare metals in China; however, Precambrian rare metal mineralization event is rarely reported or studied. The Jiangnan Orogen (JO) is a well-preserved Neoproterozoic orogenic belt in South China, and although it abounds with a huge amount of Neoproterozoic granitoids, lacks the equivalent amount granitic pegmatite. In this study, the geology, mineralogy, whole-rock composition, zircon U-Pb age and Hf isotope compositions of the Fanjingshan granite and surrounding rare metal pegmatites, and bulk composition of sedimentary wall rocks of the Taojinhe Formation in Guizhou province, western Jiangnan Orogen (JO), were studied to reveal the petrogenesis of the granite and pegmatite and the source relationship of the pegmatite with the Paleozoic and Mesozoic rare metal ore deposits in South China. The Fanjingshan granite and pegmatite both show Sn-Ta-Nb mineralization and have consistent zircon U-Pb ages of ca. 830 Ma, indicating the existence of the Neoproterozoic rare metal granite-pegmatite suite in the JO. The geology, mineralogy, whole-rock composition and zircon U-Pb age and Hf isotope study results demonstrate that the Fanjingshan rare metal pegmatite belongs to the Li-P-B-Sn-Ta-Nb granitic pegmatite in the Chemical composition-Mineral assemblage-Structural geology (CMS) classification (Dill, 2016), and has close spatial–temporal and source-differentiation connections with the Fanjingshan granite. The petrography and whole-rock composition studies revealed that the Taojinhe formation was formed by the deposition of mature and immature source materials from acidic igneous rocks in a continental arc setting. Comparison of the Hf isotope compositions of the Fangjingshan granite-pegmatite suite with those of the Fangjinshan Group and the high Li, Sn, Rb, W, Ta and Nb background concentrations in the Taojinhe Formation support the conclusion that the Taojinhe Formation was a contributing source to the granite-pegmatite suite. A comparative study of the Fanjingshan granite with synchronous S-type granitoids revealed that the granitoids in the eastern and western JO have distinct sources and degrees of differentiation, indicating the limited ore-forming potential of the Neoproterozoic granitoids in the eastern JO. The Fanjingshan rare-metal granite-pegmatite suite has consistent Hf isotope model ages of 1.6–2.3 Ga with the Paleozoic and Mesozoic Nb-Ta ± Sn-W ± Be-Li ore deposits in South China, indicating a common origin from the Paleoproterozoic crust and the source inheritance of the western JO from the Cathaysia Block.
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•REEs are strongly fractionated from a magmatic stage to hydrothermal stage.•The lanthanide tetrads are consistent with the liquid immiscibility.•Negative Ce anomalies are reported ...for the first time in terrestrial zircon from pegmatite.
The lanthanide tetrad effect and Y-Ho fractionation are commonly observed in highly fractionated melts. In pegmatites, they are attributed to liquid immiscibility, although this explanation has recently been debated. Based on the potential relationship between the lanthanide tetrad effect and liquid immiscibility in pegmatite-forming melts, the rare earth element compositions (REEs, including Y) in three types of zircons from the magmatic stage (Zone II), magmatic-hydrothermal transition stage (Zones III and V) and hydrothermal stage (Zone VI) of the Kelumute No. 112 pegmatite, Chinese Altai, were analyzed by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) in this study. The results show that the REEs are sharply fractionated from the magmatic stage to the hydrothermal stage. According to the REE variations in the three types of zircons that formed during different stages and the evidence from inclusions, the intense lanthanide tetrad effect and suprachondritic Y/Ho ratios in zircons from Zones III, V and VI result from selective incorporations of REEs in immiscible fluoride melt, which generated the W-type tetrad effect and subchondritic Y/Ho ratios in the fluoride melt and the complementary M-type tetrad effect and suprachondritic Y/Ho ratios in the coexisting silicate melt and aqueous fluid. The results further reflect that the liquid immiscibility of the silicate melt, fluoride melt and aqueous fluid occurred during the magmatic-hydrothermal transition stage of the pegmatite-forming melt. In addition, for the first time, a negative Ce anomaly was identified in the terrestrial zircon from Zone VI of the No. 112 pegmatite; this anomaly is attributed to the preferential incorporation and/or adsorption of Ce in/by the Fe-Mn oxyhydroxides prior to or during the crystallization of zircon in the hydrothermal stage.
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•Columbite minerals from zone I is coumbite-(Fe), and zircons are magmatic origin.•The Nanping pegmatites are emplaced at approximately 387Ma.•Pegmatites melt were derived from the ...Paleoproterozoic metasedimentary rocks.
The Nanping pegmatite deposit is a large Ta-Nb-Sn deposit in the northeastern Cathaysia Block, SE China. Columbite-group minerals from zone I in the Nanping No. 31 pegmatite vein belong to columbite-(Fe). The compositions and texture features of zircon grains from the same zone identify their magmatic origin. Columbite-(Fe) U-Pb age coincides well with the U-Pb age of zircon, and these age data constrain the absolute formation timing of this pegmatite vein to approximately 387Ma. Zircon εHf(t) values from the Nanping No. 31 pegmatite range from −13.81 to −11.60 with the TDM2 model ages ranging from 2107 to 2246Ma, implying that the Nanping pegmatite-forming melts are derived from Paleoproterozoic metasedimentary rocks. The differences in emplacement age and Hf isotopic features preclude the surrounding granites from being the parental granite of the pegmatite vein.
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•Li mineralization of spodumene-bearing pegmatites in the Altai is mainly controlled by melt fractional crystallization.•Li gradually accumulates during magmatic-hydrothermal progress ...from the outer zones to inner zones.•The late-stage hydrothermal fluids mainly composed of Na, K, Ca-rich fluids and Li, F-rich fluids.•The reactivation and migration of Li in the hydrothermal stage would destroy Li mineralization in the magmatic stage.
Pegmatite lithium (Li) deposits are usually associated with high fractionation and complex evolution of the magmatic–hydrothermal system. However, the mechanism that accounts for the evolution of the magmatic–hydrothermal system and Li mineralization remains unclear. The Li-mineralized pegmatites in the Altai orogenic belt in northwest of China, including the Koktokay No.3 pegmatite, Xiaohusite No.91 pegmatite, and Talati No.1 pegmatite used in this study, show different rock-formation ages and ore deposit scales but similar magmatic–hydrothermal evolution and ore mineral assemblage. This study focuses on the relative contributions of magmatic and hydrothermal processes to the formation of Li deposits. Therefore, the texture and compositions of Li-rich minerals (micas, spodumene, montebrasite, and holmquistite) were systematically analyzed in these three pegmatites. From the outer to the inner zones of the studied pegmatites, micas varied from muscovite to Li-bearing muscovite and Li-bearing phengite to zinnwaldite to lepidolite, with decreasing K/Rb ratios (27.4–5.3, 27.0–4.1, and 15.5–5.0, respectively, in Koktokay No.3 pegmatite, Xiaohusite No.91 pegmatite and Talati No.1 pegmatite) and increasing Li (545–12540, 652–35519, and 627–2599 ppm), Rb (3388–16820, 3447–20970, and 5930–17096 ppm), Cs, Ta, and F concentrations, showing that fractional crystallization is the most important factor controlling Li mineralization in the magmatic stage. However, primary muscovite, spodumene, and montebrasite were altered by subsequent hydrothermal fluids, forming F, Li-rich mica rims, secondary montebrasite, secondary spodumene, and other secondary minerals. The occurrence of holmquistite indicated that Li-rich hydrothermal fluids entered into wall rock. These processes indicate that Li reactivation and migration during the hydrothermal stage would destroy Li mineralization in the pegmatite.
A thorough understanding of the denting behaviour is significant for the design of sandwich pipes. The aim of this paper is to investigate the denting behaviour of the sandwich pipe and propose a ...method for optimizing the cross-sectional configuration of the sandwich pipes against the denting force. The deformation process, load-displacement curve, equivalent plastic strain and energy dissipation characteristics of the sandwich pipe in the stages of dent generation and rebound are numerically examined. The subsequent parametric study shows that the hollow ratio, the thickness-to-radius ratios of the outer and inner tubes have significant impacts on the denting resistance and dent rebound performance of the sandwich pipes. The Pareto solution set for maximizing the denting resistance and minimizing the overall mass is obtained by using the non-dominated sorting genetic algorithm (NSGA-II) combined with response surface methodology. The obtained Pareto frontier is of guiding significance to the optimization design of sandwich pipes.
Objectives
Recurrence rate is up to 70% at 5 years for hepatocellular carcinoma (HCC) after initial resection, but the management of recurrent HCC remains unclear. To compare the efficacy and safety ...of radiofrequency ablation (RFA) and repeat resection as the first-line treatment in recurrent HCC.
Methods
This multicenter retrospective study analyzed 290 patients who underwent RFA (
n
= 199) or repeat resection (
n
= 91) between January 2006 and December 2016 for locally recurrent HCC (≤ 5 cm) following primary resection. We compared the overall survival (OS), progression-free survival (PFS), and complications between the two treatment groups for the total cohort and the propensity score matched (PSM) cohort.
Results
The 1-, 3-, and 5-year OS (90.7%, 69.04%, 55.6% vs. 87.7%, 62.9%, 38.1%,
p
= 0.11) and PFS (56.5%, 27.9%, 14.6% vs. 50.2%, 21.9%, 19.2%,
p
= 0.80) were similar in the RFA group and the repeat resection group. However, RFA was superior to repeat resection in complication rate and hospital stay (
p
≤ 0.001). We observed similar findings in the PSM cohort of 48 pairs of patients and when OS and PFS were measured from the time of the primary resection. The OS of the RFA group was significantly better than repeat resection group among those with 2 or 3 recurrent tumor nodules in both the total cohort (
p
= 0.009) and the PSM cohort (
p
= 0.018).
Conclusion
RFA has the same efficacy as repeat resection in recurrent HCC patients, but with fewer complications. RFA is more efficient and safer than repeat resection in patients with 2 or 3 recurrent tumor nodules.
Key Points
• Recurrence rate is up to 70% at 5 years for hepatocellular carcinoma (HCC) after initial resection.
• RFA has the same efficacy as repeat resection in recurrent HCC patients, but with fewer complications.
• RFA may be preferred for those with 2 or 3 recurrent HCC nodules.
