Negative Haloes and Geochemical Field Systems of Hydrothermal Deposits

Primary haloes of hydrothermal deposits were previously considered as positive haloes. Although it has been recently suggested that primary haloes incude positive and negative ones, almost all the research work on primary haloes has still focused on positive haloes for various reasons. In order to understand the source of ore substances a number of large hydrothermal deposits related to magmatism including porphyry, skarn and vein type deposits have been studied. It has been found that negative haloes exist on the peripheries of positive haloes of a mineral deposit. On the basis of the study the authors propose the concept of the geochemical field system of ore-forming elements of hydrotherreal deposits, i. e., with the orebody as the centre outwards there occur the mineralized field, positive halo field, depleted field and background field successively.     

热液矿床的负晕和地球化学场系

热液矿床原生晕以往都被视为正晕。近年来虽已提出原生晕包括正晕和负晕,但由于多种原因,到目前为止,原生晕的研究几乎仍局限于正晕。作者为研究矿质来源,对一批与岩浆活动有关的斑岩型、夕卡岩型和脉型等大型热液矿床进行了研究,发现在矿床的正晕外围都有成矿元素负晕。根据研究结果还提出了热液矿床成矿元素地球化学场系,即以矿体为中心,向外依次为矿化场、正晕场、降低场和背景场。     

Some aspects of the problem of geochemical methods of prospecting for concealed mineralization

This paper describes a number of different geochemical approaches to the search for concealed ore deposits.The first approach discussed is a broad one that relates mineralization to the types of rock that may occur in a region. Attention is focussed on hydrothermal deposits and their association with specific types of igneous rocks and their differentiation trends.A second considers the control of the structure and physico-chemical properties of the host rocks on the localization of ore bodies. A number of factors, such as effective and total porosity and the brittleness of rocks also plays an important role in determining the nature and extent of dispersion haloes of the elements around ore deposits.In some instances it is possible to predict the presence of ore bodies at depth from the type of composition of metasomatized rocks that occur at the surface.The use of mercury and fluorine in the search for concealed deposits has been given detailed consideration. Methods based on fluorine may be effective in the discovery of skarn, greisen, hydrothermal and rare metal deposits. When using the fluorine content of waters from a taiga-permafrost terrain, it is important to consider the effect of the organic content of the water.In searching for Cu-Ni deposits of the Noril'sk type it is suggested that intrusive complexes characterized by high degrees of differentiation and containing picritic and taxitic facies enriched in Mg, Ni and Co and depleted in alkalis are the most prospective. Ore deposits of this type may have dispersion haloes of Ag, Bi, Zn and Pb which are associated with ore-controlling faults. Magnesian and calcareous skarns, feldspathic and serpentine-chlorite-prehnite rocks may form broad contact haloes with ore-bearing intrusions.The use of gases in prospecting for Cu-Mo deposits in Central Kazakhstan have been investigated with positive results. Gas surveys carried out in conjunction with geophysical methods makes it possible to distinguish zones of Cu-Mo mineralization from zones containing pyrite and carbonaceous material, all of which give similar geophysical responses.The occurrences of uranium in aquifers on the flanks of artesian basins within arid regions is used as an example of the use of geochemical zonation in prospecting. The same approach may be used in prospecting for copper-bearing sandstones.     

Procedure for the evaluation of lithogeochemical anomalies in large-scale mineral exploration

The objective of geochemical exploration is to detect anomalous concentrations of ore elements and evaluate their ore potential. Methods for the detection and evaluation of geochemical anomalies related to exposed deposits are now rather well developed. Recent successes in the development of geochemical exploration methods for blind and shallowly covered hydrothermal mineralization deserve special consideration. They are based on the characteristic features of composition and on the arrangement of primary geochemical haloes. Primary haloes are normally much larger than orebodies proper and thus extend the effective area for anomaly evaluation several fold as compared with ore occurrences themselves.     

The Iberian type of volcano-sedimentary massive sulphide deposits

The Iberian Pyrite Belt, located in the SW Iberian Peninsula, contains many Paleozoic giant and supergiant massive sulphide deposits, including the largest individual massive sulphide bodies on Earth. Total ore reserves exceed 1500 Mt, distributed in eight supergiant deposits (>100 Mt) and a number of other smaller deposits, commonly with associated stockwork mineralizations and footwall alteration haloes. Massive sulphide bodies largely consist of pyrite, with subordinated sphalerite, galena and chalcopyrite and many other minor phases, although substantial differences occur between individual deposits, both in mineral abundance and spatial distribution. These deposits are considered to be volcanogenic, roughly similar to volcanic-hosted massive sulphides (VHMS). However, our major conclusion is that the Iberian type of massive sulphides must be considered as a VHMS sub-type transitional to SHMS. This work is an assessment of the geological, geochemical and metallogenic data available up to date, including a number of new results. The following points are stressed; (a) ore deposits are located in three main geological sectors, with the southern one containing most of the giant and supergiant orebodies, whereas the northern one has mainly small to intermediate-sized deposits; (b) ore deposits differ one from another both in textures and mineral composition; (c) Co and Bi minerals are typical, especially in stockwork zones; (d) colloidal and other primary depositional textures are common in many localities; (e) a close relation has been found between ore deposits and some characteristic sedimentary horizons, such as black shales. In contrast, relationships between massive sulphides and cherts or jaspers remains unclear; (f) footwall hydrothermal alterations show a rough zoning, the inner alteration haloes being characterized in places by a high Co/Ni ratio, as well as by mobility of Zr, Y and REE; (g) ¹⁸O and D values indicate that fluids consist of modified seawater, whereas ³⁴S data strongly suggest the participation of bacterial-reduced sulphur, at least during some stages of the massive sulphide genesis, and (h) lead isotopes suggest a single (or homogeneized) metal source, from both the volcanic piles and the underlying Devonian rocks (PQ Group). It is concluded that, although all these features can be compatible with classical VHMS interpretations, it is necessary to sketch a different model to account for the IPB characteristics. A new proposal is presented, based on an alternative association between massive sulphide deposits and volcanism. We consider that most of the IPB massive orebodies, in particular the giant and supergiant ones, were formed during pauses in volcanic activity, when hydrothermal activity was triggered by the ascent and emplacement of late basic magmas. In these conditions, deposits formed which had magmatic activity as the heat source; however, the depositional environment was not strictly volcanogenic, and many evolutionary stages could have occurred in conditions similar to those in sediment-hosted massive sulphides (SHMS). In addition, the greater thickness of the rock pile affected by hydrothermal circulation would account for the enormous size of many of the deposits. Received: 8 September 1998 / Accepted: 4 January 1999     

Research and application of soil-gas mercury surveys for locating deep uranium orebodies

This paper discusses the distribution of mercury in four kinds of uranium deposits and the form of the corresponding soil-gas mercury haloes. Uranium deposits can be divided into three levels according to their mercury contents. Carbonatite-type uranium deposits are often associated with high levels of mercury, which forms large, high-concentration and high-contrast soil-gas haloes in residual alluvium. Mercury concentration goes up with increasing sampling depths and has been used successfully to locate deep uranium orebodies around siliceous limestone-hosted uranium deposits.     

构造叠加晕结合五方位测井在甘肃省贾公台金矿寻找深部矿体中的应用

贾公台金矿为甘肃党河南山地区规模最大的金矿床。为探索深部矿化、寻找盲矿体,在贾公台矿段开展原生晕研究,建立原生叠加晕轴向分带,发现贾公台金矿具反向分带特征。说明该矿体深部存在多期次成矿作用。结合地井五方位测井,预测深部3 200 m标高以下存在盲矿体。深部钻探发现了厚度大、品位高的多层金矿体,新增金资源量12吨,取得了显著找矿成果。构造叠加晕结合地井五方位测井成功圈定贾公台金矿深部矿体的实践,对同类矿床的深部找矿具有重要指导意义。     

贵州镇宁重晶石矿中硅质岩稀土元素地球化学研究

通过对镇宁泥盆系重晶石矿中硅质岩稀土元素地球化学特征研究,发现硅质岩稀土总量较低,轻稀土富集,δCe呈弱的负异常,δEu呈负异常到正异常,{La/Sm}N和{Gd/Yb}N值表明轻稀土分异强;通过∑REE、Ce/Ce＊、Eu/Eu＊、{La/Ce}N和{La/Lu}N参数综合分析,硅质岩沉积成岩过程中有明显的热水参与,...     

岩(矿)石磁参数与原生晕关系的研究及其地质意义

本文阐述了岩浆热液矿床中含磁性的岩(矿)石磁参数和其些元素原生晕的数据处理。发现岩(矿)石磁性和某些元素热液渗滤晕之间存在着某种关系。通过获取某特征值,可以发掘元素组合、成矿阶段、矿体赋存规律等方面的信息。这些信息,具有很重要的地质找矿意义。     

区域次生地球化学负异常模型及其意义

原生地球化学负异常的研究已经引起重视,特别是前苏联的化探工作者还总结出利用地球化学原生负异常对热液矿床进行普查和评价的准则.但是,由于缺乏可供对比的划分负异常的适当方法,使得对负异常的研究不能系统化,研究结果也不能互相对比,尤其是对于区域水系沉积物测量中发现的负异常研究很少.本文通过对几个地区衬值负异常的分析,系统地探讨了区域性负异常的分布特征、负异常与正异常的关系、负异常的地质意义和找矿信息等.总结出单元素和多元素区域负异常的分布模型.建立了AU和Cu矿床的区域正负、异常模型.提出了地球化学异常是由正异常和负异常组成的.     

相山铀矿成矿古水文地质分析

相山矿田是我国著名的大型热铀矿田。该矿田产于生代相山火山岩盆地古水热系统之中,是水热系统中水－岩相互作用的产物。因此,查明当时的古水文地质条件对于研究矿床成因、指导找矿具有重要意义。本文根据相山地区的地质基础资料、构造演化历史和古气候条件、运用构造、古水文地质分析法,对该矿田进行了古水文地质分期、分区、分析了古地下水的补给区、排泄区和径流途径,并对成矿古水热系统的形成条件进行了探讨。     

个旧老厂Sn-Cu矿床内外接触带矿体原生晕分带与深部矿体预测模型

矿床的原生晕通常形成在矿体周围,与蚀变矿物和矿石矿物同时形成。矿床原生晕的分带规律能够提供较为准确的找矿目标。一些金属矿床的原生晕具有示踪隐伏矿体的作用,从而为探测深埋矿体提供了重要的线索。老厂大型锡多金属矿床是个旧巨型锡多金属矿床的重要组成部分,以广泛发育夕卡岩化矿化为其特征。根据其空间分布夕卡岩矿化可分为两类:内夕卡岩矿化和外夕卡岩矿化。前者发生在侵入体内蚀变带,后者主要形成于侵入体附近的蚀变碳酸盐岩中。它们在地球化学特征上有以下异同:(1)内夕卡岩和外夕卡岩矿体的轴向分带序列(从矿体的头部到尾部)分别为Ag-As-Bi-Cu-F-Pb-Sn-Zn-B→Ba-Co-Cr-Ni-Sb-V→Be-Mo-W和F-B-Ba-W→Cu-Sb-Be-Cr→Sn-Pb-Zn-Ni-Ag→Co-Mo-Bi-As。这表明异常元素的种类具有高度一致性,但轴向分带序列存在很大差异。(2)统计分析表明内夕卡岩矿化具有三种主要成矿元素组合:(a)As-B-Be-Co-Sn组合代表发育在花岗岩内蚀变带的云英岩化有关的锡石-硫化物-电气石蚀变矿化组合;(b)Mo-W代表与高温夕卡岩化相关的辉钼矿-白钨矿矿化组合;(c)Ag-Pb-Cu-Zn代表后期叠加于内蚀变带角银矿-方铅矿-闪锌矿-黄铜矿矿化组合。(3)外夕卡岩矿化也具有三种主要成矿元素组合:(a)Ag-Bi-Sn-Cu代表发育在外夕卡岩带角银矿-辉铋矿-黄锡矿(锡石)-黄铜矿中低温矿化组合;(b)As-Zn-Pb代表发育在外夕卡岩带毒砂-闪锌矿-方铅矿中温硫化物组合;(c)F-Be-W-Mo代表靠近侵入体一侧萤石-绿柱石-白钨矿-辉钼矿高温矿化组合。上述表明矿化具有多期多阶段特点。最后,在原生晕轴向分带序列的基础上,分别建立了内、外夕卡岩带深部矿体预测模型,为深部成矿预测提供强有力工具。     

Genetic Aspects of the Manto-type Copper Deposits Based on Geochemical Studies of North Chilean Deposits

Recent studies on mineralogy, geochronology, fluid inclusion and stable isotope (Pb, Os, S, C, O, Sr) characteristics were reviewed to determine constraints for genetic models of the Chilean manto‐type copper deposits. The Chilean manto‐type deposits are divided into the two geologic categories of the northern areas (Arica–Iquique, Tocopilla–Taltal) and the central areas (Copiapó, La Serena, Santiago). The former is distributed in the coastal range composed of Jurassic andesite‐dominated volcano‐sedimentary piles and younger plutonic intrusions, and yields chalcocite (‐digenite) and bornite as the principal hypogene copper sulfides. The latter is hosted mostly in Lower Cretaceous volcano‐sedimentary sequences, and has chalcopyrite‐rich mineral associations. The fluid inclusion data indicate that the primary copper mineralization was commonly generated in the temperature range 150–360°C under low‐pressure conditions near the boiling curve, mediated with relatively saline brines. Generally, homogeneous Pb and S isotope compositions for primary copper minerals imply direct magma source or leaching of igneous rocks. Pb and Os isotope data published for some deposits, however, suggest that ore‐forming metals were derived mainly from the volcano‐sedimentary host rocks. The noticeably negative isotope ratios of primary sulfide sulfur and hydrothermal calcite carbon of some central area deposits indicate influx of sedimentary rock components, and the high ⁸⁷Sr/⁸⁶Sr initial ratios of hydrothermal calcite from the Tocopilla–Taltal area deposits imply contribution of the contemporaneous seawater or marine carbonates. These isotopic constraints imply a formation mechanism in which the Chilean manto‐type copper deposits formed epigenetically in the process of hydrothermal interaction of non‐magmatic surface‐derived brine with the volcano‐sedimentary host rocks, which is inferred to have been induced by a deep‐seated plutonic complex as the possible heat source.     

秦岭造山带泥盆系热水沉积岩相应用研究及实例

构造-热水沉积岩相与盆地的古地理环境, 热水沉积岩相与热水沉积成矿,热(水) 流体岩相与构造背景、构造古地理,它们之间有密切地内在联系.应用热水沉积岩相、沉积相及沉积体系分析方法，对凤县铅硐山-双石铺三级构造热水成矿盆地进行研究。     

松辽盆地白垩纪火山期后热液活动的岩石地球化学和年代学及其地质意义

在松辽盆地东南隆起区营城组标准剖面营三段古火山口附近识别出岩浆期后热液活动的地质记录。岩石学特征表现为隐爆角砾岩,即,原有的近火山口相岩石(原岩)被高压流体炸碎形成原地角砾、之后又被灌入的富含矿物质"岩汁"胶结形成的原地角砾岩。采集隐爆角砾岩及其上覆和下伏三个层位共10个样品进行地球化学和年代学对比研究,包括两套4个对应的原岩和岩汁、下伏4个玄武粗安岩和上覆2个流纹岩。原岩高精度~(39)Ar/~(40)Ar坪年龄113.4±0.7Ma;岩汁为含铁酸性流体的隐晶质析出物,其~(39)Ar/~(40)Ar坪年龄112.9±19.6Ma;二者的年龄差反映岩浆主期与期后热液活动的时代间隔(1Ma之内)。10个样品的共性是:(1)稀土总量中-高(∑REE=81×10~(-6)～202×10~(-6))且轻重稀土分异明显((La/Yb)_N=4.91～11.45);(2)MORB标准化蛛网图上P和部分不相容元素(Cs、Th、La和Zr)正异常,而另一部分不相容元素(Sr和Pb)负异常。整体表现为双峰式裂谷火山岩特点。主要差别在于:(1)铕和钡表现为两种情况,下伏玄武粗安岩和隐爆角砾岩中的粗面岩具正异常,而隐爆角砾岩中的流纹岩和岩汁及其上覆的流纹岩具负异常;(2)只有2个岩汁样品显示K负异常,其它8个岩石样品均为K正异常;(3)下伏玄武粗安岩(4个样)显弱的Ti正异常且Rb/Sr比低(0.04～0.05),而其它6个样品为Ti负异常且Rb/Sr比高(0.62～2.83),其中的2个岩汁样品Ti负异常最强。岩汁与其下伏粗面质原岩差别显著,而与其上覆流纹岩(SHRIMP年龄110.6Ma)的地化特征相似(见正文)。该火山期后热液活动是深源热流体萃取壳源物并沿古火山通道(构造薄弱带)运移到近地表的,可能是后续流纹质火山活动的先驱。这种高压的岩浆期后热液导致围岩炸裂、发生角砾岩化、形成大量角砾间孔和裂缝。这是造成火山口-近火山口相带成为优质储层的重要因素。该类火山岩储层改善作用早于烃类运移,可构成有利于成藏的时空配置。与该期热液活动相伴生的深源天然气早于上覆圈闭的形成,因此对成藏没有贡献。     

秦岭造山带泥盆系热水沉积岩相应用研究及实例

构造-热水沉积岩相与盆地的古地理环境,热水沉积岩相与热水沉积成矿,热 (水 )流体岩相与构造背景、构造古地理,它们之间有密切地内在联系.应用热水沉积岩相、沉积相及沉积体系分析方法,对凤县铅硐山-双石铺三级构造热水成矿盆地进行研究.     

四川杨柳坪热液型富铂族元素矿石的发现及其意义

四川杨柳坪是中国最主要的铂族元素矿床之一，但以往控制的97％以上的储量赋存在蚀变超基性岩体中，品位普遍不高，笔者等1999年通过对杨柳坪主矿体外围热液型矿体的调查，认为其中的热液型矿石可能富含铂族元素，经过初步的分析测试，证实了这一推测，并发现热液成民岩浆作用在杨柳坪地区具有明显不同的表现形式，根据最近在鱼海子等地地调查的新发现，建议在扬子地台西缘进一步开展找热液型铂族元素矿床的工作。     

“岩浆热场”说及其成矿意义(下)

上篇(张旗等[1])初步讨论了岩浆热场说的概念,本文为下篇,主要谈应用,探讨它与成矿作用的关系。研究表明,岩浆热场说对热液成矿作用有重要的意义,可能解决了岩浆热液成矿作用中许多很难解释和争议很大的问题:如钨锡与金铜为什么相伴的问题,矿床为什么大多是多金属成矿的问题,远离侵入体的夕卡岩成因问题,成矿为什么滞后于花岗岩的问题,为什么有些岩体成矿,有些岩体不成矿的问题,为什么大规模岩浆活动与大规模成矿作用息息相关的问题等。岩浆热场与煤和油气成藏有关是一个重要的发现。岩浆热场对煤和油气生成、运移、聚集的影响主要表现在加速烃源岩的热演化,使生油门限变浅,使烃源岩进入高成熟或过成熟,使烃源岩中残余有机质丰度降低。令人感兴趣的是,岩浆热场说还导出了一个"成矿组合"的概念,所谓成矿组合是指在一个或大或小的区域内,在岩浆活动集中的时间段范围内,在热场的统一作用下所形成和影响的所有矿床,不论成因和矿种,均属于一个成矿组合。它包括下述4种类型的矿床:岩浆热液矿床、热泉型矿床、层状热液矿床及生物有机质矿床等。岩浆热场说对于找矿也有启示:首先,我们可以从3个不同的级别上(大规模岩浆活动级别;成矿带、成矿区、矿集区级别;单个矿床级别)规划找矿布局;其次,在岩浆热场的统一影响下将金属矿床和非金属矿床、热液矿床和沉积矿床、无机质矿床和有机质矿床联系起来;第三,推进不同类型矿床研究的互补和交流。看来,岩浆热场对于成矿的作用是最值得学术界关注的,它也许可以改变我们目前对成矿作用的某些根深蒂固的认识,开拓出一个新的领域,推进矿床学研究进入新的时代。     

相山铀矿田成矿古水文地质分析

相山矿田是我国著名的大型热液铀矿田。该矿田产于中生代相山火山岩盆地古水热系统之中，是水热系统中水－岩相互作用的产物。因此，查明当时的古水文地质条件对于研究矿床成因、指导找矿具有重要意义。本文根据相山地区的地质基础资料、构造演化历史和古气候条件，运用构造－古水文地质分析法，对该矿田进行了古水文地质分期、分区，分析了古地下水的补给区、排泄区和径流途径，并对成矿古水热系统的形成条件进行了探讨。     

Carbon and oxygen isotope zoning around Carlin-type gold deposits: a reconnaissance survey at Twin Creeks, Nevada

This study was undertaken to determine whether wallrocks around the Twin Creeks Carlin-type gold deposits exhibit oxygen isotope haloes similar to those found around other types of hydrothermal deposits. Mineralization at Twin Creeks is hosted by Ordovician Sequence shales containing some carbonate minerals and by Pennsylvanian–Permian Etchart Formation limestone. Analysis of orthophosphate-soluble carbonate from these rocks shows that oxygen isotope haloes are detectable in Ordovician Sequence shales but not in Etchart Formation limestone. The soluble fraction of Ordovician Sequence shales at Twin Creeks has δ¹⁸O values of 12 to 24‰ and δ¹³C values of 0 to −10‰. Most samples fall along a poorly defined trend that extends from δ¹⁸O of about 24‰ and δ¹³C values of about 0, which are typical of unaltered limestones, toward lower values for both isotope systems, which are typical of rocks that have undergone alteration by hydrothermal fluids. Plots of these values along two sections through the ore body show that δ¹⁸O values of wallrocks are lowest in the ore zone and increase outward, forming a halo several hundred meters in size. In the same plots, δ¹³C values of the wallrocks do not show systematic spatial variations. The soluble fraction of Etchart Formation limestones at Twin Creeks have δ¹⁸O values of 25 to 5‰ and δ¹³C values of 4 to −10‰, but do not show any systematic spatial variation relative to mineralization at the scale of our samples. Failure of the Etchart Formation samples to show detectable haloes is probably related to deposition of post-ore carbonate minerals or lower ore fluid : rock ratios. Material balance calculations used to model the isotopic composition of average Ordovician Sequence shales indicate that changes in temperature and water : rock ratio were probably not sufficient to account for the wide range of isotope compositions observed in these rocks. The most likely additional factor contributing to this range of values was a change in the composition of the altering fluid, probably by mixing of the ore fluid with surrounding meteoric water. These results suggest that Carlin-type gold deposits are surrounded by haloes of low δ¹⁸O values, but that detection of these haloes could be complicated by local compositional variations and post-ore modification of the wallrocks.