Ion microprobe analysis of oxygen isotope ratios in quartz from Skye granite: healed micro-cracks,fluid flow,and hydrothermal exchange

 Quartz grains in hydrothermally altered granites from the Isle of Skye are highly heterogeneous and not equilibrated in oxygen isotope ratio at the 20 μm scale. Ion microprobe analysis of one grain shows a gradient of 13‰ over 400 μm and a greater range in δ ¹⁸O than all quartz previously analyzed on the Isle of Skye. Other crystals from the same outcrop are homogeneous. Digitized cathodoluminescence images reveal patterns of magmatic zoning and brittle fracturing not otherwise detectable. The ion probe analysis correlates low δ ¹⁸O values on a micro-scale to one set of healed cracks. Thus, quartz exchanges oxygen isotopes primarily by solution and reprecipitation along fractures, in contrast to more reactive feldspar that appears to exchange from the grain boundary inward. Macroscopic models of isotope exchange are not realistic for these rocks; the flow of hydrothermal fluids was heterogeneous, anisotropic and crack controlled. Received: 23 October 1995/Accepted: 9 April 1996     

High integrated fluid/rock ratios during metamorphism at Naxos: evidence from carbon isotopes of calcite in schists and fluid inclusions

Calcite in schists of the metamorphic complex at Naxos is depleted both in ¹³C and in ¹⁸O with respect to massive marbles. This effect is attributed to isotope exchange with circulating CO₂-rich fluids, which had an >0.5 according to fluid inclusions. The carbon isotopic composition of the calcites is close to equilibrium with fluid inclusion CO₂ at metamorphic temperatures. Mass balance calculations assuming initial ¹³C values of 0 for calcite and –5 for the fluid, give integrated fluid/rock volume ratios between 0.1 and 2.0. Such high fluid/rock ratios are supported by observations on the distribution of CO₂/H₂O ratios of fluid inclusions, carbon isotopic compositions of fluid inclusion CO₂ and oxygen isotope systematics of silicates.     

岩石变形、流体压力与热液成矿关系的研究现状

地壳中岩石的变形模式受构造应力、流体压力和上覆岩层重力共同作用的影响。岩石组成和构造应力的大小、方向决定着岩石的变形过程,同时岩石的破裂还受先存断裂构造的影响。流体压力增大,岩石可以发生水力破裂,而引起水力引张破裂的条件是σ1-σ3<4T和Pf=σ3+T。随着深度的增加,受地温梯度的影响,岩石由脆性变形向韧性变形转变。在无流体超压影响的情况下,脆韧性转换的温度在300~450℃之间,大约在地壳15km处。当流体压力和应变速率增大时,韧性条件下的岩石变形行为由韧性向脆性变化,脆韧性转变的深度随之增大。从构造角度探讨热液成矿作用,热液矿床形成的深度与流体压力、应变速率、裂隙的发育、介质的渗透率、温度变化等相关。岩石断裂的类型和方向影响岩石的渗透率,提供流体运移的通道和聚集场所,控制矿床形成的深度、位置和矿体产状。     

岩石变形、流体压力与热液成矿关系的研究现状

地壳中岩石的变形模式受构造应力、流体压力和上覆岩层重力共同作用的影响。岩石组成和构造应力的大小、方向决定着岩石的变形过程,同时岩石的破裂还受先存断裂构造的影响。流体压力增大,岩石可以发生水力破裂,而引起水力引张破裂的条件是σ1-σ3<4T和Pf=σ3+T。随着深度的增加,受地温梯度的影响,岩石由脆性变形向韧性变形转变。在无流体超压影响的情况下,脆韧性转换的温度在300~450℃之间,大约在地壳15km处。当流体压力和应变速率增大时,韧性条件下的岩石变形行为由韧性向脆性变化,脆韧性转变的深度随之增大。从构造角度探讨热液成矿作用,热液矿床形成的深度与流体压力、应变速率、裂隙的发育、介质的渗透率、温度变化等相关。岩石断裂的类型和方向影响岩石的渗透率,提供流体运移的通道和聚集场所,控制矿床形成的深度、位置和矿体产状。     

An absolute paleotemperature record from 10 to 6 Ka inferred from fluid inclusion D/H ratios of a stalagmite from Vancouver Island, British Columbia, Canada

By using continuous helium flow during the crushing of calcite speleothem samples, we are able to recover liberated inclusion waters without isotopic fractionation. A paleotemperature record for the Jacklah Jill Cave locality, Vancouver Island, BC, was obtained from a 30-cm tall stalagmite that grew 10.3-6.3 Ka ago, using δ¹⁸O values of the crushed calcite and of the inclusion water as inferred from its δD. It is found that the locality experienced mean annual temperature variations up to 11 °C over a 4-Ka period in the early Holocene. At the beginning of the period, local temperature quickly increased from a minimum of ∼1 °C to around 10 °C, but this early climate optimum, about 3 °C warmer than today, only lasted for ∼1200 years. About 8.6 Ka ago, temperature had declined to ∼7 °C, approximately the same as the modern cave temperature. Since then, the study area has experienced only minor temperature fluctuations, but there was a brief fall to ∼4 °C at around 7 Ka ago, which might be caused by a short lived expansion of local alpine glaciers. The long-term T-dependence of δD was 1.47‰/°C, identical to the value in modern precipitation.     

Isotopic constraints on fluid/rock ratios in carbonate rocks: Barite-sulfide mineralization in the Schwaz Dolomite, Tyrol (Eastern Alps, Austria)

The significance of isotopic data on constraining the physical conditions of fluid-rock interaction and mineralization processes in carbonate rocks is discussed, based on the example of barite-tetrahedrite mineralization in Lower Devonian platform carbonates of the Western Greywacke Zone (Tyrol, Austria). Available strontium, oxygen, carbon and sulfur isotopic data are complemented with oxygen isotopic data for barite. Barites are homogeneous in δ¹⁸O_V-SMOW and δ³⁴S_CDT with values of + 15.4 and + 23.5‰, respectively. Their ⁸⁷Sr/⁸⁶Sr ratios vary between 0.7128 and 0.7113 for the first generation and between 0.7117 and 0.7123 for younger remobilization. The dolomitic host rock shows a significant variation in Sr, O and C isotopic composition between non-mineralized and mineralized zones: ⁸⁷Sr/⁸⁶Sr ratios vary between 0.7076 and 0.7133, δ¹⁸O_V-SMOW-values between +28.11 and +20.65‰, and δ¹³C_PDB-values between −1.15 and + 3.06‰. Fluid/rock volume ratios on the order of 1.3–3.2 are calculated for open-system behaviour by modelling Sr, O and C isotopic shifting capacities. The isotope data combined with other geological evidence support the following genetic model: Subsequent to synsedimentary sulfide mineralization during an Early Devonian rifting stage, collision tectonics in Carboniferous time led to the expulsion of Ba- and Sr-rich orogenic brines, which evolved from metamorphic fluids consisting essentially of H₂O and some CH₄, into an external sedimentary fold-and-thrust belt. The brines remobilized the synsedimentary sulfides, mixed with meteoric waters in the platform carbonates, reacted with evaporitic horizons and finally caused the recrystallization of dolomite and the precipitation of Sr-rich barite in structurally weak zones at 70–130°C. During the later Alpine orogeny supergene oxidation products were formed, and sulfates, sulfides and carbonates were further remobilized into late faults and fractures.     

Stable-isotope and solute-chemistry approaches to flow characterization in a forested tropical watershed,Luquillo Mountains,Puerto Rico

The prospect of changing climate has led to uncertainty about the resilience of forested mountain watersheds in the tropics. In watersheds where frequent, high rainfall provides ample runoff, we often lack understanding of how the system will respond under conditions of decreased rainfall or drought. Factors that govern water supply, such as recharge rates and groundwater storage capacity, may be poorly quantified. This paper describes 8-year data sets of water stable isotope composition (δ²H and δ¹⁸O) of precipitation (4 sites) and a stream (1 site), and four contemporaneous stream sample sets of solute chemistry and isotopes, used to investigate watershed response to precipitation inputs in the 1780-ha Río Mameyes basin in the Luquillo Mountains of northeastern Puerto Rico. Extreme δ²H and δ¹⁸O values from low-pressure storm systems and the deuterium excess (d-excess) were useful tracers of watershed response in this tropical system. A hydrograph separation experiment performed in June 2011 yielded different but complementary information from stable isotope and solute chemistry data. The hydrograph separation results indicated that 36% of the storm rain that reached the soil surface left the watershed in a very short time as runoff. Weathering-derived solutes indicated near-stream groundwater was displaced into the stream at the beginning of the event, followed by significant dilution. The more biologically active solutes exhibited a net flushing behavior. The d-excess analysis suggested that streamflow typically has a recent rainfall component (∼25%) with transit time less than the sampling resolution of 7 days, and a more well-mixed groundwater component (∼75%). The contemporaneous stream sample sets showed an overall increase in dissolved solute concentrations with decreasing elevation that may be related to groundwater inputs, different geology, and slope position. A considerable amount of water from rain events runs off as quickflow and bypasses subsurface watershed flowpaths, and better understanding of shallow hillslope and deeper groundwater processes in the watershed will require sub-weekly data and detailed transit time modeling. A combined isotopic and solute chemistry approach can guide further studies to a more comprehensive model of the hydrology, and inform decisions for managing water supply with future changes in climate and land use.     

The role of volatile exsolution and sub-solidus fluid/rock interactions in producing high Fe/Fe ratios in siliceous igneous rocks

Highly differentiated igneous rocks can, in some cases, have ⁵⁶Fe/⁵⁴Fe ratios that are significantly higher than those of mafic- to intermediate-composition igneous rocks. Iron isotope compositions were obtained for bulk rock, magnetite, and Fe silicates from well-characterized suites of granitic and volcanic rocks that span a wide range in major- and trace-element contents. Sample suites studied include granitoids from Questa, N.M. (Latir volcanic field) and the Tuolumne Intrusive Series (Sierra Nevada batholith), and volcanic rocks from Coso, Katmai, Bishop Tuff, Grizzly Peak Tuff, Seguam Island, and Puyehue volcano. The rocks range from granodiorite to high-silica granite and basalt to high-silica rhyolite. The highest δ⁵⁶Fe values (up to +0.31‰) are generally restricted to rocks that have high Rb (>100 ppm), Th (>∼15 ppm) and SiO₂ (>70 wt.%) but low Fe (<2 wt.% total Fe as Fe₂O₃) contents. Magnetite separated from these rocks has high δ⁵⁶Fe values, whereas Fe silicates have δ⁵⁶Fe values close to zero. Although in principle crystal fractionation might explain the high δ⁵⁶Fe values, trace-element ratios in high-δ⁵⁶Fe igneous rocks indicate that crystal fractionation is an unlikely explanation. The highest δ⁵⁶Fe values occur in volcanic and plutonic rocks that contain independent evidence for fluid exsolution, including sub-chondritic Zr/Hf ratios, suggesting that loss of a low-δ⁵⁶Fe ferrous chloride fluid is the most likely explanation for the high δ⁵⁶Fe values in the bulk rocks. Based on magnetite solubility in chloride solutions and predicted Fe isotope fractionations among Fe silicates, magnetite, and ferrous chloride fluids, the increase in δ⁵⁶Fe values of bulk rocks may be explained by isotopic exchange between magnetite and , which predicts an increase in the δ⁵⁶Fe values of magnetite upon fluid exsolution. This model is consistent with the δ⁵⁶Fe values measured in this study for bulk rocks, as well as magnetite and Fe silicates. Our results suggest that fluid exsolution from siliceous hydrous magmas, which sometimes produce porphyry-style Cu, Mo, or Cu-Au mineralization, may be traced using Fe isotopes.     

The correlation of reaction and isotope fronts and the mechanism of metamorphic fluid flow

 Infiltration of a metabasite sill from Islay, Scotland by an H₂O-CO₂ fluid caused (1) modification of δ¹⁸O and (2) carbonation at the sill margins. Maps of δ¹⁸O and reaction progress were constructed from a 20 × 47.7 metre sample grid across the sill. The grid consisted of 300 samples, spaced at m, dm and cm intervals, many of which were analysed for both δ¹⁸O and reaction progress. The δ¹⁸O was determined by laser fluorination of whole rock silicate powders and reaction progress was determined by rapid field-based measurement of % calcite (“fizz-o-meter”, Skelton et al. 1995). Reaction and isotope fronts outlined tube-like features that emanate from the sill margin and discrete nodes that, although detached from the sill margin in two dimensions, are thought to represent sections through similar tubes in three dimensions. We envisage that these protrusions are the fossil record of metamorphic “fluid pathways” whereby fluid permeated the sill. Isotope and reaction fronts are found to correlate spatially as predicted by a modified form of the chromatographic equation which describes this envisaged geometry, that is where isotopic and reactive transport in the fluid phase are facilitated by advection along specific fluid pathways and transverse diffusion in the surrounding rock. These fluid pathways consist of bundles of anastomosing grain boundary channels or micro-cracks, which are thought to propagate through transient cyclic infiltration, reaction, porosity enhancement and fracturing. This mechanism is self-perpetuating and accentuates random perturbations at the sill margin to form the observed tubes. We argue that this is the earliest stage of the infiltration process which has affected metabasites of the SW Scottish Highlands and that subsequent shear deformation of the reacted rims of these pathways, has caused their re-orientation and juxtaposition to form the reacted sill margins described by Skelton et al. (1995). Received: 17 February 1998 / Accepted: 6 December 1999     

不同侧压力系数下裂隙网络岩体非线性渗流特性

基于人工裂隙网络模型,展开一系列不同边界荷载作用下含不同交叉点个数的裂隙网络渗流试验。针对所有试验工况,模型进水口水压力范围均为0～0.6 MPa,侧压力系数均由1.0增加至5.0。试验结果表明：裂隙网络体积流速和水力梯度之间的相关性可以通过Forchheimer函数进行拟合,拟合方程中线性和非线性项系数均随着侧压力系数的增加逐渐增大,而随着裂隙网络交叉点个数的增加逐渐减小;渗流试验过程中,非线性效应系数E和水力梯度J之间的相关性可采用一个幂指数函数进行描述,随着水力梯度的增加,非线性效应系数逐渐增大;随着侧压力系数的增加,裂隙网络临界水力梯度呈现逐渐增大的趋势,对于所有裂隙网络交叉点个数（1～12）,当侧压力系数由1.0增加至5.0,临界水力梯度由0.63～12.13增加至6.01～81.55;提出数学模型 对归一化导水系数 随水力梯度的增大而减小的特征进行分析,随着侧压力系数的增加,两者之间的拟合曲线逐渐上移,拟合系数 整体呈现逐渐增大的趋势。裂隙网络的等效渗透系数随侧压力系数的增加逐渐降低。     

Self-organizing thermal fluid flow in fractured crystalline rock: a geochemical and theoretical approach to evaluating fluid flow in the southern Idaho batholith,USA

Thermal springs in the Idaho batholith (USA) discharge at discrete locations along a 50+ km reach of the Middle Fork of the Boise River (MFBR). Recharge water flows through Basin and Range extension fractures where it is heated by the geothermal gradient and ultimately discharges from the damage zone of the trans-Challis faults located near the bottom of the MFBR. Stable isotopes of water, ¹⁴C groundwater ages, fracture and fault orientations, fracture volume changes due to chemical evolution, and recharge area calculations suggest that the thermal springs issue from individual hydrothermal systems and that they are self-organizing. Water evolves chemically along flow paths, dissolving feldspars and precipitating secondary minerals. Secondary minerals accumulate in less-efficient fractures and are flushed from the more efficient ones. Flow-area calculations using heat-flow, exponential decay-of-porosity, and curve-intersection methods show that many of the thermal systems extend beyond their immediate topographic watershed, and that some capture water from adjacent watersheds. Geochemical/flow feedback loops that provide a mechanism for self-organization are modeled using PHREEQC, and positive and negative fracture volume changes are calculated. Criteria for identifying self-organizing granitoid thermal groundwater systems are suggested.     

革新钻井液技术以促进干热岩产业化开发

我国干热岩资源丰富,利用系数高,可为电力提供稳定基础荷载,被认为是能够担负起能源革命重任的可再生清洁能源,其规模开发对我国实现“碳达峰和碳中和”具有重要意义。然而,经历近半个世纪,目前世界范围内仅有少量利用EGS技术开发的干热岩示范项目有微量发电,实现产业化目标尚有许多技术瓶颈。通过研究EGS开发过程和钻井液技术,笔者提出：EGS钻井过程中存在钻井液漏失。因此,钻井液组分自身、钻井液与岩屑或井壁岩石、钻井液与热储裂缝表面岩石,在高温高压下会发生各种理化反应,生成新的物质。这些新的物质可能会沉淀在井壁和裂缝表面,甚至可能与井壁或裂缝表面岩石固结成一体,降低裂缝的有效空间,甚至封堵裂缝,且难以清除,使热储导流能力极大降低,难以达到发电要求的流量。因此,革新钻井液技术理念,研究EGS高温高压环境下钻井液组分和岩屑与温压之间的相互关系及其对钻井液性能的影响,利用先进的计算机数据统计、分析和计算技术,对钻井液性能、钻井液在井筒的流动特性以及钻井液与热储岩石的配伍性进行精准预测和控制,避免或减少钻井液漏失以及钻井液在热储环境下与岩石的反应,消除钻井液对热储伤害,提高渗透率,可能是干热岩产业化的技术突破。     

Modelling dynamic breakage in rock blocks with different elongation and flatness ratios upon impact

The two crucial shape factors (elongation ratio and flatness ratio) of brittle particles may influence the dynamic breakage of brittle particles upon impact. Hence, three-dimensional discrete element method simulations of brittle rock blocks with different shapes upon normal impact were performed. The simulated results indicate that the elongation ratio, that is, ratio of width to length and flatness ratio, that is, ratio of thickness to width can significantly affect the breakage of brittle rock blocks. Three fracture mechanisms, that is, fragmentation, horizontal tensile fracture and vertical tensile fracture, were revealed, which determine the dynamic breakage of rock blocks. The fragmentation results in numerous single-sphered fragments with velocities even larger than 2 times of the initial velocities. Fragmentation can provide a buffering effect at high impact velocities of larger than 4 m/s. With an increasing elongation ratio or flatness ratio, the phenomenon of fragmentation gradually disappears. The reflection of a compression stress wave results in horizontal tensile fracture. The expansion in the plane perpendicular to the impact velocity results in vertical tensile fracture.     

Fluid–rock interaction at the roots of an Eopaleozoic epithermal system, Sierra Norte de Córdoba, Argentina: Paragenesis, thermometry and fluid sources

A deep epithermal vein system hosted in Late Proterozoic to Cambrian granodiorite has been identified in the Sierra Norte de Córdoba, the easternmost range of the Sierras Pampeanas Orientales of Argentina. The vein swarm extends over an area of 3 km² parallel to a mylonitic belt and formed in fractured granodiorite. Thicknesses of veins are less than 0.5 m and their visible strike length is less than 100 m. Veins are either barren or weakly mineralized in base-metal sulfides. Most veins have mineral associations dominated by calcite and quartz with lesser amounts of chlorite, sericite, pyrite, and minor illite. In other less exposed albite-rich, adularia-bearing veins, chalcopyrite, bornite, galena, sphalerite, chalcocite and covellite may occur. The widespread occurrence of bladed calcite without any petrographic or microthermometric evidence of boiling implies that this particular habit of calcite may also develop under sub-near boiling fluid conditions. Thermometric calculations based on fluid inclusion data, chlorite composition and oxygen isotopes in the quartz–calcite pair, constrain the formation of the system between 300 and 350 °C, at pressures between 42 and 64 MPa (1.5–2.3 km). Stable isotope data suggest that W/R interaction might have been the most probable mechanism of alteration, involving the participation of meteoric fluids; nevertheless, the metallic signature of some weakly mineralized veins as well as intermediate fluid inclusion salinities favor a magmatic input and a mixed origin for the fluids. Textures and mineral associations, as well as the absence of evidence of boiling in fluid inclusions, all suggest that the silica–carbonate vein system formed deeper than typically shallow Au and Ag-bearing boiling solutions. A 485 (±25) Ma lamprophyre dike crosscuts some of these veins locally producing metasomatic reactions and skarn formation, which constrains the age of the hydrothermal system to the Cambrian-Early Ordovician time span.     

同一岩石试样的Lu-Hf和Sm-Nd快速分离及国家岩石标准物质的Hf-Nd同位素比值精确测定

本文报道基于Li_2B_4O_7熔融样品、采用AG50W-X8和HDEHP组合或RE和HDEHP组合色谱交换柱,对同一岩石试样快速分离Sm-Nd-Lu-Hf的方法。用这两种方法对国际岩石标准BHVO-2、GSP-2和JB-1进行了Lu-Hf、Sm-Nd分离和~(143) Nd/~(144)Nd、~(176)Hf/~(177)Hf测定,并测定了BHVO-2、JB-1和JB-3的Lu/Hf和Sm/Nd比值,获得的结果在误差范围内与这些样品的参考值一致。同时,我们对国家岩石标准物质GBW07109、GBW07110和GBW07113进行了多次平行分析,首次获得了这些岩石标准的Nd-Hf同位素结果。     

The genesis of the west shropshire orefield: Evidence from fluid inclusions,sphalerite chemistry,and sulphur isotopic ratios

The Pb + Zn + Ba veins of West Shropshire, England, occupy fractures in Ordovician and Precambrian rocks of the Shelve Inlier. Precipitation of sphaleritic ores was succeeded by galena + baryte mineralization, with chalcopyrite also occurring late in the mineralizing episode. Three generations of sphalerite are recognized, and second being chemically zoned with distinct Fe + Cd-rich growth zones. Associated with these iron-rich bands are smaller (∼ 10 μm) zones rich in indium (>1.0 wt%) and copper, electron electron probe microanalyses suggesting coupled substitution of Cu⁺ + In⁺³ in the ZnS. Based on the sequence of growth zones and their chemistry a sphalerite stratigraphy can be recognized within the orefield. Fluid inclusions studies reveal the mineralizing fluids to be highly saline (18–30 wt% CaCl₂ equivalent) Na + Ca-richbrines, with mineralizing temperatures in the range 200–120°C. A trend from higher temperature-low salinity to low temperature-high salinity fluids with time is recognized. Sulphide sulphur isotopic ratios are consistent and suggest a ΔS³⁴S_H2S of the mineralizing fluid of 10%, while ³⁴S_baryte values are in the range + 14 to + 19%, indicating separate sulphate and sulphide sulphur sources. The mineralogical, fluid inclusion, and isotopic data suggest the saline fluids rose into an open plumbing system where mineral precipitation was mainly controlled by fluid cooling. The baryte however, formed due to mixing with oan overlying sulphate-bearing reservioir. Theree possible fluid sources are considered, namely: Lower Carboniferous seawater, basinal brines, and metamorphic fluids. However, the information available does not allow the source to be positively identified.     

粤北书楼丘矿床围岩蚀变特征与流体成矿作用

文章以粤北长江铀矿田书楼丘矿床矿体外围蚀变岩石为研究对象,系统地将流体水岩作用导致的蚀变划分为4期11种类型.以各类蚀变在水平方向的发育程度、组合变化等为依据,将蚀变岩划分为矿化中心带、矿旁强蚀变带、矿旁弱蚀变带、正常花岗岩4个分带.以各分带蚀变岩石岩相学、矿物学、岩石学以及元素地球化学特征变化为依据,探讨流体作用与铀...     

岩石样品中低含量铂族元素和锇同位素比值的高精度测量方法

铂族元素（Os,Ir,Pt,Ru,Rh,Pd)具有强亲铁性和强亲铜性,为一组地球化学性质相近的相容元素,铂族元素包含两个同位素衰变体系（^190Pt-^186Os和^187Re-^187Os)。近年来,铂族元素和Re-Os同位素在研究各类不同地持作用过程中,尤其是在地幔岩石的研究中,作用独特,效果显著。由于地幔岩石的铂族元素含量较低,因此高精度,高灵敏度的分析测试方法的研究就显得十分重要。以往的分析方法（如常规的ICP－MS和中子活化分析方法）,对含10^-9-10^012级低含量铂族元素的产品分析精度一般较差（＞15％－100％）。所采用的分析流程通常也无法同时获得样品的铂族元素含量和Os同位素比值。本文采用新的熔样方法（HAP－S高温高压釜酸溶法）,新的化学流程（溶剂萃取和阴离子交换树脂柱）和新的分析仪器（多接收等离子体质谱MC－ICPMS和负离子热电离质谱N－TIMS）。用同位素稀释法对低含量地幔橄榄岩样品同时测定的铂族元素含量和Os同位素比值,获得了高精度的分析结果。对所分析的地橄榄样品中的铂族元素分配曲线和Os同位素组成的地质意义进行了初步探讨。