Gold and antimony metallogenic relations and ore-forming process of Qinglong Sb(Au) deposit in Youjiang basin, SW China: Sulfide trace elements and sulfur isotopes

In the northwestern margin of the Youjiang basin(NWYB)in SW China,many Carlin-like gold deposits are highly antimony(Sb)-rich,and many vein-type Sb deposits contain much Au.These deposits have similar ages,host rocks,ore-forming temperatures,ore-related alterations and ore mineral assemblages,but the Au and Sb metallogenic relations and their ore-forming process remain enigmatic.Here we investigate the large Qinglong Sb deposit in the NWYB,which has extensive sub-economic Au mineralization,and present a new metallogenic model based on in-situ trace elements(EPMA and LA-ICP-MS)and sulfur isotopes(NanoSIMS and fs-LA-MC-ICPMS)of the ore sulfides.At Qinglong,economic Sb ores contain coarse-grained stibnite,jasperoid quartz and fluorite,whilst the sub-economic Au–Sb ores comprise dominantly veined quartz,arsenian pyrite and fine-grained stibnite.Three generations of ore-related pyrite(Py1,Py2 and Py3)and two generations of stibnite(Stb1 and Stb2)are identified based on their texture,chemistry,and sulfur isotopes.The pre-ore Py1 is characterized by the lower ore element(Au,As,Sb,Cu and Ag)contents(mostly below the LA-ICP-MS detection limit)and Co/Ni ratios(average 0.31)than the ore-stage pyrites(Py2 and Py3),implying a sedimentary/diagenetic origin.The Py2 and Py3 have elevated ore element abundance(maximum As=6500 ppm,Au=22 ppm,Sb=6300 ppm,Cu=951 ppm,Ag=77 ppm)and Co/Ni ratios(average 1.84),and have positive As vs.Au–Sb–Cu–Ag correlations.Early-ore Stb1 has lower As(0.12–0.30 wt.%)than late-ore Stb2(0.91–1.20 wt.%).These features show that the progressive As enrichment in ore sulfides is accompanied by increasing Au,Sb,Cu and Ag with the hydrothermal evolution,thereby making As a good proxy for Au.As-rich,As-poor and As-free zones are identified via NanoSIMS mapping of the Au-bearing pyrite.The As-rich zones in the Qinglong Au-bearing pyrites(Py2 and Py3)and ore stibnites(Stb1 and Stb2)have narrowδ^(34)SH_(2)S ranges(-8.9‰to +4.1‰,average-3.1‰)and-2.9‰to +6.9‰,average + 1.3‰),respectively,indicating that the Au-rich and Sb-rich fluids may have had the same sulfur source.Published in-situ sulfur isotopic data of pyrite As-rich zones from other Carlin-like Au deposits(Shuiyindong,Taipingdong,Nayang,Getang and Lianhuashan)in the NWYB have similar ore-fluidδSH_(2)S values(-4.5‰to +6.7‰,average-0.6‰)to those of Qinglong.Therefore,we infer that the sulfur of both Au and Sb mineralization was derived from the same magmatic-related source(0±5‰)in the NWYB.Moreover,the core of pyrites(Py1)has variable S isotope fractionation(-18.9‰to +18.1‰,mostly +3‰to +12‰),suggesting that the higher-^(34)S H_(2)S was produced by bacterial sulfate reduction(BSR).The hydrothermal pyrite(Py2 and Py3)δ^(34)S values gradually decrease with increasing As concentrations,and ultimately,within the restricted range(-5‰to +5‰)in As-rich zones.This variation implies that the As-rich pyrite was formed through ongoing interactions of the magmatic-hydrothermal fluid with pre-existing sedimentary pyrites,causing the progressive decreasing δ^(34)S values with As content increase,Hence,the fluid/mineral interaction may have generated the observed variation in δ^(34)S and As contents.Overall,comparing the Au and Sb deposits in the NWYB,we favor a magmatic-related source for the Au–Sb–As-rich fluids,but the Au-and Sb-ore fluids were likely evolved at separate stages in the ore-forming system.

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 Carlin-type,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.

Source characteristics and genesis of Sb mineralization from the Au and Sb deposits of the Youjiang Basin,SW China:constraints from stibnite trace element and isotope geochemistry

The Youjiang Basin is characterized by a wide distribution of Au and Sb deposits.These deposits are mainly hosted by sedimentary rocks from Cambrian to Triassic and are structurally controlled by faults and folds.Three types of Sb mineralization can be distinguished based on geologic characteristics,economic metals,and mineral associations.The first type is dominated by Sb mineralization but contains minor or little Au,similar to the large Qinglong deposit.The second type has a spatial association with the gold deposit but formed independent Sb mineralization,reminiscent of the Badu deposit.In the third type,Sb generally formed as an accompanying element in the Carlin-type gold deposit,and stibnite occurred as euhedral crystals filling the open space and faults in the late stage of gold mineralization,analogous to the Yata deposit.Trace element concentrations and sulfur isotopic ratio of stibnite,and oxygen isotope of stibnite bearing quartz were analyzed to infer the ore source(s)for Sb mineralization and genesis.To distinguish the various types of stibnite mineralization between the deposits,Cu,Pb,and As have recognized most diagnostic,with an elevated concentration in Au and Au-Sb deposits and depleted in Sb deposit.Theδ34S isotopic composition of stibnite samples from three deposits show a wide variation,ranging from-6.6%to+17.45%.Such isotopic values may indicate the sedimentary sulfur source,introduced by fluid–rock interaction.On the other hand,fluid mixing of several end members cannot be excluded.The calculatedδ18O isotopic data of Sb-bearing quartz show the initial ore fluid in Au and Au-Sb deposits most likely have a magmatic or metamorphic origin that enriched during fluid–rock interaction,and Sb deposit characterized by initial meteoric water.From these data,we proposed that different lithologies,fluid–rock interaction,fluid pathways,and different ore fluids controlled the compositional evolution of fluids,which might be the main reason for the diversity of Au or Sb mineralization.

Devonian-Carboniferous Pillow OIB-Type Basalts in the Youjiang Basin,SW China:Implications for the Eastern Extension of the Paleo-Tethys Branch Ocean

Late Paleozoic pillow basalts are well preserved in the Youjiang Basin of SW China.In this study,we conducted geochemical and Sr-Nd isotopic study on the Late Devonian and Late Carboniferous basalts in Napo area,Youjiang Basin.The analyzed samples comprise moderate SiO2,TiO2,Mg#,and REE contents,with slightly positive or negative Eu anomalies,similar to the chemical nature of OIB(Oceanic island basalt).All basalts show low(^(143)Nd/^(144)Nd)iand(^(87)Sr/^(86)Sr)ivalues,close to EMI-type(I-type Enriched Mantle)magma source.Late Carboniferous basalts display higher(^(87)Sr/^(86)Sr)i,Nb/Th,and lowerε_(Nd)(t),Zr/Nb values than those of the Late Devonian basalts,implying progressively decreased enrichment components in the magma source processes.Such evolution trend reflects a continuous lithospheric thinning event,supporting a progressive rifting setting of the Youjiang Basin along the southwestern margin of the Yangtze Block in Late Paleozoic.Combined with regional geological background,the Youjiang Basin is viewed as a continental rift basin related to the opening of the Paleo-Tethys Ocean in Late Devonian and became a passive continental margin basin in Carboniferous.The Paleo-Tethys branch ocean probably extended further to the southern Youjiang Basin,likely corresponding to the Song Ma suture zone.

Evolution of Sedimentation and Tectonics of the Youjiang Composite Basin, South China

Located at the southern margin of the South China plate, the Youjiang basin is a closely related to the NW- and NE-trending syndepositional faults in respect to the configuration and structure of the basin. The evolution of the Youjiang basin progressed through two stages. In the Hercynian period, the opening of the Ailaoshan-Honghe ocean basin gave rise to a number of NW-trending rift belts in the Youjiang area. During this period, deep-water sediments were dominant and the basin was possesed of the characteristics of the rift system of passive continental margins. In the early Indosinian after the Dongwu movement, the circum - Pacific tectonism led to a major change in the configuration and structure of the basin. In the meantime, the Ailaoshan ocean basin began to be subducted towards the northeast, thus causing the basin to be split and expand again, and then the basin developed into the stage of the back -arc basin. At the end of the Indosinian period, the basin gradually closed from east to west, thus ending up the history of development of the Youjiang basin. In the various developmental stages, sediments in the basin, also limited by the Dongwu movement, were formed by superposition of sedimentation systems with different features, and a typical two-layered structure, which consisted of starved and compensated sediments, also occurred in the early stage. Likewise, volcanic activity in the basin involved two stages. Basin volcanic rocks of alkali and alkali-calcic series, which were controlled by NW-trending faults, occurred in the early stage, and basic and intermediate-acid volcanic rocks of calc-alkali and calcic series, which were controlled by NW- and NE-trending faults. From the above it follows that the Youjiang basin was formed by the combined action of the Palaeotethys and circum -Pacific tectonism.

Depositional chemistry of chert during late Paleozoic from western Guangxi and its implication for the tectonic evolution of the Youjiang Basin

Continual deep-water sediments from the late Early Devonian to the Late Permian extended in wide areas of western Guangxi. We analyzed the major, trace, and rare earth elements of the Upper Paleozoic cherts in Badu, western Guangxi. High non-terrigenous SiO2 contents （Sinon_ter/Sibulk（%）〉 80%） and pure chert components （〉 70%） indicate a large extent of silicifi- cation in the Upper Paleozoic cherts, except for the Upper Devonian-Lower Carboniferous Luzhai Formation cherts, which have lower non-terrigenous SiO2 contents （avg. 71.8%） and pure chert components （40%-70%）. The Al/（AI＋Fe＋Mn） ratios and Feter/Febulk（%） values of samples from the lowest horizon of the Pingen Formation are 0.05-0.26, 13.1%-14.5%, respec- tively, indicating hydrothermal origins. All other samples show high Al/（Al＋Fe＋Mn） ratios （0.39±0.81） and high Feter/Febulk（%） values （23.1%-186.8%）, indicating non-hydrothermal origins. The Pingen Formation and Liujiang Formation cherts show slightly-moderately negative Ce anomalies （0.71±0.07, 0.81±0.08, respectively） and higher Y/Ho ratios （33.49±1.27, 36.10±2.05, respectively） than PAAS. This suggests that these cherts were deposited in the open marine basin, rather than in the intracontinental rift basin as previously assumed. The Luzhai Formation cherts may be deposited near the seamount or sea- floor plateaus with no negative Ce anomalies （1.09±0.07） and no significant Y-Ho fractionation （Y/Ho=28.60±1.25）. The Nandan Formation and Sidazhai Formation cherts were deposited in the open-ocean basin with moderately negative Ce anom- alies （0.67±0.08, 0.73±0.11, respectively） and high Y/Ho ratios （36.01±1.00, 32.00±2.25, respectively）. On the basis of our studies about cherts, we conclude that the Youjiang Basin originated as part of the Paleo-Tethys that controlled the deposition- al environments of cherts during late Paleozoic. The rift of the Youjiang Basin had occurred at least since the Early-Middle Devonian. The basin had a trend of evolving into an open-ocean basin during the Early-Middle Permian.

Geochemistry of the Late Paleozoic cherts in the Youjiang Basin:Implications for the basin evolution

We analyzed the major and rare earth element compositions of siliceous deposits from the Upper Devonian Liujiang Formation,Lower Carboniferous Luzhai Formation,Lower-Middle Permian Sidazhai Formation and Tapi Formation,which are widely distributed as bedded cherts in the interplatform basinal successions of the Youjiang Basin.The Liujiang Formation and Luzhai Formation cherts generally have high Al/(Al+Fe+Mn) values(0.38-0.94) and are non-hydrothermal cherts.These cherts are generally characterized by moderately negative Ce anomalies and high Y/Ho values relatived to PAAS,indicating that the Youjiang Basin might have evolved into an open rift basin during the Late Devonian-Early Carboniferous.The Sidazhai Formation cherts from Ziyun generally have high Al/(Al+Fe+Mn) values(0.60-0.78),suggesting negligible contribution from a hydrothermal component.The Sidazhai Formation cherts from Hechi and the Tapi Formation cherts from Malipo generally have low Al/(Al+Fe+Mn) values(0.09-0.41),indicating an intense hydrothermal input.Relatived to the Sidazhai Formation cherts,the Tapi Formation cherts have higher Ce/Ce*values(0.68±0.19) and lower Y/Ho values(41.83±13.27),which may be affected by the terrigenous input from the Vietnam Block.The Sidazhai Formation cherts from Ziyun and Hechi exhibit negative Ce anomalies(0.43±0.12,0.33±0.17,respectively) with high Y/Ho values(57.44±16.20,46.02±4.27,respectively),resembling the geochemical characteristics of open-ocean basin cherts.These cherts were deposited on a passive continental margin adjacent to the Babu branch ocean,which may have contributed to upwelling.Detailed spatial studies on geochemical characteristics of the Late Paleozoic cherts can unravel the evolution of the Youjiang Basin.

Source and Evolution of the Ore-Forming Fluids of Carlin-Type Gold Deposit in the Youjiang Basin,South China:Evidences from Solute Data of Fluid Inclusion Extracts

The source and evolution of ore-forming fluids is important to understand the genesis of Carlin-type gold deposit.Constraints on the source and evolution of ore fluid components by the con-ventional geochemical methods have long been a challenge due to the very fine-grained nature and complex textures of hydrothermal minerals in these deposits.In this study,we present the crush-leach analyzed solute data of fluid inclusion extracts within quartz,calcite,realgar,and fluorite from the Shuiyindong,Nibao,and Yata gold deposits in the Youjiang Basin,providing new insights into the source and evolution of ore-forming fluids.The results show that the high molar Cl/Br ratios up to 2508 in fluid inclusion extracts are indicative of a contribution of magmatic hydrothermal fluids.Flu-ids mixing between basinal and magmatic-hydrothermal fluids are evident on the plots of Cl/Br versus Na/K ratios,showing that ore-stage milky quartz near the magmatic-hydrothermal fluids reflects magma origin of the ore-forming fluids,whereas late ore-stage drusy quartz and realgar near the de-fined basinal fluids suggest the later input of basinal fluids in late-ore stage.Although the predominate-ly host rocks in Shuiyindong,Nibao and Yata gold deposit are bioclastic limestone,sedimentary tuff,and calcareous siltstone,respectively,the solute data of fluid inclusion extracts records they underwent the similar fluid-rocks reactions between the Na-rich magmatic hydrothermal fluids and the Ca-and Mg-rich host rocks.This study highlights the solute data of fluid inclusion extracts obtained by crush-leach analyses have the potential to fingerprint the source and evolution of ore-forming fluids of the Carlin-type gold deposit.

Fluid flow and mineralization of Youjiang Basin in the Yunnan-Guizhou-Guangxi area, China

Comprehensive studies, based on isotope geochemistry of C, H, O, S and Sr, chronology, common element and trace element geochemistry of fluid inclusions for the epithermal Au, As, Sb and Hg deposits in the Youjiang Basin and its peripheral areas, suggested that the ore fluid was the basin fluid with abundant metallic elements and the large-scale fluid flow of the same source in the late Yenshan stage was responsible for huge epithermal mineralization and silicification. The ore fluid flowed from the basin to the platform between the basin and the platform and migrated from the inter-platform basin to the isolated platform in the Youjiang Basin. The synsedimentary faults and paleokast surface acted respectively as main conduits for vertical and lateral fluid flow.

右江盆地卡林型金矿成矿年代学研究进展

右江盆地是全球仅次于美国内华达地区的第二大卡林型金矿床集中分布区。由于成矿时代的不确定性,盆地内卡林型金矿床的成矿动力学背景一直不清。为准确确定这些金矿床的成矿时代,近四十年来国内外矿床学家进行了孜孜不倦的探索,从早期以石英裂变径迹和流体包裹体Rb-Sr等时线法为代表的定年,到中期以硫化物Re-Os等时线法为代表的单矿物溶样法定年,再到最新以热液金红石、独居石和磷灰石U-Th-Pb法为代表的微区原位定年,其定年对象和方法见证了同位素地质年代学的发展历程。现已基本明确,右江盆地主要发育两期卡林型金矿成矿作用,分别为215~200 Ma和155~140 Ma,相当于印支期和燕山期,其动力学背景分别对应于印支-华南-华北地块碰撞后的印支期陆内造山过程以及燕山期软流圈上涌诱发的岩石圈伸展作用。

右江盆地大际山U-(Mo)矿床围岩蚀变特征及微量元素迁移规律——对区域内U、Au成生关系的指示

位于扬子地块西南缘的右江盆地,是全球第二大的卡林型Au矿(共伴生有Sb、Hg、Tl异常/矿化)矿集区,有着滇黔桂“金三角”的美誉。值得注意的是,该区除发育Au(-Sb-Hg-Tl)矿床外,还产有大量赋矿岩性和控矿构造相似的U矿床(点),成矿特色鲜明。前人对该区Au矿开展了大量研究,而U矿研究较少,对U、Au的成生关系尚不清楚。基于此,文章选取右江盆地内典型的U矿床——大际山U-(Mo)矿床为研究对象,通过开展岩矿相学研究和地球化学分析,厘定了矿化的围岩蚀变为硫化、沥青质化、磷铝锶石化、硅化和伊利石化,揭示了矿化过程中Re、Tl、Mo、U、Cd、Ni、Co、As、Sb、MREE的相对富集。蚀变矿物组合及元素迁移规律约束大际山U-(Mo)矿床中成矿物质可能来源于牛蹄塘组,成矿流体应为还原性有机流体与地表-近地表酸性、氧化性流体的混合,矿质沉淀发生在低温、酸性、还原环境中。综合分析认为,右江盆地内U、Au分布特征及矿床成因具有明显差异,二者应是不同成矿事件的产物。

右江盆地金、锑成矿过程:来自晴隆锑矿床和泥堡金矿床萤石LA-ICP-MS微量元素研究的制约

位于“滇-黔-桂”接壤处的右江盆地中发育大量的金、锑矿床,金、锑相互伴生,具共生分异特征。然而,金、锑之间的成矿联系和成矿过程异同仍需要进一步的研究工作。萤石作为热液矿床中广泛出现的脉石矿物,前人已经对其开展了大量的研究用于揭示矿床的形成过程。右江盆地中的晴隆锑矿床和泥堡金矿床具有相似的成矿时代以及围岩蚀变特征,是研究金、锑共生分异的理想对象。因此,本文选择晴隆锑矿床和泥堡金矿床中与成矿相关的萤石展开原位LA-ICP-MS微量元素研究,旨在揭示金、锑矿床成矿过程的差异。萤石矿物化学及阴极发光(CL)研究显示,晴隆锑矿床中与成矿相关的萤石沉淀可以划分为三个阶段,第一阶段稀土元素呈LREE富集HREE亏损的右倾特征,第二阶段呈“中稀土(MREE)”富集,第三阶段沉淀的萤石基本继承了第二阶段的稀土元素的配分特征,但ΣREE更低。整体上,随着成矿过程进行,三个阶段萤石ΣREE随着成矿过程逐渐下降,且均伴随Ce的负异常。泥堡金矿床中与成矿相关的萤石沉淀可以划分为两个阶段,第一阶段萤石稀土元素也呈右倾特征,第二阶段萤石呈MREE富集特征,整体上与晴隆萤石大致相似。不同阶段萤石Y/Ho、La/Ho、Tb/Ca和Tb/La图解显示,锑、金矿床中成矿早阶段和晚阶段萤石具有不同成因特征。其中,成矿早阶段萤石主要为热液充填成因,成矿晚阶段与水/岩反应密切相关,随着水/岩反应加剧,大量围岩组分进入流体形成晚阶段萤石。同时,这一过程导致成矿流体pH的逐渐升高和稀土元素总量的逐渐降低。综合分析认为,锑成矿流体为酸性流体,强烈的水/岩反应促使碳酸盐岩围岩溶解形成大量的萤石;同时成矿环境p H的增高和成矿流体温度的降低可能是导致辉锑矿大量沉淀的原因之一;而金成矿流体呈弱酸-中性特征,去碳酸岩化作用不彻底,形成少量萤石并伴生大量白云石,有利于大量含金黄铁矿的形成。通过对已有的锑矿床中辉锑矿及成矿阶段脉石矿物稀土元素研究数据统计发现,成矿阶段脉石矿物稀土元素呈MREE富集特征可能是大量辉锑矿对轻稀土元素(La)的富集作用所导致的。

右江盆地富宁地区石炮组化石及顶部凝灰岩年代学特征及意义

通过野外地质调查,笔者在右江盆地富宁地区中三叠统板纳组与下伏下三叠统石炮组界面之下约100 m采获早三叠世双壳类和菊石等化石,在T_(1)/T_(2)界面之间新发现一套厚约5 m凝灰岩层,对其进行LA-ICP-MS U-Pb同位素定年,自下而上分别获得(249.0±1.9)Ma、(247.9±3.4)Ma、(245.5±1.6)Ma同位素年龄,在误差范围内一致,首次获得石炮组顶界年龄为下三叠统奥伦尼克阶。本次新发现的凝灰岩层及化石可作为早—中三叠世等时地层标志进行区域对比,丰富了右江盆地早三叠世火山岩分布范围,认为右江盆地滇东南地区T_(1)/T_(2)的划分标志以该套凝灰岩作为标志较为合理。结合前人资料,这套凝灰岩、生物化石为华南陆块T_(1)/T_(2)界线的划分提供了重要年代学及古生物证据,认为安尼阶/奥伦尼克阶界线年龄应定为245.5 Ma,可能更为合理。

广西西大明山矿集区德立铅锌矿床成矿时代及其找矿勘查启示

右江前陆盆地形成于华南板块向印支板块俯冲拼合过程中,保留了大量印支期构造形迹。然而盆地中印支期岩浆及其相关成矿作用鲜有报道。选择右江盆地东南缘西大明山矿集区新发现的与有机质关系密切的德立矿床为研究对象,采用闪锌矿Rb–Sr同位素等时线测年方法,获得德立矿床成矿时代为207.1±0.6 Ma,表明该矿床形成于晚三叠世。Sr同位素初始比值(^(87)Sr/^(86)Sr)i为0.728379~0.739226,对比显示,闪锌矿Sr同位素组成与矿集区及周边晚白垩世长英质岩体、晚侏罗世高镁安山岩低Sr同位素组成具有明显差异,而与区域内三叠纪长英质岩体具有相似的Sr同位素组成,表明德立铅锌矿床成因可能与三叠纪岩浆关系密切,也暗示西大明山矿集区深部或周边存在隐伏三叠纪岩浆岩。此外,该矿床的矿体产出部位与富有机质地层关系密切,泥盆系和寒武系之间的硅钙界面破碎带是寻找铅锌矿床的有利位置。此次研究指示在西大明山矿集区不仅有晚白垩世铅锌成矿作用,矿集区西侧还存在印支期铅锌成矿作用,不排除在局部地区发育两期成矿作用的叠加,为今后矿集区找矿勘查拓展了新的思路和方向。

贵州西南部陇要钙碱性煌斑岩磷超常富集与成因初探

幔源岩浆岩是地球各圈层之间无机磷循环研究的重要对象之一。尽管已有多项研究对地球深部的磷含量进行了探讨,但对特定富磷岩浆岩的成因研究仍有待深入。本研究于贵州省西南部识别出一类钙碱性煌斑岩,该煌斑岩w(P_(2)O_(5))介于3.16%~4.74%,平均4.01%,载磷矿物主要为自形-半自形磷灰石,通过与全球不同类型煌斑岩w(P_(2)O_(5))对比,发现如此超常富磷的钙碱性煌斑岩在全球罕见。结合全球富磷超基性岩成因认识与陇要岩体矿物学和地球化学特征,对陇要岩体富磷的可能机制进行了初步探讨,提出富磷煌斑岩的成因除了可能受到地幔源区富磷控制之外,地幔低程度部分熔融、岩浆分离结晶作用、富Ti-P熔体的熔离作用、富磷地质体混染也可能影响煌斑岩磷的超常富集。

广西凤山县林老平金矿地球化学特征与找矿

林老平金矿处于右江盆地,该盆地成矿条件优越,是寻找卡林型金矿的重点远景区。区内基岩出露少,传统的地质找矿方法在该区受到严重制约,但其丰富的水系和茂盛的植被,有利于水系沉积物和土壤的形成与保留,为次生晕的形成提供了基本条件。为了取得该区找矿突破,开展了1∶5万水系沉积物地球化学测量,圈定了AS-3巴岩(甲2类)和AS-8来花(乙2类)Au-As-Hg-Sb综合异常。通过异常查证工作,将两者分别进一步缩小为林那和来花1∶1万土壤Au-As-Hg-Sb异常,异常沿林老平背斜核部呈近SN向带状展布,与1∶5万水系异常吻合度高,元素套合性好。异常浓集中心经探槽(剥土)工程揭露,圈定了6条金矿体和8条金矿化体,查证为矿致异常。土壤Au-As-Hg-Sb异常浓集中心基本上反映了金矿(化)体的位置,是很有效的找矿指示元素。金矿(化)体直接赋存于林老平背斜核部断裂破碎带或其旁侧的次级裂隙中,硅化、褐铁矿化、黄铁矿化和高岭土化等与成矿关系密切。水系沉积物地球化学测量和土壤地球化学剖面测量方法在该区找矿效果显著,在右江盆地寻找卡林型金矿该方法值得借鉴。

右江盆地构造演化与卡林型金矿成矿作用

右江盆地(又称南盘江盆地)经历了古生代—早中生代原型盆地-叠合盆地的复杂构造演化,最终表现为残留盆地。根据大地构造背景、沉积系列组合和岩浆岩发育情况,加里东运动之后右江盆地演化过程分为6个阶段:陆内伸展盆地(早期裂谷)演化阶段(D^(2)_(1)-D^(1)_(2))、大洋伸展盆地(裂陷洋盆)演化阶段(D_(2)-T_(1))、洋盆消亡及前陆挠曲盆地演化阶段(T^(2)_(1)-T^(1)_(3))、褶皱造山及碰撞后伸展阶段(T^(1)_(3)-J_(1))、NW向陆内挤压造山阶段(J_(2)-K^(2)_(1))和局部伸展阶段(K^(3)_(1)-E)。盆地内产出中国重要的卡林型金矿,矿体多赋存于冲断-褶皱带中。这些金矿具有多期成矿特征,大规模成矿主要开始于挤压背景,并持续至造山后伸展阶段,其中集中成矿期有2个。第1期形成于挤压碰撞相关的前陆挠曲盆地演化阶段-碰撞后伸展阶段(235~193 Ma,盆地中南部卡林型金矿),该期成矿受扬子板块和印支板块碰撞造山与古太平洋板块向欧亚板块的俯冲叠加诱发的岩浆熔融作用及其相关热液活动或变质热液控制。第2期为NW向陆内挤压造山-局部伸展阶段(148~103 Ma,整个右江盆地卡林型金矿),该期成矿主要受NW向挤压造山对先存构造叠加改造过程中的岩浆-热液活动影响。早三叠世前伸展背景下岩浆-热液活动对金具有初次富集作用,早白垩世晚期后岩浆-热液活动对金成矿具有叠加改造作用。成矿流体具有混合来源特征,盆地中南部卡林型金矿成矿热液以变质热液为主,盆地中部多为混合来源热液,盆地北部则主要为岩浆热液。通过对比分析,认为不同测年方法获得的年龄可在一定程度上代表成矿年龄,建议利用多种方法联合应用限制卡林型金矿的成矿时代。

晚古生代—中三叠世右江盆地的格局和转换

晚古生代—中三叠世右江盆地是在夷平的南华加里东造山带基础上再生裂陷的大陆边缘盆地,该盆地的形成与金沙江—哀牢山古特提斯洋盆关系密切,是一个具有台地与台间海槽相间结构的大陆边缘裂谷盆地。右江盆地自早泥盆世埃姆斯晚期开始裂陷,到石炭纪盆地与越北地块之间出现一个与古特提斯洋相关的局限小洋盆或深海盆。至二叠纪,该洋盆开始向西南俯冲于越北地块之下,形成活动大陆边缘。早三叠世晚期以后,随着该洋盆的闭合和碰撞造山,在凭祥、那坡等地出现同碰撞型的火山活动,右江盆地也于中三叠世转变为以复理石为特征的前陆盆地。因此右江盆地经历了裂谷盆地(早泥盆世晚期—晚泥盆世)、被动大陆边缘(早石炭世—早三叠世)、前陆盆地(中三叠世)的构造演化阶段。

华南右江复合盆地的沉积构造演化

位于华南板块南缘的右江盆地的轮廓和内部结构,与NW向及 NE向同沉积断裂关系密切。它的发展可分为两个不同的阶段。海西 构造阶段。由于哀牢山—红河洋盆开裂,右江地区出现若干平行分布的 NW向裂陷带,沉积物以深水相为主,盆地具有大陆被动边缘裂谷系特 点。东吴运动后开始的印支阶段,由于滨太平洋构造的作用,盆地轮廓 和结构发生了较大的改变,与此同时开始的哀牢山洋盆向NE方向的俯 冲消减作用。盆地再次发生张裂和扩张,从而进入弧后盆地发展阶段。 印支期末,盆地由东向西逐渐封闭,结束了右江盆地的发展历史。在不 同的发展阶段,盆地内的沉积物,也以东吴运动为界,分别由特征不同的沉积体系叠覆而成,早 期还出现典型的由非补偿性和补偿性沉积组成的双层结构。同样的盆地内的火山活动也分为 两个阶段,早期货段以碱性及碱钙性系列的基性火山岩为主,主要受NW向构造控制;晚期阶 段为钙碱性及钙性系列的基性及中酸性火山岩,同时受NW及NE向构造控制。由此可见右 江盆地是在古特提斯构造和滨太平洋构造的复合作用下形成的。

右江盆地晚古生代—三叠纪盆地转换及其构造意义

右江盆地是在南华加里东造山带夷平的基础上经再次裂陷形成的,它的形成与金沙江—红河—马江洋盆关系密切,是该洋盆与扬子板块之间的大陆边缘盆地。早泥盆世晚期—石炭纪随着金沙江—红河—马江洋盆的形成,扬子板块南部边缘开始裂陷,形成特殊的台地与台间海槽相间的大陆边缘裂谷盆地。二叠纪—早三叠世初期随着该洋盆的俯冲消减,形成越北岛弧,右江盆地进入弧后(裂陷)盆地阶段。早三叠世晚期以后,随着该洋盆的闭合和碰撞造山,在红河—马江造山带与扬子板块之间形成以复理石为特征的弧后前陆盆地。因此右江盆地经历了大陆边缘裂谷盆地(早泥盆世晚期—石炭纪)、弧后盆地(二叠纪—早三叠世早期)、弧后前陆盆地(早三叠世晚期—中三叠世)的构造演化阶段。