甘肃阳山超大型卡林-类卡林型复合式金矿床特征

阳山金矿于世纪之交勘查并扩大为超大微细浸染型金矿,矿床形成受地层、浅成花岗斑岩、韧-脆性剪切构造及热液活动的多种因素的叠加与改造控制,研究认为矿床具有卡林型和类卡林型两种矿化类型特点,卡林型矿化于韧性剪切早、早—中期阶段和晚期阶段,分别出现含砷黄铁矿-毒砂-次显微金-白云石-石英矿化组合及黄铁矿-辉锑矿-石英方解石矿化组合,及Au-As-Sb-Hg的成矿地球化学组合;类卡林型矿化出现在脆性中—晚期阶段,以黄铁矿-毒砂-自然金-碲铋矿-白云石-石英矿化(含黄铜-闪锌-方铅矿)组合为特征,及Au-As-Cu-Pb-Zn-Te-Bi成矿地球化学组合。阳山复合式金矿含矿地层中沉积成岩黄铁矿δ34S为-24.6‰～-29.0‰,早期—早中期韧-脆性剪切金属硫化物矿化产物δ34S值为5.0‰～7.0‰,中—晚期蚀变花岗斑岩中金属硫化物矿化产物δ34S值为-2.9‰～-2.1‰,显示地层中生物硫、强变形造山带地壳硫、少量岩浆硫混入的多源特征。流体包裹体氢氧同位素与硫同位素近同步特征,成矿热液显示地下流体、强烈改造水和少量岩浆水的混合。     

新疆阿图什地区木吉一带的火成碳酸岩——来自地质、地球化学分析的证据

西昆仑木吉西北地区产有一种特殊类型的碳酸盐质岩体。该岩体内发育围岩的捕虏体,并与围岩呈港湾状侵入式接触,其边部发育穿入围岩的岩枝和岩脉,这些地质特征表明这种碳酸盐质岩体实为火成碳酸岩岩体。该碳酸岩在地球化学上具有富CaO、CO2,贫SiO2、TiO2、K2O、Na2O、Al2O3、FeO、Fe2O3、MnO、P2O5的特征,各种稀土和微量元素的含量和稀土元素的总量均很低,轻重稀土元素比值较小,稳定同位素δ18O、δ13C高,显示壳源碳酸岩的成因特点,明显不同于幔源成因的碳酸岩。据上述特征判断,该碳酸岩为沉积碳酸盐岩在内侵幔源岩浆作用下发生熔融而形成的壳源成因的火成碳酸岩。     

Supercontinent evolution and the Proterozoic metallogeny of South America

The cratonic blocks of South America have been accreted from 2.2 to 1.9 Ga, and all of these blocks have been previously involved in the assembly and breakup of the Paleoproterozoic Atlantica, the Mesoproterozoic to Neoproterozoic Rodinia, and the Neoproterozoic to Phanerozoic West Gondwana continents. Several mineralization phases have sequentially taken place during Atlantica evolution, involving Au, U, Cr, W, and Sn. During Rodinia assembly and breakup and Gondwana formation, the crust-dominated metallogenic processes have been overriding, responsible for several mineral deposits, including Au, Pd, Sn, Ni, Cu, Zn, Mn, Fe, Pb, U, P₂O₅, Ta, W, Li, Be and precious stones. During Rodinia breakup, epicontinental carbonate-siliciclastic basins were deposited, which host important non-ferrous base metal deposits of Cu–Co and Pb–Zn–Ag in Africa and South America. Isotope Pb–Pb analyses of sulfides from the non-ferrous deposits unambiguously indicate an upper crustal source for the metals. A genetic model for these deposits involves extensional faults driving the circulation of hydrothermal mineralizing fluids from the Archean/Paleoproterozoic basement to the Neoproterozoic sedimentary cover. These relations demonstrate the individuality of metal associations of every sediment-hosted Neoproterozoic base-metal deposit of West Gondwana has been highly influenced by the mineralogical and chemical composition of the underlying igneous and metaigneous rocks.     

Arsenic-contaminated groundwater from parts of Damodar fan-delta and west of Bhagirathi River,West Bengal,India: influence of fluvial geomorphology and Quaternary morphostratigraphy

Arsenic contamination in groundwater affecting West Bengal (India) and Bangladesh is a serious environmental problem. Contamination is extensive in the low-lying areas of Bhagirathi–Ganga delta, located mainly to the east of the Bhagirathi River. A few isolated As-contaminated areas occur west of the Bhagirathi River and over the lower parts of the Damodar river fan-delta. The Damodar being a Peninsular Indian river, the arsenic problem is not restricted to Himalayan rivers alone. Arsenic contamination in the Bengal Delta is confined to the Holocene Younger Delta Plain and the alluvium that was deposited around 10,000–7,000 years bp, under combined influence of the Holocene sea-level rise and rapid erosion in the Himalaya. Further, contaminated areas are often located close to distribution of abandoned or existing channels, swamps, which are areas of surface water and biomass accumulation. Extensive extraction of groundwater mainly from shallow aquifers cause recharge from nearby surface water bodies. Infiltration of recharge water enriched in dissolved organic matter derived either from recently accumulated biomass and/or from sediment organic matter enhanced reductive dissolution of hydrated iron oxide that are present mainly as sediment grain coatings in the aquifers enhancing release of sorbed arsenic to groundwater.     

粤西河流阶地的分布与特征

依据广东西部超过18条河流、39处河流阶地、至少35个14C、热释光的冲积层测龄数据等情况,可知粤西最多有4级河流阶地(不包括湛江组和北海组阶地);多数河流最高阶地靠近现代主河床分布,深切曲流中有河流阶地,反映近数十万年来河床改道不大;西江在封开有广东高度最高(76 m)的河流阶地,而广东高度最高的地下河阶地是111 m,大致显示出地面与地下剥蚀强度的差异;通常山区河流长度越大,河漫滩和河流阶地的高度越大,河流阶地的级数和级别也常增加;在河流上游的下段和中游的上段,河流阶地的高度最大且级数也最多;在晚更新世之前与后,河谷中下游地区的新构造运动趋势由上升变为稳定或沉降;连滩盆地是广东全新世构造沉降最典型的山间盆地。     

Regional difference of annual precipitation and discharge variation over west China during the last 50 years

Using annual precipitation and discharge data measured in the past five decades,this paper analyzed the regional differences over west China in terms of climate and discharge variations,and investigated the relationship between the regional characteristics and the activities of South and East Asian sum-mer monsoon. Results revealed that the precipitation and discharge in the upper reaches of the Yellow River (Central West China) have a negative correlation with those in Xinjiang (northwest China) and the Yarlung Zangbo River (the upper reaches of the Brahmaputra Rive,southwest China) regions. The geographical patterns of precipitation and discharge variations are different over west China,i.e. the regional climate displays the alteration of dry-wet-dry or wet-dry-wet from north to south in west China. The negative correlation of annual discharges between Xinjiang and the upper reaches of the Yellow River is found statistically significant in the decadal scale,and that between the Yarlung Zangbo River and the upper reaches of the Yellow River is found active in the interannual scale. The regional char-acteristics indicate that the discharge/precipitation variations in the upper reaches of the Yellow River are dominated by the East Asian summer monsoon while their variations in Xinjiang are affected by both the west wind and East Asian summer monsoon.     

Retrieval of source parameters of an event of the 2000 West Bohemia earthquake swarm assuming an anisotropic crust

We propose an inversion scheme for retrieval of characteristics of seismic point sources, which in contrast to common practice, takes into account anisotropy. If anisotropy is neglected during inversion, the moment tensors retrieved from seismic waves generated by sources situated in anisotropic media may be biased. Instead of the moment tensor, the geometry of the source is retrieved directly in our inversion; if necessary, the moment tensor can be then determined from the source geometry aposteriori. The source geometry is defined by the orientation of the slip vector and the fault normal as well as the strength of the event given by the size of the slip and the area of the fault. This approach allows direct interpretation of the source geometry in terms of shear and tensile faulting. It also makes possible to identify volumetric source changes that occur during rupturing. We apply the described algorithm to one event of the 2000 West Bohemia earthquake swarm episode. For inversion we use information of the direct P waves. The structure is approximated by three different models determined from travel-time observations. The models are inhomogeneous isotropic, inhomogeneous anisotropic, and homogeneous anisotropic. For these models we obtain seismic moments M_T = 3.2 − 3.8 × 10¹⁴ Nm and left-lateral near-vertical oblique normal faulting on a N-S trending rupture surface. The orientation of the rupture surface is consistent with fault-plane solutions of earlier studies and with the spatial distribution of other events during this swarm. The studied event seems to be accompanied by a small amount of crack opening. The amount of crack opening is slightly reduced when the inhomogeneous anisotropic model is assumed, but it persists. These results and additional independent observations seem to indicate that tensile faulting occurs as a result of high fluid pressure.     

Geology,Pb Isotope Geochemistry and Ore Genesis of the Liziyuan Gold Deposit,West Qinling Orogen,Central China

The Liziyuan gold deposit, situated on the south side of the Shangdan suture zone, West Qinling Orogen, occurs in metamorphic volcanic rocks(greenschist facies) of the early Paleozoic Liziyuan Group and in Indosinian Tianzishan monzogranite. Orebodies in the Liziyuan gold field are controlled by the ductile-brittle shear zone, and by thrusting nappe faults related to the Indosinian orogeny. In detail, this paper analyzed the geological characteristics of the Liziyuan gold field, and the Pb isotopes of the Lziyuan host rocks, granitoids(Tianzishan monzogranite and Jiancaowan syenite porphyry), sulfides, and auriferous quartz veins by multiple-collector inductively coupled plasma mass spectrometry(MC-ICPMS). In addition, previous data on the sulfur, hydrogen, and oxygen isotopes were employed to discuss the possible sources of the ore-forming fluids and materials, and to further understand the tectonic setting of the Liziyuan gold deposit. The sulfides and their host rocks(Lziyuan Group), Tianzishan monzogranite and Jiancaowan syenite porphyry, and auriferous quartz veins have similar Pb isotopic compositions.Zartman's plumbotectonic model diagram shows that most of the data for the deposit fall near the orogenic Pb evolutionary curve or within the area between the orogenic and mantle Pb evolutionary curves. In the△β-△γ diagram, which genetically classifies the lead isotopes, most of the data fall within the range of the subduction-zone lead mixed with upper crust and mantle. This indicates that a complex source of the ore lead formed in the orogenic environment. The δ~(34)S values of the sulfides range from 3.90 to 8.50‰(average6.80‰), with a pronounced mode at 5.00‰-8.00‰. These values are consistent with that of orogenic gold deposits worldwide, indicating that the sulfur sourced mainly from reduced metamorphic fluids. The isotopic hydrogen and oxygen compositions support a predominantly metamorphic origin of the oreforming fluids, with possible mixing of minor magmatic fluids, but the late stage was dominated by meteoric water. The characteristics of the Liziyuan gold deposit formed in the Indosinian orogenic environment of the Qinling Orogen are consistent with those of orogenic gold deposits found worldwide.     

西昆仑奥依塔格石炭-二叠纪岩浆岩:弧后盆地的产物?

目前对西昆仑石炭-二叠纪火山岩分带性、形成环境、深部地幔源区特征还缺乏较好的约束。在区域地质填图、综合研究的基础上,将西昆仑石炭-二叠纪岩浆岩空间上分为南带、北带。本文展示了北带岩浆岩集中出露的奥依塔格地区玄武岩、辉绿岩、辉长岩的地球化学和Sr、Nd、Pb同位素以及与辉长岩共生的斜长花岗岩的锆石LA-ICP-MS测年数据,以约束该区基性岩形成的时代、构造环境和地幔源区特征,同时与库地玄武岩、阿羌基性火山岩进行了比较。目前的数据表明:(1)斜长花岗岩单颗粒锆石LA-ICP-MS测年得到313.6±1.6Ma、291.6±1.7Ma两组年龄,后者代表斜长花岗岩和辉长岩的侵位时代,前者可能代表玄武岩的年龄。(2)球粒陨石标准化稀土元素配分模式图中,玄武岩显示轻稀土略富集的向右缓倾模式,辉绿岩、辉长岩均为轻稀土略亏损的近平坦型;原始地幔标准化微量元素值均表现为大离子亲石元素相对富集,Nb、Ta谷明显,高场强元素中后半部分呈平坦型模式。(3)地球化学指标显示奥依塔格一带基性岩未受到或很少受到地壳物质混染,样品的Nd、Pb组成可以用来代表地幔源区的成分特点,Nd-Pb、Pb-Pb图解显示其代表的地幔源区具有"Dupal"异常,并于金沙江蛇绿岩中玄武岩代表的地幔源区有较高的一致性。(4)综合岩石地球化学、沉积组合认为奥依塔格基性岩形成于弧后盆地构造环境,区域对比,指出它与库地一些克沟组玄武岩、于田县阿羌组火山岩同为康西瓦-麻扎混杂岩带代表的洋盆向北俯冲,引发弧后盆地扩展的结果。     

新疆西天山备战基性-超基性岩年代学和岩石地球化学研究及其对铁成矿背景的制约

对新疆西天山备战铁矿区附近的基性-超基性岩体———金云母辉石橄榄岩与侵入其中的闪长岩脉进行了年代学和岩石地球化学研究。金云母辉石橄榄岩中金云母~(40)Ar/~(39)Ar坪年龄为298.1±1.9 Ma,该岩石的锆石U-Pb年龄为302.5±1.3 Ma,与备战铁矿的成矿年龄相近。备战金云母辉石橄榄岩具有低Si O_2(42.51%~50.82%)、Al_2O_3(4.87%~7.38%)、Ti O_2(0.25%~0.77%)和全碱(Na_2O+K_2O=0.87%~1.87%)含量,而高Mg O(26.36%~30.17%)、TFe O(12.33%~15.99%)含量的特征,过渡元素丰度(Cr=523×10~(-6)~7 026×10~(-6),Ni=906×10~(-6)~1 088×10~(-6),Co=109×10~(-6)~132×10~(-6))和Mg~#值(0.76~0.79)均较高,表明岩浆经历了橄榄石堆晶作用。由橄榄石最高Fo值(0.79)和岩石的TFe O含量计算得其母岩浆为玄武质岩浆。所有的岩石具有相似的稀土、微量元素配分模式,均呈轻稀土元素富集的右倾型,且重稀土元素较平坦[(Gd/Lu)_N=0.70~2.00],明显富集大离子亲石元素Rb、Ba、U、K,亏损高场强元素Nb、Ta、Zr、Hf和Ti。总体上Sr、Nd同位素较均一,金云母辉石橄榄岩的(~(87)Sr/~(86)Sr)_i=0.704 4~0.704 7,εNd(t)=2.23~3.90,闪长岩(~(87)Sr/~(86)Sr)_i=0.704 4,εNd(t)=3.79~4.07,表明金云母辉石橄榄岩和闪长岩为同源演化的岩石。微量元素特征表明金云母辉石橄榄岩起源于尖晶石相,源区为受俯冲流体或熔体交代的软流圈地幔。结合区域构造背景,推测金云母辉石橄榄岩的形成与西天山造山带在晚古生代的山根拆沉引起的软流圈上涌有关,而备战铁矿晚期成矿事件很可能形成于相同的深部动力学背景下。