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1.
中甸浪都铜矿位于印支期义敦岛弧南段的中甸岛弧,浪都二长斑岩体出露于矿区中北部,呈岩株状侵入于曲嘎寺组砂岩、灰岩中.本文应用LA-ICP-MS分析了二长斑岩中锆石的微量元素组成和U-Pb同位素年龄.获得该二长斑岩成岩年龄为223±1 Ma,与近几年报道的中甸岛弧晚三叠世中酸性侵入岩的Rb-Sr、K-Ar、锆石U-Pb年龄基本一致,属同一构造期的产物.该二长斑岩中锆石的ΣREE值为1168.55×10-6~2125.76×10-6,较集中.结合岩石主量、微量元素组成,我们认为其岩浆为地幔和部分地壳混熔作用形成,是甘孜-理塘洋在晚三叠世向西俯冲消减过程中形成的岛弧型花岗质岩石.该二长斑岩中锆石的REE球粒陨石标准化配分模型具有强烈的Ce正异常和中度的Eu负异常,指示其成岩岩浆具有较高的氧逸度,结合浪都矿区铜矿化与该岩体密切的时空关系和成因联系,表明岩浆的较高氧逸度对该矿区矽卡岩-斑岩型铜矿化具有重要意义.  相似文献   

2.
曹殿华 《地质学报》2009,83(10):1430-1435
长期以来,关于雪鸡坪斑岩铜矿的成岩成矿时代具有很大的争议。为了限定成矿作用开始的时限,本文选择代表成矿前岩浆岩的绢英岩化带内含矿斑岩进行锆石SHRIMP年代学测试,获得了215.2±1.9Ma的成岩年龄,说明雪鸡坪斑岩铜矿形成于215Ma之后。锆石Hf同位素测试结果显示岩浆主要来源于地幔源区,但是锆石Hf同位素分布不均匀,8颗锆石εHf(t)的结果分布于1.1~2.1,二阶段模式年龄平均值为1150Ma,两颗锆石εHf(t)值为7.4和6.0,对应的二阶段模式年龄分别为778Ma和869Ma,暗示存在两种不同的岩浆源区,可能发生过岩浆混合作用,但需进一步的研究证实。区域同位素年代学对比结果表明,215Ma左右的岩浆活动是中甸弧主要的控制斑岩铜矿成矿的热事件。  相似文献   

3.
罗卜岭斑岩铜钼矿床是紫金山Cu-Au-Mo浅成低温-斑岩矿田内新近发现的大型斑岩铜钼矿床,本文在岩芯及光薄片系统观察的基础上,分析了矿化斑岩锆石LA-ICP-MS U-Pb年龄及锆石Ce4/Ce3+比值.罗卜岭赋矿斑岩体可分为两期,早期为角闪黑云母花岗闪长斑岩及黑云母花岗闪长斑岩,晚期为黑云母花岗闪长斑岩.早期角闪黑云母花岗闪长斑岩和黑云母花岗闪长斑岩锆石LA-ICP-MS U-Pb年龄分别为103.7±1.2Ma,MSWD=0.33和103.0±0.9Ma,MSWD=1.00;晚期黑云母花岗闪长斑岩锆石LA-ICP-MS U-Pb年龄为97.6±2.1Ma,MSWD=6.00.罗卜岭成矿斑岩基质普遍发育硬石膏,两期成矿斑岩锆石都具较高的Ce4 +/Ce3平均值,在630 ~770之间,高于区内非成矿花岗岩锆石的Ce4+/Ce3+平均值(182 ~577),显示罗卜岭斑岩矿床成矿岩浆具有高氧逸度的特征.据罗卜岭斑岩矿床的形成时代、高氧逸度岩浆特征,结合华南地区中生代构造背景,我们初步认为罗卜岭斑岩矿床的形成可能和中生代古太平洋向北西西方向俯冲有关.  相似文献   

4.
长期以来,关于雪鸡坪斑岩铜矿的成岩成矿时代具有很大的争议。为了限定成矿作用开始的时限,本文选择代表成矿前岩浆岩的绢英岩化带内含矿斑岩进行锆石SHRIMP年代学测试,获得了215.2±1.9Ma的成岩年龄,说明雪鸡坪斑岩铜矿形成于215Ma之后。锆石Hf同位素测试结果显示岩浆主要来源于地幔源区,但是锆石Hf同位素分布不均匀,9颗锆石εHf(t)的结果分布于1.1~2.1,二阶段模式年龄平均值为1150Ma,两颗锆石εHf(t)值为7.4和6.0,对应的二阶段模式年龄分别为778Ma和869Ma,暗示存在两种不同的岩浆源区,可能发生过岩浆混合作用,但需进一步的研究证实。区域同位素年代学对比结果表明,215Ma左右的岩浆活动是中甸弧主要的控制斑岩铜矿成矿的热事件。  相似文献   

5.
黑龙江多宝山斑岩Cu-Mo矿床成岩成矿时代研究   总被引:12,自引:4,他引:8  
多宝山斑岩型铜(钼)矿床是中国东北地区重要的斑岩型铜(钼)矿床,文章对矿区主要成矿岩体及辉钼矿样品进行了系统的成岩成矿年代学研究。对成矿岩体采用高精度LA-ICP-MS锆石U-Pb测年,获得成矿母岩花岗闪长斑岩的锆石U-Pb年龄为(474.8±4.7) Ma,矿体寄主岩石花岗闪长岩的锆石U-Pb年龄为(478.1±4.1) Ma,以及矿体外围黑云母花岗闪长岩的锆石U-Pb年龄为(483.9±4.5) Ma;矿体辉钼矿的Re-Os同位素模式年龄加权平均值为(475.1±5.1) Ma。测年结果显示,多宝山斑岩铜(钼)矿床形成于早奥陶世。结合含矿地层、矿区岩石组合特征,以及前人研究的岩石地球化学特征,推测多宝山矿床形成于早奥陶世与板块俯冲有关的岛弧环境,说明在区域上寻找类似多宝山的斑岩铜矿应沿早奥陶世多宝山-伊尔斯岩浆岛弧带开展。  相似文献   

6.
中甸春都铜矿区岩体成岩时代及地质意义   总被引:6,自引:0,他引:6  
春都斑岩铜矿床位于中甸铜多金属成矿带的西带南段,矿区主要出露由闪长玢岩和花岗闪长斑岩组成的复式岩体,后者呈岩枝或岩脉产于闪长玢岩体中,并与斑岩铜矿有密切成因关系。本文应用LA-ICP-MS U-Pb定年方法,对闪长玢岩以及花岗闪长斑岩的锆石进行年代学研究。结果表明:岩石中的锆石颗粒为浅黄色-无色透明,呈正方双锥状、柱状的自形晶体,内部发育完好的韵律环带,并具较高的Th/U比值,属典型的岩浆成因锆石;主岩体——闪长玢岩体中的锆石LA-ICP-MS U-Pb年龄为(212±3)Ma,成矿花岗闪长斑岩锆石LA-ICP-MS U-Pb年龄分别为(217±2)Ma和(218±2)Ma。锆石LA-ICP-MS U-Pb年龄数据与地质体穿切关系的矛盾,可能与测试数据较少等因素有关。我们认为,矿区斑岩铜矿的成岩成矿时代均为晚三叠世,与义敦岛弧在237~208Ma之间发生大规模的岛弧岩浆活动相吻合。  相似文献   

7.
“三江”构造带中甸弧北部的印支期岩浆活动目前尚无正式的研究报道.本文的岩石学及年代学的研究表明,中甸弧北部的翁水地区存在印支期中酸性岩浆活动,锆石U-Pb定年结果显示这些火山岩在211.1±1.5Ma喷发,与该地区的印支期火山岩与斑岩矿床的成矿斑岩的形成时代一致.翁水安山岩岩石地球化学特征显示其以中性的安山岩为主,具有亏损Nb、Ta、Ti等高场强元素的典型岛弧岩浆成分特征.与同一构造单元内中句弧南部的烂泥塘-浪都安山岩进行主、微量元素的对比研究发现,两者均具有正常岛弧火山岩的成分组成特征.结合其形成时代和构造背景,初步认为中甸弧北部的翁水和南部的烂泥塘-浪都安山岩以及该区域的成矿斑岩很可能形成于同一构造-岩浆事件,都是甘孜-理塘洋晚三叠世俯冲作用的岩浆产物.  相似文献   

8.
应用高精度离子探针锆石U-Pb测年方法,获得普朗斑岩铜矿床中3件矿化石英二长斑岩的锆石年龄分别为228±3Ma、226.3±2.8Ma、226±3Ma。锆石形态和铀钍参数均属典型的岩浆锆石特征,年龄值在误差范围内近似一致,表明形成矿化斑岩的中酸性岩浆从岩浆房快速上升侵位。结合前人已发表的矿化斑岩的黑云母Ar-Ar坪年龄及辉钼矿Re-Os同位素年龄等数据,推测普朗斑岩铜矿的岩浆—热液系统从岩浆侵入至矿化阶段的持续时间可能长达10Ma以上,主成矿期约为216~214Ma。从岩浆房分异出的富含成矿物质和挥发份的岩浆流体在相对较晚阶段对普朗复式岩体发生了强烈的蚀变作用并可能进一步萃取了岩体中的成矿物质。  相似文献   

9.
拉萨地体南缘的晚三叠世—中侏罗世岩浆岩被认为是新特提斯洋早期北向俯冲的岩浆记录,并形成与之相关的雄村特大型斑岩-浅成低温热液铜-金矿床。对该时期岩浆岩成因背景的研究有助于评价其成矿潜力。选取拉萨地体南缘日喀则西北部花岗岩类进行锆石U-Pb测年及Lu-Hf同位素分析。花岗岩类LA-ICP-MS锆石U-Pb定年结果为175~180.1Ma,εHf(t)平均值为+13.4,显示幔源特征,为岛弧(洋内弧)背景成因,具有斑岩铜金成矿潜力。结合前人对拉萨地体南缘晚三叠世—白垩纪岩浆岩的研究,认为拉萨地体南缘未被剥蚀的晚三叠世—白垩纪火山岩中有可能保存有新特提斯洋俯冲形成的斑岩铜金成矿系统。  相似文献   

10.
对金沙江缝合带东侧雪鸡坪同碰撞石英闪长玢岩进行了岩石学、岩石化学、稀土元素、锆石SHRIMP U-Pb定年等研究,石英闪长玢岩锆石SHRIMP U-Pb年龄为215Ma.结合前人的资料,认为金沙江洋盆闭合、板块碰撞的时间应为266Ma,碰撞阶段的年龄范围为266~215Ma.对无老核的岩浆型锆石的形成条件、结构简单的典型纯岩浆型锆石定年的测试点数量等方面也进行了讨论.  相似文献   

11.
The western Awulale metallogenic belt in northwestern China hosts a number of small‐ to medium‐sized porphyry Cu deposits that are associated with albite porphyry. The common presence of plagioclase (albite) as phenocrysts and the absence of hydrous minerals (amphibole and biotite) indicate that the water content of albite porphyry is low. Trace‐element compositions of whole rocks and zircon grains from these ore‐bearing porphyries were measured. Zircon grains from albite porphyries exhibit Ce4+/Ce3+ ratios ranging from 7.75 to 95.1, which indicate that these porphyries have a low oxygen fugacity. Trace element compositions of ore‐bearing porphyries exhibit (La/Yb)N ratios ranging from 1.09 to 11.1 and Eu/Eu* ratios ranging from 0.10 to 0.66. These ore‐bearing porphyries have Zr values ranging from 171 to 707 ppm and Hf values ranging from 8.30 to 18.9 ppm. Combining these porphyries with other ore‐bearing porphyries that formed in the Central Asian Orogenic Belt (CAOB) and the Pacific Rim metallogenic belt, we found that the (La/Yb)N and Eu/Eu* ratios of ore‐bearing porphyries in western Awulale are low, while the Zr and Hf values are high. Specifically, REEs can be used to evaluate the degree of differentiation and degree of partial melting, and Zr and Hf can be used to evaluate the redox conditions and water content of magmatic rocks. Our findings indicate that ore‐bearing porphyries in western Awulale have a lower oxygen fugacity, degree of differentiation, and water content than do others in the CAOB and the Pacific Rim metallogenic belt. Compared to those of ore‐bearing porphyries with lower zircon Ce4+/Ce3+ ratios, the (La/Yb)N ratios of ore‐bearing porphyries in our study are low, and the Zr and Hf values are high. This finding indicates that, under reducing conditions, the degree of evolution and water content may have an important influence on the metal abundance in magmas. There is also a clear relationship between (La/Yb)N, Eu/Eu*, Zr, Hf, and the size of the deposits. Large‐ (>4 Mt Cu) and intermediate (1.5–4 Mt Cu)‐sized porphyry Cu deposits are associated with granitic intrusions that have higher (La/Yb)N and Eu/Eu* ratios and lower Zr and Hf values. This finding indicates that, in addition to oxygen fugacity, the degree of evolution and water content are controlling parameters for metal abundance in magmas, especially in low oxygen fugacity porphyry Cu deposits. Such a conclusion may be useful in the exploration for other concealed porphyry Cu deposits.  相似文献   

12.
The Tibetan Plateau is one of the most significant Cu poly-metallic mineralization regions in the world and preserves important information related to subductional and collisional porphyry Cu mineralization. This study investigates a new occurrence of Cu mineralization-related andesitic porphyries in the western domain of the Gangdese magmatic belt and assesses its petrologic, zircon U-Pb geochronology, whole-rock chemistry, and Sr-Nd-Hf-Pb isotope data. Zircon U-Pb dating of three ore-related porphyries yields crystallization ages of 212–211 Ma. These ages are consistent with previous molybdenite Re-Os dating, indicating a late Triassic magmatic and Cu mineralization event in the western Gangdese magmatic belt. Nb, Ta, and Ti depletion, Th and LREE enrichment, and high La/Yb and Th/Yb ratios in addition to high U/Yb ratios from zircons suggest that the magma was generated in an active continental arc setting. The porphyries have radiogenic isotopic compositions with (87Sr/86Sr)i 0.70431–0.70473, εNd(t) +1.1 to +3.8, (207Pb/204Pb)i 15.601–15.622, and (208Pb/204Pb)i 38.450–38.693, as well as high positive zircon εHf(t) values from +6.2 to +10.6 (mean value 8.3), corresponding to model ages (TDM) ranging from 509 Ma to 819 Ma (mean 646 Ma). This suggests that the andesitic magmatism was dominantly sourced from depleted mantle materials that were modified by subducted oceanic sediment-derived melts during the subduction of the Neo-Tethys Ocean. The mineralization-related porphyries contain amphibole and epidote, as well as high whole-rock Fe2O3/FeO and zircon Ce4+/Ce3+ ratios, suggesting hydrous and highly oxidized parent magmas. Considering the existing Cu mineralization and highly oxidized magma of the well-preserved Triassic andesitic igneous rocks in the western Gangdese belt, the subduction-related continental arc magma system is favorable for subduction-related porphyry Cu deposits. The existence of Luerma porphyry mineralization demonstrates that there are at least five generations of porphyry Cu-(Mo-Au) mineralization in the Gangdese magmatic belt, which advances the timeframe of porphyry mineralization to the late Triassic.  相似文献   

13.
Yulong ore-bearing porphyries, along the northwestern extension of the Red River–Ailao Shan fault system in eastern Tibet, consist of five porphyry deposits, containing a total of more than 8 million tons of copper resources. U–Th–Pb laser inductively coupled plasma mass spectrometry dating of zircon shows that the porphyries were emplaced in Early Tertiary (41.2–36.9 Ma), covering a period of ∼4.3 Ma, with formation ages decreasing systematically from northwest to southeast. The start of porphyry magmatism coincided with the onset of transpressional movement along the Red River–Ailao Shan fault system, implying a close link between these two events. Age sequence in intrusions can be plausibly explained by assuming that a region of melting in the lower northwestern plate moved southeasternward along the Tuoba–Mangkang fault relative to the upper plate. Zircon grains from the Yulong ore-bearing porphyries have higher Ce4+/Ce3+ than those from barren porphyries in the region. This suggests that the ore-bearing porphyries crystallized from a relatively oxidized magma, which has important implications for future ore exploration in the region and other Cu deposits in convergent margin environments in general.  相似文献   

14.
The Tongcun Mo porphyry deposit in northwest Zhejiang is hosted in three porphyry units: Huangbaikeng, Songjiazhuang, and Tongcun, from southwest to northeast. U–Pb zircon ages of 162?±?3.0 Ma for the Huangbaikeng porphyry, 159.9?±?3.0 Ma for the Songjiazhuang porphyry, and 167.6–155.6 Ma for the Tongcun porphyry indicate that these intrusions formed during the Jurassic and are most likely associated with the northwestward subduction of the Izanagi Plate. Trace element compositions of zircons from the Tongcun deposit constrain the oxygen fugacity (fO2) of the magma using zircon Ce anomalies and Ti-in-zircon temperatures. The average magmatic fO2 for the porphyries in the Tongcun deposit is fayalite–magnetite–quartz (FMQ)?+?2.7, which is similar to the Shapinggou (FMQ?+?3.2) and Dabaoshan (FMQ?+?3.5) Mo porphyry deposits, but much higher than that of the reduced Cretaceous ore-barren Shangjieshou porphyry (FMQ-1.1) around 8 km away from the Tongcun deposit. The distinct difference in magmatic oxygen fugacity between the Jurassic and Cretaceous porphyries may help to explain the absence of Mo porphyry mineralization in northwest Zhejiang during the Cretaceous.  相似文献   

15.
The Chalukou porphyry Mo deposit, located in the Great Hinggan Range, is the largest Mo deposit in northeast China, although the age and genesis of the associated magmatic intrusions remain debated.Here we report zircon U-Pb ages and trace elements, whole rock geochemistry and Sre Nd isotope data with a view to understand the relationship between the magmatism and molybdenum mineralization.Zircon U-Pb analysis yield an age of 475 Ma for rhyolite in the older strata, 168 Ma for the premineralization monzogranite, and 154 Ma for the syn-mineralization granite porphyry. The granite porphyry and quartz porphyry are considered as the ore-forming intrusions. These rocks are peraluminous, alkali-calcic, and belong to high-K to shoshonitic series with a strong depletion of Eu. They also display characteristics of I-type granites. The rocks exhibit wide variations of(87 Sr/86 Sr)iin the range of 0.705426 -0.707363, and ε_(Nd)(t) of -3.7 to 0.93. Zircon REE distribution patterns show characteristics between crust and the mantle, implying magma genesis through crust-mantle interaction. The Fe_2O_3/FeO values(average 1) for the whole rock and EuN/Eu*Nvalues(average 0.45), Ce~(4+)/Ce~(3+) values(average 301)for zircon grains from the granite porphyry are higher than those from other lithologies. These features suggest that the ore-forming intrusions(syn-mineralization porphyry) had higher oxygen fugacity conditions than those of the pre-mineralization and post-mineralization rocks. The Chalukou Mo deposit formed in relation to the southward subduction of the Mongol-Okhotsk Ocean. Our study suggests that the subduction-related setting, crust-mantle interaction, and the large-scale magmatic intrusion were favorable factors to generate the super-large Mo deposits in this area.  相似文献   

16.
《China Geology》2022,5(4):662-695
The porphyry copper belt in the Geza island arc in southwestern China is the only Indosinian porphyry copper metallogenic belt that has been discovered and evaluated so far. The Pulang porphyry copper deposit (also referred to as the Pulang deposit) in this area has proven copper reserves of 5.11×106 t. This deposit has been exploited on a large scale using advanced mining methods, exhibiting substantial economic benefit. Based on many research results of previous researchers and the authors’ team, this study proposed the following key insights. (1) The Geza island arc was once regarded as an immature island arc with only andesites and quartz diorite porphyrites occurring. This understanding was overturned in this study. Acidic endmember components such as quartz monzonite porphyries and quartz monzonite porphyries have been identified in the Geza island arc, and the mineralization is mainly related to the magmatism of quartz monzonite porphyries. (2) Complete porphyry orebodies and large vein orebodies have developed in the Pulang deposit. Main orebody KT1 occurs in the transition area between the potassium silicate alteration zone of quartz monzonite porphyries and the sericite-quartz alteration zone. Most of them have developed in the potassium silicate alteration zone. The main orebody occurs as large lenses at the top of the hanging wall of rock bodies, with an engineering-controlled length of 1920 m and thickness of 32.5‒630.29 m (average: 187.07 m). It has a copper grade of 0.21%‒1.56% (average: 0.42%) and proven copper resources of 5.11×106 t, which are associated with 113 t of gold, 1459 t of silver, and 170×103 t of molybdenum. (3) Many studies on diagenetic and metallogenic chronology, isotopes, and fluid inclusions have been carried out for the Pulang deposit, including K-Ar/Ar-Ar dating of monominerals (e.g., potassium feldspars, biotites, and amphiboles), zircon U-Pb dating, and molybdenite Re-Os dating. The results show that the porphyries in the Pulang deposit are composite plutons and can be classified into pre-mineralization quartz diorite porphyrites, quartz monzonite porphyries formed during the mineralization, and post-mineralization granite porphyries, which were formed at 223±3.7 Ma, 218±4 Ma, and 207±3.9 Ma, respectively. The metallogenic age of the Pulang deposit is 213‒216 Ma. (4) The petrogeochemical characteristics show that the Pulang deposit has the characteristics of volcanic arc granites. The calculation results of trace element contents in zircons show that quartz monzonite porphyries and granite porphyries have higher oxygen fugacity. The isotopic tracing results show that the diagenetic and metallogenic materials were derived from mixed crust- and mantle-derived magmas.©2022 China Geology Editorial Office.  相似文献   

17.
The Pulang porphyry copper deposit is located in the Zhongdian island arc belt, NW Yunnan, in the central part of the Sanjiang area, SW China, belonging to the southern segment of the Yidun island arc belt on the western margin of the Yangtze Platform. In the Yidun island arc, there occur well-known "Gacun-style" massive sulfide deposits in the northern segment and plenty of porphyry copper deposits in the southern segment, of which the Pulang porphyry copper deposit is one of the representatives. Like the Yulong porphyry copper deposit, this porphyry copper deposit is also one of the most important porphyry copper deposits in the eastern Qinghai-Tibet Plateau. But it is different from other porphyry copper deposits in the eastern Qinghai-Tibet Plateau (e.g. those in the Gangdise porphyry copper belt and Yulong porphyry copper belt) in that it formed in the Indosinian period, while others in the Himalayan period. Because of its particularity among the porphyry copper deposits of China, this porphyry copp  相似文献   

18.
The Tuwu–Yandong porphyry copper belt lies in the eastern Tianshan mountains, eastern section of the Central Asian orogenic belt. The copper mineralization is mainly hosted in plagiogranite porphyries intruded into early Carboniferous volcanic rocks of the Paleozoic Dananhu island arc between the Tarim and Siberian plates. The plagiogranite porphyries have contents of 65–73 wt% SiO2, 14–17 wt% Al2O3, 0.9–2.2 wt% MgO, 3–16 ppm Y, 0.4–1.40 ppm Yb, 347–920 ppm Sr, and positive Eu anomalies. The rocks also exhibit positive ɛ Nd(t) values (+5.0 to +9.4) and low initial 87Sr/86Sr values (0.70316–0.70378). Such features are similar to those of adakites derived from partial melting of a subduction-related oceanic slab. The mineralization age is early Carboniferous (350–320 Ma), which is close to that of the porphyries. The close relationship between the Cu mineralization and the porphyry is also indicated by their similar Sr-Nd-Pb isotopic compositions. We suggest that the copper porphyry (magma) system in the Dananhu island arc was formed by direct melting of an obliquely subducting early Carboniferous oceanic slab.  相似文献   

19.
Copper, gold and molybdenum mineralization of the Kalmakyr porphyry deposit in Uzbek Tien Shan occurs as stockworks, veinlets and disseminations in the phyllic and K-silicate alteration zones developed predominantly in a middle to late Carboniferous intrusive complex composed of monzonite and granodiorite porphyry. Zircon U–Pb dating yielded an age of 327.2 ± 5.6 Ma for the ore-hosting monzonite and an age of 313.6 ± 2.8 Ma for the ore-bearing granodiorite porphyry. Re–Os dating of seven molybdenite samples from stockwork and veinlet ores yielded model ages from 313.2 to 306.3 Ma, with two well-constrained isochron ages of 307.6 ± 2.5 Ma (five stockwork ores) and 309.1 ± 2.2 Ma (five stockwork ores and two veinlet ores), respectively. These results indicate that Cu–Au mineralization post-dated the emplacement of the monzonite, started right after the emplacement of the granodiorite porphyry, and lasted for ca. 7 Ma afterward. The geochronological and geochemical data suggest that the Kalmakyr deposit was formed in a late Carboniferous mature magmatic arc setting, probably related to the latest subduction process of the Turkestan Ocean beneath the Middle Tien Shan. The εHf(t) values of zircon grains from the monzonite vary from +11 to +1.7, with an average of +5.1, and those of zircon grains from the granodiorite porphyry range from +5.7 to −1.8, with an average of +2.4. These data indicate that the magma of both monzonite and granodiorite porphyry was derived from partial melting of a thickened lower crust with input of mantle components and variable crustal contamination, and that there was more mantle contribution to the formation of the monzonite than the granodiorite porphyry. The high rhenium concentrations of molybdenite (98–899 ppm) also indicate major mantle contribution of rhenium and by inference ore metals. The relatively high EuN/EuN1 values (average 0.68), Ce4+/Ce3 values (average 890) and Ce/Nd values (average 36.8) for zircon grains from the granodiorite porphyry than those from the monzonite (average EuN/EuN1 = 0.33, average Ce4+/Ce3 = 624, average Ce/Nd = 3.9) suggest that the magma for the syn-mineralization granodiorite porphyry has higher oxygen fugacity than that for the pre-mineralization monzonite. Based on these data, it is proposed that while the monzonite was emplaced, the oxygen fugacity and volatile contents in the magma were relatively low, and ore metals might disperse in the intrusive rock, whereas when the granodiorite porphyry was emplaced, the oxygen fugacity and volatile contents in the magma were increased, favoring copper and gold enrichment in the magmatic fluids. The Kalmakyr deposit formed from a long-lived magmatic-hydrothermal system connected with fertile magmatic sources in relation to the subduction of the Turkestan Ocean beneath the Middle Tien Shan.  相似文献   

20.
Porphyry-type Cu (Mo, Au) deposits have been discovered along the Gangdese magmatic arc in the southern Tibetan Plateau. Extensive field investigations and systematic studies of geochemistry, S–Pb isotopic tracing, together with Re–Os and 40Ar/39Ar isotopic dating indicate that the mineralisation of the copper belt is genetically related to emplacement of late orogenic granitic porphyries during the post-collisional crustal relaxation period of the Late Himalayan epoch. These porphyries are petrochemically K-enriched and belong to shoshonitic to high-K calc-alkaline series. They display enrichment of large ion lithophile elements (LILE) Rb, K, U, Th, Sr, Pb and depletion of high field strength elements (HFSE) Nb, Ta, Ti and the heavy rare earth elements (HREE) and Y without Eu anomalies. These characteristics demonstrate that subduction played a dominant role in their petrogenesis and residual garnet was left in the magma sources. Pb isotope data show a linear correlation in the plumbotectonic framework diagram ranging from orogenic Pb in the eastern segment of the copper belt to mantle Pb in the western segment. These constitute a mixing line of the Indian Oceanic MORB with Indian Oceanic sediments and suggest that the porphyry magmas were dominantly derived from partial melting of subducted oceanic crusts mixed with a minor quantity of sediments and mantle wedge components.The Gangdese porphyry copper polymetallic belt has alteration characteristics and zonation typical of porphyry-type copper deposits which include potassic alteration (K-feldspathisation and biotitisation), silicification, sericitisation, and propylitisation. Mineralisation mainly occurs in strongly altered granitic cataclasite at the exo-contact with veinlet-disseminated textures. The porphyries themselves are weakly mineralised with disseminated pyrite and chalcopyrite. The copper deposits contain simple ore mineral associations consisting of chalcopyrite, pyrite, bornite, molybdenite, sphalerite and oxidised minerals of malachite, covellite and molybdite. During supergene oxidation, primary ores underwent secondary enrichment to form economic orebodies with Cu grade ranging from 1% to 5%.Ore sulphides of the copper belt display S and Pb isotopic compositions identical to the ore-bearing porphyries. Their δ34S values vary between − 3.8‰ and + 2.4‰ and are typical of mantle sulphur. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios vary in the ranges: 18.106 to 18.752, 15.501 to 15.638, and 37.394 to 39.058, respectively, and yielded radiogenetic lead-enriched signatures. Twelve molybdenite samples from the copper belt yielded isochron ages of 14.76 ± 0.22 Ma and 13.99 ± 0.16 Ma for the Nanmu and Chongjiang deposits and model ages of 13.5 to 13.6 Ma for the Lakang'e deposit. Meanwhile, 40Ar/39Ar isotopic dating of two biotite phenocrysts from the Chongjiang and Lakang'e deposits give plateau ages of 13.5 ± 1.0 Ma and 13.42 ±0.10 Ma, respectively. During the geodynamic evolution of the Gangdese collision-orogenic belt, intrusion of the ore-bearing porphyries took place just before the rapid uplift and E–W extension of the southern Plateau. And the ore-forming process may have occurred simultaneously with the uplift and extension (14 ± 0.1 Ma).  相似文献   

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