Stratiform copper deposits and interactions with co-existing atmospheres, hydrospheres, biospheres and lithospheres

Fundamental evidence from world-class stratiform copper deposits repeatedly indicates that they originated by a two-stage mineralization process: a syn-diagenetic enrichment of the host sediment in iron sulfide, followed by a sub-surface addition of copper during early diagenesis of the sediment. In contrast to the previously favored syngenetic hypothesis, which suggested an open equilibration between atmosphere, hydrosphere, biosphere and upper lithosphere during mineralization, the two-stage model implies that only the initial deposition of iron sulfides should take place with open exchanges between the upper “spheres”. The sub-surface emplacement of copper should occur in relative isolation from surface environments and, therefore, the occurrence and distribution of stratiform copper deposits through time and space should not be used to make direct interpretations of contemporaneous conditions in the upper “spheres”.     

新疆阿尔泰克因布拉克铜锌矿床地质特征及成矿作用

克因布拉克中型铜锌矿床赋存于早二叠世花岗岩外接触带的上志留统-下泥盆统康布铁堡组黑云石英片岩、变质石英砂岩中。矿床的形成经历了夕卡岩期、热液期和表生期,铜锌矿主要形成于热液期。矿石中石英和方解石流体包裹体划分为H_2O-NaCl型和H_2O-CO_2(±CH_4/N_2)-NaCl型。成矿温度变化于146～448℃,在170℃、270℃和350℃出现峰值;流体盐度变化于0.2%～46.9%NaCl_(eq),峰值为1.5%NaCl_(eq)和5.5%NaCl_(eq);流体的密度0.55～1.19g/cm~3。硫化物的δ~(34)S集中变化于-8.4‰～1.9‰,峰值为0‰,表明硫来自岩浆。石英和方解石δD_(SMOW)介于-130‰～-79‰,δ~(18)O_(SMOW)值介于8.0‰～11.6‰,δ~(18)O_(H2O)值为-1.7‰～4.43‰,表明成矿流体主要是岩浆水,混合大气降水。方解石中δ~(13)C_(PDB)变化于-5.3‰～-1.1‰,暗示碳来自花岗质岩浆。成矿时代为早中二叠世,成矿作用与花岗质岩浆期后的热液活动有关。     

Experiment on morphological and hydraulic adjustments of step-pool unit to flow increase

Exceptional flood events with a return period of about 50 years can be destructive to step-pool channel segments. However, field investigations and flume experiments have not examined the hydraulic and morphological feedbacks of step-pool morphology during unsteady hydrographs of exceptional flood events. We performed a series of flume experiments with a manually constructed step model, perturbed with three hydrographs that varied in the rate of water supply change. The bed texture, topography, flow regimes, surface flow field and water depth were characterized and measured as the flow rate was increased during the experiments. A distinct pool feature emerged downstream of the manually constructed step when the flow rate exceeded the threshold scaled to the peaks of ordinary flood events in well-graded mountain streams. The pool feature was modified in several different ways with flow rate increase. The bed surface steadily coarsened, micro-bedforms developed and became more pronounced, the bed topography became more spatially complex based on analysis using the Hurst exponent, and last, pool depth steadily increased. Pool modification was also linked to the flow regime: the impinging jet regime led to grain size segmentation in the pool while the jump regime contributed to decelerating flow velocity. The steeper rising limb of hydrograph led to a less developed pool feature, with smaller sized micro-bedforms in the pool bottom to outlet, and higher discharge threshold for distinct coarsening and scouring in the pool. The estimated energy dissipation within the step-pool unit decreased as a power function from low to high flow, quantified as the ratio h_c/H_S, where h_c is the critical water depth and H_S is scour depth. Our results highlight the interaction between morphology, hydraulics, and energy dissipation of step-pool unit and the crucial role of hydrograph shape on the interaction during flow increase © 2019 John Wiley & Sons, Ltd.     

新疆阿尔泰铁木尔特铅锌矿床流体包裹体研究及地质意义

铁木尔特中型铅锌矿是阿尔泰山南缘克兰盆地内的重要VMS型矿床。矿床赋存于上志留统-下泥盆统康布铁堡组上亚组第二岩性段,容矿岩石为大理岩、绿泥石英片岩、变钙质粉砂岩、夕卡岩。矿体呈似层状和透镜状。矿床的形成经历了喷流沉积期、叠加改造期和表生期。石英、长石、方解石和石榴子石中包裹体类型主要为液体包裹体,在石英中另出现了气体包裹体、纯气体包裹体、含子矿物多相包裹体、含液体CO2的三相包裹体和两相CO2包裹体。喷流沉积期成矿流体均一温度变化于150～330℃,其峰值是165℃和285℃,成矿流体盐度(NaCleq)为4%～16%,流体密度为0.77～0.97g/cm3,流体阳离子主要以Na+为主,次之为K+,阴离子以Cl-为主,其次是SO42-,气相成分主要是H2O和CO2。叠加改造期均一温度范围是150～480℃,峰值为285℃,盐度(NaCleq)为2.2%～17.08%和33.93%～47.2%,流体密度变化于0.61～1.03g/cm3之间,流体阳离子主要以Na+为主,次为K+、Mg2+、Ca2+,阴离子以Cl-为主,其次是SO42-,气相成分主要是H2O和CO2,其次为N2、CH4,含有少量C2H6。     

新疆包古图斑岩铜矿床成矿流体及成矿物质来源——来自硫、氢和氧同位素证据

包古图大型斑岩铜矿位于准噶尔盆地西缘。铜矿化主要呈浸染状、细脉浸染状分布于似斑状(石英)闪长岩、闪长玢岩、隐爆角砾岩和少量花岗闪长岩中。依据矿脉的穿插关系和矿物组合,成矿过程经历了黑云母-钾长石-钠长石阶段、石英-硫化物阶段和石英碳酸盐阶段。矿脉中石英的δDSMOW值介于-107‰～-86‰,δ18OSMOW值变化于11.3‰～16.2‰,δ18OH2O值为4.4‰～9.3‰,表明成矿流体来源为深源的岩浆水。硫化物的δ34S值介于-5.1‰～0.7‰,平均为-1.8‰,表明硫来源于深部岩浆或地幔。结合Ⅱ、Ⅲ和Ⅴ号含矿岩体锆石LA-ICP-MSU-Pb年龄及辉钼矿Re-Os年龄,推断包古图铜矿床成矿作用发生在晚石炭世,与中酸性斑岩体的侵入有密切成因关系。     

阿尔泰南缘克朗盆地铁木尔特花岗岩体年龄、地球化学特征及成因

铁木尔特黑云母花岗岩出露于阿尔泰造山带南缘克朗盆地北西侧,岩体主要为黑云母花岗岩。锆石的SHRIMPU-Pb定年结果表明该岩体结晶年龄为459±4.9Ma。岩石具有高的SiO_2(71.92%～76.58%)和Al_2O_3(12.92%～14.55%)含量,富碱(K_2O+Na_2O=7.09%～8.11%)、高钾(K_2O/Na_2O=1.1～1.62)、低P_2O_5(0.14%)和MgO+FeO(5%)含量,强过铝质(ACNK=1.13～1.34);富集LREE和Th、U、Pb,贫Ba、P、Sr、Ti、Nb,呈现明显的Eu负异常(δEu=0.33～0.53);并具有低的Al_2O_3/TiO_2(100)比值和高的CaO/Na_2O(0.3)比值。以上特征表明该岩体属高钾钙碱性高温型强过铝花岗岩。同时岩石具有低的Sr初始值(~(87)Sr/~(86)Sr=0.701727～0.709951)和相对高的ε_(Nd)(459Ma)(-1.43～-0.98)值,两阶段Nd模式年龄较为均一(t_(2DM)=1.2～1.3Ga)。岩体的原始岩浆可能是富含白云母和黑云母的变泥质岩在大于875℃的条件下脱水熔融的产物,在部分熔融过程中有磷灰石、斜长石、钛铁矿等矿物的残留,并混入少量的幔源物质。结合阿尔泰南缘的区域地质背景综合分析,推测岩体形成于俯冲作用的初期,可能是在挤压背景下由于局部伸展减压以及异常地幔和深部热流不均匀上升提供的热影响发生的部分熔融产生。     

Heterogeneous Chemistry and the O3 Budget in the Lower Mid-Latitude Stratosphere

A photochemical box model including a detailed heterogeneous chemistrymodule has been used to analyze in detail the effects of temperature andaerosol surface area on odd oxygen production/depletion in the lowerstratosphere at 30° S. Results show that for background aerosolloading, the hydrolysis of BrONO₂ and N₂O₅are most important atall temperatures studied except when the temperature falls below about205 K, when ClONO₂ hydrolysis becomes most important. Thisprocessing leads to removal of active nitrogen to form nitric acid andenhancement of HO_x, BrO_x, ClO_x levels. Detailed O₃ budgets asa function of temperature are presented showing how ozone loss andproduction terms vary with changes in stratospheric sulfate aerosol loadingfor the individual families. For (most) aerosol loading levels, thelargest ozone losses occurred at warmer temperatures due to the strongtemperature dependence of the NO_x ozone-destroying reactions. Theexception to this occurred for the conditions representative of volcanicloading, which showed a strong increase in ozone destruction due toincreases in destruction from the ClO_x and HO_x families.The ozoneproduction term k[NO][HO₂] did not show a strong dependence oneithertemperature or aerosol loading, due to the offsetting effect of reducedNO_xand increased HO_x concentrations.     

Variable hillslope-channel coupling and channel characteristics of forested mountain streams in glaciated landscapes

Channel morphology of forested, mountain streams in glaciated landscapes is regulated by a complex suite of processes, and remains difficult to predict. Here, we analyze models of channel geometry against a comprehensive field dataset collected in two previously glaciated basins in Haida Gwaii, B.C., to explore the influence of variable hillslope–channel coupling imposed by the glacial legacy on channel form. Our objective is to better understand the relation between hillslope–channel coupling and stream character within glaciated basins. We find that the glacial legacy on landscape structure is characterized by relatively large spatial variation in hillslope–channel coupling. Spatial differences in coupling influence the frequency and magnitude of coarse sediment and woody material delivery to the channel network. Analyses using a model for channel gradient and multiple models for width and depth show that hillslope–channel coupling and high wood loading induce deviations from standard downstream predictions for all three variables in the study basins. Examination of model residuals using Boosted Regression Trees and nine additional channel variables indicates that ~10 to ~40% of residual variance can be explained by logjam variables, ~15–40% by the degree of hillslope–channel coupling, and 10–20% by proximity to slope failures. These results indicate that channel classification systems incorporating hillslope–channel coupling, and, indirectly, the catchment glacial legacy, may present a more complete understanding of mountain channels. From these results, we propose a conceptual framework which describes the linkages between landscape history, hillslope–channel coupling, and channel form. © 2018 John Wiley & Sons, Ltd.     

What controls the disequilibrium state of gravel-bed rivers?

A river at equilibrium is described by a statistically-stationary mean bed elevation profile that arises in response to steady supplies of relief, water and sediment. Outside of the profile shape, how is the equilibrium state of a river most reliably identified and rigorously defined? Motivated by a proposed link between equilibrium and physical processes, we use scaling theory to develop the dimensionless channel response number ξ=KU_b/U_p. ξ is a metric for the local disequilibrium state of gravel-bed mountain streams, which reflects a balance between the rate of topographic adjustment U_b, and the rate of bed sediment texture adjustment U_p. The coefficient K can take one of two forms depending on choice of length scale for topographic adjustment. We hypothesize that equilibrium occurs where and when ξ≈O(1), and consequently, disequilibrium is the more general state captured by conditions of ξ≉O(1). The rates U_b and U_p are controlled by the mechanics of sediment deposition and entrainment at the local scale of the channel width. The extent to which either process regulates disequilibrium depends on the bed strength, which is set by the time-varying grain size distribution and packing. We use flume experiments to understand ξ and find that in the limit ξ>>1, the time-varying response of an experimental channel depends sensitively on the spatially-averaged bed shear stress ratio τ/τ_ref. When τ/τ_ref≈1.5, U_b was the dominant control on disequilibrium. However, when τ/τ_ref≈2.0, U_p contributed more significantly to disequilibrium. These results suggest that after an upstream supply perturbation, the equilibrium timescale is governed by U_p, which we show is consistent with expectations from linear damping theory. Our experimental test of ξ is promising, but inconclusive with respect to our hypothesis. This uncertainty can be readily addressed with numerical or additional physical experiments. © 2019 John Wiley & Sons, Ltd.