Discriminating characters of ore-forming intrusions in the super-large Chalukou porphyry Mo deposit,NE China

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.     

黑龙江省岔路口斑岩钼矿床流体包裹体和稳定同位素特征

岔路口超大型斑岩钼矿床位于大兴安岭北部,是目前中国东北地区最大的钼矿床,矿体赋存于中酸性杂岩体及侏罗系火山-沉积岩内,其中花岗斑岩、石英斑岩、细粒花岗岩与钼矿化关系密切.流体包裹体研究表明,岔路口矿床主要发育富液两相包裹体、富气两相包裹体和含子矿物多相包裹体.花岗斑岩石英斑晶中流体包裹体的形成温度集中在230 ～ 440℃和470～510℃两个温度区间,盐度分别介于0.7％ ～ 53.7％ NaCl eqv和6.2％～61.3％ NaCl eqv两个区间;成矿早阶段钾长石-石英-磁铁矿脉中流体包裹体的形成温度集中在320～440℃、盐度介于4.2％ ～ 52.3％NaCl eqv;成矿中阶段石英-辉钼矿脉和角砾岩中流体包裹体的形成温度集中在260～410℃、盐度介于0.4％～52.3％ NaCleqv;成矿晚阶段石英-萤石-方铅矿-闪锌矿脉中流体包裹体的形成温度集中在170～320℃、盐度介于0.5％ ～ 11.1％ NaCleqv.成矿流体具高温、高盐度及高氧逸度的特征,总体上属于富F的H2O-NaCl±CO2体系.成矿流体的δ 18Ow值为-4.5‰～3.2‰,δDw值为-138‰～-122‰,表明成矿流体为岩浆水与雨水的混合流体.金属硫化物的δ34S值介于-1.9‰～+3.6‰,均值为+1.6‰,表明成矿物质主要来自深源岩浆.多期次的流体沸腾作用是该矿床的主要成矿机制.     

黑龙江岔路口钼多金属矿床辉钼矿铼-锇同位素年龄及地质意义

岔路口矿床是迄今为止在中国北方发现的最大规模钼多金属矿床,钼、铅锌和银的储量分别为134万t、37万t和4200 t.考虑到大规模地质勘查工作仍在进行中,金属储量的增加只是个时间问题.为了进一步查明岔路口矿床的形成时间,笔者对主要钼多金属矿体8件辉钼矿样品进行了铼-锇同位素分析,所获同位素等时线年龄为(146.96±0...     

Fluid evolution of the Chalukou giant Mo deposit in the northern Great Xing'an Range,NE China

The Chalukou giant Mo deposit in the Heilongjiang Province, northeastern China, is a porphyry deposit hosted in an intermediate‐felsic complex surrounded by Mesozoic volcano–sedimentary rocks. The mineralization process is composed of four stages, including quartz + K‐feldspar (Stage I), quartz + molybdenite (Stage II), pyrite + chalcopyrite + quartz ± other sulphides (Stage III) and carbonate ± fluorite ± quartz (Stage IV). The mineralization is generally associated with intense K‐feldspar‐, fluorite‐, phyllic‐ and propylitic alteration. Primary fluid inclusions (FIs) in quartz include four compositional types, i.e. pure carbonic (PC‐type), aqueous‐carbonic (C‐type), daughter mineral‐bearing (S‐type) and aqueous (W‐type) inclusions. Halite, sylvite and hematite are recognized as the daughter minerals in Stage I S‐type FIs, whereas molybdenite and chalcopyrite occur as daughter minerals in Stage II S‐type FIs. High‐salinity and high pressure (>220 MPa) FIs exist in Stage I quartz veins, characterized by homogenization through halite dissolution at temperatures of 324 to 517 °C. The paucity of coexisting vapour‐rich FIs with similar homogenization temperatures at this stage indicates that the initial S‐type inclusions have directly exsolved from the magma rather than boiling off of a low‐salinity vapour. Stage I quartz has captured the C‐ and W‐type FIs, which have totally homogenized at 270–530 °C with salinities of 1.6–17.0 wt.% NaCl equiv. At Stage II, the coexistence of all FI types were only observed at pressures of 150–218 MPa and temperatures of 352–375 °C, with two salinity clusters of 0.9–16.6 wt.% NaCl equiv. and 37–56 wt.% NaCl equiv. Stage III quartz contains W‐type FIs with homogenization temperatures of 158–365 °C, salinities of 0.5–9.0 wt.% NaCl equiv., and minimum pressures of 12–116 MPa; whilst Stage IV fluorite or calcite only contains W‐type FIs with homogenization temperatures of 121–287 °C, salinities of 0.5–5.3 wt.% NaCl equiv., and minimum pressures of 10–98 MPa. The estimated trapping pressure from Stages II to III suggests an alternating lithostatic–hydrostatic fluid‐system caused by fluid boiling. Ore fluids at the Chalukou Mo deposit may have been evolved from a CO₂‐rich, high‐salinity, and high‐oxygen fugacity (fO₂) magma system, to a CO₂‐poor, low‐salinity, and low‐fO₂ epithermal system. Two key points may have contributed to the formation of the Chalukou giant Mo deposit: The magmatic origin and fluid boiling that has resulted in decompression and rapid precipitation of metals. Copyright © 2014 John Wiley & Sons, Ltd.     

黑龙江省多宝山斑岩型铜(钼)矿床成矿流体特征及演化

黑龙江省多宝山斑岩铜(钼)矿床位于小兴安岭西北部,是中亚-兴蒙造山带北东段最大的斑岩型铜(钼)矿床,矿体产于加里东期花岗闪长岩和中奥陶世多宝山组安山岩、凝灰岩中。铜矿化与绢英岩化关系密切,而钼矿化主要产于钾硅化带中。矿区内脉体广泛发育,从早到晚依次为:石英+钾长石脉、早阶段石英+辉钼矿脉、晚阶段石英+辉钼矿脉、石英+黄铜矿+黄铁矿脉、石英+黄铁矿脉和方解石+石英脉。脉石英中广泛发育流体包裹体,包括气液两相水溶液包裹体(W型)、纯气相包裹体(G型)、含CO2三相包裹体(C型)及含子矿物多相包裹体(S型)。石英+钾长石脉中仅发育气液两相包裹体,均一温度峰值﹥550℃、盐度为16.2%～18.1%NaCleqv;早阶段石英+辉钼矿脉中发育大量气液两相包裹体和含子矿物多相包裹体,并见少量含CO2三相包裹体,均一温度集中在350～450℃、盐度变化于1.1%～﹥65.3%NaCleqv;晚阶段石英+辉钼矿脉体发育大量含CO2三相包裹体和含子矿物多相包裹体,另有少量气液两相包裹体,均一温度集中在270～350℃、盐度为0.8%～42.4%NaCleqv;石英+黄铜矿+黄铁矿脉中发育丰富的气液两相包裹体,见少量含子矿物多相包裹体、含CO2三相包裹体和纯气相包裹体,均一温度峰值在230～330℃、盐度为0.8%～42.4%NaCleqv;石英+黄铁矿脉和方解石+石英脉中仅发育气液两相包裹体,均一温度变化于110～200℃、盐度为3.9%～8.4%NaCleqv。成矿流体在古深度4.1km左右,温度在230～450℃之间、压力在10～41MPa之间,发生了强烈的流体沸腾作用,大量CO2等气体从流体中释放出来,黄铜矿、斑铜矿和辉钼矿等巨量沉淀下来,形成了铜(钼)矿体。成矿流体总体上属H2O-CO2-NaCl体系,多期次的流体沸腾作用是该矿床的主要成矿机制。     

大兴安岭北段岔路口斑岩钼矿床成矿年代学、岩石地球化学及其地质意义

黑龙江省岔路口超大型斑岩钼矿床位于大兴安岭北部,是目前中国东北地区最大的钼矿床,矿体赋存于中酸性杂岩体及侏罗系火山-沉积岩内,其中,晚侏罗世花岗斑岩、石英斑岩、细粒花岗岩与钼矿化关系密切。6件辉钼矿样品的铼-锇等时线年龄为（148±1）Ma。中侏罗世二长花岗岩属钾玄岩系列,w（SiO₂）为69.48% ~ 74.98%,w（Al₂O₃）为12.35%~14.48%,w（K₂O+Na₂O）为7.67%~10.42%,K₂O/Na₂O比值介于1.07~2.81。轻、重稀土元素分馏较强,具有较弱的铕负异常,HFSE和LILE分异明显,Rb、K等元素富集,Ta、Nb、P、Ti等元素亏损,显示正ε_Hf（t）值;晚侏罗世花岗斑岩、石英斑岩属钾玄岩系列,而细粒花岗岩属高钾钙碱性系列,w（SiO₂）为73.87%~78.95%,w（Al₂O₃）为10.35%~13.47%,w（K₂O+Na₂O）为8.06%~10.02%,K₂O/Na₂O比值介于1.03~8.20。轻、重稀土元素分馏较强,具有明显的铕负异常,HFSE和LILE分异明显,Rb、K、Th等元素富集,P、Ti、Ba、Sr等元素亏损,显示正ε_Hf（t）值。二长花岗岩、花岗斑岩、石英斑岩及细粒花岗岩均为高硅、富碱的高分异I型花岗岩,岩浆源区组成类似,主要来自于新元古代期间亏损地幔增生的年轻下地壳物质。岔路口斑岩钼矿床是晚侏罗世大陆内部构造-岩浆活化的产物,形成于蒙古-鄂霍次克造山带后碰撞伸展环境,同时,可能受到古太平洋板块俯冲诱发的弧后伸展作用的叠加。     

河南省新县姚冲钼矿床流体包裹体研究

河南省新县姚冲钼矿床产于大别造山带,属于陆-陆碰撞体制的斑岩型矿床,其流体成矿过程可以分为早、中、晚三个阶段,分别以石英+钾长石±黄铁矿±磁铁矿、石英±钾长石+辉钼矿±其他硫化物和石英±碳酸盐±萤石组合为标志.热液石英和萤石中发育纯CO2包裹体(PC型)、CO2-H2O型包裹体(C型)、水溶液包裹体(W型)和含子晶多相包裹体(S型).早阶段石英中发育纯CO2包裹体、CO2-H2O型包裹体和含子晶多相包裹体,中阶段的石英则发育CO2-H2O型包裹体、水溶液包裹体和含子晶多相包裹体,在晚阶段的无矿石英脉中发育水溶液包裹体和少量的CO2-H2O型包裹体,石英-碳酸盐-(萤石)脉石英与萤石中只发育水溶液包裹体.早阶段流体包裹体的均一温度为277～ 380℃,集中于300～ 360℃,盐度变化于3.0％～10.3％ NaCleqv之间.中阶段包裹体均一温度介于185 ～ 351℃之间,集中在260～ 320℃,盐度介于2.4％ ～9.3％NaCleqv;晚阶段包裹体均一温度为139 ～245℃,盐度介于0.7％ ～6.3％ NaCleqv之间.中阶段多相包裹体中常见黄铜矿和其他透明子矿物,表明流体具有还原性、过饱和的特征,是矿石矿物沉淀的主要阶段.估算早、中阶段流体捕获压力分别集中于47 ～ 131MPa和26 ～118MPa,所对应的成矿深度分别约为4.7km和2.6～4.2km.上述流体包裹体的研究表明姚冲钼矿床的初始成矿流体具有高温、高盐度、富CO2的特征,同时预测了深部找矿潜能.     

Ore Genesis and Formation Age of the Gaogangshan Mo Deposit,Heilongjiang Province,NE China

The Gaogangshan Mo deposit, located in the northern part of the Lesser Xing'an Range (the eastern part of the Xing'an–Mongolia Orogenic Belt), is one of the newly discovered Mo deposits in northeast China. Ore bodies occur in the granite and are generally in vein and stockwork forms. Major metallic minerals in the ore include pyrite and molybdenite. The styles of mineralization are disseminated, veinlet–disseminated, and veinlet. The major types of wall–rock alteration are silicification–potassic alteration, phyllic alteration and propylitization. Fluid inclusion analyses indicate that the ore‐forming fluid during the major mineralization stage is an H₂O–NaCl–CO₂ system, with wide homogenization temperature and salinity ranges. The abundant CO₂–rich and coexisting halite–bearing fluid inclusion assemblages in the main stage of mineralization highlight the significance of intensive fluid boiling for porphyry Mo mineralization. Comprehensive study of the ore‐forming conditions, geological features of the deposit, micro‐thermometric analysis of fluid inclusions and comparison of the Gaogangshan deposit with other typical porphyry deposits leads to the conclusion that the deposit is a porphyry type. We obtained a weighted mean age of the molybdenite deposit at Gaogangshan of 250.7 ± 1.8 Ma. The isotopic dating results indicate that the Gaogangshan deposit was formed in the Permo–Triassic, which is the earliest Mo–only deposit in northeast China. The formation of the Gaogangshan Mo deposit may be related to the extension and break–up of the Songnen Block and Jiamusi Block in the Permo–Triassic.     

黑龙江多宝山斑岩铜(钼)矿床蚀变-矿化阶段及其流体演化

黑龙江多宝山斑岩铜(钼)矿床是大兴安岭中北部多宝山-阿尔山铜(钼)成矿带内最大的斑岩型矿床,位于兴蒙造山带的最东端。矿床赋存于花岗闪长岩及多宝山组下部地层中。据野外脉体类型和穿插关系、围岩蚀变类型、矿物组合,将多宝山斑岩铜(钼)矿床的蚀变和矿化自早至晚划分为4个阶段:Ⅰ钾硅化阶段;Ⅱ 硅化-钼矿化阶段;Ⅲ绢英岩化-铜矿化阶段;Ⅳ碳酸盐石英阶段。石英中包裹体类型主要有水溶液包裹体、富CO₂包裹体、含子晶多相包裹体、纯CO₂包裹体。成矿流体从早阶段到晚阶段具有规律性演化特征:钾硅化阶段发育水溶液包裹体、富CO₂包裹体,盐度集中在6%~10% NaCleqv,密度0.5~0.9g·cm^-3,均一温度峰值为245~400℃;硅化-钼矿化阶段发育水溶液包裹体、富CO₂包裹体、含子晶多相包裹体均一温度峰值为260~300℃,盐度1.7%~39% NaCleqv,密度0.3~1.1g·cm^-3;绢英岩化-铜矿化阶段发育水溶液包裹体、富CO₂包裹体,均一温度峰值220~280℃,盐度0.1%~24.8% NaCleqv,峰值集中在6%~12%,密度0.5~1.0g·cm^-3;碳酸盐阶段仅发育水溶液包裹体包裹体,均一温度峰值为125~170℃,盐度0.5%~12.8% NaCleqv,密度0.8~0.9g·cm^-3。激光拉曼探针分析结果表明成分主要为H₂O和CO₂。本文对多宝山矿床主成矿期压力进行了估算,Ⅰ、Ⅱ、Ⅲ阶段捕获压力分别为110~160MPa、58~80MPa、8~17MPa。测温实验结合野外现象及包裹体岩相学表明多宝山斑岩铜(钼)矿床是一个复杂的构造-岩浆成矿系统,与成矿有关的热流体不是单一的岩浆分异的结果,构造裂隙系统也为含矿流体提供了很好的导矿与容矿空间,矿床沉淀机制为温度压力的变化及空间的开放导致流体不混溶与沸腾作用,不同流体的混合、水岩反应致使流体pH值、成分发生变化,从而导致铜、钼的矿化。     

黑龙江鹿鸣钼矿床成矿流体特征

鹿鸣钼矿床是小兴安岭—张广才岭成矿带上典型的特大型斑岩型钼矿床,矿体主要产于早中生代早期中细粒似斑状二长花岗岩内,矿化类型以细脉浸染状矿化为主。根据矿物共生组合及脉体穿插关系将鹿鸣钼矿床划分为4个成矿阶段:黄铁矿-石英阶段(Ⅰ),石英-辉钼矿阶段(Ⅱ),绿泥石-辉钼矿-石英阶段(Ⅲ),石英-碳酸盐阶段(Ⅳ)。成矿流体包裹体有3类:A型气液两相包裹体(L+V),B型含子晶三相包裹体(L+V+S),C型气相包裹体(V)。不同阶段流体包裹体的成分、均一温度、盐度等特征显示成矿流体由早阶段的高温、高盐度的H_2O-CO_2-NaCl体系逐渐演变为晚阶段的低温、低盐度的H_2O-NaCl体系。氢氧同位素特征显示成矿早阶段以岩浆水为主,随成矿演化有不同程度大气水的加入。根据矿床产出特征、矿物共生组合和流体包裹体特征,认为流体的沸腾作用和CO2等气相组分大量逸失是成矿流体形成矿床的主要因素。     

黑龙江省多宝山Cu-Mo矿床成矿斑岩锆石U-Pb年龄及地球化学特征

多宝山矿床位于大兴安岭北部,是中国东北地区规模最大的斑岩型Cu-Mo矿床。文章对该矿床中与成矿关系密切的花岗闪长斑岩进行了详细的LA-ICP-MS锆石U-Pb定年、主量元素、微量元素及Hf同位素研究。结果表明,花岗闪长斑岩的LA-ICP-MS锆石U-Pb年龄为(474.9±1.8)Ma,其w(Si O2)为70.73%~73.45%,w(K2O)和w(Na2O)分别为2.99%~3.88%、3.86%~4.38%,属高钾钙碱性系列。岩石富集轻稀土元素,(La/Yb)N=6.32~12.76,显示出Ba、K、La、Sr、Zr、Hf、Sm等元素富集,Th、Ta、Nb、Ce、P、Ti等元素亏损的特征。锆石εHf(t)值介于10.3~14.6。详尽的元素和同位素地球化学特征表明多宝山花岗闪长斑岩可能形成于大陆边缘弧环境,来源于加厚陆壳条件下亏损地幔新增生的年轻地壳物质的部分熔融过程。     

Two different types of granitoids in the Suyunhe large porphyry Mo deposit,NW China and their genetic relationships with molybdenum mineralization

The Suyunhe large porphyry Mo deposit (∼0.57 Mt molybdenum), located in the West Junggar, NW China, is the largest known porphyry Mo deposit in Xinjiang. Granitoids in this deposit are mainly characterized by three closely spaced intrusive centers (known as stocks I, II and III respectively). The stocks I and III mainly consist of barren granodiorite porphyry and tonalite porphyry, whereas the stock II is mainly composed of fertile monzonitic granite porphyry and granite porphyry. Based on detailed major and trace element, and Sr–Nd isotopic analyses, two distinct compositional groups can be identified. The first group of high-silica end-members (HSE) is characterized by high SiO₂ (mostly >75 wt%), low MgO (0.07–0.69 wt%) and Mg# (0.19–0.36), significant Eu depletion in the chondrite-normalized diagram, and low Sr/Y and La/Yb, as well as noticeably negative anomalies of Ba, Sr, P and Ti in the primitive mantle-normalized diagram. The second group of low-silica end-members (LSE), however, displays adakite-like features with lower SiO₂ (<75 wt%), higher MgO (0.52–1.32 wt%) and Mg# (0.32–0.52; mostly >0.4), and higher Sr/Y (mostly >20) and La/Yb (>8). The depleted Sr–Nd isotopic characteristics (ε_Nd(T) = 3.5–6.4 and I_sr = 0.7026–0.7055) and young two-stage model ages of HSE and LSE indicate that they were both derived from partial melting of juvenile lower crust that might be triggered by asthenosphere upwelling subsequent to a slab rollback event. However, the depths of initial melting might be different. The current evidence demonstrates that HSE in the Suyunhe deposit formed by partial melting of juvenile crust at depths of less than ∼33 km with a plagioclase residue, whereas that for LSE occurred at depths of >40 km where a garnet residue existed and the crust was thickened. The lower source depth, as well as subsequently strong plagioclase fractionation, results in the absence of adakite-like characteristics in HSE.The Ce⁴⁺/Ce³⁺and Eu_N/Eu_N1 ratios in zircons of HSE are much lower than ore-forming intrusions from porphyry Cu deposits in the Central Asian Orogenic Belt, but noticeably higher than barren intrusions from the Lachlan fold belt and ore-bearing intrusions from small-intermediate porphyry Mo deposits from the East Qinling–Dabie and the Nanling metallogenic belts, China, indicating that neither too high nor too low oxygen fugacities are favorable for large porphyry Mo deposits. Based on previous studies of adakitic rocks in the world, adakite-like LSE in the Suyunhe deposit are believed to have higher oxygen fugacities, and thus be less fertile than HSE. We finally suggest that adakites and adakite-like rocks are unproductive for porphyry Mo deposits.     

河南省东沟超大型钼矿床流体包裹体研究

河南省东沟钼矿床是东秦岭钼矿带新发现的燕山期超大型斑岩钼矿床,是大陆碰撞成矿理论预测在先,勘查突破在后的成功范例。该矿床的形成与东沟A型花岗斑岩有关,矿体产于斑岩体外接触带的熊耳群火山岩中。以岩体为中心发育典型的斑岩蚀变分带,由内到外依次是钾化、绢英岩化和青磐岩化。流体成矿过程包括早、中、晚3个阶段,分别以石英-钾长石组合、石英-(钾长石)-多金属硫化物组合和石英-碳酸盐-萤石组合为标志,矿石矿物主要沉淀于中阶段。早、中阶段热液石英中发育CO₂-H₂O型包裹体(C型)、水溶液包裹体(W型)和含子晶多相包裹体(S型),但晚阶段只发育水溶液包裹体(W型)。早阶段C型和W型包裹体均一温度集中于380~550℃,盐度为7.70%~18.28% NaCleqv;S型包裹体中常见石盐、黄铜矿、方解石和未知透明子矿物,其均一温度范围为318~516℃,加热过程中除石盐外其他子矿物不熔;不包括不熔子矿物的贡献,该类包裹体盐度变化于12.85%~17.87 和35.55%~47.67% NaCleqv。中阶段C型和W型流体包裹体均一温度集中于260~410℃,盐度为4.62%~18.28% NaCleqv;除不熔子矿物外,S型包裹体均一温度为197~436℃,盐度变化于7.45%~19.30% NaCleqv和31.71%~49.22% NaCleqv。晚阶段流体包裹体均一温度集中于125~225℃,盐度介于0.5%~7.25% NaCleqv之间。估算的早、中阶段流体捕获压力分别为63~117MPa和12~67MPa,推测最大成矿深度为4.7km。上述流体包裹体研究表明成矿流体由早阶段高温、富CO₂的岩浆热液演化为晚阶段低温、贫CO₂的大气降水热液。这种高温、富CO₂的岩浆热液可视为大陆内部体制斑岩成矿系统的标志性特征,以区别于岩浆弧区同类矿床高温、贫CO₂的岩浆热液。通过对比东秦岭-大别钼矿带典型斑岩成矿系统,认为成矿流体中CO₂等挥发组分的含量和围岩性质(化学成分、结晶程度、抗剪抗压程度等)是控制矿体空间定位的重要因素。     

河北省安妥岭斑岩型钼矿床围岩蚀变特征

文章从安妥岭斑岩型钼矿床的地质、蚀变特征及蚀变分带研究入手,认为硅化和钾长石化岩石的钼含矿性最强,硅化和钾长石化与钼成矿关系密切.蚀变类型有:硅化、钾化、绢云母化、青磐岩化（绿泥石-绿帘石-碳酸盐化）、水黑云母化、黄铁矿化等,各种类型互相过渡,互相迭加,呈现了多期多阶段的蚀变特征.研究表明,围岩蚀变始终伴随着钼成矿作用...     

Fluid evolution of the Yuchiling porphyry Mo deposit,East Qinling,China

The Yuchiling Mo deposit, East Qinling, China, belongs to a typical porphyry Mo system associated with high-K calc-alkaline intrusions. The pure CO₂ (PC), CO₂-bearing (C), aqueous H₂O-NaCl (W), and daughter mineral-bearing (S) fluid inclusions were observed in the hydrothermal quartz. Based on field investigations, petrographic, microthermometric and LA-ICP-MS studies of fluid inclusions, we develop a five-stage fluid evolution model to understand the ore-forming processes of the Yuchiling deposit. The earliest barren quartz ± potassic feldspar veins, developed in intensively potassic alteration, were crystallized from carbonic-dominant fluids at high temperature (> 416 °C) and high pressure (> 133 MPa). Following the barren quartz ± potassic feldspar veins are quartz-pyrite veins occasionally containing minor K-feldspar and molybdenite, which were formed by immiscible fluids at pressures of 47–159 MPa and temperatures of 360–400 °C. The fluids were characterized by high CO₂ contents (approximately 8 mol%) and variable salinities, as well as the highest Mo contents that resulted in the development of quartz-molybdenite veins. The quartz-molybdenite veins, accounting for > 90% Mo in the orebody, were also formed by immiscible fluids with lower salinity and lower CO₂ content of 7 mol%, at temperatures of 340–380 °C and pressures of 39–137 MPa, as constrained by fluid inclusion assemblages. After the main Mo-mineralization, the uneconomic Cu-Pb-Zn mineralization occurred, as represented by quartz-polymetallic sulfides veins consisting of pyrite, molybdenite, chalcopyrite, digenite, galena, sphalerite and quartz. The quartz-polymetallic sulfide veins were formed by fluids containing 5 mol% CO₂, with minimum pressures of 32–110 MPa and temperatures of 260–300 °C. Finally, the fluids became dilute (5 wt.% NaCl equiv) and CO₂-poor, which caused the formation of late barren quartz ± carbonate ± fluorite veins at 140–180 °C and 18–82 MPa.It is clear that the fluids became more dilute, CO₂-poor, and less fertile, with decreasing temperature and pressure from quartz-pyrite to late barren veins. Molybdenite and other sulfides can only be observed in the middle three stages, i.e., quartz-pyrite, quartz-molybdenite and quartz-polymetallic sulfide veins. These three kinds of veins are generally hosted in potassic altered rocks with remarkable K-feldspathization, but always partly overprinted by phyllic alteration. The traditional porphyry-style potassic–phyllic–propylitic alteration zoning is not conspicuous at Yuchiling, which may be related to, and characteristic of, the CO₂-rich fluids derived from the magmas generated in intercontinental collision orogens.Among the fluid inclusions at Yuchiling, only the C-type contains maximum detectable Mo that gradationally decreases from 73 ppm in quartz-pyrite veins, through 19 ppm in quartz-molybdenite veins, and to 13 ppm in quartz-polymetallic sulfide veins, coinciding well with the decreasing CO₂ contents from 8 mol%, through 7 mol%, to 5 mol%, respectively. Hence it is suggested that decreasing CO₂ possibly results in decreasing Mo concentration in the fluids, as well as the precipitation of molybdenite from the fluids. This direct relationship might be a common characteristic for other porphyry Mo systems in the world.The Yuchiling Mo deposit represents a new type Mo mineralization, with features of collision-related setting, high-K calc-alkaline intrusion, CO₂-rich fluid, and unique wall-rock alterations characterized by strong K-feldspathization and fluoritization.     

黑龙江金厂斑岩型富钴矿床钴赋存状态和富集规律研究

斑岩型矿床作为典型的岩浆热液型矿床, 为我国及世界提供了大量的铜、钼、金, 以及铼、硒、碲等关键矿产。然而目前尚无典型富钴斑岩型矿床的报道。黑龙江金厂矿床为一大型斑岩型金矿, 探明金资源量76t, 伴生铜资源量4683t。金厂矿化类型可分为隐爆角砾岩筒型、裂控型和细脉浸染型, 前期研究揭示角砾岩型矿化伴生钴的富集。手持X射线荧光分析结果显示金厂矿床J0角砾岩型矿石中存在明显的钴富集, 钴含量为237×10^-6~5256×10^-6。扫描电镜和电子探针分析揭示钴主要以类质同象形式在黄铁矿中富集, 其次赋存在硫镍钴矿和辉砷钴矿中。根据黄铁矿产状与共生矿物组合, 将黄铁矿分为三种不同的类型: Ⅰ型、Ⅱ型和Ⅲ型黄铁矿。Ⅰ型黄铁矿为早期生成的与磁铁矿共生的自形黄铁矿, 并可进一步分为钴均匀富集型(I-1)和核部富钴型(I-2)两个亚类。Ⅱ型黄铁矿为晚期生成的半自形-自形黄铁矿, 多被黄铜矿、石英、碳酸盐矿物包裹, 可进一步分为边部富钴型(Ⅱ-1)、幔部富钴型(Ⅱ-2)和具有复杂钴环带型(Ⅱ-3)三个亚类。Ⅲ型黄铁矿为晚期石英-黄铁矿脉中的半自形-自形黄铁矿, 内含石英或硅酸盐矿物包裹体。含Ⅰ型黄铁矿的样品钴含量最高(约1800×10^-6~5200×10^-6), 含Ⅱ型黄铁矿的样品钴含量中等(约800×10^-6~1600×10^-6), 而含Ⅲ型黄铁矿的样品中钴含量相对较低(约240×10^-6~360×10^-6)。早期形成的样品具有较高的钴含量, 说明钴的富集可能主要发生在矿床形成的早期。值得注意的是含有Ⅰ型黄铁矿的矿石最具钴资源开发潜力, 选矿过程中应留意此类型矿石。通过总结前人发表的金厂矿床硫、氢-氧、铅、铼-锇和氦同位素数据, 作者提出金厂矿床中的钴极有可能来源于深部的幔源岩浆。本文对金厂矿床富钴特征的研究将为斑岩型富钴矿床提供范例。

     

Geochemical signature of porphyries in the Baogutu porphyry copper belt, western Junggar, NW China

The Baogutu porphyry copper belt lies in the Darbut transitional island arc of the western Junggar, in the western section of the Central Asian Orogenic Belt in NW China. Our new petrographic results for the ore-bearing porphyry stocks in the Baogutu porphyry copper belt recognize them as diorite porphyry stocks rather than the granodiorite porphyry stocks as previously identified. The copper mineralization is hosted in the diorite, diorite porphyries and related breccias of the diorite porphyry stocks.Geochemical data indicate that the ore-bearing porphyries have a predominantly intermediate composition with a transitional character from tholeiite to calc-alkaline, and are enriched in large ion lithophile elements (LILE) and depleted in high field strength elements (HFSE) with a clear negative Nb anomaly. REE patterns show distinct enrichments in LREE relative to HREE. The rocks also exhibit high initial εNd(t) (+ 2.7 to + 6.3) ratios and low initial ⁸⁷Sr/⁸⁶Sr values (0.70359–0.70397). Many samples are chemically similar to adakites (e. g. Yb < 1.9 ppm, Y < 18 ppm, Sr/Yb > 20, ⁸⁷Sr/⁸⁶Sr < 0.7045). These data are consistent with a transitional island arc from immature arc to mature arc and suggest that the ore-bearing porphyry system was derived from the partial melting of multiple sources including oceanic crust and a subduction-modified mantle wedge, with melts undergoing significant crystal fractionation during convergence between the paleo-Junggar ocean and the Darbut arc.     

黑龙江金厂金矿流体地球化学特征

通过对黑龙江省金厂金矿床内包裹体的研究,对比不同矿化程度岩石中包裹体特征,认识到矿化程度与岩浆-流体的演化程度有密切的关系。矿化主要为黄铁矿化,还见有黄铜矿、方铅矿、闪锌矿、毒砂等硫化物矿物,主要呈脉状、条带状及浸染状产出。矿化程度高的钻孔岩芯内,包裹体类型发育完整,流体包裹体、熔融包裹体、熔-流包裹体均有发现。进一步研究发现,矿化与岩浆的结晶分异作用、流体的沸腾作用及流体的混合作用关系密切。分异作用使成矿物质得到富集,沸腾与混合作用使矿质进一步富集并沉淀析出。