Detection of hydrothermal alteration zones in a tropical region using satellite remote sensing data: Bau goldfield,Sarawak, Malaysia

Remote sensing for geology in tropical environments is very challenging, because of the dense vegetation cover and the problem of persistent cloud cover. In this research paper, we have investigated and demonstrated the detection of hydrothermal alteration zones and structural elements associated with intrusion-related gold mineralization using various types of remote sensing data in the Bau gold mining district in the State of Sarawak, East Malaysia, on the island of Borneo. The climate of Bau is tropical with persistent cloud cover and very dense vegetation ground. Geological analyses coupled with remote sensing data were used to detect hydrothermally altered rocks and structural elements associated with gold mineralization in the Bau area. Landsat Enhanced Thematic Mapper⁺ (ETM⁺), Hyperion and Phased Array type L-band Synthetic Aperture Radar (PALSAR) data were used to carry out lithological–structural mapping of the mineralized zones in the study area and surrounding terrain. Hydrothermal alteration zones were detected along the SSW to NNE structural trend of the Tai Parit fault that corresponds with the occurrence of other gold mineralization in the Bau Limestone. The results show that the known gold prospects and potential areas of mineralization are recognizable by the methods used, despite limited bedrock exposure. The approach used in this study is broadly applicable to the detection of gold mineralization using ETM⁺, Hyperion and PALSAR data in tropical/sub-tropical regions.     

东昆仑巴隆河西金矿地质特征与找矿标志

巴隆河西金矿床是东昆仑金成矿带近年来新发现的金矿床,其形成时代、地质特征与矿床类型尚不明确。本次在详细野外地质调查的基础上,通过构造-蚀变填图、锆石U-Pb定年和综合对比等方法,研究巴隆河西矿床的成矿特征和岩体侵位时代,以确定该矿床的成因类型与成矿时代。构造-蚀变填图发现巴隆河西矿床的金矿化赋存于花岗质岩体的9条构造蚀变带,明确了5个金矿体呈带状分布于北西西向断裂中,揭示金矿化与高岭土化、褐铁矿化、硅化和黄铁矿化等蚀变密切相关。赋含金矿化的花岗闪长岩和花岗斑岩的锆石U-Pb定年结果表明,其侵位时代分别为202.5±1.8 Ma和222.1±1.1Ma,属于印支晚期,约束了巴隆河西金矿的形成时代。结合区域岩浆活动时限、巴隆金矿地质特征、矿体产状与中低温矿物组合特征,提出巴隆河西矿床为造山带型金矿,推断逆断层及其伴随的热液活动是巴隆河西矿床金元素活化、迁移和富集的关键因素,指出北西西向构造蚀变带是该区带金矿成矿的有利部位。     

Recognition of two contrasting structural-and mineralogical-gold mineral systems in the Youjiang basin,China-Vietnam:Orogenic gold in the south and Carlin-type in the north

The gold deposits in the Youjiang basin,totaling 25 Moz gold,have traditionally been thought to be of Carlintype,particularly those with extensional structural geometries in the northern basin dominated by platform sedimentary sequences.However,the structural geometries,mineralization styles and alteration types for the Jinya,Gaolong and Nakuang gold deposits in the south-central part of the basin are remarkably similar to those of unequivocal orogenic gold deposits.Structural studies show that gold mineralization in the three gold deposits was controlled by tight "locked-up"anticlines with NW—SE-to E-W-trending and/or concomitant thrusts and/or shear zones,which resulted from NE-SW-to N-S-trending compression or transpression following the Early Triassic closure of the Paleo-Tethyan Ocean.Alteration zones in these deposits are dominated by silicification(quartz),sericitization,sulfidation and carbonation.Zoned pyrites in these deposits comprise Au-poor cores and invisible Au-bearing rims with minor external free gold.Euhedral to subhedral auriferous arsenopyrites also contribute to the gold budget.These features indicate that the three gold deposits are sediment-hosted orogenic gold deposits that contrast markedly with the Carlin-type gold deposits in the northern part of the Youjiang basin in terms of structural geometry and timing,mineralization style and nature of associated alteration.Although additional reliable ages using robust methodologies are still required,the older isotopic ages of the gold deposits in the south-central Youjiang basin are also consistent with earlier formation during transpression that predated extension during orogenic collapse,the period of formation of the Carlin-type gold deposits in the northern Youjiang basin.     

Relative timing of deformation and two-stage gold mineralization at the Hutti Mine, Dharwar Craton, India

Gold mineralization at Hutti is confined to a series of nine parallel, N–S to NNW–SSE trending, steeply dipping shear zones. The host rocks are amphibolites and meta-rhyolites metamorphosed at peak conditions of 660±40°C and 4±1 kbar. They are weakly foliated (S₁) and contain barren quartz extension veins. The auriferous shear zones (reefs) are typically characterized by four alteration assemblages and laminated quartz veins, which, in places, occupy the entire reef width of 2–10 m, and contain the bulk of gold mineralization. A <1.5 m wide distal chlorite-sericite (+biotite, calcite, plagioclase) alteration zone can be distinguished from a 3–5 m wide proximal biotite-plagioclase (+quartz, muscovite, calcite) alteration zone. Gold is both spatially and temporally associated with disseminated arsenopyrite and pyrite mineralization. An inner chlorite-K-feldspar (+quartz, calcite, scheelite, tourmaline, sphene, epidote, sericite) alteration halo, which rims the laminated quartz veins, is characterized by a pyrrhotite, chalcopyrite, sphalerite, ilmenite, rutile, and gold paragenesis. The distal chlorite-sericite and proximal biotite-plagioclase alteration assemblages are developed in microlithons of the S₂–S₃ crenulation cleavage and are replaced along S₃ by the inner chlorite-K-feldspar alteration, indicating a two-stage evolution for gold mineralization. Ductile D₂ shearing, alteration, and gold mineralization formed the reefs during retrograde evolution and fluid infiltration under upper greenschist to lower amphibolite facies conditions (560±60°C, 2±1 kbar). The reefs were reactivated in the D₃ dextral strike-slip to oblique-slip environment by fault-valve behavior at lower greenschist facies conditions (ca. 300–350°C), which formed the auriferous laminated quartz veins. Later D₄ crosscutting veins and D₅ faults overprint the gold mineralization. The alteration mineralogy and the structural control of the deposit clearly points to an orogenic style of gold mineralization, which took place either during isobaric cooling or at different levels of the Archean crust. From overlaps in the tectono-metamorphic history, it is concluded that gold mineralization occurred during two tectonic events, affecting the eastern Dharwar craton in south India between ca. 2550 – 2530 Ma: (1) The assemblage of various terranes of the eastern block, and (2) a tectono-magmatic event, which caused late- to posttectonic plutonism and a thermal perturbation. It differs, however, from the pre-peak metamorphic gold mineralization at Kolar and the single-stage mineralization at Ramagiri. Notably, greenschist facies gold mineralization occurred at Hutti 35–90 million years later than in the western Dharwar craton. Editorial handling: G. Beaudoin     

Fault/fracture density and mineralization: a contouring method for targeting in gold exploration

A widely observed correlation between high fracture density and mineralization throughout terranes and geological time indicates a fundamental underlying ore-forming process. In Archaean greenstone-hosted deposits, high-density fracturing was accompanied by enhanced fluid flow during fault/fracture network development, producing regional-scale fluid pressure gradients that focussed hydrothermal fluids into preferentially fractured areas. Fracture density is both increased and decreased during faulting and fault healing, and fracture density accumulates over time, in zones of high palaeo-fluid flow. Localised zones where the density of fracturing is increased by deformation, become permeability nodes for migrating hydrothermal fluids leading to large zones of alteration and gold precipitation. The Ora Banda mining centre in Western Australia contains significant gold deposits that appear to demonstrate a close association between high-density fracturing and gold precipitation. Fracture density in the Ora Banda mines was enhanced by fault–fault intersections, fault–contact intersections and changes in fault geometry. The mine-scale relationships between fracture density and gold mineralization are repeated at smaller and larger scales, hence these relationships may be used in targeting for gold exploration. Contouring the density of fracturing in a region provides a semi-quantitative way to rank areas for exploration and uses data from mapping, drilling and high-quality geophysical data as a basis for analyses. Fracture density contouring is complementary to other prospectivity-analysis methods.     

The geology of the Lega Dembi gold deposit, southern Ethiopia: implications for Pan-African gold exploration

The Lega Dembi deposit is the largest gold producer in Ethiopia. It is situated in late-Precambrian metamorphosed sediments of the N-S trending, volcano-sedimentary Megado belt, which forms part of the late-Proterozoic Adola granite-greenstone terrane in southern Ethiopia. The lode-gold mineralization occurs in a N-S trending, steep westerly dipping quartz-vein system that follows the structural contact between underlying feldspathic gneisses and the volcanosedimentary sequence of the Megado belt. This contact also marks the northernmost extension of the regional-scale, sinistral strike-slip Lega Dembi-Aflata shear zone. Mineralization and intense quartz-veining is best developed in graphite-rich sediments within an area not more than 80 m away from this tectonic contact. Hydrothermal wall-rock alteration includes actinolite/tremolite-biotite-calcite-sericite and chlorite-calcite-epidote assemblages. Gold occurs preferentially in the sericite alteration zone, where it is closely associated and intergrown with galena. The variable deformation of the gold-quartz veins suggests a syn-kinematic timing for the gold mineralization during transcurrent shearing in a dilational segment of the shear zone. In addition to the structural control, lithological control on gold deposition is indicated by the almost exclusive occurrence of the gold mineralization in graphite-rich metasediments. This close relationship suggests that gold precipitation was the result of chemical reduction of regional ore-bearing fluids. Temperature conditions of mineralization are constrained by the actinolite-biotite alteration assemblage and by arsenopyrite chemistry, which indicate that ore deposition occurred at or close to peak metamorphic conditions at upper-greenschist to lower-amphibolite metamorphic grades. Rb-Sr dating of sericite indicates an age of about 545 Ma. for hydrothermal alteration and, thus, for gold mineralization. The style of gold mineralization, structural pattern and lithological assemblages at Lega Dembi are very similar to lode-gold deposits most commonly reported from Archaean granite-greenstone terranes. These similarities may open new perspectives for the exploration of lode-gold deposits, which has previously primarily focused on Archaean greenstone belts rather than Proterozoic or even Phanerozoic meta-volcanosedimentary belts. Received: 26 July 1996 / Accepted: 8 January 1997     

黑龙江金厂J-1号金矿体地质特征及深部预测

黑龙江东宁金厂金矿床是与印支-燕山期中酸性火山-次火山岩有关的大型金矿床，矿化类型主要有隐爆角砾岩型，多金属硫化物细脉充填型及破碎蚀变岩型，矿体主要受隐爆角砾岩筒，环状，放射状构造控制，筒状角砾岩型金矿的资源量占全区的80%以上。矿区内最主要的J-1号金矿体矿化类型为隐爆角砾岩型。品位高且稳定，在系统总结该矿体地质特征的基础上，对其深部远景进行了预测。     

胶东玲珑金矿田171号脉深部金矿床特征及构造控矿作用

玲珑金矿田171号脉赋存于招平断裂北段破头青断裂中,在其深部探明金资源储量150余吨,确定其为超大型破碎带蚀变岩型金矿床。为了揭示构造与成矿、深部矿与浅部矿、石英脉型矿与蚀变岩型矿等的关系,为深部找矿提供典型实例和理论依据,文章通过大量矿区地质勘探、野外地质调查和区域地质综合研究,剖析了矿床特征,揭示了构造控矿规律。171号金矿脉深部共有7个金矿体,均为盲矿体。其中,171_1号主矿体埋深120~1700m,呈似层状、大脉状分布,沿走向及倾向显舒缓波状。矿体总体走向60°,倾向SE,倾角36.5~43.5°。矿体长2500m,斜深510~3100 m,平均厚度4.23 m,平均金品位2.71×10~(-6),矿石主要为黄铁绢英岩型(蚀变岩型)。矿脉和矿体受断裂构造控制,矿化、构造、蚀变分带具有一致性。由控矿断裂的主裂面至远离主裂面,构造变形强度由强变弱,蚀变强度和矿化强度也由强变弱。招平断裂是一条切割早期韧性剪切带的脆性断裂,总体呈舒缓波状展布,大部分地段发育于早前寒武纪变质岩系与侏罗纪玲珑型花岗岩之间,断裂上盘脆性变形较弱,下盘脆性变形带宽大,是沿不同时代地质体之间发育的左行铲式正断层,类似于拆离断层,是胶东白垩纪伸展构造的组成部分。玲珑金矿田是典型的石英脉型金矿产地,但大型金矿床多为赋存于断裂构造中的蚀变岩型金矿床,石英脉型金矿床与蚀变岩型金矿床是同一构造系统中不同构造位置的产物;一般在主断裂中赋存蚀变岩型金矿床,在主断裂下盘的次级张裂隙中产出石英脉型金矿床。胶东以正断层为主的伸展构造系统为大规模成矿提供了有利条件,构造、蚀变分带和不同类型金矿床的关系是金矿找矿的重要标志。     

内蒙古阿拉善左旗查干德日斯铜(金)矿化地质特征及找矿前景

通过对查干德日斯铜(金)矿区地质地球化学勘查工作,区内发现铜矿体1条、铜(金)矿化体1条、铜矿化蚀变带8条。铜(金)矿化体均赋存于NEE向、NNW向断裂破碎带内,且以NEE向为主;矿化与褐铁矿化石英脉密切共生,伴随明显的硅化、钾化热液蚀变。认为矿区Cu-Au-Ag原生晕组合异常明显,与断裂构造套合良好;铜(金)矿化受构造控矿特征明显,热液充填-交代作用强烈,初判为热液充填交代型矿床。矿区深部矿成矿地质条件优越,找矿前景良好。     

Structural controls on Tertiary orogenic gold mineralization during initiation of a mountain belt, New Zealand

Two types of structurally controlled hydrothermal mineralization have occurred during folding of fissile schist in southern New Zealand: fold-related mineralization and normal fault-related mineralization. Both types have the same mineralogy and textures, and are dominated by quartz–ankerite veins and silicified breccias with ankeritic alteration. Most mineralized zones are thin (centimetre scale), although host schist is commonly impregnated with ankerite up to 20 m away. Thick (up to 5 m wide) mineralized zones are generally gold-bearing and contain pyrite and arsenopyrite with stibnite pods locally. Some of these auriferous zones have been extensively mined historically despite rugged topography and difficult access. Mineralization occurred during regional tectonic compression in the initial stages of development of the Southern Alps mountain belt at the Pacific–Australian plate boundary in the Miocene. Most of the gold-bearing deposits occur in east to south-east, striking normal faults that cut across mesoscopic folds in a belt that coincides with the southern termination of a regional-scale north trending antiform. Mineralized zones have similar structural control and relative timing to a nearby swarm of Miocene lamprophyre dykes and carbonatites. Limited stable isotopic data (C and O) and trace element geochemistry suggest that there was probably no genetic link between the igneous activity and gold mineralization. However, these two types of fluid flow have been controlled by the same tectonically created crustal plumbing system. This Miocene hydrothermal activity and gold deposition demonstrates that orogenic (mesothermal) mineralization can occur during the inception of an orogenic belt, not just in the latter stages as is commonly believed. These Miocene structures have been preserved in the orogen because the locus of uplift has moved northwards, so the early-formed gold deposits have not yet been structurally overprinted or eroded.     

Porphyry,epithermal, and orogenic gold prospectivity of Argentina

This paper presents a review of the available information on the significant porphyry, epithermal, and orogenic gold districts in Argentina, including the tectonic, geological, and structural settings of large deposits or deposits that have been exploited in the past. Based on this review of the geology and mineralization, targeting models are developed for epithermal and orogenic gold systems, in order to produce GIS-based prospectivity models. Using publically available digital geoscience data, weights of evidence and fuzzy logic prospectivity maps were generated for epithermal and orogenic gold mineralization in Argentina. The results of the prospectivity mapping highlight existing gold deposits within known mineralized districts throughout Argentina, as well as other highly prospective areas with no known deposits within these districts. Additionally, areas within Argentina that have no known gold mineralization (based on publically available information) were highlighted as being highly prospective based on the models used.     

澳大利亚伊尔岗地块诺斯曼-维卢纳绿岩带金矿成矿作用

诺斯曼-维卢纳金成矿带位于澳大利亚西澳克拉通伊尔岗地块东部黄金省次级地体内,是澳大利亚最重要的绿岩带型金矿成矿区。区内矿床可分为3类：剪切带中的蚀变晕±石英脉型,是区内最为重要的矿化类型,典型矿床为卡尔古利金哩矿床,矿床赋存在金哩粗玄岩中,矿化发生在绢云母-黄铁矿化蚀变带内;石英网脉型,典型矿床为卡尔古利夏洛特山金矿床。矿床也产于金哩粗玄岩中,矿化主要发生在硅化外围的碳酸盐-黄铁矿化蚀变带内;纹层状石英脉型,矿化表现出层控的特点,并多发育绿泥石化。通过对区域和典型矿床地质特征和区域成矿特征的总结,认为诺斯曼-维卢纳金成矿带的金主要赋存于铁硫化物或毒砂中,矿化与大规模的蚀变作用联系密切,太古宙绿岩带和条带状铁建造、深大断裂、褶皱等因素控制了矿床的分布。在此基础上,总结了绿岩带型金矿的找矿标志,并为在区内找矿提出若干建议。     

剪切带型金矿中金沉淀的力化学过程与成矿机理探讨

剪切带型金矿是一种重要的金矿床类型,有关该类型金矿的成因问题已开展了大量研究,但对于剪切带中金的沉淀析出机制和成矿过程仍存在较大争议,对于赋矿部位的构造属性与矿床关系的研究尚显薄弱。对此笔者整理分析了近年来国内外有关剪切带型金矿的研究进展,并结合我国胶东金矿的研究实例,运用断层阀和力化学理论分析发现,无论是脆性还是韧性剪切带,无论是脉型还是蚀变岩型金矿,其成矿的关键部位均与构造应力集中而导致的脆性破裂(特别是R、T、R’破裂的产生)和碎裂作用以及(多期)岩体侵位密切相关,并且脆性破裂所导致的压力骤降从而引发流体闪蒸的力化学过程可能是造成金沉淀析出成矿的有效机制,其中多期岩体侵位所提供的流体是成矿的物质基础。此外,从国内外实例可以看出,剪切带中的脆性破裂不仅发生于脆性或脆韧性构造域,也可以发生在较深层次的韧性构造域中,尽管韧性域中产生脆性破裂的原因还不十分清楚,但这可能是韧性剪切带成矿的关键机制之一。最后,综合岩体、流体、剪切带三者对成矿的耦合作用,文中提出剪切带型金矿的成矿机理为:(多期)岩体侵位-热液活动-构造剪切-应力集中-脆性破裂(碎裂)产生-压力骤降-流体闪蒸-元素(金)析出,如此循环往复方可形成大型剪切带型金矿。     

西天山金矿遥感地质调查及重点地区金成矿条件研究

本文介绍了TM和SPOT等多源数据融合处理，以及提取蚀变影像信息和增强冻融带影像信息的方法。根据断裂构造（包括线性断裂、环状和弧形断裂构造）、地层、冻融带及蚀变带的解译，总结了西天山地区金矿成矿环境和成矿条件。在与邻区穆龙套、库姆托尔金矿对比研究的基础上，选定了重点研究地区，勾划了与金矿化关系密切的冻融带及构造蚀变带，为该区进一步开展金矿普查找和矿提供依据。     

The New Consort Gold Mine,Barberton greenstone belt,South Africa: orogenic gold mineralization in a condensed metamorphic profile

The New Consort Gold Mine in the Palaeo- to Mesoarchaean Barberton greenstone belt, South Africa is one of the oldest recognized orogenic gold deposits on Earth. The gold mineralization is hosted by discrete mylonitic units that occur at, or close to, the contact between the mafic and ultramafic volcanic rocks of the c. 3,280 Ma Onverwacht Group and the mainly metasedimentary rocks of the overlying c. 3,260–3,230 Ma Fig Tree Group. This contact, locally referred to as the Consort Bar, formed during ductile D₁ imbrication of the metavolcanosedimentary sequence and predates the main stage of the gold mineralization. The imbricate stack is situated in the immediate hanging wall of the basal granitoid–greenstone contact along the northern margin of the greenstone belt. It is characterized by a condensed metamorphic profile in which the metamorphic grade increases from upper greenschist facies conditions (510–530°C, 4 kbar) in rocks of the Fig Tree Group to upper amphibolite facies grades (600–700°C, 6–8 kbar) in the basal Onverwacht Group. Detailed structural and petrological investigations indicate that the Consort Bar represents a major structural break, which is largely responsible for the telescoping of metamorphic isograds within the structural sequence. Two stages of mineralization can be distinguished. Loellingite, pyrrhotite, and a calc–silicate alteration assemblage characterize an early high-T mineralization event, which is restricted to upper amphibolite facies rocks of the Onverwacht Group. This early mineralization may correlate with the local D₁ deformation. The second and main stage of gold mineralization was associated with renewed ductile shearing during D₂. The D₂ deformation resulted in the reactivation of earlier structures, and the formation of a NNW trending, steeply dipping shear zone system, the Shires Shear Zone, which separates two regional SE plunging D₁ synclines. The mineralized shear zones are intruded by abundant syn-kinematic pegmatite dykes that have previously been dated at c. 3040 Ma. Petrological and geothermobarometric data on ore and alteration assemblages indicate that the main stage of gold mineralization, which affected a crustal profile of ca. 1.5 km, was characterized by increasing temperatures (c. 520 to 600°C) with increasing structural depth. Sulfide assemblages in the ore bodies change progressively with metamorphic grade, ranging from arsenopyrite + pyrite + pyrrhotite in the structurally highest to arsenopyrite + pyrrhotite + chalcopyrite + loellingite in the structurally deepest part of the mine. The main stage of gold mineralization was broadly syn-peak metamorphic with respect to the Fig Tree Group, but postdates the peak of metamorphism in upper amphibolite facies rocks of the structurally underlying Onverwacht Group. This indicates that the mineralization coincided with the juxtaposition of the two units. As the footwall rocks were already on their retrograde path, metamorphic devolatilisation reactions within the greenstone sequence can be ruled out as the source of the mineralizing fluids.     

坦桑尼亚马拉-穆索马绿岩带金矿地质特征及成矿规律浅析

坦桑尼亚太古代马拉-穆索马绿岩带位于坦桑尼亚西北部、维多利亚湖东部地区,是坦桑尼亚重要的金矿聚集区。该地区主要金矿床类型为受陡倾或缓倾剪切构造带控制的构造蚀变岩型和石英脉型金矿床。本文通过对亚斯罗利、瑞万科玛和尼亚布隆渡等3个典型金矿床进行对比研究,系统分析了金矿床的成矿地质条件、矿化蚀变特征及矿石结构构造特征,总结了马拉-穆索马绿岩带金成矿规律,认为金矿床的形成与镁铁质火山-沉积岩、韧-脆性剪切构造带及岩浆活动有密切关系,近东西向韧-脆性剪切带是区内最主要的控矿构造,控制着主要工业矿体的分布。     

Synvolcanic gold mineralization within a deformation zone: the Chevrier deposit, Chibougamau, Abitibi Subprovince, Canada

The Chevrier gold deposit is located in the northeastern part of the Abitibi Subprovince within the Chevrier volcanic centre (CVC). This calc-alkaline volcanic centre evolved from mafic to felsic in a submarine environment, and the Chevrier deposit is spatially associated with the uppermost unit composed mostly of massive dacite to rhyolite, dated at 2730 Ma. The Chevrier deposit is divided in two zones. The North Zone is composed of high-grade, discordant quartz-carbonate veins and disseminated pyrite mostly within melanocratic gabbro dykes, whereas, the South Zone is within a low-grade, concordant pyrite envelope associated with quartz-carbonate-pyrite veinlets. Both zones are highly deformed and show strong carbonate, sericite and chlorite alterations. Although these zones share many characteristics with orogenic deposits, the crosscutting of the Chevrier deposit by structures associated with the major deformation events suggests that mineralization was prior to these events. Furthermore, felsic dykes associated with the formation of the CVC crosscut auriferous veins and zones, therefore suggesting a synvolcanic timing for the gold mineralization. Characteristics of the zones, such as similar vein composition and alteration mineral assemblages and location within the volcanic pile, suggest that they are part of a single hydrothermal event where the South Zone represents the shallower part of the deposit. The Chevrier deposit is classified as a noncarbonate-hosted stockwork and disseminated deposit and shows many similarities with strata-bound gold deposits of the Andacollo mining district of Chile. Dating of mineralization at the Chevrier deposit indicates that the emplacement of gold occurred more than 25 Ma before the onset of the orogeny affecting this part of the Abitibi subprovince. It also illustrates how synvolcanic mineralization can be misinterpreted as an orogenic deposit without the presence of crosscutting relationships with dykes, faults or other structures.Contribution No. 2005-5130-01 of the Ministère des Ressources naturelles et de la Faune du Québec.     

The Bereznjakovskoje gold trend, southern Urals, Russia

The East Uralian Zone south of Cheljabinsk consists of a Silurian to Early Carboniferous volcanosedimentary sequence on Proterozoic basement, intruded by postorogenic Permian granitic rocks. The 7 by 1–2 km Bereznjakovskoje gold trend is hosted by dacitic to andesitic volcanic-subvolcanic units of Late Devonian age. Epithermal gold mineralization is of the sulfide-rich low-sulfidation (adularia-sericite) type with the metal spectrum of Au-Ag-As-Sb-Cu-Zn-Pb and a characteristic Te component. Silicic and sericitic alteration overprints barren propylitic pyrite-rich assemblages in stockworks and shear zones. Precious-metal mineralization is related to a fahlore-telluride stage overprinting earlier pyrite. Late stage redistribution and weathering liberates gold from telluride mineral phases with fixation of native gold (high fineness) on vugs and grain boundaries, and in intergrowth aggregates with supergene jarosite/limonite. Epithermal mineralization formed below the boiling level and is possibly related to a porphyry system at depth. Received: 23 February 1998 / Accepted: 12 July 1998     

ASTER spectral analysis for alteration minerals associated with gold mineralization

This study presents classifications of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery based on spectral analysis of alteration minerals associated with gold mineralization in Abo Marawat area which is located in the Central Eastern Desert of Egypt. Spectral analysis of continuum removed reference spectra of alteration minerals alunite, kaolinite, sericite, and calcite from USGS and JPL spectral libraries show shifts in position, shape, and strength most probably related to changes in sample purity and particle size of analyzed samples. Spectral Information Divergence (SID) classification method proved successful for mapping sericite, calcite, and clay minerals. Spectral Angle Mapper (SAM) classification identified only sericite and calcite alteration minerals. The identified alteration zones are coincidence with the field sampling and geological map of the study area. The microscopic examination of samples collected from the quartz veins and hydrothermally altered wall-rocks from near surface and subsurface at Abu Marawat gold mine shows sericitization, argillaceous, and carbonatization alteration zones. Gold occurs as very fine inclusions in pyrite, chalcopyrite, and sphalerite and also found filling the fractures between chalcopyrite grains. This study concludes that ASTER image classifications using reference spectra are a stable and reproducible technique for mapping gold related hydrothermal alteration zones in areas with no dominant vegetation cover.     

浙江诸暨璜山金矿构造特征及深部找矿预测

诸暨璜山金矿是浙江省著名的金矿之一,位于江山-绍兴断裂带北东段。本文通过对璜山金矿和庙下畈金矿的构造特征进行对比研究,认为这两个金矿形成的构造背景和成矿时代基本相同,但矿体走向和剪切动向截然不同,璜山金矿赋存于NE走向的剪切带内,庙下畈金矿位于NW走向的剪切带内,二者构成共轭剪切带,叠加在江山-绍兴主干韧性剪切带之上。成矿后该区先后受到NW-SE和NNE-SSW方向的挤压,形成NW走向和近SN方向的脆性断裂,对矿体起到破坏作用。依据共轭剪切带的空间分布,推测江绍断裂南东侧可能存在与璜山金矿对应的赋矿剪切带,该带位于新元古代陈蔡群变质岩之下,埋藏较深,是璜山地区深部找矿的有利勘探区。