库车坳陷古近纪石盐岩空间展布及找钾意义

新疆库车坳陷古近纪发育巨厚的蒸发岩沉积,厚度从几十米至上千米不等。主要蒸发岩沉积(特别是石盐岩沉积)发生在古新世-始新世的库姆格列木群沉积期。依据3Dmine矿业工程软件、库车坳陷地形点三维坐标统计数据、部分钻井数据(包括孔位、孔深、孔斜)、石盐岩层在钻井中的沉积厚度及蒸发岩沉积旋回,对坳陷库姆格列木群蒸发岩沉积期石盐岩空间展布进行研究,绘制库车坳陷古新统-始新统石盐岩空间分布模型,探讨盆地找钾意义。通过石盐岩空间模型展布特征分析,石盐岩体与库车坳陷的地形特征和构造特征紧密相关,石盐岩受构造挤压并于与地形的总体起伏基本一致。从石盐岩体空间模型南北向剖面变化规律分析,古新世-始新世,库车坳陷西部出现2个蒸发岩沉积中心,分别位于西盐山口盐场一带和拜城凹陷。为库车次级古盐湖发育区,而钾盐的富集一般产于大的坳陷当中的次级构造单元,为有利的找钾区域。     

塔西南坳陷中新生代蒸发岩沉积初探

通过资料搜集、蒸发岩野外露头地质调查、石盐岩沉积特征分析及盐类矿物学研究,对塔里木盆地塔西南坳陷中新生代蒸发岩的分布、层位、盐类矿物组合、成因进行了初步探讨。塔西南坳陷石盐岩沉积呈透镜体状,主要沿西昆仑山前分布,常含有褐红色、灰绿色泥砾,泥砾岩性与吐依洛克组下段岩性一致,推测应为吐依洛克组沉积晚期海退期成盐,其层位应归属于吐依洛克组上段。石盐岩透镜体在横向分布上不连续,反映了当时塔西南坳陷内部可能存在多个古盐湖次级凹地,其在干旱气候条件下经浓缩蒸发成盐。蒸发岩矿物除石盐、石膏外,还见有杂卤石、钙芒硝等,其中杂卤石可能为后期富钾卤水交代原生石膏的产物,而乌泊1井石盐表面大量的次生钙芒硝可能为盐湖后期石盐析出阶段含钙地下水缓慢持续补给盐湖的产物。     

古盐湖卤水温度对钾盐沉积的控制作用探讨

古盐湖卤水的温度对钾盐沉积的控制作用的定量研究是钾盐成矿机理分析的重点和难点。本文分析和测试陕北盐盆奥陶系马家沟组、四川盆地三叠系嘉陵江组、云南兰坪-思茅盆地白垩系及老挝沙空那空盆地白垩系等八个含盐系的石盐岩中的流体包裹体,并利用均一温度计算了古盐湖的蒸发速率。若以老挝白垩纪时盐湖的蒸发速率为标准值100,陕北奥陶纪、四川三叠纪、云南白垩纪的蒸发速率标准值分别为54、68和90,而目前在老挝和云南白垩系都找到了一定规模的钾盐矿,因此高温(气温及水温)是盐湖成钾的有利条件,在卤水演化成钾的过程中可以起到重要的"催化"作用。     

新疆库车盆地古近纪—新近纪盐湖成钾与靶区预测

库车前陆盆地位于塔里木盆地北部,属于副特提斯域,古近纪受副特提斯海海水补给,古近纪—新近纪发育巨厚蒸发岩。研究显示,库车盆地始新世和中新世古盐湖卤水已演化至钾盐析出阶段,在地层中广泛发现了原生钾盐矿物,如钾石盐、光卤石、杂卤石等;通过岩芯岩屑地球化学及矿物学分析,基本确定了至少3个富钾层或成钾层位,其中始新统中上部两个和中新统中上部一个,钾离子含量最高达3%,另外,上新统可能存在一个成钾层位。本文在综述此前库车盆地构造、蒸发岩、盐类矿物学、地球化学与盐湖沉积等研究基础上,建立了新的库车盆地古盐湖构造- 沉积演变、成钾模式;提出了4个钾盐成矿区带,即北部克拉苏成矿带、中部秋里塔克成矿带、南部沙雅构造沉降成矿带以及东部阳霞凹地成钾区,这些关键认识为库车盆地的钾盐勘查提供了重要的理论和科学依据。     

江陵凹陷沙钾3井古近系沙市组地球化学特征及成钾指示

在盐湖沉积演化过程中,钾镁盐在盐类矿物沉积的中晚期才开始结晶析出。因此,研究含盐系地层中盐类矿物的沉积地球化学特征,不仅可以从侧面获取岩盐的沉积物物质来源和成盐期古卤水蒸发浓缩程度等地球化学信息,而且可以直接揭示古盐湖期钾盐富集趋势及规律。目前,除在江陵凹陷的古近系沙市组等含盐系内发现了富钾卤水外,还在中-南部的钻孔盐矿盐岩中,发现了微量钾石盐和钾石膏,这些说明该凹陷古近纪具有成钾潜力。本文通过对SK3井蒸发岩特征研究及岩芯中K、Mg、Cl、Br离子含量与Br×103/Cl系数的垂向变化分析,揭示古盐湖浓缩演化与钾盐富集趋势,进一步揭示该层段沉积时期及所在凹陷古盐湖卤水钾的富集程度。     

库车前陆盆地古近系蒸发岩岩石学、矿物学与成钾环境分析

库车盆地内古近系—新近系发育巨厚的蒸发岩沉积, 尤其是盆地的中部和西部盐层发育好, 厚度大, 局部盐层己暴露地表, 是找寻各种盐类矿床及钾盐的有利地区。DZK01孔是近年来在库车盆地实施的一口以找钾为目的的科研探井。本文主要通过对钻孔古近系蒸发岩岩芯样品进行岩石学及矿物学特征研究, 进而对盆地成钾环境进行分析。DZK01孔古近系蒸发岩以含泥砾石盐岩为主, 含泥砾石盐岩为构造成因, 是古盐湖高度浓缩的产物。盆地古近系蒸发岩以沉积石盐为主, 钻孔中含钾矿物为钾石膏, 钾石盐和光卤石, 同时含钾矿物的发现证明了库车盆地古盐湖可能达到钾盐析出阶段。通过样品分析可知, 库车盆地古近纪时期古盐湖沉积环境为封闭的浅湖沉积环境, 盐湖发育过程中有五次较大规模的淡化事件, 盐类物质得到很好的聚集, 具有良好的成钾环境。     

北羌塘坳陷早—中侏罗世雀莫错期岩相古地理特征与成钾意义

北羌塘坳陷下—中侏罗统雀莫错组广泛发育一套巨厚的蒸发岩沉积。本文依据羌科 1井、羌资 16井和地表露头资料,通过地层划分对比、沉积微相分析、沉积序列研究等方法,对北羌塘坳陷早—中侏罗世岩相古地理环境进行了恢复,分析了成钾条件。研究表明,北羌塘坳陷早—中侏罗世受班公湖—怒江中特提斯洋盆进一步扩张的影响,进入了被动大陆边缘盆地演化阶段,裂陷作用在坳陷内形成的两个裂陷槽控制着雀莫错组沉积。羌塘中部地带的隆起,使得海水仅从双湖狭小的通道向北浸漫。受海水和淡水的共同作用,在坳陷内发育一套咸水—半咸水陆缘近海湖泊相沉积。北羌塘坳陷雀莫错期海（湖）平面和古气候经历了多次旋回,半封闭的古构造格局,频繁的海侵的盐类物源补给和极端炎热干旱气候条件耦合下,北羌塘坳陷雀莫错期古盐湖具备成盐成矿条件,其中半岛湖—普若岗日底隆起区是成盐成钾的有利区。     

蒸发岩序列中氯化物盐的氯同位素分馏效应及应用——兼论塔里木盆地、柴达木盆地古代岩盐的沉积阶段

卤水蒸发析盐到晚期阶段,才有可能析出溶解度极大的钾盐类矿物,因此在一个成盐盆地要找到钾盐矿床,除判断物源特征外,还必须找到最晚沉积阶段的区域和层位。本文通过对实验室配制溶液和盐湖卤水蒸发析出的不同氯化物矿物、钾盐矿床沉积序列不同阶段盐类矿物对比分析,讨论了氯同位素的分馏规律。结果表明,不同蒸发浓缩阶段的氯化物盐,氯同位素发生显著分馏。一般钾盐沉积层位的石盐δ³⁷Cl值小于0,钾石盐及其以后沉积的氯化物δ³⁷Cl值小于-0.5‰,特别是钾石盐以后析出的氯化物更为偏负,光卤石一般小于-1.00‰,而钾盐沉积阶段之前早期沉积石盐的δ³⁷Cl值显著偏正。因此,δ³⁷Cl值是判断岩盐沉积阶段的有效指标。基于此,对塔里木库车盆地第三纪、莎车盆地白垩-第三纪部分代表性盐矿点以及柴达木盆地西部不同构造单元、不同层位第三纪岩盐沉积做了氯同位素分析。初步结果表明塔里木莎车盆地晚白垩世岩盐的沉积阶段明显晚于库车盆地第三纪沉积,特别是莎车盆地喀什次级凹陷δ³⁷Cl值最低,大部分样品小于-0.5‰,推测该区成盐古卤水已浓缩到晚期或接近晚期钾盐沉积阶段,应是今后一重点开展钾盐找矿的区域。柴达木盆地油墩子、南翼山地区中新统、上新统蒸发岩沉积序列δ³⁷Cl值普遍偏正,推测当时卤水浓缩演化可能只达到石盐沉积阶段,浓缩到后期阶段的富K⁺、Mg²⁺盐溶液随西部隆起迁移到柴达木盆地南部地区,因此认为第三纪地层虽然石盐沉积层位多,厚度大,但找到大规模钾盐矿床的可能性不大。     

新疆莎车盆地上白垩统-古近系蒸发岩沉积及成钾前景

新疆莎车盆地发育大范围的蒸发岩。蒸发岩沉积与海侵-海退密切相关,自晚白垩世—渐新世以来,莎车盆地至少有5次小规模海侵-海退旋回,除阿尔塔什组石膏岩为断续海侵期沉积外,其余基本为海退期沉积。莎车盆地主要的蒸发岩沉积层位为吐依洛克组上段及阿尔塔什组。野外调查显示,吐依洛克组石盐岩露头主要沿西昆仑山前呈长条状分布,基本呈透镜体,阿尔塔什组石膏岩露头则见于盆地大部分地区,包括西昆仑山前、南天山山前及麦盖提斜坡,横向上持续稳定。野外调查及室内分析显示,盐类矿物主要为石盐、石膏、硬石膏,少量杂卤石、钙芒硝及钾石膏。盆地中石盐岩透镜体在横向上的不连续性,可能反应了吐依洛克组沉积晚期西昆仑山前存在多个次级古盐湖凹地,在干旱条件下浓缩成盐,而次级古盐湖在演化过程中大范围巨厚石膏岩的缺失,可能与当时的海退时间极短有关。依据莎车盆地蒸发岩沉积特征、盐类矿物组合、古盐湖演化环境,推测盆地有利的成钾层位为吐依洛克组上段,在乌帕尔一带发现成钾显示,可能为有利的成钾区域;而盆地小范围、厚度不大的石盐沉积及埋藏深度大为不利的找钾因素。     

江汉盆地大型富锂卤水矿床成因与资源勘查进展:综述

古近纪时期,华南江汉盆地的潜江凹陷和江陵凹陷发育盐湖,沉积了巨厚的蒸发岩,并形成和储藏了富锂、钾、铷、铯、溴、碘等元素的卤水资源,这些元素含量达到工业品位或综合利用品位;富锂卤水属于深层地下卤水型锂矿资源,镁锂比值低,是非常优质的锂资源。本文总结了江汉盆地大地构造特征、火成岩及古气候背景,论述了古盐湖沉积岩相特征、富锂卤水水化学、分布及储层特征、卤水中锂的来源与富集机理、卤水型锂矿成矿模式以及富锂卤水勘查与开采技术进展,提出了卤水开发利用中存在的问题和解决途径。江汉盆地富锂卤水成因包括:古盐湖锂可能主要来自高温水岩反应产生的富锂热液流体的补给;在干旱的气候下,古湖水不断蒸发浓缩,导致卤水中锂浓缩富集;在盐湖演化末期,逐渐埋藏的盐类晶间富锂卤水被转移至裂隙、砂岩及玄武岩储层中储集;在较高的地热背景值下,埋藏卤水与储层岩石可能发生水岩反应,进一步促进了卤水中锂的富集。江汉盆地深层卤水初步勘查显示,氯化锂资源量已达到大型工业规模,展示了巨大的资源潜力。此外,卤水锂开采技术已基本形成,建议进一步加强富锂卤水的绿色开发技术研究,制定相关勘查开发规范。     

氯化物型钾盐矿床氯同位素地球化学的初步研究

根据国内外许多钾盐矿床大量样品测定的结果,通常石盐（岩）的３７Ｃｌ／３５Ｃｌ比值和δ３７Ｃｌ值高于钾石盐（岩）,而钾石盐（岩）又高于光卤石（岩）,说明这些蒸发岩是在不同水体、不同浓缩阶段形成的,是氯同位素分馏作用长期进行的结果。这些蒸发岩的氯同位素组成与其Ｂｒ、Ｋ、Ｍｇ含量变化有密切关系。今后在我国找钾过程中,应把氯同位素组成及其Ｂｒ、Ｋ、Ｍｇ含量结合起来,作为找钾标志考虑。     

Geochemical and isotopic constraints on the interaction between saline lakes and groundwater in southeast Australia

Major ion and stable isotope geochemistry allow groundwater/surface-water interaction associated with saline to hypersaline lakes from the Willaura region of Australia to be understood. Ephemeral lakes lie above the water table and locally contain saline water (total dissolved solids, TDS, contents up to 119,000 mg/L). Saline lakes that lack halite crusts and which have Cl/Br ratios similar to local surface water and groundwater are throughflow lakes with high relative rates of groundwater outflows. Permanent hypersaline lakes contain brines with TDS contents of up to 280,000 mg/L and low Cl/Br ratios due to the formation of halite in evaporite crusts. These lakes are throughflow lakes with relatively low throughflow rates relative to evaporation or terminal discharge lakes. Variations in stable isotope and major ion geochemistry show that the hypersaline lakes undergo seasonal cycles of mineral dissolution and precipitation driven by the influx of surface water and evaporation. Despite the generation of highly saline brines in these lakes, leakage from the adjacent ephemeral lakes or saline throughflow lakes that lack evaporite crusts is mainly responsible for the high salinity of shallow groundwater in this region.     

Stable chlorine isotopes in Phanerozoic evaporites

Modern seawater has a uniform δ³⁷Cl value (0.0‰), with an exception in the upper current of the Bosphorus (0.4‰). Marine halite ranging in age from Cambrian to Miocene has δ³⁷Cl values of 0.0 ± 0.9‰, with most of the data in the range 0.0 ± 0.5‰. Mean δ³⁷Cl values differ measurably between basins, with no evident relationship to basin size or to age. Smaller evaporite bodies have the largest δ³⁷Cl ranges. Potash facies halite has mean δ³⁷Cl values lower than those of halite facies salt in the East Siberia and Zechstein basins. The bulk δ³⁷Cl of bedded halite preserving sedimentary textures cannot be shifted measurably after deposition under plausible natural conditions. During the Phanerozoic, a detectable change in the δ³⁷Cl values of the oceans is unlikely as a result of Cl fluxes to and from the mantle and evaporites. In halite, the values of δ³⁷Cl that cannot be explained by fractionation occurring on crystallization are best explained by the addition of non-marine Cl with δ³⁷Cl ≠ 0.0‰ to evaporite brine.     

浙江江山寒武纪沉积相研究

浙江江山寒武纪为一套深色海相碳酸盐沉积，包含了湖相和台地相组成的海进相序。本文在江山一带沉积相研究的基础上，结合区域地质资料，探讨了浙皖海盆东南缘的区域古地理格局的演变规律及其构造意义     

Origin and geochemistry of Miocene marine evaporites associated with red beds: Great Kavir Basin,Central Iran

During the Cenozoic numerous shallow epicontinental evaporite basins formed due to tectonic movements in the Northern Province of the Central Iran Tectonic Zone (the Great Kavir Basin). During the Miocene, due to sea‐level fluctuations, thick sequences of evaporites and carbonates accumulated in these basins that subsequently were overlain by continental red beds. Development of halite evaporites with substantial thickness in this area implies inflow of seawater along the narrow continental rift axis. The early ocean basin development was initiated in Early Eocene time and continued up to the Middle Miocene in the isolated failed rift arms. Competition between marine and non‐marine environments, at the edge of the encroaching sea, produced several sequences of both abrupt and gradual transition from continental wadi sediments to marginal marine evaporites in the studied area. These evaporites show well‐preserved textures indicative of relatively shallow‐brine pools. The high Br content of these evaporites indicates marine‐derived parent brines that were under the sporadic influence of freshening by meteoric water or replenishing seawater. However, the association of hopper and cornet textures denotes stratified brine that filled a relatively large pool and prevented rapid variations in the Br profile. Unstable basin conditions that triggered modification of parent brine chemistry prevailed in this basin and caused variable distribution patterns for different elements in the chloride units. The presence of sylvite and the absence of Mg‐sulphate/chlorides in the paragenetic sequence indicate SO₄−depleted parent brine in the studied sequence. Petrographic examinations along with geochemical analyses on these potash‐bearing halites reveal parental brines which were a mixture of seawater and CaCl₂‐rich brines. The source of CaCl₂‐rich brines is ascribed to the presence of local rift systems in the Great Kavir Basin up to the end of the Early Miocene. Copyright © 2007 John Wiley & Sons, Ltd.     

An evaporated seawater origin for the ore-forming brines in unconformity-related uranium deposits (Athabasca Basin, Canada): Cl/Br and δCl analysis of fluid inclusions

Analyses of halogen concentration and stable chlorine isotope composition of fluid inclusions from hydrothermal quartz and carbonate veins spatially and temporally associated with giant unconformity-related uranium deposits from the Paleoproterozoic Athabasca Basin (Canada) were performed in order to determine the origin of chloride in the ore-forming brines. Microthermometric analyses show that samples contain variable amounts of a NaCl-rich brine (Cl concentration between 120,000 and 180,000 ppm) and a CaCl₂-rich brine (Cl concentration between 160,000 and 220,000 ppm). Molar Cl/Br ratios of fluid inclusion leachates range from ∼100 to ∼900, with most values between 150 and 350. Cl/Br ratios below 650 (seawater value) indicate that the high salinities were acquired by evaporation of seawater. Most δ³⁷Cl values are between −0.6‰ and 0‰ (seawater value) which is also compatible with a common evaporated seawater origin for both NaCl- and CaCl₂-rich brines.Slight discrepancies between the Cl concentration, Cl/Br, δ³⁷Cl data and seawater evaporation trends, indicate that the evaporated seawater underwent secondary minor modification of its composition by: (i) mixing with a minor amount of halite-dissolution brine or re-equilibration with halite during burial; (ii) dilution in a maximum of 30% of connate and/or formation waters during its migration towards the base of the Athabasca sandstones; (iii) leaching of chloride from biotites within basement rocks and (iv) water loss by hydration reactions in alteration haloes linked to uranium deposition.The chloride in uranium ore-forming brines of the Athabasca Basin has an unambiguous dominantly marine origin and has required large-scale seawater evaporation and evaporite deposition. Although the direct evidence for evaporative environments in the Athabasca Basin are lacking due to the erosion of ∼80% of the sedimentary pile, Cl/Br ratios and δ³⁷Cl values of brines have behaved conservatively at the basin scale and throughout basin history.     

A depositional model for the terminal Neoproterozoic–Early Cambrian Ara Group evaporites in south Oman

Abstract Six evaporite–carbonate sequences are recognized in the terminal Neoproterozoic–Early Cambrian Ara Group in the subsurface of Oman. Individual sequences consist of a lower, evaporitic part that formed mainly during a lowstand systems tract. Overlying platform carbonates contain minor amounts of evaporites and represent transgressive and highstand systems tracts. Detailed sedimentological and geochemical investigation of the evaporites allowed reconstruction of the depositional environment, source of brines and basin evolution. At the beginning of the evaporative phase (prograding succession), a shallow-water carbonate ramp gradually evolved into a series of shallow sulphate and halite salinas. Minor amounts of highly soluble salts locally record the last stage of basin desiccation. This gradual increase in salinity contrasts sharply with the ensuing retrograding succession in which two corrosion surfaces separate shallow-water halite from shallow-water sulphate, and shallow-water sulphate from relatively deeper water carbonate respectively. These surfaces record repeated flooding of the basin, dissolution of evaporites and stepwise reduction in salinity. Final flooding led to submergence of the basin and the establishment of an open-water carbonate ramp. Marine fossils in carbonates and bromine geochemistry of halite indicate a dominantly marine origin for the brines. The Ara Group sequences represent a time of relatively stable arid climate in a tectonically active basin. Strong subsidence allowed accommodation of evaporites with a cumulative thickness of several kilometres, while tectonic barriers simultaneously provided the required restricted conditions. Subsidence allowed evaporites to blanket basinal and platform areas. The study suggests a deep-basin/shallow-water model for the evaporites.     

The evolution of marine evaporitic brines in inland basins: The Jordan-Dead Sea Rift valley

Marine-evaporitic brines frequently display Na, Cl and Br concentrations that significantly deviate from seawater evaporation paths, yielding markedly conflicting degrees of evaporation calculated for a specific brine. Here we present 493 new and 33 previously reported analyses of Ca-chloridic waters of Neogene age from the Dead Sea Rift (DSR) valley to explain such offsets. The DSR brines plot along an almost perfect mixing line (R² = 0.990) on a Br/Cl-Na/Cl diagram, extending between two end members A and B. Points A and B are located at Na/Cl = 0.804 and Br/Cl = 0.00193, and at Na/Cl = 0.00773 and Br/Cl = 0.0155, respectively, within the halite and bischofite stability fields.Brines A and B originated in a dual-mode evaporation basin. Brine A formed under the classic lagoon scenario (mode A), with seawater inflow and brine outflow at steady state. Occasional drops in water level, imposed by climatic or tectonic causes, resulted in outflow cutoff and in rapid concentration buildup. The second mode (B) initiated upon equilibration of the activity of water in the brine with the overlying relative humidity, resulting in composition and salinity approaching that of brine B, sustaining it until the next reversal to mode A.Thick evaporite deposits inhibited infiltration of brines A and B into the subsurface terrain, a process that was enabled only when the brine reached the permeable carbonate rock rim and border faults of the basin. Hence, brines that formed during the relatively short shifts from mode A to mode B could not penetrate into the deep subsurface, and bittern minerals that were formed during the frequent mode shifts were dissolved and flushed out into the sea upon the next resumption of outflow.The proposed model accounts for the deviations of brines from the marine evaporitic evolution curve by brine mixing, rather than due to a change in ocean chemistry. It also explains the absence of bittern minerals in the thick halite and gypsum/anhydrite succession, and the compositional gap between the widely different end member hypersaline fluids. This model applies directly to the studied DSR brines and evaporites, but it may be relevant to other inland evaporitic basins.     

江西省九瑞地区黄龙组层、相、位对层控矿床的控制

一、概述九瑞地区位于扬子准地台下扬子台坳之西段,南北分别与江南台隆、淮阳隆起毗邻,处于构造转折部位。已知矿床主要有斑岩型、矽卡岩型和层控型,其中层控型矿床的空间分布受区域地质背景中特定地层、岩相及构造部位的控制,具层、相、位控矿特点。矿床周围有大片志留系、石炭系、二叠系、三叠系地层出露,局部出露奧陶系地层。前奥陶系、侏罗系、白垩系地层分布于西南及东南边缘。区内构造发育史可分为三个阶段,即地槽发展阶段、准地台发展阶段和大陆边缘活动阶段,具多元结构特点。晋宁运动使前震旦纪地槽型沉积褶皱回返转为准地台,形成近EW     

Brines in the Carboniferous Sydney Coalfield,Atlantic Canada

Formation waters within Upper Carboniferous sandstones in the sub-sea Prince and Phalen coal mines, Nova Scotia, originated as residual evaporative fluids, probably during the precipitation of Windsor Group (Lower Carboniferous) salts which underlie the coal measures. Salinity varies from 7800 to 176,000 mg/l, and the waters are Na–Ca–Cl brines enriched in Ca, Sr and Br and depleted in Na, K, Mg and SO₄ relative to the seawater evaporation curve. Br:Cl and Na:Cl ratios suggest that the brine composition corresponds to an evaporation ratio of as much as 30. The brines lie close to the meteoric line on H/O isotopic plots but with a compositional range of δ¹⁸O from −4.18 to −6.99 and of δD from −42.4 to −23.5, distant from modern meteoric or ocean water. Mine water composition contrasts with that of nearby salt-spring brines, which are inferred to have originated through dissolution of Windsor Group evaporites by modern meteoric waters. However, a contribution to the mine waters from halite dissolution and from Br in organic matter cannot be ruled out. Present concentrations of several elements in the brines can be explained by water–rock interaction. The original Windsor brines probably moved up into the overlying coal-measure sandstones along faults, prior to the Late Triassic. The high salinity and irregular salinity distribution in the Phalen sandstones suggests that the brines have undergone only modest dilution and are virtually immobile. In contrast, Prince waters show a progressive increase in salinity with depth and are inferred to have mixed with surface waters. Basinal brines from which these modern formation fluids were derived may have been important agents in base-metal and Ba mineralisation from the mid-Carboniferous onwards, as saline fluid inclusions are common in Zn–Pb sulphide deposits in the region.