龙胜地区镁铁质侵入体:年龄及其地质意义

对镁铁质侵入体进行了单颗粒锆石U-Pb年代学和Sm-Nd同位素示踪研究。结果表明:镁铁质侵入体是起源于长期亏损地幔源区的岩浆在760Ma侵位结晶的产物,其侵位过程中遭受地壳物质的混染。该年龄结果限定了丹洲群地层的沉积上限年龄,并为龙胜地区不存在蛇绿岩套的认识提供重要的年代学制约。镁铁质岩浆的形成、侵位可能与Rodinia超大陆～825Ma裂解之后的另一次裂解事件相联系。     

中天山白石泉镁铁-超镁铁质岩体岩石学与矿物学研究

白石泉地区镁铁一超镁铁质岩体处于塔里木板块前缘活动带与中天山地块接合部位，是中天山地块华力西中期岩浆活动的产物。主要岩石类型有辉石橄榄岩（斜方辉石橄榄岩、斜长二辉橄榄岩）、橄榄辉石岩、橄长岩、辉长岩及角闪辉长岩等，主要造岩矿物为橄榄石、斜方辉石、单斜辉石、角闪石、斜长石及黑云母。橄榄石均为贵橄榄石，其Fo值（78-85）位于含铜镍硫化物矿橄榄石的Fo值范围之内；辉石主要有顽火辉石、古铜辉石、紫苏辉石、透辉石等；斜长石的环带构造较为发育；角闪石的FeO含量随着岩浆的演化逐渐增加。它们与造山带环境中的东疆型镁铁一超镁铁杂岩中的造岩矿物具有相同的特征。这些特征表明了白石泉地区的镁铁一超镁铁质岩体的原始岩浆为高镁的拉斑玄武质岩浆。     

浙东晚中生代壳幔相互作用的新例证——新昌儒岙辉绿岩-花岗岩复合岩体的年代学与地球化学

在浙东新昌地区,新发现了一个由辉绿岩和花岗岩组成的复合岩体。辉绿岩主要由斜长石(An=45～55,50%～60%)、普通辉石(20%～30%)、普通角闪石(10%～15%)等组成,全岩 Ar-Ar 同位素年龄为109.1±2.8Ma;花岗岩主要由石英(25%～30%),钾长石(50%～60%),斜长石(An=20±,10%～15%)及少量的黑云母(<5%)组成,锆石 SHRIMP U-Pb 年龄值为129～109Ma,其最小年龄值109Ma 与辉绿岩的相同,证明辉绿岩和花岗岩近同时冷凝固结。在岩石地球化学上,它们同属钙碱性岩石系列,具有轻稀土元素和大离子亲石元素富集、高场强元素亏损等特点,稀土元素、微量元素配分型式基本相同,(~(87)Sr/~(86)Sr)_i=0.7074～0.7079,ε_(Nd)(t)=-3.5～-4.4,指示它们的微量元素和同位素发生过充分的交换。这与浙东晚中生代玄武岩-流纹岩复合岩流的相似,也与福建沿海同时代复合火成岩的基本一致。它们是起源于受消减作用影响的岩石圈地幔部分熔融而产生的玄武岩浆底侵,并与深融的壳源花岗岩浆相互作用的结果,是壳幔作用的产物。新昌复合岩体的发现与研究,为研究浙东地区和浙闽沿海的壳幔作用和构造-岩浆作用提供了一个新的实例。     

Intrusion–Related Vein Gold Deposits: Types, Tectono-Magmatic Settings and Difficulties of Distinction from Orogenic Gold Deposits

Abstract: A spectrum of intrusion-related vein gold deposits is recognized. Representative examples are described of the following geochemical associations: Au-Fe oxide–Cu, Au–Cu–Mo–Zn, Au–As–Pb–Zn–Cu, Au–Te–Pb–Zn–Cu and Au–As–Bi–Sb. The associated intrusions range from small outcropping stocks to complex batholiths. The different vein associations are believed to reflect the compositions of related intrusions, which themselves characterize distinct tectonic settings. The Au-Fe oxide–Cu and Au–Cu–Mo–Zn associations belong to two broad groups of deposits, Fe oxide–Cu–Au and porphyry Cu–Au, both of which are related to highly oxidized calc-alkaline intrusions emplaced in sub–duction–related arcs. The Au–As–Pb–Zn–Cu association seems to be linked to somewhat less oxidized intrusions emplaced in a similar setting. The Au–Te–Pb–Zn–Cu association, which possesses well-known epithermal counterparts, is also found with highly oxidized intrusions, but of alkaline composition and back-arc location. In contrast, the Au–As–Bi–Sb association, part of a newly recognized class of intrusion-hosted Au–Bi–W–As deposits, is related to relatively reduced intrusions, spanning the boundary between the magnetite– and ilmenite–series. Such intrusions, which may host major bulk-mineable gold deposits, were emplaced along the landward sides of arcs, possibly during lulls in subduction, as well as in continental collision settings. Therefore, a variety of geological environments is prospective for vein and, by extrapolation, other styles of gold mineralization, not all of them fully appreciated in the past. Several features of vein gold deposits, including imprecise relationships to individual intrusive phases, poorly developed mineral and metal zoning, apparent time gaps between intrusion and mineralization and presence of low–salinity, CO₂–rich fluid inclusions, are commonly taken to indicate a non-igneous origin and to be more typical of orogenic (mesothermal) gold deposits generated during accretionary tectonic events. However, several or all of these features apply equally to some intrusion– related vein gold deposits and, therefore, do not constitute distinguishing criteria. The currently popular assignment of most gold-rich veins to the orogenic category requires caution, because of the geological convergence that they show with some intrusion-related deposits. A proper distinction between intrusion-related and orogenic gold deposits is crucial for exploration planning.     

新疆谢米斯台地区小岩体型矿化遥感探测

中酸性小岩体易被地质填图遗漏,严重制约了该类型矿化的发现。在新疆西准噶尔谢米斯台地区找矿工作中,首先利用ETM+数据进行小岩体扫面,进而选取重点区采用ETM+和中巴资源卫星02B HR数据进行分辨率融合后解译、识别中酸性小岩体,并利用主成分分析法提取蚀变遥感异常,结合地质、化探信息综合分析后确定重点检查区域。利用此方法共解译出14个钾质花岗岩和3个黑云母花岗岩小岩体,这些小岩体大多被野外检查所证实。经野外检查发现了5处铜、金矿化点,证实了该方法的有效性。本研究中采用的方法可以为西部地区地质填图和中酸性小岩体型矿产资源勘查提供借鉴。     

吉尔吉斯马克马尔金矿床地质特征及其意义

马克马尔大型金矿床位于吉尔吉斯中天山造山带,属中-酸性侵入体接触交代型金矿床。新疆是中-酸性侵入岩分布广泛地区,目前已发现多处金矿床或矿点分布于中-酸性侵入体内或外接触带。新疆具备这类金矿床的成矿条件和找矿远景,并已找到多纳拉萨依等多个该类型金矿,但目前该类型金矿产地不多,规模不大,笔者通过对马克马尔接触交代型金矿床地质特征的总结,以期对新疆地区该类型金矿床的查找有所帮助。     

Thermal waters in the Lower Yarmouk Gorge and their relation to surrounding aquifers

Sources and mineralization of groundwaters from Cretaceous A7/B2 and B4 limestone aquifers in the Golan and Ajloun Heights are derived from conjoint discussion of stable isotopes of water and sulphate, major ion chemistry, rare earth distribution patterns and the (hydro)geological setting. Isotope fractionation of precipitation was used to derive elevation and continental influence of recharge areas. Positive shift of δ¹⁸O and δ²H occur due to evaporation before replenishment and the interaction with basalts. Major infiltration areas for Golan Heights are the limy foothills of the Mt. Hermon and for the Ajloun Heights the Plateau itself. To a less degree, precipitation infiltrates also the basaltic catchments. Groundwaters are mineralized by water/rock (i) variably altered limestones by diagenesis, (ii) evaporates and seawater brines enclosed in limestone matrix and (iii) locally occurring basaltic intrusiva. In the Yarmouk Gorge, a deep-seated brine of the Ha’on type ascends and mixes with the fresh shallow groundwater.Contrasting the macro chemical composition, REY distribution patterns indicate the lithology of the recharge areas. Infiltration over basalts results in REY patterns distinctly different to those derived from limy catchments.REY and isotope fingerprints prove that water from the Syrian Hauran Plateau is recharging springs and wells in the lowermost Yamouk gorge. The basaltic cover of the Golan Heights is of minor importance for recharge of the underlying A7/B2 aquifer, which becomes recharged at the foothills of Mt. Hermon and gets confined southwards. Even the wells in the basaltic cover receive water from the underlying limestone aquifer.Anomalous heat flux near the Yarmouk gorge and locally in the western escarpment of the Ajloun may be produced by ascending fluids from greater depth and/or by basaltic intrusions.     

Extensional Setting of Hainan Island in Mesoproterozoic: Evidence from Granitic Intrusions in the Baoban Group

The Mesoproterozoic Baoban Group is the oldest basement in Hainan Island and has played an important role in Columbia (Nuna) supercontinent reconstructions. The Mesoproterozoic granitic intrusions in the Baoban Group are the most widely-exposed Precambrian magmatic rocks and are the key to understanding the tectonic settings of Hainan Island and its relationship with the South China Block and the Columbia supercontinent. New LA-ICP-MS zircon U-Pb dating on three mylonitic granite samples from the Tuwaishan and Baoban areas yield ages ranging from 1447 Ma to 1437 Ma, representing the absolute timing of the emplacement of the granitic intrusions. Combined with previously published geochronological data for rocks from the Baoban Group and regional mafic intrusions, it is concluded that the Baoban Group formed at 1460–1430 Ma, coeval with the emplacement of the granitic and mafic intrusions. New in-situ zircon Lu-Hf isotope analyses for the three mylonitic granite samples yielded positive εHf(t) values, ranging from +0.49 to +8.27, with model ages (TCDM) ranging from 2181 Ma to 1687 Ma, suggesting that the granitic intrusions originated from a mixed source of Paleoproterozoic crust with juvenile crust. New zircon trace element data show characteristics of high Th/U values of 0.24–1.50, steep slopes from LREE to HREE and negative Pr, Eu anomalies with positive Ce, Sm anomalies, representing typical magmatic zircons formed in continental crust. Compared with available magmatic and detrital zircon ages from Precambrian rocks in the Cathaysia Block, Yangtze Block and western Laurentia, it is inferred that Hainan Island was separated from both the Cathaysia Block and the Yangtze Block, instead being connected with western Laurentia in the Columbia supercontinent. Considering the decreasing tendency of basin deposition time along the western margin of Laurentia, it is proposed that Hainan Island was located to the north or northwest of the Belt-Purcell Supergroup, along the western margin of Laurentia, during the breakup of the Columbia supercontinent.     

扬子地台西南缘康滇断隆带海孜双峰式侵入岩体年代学、地球化学及其地质意义

海孜辉绿岩-花岗斑岩双峰式侵入岩体位于扬子地台西南缘康滇断隆带中的武定-元江裂陷槽内,本文对海孜辉绿岩和花岗斑岩主要进行了LA-ICP-MS锆石U-Pb定年和地球化学研究。花岗斑岩的定年结果为1764±18Ma,辉绿岩的定年结果为1765±5.4Ma。岩相学及地球化学测定数据显示海孜地区辉绿岩具有细粒和粗粒两种结构,与花岗斑岩之间存在明显的组分间断,形成双峰态,其中花岗斑岩为钙碱性(Si O2=70.93%~73.04%,σ=1.28),辉绿岩属过碱性(Si O2=42.46%~48.26%,σ=15.3),Hf同位素特征表明两者可能均与幔源母岩浆相关。而海孜双峰式分布特征显示大陆裂谷拉张环境的构造背景,暗示海孜岩体是1.7Ga时昆阳裂谷裂解时期产物,与全球Columbia超大陆的裂解事件相呼应。作为扬子地台西南缘首次发现的1.7Ga双峰式侵入岩,海孜双峰式侵入岩的发现具有重要的地质意义。     

豫西矿集区幔枝构造约束下的小岩体成大矿

文章通过分析豫西地区的大量地质矿产资料后发现,区内存在"小岩体成大矿"的规律。认为豫西地区自燕山期以来,随着地幔热柱的演化,区内地壳运动转为伸展活动,地壳减薄、地幔不均衡上隆和中酸性岩浆脉动式上侵;中酸性岩浆脉动式上侵过程打通了深部成矿物质上升的通道,使得含矿流体能够到达地壳上部,并在幔枝构造外围主次级拆离带、岩体内外接触带、构造裂隙等适宜部位集聚成矿。