Journal of Asian Earth Sciences 81 (2014) 142–152
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Journal of Asian Earth Sciences
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Geology, geochemistry and geochronology of the Jiaojiguanliangzi Fe-polymetallic deposit, Tengchong County, Western Yunnan (China): Regional tectonic implications ⇑ Hua-Wen Cao a,b, Shou-Ting Zhang a,b, , Jin-Zhan Lin a,b, Luo Zheng a,b, Jun-De Wu c, Dong Li a a State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China b Key Laboratory of Tectonic Controlled Mineralization and Oil Reservoir, Ministry of Land and Resources, Chengdu University of Technology, Chengdu 610059, China c Yunnan Tin Company Group, Gejiu 610000, China article info abstract
Article history: The Jiaojiguanliangzi Fe-polymetallic deposit, located near the Sino-Burmese border of the Tengchong Received 3 May 2013 County, western Yunnan in China, is a medium to large scale skarn Fe-polymetallic deposit that was Received in revised form 4 November 2013 recently discovered in this area. Zircons from monzonite granite-porphyry in the mining area yield an Accepted 5 November 2013 U–Pb age of 120 ± 0.6 Ma, and show eHf(t) values ranging from À1.9 to À4.9, suggesting that the magma Available online 13 November 2013 was derived from dominantly pelitic sedimentary protoliths. The porphyry is part of muscovite-bearing peraluminous S-type granitoid formed at the late stage of Early Cretaceous. The molybdenite Re–Os age Keywords: of 122 ± 0.7 Ma from this deposit is consistent with the age of the monzonite granite-porphyry. The Geochemistry monzonite granite-porphyry that hosts the skarn deposit belongs to syn- to post-collisional granitoid, Zircon U–Pb geochronology Hf isotope composition representing the culmination of the collision of Tengchong block with Baoshan block, and the initiation Molybdenite Re–Os ages of post-collisional extension event. The Mesozoic granite and Fe-rich polymetallic deposits in the Teng- Bangong–Nujiang metallic belt chong area are similar to their counterparts in Bangong–Nujiang magmatic/metallogenic belt in terms of formation age and geological characteristics. This indicates that these two areas underwent a similar intense magmatic activities and mineralization events during the Cretaceous. The Tengchong area has considerable prospecting potential. We believe that the Tengchong area is an important part of the southeast extension of the Bangong–Nujiang metallic belt. Ó 2014 Published by Elsevier Ltd.
1. Introduction magmatic rocks and related mineralization in the Bangong– Nujiang magmatic/metallogenic belt (Zhu et al., 2011a). The Bangong–Nujiang metallogenic belt (BNMB) runs from Ritu The N–S trending Tengchong block (TCB) is located between County in the west, through Geji, Gaize, Cuoqin, Shenzha and the Bangong–Nujiang suture zone (BNSZ) and the Indus– Bange eastward, turning southward to Dangxiong, striking nearly Yarlung–Myitkyina suture zone (IYMSZ) (Fig. 1a). The block is part EW, and is located between 31°N and 34°N(Fig. 1a). The belt is of the Chayu–Tengchong volcanic-magmatic arc in Sanjiang- tectonically located in the northern margin of Lhasa block (NLSB), Tethys metallic belt (Hou et al., 2007) and the northward extension bound between the Qiangtang block (QTB) and Lhasa block (LSB) of the SE-Asia tin ore belt (Schwartz et al., 1995; Jiang et al., 2012). (Fig. 1a), and is part of the hydrothermal metasomatic (skarn type) The Jiaojiguanliangzi (JJGLZ) deposit in the Tengchong County is iron, copper, tin, lead, bismuth and indium polymetallic belt in the a medium to large skarn Fe-polymetallic deposit that was recently Tethys-Himalaya metallogenic province (Zhao et al., 2011; Deng discovered near the Sino-Burmese border area (Fig. 1b). The depos- et al., 2013; Li et al., 2013; Wang et al., 2013). The collision of it is divided into two segments by the national boundaries, the Qiangtang block and Lhasa block during Late Jurassic and that southern part is located in the Tengchong County, Yunan, China of the Lhasa block and Indian plate during Early Paleocene gener- (Fig. 1c), whereas the northern part is located in the Kachin State, ated massive volumes of Mesozoic–Cenozoic intermediate-acid Burma. The location of the deposit has therefore posed restrictions on detailed studies in the past. This paper reports field observations, element compositions obtained by XRF and ICP–MS methods, LA–MC–ICP–MS zircon ⇑ Corresponding author at: State Key Laboratory of Geological Processes and U–Pb data, and Hf isotope compositions for the monzonite gran- Mineral Resources, China University of Geosciences, Beijing 100083, China. Tel.: +86 ite-porphyry, as well as molybdenite Re–Os age data for the 10 82322352. Fe-polymetallic deposit for the first time. The aim of this study is E-mail address: [email protected] (S.-T. Zhang).
1367-9120/$ - see front matter Ó 2014 Published by Elsevier Ltd. http://dx.doi.org/10.1016/j.jseaes.2013.11.002 H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152 143
Fig. 1. (a) Generalized tectonic map of the Lhasa block and Tengchong block (modified from Zhu et al., 2011a). (b) Simplified geologic map of the Tengchong area showing major geologic units (modified from Xu et al., 2012). (c) Geological map of the JJGLZ skarn Fe-polymetallic deposit. Abbreviations: JSSZ-Jinsha suture zone, BNSZ-bangong Nujiang suture zone, IYMSZ-Indus Yarlung Myitkyina suture zone, QTB-Qiangtang Block, NLSB-Northern Lhasa Block, CLSB-Central Lhasa Block, SLSB-Southern Lhasa Block, TCB-Tengchong Block, BSB-Baoshan Block, BNMB-Bangong Nujiang metallogenic belt, GDMB-Gangdese metallogenic belt, YLMB-Yulong metallogenic belt, F1-Nujiang fault, F2-Longchuanjiang fault, F3-Guyong fault, F4-Qipanshi fault, F5-Binglangjiang fault, 1-Jiaojiguanliangzi Fe deposit, 2-Diantan Fe deposit, 3-Dadongchang Cu–Pb–Zn deposit, 4-Jiagushan Sn polymetallic deposit, 5-Xiaolonghe Sn deposit, 6-Tieyaoshan W-Sn deposit, 7-Xinqi Rn-W-Sn deposit, 8-Tiechang Sn deposit.
to provide insights on the nature and timing of magmatism and The Tengchong block and the Baoshan block (BSB) in the east is mineralization in the JJGLZ deposit with implications on regional considered to have collided along the Bangong–Nujiang suture prospecting. zone during Yanshanian (Cretaceous) (Fig. 1)(Sato et al., 2001; Xu et al., 2012). Recent studies have recognized the nearly NS-trending Early Cretaceous Gaoligong granitic belt (126 –118 2. Regional geological setting Ma, Yang et al., 2006; Xu et al., 2012) in the Tengchong–Lushui– Fugong area of the Nujiang River suture zone in eastern Tengchong The northern margin of Lhasa block witnessed the formation of block (Fig. 1a). This belt is connected to Chayu–Bomi magmatic several S-type and minor I-type granites during the closure of the rocks in the east margin of Lhasa terrane (Fig. 1a) (130 –110 Ma, Meso-Tethys Ocean (Bangong–Nujiang Ocean) along the Bangong– Chiu et al., 2009; Zhu et al., 2009b; Liu et al., 2009), and extends Nujiang suture zone in the Mesozoic era (Fig. 1a). Debates westward into the northern margin of the Lhasa block (Fig. 1a) surround the genesis of these granites and their tectonic evolution (143 –102 Ma, Zhu et al., 2009a, 2011a; Gao et al., 2011; Zhang and the major views are as follows. et al., 2012a). The Tengchong block corresponds to Lhasa block with regard to its geotectonic position. (1) Northward subduction of Meso-Tethys or Neo-Tethys oce- The Paleoproterozoic Gaoligongshan Group comprises amphib- anic slab (Zhang et al., 2004, 2012b; Li et al., 2013). olite facies metamorphic rocks, and is also part of the Tengchong (2) Southward subduction of Meso-Tethys oceanic slab (Zhu block crystalline basement (Fig. 1b). It extends southwest into Bur- et al., 2009a, , 2011a; Kang et al., 2010; Chang et al., 2011; ma, as the Mogok gneissic rock series (Schwartz et al., 1995). The Li et al., 2012a; Qin et al., 2012). Neoproterozoic Meijiashan Group is a formation of sandy mud- (3) The two-directional subduction of Meso-Tethys oceanic stone and calcareous sandstone intercalated with carbonate rocks basin (Du et al., 2011). and intermediate-acid volcanic formations. The Early Devonian (4) Melting of the thickened crust induced by the collision of strata include a succession of river-delta facies and littoral–neritic Lhasa block with Qiangtang block (Xu et al., 2012). (facies) deposition, with banded lead, zinc and manganese miner- (5) During the subduction of Neo-Tethys Ocean, Lhasa terrane alization exposed in some horizons. Permian strata are the ore- subducted northward beneath Qiangtang block along the hosting wall rocks (Fig. 1c), and mainly represent littoral–neritic Bangong–Nujiang suture zone (Kapp et al., 2005, 2007). 144 H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152 deposition which are dominantly purplish grey, gray medium- matism and the main rock types are skarn and hornfels with some thickly bedded feldspar–quartz greywacke bearing conglomerate marble and metaquartz sandstone. The relatively well-developed debris, intercalated with limestone lenses. After the closure of wall rock alteration is characterized by of skarnization, silicifica- Paleo-Tethys, during the Indosinian orogeny, the whole area was tion, pyritization, and greisenization. The skarnization is presented uplifted and suffered from erosion. During the Late Triassic period as diopside, garnet, and phlogopite, commonly in association with marginal littoral–neritic carbonate rock platform facies was depos- pyrite, pyrrhotite, chalcopyrite, magnetite, galena, sphalerite, ited locally. During the Mesozoic–Cenozoic, there was no deposi- scheelite, cassiterite and molybdenite. The silification is repre- tion, but the Yanshanian–Himalayan granites were developed sented by stockworks composed of fine-grained quartz aggregates, widely (Xu et al., 2012). Most Cenozoic strata were spread in inter- commonly associated with magnetite, pyrite and chalcopyrite. The mountain basins, with alluvial–deluvial and slope–eluvial tin pyritization occurs as veinlets or disseminations in the various deposits. rocks. Interstratified fractured zone with pyrite is commonly asso- The regional tectonic framework includes the Nujiang fault (F1), ciated with tin mineralization. The greisenization is represented by Longchuanjiang fault (F2), Guyong fault (F3), Qipanshi fault (F4) radial, sheaf-like muscovite occurring in gaps between coarse and Binglangjiang fault (F5) (Fig. 1b). Magmatic rocks are well quartz grains. developed in the study area. The Cretaceous and Paleogene gran- Massive ores near the surface have been mostly oxidized into ites are closely related with mineralization (Fig. 1b). limonite. The ore minerals mainly include geothite, magnetite, pyr- ite and tinstone with minor wolframite and molybdenite. Major gangue minerals are quartz, feldspar and sericite with minor 3. Geological characteristics of the ore deposit chlorite and calcite. Ores show massive, small mass-shaped and partial veinlet-disseminated structures with euhedral–subhedral The rock types in the mining area mainly belong to the Permian grains and metasomatic relict textures. Ore types are dominated Kongshuhe Formation, which is the principal host of the Fe- by massive magnetite, with subordinate veinlet-disseminated polymetallic deposits in the area (Fig. 1c). The formation strikes magnetite. Other than Fe, elements like Cu, Pb, Zn, Sn, In, Au and north–south and dips to the west. The major rock types are horn- Ag are also important metals in the JJGLZ Fe-polymetallic deposit. fels intercalated with dark gray bioclastic crystalline limestone, marble and garnet–tremolite–epidote skarn lenses. Phlogopitiza- tion and iron mineralization are well developed. The NW–EW 4. Analytical methods striking faults dip to northeast, cutting across the center of the orebodies. Geochemical analysis for major and trace elements were carried Early Cretaceous medium-fine grained biotite monzogranite out on 13 samples of fresh monzogranite-porphyry. Zircon U–Pb widely intruded the Permian Kongshuhe formation as stocks, dating and Hf isotope analysis were performed on one sample extending from south to north into the Burma territory. The min- and Re–Os dating analysis was carried out on 6 molybdenite-bear- eralization and alteration mainly occurs around NS-trending ing ore samples collected from the JJGLZ mining area. dyke-like monzonite granite-porphyry (Fig. 1c). The monzonite Major and trace elements analyses were carried out in XRF & granite-porphyry shows porphyritic texture (Fig. 2) and the pheno- LA–ICP–MS microanalysis laboratory, China University of Geosci- crysts are mainly potash feldspar (15–20%), plagioclase (10–15%), ences, Beijing. The experimental procedures are similar to those quartz (10–15%), biotite (3–5%) and muscovite (0–3%). The matrix described by Zhang et al. (2012c). Major element compositions is composed of quartz and feldspar with minor magnetite, zircon, were determined using SHIMADZU XRF-1800 sequential X-ray sphene, apatite, epidote, etc. fluorescence spectrometer, with accuracy better than 5%. Trace The Kongshuhe Formation within the mining area underwent elements were analyzed using Thermo Scientific X Series II Induc- regional metamorphism superposed with hydrothermal metaso- tively Coupled Plasma Mass Spectrometry (ICP–MS), with accuracy
Fig. 2. Photomicrographs of the JJGLZ monzonite granite-porphyry (transmitted light, crossed polarized). Porphyritic texture, matrix is composed of fine-grain quartz and plagioclase. Qz-quartz, Pl-plagioclase, Kf-potash feldspar, Bit-biotite, Mus-muscovite. H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152 145
Table 1 Bulk-rock major and trace elements data of the monzonite granite-porphyry rock in the JJGLZ.
Sample JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- JJGLZ- No. 340 342 449 450 451 453 454 455 456 457 458 459 460 XRF-major element (wt.%)
P2O5 0.05 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
Al2O3 13.60 13.24 12.90 13.79 13.74 14.31 14.12 13.17 13.29 13.61 12.43 13.28 13.68
SiO2 72.96 74.16 73.62 72.33 73.05 72.32 72.95 71.94 73.92 73.66 74.25 73.76 73.32
Na2O 2.60 3.57 3.07 3.22 3.32 3.35 3.30 2.05 3.10 2.74 3.37 3.37 3.19 MgO 0.23 0.21 0.27 0.24 0.26 0.27 0.29 0.28 0.22 0.28 0.24 0.22 0.23
K2O 4.20 4.32 4.02 4.06 4.22 4.38 4.50 4.06 4.58 4.22 4.69 4.35 4.62 CaO 2.21 0.78 1.01 1.73 0.81 1.02 0.36 1.56 0.78 1.40 0.82 0.52 0.35
TiO2 0.15 0.14 0.15 0.16 0.16 0.15 0.15 0.15 0.14 0.15 0.16 0.16 0.14 MnO 0.04 0.04 0.04 0.03 0.03 0.03 0.04 0.04 0.04 0.04 0.04 0.03 0.04
TFe2O3 1.35 1.26 1.52 1.29 1.59 1.39 1.57 1.53 1.46 1.52 1.42 1.52 1.50 LOI 1.90 2.12 2.44 2.60 2.12 2.11 1.90 1.99 2.13 2.20 1.89 2.32 2.01 Total 99.27 99.88 99.08 99.49 99.33 99.37 99.22 96.80 99.70 99.86 99.35 99.57 99.14 ICP–MS-trace element (ppm) La 30.33 30.60 27.22 30.49 33.30 31.88 31.13 30.44 32.98 29.45 30.52 34.79 33.36 Ce 62.50 63.52 56.56 63.74 69.01 67.50 65.46 63.69 69.50 62.54 64.31 71.68 69.19 Pr 6.73 6.84 6.12 6.85 7.35 7.20 7.02 6.81 7.46 6.72 6.91 7.64 7.42 Nd 24.49 24.55 21.94 24.71 26.38 25.72 25.24 24.44 26.91 24.28 24.98 27.56 26.68 Sm 5.55 5.41 4.88 5.57 5.76 5.56 5.65 5.41 6.08 5.49 5.54 6.05 5.88 Eu 0.47 0.41 0.33 0.43 0.40 0.38 0.40 0.35 0.45 0.37 0.36 0.45 0.41 Gd 6.03 5.61 5.00 5.66 5.80 5.59 5.80 5.58 6.27 5.64 5.68 6.34 5.82 Tb 1.04 0.92 0.81 0.93 0.92 0.89 0.95 0.93 1.03 0.94 0.93 1.06 0.93 Dy 6.58 5.88 4.93 5.78 5.55 5.41 5.98 5.95 6.40 5.87 5.72 6.59 5.73 Ho 1.36 1.21 1.02 1.18 1.13 1.10 1.23 1.19 1.32 1.19 1.17 1.36 1.17 Er 4.27 3.79 3.23 3.73 3.55 3.52 3.92 3.87 4.19 3.76 3.68 4.22 3.69 Tm 0.67 0.61 0.51 0.59 0.56 0.56 0.62 0.61 0.66 0.60 0.59 0.66 0.59 Yb 4.54 4.16 3.60 4.28 3.91 3.90 4.30 4.25 4.56 4.12 4.18 4.46 4.12 Lu 0.69 0.64 0.56 0.63 0.59 0.59 0.66 0.65 0.69 0.63 0.62 0.68 0.63 Y 43.97 38.32 29.62 36.09 34.14 33.67 37.87 35.37 41.46 36.36 35.91 41.15 35.54 RREE 155.22 154.15 136.70 154.57 164.20 159.80 158.36 154.14 168.50 151.60 155.19 173.52 165.62 LREE/ 5.17 5.75 5.95 5.78 6.46 6.41 5.75 5.70 5.71 5.66 5.87 5.85 6.30 HREE
LaN/YbN 4.54 5.00 5.14 4.84 5.79 5.55 4.91 4.87 4.91 4.86 4.96 5.30 5.50 Eu/Euà 0.25 0.22 0.20 0.23 0.21 0.21 0.21 0.19 0.22 0.20 0.19 0.22 0.21 Ce/Ceà 1.02 1.02 1.02 1.03 1.02 1.04 1.03 1.03 1.03 1.04 1.03 1.02 1.02 Rb 408 403 414 424 422 441 415 463 434 453 514 413 432 Ba 171 233 199 191 221 201 204 210 225 205 259 216 217 Th 36.2 36.8 35.6 39.4 38.3 37.4 37.9 35.3 38.8 36.3 36.7 39.3 38.5 U 7.25 6.90 7.43 7.41 7.23 7.08 7.34 7.23 7.88 7.18 7.17 7.68 7.48 Nb 16.20 15.81 15.12 16.49 16.38 15.66 15.60 16.37 16.26 15.62 15.87 17.20 16.02 Ta 2.03 2.04 1.96 2.04 1.99 1.90 1.98 1.97 2.08 1.89 1.95 2.08 1.97 Pb 29.92 25.59 20.81 23.06 13.07 22.98 20.42 20.36 28.77 26.15 23.89 19.57 26.96 Sr 59.13 82.47 52.58 65.40 72.18 66.73 71.29 55.43 76.55 53.94 74.98 71.33 73.98 Nd 24.49 24.55 21.94 24.71 26.38 25.72 25.24 24.44 26.91 24.28 24.98 27.56 26.68 Zr 86.00 81.35 89.77 86.62 91.35 86.36 85.26 89.37 94.82 95.14 92.26 97.04 92.03 Hf 4.91 5.20 4.84 4.87 4.74 4.65 4.66 4.71 5.03 4.85 4.90 4.98 4.83 Y 43.97 38.32 29.62 36.09 34.14 33.67 37.87 35.37 41.46 36.36 35.91 41.15 35.54 V 8.71 8.45 8.36 9.06 9.07 8.45 8.16 8.88 8.47 8.87 8.79 9.35 8.17 Cr 2.28 2.38 2.17 2.34 2.26 2.04 2.18 2.26 2.12 2.20 3.49 2.36 2.21 Co 138 177 114 125 113 124 117 113 122 113 125 117 120 Ni 8.71 11.82 7.28 8.20 7.23 7.72 7.39 7.41 7.67 7.27 8.30 7.20 7.68 Ga 19.72 18.07 14.95 18.30 17.66 19.41 17.25 16.66 16.94 17.21 13.35 17.04 17.06
à à LOI = loss on ignition, LaN/YbN values are La/Yb ratios normalized to chondrite values after McDonough and Sun (1995), Eu/Eu =2Ãw(Eu)N/[w(Sm)N + w(Gd)N], Ce/Ce =2-
Ãw(Ce)N/[w(La)N + w(Pr)N].
better than 5–8%. 50 mg powders from each sample were dissolved by Zhang et al. (2012c). The spot sizes of the Laser Ablation System in high-pressure Teflon bombs using HCl + HF + HNO3 + HClO4 were 35 lm for zircon U–Pb ages analyses and 50 lm for Hf mixture. An internal standard solution containing single element isotopes analyses. TEMORA standard zircon was taken as standard Rh was used for monitoring signal drift during ion counting. The for U–Pb dating, and was analyzed twice every 5 analyses. USGS standard GSP-2 and Chinese National standards GSR-1 and Common lead correction was carried using the EXCEL program GSR-2 were used for calibration of element concentrations of the ComPbCorr#3 15G (Andersen, 2002). NIST612 is the external stan- unknowns. During analysis, data quality was monitored by the dard for the elemental compositions, Si is the internal standard. repeated analyses of rock reference materials, together with The data were processed through ICPMSDataCal (Liu et al., 2010) regular monitoring of total procedural blanks. and Isoplot software (Ludwig, 2012), by zircon weighted mean Zircon U–Pb ages and Hf isotopes were measured on a Thermo age calculating and preparing Concordia diagrams. Errors on indi- Scientific Neptune multi-collector Inductively Coupled Plasma vidual analyses by LA–ICP–MS are quoted at the 95% (1r) confi- Source Mass Spectrometry (MC-ICPMS), coupled with 193 nm dence level. Laser Ablation System at Tianjing Institute of Geology and Mineral During the process of zircon Hf isotope analysis, the equipment Resources. The analytical procedures are similar to those described was monitored and samples were corrected to standard zircon 146 H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152
GJ-1. For detailed testing procedures, equipment operating condi- tions, etc. see Geng et al. (2011a). The 176Hf/177Hf and 176Lu/177Hf ratios of standard zircon GJ-1 were 0.281988 ± 18 (n = 19) and 0.0003 (n = 19) respectively, which agree well with the recom- mended values (Morel et al., 2008). Molybdenite Re–Os were analyzed on TJA X-series Inductively Coupled Plasma Source Mass Spectrometer (ICP–MS) to measure the isotope ratios in National Research Center for Geoanalysis, Chi- nese Academy of Geological Sciences. Standard material for the analysis is GBWO04435 (JDC) (141 ± 1.9 Ma). Re and Os chemical separation procedure and mass spectrometer analyses followed those described in Smoliar et al. (1996). The data were processed through calculating isochronal and weighted mean ages and pre- paring concordia diagrams with Isoplot software (Ludwig, 2012).
5. Analysis results
5.1. Geochemical characteristics of monzonite granite-porphyry
The major and trace element data from the JJGLZ monzonite
granite-porphyry are shown in Table 1. The contents of SiO2 (71.94–74.25 wt.%), Al2O3 (12.43–14.31 wt.%), and differentiation index (DI) (85–93) are relatively high. Total alkali content (ALK)
shows a range of 6.11–8.06%, and the K2O/Na2O ratio is 1.21–1.98. The rocks are poor in MgO, Fe2O3 and CaO. Their alumi- num alkali index (AKI) is 0.65–0.86, the alkalinity ratio index (A.R.)
is 1.77–3.08, and Rittmann index (r43) is 1.54–2.08, indicating high K calc-alkaline features. The aluminum saturation index (A/CNK) is 1.03–1.29 with an average of 1.16, A/NK is 1.17–1.69 (averaging at Fig. 3. Chondrite normalized REE patterns and primitive mantle normalized trace 1.39), and the normative corundum ranges from 0.44% to 3.36% elements patterns for the JJGLZ monzonite granite-porphyry (normalized data after with an average of 1.99%, suggesting that the JJGLZ McDonough and Sun, 1995).
Table 2 Zircons U–Pb age data of the monzonite granite-porphyry rock in the JJGLZ.
Spot Content (ppm) Isotopic rations Age (Ma)
No. 206 Ã 238 207 Ã 235 207 Ã 206 Ã 206 238 207 235 207 206 Pbc U Th Th/ Pb / U1r Pb / U1r Pb / Pb 1r Pb/ U1r Pb/ U1r Pb/ Pb 1r U 1 7 266 178 0.67 0.0188 0.0002 0.1393 0.0053 0.0537 0.0019 120 1 132 5 3359 81 2 5 167 165 0.99 0.0188 0.0002 0.1288 0.0085 0.0497 0.0033 120 1 123 8 180 154 3 12 423 402 0.95 0.0188 0.0002 0.1395 0.0075 0.0539 0.0023 120 1 133 7 369 97 4 31 303 247 0.82 0.0777 0.0007 0.6374 0.0061 0.0595 0.0006 483 4 501 5 585 21 5 4 125 223 1.79 0.0189 0.0002 0.1253 0.0102 0.0482 0.0039 120 2 120 10 109 193 6 6 224 243 1.09 0.0184 0.0002 0.1249 0.0110 0.0493 0.0044 117 1 120 11 164 207 7 22 839 1422 1.69 0.0169 0.0001 0.1357 0.0021 0.0582 0.0009 108 1 129 2 538 33 8 11 413 579 1.40 0.0185 0.0002 0.1263 0.0039 0.0495 0.0015 118 1 121 4 173 72 9 8 304 349 1.15 0.0189 0.0002 0.1255 0.0075 0.0482 0.0028 121 1 120 7 110. 138 10 11 388 643 1.65 0.0188 0.0002 0.1255 0.0043 0.0483 0.0016 120 1 120 4 115 80 11 11 395 508 1.29 0.0190 0.0002 0.1262 0.0097 0.0482 0.0037 121 1 121 9 108 179 12 9 356 429 1.20 0.0188 0.0002 0.1258 0.0044 0.0485 0.0017 120 1 120 4 122 82 13 36 164 161 0.98 0.0615 0.0013 5.1144 0.1006 0.6033 0.0044 385 8 1839 36 4516 11 14 11 416 441 1.06 0.0189 0.0003 0.1255 0.0122 0.0482 0.0046 121 2 120 12 111 223 15 12 451 639 1.42 0.0185 0.0002 0.1279 0.0076 0.0501 0.0029 118 1 122 7 197 134 16 22 649 895 1.38 0.0185 0.0002 0.1268 0.0029 0.0496 0.0010 118 1 121 3 178 45 17 7 259 314 1.21 0.0189 0.0002 0.1240 0.0081 0.0476 0.0030 121 1 119 8 78 152 18 9 362 357 0.99 0.0189 0.0002 0.1259 0.0079 0.0485 0.0030 120 1 120 8 121 145 19 6 301 19 0.06 0.0190 0.0002 0.1256 0.0059 0.0480 0.0022 121 1 120 6 100 108 20 10 377 355 0.94 0.0188 0.0002 0.1322 0.0081 0.0510 0.0025 120 2 126 8 239 115 21 11 465 423 0.91 0.0185 0.0002 0.1238 0.0046 0.0485 0.0017 118 1 119 4 123 85 22 13 552 460 0.83 0.0185 0.0002 0.1264 0.0046 0.0495 0.0017 118 1 121 4 174 81 23 38 1393 1308 0.94 0.0191 0.0002 0.1270 0.0025 0.0481 0.0009 122 1 121 2 106 47 24 21 798 679 0.85 0.0191 0.0003 0.1277 0.0043 0.0485 0.0009 122 2 122 4 121 42 25 11 423 387 0.91 0.0192 0.0002 0.1268 0.0034 0.0479 0.0012 123 1 121 3 94 60 26 16 664 608 0.91 0.0186 0.0002 0.1257 0.0028 0.0491 0.0011 119 1 120 2 151 52 27 38 1188 2324 1.96 0.0191 0.0002 0.1256 0.0015 0.0478 0.0006 122 1 120 1 87 30 28 9 345 390 1.13 0.0190 0.0002 0.1289 0.0080 0.0491 0.0030 122 1 123 8 154 143
Errors are 1r representing standard deviation; Pbc and Pbà indicate the common and radiogenic portions, respectively. Error in Standard calibration was 0.16% (not included in above errors but required when comparing data from different mounts). (1) Common Pb corrected using measured 204Pb. (2) Common Pb corrected by assuming 206Pb/238U–207Pb/235U age-concordance. H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152 147
Fig. 4. CL images of zircon for the JJGLZ monzonite granite-porphyry.
monzogranite-porphyry belongs to peraluminous-strongly peralu- 5.3. Zircon Hf isotopes minous granitoid type. The monzonite granite-porphyry shows high total REE, (RREE = Some zircons from Sample JJGLZ-448 for U–Pb dating were also
136.7–173.52 ppm); LREE/HREE = 5.2–6.5, and (La/Yb)N = 4.5–5.8. analyzed for Hf isotopes (Table 3 and Fig. 4). Total 14 spots were The rocks are characterized by LREE enrichment and all the analyzed for Hf isotopes. The results show that the monzonite samples display obvious negative Eu anomalies (Eu/Euà = 0.19– granite-porphyry has high 176Hf/177Hf ratio and a low 176Lu/177Hf 0.25) (Fig. 3). ratio, with the average at 0.2826 and 0.0013 respectively. The data Trace elements spider diagram for the monzonite granite- suggest that the zircons have very low radiogenic Hf concentration. porphyry (Fig. 3) shows relative enrichment of large ion lithophile Therefore, the measured 176Hf/177Hf ratios can be taken to repre- elements (LILE) such as Rb, Th, U, K and Pb, and high field strength sent the Hf isotope composition of the system during zircon element (HFSE), with depleted Ba, Nb, Sr, P, Ti, Eu, etc. High Rb and crystallization (Amelin et al., 2000). All zircon eHf(t) values are low Ba and Sr might suggest fractional crystallization of orthoclase negative, ranging from À1.9 to À4.9 (average at À3), indicating and plagioclase, whereas the Eu depletion is probably related to that the magma was sourced from the crust. plagioclase fractionation. The depletion in P and Ti indicate that the magma witnessed fractional crystallization of apatite, sphene, 5.4. Molybdenite Re–Os dating and Ti-rich minerals. Results from molybdenite Re–Os analyses on 6 samples from the JJGLZ Fe-polymetallic deposit and the reference material are 5.2. Zircon U–Pb dating presented in Table 4. The data show consistent model ages, ranging from 120.8 ± 1.7 Ma to 123.2 ± 1.7 Ma, with a weighted mean age The results of U–Pb analyses of zircon grains from sample JJGLZ- of 122 ± 0.7 Ma (MSWD = 1.7). The 187Re–187Os diagram shows a 448 in the JJGLZ monzonite granite-porphyry are summarized in linear distribution yielding a well-defined isochron age of Table 2. Zircon grains from sample JJGLZ-448 occur as automorphic 124.7 ± 3.7 Ma (Fig. 6), which is taken to represent the timing of crystals, and are mostly elongate columnar (Fig. 4). Total 28 spots mineralization. were measured on 25 zircon grains. Except for Spot 19, the Th/U ratios range from 0.67 to 1.96. All the 25 zircon grains have relatively clear oscillatory zones under Cathodoluminescence, indi- 6. Discussion cating the characteristics of magmatic zircons (Rubatto, 2002). Spot 4 and 13 yield an age of 482 Ma and 385 Ma respectively. 6.1. Genesis of monzonite granite-porphyry The other spots have similar ages, with 206Pb/238U age ranging from 117 Ma to 123 Ma, and all of these plot in the U–Pb age con- 6.1.1. Rock types cordia diagram (Fig. 5), yielding a weighted mean age of 120 ± The JJGLZ monzonite granite-porphyry is rich in Si, Al and K, and 0.6 Ma (n = 25, MSWD = 1.6), representing the time of JJGLZ mon- poor in Mg, Fe and Ca, with an average aluminum saturation index zonite granite-porphyry crystallization. (A/CNK) of 1.16. In terms of mineral composition, the presence of 148 H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152
Fig. 5. Zircon U–Pb concordia diagrams and weighted mean model ages for the JJGLZ monzonite granite-porphyry. Fig. 6. Molybdenite Re–Os isochron and weighted mean model ages for JJGLZ skarn Fe-polymetallic deposit. muscovite indicates peraluminous nature. The concentrations of high field strength elements, such as Zr, Hf and Nb are generally 1989), and belongs to the group of muscovite-bearing peralumi- ten times that of primitive mantle (Fig. 3), lower than typical A- nous granitoid (MPG) according to the classification of Barbarin type granite, higher than I-type granite and close to S-type granite (1999). (Chappell and White, 2001). All the eHf (t) values of zircons are negative, ranging from À1.90 to À4.86 with an average of À2.96, 6.1.2. Melting conditions suggesting crustal source for the magma. Combining the regional The Al2O3/TiO2 ratio of peraluminous granite depends on the tectonics, lithology, mineralogy, and geochemical characteristics, partial melting temperature of the source region. Ti-bearing miner- the monzonite granite-porphyry in the study area is considered als (e.g. biotite and ilmenite) are more easily decomposed so that as a continental collision granitoid (CCG, Maniar and Piccoli, substantial TiO2 is dissolved into magmas under high temperature.
Table 3 Zircons Hf isotopic data of the monzonite granite-porphyry rock in the JJGLZ.
176 177 176 177 176 177 Spot No. t (Ma) Yb/ Hf 2r Lu/ Hf Hf/ Hf eHf (0) eHf (t) THf1 (Ma) THf2 (Ma) fLu/Hf 1 120 0.063 0.002 0.001 0.283 À4.7 À2.2 878 1315 À0.96 2 120 0.042 0.001 0.001 0.283 À4.4 À1.9 861 1294 À0.97 3 120 0.034 0.001 0.001 0.283 À5.1 À2.6 886 1336 À0.97 4 108 0.061 0.001 0.002 0.283 À5.2 À2.9 905 1349 À0.95 5 121 0.047 0.001 0.001 0.283 À4 À1.4 848 1265 À0.96 6 118 0.041 0.001 0.001 0.283 À6.3 À3.8 937 1414 À0.96 7 120 0.035 0.001 0.001 0.283 À5.9 À3.4 917 1387 À0.97 8 120 0.059 0.001 0.002 0.283 À7.4 À4.9 994 1482 À0.95 9 121 0.035 0.001 0.001 0.283 À4.5 À1.9 862 1297 À0.97 10 120 0.022 0.001 0.001 0.283 À6.3 À3.7 924 1410 À0.98 11 120 0.042 0.001 0.001 0.283 À4.9 À2.4 883 1324 À0.96 12 118 0.094 0.001 0.003 0.283 À4.7 À2.3 912 1321 À0.92 13 119 0.036 0.001 0.001 0.283 À6.8 À4.2 951 1441 À0.97 14 122 0.044 0.001 0.001 0.283 À6.4 À3.9 939 1419 À0.97
176 177 176 177 176 177 176 177 kt 176 177 176 177 kt eHf(0) = (( Hf/ Hf)S/( Hf/ Hf)CHURÀ1)  10000, eHf(t)=(( Hf/ Hf)SÀ( Lu/ Hf)S  (e À1))/(( Hf/ Hf)CHURÀ( Lu/ Hf)CHUR  (e À1))À1)  10000; THf1 =1/ 176 7 176 177 176 177 176 177 176 177 176 177 176 k  ln[1 + (( Hf/ Hf)SÀ( Hf/ Hf)DM)/(( Lu/ Hf)SÀ( Lu/ Hf)DM)]; THf2 = THf1À(THf1Àt)(fCCÀfS)/(fCCÀfDM); fLu/Hf =( Lu/ Hf)S/( Lu/ Hf)CHURÀ1; ( Lu/ 177 176 177 176 177 176 177 Hf)CHUR = 0.0332, ( Hf/ Hf)CHUR = 0.282772 (Blichert-Toft and Albarède, 1997), ( Lu/ Hf)DM = 0.0384, ( Hf/ Hf)DM = 0.28325 (Griffin et al., 2000), fCC = 176 177 176 177 176 177 176 177 À11 À1 [( Lu/ Hf)mean crust/( Lu/ Hf)CHUR]À1, fDM =[( Lu/ Hf)DM/( Lu/ Hf)CHUR]À1, k = 1.867  10 year (Söderlund et al., 2004), t = crystallization age of zircon. The 2r represents standard deviation.
Table 4 Re–Os isotopic analyses of molybdenite from JJGLZ skarn Fe-polymetallic deposit.
Sample No. Sample weight (g) Re (ppm) 187Re (ppm) 187Os (ppb) Model age (Ma) Measured 2r Measured 2r Measured 2r Measured 2r JJGLZ-301 0.00327 273.1 2.9 171.7 1.8 349 3 121.9 1.9 JJGLZ-302 0.0033 285.6 2.2 179.5 1.4 361.8 3 120.8 1.7 JJGLZ-305 0.00338 374.2 2.8 235.2 1.8 474.5 4.3 121 1.7 JJGLZ-306 0.00318 423.3 3.7 266 2.3 453.6 4.8 122.5 1.8 JJGLZ-309 0.00316 354.9 2.7 223 1.7 458.2 3.9 123.2 1.7 JJGLZ-334 0.00331 390.2 3 245.2 1.9 500.9 4.1 122.5 1.7 JDC 0.05001 17.1 0.14 25.15 0.2 141 1.9
Decay constant: k (187Re) = 1.666 Â 10À11/year (Smoliar et al., 1996). Uncertainties are absolute at 2r with error on Re and 187Os concentrations and the uncertainty in the 187Re decay constant. H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152 149
Fig. 9. Plot of zircon eHf(t) vs. U–Pb ages. For comparison, the fields of the Lhasa Fig. 7. SiO2–TFeO + MgO + TiO2 diagram for the JJGLZ monzonite granite-porphyry, compared to experimental vapor-absent 10 kbar melts of natural pelite, synthetic block (Zhu et al., 2011a) and Tengchong block (Cong et al., 2011; Qi et al., 2011; Xu biotite gneiss and natural volcanoclasitc paragneiss (after Sylvester, 1998). Tem- et al., 2012; Li et al., 2012a,b) are outlined. peratures of the experiments and percentages of basalt mixing are indicated.
the zircon saturation temperature is relatively low during magma crystallization (Watson and Harrison, 1983), ranging from 737 °C to 756 °C. Therefore, magmas of the JJGLZ monzonite granite- porphyry were probably formed between 750 °C and 900 °C, a tem- perature range that is lower than that of peraluminous-strongly peraluminous high-temperature granite in the Early Cretaceous Gaoligong granite zone (875–975 °C, Yang et al., 2006).
6.1.3. Characteristics of magma source region The zircon eHf(t) for the monzonite granite-porphyry show neg- ative values with an average at À2.96. The single-stage model age
(THf1) shows a mean at 907 Ma, and the two-stage model age (THf2) at 1361 Ma, suggesting that the monzonite granite-porphyry formed by the partial melting of ancient crust. Early Cretaceous mineralized porphyries with zircon Hf isotope features suggesting derivation through the recycling of crustal components have been reported from several regions in East Asia including those from the Jiaodong Peninsula (Yang et al., 2013). Experimental petrologic studies and compositional data on granites from global orogens (Sylvester, 1998) show that in
strongly peraluminous granites with SiO2 content ranging from 67 wt.% to 77 wt.%, the TFeO + MgO + TiO2 content reflects the characteristics of source composition. The markedly peraluminous
JJGLZ granite has high SiO2 content (greater than 71 wt.%) and low Fig. 8. Rb–Hf–Ta, Rb–Yb + Ta and Rb–Y + Nb discrimination diagrams for tectonic TFeO + MgO + TiO2 values ranging from 1.48 wt.% to 1.85 wt.% (less settings for the JJGLZ monzonite granite-porphyry (after Harris et al., 1986 and than 4 wt.%). The TFeO + MgO + TiO2 value remains steady with the Pearce, 1996). WPG = within plate granitoid, ORG = ocean ridge granitoid, Syn- COLG = syn-collision granitoid, Post-COLG = Post-collision granitoid. variation of SiO2 content, consistent with the experimental results of natural pelite melting (Fig. 7)(Patiño and Johnston, 1991), and suggest that magmas of the JJGLZ monzonite granite-porphyry were possibly derived from sedimentary protoliths of dominantly As a result, the Al2O3/TiO2 ratio (<100) under high temperature pelitic composition. (875–950 °C) is markedly different (>100) under low temperature (825–875 °C) (Sylvester, 1998).
The JJGLZ monzonite granite-porphyry shows Al2O3/TiO2 ratio 6.1.4. Tectonic setting ranging from 79 to 95, with an average at 89, which is less than In RbÀHfÀTa (Harris et al., 1986), RbÀ(Yb + Ta) and but close to 100, indicating that the partial melting temperature RbÀ(Y + Nb) (Pearce, 1996) diagrams (Fig. 8), samples of the JJGLZ of the source region might have been around 900 °C(Sylvester, monzonite granite-porphyry plot near the domains of syn- and 1998). The Zr content of the porphyry ranges from 81.35 ppm to post-collisional granites. Hence, the formation of this peralumi- 97.04 ppm (Table 1). Calculation based on Zr content shows that nous granite marks the end of the syn-collision-compression event 150 H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152
Table 5 Dating results of part deposits in Bangong–Nujiang suture zone.
Section County/deposit Age (Ma) Testing target Dating Date resource method Bangong–Nujiang Western Geji/Garqiong porphyry copper deposit 112 ± 2.3/86.8 ± 0.5 Zircon/ SHRIMP/ Qu and Xin (2006) metallic belt Molybdenite Re–Os Geji/Galale skarn gold (copper) deposit 86.5 ± 0.4 Zircon LA–ICP–MS Lü et al. (2011) Ritu/Chaimaskarn iron polymetallic 138.3 ± 6.9 Whole rock Rb–Sr Feng et al. (2006) deposit Ritu/Fuye skarn iron deposit 130 ± 1.4 Zircon SHRIMP Geng et al. (2011b) Gaize/Duobuza porphyry copper 120.9 ± 2.4/118 ± 1.5 Zircon / SHRIMP / She et al. (2009), Li deposit Molybdenite Re-Os et al. (2013) Gaize/Bolong porphyry gold deposit 119.4 ± 1.3 Molybdenite Re–Os Zhu et al. (2011b) Gaize/Tiegeshan gold deposit 123.3 ± 1.8 Whole rock K–Ar Li et al. (2005) Cuoqing/Nixiong skarn iron (copper) 112.6 ± 1.6 Zircon LA–ICP–MS Zhu et al. (2011b) deposit Middle Bange/Xueru and Chapula skarn iron 79.7 ± 0.5/76.1 ± 0.4 Zircon LA–ICP–MS Wang et al. (2012) (copper) deposit Shenzha/Xiongmei porphyry copper 106.1 ± 0.5 Zircon LA–ICP–MS Qu et al. (2012) deposit Shenzha/Shesuo skarn copper 116.2 ± 0.9/116.2 ± 1.9 Zircon/ LA–ICP– Zhao et al. (2011) polymetallic deposit Molybdenite MS/Re–Os Eastern Dangxiong/Lawu skarn copper lead and 109 ± 1.3 Whole rock K–Ar Du et al. (2004) zinc deposit Tengchong Block Southeastward Tengchong/Dadongchang skarn copper, 127/118 ± 2.4 Whole rock/ Rb–Sr/Re– Dong et al. (2005) lead and zinc deposit molybdenite Os Tengchong/JJGLZ skarn iron 120 ± 0.6/122 ± 0.7 Zircon/ LA–ICP– This paper polymetallic deposit Molybdenite MS/Re–Os
and the beginning of post-collisional-extension along the Ban- 6.3. Comparison with Bangong–Nujiang magmatic/metallogenic belt gong–Nujiang suture zone (Fig. 1a). The tectonic scenario emerging from our study is as follows. The Our data show that the ages and eHf(t) values of the JJGLZ mon- Bangong–Nujiang oceanic plate started to subduct towards south zonite granite-porphyry, and the formation age (139–118 Ma, Cong in the Late Jurassic-Early Cretaceous (Zhu et al., 2011a). Subse- et al., 2011; Qi et al., 2011; Li et al., 2012a, 2012b) of the Early quently, the Meso-Tethys Ocean was closed and the Tengchong Cretaceous granite widely distributed in Tengchong block, are coe- block collided with Baoshan block, at the beginning of the Early val with the formation age and eHf(t) values of the granites in the Cretaceous (Xu et al., 2012). During the collision, the tectonic central and northern margin of Lhasa terrane (the northern Gang- framework of the Tengchong block transformed from compres- dese magmatic belt) (Zhu et al., 2011a)(Fig. 9). This suggests that sion–crustal thickening to extension-crust thinning. The JJGLZ the Tengchong block and Lhasa terrane underwent similar and peraluminous S-type granite was formed at ca. 120 Ma. extensive magmatic activities along the Bangong–Nujiang suture zone in the Early Cretaceous. Given the peraluminous S-type nature of the monzonite gran- 6.2. Genesis of Fe polymetallic deposit ite-porphyry in Tengchong, we consider that the JJGLZ monzonite granite-porphyry in Tengchong formed in a post-collisional exten- Molybdenites from the JJGLZ Fe-polymetallic deposit yield a sional environment after crustal thickening through the collision of Re–Os age of 122 ± 0.7 Ma, and zircon grains from the monzonite the Tengchong and Baoshan blocks. We also infer that the closure granite-porphyry yield U–Pb age of 120 ± 0.6 Ma, suggest that the of Bangong–Nujiang Ocean (Meso-Tethys Ocean) in Tengchong magmatism was coeval with the timing of mineralization. These area occurred prior to 120 Ma. ages are slightly older than that of the Datongchang skarn The age data on some of the ore deposits occurring along the copper–lead–zinc mineralization to the south (118 ± 2.4 Ma, Dong Bangong–Nujiang suture zone show that the main metallogenic et al., 2005)(Fig. 1b). The age data show that both metallic deposits events occurred in the middle Yanshanian (138 –106 Ma) and late have close relationships with the Early Cretaceous magmatic activ- Yanshanian (86 –76 Ma) (Table 5). However, the mineralization of ities in Tengchong County. the Gangdese metallogenic belt (Fig. 1b), occurred mainly during The JJGLZ Fe-polymetallic deposit occurs in the outer contact 50 –40 Ma and 20 –10 Ma, related to the syn-collision and post- zone between monzonite granite-porphyry dykes and Kongshuhe collision settings of the Indian continent with the Asian (Qin Formation carbonate rocks (Fig. 1c). The orebodies show a grada- et al., 2012). The anatexis–mineralization age and geological char- tional transition with the wall rocks. The skarn orebodies are irreg- acteristics of the JJGLZ skarn Fe-polymetallic deposits are markedly ularly lenticular, stratoid, sack-like and wedged shape. The major similar to their counterpart in the Bangong–Nujiang metallogenic ore in the deposit is iron, although associated (syngenetic) copper, belt, suggesting that Tengchong area probably belongs to the lead, zinc, tin, tungsten, gold, silver, germanium, indium also occur. southeastward extension of the Bangong–Nujiang metallogenic The gangue minerals are principally quartz, garnet, diopside, epi- belt (Fig. 1 and Table 5). dote and phlogopite. In general, the Bangong–Nujiang metallogenic belt is older than The geological features and mineralization ages indicate that the Gangdese metallogenic belt (Table 5 and Fig. 9). The Bangong– the skarnization and formation of the metallic oxides in the JJGLZ Nujiang metallogenic belt is another significant metallogenic belt deposit are mainly related to metasomatism under hydrothermal after the Yulong and Gangdese metallogenic belts in Tibet Plateau conditions. This skarn-type Fe-polymetallic deposit is geologically (Li et al., 2011)(Fig. 1a). The Bangong–Nujiang belt probably ex- similar to iron-rich skarn-type deposits in the Bangong–Nujiang tends southwards to Tengchong in western Yunnan. metallogenic belt (Zhao et al., 2011; Wang et al., 2012). H.-W. Cao et al. / Journal of Asian Earth Sciences 81 (2014) 142–152 151
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