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1.
中甸岛弧成矿斑岩的锆石年代学及其意义   总被引：11，自引：5，他引：6  
任江波  许继峰  陈建林 《岩石学报》2011,27(9):2591-2599
义敦岛弧南段的中甸岛弧印支期浅成-超浅成斑岩体与成矿密切相关,本文对该地区代表性的成矿斑岩如西侧的雪鸡坪、东侧的欠虽等岩体开展了高精度的LA-ICPMS锆石U-Pb定年,获得雪鸡坪成矿斑岩的年龄为213.4±1.5Ma,欠虽石英闪长玢岩年龄为217.1±1.5Ma。本研究和近几年发表的高精度锆石U-Pb年代学成果发现前人划分的中甸岛弧地区东、西成矿斑岩带的斑岩体形成时代没有明显的差异,这些斑岩体呈面状分布,其形成时代集中在223~211Ma,应该属于同一构造作用的产物。同时,这些成矿斑岩的锆石REE配分模式图显示一致的成分趋势,具有强烈的Ce正异常和相对较低的Eu负异常,指示出岩浆过程具有高的氧逸度。结合它们埃达克质的地球化学研究成果,我们认为中甸岛弧成矿斑岩以及相关的斑岩矿床是在东侧的甘孜-理塘洋晚三叠世俯冲过程中形成的,俯冲板片熔体的参与形成了高氧逸度富金属的岩浆,其对区内成岩和成矿过程具有重要意义。  相似文献   

2.
东南沿海分布大面积的白垩纪晚期侵入岩。这些岩石可分为两期:其中115~100Ma以钙碱性系列岩石为主,岩石组合为辉长岩-闪长岩-花岗闪长岩-二长花岗岩-碱性长石花岗岩;而100~86Ma的岩石为碱性系列,岩石组合为石英二长斑岩-正长斑岩-碱性长石花岗岩。115~100Ma的辉长岩以角闪辉长岩为主,具有极高的CaO、MgO和Al_(2)O_(3)含量,具有极低的SiO_(2)(42.9%~53.8%)、全碱(K_(2)O+Na_(2)O:0.86%~5.28%)、Ba、Nb、Th、Rb和Zr含量,也具有极低的FeO^(T)/MgO、La/Yb和Zr/Hf比值,较高的Eu/Eu^(*)、Sr/Y比值和Sr含量,为基性-超基性堆晶岩。与辉长岩同期的闪长岩和细粒暗色包体具有较高的SiO_(2)(50.34%~63.68%),较低的CaO、P_(2)O_(5)、MgO、Al_(2)O_(3)含量,相对低的Eu/Eu^(*)和Sr/Y比值,变化较大的La/Yb和Zr/Hf比值,代表了从基性岩浆储库中抽取的富硅熔体。115~100Ma的花岗闪长岩和二长花岗岩类岩石为准铝质岩石,SiO_(2)含量变化较大(61.7%~75.3%),具有较低的FeO^(T)/MgO、Ga/Al比值和Nb、Zr及Nb+Zr+Ce+Y元素含量,显示出典型I型花岗岩的特征。这些花岗岩具有相对高的La/Yb、Eu/Eu^(*)和Zr/Hf比值和高的Sr、Ba和Zr含量。结合岩相学特征,这些花岗岩为堆晶花岗岩。而115~100Ma的碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),低的Eu/Eu^(*)、La/Yb、Zr/Hf和Sr/Y比值,具有低的Ba、Sr和Zr含量和高的Rb、Nb、Y和Th含量和Rb/Sr比值,表明这些花岗岩是由富硅岩浆储库中抽离的高硅熔体侵入地壳形成。100~86Ma期间形成的二长斑岩和正长斑岩具有极高的全碱含量,可以达到8%~12%,其SiO_(2)主要集中在60%~70%,具有极高的Zr、Sr和Ba含量和Eu/Eu^(*)、La/Yb和Sr/Y比值,显示出堆晶花岗岩的特征。而100~86Ma期间形成的大部分碱性长石花岗岩具有极高的SiO_(2)含量(大于75%),并显示出A型花岗岩的特征,具有高的Rb/Sr比值和高的Rb、Y和Th和低的Ba、Sr含量和低的Zr/Hf、La/Yb、Eu/Eu^(*)和Sr/Y比值,表明它们是由富硅岩浆储库抽离的高硅熔体侵入浅部地壳形成。东南沿海高硅花岗岩的形成和穿地壳岩浆系统密切相关,高硅花岗岩是由浅部地壳内晶体-熔体分异产生的熔体侵入地壳所形成,而高硅花岗岩的地球化学特征与岩浆储库的水及挥发份含量密切相关。115~100Ma期间,从富水的岩浆储库抽离的熔体形成具有低高场强元素含量和低Rb/Sr比值的高硅花岗岩,这一过程与古太平洋板块俯冲有关;100~86Ma期间,从富挥发份的岩浆储库抽离的熔体形成碱性特征、富含高场强元素和具有高的Rb/Sr比值的高硅花岗岩,这一过程和古太平洋板块回撤软流圈上涌有关。  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.
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   

5.
We have determined the ages of the ore-bearing Tinggong porphyries and the Eocene granites using the LA-ICPMS zircon U-Pb method. Zircons from one adamellite porphyry and two diorite porphyries yield ages of 15.54±0.28 Ma, 15.02±0.25 Ma and 14.74±0.22 Ma, respectively. The ages of two granites are 50.48±0.71 Ma and 50.16±0.48 Ma. Light Rare Earth Elements(LREE) are enriched in the ore-bearing adamellite porphyries, which are high-K calc-alkaline and metaluminous, while Heavy Rare Earth Elements(HREE) and Y are strongly depleted, indicating an adakitic affinity. The Large Ion Lithophile Elements(LILE) of the adamellite porphyries are highly enriched, whereas some High Field Strength Elements(HFSE) are depleted. The diorite porphyry in this study is chemically similar to the adamellite porphyries, except that the Mg# of the diorite porphyry is a little higher, demonstrating more mantle contamination. Four samples from different rocks are selected for in situ zircon Hf isotopic analyses. The samples show positive εHf(t) values and young Hf model ages, indicating their derivation from juvenile crust. However, the adamellite porphyry and diorite porphyry formed in the Miocene exhibit more heterogeneous Hf isotopic ratios, with lower εHf(t) values than the granites formed in the Eocene, suggesting the involvement of old Indian continent crust in their petrogenesis. The geochronology and geochemistry of the adamellite porphyries and the diorite porphyries indicate that they formed from the same source region in a post-collisional environment, but contaminated by crust and mantle materials in different ratios. The metallic minerals formed mainly during the older adamellite porphyry stage, but they were recycled and reactivated by the diorite porphyry intrusion.  相似文献   

6.
王翠云  李晓峰  肖荣  白艳萍  杨锋  毛伟  蒋松坤 《岩石学报》2012,28(12):3869-3886
德兴铜矿是中国华南地区重要的大型斑岩铜矿,由朱砂红、铜厂和富家坞3个矿床组成。在系统的钻孔样岩相观察基础上,本文把德兴朱砂红花岗闪长斑岩划分为3种类型蚀变岩(钾化-黑云母化蚀变岩、绿泥石化蚀变岩、石英-绢(白)云母化蚀变岩),其主要标志性蚀变矿物依次为:钾长石(黑云母)→绿泥石→石英+绢(白)云母,且热液蚀变程度依次增强。以Al2O3作为不活动组分,通过Isocon分析法表明:随着热液蚀变作用的持续进行,蚀变程度的逐渐增强,主量元素(P2O5)行为较稳定,Na2O、Sr元素大量活化迁出;高场强元素Hf、Th、U、V、Co、Nb、Ta等表现为弱活动性或不活动性;成矿元素Cu、Pb、W显示出大量带入,表明热液流体和成矿流体可能属于同一流体系统。稀土元素均发生一定程度的活化迁移,其中绿泥石化蚀变岩的LREE、HREE均较原岩亏损,而石英-绢(白)云母化花岗闪长斑岩的LREE、HREE富集/亏损情况因样品而异,相对增量/减量变化幅度较大。各类蚀变花岗闪长斑岩球粒陨石化配分模式表现较一致,均为轻稀土相对于重稀土富集的右倾分布,极弱Eu负异常,曲线左陡右平缓,尾部轻微上翘,形似铲状,反映岩浆源区角闪石的分离结晶作用。蚀变花岗闪长斑岩的Y/Ho比值与球粒陨石的Y/Ho比值基本一致,表明Y-Ho在热液蚀变过程中未发生明显分离。弱蚀变花岗闪长斑岩具有较高Sr/Y比值、La/Sm比值以及中等Sm/Yb比值,暗示源区残留相主要为角闪石±石榴子石。  相似文献   

7.
The Duolong porphyry Cu–Au deposit (5.4 Mt at 0.72% Cu, 41 t at 0.23 g/t Au) was recently discovered in the southern Qiangtang terrane, central Tibet. Here, new whole‐rock elemental and Sr–Nd–Pb isotope and zircon Hf isotopic data of syn‐ and post‐ore volcanic rocks and barren and ore‐bearing granodiorite porphyries are presented for a reconstruction of magmas associated with Cu–Au mineralization. LA–ICP–MS zircon U–Pb dating yields mean ages of 117.0 ± 2.0 and 120.9 ± 1.7 Ma for ore‐bearing granodiorite porphyry and 105.2 ± 1.3 Ma for post‐ore basaltic andesite. All the samples show high‐K calc‐alkaline compositions, with enrichment of light rare earth elements (LREE) and large ion lithophile elements (LILE: Cs and Rb) and depletion of high field strength elements (HFSE: Nb and Ti), consistent with the geochemical characteristics of arc‐type magmas. Syn‐ and post‐ore volcanic rocks show initial Sr ratios of 0.7045–0.7055, εNd(t) values of −0.8 to 3.6, (206Pb/204Pb)t ratios of 18.408–18.642, (207Pb/204Pb)t of 15.584–15.672 and positive zircon εHf(t) values of 1.3–10.5, likely suggesting they dominantly were derived from metasomatized mantle wedge and contaminated by southern Qiangtang crust. Compared to mafic volcanic rocks, barren and ore‐bearing granodiorite porphyries have relatively high initial Sr isotopic ratios (0.7054–0.7072), low εNd(t) values (−1.7 to −4.0), similar Pb and enriched zircon Hf isotopic compositions [εHf(t) of 1.5–9.7], possibly suggesting more contribution from southern Qiangtang crust. Duolong volcanic rocks and granodiorite porphyries likely formed in a continental arc setting during northward subduction of the Bangong–Nujiang ocean and evolved at the base of the lower crust by MASH (melting, assimilation, storage and homogenization) processes. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献   

8.
西藏冈底斯矿带发育大量斑岩铜钼矿床及铜铅锌多金属矿床,形成斑岩铜矿带及多金属矿带。过去的工作表明,冈底斯带南部矿床同位素年龄多小于30Ma,形成于碰撞期后伸展环境。本文测定了冈底斯矿带南缘克鲁-冲木达矽卡岩型铜(金、钼)矿集区桑布加拉矽卡岩型铜(金)矿化岩体锆石LA-ICP-MSU-Pb年龄及锆石Ce4+/Ce3+比值。矿化岩体锆石U-Pb年龄:92.1±0.6Ma,MSWD=1.0,锆石Ce4+/Ce3+比值在90～562之间,平均值为287。锆石Ce4+/Ce3+比值和玉龙矿带含矿岩体锆石的比值基本一致,显示矽卡岩矿化岩体岩浆氧逸度较高。印度板块与欧亚板块碰撞时间在65～45Ma之间,桑布加拉矽卡岩型铜矿化岩体锆石U-Pb年龄表明冈底斯带不但发育碰撞期后大规模成矿作用,也发育与洋壳俯冲构造岩浆事件有关的成矿作用。这为冈底斯矿带洋壳俯冲有关矿床的寻找提供了依据。  相似文献   

9.
The Early Cretaceous Duolong gold‐rich porphyry copper deposit is a newly discovered deposit with proven 5.38 Mt Cu resources of 0.72% Cu and 41 t gold of 0.23 g t?1 in northern Tibet. Granodiorite porphyry and quartz diorite porphyrite are the main ore‐bearing porphyries. A wide range of hydrothermal alteration associated with these porphyries is divided into potassic, argillic and propylitic zones from the ore‐bearing porphyry center outward and upward. In the hydrothermal alteration zones, secondary albite (91.5–99.7% Ab) occurs along the rim of plagioclase phenocryst and fissures. Secondary K‐feldspar (75.1–96.9% Or) replaces plagioclase phenocryst and matrix or occurs in veinlets. Biotite occurs mainly as matrix and veinlet in addition to phenocryst in the potassic zone. The biotite are Mg‐rich and formed under a highly oxidized condition at temperatures ranging from 400°C to 430°C. All the biotites are absent in F, and have high Cl content (0.19–0.26%), with log (XCl/XOH) values of ?2.74 to ?2.88 and IV (Cl) values of ?3.48 to ?3.35, suggesting a significant role of chloride complexes (CuCl2‐ and AuCl2‐) in transporting and precipitating copper and gold. Chlorites are present in all alteration zones and correspond mainly to pycnochlorite. They have similar Fe/(Fe+Mg), Mn/(Mn+Mg) ratios, and a formation temperature range of 280–360°C. However, the formation temperature of chlorite in the quartz‐gypsum‐carbonate‐chlorite vein is between 190°C and 220°C, indicating that it may have resulted from a later stage of hydrothermal activity. Fe3+/Fe2+ ratios of chlorites have negative correlation with AlIV, suggesting oxygen fugacity of fluids increases with decreasing temperature. Apatite mineral inclusions in the biotite phenocrysts show high SO3 content (0.44–0.82%) and high Cl content (1–1.37%), indicating the host magma had a high oxidation state and was enriched in S and Cl. The highest Cl content of apatite in the propylitic zone may have resulted from pressure decrease, and the lowest Cl content of apatite in the argillic zone may have been caused by a low Cl content in the fluids. The low concentration of SO3 content in the hydrothermal apatite compared to the magmatic one may have resulted from the decrease of oxygen fugacity and S content in the hydrothermal fluid, which are caused by the abundant precipitation of magnetite.  相似文献   

10.
The Dexing porphyry copper deposit, part of the circum-Pacific porphyry copper ore belt, is the largest porphyry copper deposit in China. We present new LA–ICP–MS zircon U–Pb and molybdenite Re–Os dating, bulk-rock elemental and Sr–Nd–Pb isotopic as well as in situ zircon Hf isotopic geochemistry for these ore-bearing porphyries, in an attempt to better constrain their petrogenesis. LA–ICP–MS zircon U–Pb dating shows that the Dexing porphyries were emplaced in the early Middle Jurassic (～171 Ma); molybdenite Re–Os dating indicates that the associated Cu–Mo mineralization was contemporaneous (～171 Ma) with the igneous intrusion. The rocks are mainly high-K calc-alkaline and show adakitic affinities, including high Sr and low Y and Yb contents, high Sr/Y and La/Yb ratios, and high Mg# (higher than pure crustal melts). These porphyries have initial 87Sr/86Sr ratios of 0.7044?0.7047, ?Nd(T) values of –1.5 to?+0.6, and ?Hf(T) (in situ zircon) values of?+2.6 to?+4.6. They show unusually radiogenic Pb isotopic compositions with initial 206Pb/204Pb ratios up to 18.41 and 207Pb/204Pb up to 15.61. These isotopic compositions are distinctly different from either Pacific MORB or Yangtze lower crust but are similar to the subducting sediments in the western Pacific trenches. Detailed elemental and isotopic data suggest that the Dexing porphyries were emplaced in a continental arc setting coupled with westward subduction of the palaeo-Pacific plate. Partial melting involved the subducted slab (mainly the overlying sediments), with generated melts interacting with the lithospheric mantle wedge, thereby forming the investigated high-K calc-alkaline porphyry magmas.  相似文献   

11.
辽宁鞍本地区位于华北克拉通东北缘,分布有诸多大型-特大型条带状铁矿床。本文对该区歪头山铁矿进行了岩石学、矿物学及年代学研究。歪头山铁建造以条带状铁矿石为主,兼含有少量的块状矿石,其顶底板围岩及矿体夹层主要为太古界鞍山群斜长角闪岩。元素地球化学分析表明,铁矿石富集重稀土[(La/Yb)PAAS=0.24~0.33],具La正异常(La/La*=1.43~1.61)、Eu正异常(Eu/Eu*=2.40~4.54)及Y正异常(Y/Y*=1.10~1.30),Y/Ho值平均30.59,Sr/Ba值平均17.62,Ti/V值平均19.45,反映成矿物质可能来源于由海底火山活动带来的高温热液与海水的混合溶液。铁矿石无明显Ce负异常(Ce/Ce*=0.92~1.06),暗示BIF沉积时海水处于缺氧环境。除Fe2O3T与SiO2外,铁矿石中其它氧化物含量均非常低,且贫Th、U、Zr等具有陆源性质的元素,表明大陆碎屑物质对BIF贡献极少。斜长角闪岩稀土元素配分型式近于平坦[(La/Yb)N=0.80~1.10],无明显Ce异常(Ce/Ce*=0.95~0.99)与Eu异常(Eu/Eu*=0.88~1.16);其大离子亲石元素富集,高场强元素无明显亏损。地球化学分析表明,斜长角闪岩原岩可能为产于弧后盆地的玄武质火山岩。锆石形态与微量元素分析显示,斜长角闪岩中的锆石均属岩浆成因。SIMS锆石U-Pb定年显示斜长角闪岩原岩形成于2533±11Ma,代表了歪头山BIF的成矿年龄;在玄武质岩浆喷发过程中,还捕获了一组年龄为2610±5Ma的锆石。电子探针分析显示磁铁矿成分纯净(FeOT=92.04%~93.05%),其标型组分特征暗示歪头山BIF属沉积变质型铁矿。综合分析认为,歪头山铁矿属Algoma型BIF,成矿与弧后盆地岩浆活动密切相关,指示了新太古代末华北克拉通普遍发育的一期BIF成矿事件。  相似文献   

12.
Classic porphyry Cu–Mo deposits are mostly characterized by close temporal and spatial relationships between Cu and Mo mineralization. The northern Dabate Cu–Mo deposit is a newly discovered porphyry Cu–Mo polymetallic deposit in western Tianshan, northwest China. The Cu mineralization postdates the Mo mineralization and is located in shallower levels in the deposit, which is different from most classic porphyry Cu–Mo deposits. Detailed field investigations, together with microthermometry, laser Raman spectroscopy, and O‐isotope studies of fluid inclusions, were conducted to investigate the origin and evolution of ore‐forming fluids from the main Mo to main Cu stage of mineralization in the deposit. The results show that the ore‐forming fluids of the main Mo stage belonged to an NaCl + H2O system of medium to high temperatures (280–310°C) and low salinities (2–4 wt% NaCl equivalent (eq.)), whereas that of the main Cu stage belonged to an F‐rich NaCl + CO2 + H2O system of medium to high temperatures (230–260°C) and medium to low salinities (4–10 wt% NaCl eq.). The δ18O values of the ore‐forming fluids decrease from 3.7–7.8‰ in the main Mo stage to ?7.5 to ?2.9‰ in the main Cu stage. These data indicate that the separation of Cu and Mo was closely related to a large‐scale vapor–brine separation of the early ore‐forming fluids, which produced the Mo‐bearing and Cu‐bearing fluids. Subsequently, the relatively reducing (CH4‐rich) Mo‐bearing, ore‐forming fluids, dominantly of magmatic origin, caused mineralization in the rhyolite porphyry due to fluid boiling, whereas the relatively oxidizing (CO2‐rich) Cu‐bearing, ore‐forming fluids mixed with meteoric water and precipitated chalcopyrite within the crushed zone at the contact between rhyolite porphyry and wall rock. We suggest that the separation of Cu and Mo in the deposit may be attributed to differences in the chemical properties of Cu and Mo, large‐scale vapor–brine separation of early ore‐forming fluids, and changes in oxygen fugacity.  相似文献   

13.
The Alkaline porphyries in the Beiya area are located east of the Jinshajiang suture, as part of a Cenozoic alkali-rich porphyry belt in western Yunnan. The main rock types include quartz-albite porphyry, quartz-K-feldspar porphyry and biotite–K-feldspar porphyry. These porphyries are characterised by high alkalinity [(K2O + Na2O)% > 10%], high silica (SiO2% > 65%), high Sr (> 400 ppm) and 87Sr/86Sr (> 0.706)] ratio and were intruded at 65.5 Ma, between 25.5 to 32.5 Ma, and about 3.8 Ma, respectively. There are five main types of mineral deposits in the Beiya area: (1) porphyry Cu–Au deposits, (2) magmatic Fe–Au deposits, (3) sedimentary polymetallic deposits, (4) polymetallic skarn deposits, and (5) palaeoplacers associated with karsts. The porphyry Cu–Au and polymetallic skarn deposits are associated with quartz–albite porphyry bodies. The Fe–Au and polymetallic sedimentary deposits are part of an ore-forming system that produced considerable Au in the Beiya area, and are characterised by low concentrations of La, Ti, and Co, and high concentrations of Y, Yb, and Sc.The Cenozoic porphyries in western Yunnan display increased alkalinity away from the Triassic Jinshajiang suture. Distribution of both the porphyries and sedimentary deposits in the Beiya area are interpreted to be related to partial melting in a disjointed region between upper mantle lithosphere of the Yangtze Plate and Gondwana continent, and lie within a shear zone between buried Palaeo-Tethyan oceanic lithosphere and upper mantle lithosphere, caused by the subduction and collision of India and Asia.  相似文献   

14.
The newly discovered Paodaoling porphyry Au deposit from the Guichi region, Lower Yangtze River Metallogenic Belt(LYRB), contains 35 tons of Au at an average grade of ~1.7 g/t. It is a porphyry ‘Au-only' deposit, as revealed by current exploration in the depths, mostly above-400 m, which is quite uncommon among coeval porphyry mineralization along the LYRB. Additionally, there are also Cu-Au bearing porphyries and barren alkaline granitoids in the Paodaoling district. Zircon LA-ICP-MS U-Pb dating of the Cu-Au-bearing porphyries yield an age of 141–140 Ma, falling within the main magmatic stage of the LYRB, whereas the barren granites give an age of 125–120 Ma, coeval with the regional Atype granites. The Cu-Au-bearing porphyries are LILE-, LREE-enriched and HFSE-depleted, typical of arc magmatic affinities. The barren granites are HFSE-enriched, with lower LREE/HREE ratios and pronounced negative Eu anomalies. The Cu-Au-bearing porphyries in the Paodaoling district have high oxygen fugacities and high water content. Pyrite sulfur isotopes of the Paodaoling gold deposit indicate a magmatic-sedimentary mixed source for the ore-forming fluids. Based on the alteration and poly-metal zonation of the deepest exploration drill hole from the Paodaoling Au deposit, we propose that Cu ore bodies could lie at depth beneath the current Au ore bodies. The magmatism and associated Cu-Au mineralization of the Paodaoling district are likely to have formed in a subduction setting, during slab rollback of the paleo-Pacific plate.  相似文献   

15.
This paper presents abundances of major and trace elements of apatites in granitic rocks associated with different types of ore deposits in Central Kazakhstan on the basis of electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry. Our results demonstrate that the concentrations and ratios of elements in apatites from different granitoid rocks show distinct features, and are sensitive to magma evolution, petrogenetic and metallogenetic processes. Apatites in the rocks associated with Mo‐W deposits have high content of F and MnO, low content of Cl, which may be indicative of sedimentary sources, while apatites from a Pb‐Zn deposit show relatively high content of Cl and low F content, which possibly suggest a high water content. In these apatites, Sr contents decrease, while Mn and Y contents increase with magma evolution. This relationship reflects that these elements in apatites are related with the degree of magmatic differentiation. Four types of REE patterns in apatites are identified. Type 1 character of highest (La/Yb)N in apatites of Aktogai porphyry Cu‐Mo deposit, Sayak‐I skarn Cu deposit and Akzhal skarn Pb‐Zn depposit is likely produced by the crystallization of heavy REE‐enriched minerals. Type 2 character of upward‐convex light REE in apatite of Aktogai porphyries likely results from La‐enriched mineral crystallization. Type 3 feature of Nd depletion in apatites of East Kounrad and Zhanet deposits both from Mo‐W deposits primarily inherits the character of host‐rock. Type 4 apatites of Aktogai deposit and Akshatau W‐Mo deposit with wide range of REE contents may suggest that apatites crystallize under a wide temperature range. Three types of apatite with distinct redox states are identified based on Eu anomaly. The Aktogai apatite with slight negative Eu anomaly displays the most oxidized state of the magma, and the apatites of other samples at Aktogai, East Kounrad and Akzhal with moderate negative Eu anomaly show moderate oxidizing condition of these rocks, while the remaining apatites with strong En anomaly indicate a moderate reductive state of these rocks.  相似文献   

16.
Abstract. The late Jurassic Tongshankou and Yinzu plutons in southeast Hubei have been investigated for their contrasting metal mineralization features. The former is closely associated with porphyry Cu‐Mo mineralization, while the latter is barren of metal mineralization, althouth both are located very close to each other. The Tongshankou granodiorite porphyries and the Yinzu granodiorites are geochemically similar to adakites, e.g., high Al2O3 and Sr contents and La/Yb and Sr/Y ratios, enriched in Na2O, depleted in Y and Yb, very weak Eu anomalies and positive Sr anomalies. However, different geochemi‐cal characteristics exist between the two plutons: the Tongshankou adakitic rocks (1) are relatively enriched in SiO2, K2O, MgO, Cr, Ni, and Sr and depleted in Y and Yb; (2) have higher degree REE differentiation; (3) have positive Eu anomalies in contrast with very weak negative or unclear Eu anomalies in the Yinzu rocks; and (4) isotopically have relatively higher ePNd(t) values (‐5.19 to ‐5.38) and lower initial 87Sr/86Sr ratios (0.7060 to 0.7062), while the Yinzu adakitic rocks have relatively lower ePNd(t) values (‐7.22 to ‐8.67) and higher initial 87Sr/86Sr ratios (0.7065 to 0.7074). The trace element and isotopic data demonstrate that the Tongshankou adakitic rocks were most probably originated from partial melting of delaminated lower crust with garnet being the main residual mineral whereas little or no plagioclase in the source. On the contrary, the Yinzu adakitic rocks were likely derived from partial melting of thickened lower crust, with residual garnet and a small quantity of plagioclase and hornblende in the source. Interactions between the adakitic magmas and mantle peridotites possibly took place during the ascent of the Tongshankou adakitic magmas through the mantle, considering that MgO, Cr, and Ni contents and ePNd(t) values of the adakitic magmas were possibly elevated and initial 87Sr/86Sr ratios were possibly lowered due to the contamination of mantle peridotites. In addition, the Fe2O3 of the adakitic magmas was likely released into the mantle and the oxygen fugacities (?o2) of the latter were obviously possibly raised, which made metallic sulfide in the mantle oxidized and the chalcophile elements such as Cu were incorporated into the adakitic magmas. The ascent of the adakitic magmas enriched in Cu and Mo will lead to the formation of porphyry Cu‐Mo deposit. Nevertheless, the Yinzu adakitic magmas were possibly lack of metallogenetic materials due to not interacting with mantle peridotite, and thus unfavorable to metal mineralization.  相似文献   

17.
The Beiya gold–polymetallic orefield, with gold reserves of 305 t, is one of the most representative porphyry-skarn orefields in the Jinshajiang–Ailaoshan Cu–Au ore belt within the Sanjiang region of southwest China. The orefield contains seven deposits: the Wandongshan, Hongnitang, Dashadi, Bijiashan, Weiganpo, Matouwan, and Bailiancun deposits. In this paper we report on the geochemistry and geochronology of porphyries associated with mineralization from the seven deposits. The results show that all the porphyries have similar geochemistry, with high alkalinity, high contents of SiO2, Al2O3, K2O, and Sr, high K2O/Na2O ratios, low MgO, Y, and Yb contents, enrichments in Ba, K, and Pb, depletions in P, Ti, Nb, and Ta, and non-evident to weak Eu depletions (δEu = 0.42–0.99). In the SiO2 vs. Th/Ce diagram, the porphyry samples are distributed in the area of thickened lower crust, and in the Sr/Y vs. Y and La/Yb vs. Yb diagrams, the porphyries broadly followed the batch-melting trend of amphibolite containing up to 10% garnet. LA-MC-ICP-MS zircon U–Pb dating analysis suggests that the porphyries were emplaced between 34.62 ± 0.25 and 36.72 ± 0.25 Ma. They were coeval with lamprophyres (34 to 36 Ma) in the Beiya area and with potassic–ultrapotassic intrusive rocks (40 to 35 Ma) within the Jinshajiang–Ailaoshan magmatic belt, indicating possible genetic relation between these rock types. We suggest that the porphyries in the Beiya gold–polymetallic orefield were derived from the partial melting of a K-rich mafic source in the thickened lower crust, with the melting triggered by asthenospheric upwelling following the removal of lower lithospheric mantle.  相似文献   

18.
The Lakange porphyry Cu–Mo deposit within the Gangdese metallogenic belt of Tibet is located in the southern–central part of the eastern Lhasa block, in the Tibetan Tethyan tectonic domain. This deposit is one of the largest identified by a joint Qinghai–Tibetan Plateau geological survey project undertaken in recent years. Here, we present the results of the systematic logging of drillholes and provide new petrological, zircon U–Pb age, and molybdenite Re–Os age data for the deposit. The ore‐bearing porphyritic granodiorite contains elevated concentrations of silica and alkali elements but low concentrations of MgO and CaO. It is metaluminous to weakly peraluminous and has A/CNK values of 0.90–1.01. The samples contain low total REE concentrations and show light REE/heavy REE (LREE/HREE) ratios of 17.51–19.77 and (La/Yb)N values of 29.65–41.05. The intrusion is enriched in the large‐ion lithophile elements (LILE) and depleted in the HREE and high field‐strength elements (HFSE). The ore‐bearing porphyritic granodiorite yielded a Miocene zircon U–Pb crystallization age of 13.58 ± 0.42 Ma, whereas the mineralization within the Lakange deposit yielded Miocene molybdenite Re–Os ages of 13.20 ± 0.20 and 13.64 ± 0.21, with a weighted mean of 13.38 ± 0.15 Ma and an isochron age of 13.12 ± 0.44 Ma. This indicates that the crystallization and mineralization of the Lakange porphyry were contemporaneous. The ore‐bearing porphyritic granodiorite yielded zircon εHf(t) values between ?3.99 and 4.49 (mean, ?0.14) and two‐stage model ages between 1349 and 808 Myr (mean, 1103 Myr). The molybdenite within the deposit contains 343.6–835.7 ppm Re (mean, 557.8 ppm). These data indicate that the mineralized porphyritic granodiorite within the Lakange deposit is adakitic and formed from parental magmas derived mainly from juvenile crustal material that partly mixed with older continental crust during the evolution of the magmas. The Lakange porphyry Cu–Mo deposit and numerous associated porphyry–skarn deposits in the eastern Gangdese porphyry copper belt (17–13 Ma) formed in an extensional tectonic setting during the India–Asia continental collision.  相似文献   

19.
《Gondwana Research》2014,25(3-4):1152-1171
Many Cu–Mo–Au deposits are considered to be related to adakitic porphyries formed in non-arc settings, e.g., in collisional orogenic zones and intra-plate environments, but their genesis is still under discussion. The Aolunhua porphyry complex and its related Mo–Cu deposit from the eastern Central Asian Orogenic Belt (CAOB) provide important insights into this issue. The porphyries are characterized by high Sr (496–705 ppm) and Sr/Y and La/Yb ratios similar to those of typical adakitic rocks, and low ISr ratios (0.7049–0.7052) and positive εNd(t) (+ 0.5 to + 1.4) and εHf(t) (+ 3.5 to + 9.8) values. These features, along with the occurrence of mafic microgranular enclaves (MMEs), compositional and textural disequilibrium of plagioclase phenocrysts and relatively high Mg# values (45–52), indicate that they were derived from mixing of felsic magma from partial melting of a juvenile arc-type lower crust and mafic magma from a lithospheric mantle previously metasomatized by subduction zone fluids/melts. High Sr/Y and La/Yb ratios are indicative of contribution from enriched mantle-derived materials (with high LILEs; e.g., Sr, La), which were strengthened by subsequent fractionation of ferromagnesian phases such as pyroxene and hornblende. MMEs hosted by the ore-bearing porphyry have zircon U–Pb ages of ca. 132 Ma, similar to those of the host rocks. The enclaves have elevated Mg# (56–63), LILEs (e.g., Sr = 660–891 ppm), LREE (LaN = 68–150, (La/Sm)N = 3.0–4.0, (La/Yb)N = 12.0–19.6) and ratios of radiogenic isotopes of Nd- and Hf (εNd = + 0.7 to + 1.6; εHf = + 3.3 to + 10.9), suggesting that their parental magmas were derived from the metasomatized mantle source. The Mo–Cu mineralization was probably related to the high water content, high oxygen and sulfur fugacity of hybrid magma. Formation of the adakitic porphyries and related Mo–Cu deposits of the eastern CAOB could be related to the Early Cretaceous lithospheric extension, caused by the subduction of the Paleo-Pacific plate and its induced reactivation of juvenile arc-type lower crust.  相似文献   

20.
The Tongshankou Cu-Mo deposit, located in southeast Hubei province, is a typical skarn–porphyry type ore deposit closely related to the Tongshankou granodiorite porphyry, characterized by a high Sr/Y ratio.Detailed in situ analyses of the trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry were performed.Scarcely any inherited zircons were observed, and the analyzed zircons yielded highly concordant results with a weighted mean 206Pb/238 U age of 143.5 ± 0.45 Ma(n=20, mean square weighted deviation was 0.75), which was interpreted to represent the crystallization age of the Tongshankou granodiorite porphyry.The chondrite-normalized rare-earth element pattern was characterized by a slope that steeply rises from the light-group rare-earth elements(LREE) to the heavy-group rare-earth elements(HREE) with a positive Ce-anomaly and inconspicuous Eu-anomaly, which was coincident with the pattern of the zircons from the Chuquicamata West porphyry, Chile.The analyzed zircons also had relatively low 176Hf/177 Hf ratios of 0.282526–0.282604.Assuming t=143 Ma, the corresponding calculated initial Hf isotope compositions(εHf(t)) ranged from-5.6 to-2.9.The results of the in situ analysis of trace elements and U–Pb and Lu–Hf isotopes in zircons from the Tongshankou granodiorite porphyry suggest that a deep-seated process involving a thickened-crust/enriched-mantle interaction may play an important role in the generation of high Sr/Y-ratio magma and potentially in the generation of porphyry Cu-Mo systems.  相似文献   

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