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1.
The Lapa gold deposit contains reserves of 2.4 Mt at 6.5 g/t Au and is one of the few deposits located directly within the Cadillac–Larder Lake Fault Zone (CLLFZ), a first-order crustal-scale fault that separates the Archean Abitibi Subprovince from the Pontiac Subprovince to the south. Gold mineralization is predominantly hosted in highly strained and altered, upper greenschist–lower amphibolite facies mafic to ultramafic rocks of the Piché Group. Auriferous ore zones consist of finely disseminated auriferous arsenopyrite–pyrrhotite?±?pyrite and native gold disseminated in biotite- and carbonate-altered wall rocks. Native gold, which is also present in quartz ± dolomite–calcite veinlets, is locally associated with Sb-bearing minerals, especially at depth ≤1 km from surface where the deposit is characterized by a Au–Sb–As association. At vertical depth greater than 1 km, gold is associated with arsenopyrite and pyrrhotite (Au–As association). The mineralogy and paragenesis of the Lapa deposit metamorphosed ore and alteration assemblages record the superposition of three metamorphic episodes (M1, M2, and M3) and three gold mineralizing events. Spatial association between biotitized wall rocks and auriferous arsenopyrite indicates that arsenopyrite precipitation is concomitant with potassic alteration. The predominant Au–As association recognized across the deposit is related to gold in solid solution in arsenopyrite as part of a pre-M2 low-grade auriferous hydrothermal event. However, the occurrence of hornblende?+?oligoclase porphyroblasts overprinting the biotite alteration, and the presence of porous clusters and porphyroblasts of arsenopyrite with native gold and pyrrhotite indicate an auriferous metasomatic event associated with peak M2 prograde metamorphism. Late retrograde metamorphism (M3) overprints the hornblende–oligoclase M2 assemblage within the host rocks proximal to ore by an actinolite–albite assemblage by precipitation of free gold and Sb–sulfosalts at lower P–T. The complex relationships between ore, structural features, and metamorphic assemblages at Lapa are related to the tectonometamorphic evolution of the Cadillac–Larder Lake Fault Zone at different times and crustal levels, and varying heat and fluid flow regimes. The Lapa deposit demonstrates that early, low-grade gold mineralization within the Cadillac–Larder Lake Fault Zone has benefited from late gold enrichment(s) during prograde and retrograde metamorphism, suggesting that multi-stage processes may be important to form gold-rich orogenic deposits in first order crustal-scale structures. 相似文献
2.
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. 相似文献
3.
甘肃李坝金矿围岩蚀变与金成矿关系 总被引：1，自引：0，他引：1
西秦岭地区是目前国内造山型和卡林型金矿找矿的热点地区之一,已发现的甘肃李坝造山型金矿为超大型规模。以李坝金矿6号矿带为例,系统地研究了其蚀变矿物组合、近矿围岩蚀变分带及相应的金矿化特征,总结了矿床(带)的蚀变分带模式。该模式具典型的中心式环带结构,可分为3个蚀变带,由中心向外依次为黄铁绢英岩化带、绢云母化带和绿泥石化带。蚀变矿物组合分别为黄铁矿+绢云母+石英±毒砂±白云母±电气石±方解石、绢云母+绿泥石+石英+黄铁矿±黑云母及绿泥石+黑云母±绢云母±黄铁矿;与这3个蚀变带相对应的是金的富集带、矿化带和无矿带。蚀变岩石物质组分迁移分析表明,围岩蚀变及其分带是热水流体/岩石反应时岩石化学组分发生迁移的结果,矿化伴随着蚀变发生,且金矿化与黄铁矿化和浸染状硅化关系最为密切。 相似文献
4.
Vostok-2—East Russia’s largest skarn deposit of high-grade sulfide-scheelite ore with substantial base-metal and gold mineralization—was formed during the Mesozoic orogenic epoch of evolution of the Far East marginal continental system as an element of the gold-tin-tungsten metallogenic belt. The deposit is related to the multistage monzodiorite-granodiorite-granite complex pertaining to the ilmenite series and spatially associated with a minor granodiorite porphyry (?) stock, which bears petrological features transi- tional to those of intrusive rocks occurring at Au-W and Au deposits. The hydrothermal metasomatic alteration of host rocks evolved from pyroxene skarn via retrograde postskarn and propylitic (hydrosilicate) metasomatic rocks to the late, low-temperature quartz-sericite metasomatic rocks often with albite, chlorite, carbonate, and apatite. The mineral assemblages of skarn and postskarn metasomatic rocks correspond to those at the reduced-type tungsten skarn deposits. Zoning of the postskarn metasomatic rocks is controlled by granodiorite stock. The hydrothermal metasomatic alteration was accompanied by development of mineralization from scheelite via sulfide-scheelite with pyrrhotite and chalcopyrite to the gold-base-metal-scheelite assemblage with arsenopyrite, Bi-Sb-Te-Pb-Zn sulfides and sulfosalts. Several scheelite generations are recognized. Scheelite of the late generations is enriched in Eu, as is typical of gold deposits. The associated gold mineralization comprises both native gold varying in fineness and Au-bearing arsenopyrite. The significant gold mineralization emphasizes genetic links of this deposit with intrusion-related Au-W and Au deposits of the reduced type. 相似文献
5.
6.
The Golden Pride gold deposit (∼3 Moz) is located in the central part of the Nzega Greenstone Belt at the southern margin
of the Lake Victoria Goldfields in Tanzania. It represents an inferred Late Archaean, orogenic gold deposit and is hosted
in intensely deformed meta-sedimentary rocks in the hanging wall of the approximately E–W striking Golden Pride Shear Zone.
The hanging-wall sequence also includes felsic (quartz porphyritic) to mafic (lamprophyric) intrusions, as well as banded
iron formations. Hydrothermal alteration phases associated with mineralisation are dominated by sericite and chlorite. Two
main ore types can be distinguished, chlorite and silica ore, both occupying dilational sites and structural intersections
in the hanging wall of the main shear zone. Sulphide minerals in both ore types include pyrrhotite, arsenopyrite, pyrite and
accessory sphalerite, galena, sulphosalts and Ni–Co–Bi sulphides. Gold and tellurides are late in the paragenetic sequence
and associated with a secondary phase of pyrrhotite deposition. Sulphur isotope compositions range from −6 to 7 per mil and
are interpreted to reflect contributions from two distinct sources to the mineralising fluids in the Golden Pride gold deposit.
A redox change, potentially induced by the intrusion of mafic melts, together with structural elements in the hanging wall
of the Golden Pride Shear Zone, are interpreted to be the main controls on gold mineralisation in this deposit. 相似文献
7.
We compare melting of potassic alteration zones in metamorphosed gold deposits with that of unaltered rocks of the same protolith
to examine their relative contributions to crust-derived magmas and to investigate the implications for ore genesis. Potassic
hydrothermal alteration, at the crustal levels where orogenic gold deposits form, stabilizes a higher proportion of muscovite
and biotite than is possible in unaltered rocks at high metamorphic grades. Because these micas contain water, they control
the melt fraction generated through dehydration melting in that a greater proportion of micas permits more extensive melting.
Orogenic gold deposits, in which mineralization is typically encapsulated by potassic alteration, form at deep-enough crustal
levels to survive repeated tectonic activity, which can lead to their being metamorphosed. In the vicinity of this metamorphosed
gold mineralization, the greatest proportion of felsic melt is generated in the more metal- and sulfur-rich rocks because
of the associated potassic alteration. Ore minerals dissolve and are physically incorporated into the resulting felsic melt,
which thereby becomes metal- and sulfur-enriched. Since melt fraction is the dominant control on strain partitioning and melt
mobilization, increased melting in K-altered mineralized rocks implies that these sites will be the first to experience melt
escape and will continue to be the focus of melt escape during ongoing metamorphism. This strain partitioning promotes shear
zone development, and once shearing is localized to K-altered mineralized domains, it may attract external magma, allowing
extension and linking with nearby active shear zones. In this way, mineralized zones may connect to a regional network of
magma transfer, allowing metal enrichment of migrating magmas. Terrains that underwent widespread K alteration associated
with mid-crustal gold enrichment are likely, when metamorphosed, to produce significant volumes of reduced, relatively metal-
and sulfur-enriched felsic magma. The ages and relative tectonic preservation potential of different K alteration-associated
ore types implies that Au, Ag, As, Sb, Bi, Te, and W may be recycled within the crust through this mechanism, whereas Cu and
Mo are unlikely to be recycled and require mantle sourcing to form new intrusion-related ores. Silicate melt derived from
preexisting zones of gold enrichment in the lower crust may contribute significantly to the metal budget of intrusion-related
gold systems, and possibly some gold-rich porphyry deposits. 相似文献
8.
西秦岭造山带是我国最重要的金成矿带之一。以往研究大多认为造山型金矿床和(类)卡林型金矿床是西秦岭主要的金矿床类型,并且两类金矿床的金成矿作用主要与造山过程中的区域变质作用有关,而与岩浆活动不存在直接的成因联系。位于西秦岭造山带西段的夏河—合作地区大面积出露花岗岩类侵入体,其周缘发育有富金的夕卡岩型铜(钨)矿床。近年来该地区新发现的多个大型—超大型石英脉型金矿床和微细粒浸染型金矿床都与中酸性侵入岩的空间关系紧密,暗示这些金矿床可能和岩浆活动有成因联系。论文在作者研究结果以及总结前人成果基础上,综述了夏河—合作地区典型金(铜)矿床的地质矿化特征、地球化学特征、时空分布特征,以及中酸性侵入岩的岩性特征、形成时代和演化过程。年代学研究结果显示,夏河—合作地区的早子沟微细粒浸染型金矿床、德乌鲁夕卡岩型金(铜)矿床和老豆石英脉型金矿床均形成于250~240 Ma,与邻近的早中三叠世花岗闪长质石英闪长质侵入岩近于同时形成。拉布在卡等石英脉型金矿床略晚于区内中三叠世末期侵位的闪长玢岩脉(约230~225 Ma)形成。H、O、S、C、B、Pb等多种同位素地球化学特征指示该地区早中三叠世金矿床的成矿热液均为岩浆来源,并且显示低氧逸度的特征。早中三叠世中酸性侵入岩的还原性钛铁矿系列花岗岩类特征,以及同时代的多种金矿化类型和成矿分带性,表明夏河—合作地区在早中三叠世(约250~230 Ma)多期次侵位的钛铁矿系列I型中酸性岩浆是金成矿作用的成矿流体和成矿物质的主要来源,其中与250~240 Ma多期金成矿事件有关的准铝质弱过铝质、高钾钙碱性系列花岗岩类侵入岩均经历了幔源基性熔体和壳源酸性熔体的岩浆混合作用,而与约230 Ma的金成矿作用有关的闪长质岩浆岩则可能指示了更多幔源基性熔体的加入。与金(铜)成矿有关的早中三叠世还原性中酸性岩是在古特提斯洋俯冲过程中局部弧后伸展条件下交代富集地幔楔部分熔融形成的基性岩浆与壳源酸性岩浆混合作用的产物。夏河—合作地区形成于早中三叠世的夕卡岩型、电气石石英脉型、石英方解石脉型和微细粒浸染型金矿床共同构成了一个与还原性侵入岩有关的金成矿系统。夏河—合作地区与还原性侵入岩有关的金成矿系统的发现,丰富了西秦岭造山带区域成矿作用的类型,并为西秦岭西段其他早中三叠世岩浆岩分布区(如青海同仁地区)的金矿勘查工作提供了新的思想和方向。 相似文献
9.
Gold deposits in the Syama and Tabakoroni goldfields in southern Mali occur along a north-northeast trending mineralised litho-structural corridor that trends for approximately 40 km. The deposits are interpreted to have formed during a craton-wide metallogenic event during the Eburnean orogeny. In the Syama goldfield, gold mineralisation in 9 deposits is hosted in the hanging-wall of the Syama-Bananso Shear Zone in basalt, greywacke, argillite, lamprophyre, and black shale. Gold is currently mined primarily from the oxidised-weathered zone of the ore bodies. In the Syama deposit, mineralisation hosted in altered basalt is associated with an intense ankerite–quartz–pyrite stockwork vein systems, whereas disseminated style mineralisation is also present in greywackes. In contrast, the Tellem deposit is hosted in quartz–porphyry rocks.In the Tabakoroni goldfield, gold mineralisation is hosted in quartz veins in tertiary splay shears of the Syama-Bananso Shear Zone. The Tabakoroni orebody is associated with quartz, carbonate and graphite (stylolite) veins, with pyrite and lesser amounts of arsenopyrite. There are four main styles of gold mineralisation including silica-sulphide lodes in carbonaceous fault zones, stylolitic quartz reefs in fault zones, quartz–Fe–carbonate–sulphide lodes in mafic volcanics, and quartz–sulphide stockwork veins in silicified sediments and porphyry dykes. The several deposit styles in the goldfield thus present a number of potential exploration targets spatially associated with the regional Syama-Bananso Shear Zone and generally classified as orogenic shear-hosted gold deposits. 相似文献
10.
Alteration and mineralization styles of the orogenic disseminated Zhenyuan gold deposit,southeastern Tibet: Contrast with carlin gold deposit 总被引：1，自引：0，他引：1
Orogenic disseminated and Carlin gold deposits share much similarity in alteration and mineralization.The disseminated orogenic Zhenyuan Au deposit along the Ailaoshan shear zone,southeastern Tibet,was selected to clarify their difference.The alteration and mineralization from the different lithologies,including meta-quartz sandstone,carbonaceous slate,meta-(ultra)mafic rock,quartz porphyry and lamprophyre were researched.According to the mineral assemblage and replacement relationship in all types of host rocks,two reactions show general control on gold deposition:(1)replacement of earlier magnetite by pyrite and carbonaceous material;(2)alteration of biotite and phlogopite phenocrysts in quartz porphyry and lamprophyre into dolomite/ankerite and sericite.Despite the lamprophyre is volumetrically minor and much less fractured than other host rocks,it contains a large portion of Au reserve,indicating that the chemically active lithology has played a more important role in gold precipitation compared to structure.LA-ICP-MS analysis shows that Au mainly occurs as invisible gold in fine-grained pyrite disseminated in the host rocks,with Au content reaching to 258.95 ppm.The diagenetic core of pyrite in meta-quartz sandstone enriched in Co,Ni,Mo,Ag and Hg is wrapped by hydrothermal pyrite enriched in Cu,As,Sb,Au,Tl,Pb and Bi.Different host rock lithology has much impact on the alteration and mineralization features.Carbonate and sericite in altered lamprophyre show they have higher Mg than those developed in other of host rocks denoting that the carbonate and sericite incorporated Mg from phlogopite phenocrysts in the primary lamprophyre during alteration.The ore fluid activated the diagenetic pyrite in meta-quartz sandstone leading the hydrothermal pyrite enriched in Cu,Mo,Ag,Sb,Te,Hg,Tl,Pb and Bi,but the hydrothermal pyrite in meta-(ultra)mafic rock is enriched in Co and Ni as the meta-(ultra)mafic rock host rock contain high content of Co and Ni.However,Au and As shear similar range in both types of host rocks indicating that these two elements most likely come from the deep source fluid rather than the host rocks.It was shown in the disseminated orogenic gold deposit that similar hydrothermal alteration with mineral assemblage of carbonate(mainly dolomite and ankerite),sericite,pyrite and arsenopyrite develops in all types of host rocks.This is different from the Nevada Carlin type,in which alteration is mainly dissolution and silicification of carbonate host rock.On the other hand,Au mainly occur as invisible gold in both disseminated orogenic and Carlin gold deposits. 相似文献
11.
川西丹巴地区磨子沟金矿床金、银赋存状态及成因 总被引：1，自引：0，他引：1
磨子沟金矿床位于四川省丹巴县,大地构造位置位于扬子准地台西缘,松潘-甘孜造山带东缘,泥盆系危关组炭质千枚岩、板岩是主要的赋矿围岩。成矿过程分为沉积成矿期、热液成矿期和表生风化期,其中热液期是金的主要成矿期。通过显微镜观察,扫描电镜、电子探针成分分析,矿物晶体化学式计算等手段和方法,研究了矿床中Au、Ag的赋存状态和主要载金矿物的特征。金以裂隙金、包裹体金、粒间金为主,银主要以类质同像赋存于方铅矿和硫盐矿物中。载金矿物黄铁矿生物结构发育,表明生物成矿作用是金矿床形成过程中的重要作用。矿体受特定层位和断裂的控制,围岩蚀变强烈。根据矿床产出的大地构造环境、赋矿围岩特征、构造控矿、层位控矿、矿物共生特点等分析结果,丹巴磨子沟金矿床为沉积-热液改造型金矿床。 相似文献
12.
新疆东部金矿床类型、成矿特点及找矿方向 总被引：6，自引：2，他引：6
据金矿类型划分标准，结合新疆东部金成矿特点，划分出韧性剪切带型金矿、浅成低温热液型金矿、岩浆热液型金矿、斑岩型金（铜）矿、硅化帽型金矿及变质岩型或绿片岩型银金矿6种成因类型，8种工业类型。通过研究，划分出以斑岩型金矿为主的大南湖－三岔口成矿带、以韧性剪切带型金矿为主的康古尔塔格－黄山成矿带、以浅成低温热液型金矿为主的马庄山－南金山成矿带、以绿片蚀变岩型银金、铅锌矿以及硅铁建造型金矿为主的玉西－铅炉子成矿带、以岩浆热液型金矿为主的金窝子－照壁山成矿带和依热达坂－红山成矿带、以韧性剪切带型和硅帽型金矿为主的头苏泉－塔林成矿带7个金矿成矿带，在此基础上确定该区区找矿主要类型和远景区。 相似文献
13.
西藏班公湖- 怒江成矿带商旭金矿成矿时代探讨及其地质意义 总被引：2，自引：0，他引：2
造山型金矿在世界范围内具有重要的经济价值和找矿潜力,也是西藏班公湖 怒江铜多金属资源基地的主攻矿床类型之一。班公湖 怒江成矿带是近十年来识别和建立的我国最重要的斑岩 浅成低温热液 矽卡岩型铜金成矿带。商旭金矿位于班公湖 怒江缝合带中段,是该成矿带上首例造山型金矿床。矿体产于中 下侏罗统木嘎岗日群沉积岩,由石英脉、碳酸盐+石英脉和蚀变岩构成,呈透镜状、块状、条带状、鞍状、浸染状、角砾状等产出,受北西西向的区域断裂构造控制。热液蚀变发育碳酸盐化、白云母化、绿泥石化和硫化物蚀变等。矿物学研究和含矿脉体特征表明,早期热液活动发育于挤压应力环境,后期挤压应力逐渐消失,对应了变形晚期的构造环境。含金石英流体包裹体的Rb- Sr同位素测试获取的等时线年龄为135. 6±2. 7Ma,87Sr/86 Sr平均初始比值为0. 713,预示成矿作用发生于早白垩世,成矿物质主要来自地壳。综合研究认为,商旭金矿形成于早白垩世初班公湖 怒江缝合带中段的闭合期,地块间挤压应力致使木嘎岗日群发生构造变形,在挤压变形晚期构造环境发生转换的过程,围岩中应力释放促成了区域的金矿化。对比研究显示,商旭金矿化与世界大型、超大型造山型金矿在矿床地质、热液蚀变特征、成矿流体性质、成矿构造环境、动力学背景等方面具有相似性,进一步表明班 怒带具备寻找造山型金矿的潜力。 相似文献
14.
Hydrothermal alteration related to Sb-Au mineralization is widespread in the Variscan Armorican Massif, but mineral replacement reactions are not well characterized, in particular the hydrothermal breakdown of ilmenite-titanohematite. Based on petrography, electron probe micro-analyzer and laser ablation-inductively coupled plasma-mass spectrometer analyses, we document mineralogical change at rock- and mineral-scale and the redistribution of Sb and others trace elements during the recrystallization of ilmenite-titanohematite to hydrothermal rutile. Hydrothermal alteration is mainly potassic with associated carbonation. The replacement mechanism is interpreted to be an interface-coupled dissolution-reprecipitation process. Results show that Mn, Zn, Co, Ni, Sn, Mo and U are released during hydrothermal alteration, whereas Sb and W are incorporated in newly-formed hydrothermal rutile from the hydrothermal fluid. Furthermore, the concentration of Sb evolves through time suggesting a change in fluid composition likely related to an enrichment of fluid in Sb during rutile crystallization. Considering that Fe-Ti oxides breakdown during hydrothermal alteration is common within epithermal and mesothermal/orogenic Au-Sb mineralizing systems, results report in this study yield important constraints about metal mobility and exchanges in hydrothermal gold systems. 相似文献
15.
美国阿拉斯加州中东部福特—诺克斯(Fort Knox)金矿床是北极圈周缘规模最大的超大型金矿床之一。对该矿床的形成背景、矿体特征、形成模式的研究表明,该矿床主要产于前寒武纪—早古生代绿片岩与白垩纪—古近纪花岗质侵入岩接触带上,受构造-岩浆活动控制明显,地表出露面积为1100×600m2,并向深部逐渐变小。与其他与侵入岩有关的金矿床不同的是,该矿床热液蚀变作用强烈,与金矿化具密切空间分布关系的热液蚀变主要为钾长石化、钠长石化、绢云母化和青磐岩化。同位素年代学证据表明,其成矿时代为晚白垩世—古近纪(92.5±0.2Ma),是多期次岩浆作用的产物。依据同位素特征、成矿流体、围岩蚀变等特征可以判定,成矿物质主要来源于花岗质熔浆,成矿作用与氧化型中酸性侵入体侵入作用及其相关流体活动有关,属于典型的与侵入岩有关的金矿床。 相似文献
16.
The Mupane gold deposit, which is one of the numerous gold occurrences in the Tati Greenstone Belt in the northeastern part of Botswana, consists of four orebodies, namely Tau, Tawana, Kwena, and Tholo deposits. The present research, which focuses on the genesis of the Tau deposit, was based on ore petrography, mineral chemistry of sulfides, and sulfur isotope data. Mineralogical characteristics of the host rocks indicate that banded iron formation at the Tau deposit includes iron oxides (magnetite), carbonates (siderite and ankerite), silicates (chlorite and amphibole), and sulfides (arsenopyrite and pyrrhotite). The deposit features arsenopyrite-rich zones associated with biotite-chlorite veins, which are indicative of the precipitation of arsenopyrite concomitant with potassic alteration. The replacement of magnetite by pyrrhotite in some samples suggests that sulfidation was likely the dominant gold precipitation mechanism because it is considered to have destabilized gold-thiocomplexes in the ore-forming fluids. Based on textural relationships and chemical composition, arsenopyrite is interpreted to reflect two generations. Arsenopyrite 1 is possibly early in origin, sieve textured with abundant inclusions of pyrrhotite. Arsenopyrite 1 was then overgrown by late arsenopyrite 2 with no porous textures and rare inclusions of pyrrhotite. Gold mineralization was initiated by focused fluid flow and sulfidation of the oxide facies banded iron formation, leading to an epigenetic gold mineralization. The mineralogical assemblages, textures, and mineral chemistry data at the Tau gold deposit revealed two-stage gold mineralizations commencing with the deposition of invisible gold in arsenopyrite 1 followed by the later formation of native gold during hydrothermal alteration and post-depositional recrystallization of arsenopyrite 1. Laser ablation inductively coupled plasma mass spectrometric analysis of arsenopyrite from the Tau deposit revealed that the hydrothermal event responsible for the formation of late native gold also affected the distribution of other trace elements within the grains as evidenced by varying trace elements contents in arsenopyrite 1 and arsenopyrite 2. The range of δ34S of gold-bearing assemblages from the Tau deposit is restricted from +1.6 to +3.9‰, which is typical of Archean orogenic gold deposits and indicates that overall reduced hydrothermal conditions prevailed during the gold mineralization process at the Tau deposit. The results from this study suggest that gold mineralization involved multi-processes such as sulfidation, metamorphism, deformation, hydrothermal alteration, and gold remobilization. 相似文献
17.
The Daraloo field is located in the southeast of Iran (Kerman province). It is associated with Oligomiocene diorite/granodiorite to quartz monzonite stocks. Copper mineralization is basically relevant to potassic and phyllic alteration zones. Petrographic and geologic studies imply that mineralization is restricted to two major parts locating in the center and east of district. The larger central mineralization has a northwest–southeast trend perpendicular to the smaller one. Hydrothermal ore fluid formation occurred in relatively deep levels thereafter faulting and fracturing provided appropriate conduits to ascend fluids through shallower depths. Early hydrothermal alteration produced a confined potassic assemblage in the central and eastern parts of the stock. Two main fluid inclusion groups in relationship with alteration ore fluids have been identified. They are liquid-rich inclusions containing solid phases, with high temperatures (257°C to 554°C) and high salinities (31 to 67 wt.% NaCl equiv.), and vapor-rich inclusions with high temperatures and low salinities without any solid phases. These magmatic source fluids are responsible for boiling and also potassic and phyllic alteration zone. They also resulted in the formation of quartz groups I and II veins and chalcopyrite deposition. Propylitic alteration is attributed to a Ca-rich meteoric fluid. Inclusions originated from this fluid are liquid-rich having low temperatures (161°C to 269°C) and low salinities (1 to 13 wt.% NaCl). Mixing descending meteoric water with magmatic fluids reduces considerably the salinity of magmatic fluid. Mixing is also the impetus of leaching copper from potassic to the phyllic zone. It is possible to conclude that all these procedures are controlled by the main faults of district having NW–SE trend. Two fundamental events affecting the mineralization are cooling ore-bearing fluids and magnetite (±pyrite) emplacement. The latter one is formed in potassic and phyllic alteration zone in which copper-bearing fluids have interaction with magnetite minerals and so chalcopyrite minerals have been formed nearby magnetites. Temperature and pressure of hydrothermal fluid differentiation could be applied as a predictive tool to discriminate between barren and productive copper porphyry deposits. A simple comparison of temperature and pressure variations between Daraloo deposit and other copper porphyry deposits located in the same belt of Iran (Sahand-Bazman belt) illuminates that Daraloo system has high range of pressure implying deeper exsolution of hydrothermal fluid. On the other hand, economic mineralization has direct relationship with temperature range of orthomagmatic fluids so that if a deposit has a wide range of high temperature fluids, it could be inferred as a barren deposit. In conclusion, it could be inferred that Daraloo district can be categorized as a sub-economic porphyry deposit. On the other hand, restricted formation of chalcopyrite and the other copper-bearing minerals besides large amounts of magnetite and pyrite can approve obviously the low grade of mineralization in Daraloo district. 相似文献
18.
秦岭造山带柞水-山阳矿集区夏家店金矿床成矿时代及其地质意义 总被引：1，自引：1，他引：0
柞水-山阳矿集区位于秦岭造山带中部,区内矿产资源丰富,金矿找矿近年来不断取得突破,发现了多个大-中型金矿床,然而区内金矿成矿时代、成矿地质背景一直存在争议,直接制约矿集区金矿床找矿工作。夏家店金矿床是该区大型金矿床,矿体受断裂构造控制,金矿石类型有角砾岩型、碎裂岩型、糜棱岩型3种。围岩蚀变强烈,主要由硅化、方解石化、绢云母化、高岭土化、萤石化、重晶石化等,与金成矿关系最密切的是硅化、方解石化、萤石化。热液成矿期可划分为石英阶段、石英-方解石-萤石-硫化物阶段、方解石阶段。文章选取夏家店金矿床主成矿期的方解石、萤石等矿物进行了Sm-Nd同位素测试工作,获得等时线年龄为(139.64±0.98)Ma,表明成矿时代为晚侏罗世。结合区域构造-岩浆成矿作用特征,认为夏家店金矿床成矿作用与晚侏罗世—早白垩世构造-岩浆事件有关。据此将柞水山阳矿集区金矿床成矿年龄厘定在140Ma左右,为秦岭造山带伸展的地球动力背景下构造-岩浆热液演化的产物。通过与区内晚侏罗世—早白垩世构造-岩浆成矿事件对比,文章首次提出柞水-山阳矿集区存在140 Ma左右的金矿床成矿事件,为下一步在柞水-山阳矿集区开展金矿床勘查工作提供了重要依据。 相似文献
19.
Imogen O.H. Fielding Simon P. Johnson Sebastien Meffre Jianwei Zi Stephen Sheppard Ross R. Large Birger Rasmussen 《地学前缘(英文版)》2019,10(1):89-105
Proterozoic orogens commonly host a range of hydrothermal ores that form in diverse tectonic settings at different times. However, the link between mineralization and the regional-scale tectonothermal evolution of orogens is usually not well understood, especially in areas subject to multiple hydrothermal events.Regional-scale drivers for mineral systems vary between the different classes of hydrothermal ore, but all involve an energy source and a fluid pathway to focus mineralizing fluids into the upper crust. The Mount Olympus gold deposit in the Proterozoic Capricorn Orogen of Western Australia, was regarded as an orogenic gold deposit that formed at ca. 1738 Ma during the assembly of Proterozoic Australia. However,the trace element chemistry of the pyrite crystals closely resembles those of the Carlin deposits of Nevada,with rims that display solid solution gold accompanied by elevated As, Cu, Sb, Hg, and Tl, surrounding gold-poor cores. New SHRIMP UeP b dating of xenotime intergrown with auriferous pyrite and ore-stage alteration minerals provided a weighted mean~(207) Pb*/~(206) Pb* date of 1769 ± 5 Ma, interpreted as the age of gold mineralization. This was followed by two discrete episodes of hydrothermal alteration at 1727 ± 7 Ma and 1673 ± 8 Ma. The three ages are linked to multiple reactivation of the crustal-scale Nanjilgardy Fault during repeated episodes of intracratonic reworking. The regional-scale drivers for Carlin-like gold mineralization at Mount Olympus are related to a change in tectonic regime during the final stages of the intracratonic 1820 -1770 Ma Capricorn Orogeny. Our results suggest that substantial sized Carlin-like gold deposits can form in an intracratonic setting during regional-scale crustal reworking. 相似文献
20.
Uranium and polymetallic U mineralization hosted within brecciated albitites occurs one kilometer south of the magnetite-rich Au–Co–Bi–Cu NICO deposit in the southern Great Bear magmatic zone (GBMZ), Canada. Concentrations up to 1 wt% U are distributed throughout a 3 by 0.5 km albitization corridor defined as the Southern Breccia zone. Two distinct U mineralization events are observed. Primary uraninite precipitated with or without pyrite–chalcopyrite?±?molybdenite within magnetite–ilmenite–biotite–K-feldspar-altered breccias during high-temperature potassic–iron alteration. Subsequently, pitchblende precipitated in earthy hematite–specular hematite–chlorite veins associated with a low-temperature iron–magnesium alteration. The uraninite-bearing mineralization postdates sodic (albite) and more localized high-temperature potassic–iron (biotite–magnetite ± K-feldspar) alteration yet predates potassic (K-feldspar), boron (tourmaline) and potassic–iron–magnesium (hematite ± K-feldspar ± chlorite) alteration. The Southern Breccia zone shares attributes of the Valhalla (Australia) and Lagoa Real (Brazil) albitite-hosted U deposits but contains greater iron oxide contents and lower contents of riebeckite and carbonates. Potassium, Ni, and Th are also enriched whereas Zr and Sr are depleted with respect to the aforementioned albitite-hosted U deposits. Field relationships, geochemical signatures and available U–Pb dates on pre-, syn- and post-mineralization intrusions place the development of the Southern Breccia and the NICO deposit as part of a single iron oxide alkali-altered (IOAA) system. In addition, this case example illustrates that albitite-hosted U deposits can form in albitization zones that predate base and precious metal ore zones in a single IOAA system and become traps for U and multiple metals once the tectonic regime favors fluid mixing and oxidation-reduction reactions. 相似文献