Petrographic and geochemical characteristics of iron-rich rocks and their significance in exploration for massive sulfide deposits, Bathurst, New Brunswick, Canada

About 25 economically significant, Kuroko-type massive sulfide bodies lie in a metamorphosed volcano-sedimentary complex (probable Middle Ordovician) known as Tetagouche Group, in Bathurst area, New Brunswick. Despite unresolved structural complexities, it does appear that they were deposited during a particular phase of volcanic activity and are, therefore, contemporaneous. Most of the sulfide bodies are closely associated with iron-rich rocks representing various facies of iron formation, and together with sulfides it constitutes the “ore horizon‘ which, therefore, is highly magnetic. Aero-magnetic and ground-magnetic techniques are useful to locate the ore horizon but problems are created because of the occurrence of iron-rich rocks with no sulfide, along another horizon in the Tetagouche Group.Petrographic and geochemical characteristics of various types of iron-rich rocks have been studied to see if the iron-rich rocks of the ore horizon can be distinguished from the iron-rich rocks of the other horizon. The iron-rich rocks found in the Tetagouche Group can be classified into five types: (1) cherty magnetitic rocks; (2) iron-rich chloritic rocks; (3) sideritic rocks; (4) basic iron formation; and (5) maroon shale. The basic iron formation, which is quite magnetic, gives a false indication of the ore horizon wherein the presence of any of the first three types of rocks is expected. Moreover, the basic iron formation is generally similar in appearance and mineralogy to some of the cherty magnetitic and chloritic rocks.Regarding major element composition, TiO₂, Na₂O, Al₂O₃ and CaO are higher whereas Fe₂O₃, FeO and MnO are lower in the basic iron formation than in the other iron-rich rocks. These geochemical characteristics can help distinguish the barren rocks of the basic iron formation from those of the ore horizon during the exploration programs.     

新疆阿尔泰凯勒克赛依铁矿地质特征、锆石LA MC ICP MS U Pb年龄及其意义

凯勒克赛依铁矿床是新疆阿尔泰唯一的小型镜铁矿床,赋存于一套变质火山-沉积岩系中,近矿围岩为白云母石英片岩,矿体呈层状,与地层产状一致,矿石具有块状、条带状、条纹状构造,矿石中金属矿物主要为镜铁矿(TFeO=87349%~88988%,TiO2=0~1042%,Al2O3=0036%~0256%),矿化具有沉积特征。近矿围岩镜铁矿白云母石英片岩锆石LA MC ICP MS U Pb谐和年龄为(3756 ± 06)Ma,限定成矿时代在376 Ma左右,即中泥盆世成矿,是阿尔泰为数不多的中泥盆世成矿作用的产物。同时也厘定含矿的变质火山-沉积岩系属中—晚泥盆世阿勒泰镇组,不是前人认为的早泥盆世康布铁堡组。     

Triassic and Jurassic radiolarians from sedimentary blocks of ophiolite mélange in the Avala Gora area (Belgrade surroundings, Serbia)

Blocks of cherty rocks and Aptychus Limestone embedded into ophiolite mélange south of Avala Gora (Serbia) contain radiolarians of different ages. We distinguished here Late Jurassic (middle Oxfordianearly Tithonian), Middle-Late Jurassic (Bathonian-early Tithonian), and Middle Triassic (early Ladinian) radiolarian assemblages. The respective stratigraphic data suggest that the ophiolite mélange was formed after the early Tithonian.     

Mineralogy and Petrology of the Gunflint Iron Formation, Minnesota-Ontario: Correlation of Compositional and Assemblage Variations at Low to Moderate Grade

Near the Ontario—Minnesota boundary, the middle Precambriansedimentary Gunflint Iron Formation has been contact metamorphosedby the Duluth Complex to the pyroxene hornfels facies. Threemetamorphic zones have been recognized based on mineralogicalchanges observed within the aureole; a fourth zone correspondsto essentially unmetamorphosed iron formation. Each zone maybe recognized by the dominant iron silicate present: zone 1—greenalitezone (unmetamorphosed), zone 2—minnesotaite zone (slightlymetamorphosed), zone 3—grunerite zone (moderately metamorphosed),zone4—ferrohypersthene zone (highly metamorphosed). Granule bearing cherty rocks of zone 2 are characterized bythe reduction of hematite to magnetite and reaction of greenaliteand siderite to minnesotaite ± magnetite. Relict texturesare well preserved in zone 2 and retrograde reactions are minimal.Grunerite first appears in banded slaty rocks of zone 3. ‘Slaty’grunerite formed principally by reaction between carbonate andstilpnomelane, while in cherty rocks grunerite formed by reactionbetween greenalite and silica. Original bulk chemical differencesbetween cherty and slaty iron formation is reflected by amphibolechemistry as shown by the higher Al content and lower Fe/Fe+ Mg ratio of slaty grunerite, and by the greater ahundanceof Na, Al-bearing amphiboles such as ferrotschermakite in slatyrocks. Hedenbergite and fayalite appear in the upper part ofzone 3; both formed by silication of carbonates and both arepartially retrograded to amphibole. Prograde grunerite-cummingtoniteis partially replaced by minnesotaite in cherty rocks of zones3 and 4. In zone 4, greenalite and siderite-bearing assemblagesreacted to ferrohypersthene, fayalite (±quartz), pigeoniteand grunerite-cummingtonite. Retrogradation is widespread andresulted mainly in the formation of grunerite. Primary textureswere destroyed in slaty rocks but are still recognizable incherty rocks. Preservation of sedimentary textures within the contact aureoleis a characteristic feature of cherty rocks. In zone l theserocks typically consist of the following textural-mineralogicalassociation: granules (greenalite, quartz, hematite), cement(quartz, siderite, ankerite, calcite) and mottles (various carbonates).Retention of these textural elements, combined with compositionaldata for assemblages in the low to moderate grade rocks, enablesidentification of numerous metamorphic reactions. In the absenceof relict phases or relict textures sedimentary assemblagescan sometimes be inferred from abundances of minor elementssuch as Al and Mn. In some slaty rocks the presence of carbonaceous or graphiticmaterial has preserved perfectly premetamorphic structures suchas siderite spherules and ankerite rhombs, enabling the recognitionof several amphibole-forming reactions. Chemographic analysis of simplified subsystems for cherty rocksof zone 1, zone 2, and the lower part of zone 3, are consistentwith observed assemblages and reactions.     

内蒙古乌拉特中旗大乌淀石墨矿床石英片岩地球化学特征与SHRIMP锆石U-Pb年代学

内蒙古乌拉特中旗大乌淀石墨矿床产于中元古代白云鄂博群尖山组一段黑色岩系中,含矿岩石为红柱石绢云绿泥石英片岩和绢云绿泥石英片岩。通过SHRIMP U-Pb测年法测定石墨矿石的沉积年龄应小于(1 792.09±17.12) Ma。对含矿岩石的岩石学和地球化学研究表明,含矿岩石富集大量亲石元素,为稳定的还原沉积环境,含矿建造具有滨浅海环境沉积的特征。因此推断该石墨矿床为沉积岩系在侵入岩热接触作用下所形成的变质微晶石墨矿床。     

安徽沙溪斑岩型铜金矿床成岩序列及成岩成矿年代学研究

沙溪矿床是长江中下游成矿带中典型的斑岩型铜金矿床,位于庐枞盆地北外缘、郯庐断裂内,矿床成岩成矿时代确定对该矿床成因研究及区域成矿规律的认识具有重要意义。在详细野外地质工作的基础上,采集沙溪矿床与成矿有关的主要岩浆岩样品(粗斑闪长玢岩、黑云母石英闪长玢岩、中斑石英闪长玢岩、细斑石英闪长玢岩和闪长玢岩)和与黄铜矿密切共生的辉钼矿,分别利用Cameca、LA-ICP-MS U-Pb和Re-Os同位素定年方法,获得矿床内主要岩浆岩的成岩年龄(130.60±0.97Ma、129.30±1.00Ma、127.10±1.50Ma、129.46±0.97Ma和126.7±2.1Ma)以及成矿年龄(130.0±1.0Ma),并重新厘定了沙溪岩体从早到晚岩浆的侵位序列。通过区域对比,提出长江中下游存在两阶段斑岩型铜金矿化,沙溪矿床为长江中下游成矿带第二阶段形成的斑岩型矿床,沙溪矿床的成岩成矿作用既不同于庐枞盆地,也不同于断隆区第一阶段的斑岩矿床,而是受郯庐断裂和长江断裂动力学演化联合作用的产物。     

青海省兴海县赛什塘铜矿床矽卡岩矿物学特征及地质意义

赛什塘铜矿位于东昆仑造山带东端的鄂拉山地区,是中国西部重要的矽卡岩型铜矿之一。矽卡岩形成于印支期石英闪长岩与中—下三叠统地层Tb2 1-2岩性段的接触带,矿体主要呈似层状、透镜状产于外接触带矽卡岩中。Tb2 1-2岩性段由中性火山岩、大理岩及变质粉砂岩构成,其中变安山质凝灰岩及安山岩与铜矿化有着密切的空间关系。岩相学研究表明,含铜矽卡岩的形成经历了矽卡岩阶段、退化蚀变阶段、石英-硫化物阶段及石英-碳酸盐阶段。矽卡岩阶段形成石榴子石、辉石及硅灰石,退化蚀变阶段则形成绿帘石、角闪石及磁铁矿,石英-硫化物阶段大量金属硫化物发生沉淀。电子探针分析表明,石榴子石与辉石矿物组分分别为Gro0.00~91.00And7.02~100.00(Pyr+Alm+Spe)0.00~4.27与Di12.80~98.08Hd2.41~79.80(Jo+Jd+Opx)0.00~13.47,表明其属于典型的钙矽卡岩类。空间上,靠近石英闪长岩与安山岩接触带处,钙铝榴石和绿帘石更富集,而向大理岩的一侧以钙铁榴石为主,并常见硅灰石及含Mn的钙铁辉石。矿物学特征及矿物成分的变化显示:从矽卡岩阶段到石英-硫化物阶段,流体性质呈幕式的变化,成矿流体至少经历了2次氧化还原性质的转变,这种变化可能与成矿流体中大气降水的不断加入有关。赛什塘铜矿属于矽卡岩型矿床,以石英闪长岩为主的岩浆活动携带了大量的热量及流体,侵入到中—下三叠统地层中,与围岩地层发生物质交换的同时,引起了大理岩、变质粉砂岩与中性火山岩之间的双交代作用,是导致矽卡岩和矿体形成的重要机制。     

Rock geochemical exploration at Mount Morgan, Queensland, Australia

The Mount Morgan Au-Cu pyritic sulphide deposit occurs in a north-northwest trending belt of Middle Paleozoic volcanic rocks located in south-central Queensland. This volcanic belt forms part of the Yarrol Basin in the Northern New England Fold Belt of the East Australian Tasman Geosyncline. The host rocks for the deposit are a normal sequence of rhyolitic and dacitic tuff that have a north-northwest regional strike and easterly dips of 20° to 30°. The tuff contains thin units of cert, jasperoid and carbonate rocks.     

新疆哈巴河县阿舍勒黄铁矿型铜-多金属矿成因初探

根据矿石学的主要特征.某些重要的成矿地质标志、矿源特征和矿床成因的关系.成矿时间、矿物包裹体测定等几个方面资料的综合探讨,初步确定阿舍勒黄铁矿型铜-多金属矿床并非火山-沉积矿床,而是和火山岩(中泥盆世)、基性潜火山岩(华力西中期)以及断裂构造关系非常密切的一般热液矿床.更确切地说,其应定为:华力西期火山旋回之后的、高位陆上环境的、浅成低温热液交代充填的Cu、Pb、Zn、Au、Ag矿床     

Zonation of chalcophile elements about the howard's pass (XY) Zn-Pb deposit, Selwyn Basin, Yukon

The Selwyn Basin comprises those rocks of Paleozoic age that were deposited in a fault-controlled epicratonic basin or aulacogen bounded by the Mackenzie Platform on the east and north, and the Cassiar Platform to the west. Boundaries between sedimentary facies within the Selwyn Basin during Ordovician to Middle Silurian time were parallel to and symetrically disposed about the long axis of that basin, consisting of chert in the central and deeper zone and shales in the flanking zones. Conodont dates indicate that the Howard's Pass (XY) Zn-Pb deposit formed during Llandoverian time in a local third-order basin within the shale facies. Various geological features such as abrupt facies changes, local thickening and slumping of sedimentary units suggest that growth faults played an important role in basin development as well as serving as conduits for the discharge of ore-forming fluids.The only sulphides recognized to date at the XY deposit are sphalerite, galena, chalcopyrite and pyrite. Sphalerite and galena can occur as concordant, fine laminations, or remobilized into sedimentary dewatering structures, or transposed and remobilized into a tectonic (slaty) cleavage. Pyrite most commonly forms diagenetic microframboids which postdate the laminated sulphides but predate the sphalerite and galena emplaced in dewatering structures.Within the main ore-bearing unit, i.e. the Active Member, the Pb/(Pb+Zn) ratio decreases stratigraphically upwards and laterally towards the margins of the deposit. This zonation accompanies a change in host-rock composition from cherty limestone at the base to carbonaceous chert towards the top of the Active Member. In addition to Zn and Pb, the other chalcophile elements concentrated in the Active Member are Cd and Hg, both of which are bound isomorphously in sphalerite.Both ore-forming and ore-associated elements are zoned stratigraphically and laterally in the host rocks of the XY deposit. The footwall carbonaceous mudstones are enriched in Ni, Cu, Co, Mo, As, Sb, Zn, Cd, Hg and Pb relative to rocks of similar age and composition located remote from mineralization. Ni, Cu, Co, Mo, As and Sb now reside in diagenetic pyrite but in whole rock chemical analyses show a strong positive correlation with organic C. On the other hand, Zn, Cd, Hg and Pb are bound in sphalerite or galena. By comparison, the overlying phosphatic chert is enriched in Ni and Cu only, both of which correlate positively with organic C.     

Ophiolitic Complex of the Matachingai River on Eastern Chukotka: Fragment of Lithosphere in Mesozoic Back-Arc Basin

The Matachingai River basin is known among the few ophiolitic complexes on eastern Chukotka as the southern boundary of the Chukotka Fold System (in terms of tectonics, the Chukotka microcontinent or a fragment of the Arctic Alaska–Chukotka microplate). This complex comprises tectonic blocks of residual spinel harzburgite with dunite bodies and pyroxenite, olivine gabbro, and leucogabbro veins; blocks of hornblende gabbro, diorite, and plagiogranite; and Upper Jurassic–Lower Cretaceous basaltic–cherty and cherty–carbonate rocks. The geological relationships of rocks within tectonic blocks, the compositions of primary minerals, the bulk geochemistry of rocks, as well as the strontium, neodymium, and lead isotopic compositions, make it possible to consider individual tectonic blocks of the complex as fragments of a disintegrated oceanic-type lithosphere that formed in a back-arc spreading center. The melts, crystallization products of which are represented by hornblende gabbro of blocks, olivine gabbro of veins, and basalts, separated from geochemically and isotopically heterogeneous mantle. Blocks composed of rocks with various modal composition are likely relicts of an oceanic lithosphere of different segments of a back-arc basin. The studied complex may be a lithosphere of one of the Middle–Late Jurassic back-arc basins. Fragments of these basins are retained in ophiolitic complexes on Great Lyakhovsky Island of the New Siberian Islands Archipelago, western Chukotka, and the Brooks Range in Alaska.     

四川若尔盖阿西金矿岩石学及岩石地球化学特征

阿西金矿地处川甘陕“金三角”成矿集中区,中三叠统为本区内最重要的金矿源层和赋矿层。阿西金矿田的形成经历了一个从沉积－成岩－富集成矿的漫长复杂的由量的积累到质的飞跃过程,是多阶段、多层次、多因素作用有机结合的产物。赋矿岩系特征表明,阿西金矿田的主要成矿环境为半深海斜坡环境。区内岩石类型极为复杂,三大岩类均有产出。主要有细砂岩、杂砂岩、沉凝灰岩、碳酸盐岩、硅质岩;变粒岩、石英岩、角岩、大理岩、夕卡岩、角砾岩;岩浆岩类主要为英安斑岩（玢岩）、闪长岩等。其中最重要的赋矿岩石为石英岩,其主要特征为具块状、不规则条带状构造,呈褐黄色／浅灰色变余层状构造。由石英（75％－80％）、高龄石（10％－15％）、绢云母（2％－3％）、钛铁质（3％－4％）、玉髓（2％－3％）及少量碳质组成。其岩石化学成分与典型硅质岩相比,SiO2偏低,Al2O3总体偏高,出现较强的高岭土化。通过研究认为,该区主要赋矿岩石石英岩的原岩应属正常碎屑沉积岩。     

The Xitieshan volcanic sediment-hosted massive sulfide deposit,North Qaidam,China: Geology,structural deformation and geochronology

The Xitieshan deposit (~ 64 Mt at 4.86% Zn, 4.16% Pb, 58 g/t Ag, and 0.68 g/t Au) is hosted by the Middle to Late Ordovician Tanjianshan Group of the North Qaidam tectonic metallogenic belt, NW China. This belt is characterized by island arc volcanic, ultra-high pressure (UHP) metamorphic and ophiolitic rocks. The Tanjianshan Group constitutes a succession of metamorphosed bimodal volcanic and sedimentary rocks, which are interpreted to have formed on the margin of a back-arc ocean basin between the Qaidam block and the Qilian block.Four stratigraphic units are identified within the Ordovician Tanjianshan Group. From northeast to southwest they are: 1) unit a, or the lower volcanic-sedimentary rocks, comprising bimodal volcanic rocks (unit a-1) and sedimentary rocks (unit a-2) ranging from carbonates to black carbonaceous schist; 2) unit b, or intermediate-mafic volcaniclastic rocks, characterized by intermediate to mafic volcaniclastic rocks intercalated with lamellar carbonaceous schist and minor marble lenses; 3) unit c, a purplish red sandy conglomerate that unconformably overlies unit b, representing the product of the foreland basin sedimentation during the Early Silurian; 4) unit d, or mafic volcanic rocks, from base to up, comprising the lower mafic volcaniclastic rocks (unit d-1), middle clastic sedimentary rocks (unit d-2), upper mafic volcaniclastic rocks (unit d-3), and uppermost mafic volcanic rocks (unit d-4). Unit a-2 hosts most of the massive sulfides whereas unit b contains subordinate amounts.The massive stratiform lenses constitute most of the Xitieshan deposit with significant amount of semi-massive and irregularly-shaped sulfides and minor amounts in stringer veins. Pyrite, galena and sphalerite are the dominant sulfide minerals, with subordinate pyrrhotite and chalcopyrite. Quartz is a dominant gangue mineral. Sericite, quartz, chlorite, and carbonate alteration of host rocks accompanies the mineralization.U-Pb zircon geochronology yields three ages of 454 Ma, 452 Ma and 451 Ma for the footwall felsic volcanic rocks in unit a-1, sedimentary host rocks in unit a-2 and hanging-wall unit b, respectively. The Xitieshan deposit is considered to be coeval with the sedimentation of unit a-2 and unit b of the Tanjianshan Group. The Xitieshan deposit has been intensely deformed during two phases (main ductile shear and minor ductile-brittle deformation). The main ductile shear deformation controls the general strike of the ore zones, whereas minor deformation controls the internal geometry of the ore bodies. ⁴⁰Ar-³⁹Ar age of muscovite from mylonitized granitic gneisses in the ductile shear zone is ~ 399 Ma, which is interpreted to date the Xitieshan ductile shear zone, suggesting that Early Devonian metamorphism and deformation post-dated the Tanjianshan Group.The Xitieshan deposit has many features similar to that of the Bathurst district of Canada, the Iberian Pyrite Belt of Spain, the Wolverine volcanogenic massive sulfide deposit in Canada. Based on its tectonic setting, host-rock types, local geologic setting, metal grades, geochronology, temperatures and salinities of mineralizing fluid and source of sulfur, the Xitieshan deposit has features similar to sedimentary exhalative (SEDEX) and VMS deposits and is similar to volcanic and sediment-hosted massive sulfide (VSHMS) deposits.     

Trace elements mineral chemistry of sulfides from the Woxi Au-Sb-W deposit,southern China

The Woxi Au-Sb-W deposit is one of the largest polymetallic ore deposits in the Xuefengshan Range, southern China, hosted in low-grade metamorphosed Neoproterozoic volcaniclastic rocks. The orebodies of the deposit are predominantly composed of banded quartz veins, which are strictly controlled by bedding and faults. Petrographic observations and geochemical results are reported on the occurrence of Au and properties of the ore-forming processes for different stages in the deposit. The veins extend vertically up to 2 km without obvious vertical metal zoning. The ore-forming process can be subdivided into four mineralization stages: Pre-ore stage; Early stage (scheelite-quartz stage); Middle stage (pyrite-stibnite-quartz stage); and Late stage (stibnite-quartz sage). Four types of pyrite (Py0, Py1, Py2, and Py3) were identified in the ores and host-rock: Py0 occurs as euhedral grains with voids in the core, ranging in size from 50 to 100 μm and formed mainly in the Pre-ore stage and Early stage; Py1 occurs as subhedral grains. Small grains (around 10 μm) of Py1 form irregularly shaped clusters of variable size ranging from tens to hundreds of μm and mainly formed in the Middle stage; Euhedral-subhedral fine-grained Py2 formed in the Late stage; Minor subhedral fine-grained Py3 was deposited in the Late-stage. Stibnite is widely distributed in the Middle and Late stage ore veins. No systemic difference was recognized in mineralogical features among stibnite formed in different stages. In addition to native gold, the lattice bound Au⁺¹ widely exists in Py1 and Py2 in the deposit, and widespread Py1 is considered as the main Au-bearing mineral with the highest Au contents. Most elements (such as Co, Ni, Cu, As, Sb, Ba, and Pb) are considered to occur as solid solution within the crystal lattice and/or invisible nanoparticles in sulfides minerals. The Co/Ni ratio of most pyrite is lower than 1, suggesting that the metals in the ore-forming fluid are sourced from sedimentary rocks. The coupled behavior between Au and As; Au and Sb suggests that the substitution of As and Sb in pyrite can enhance the incorporation of Au. Variation of trace elements in pyrites of different stages suggests some information on the mineralization processes: Large ion lithophile elements (such as Ba and Pb) are enriched in Py0 indicating that water-rock reaction occurred in the Early stage; Fine-grained Py1 with a heterogeneous distribution of elements suggests fast crystallization of pyrite in the Middle stage.     

贵州省松桃县木耳溪锰矿地质特征及找矿方向

贵州松桃县木耳溪锰矿为典型的层控型锰矿床,矿体呈层状赋存于南华系下统大塘坡组第一段(Pt2b3d 1)底部的炭质页岩中,产出层位稳定,矿体产状与围岩产状一致。通过统计对比,锰矿层的矿化程度与含锰岩系的厚度呈正比,即当南华系大塘坡组地层厚度大于15m时,有可能成为锰矿的主要找矿方向。     

Stratiform base-metal deposits in the Eastern province of the Southern Urals, Russia

The stratiform base-metal Biksizak and Amur deposits, Kolpakovsky and Andree-Yul??evsky group of ore occurrences localized in the Eastern province of the Southern Urals and the adjacent Central Urals are considered in this paper. Their geology, composition of ore, and orebody morphology are characterized. These objects and occurrences occupy different geological positions, being hosted in (1) Ordovician, Silurian, and Devonian limestones formed in an island-arc setting (Biksizak deposit, Kolpakovsky occurrence); (2) Middle and Upper Devonian flyschoid sequences at a distance from the active volcanic zone (Amur deposit); and (3) Riphean (?) platform cover (Andree-Yul??evsky group of occurrences). The objects considered differ in origin. The hydrothermal Pb-Zn ores of the Biksizak deposit and the Kolpakovsky occurrence are epigenetic with respect to the host rocks. They were formed in the Early Carboniferous and related to early collisional minor andesite and quartz diorite porphyry intrusions. The hydrothermal-sedimentary Amur massive sulfide Zn deposit of the Filizchai type was formed at the end of Middle Devonian. Zinc occurrences of the Andree-Yul??evsky group are probably products of regeneration of older stratiform lodes.     

Geology and Geochemistry of the Pre-early Cambrian Rocks in the Sandikli Area: Implications for the Pan-African Evolution of NW Gondwanaland

The pre-Early Cambrian Sandikli Basement Complex in western Central Anatolia comprises a low-grade meta-sedimentary succession (Güvercinoluk Formation) and meta-rhyolites intruded by meta-quartz porphyry rocks (Kestel Cayi Porphyroid Suite). The Güvercinoluk Formation consists of alternation of meta-siltstones and meta-sandstones with olistostromal conglomerates, rare black chert and cherty meta-dolomite lenses. The Kestel Cayi Porphyroid Suite is a deformed, highly sheared dome-shaped rhyolitic body with quartz porphyry rocks. Quartz porphyry dykes intrude both the volcanic carapace and the meta-sedimentary rocks of the Güvercinoluk Formation. Both the meta-quartz porphyry rocks and meta-rhyolites are typically mylonitic with relict igneous textures. Geochemical data indicate that the felsic rocks of the Kestel Cayi Porphyroid Suite are subalkaline and display characteristic features of post-collisional, I-type granitoids. The basement complex is unconformably overlain by variegated conglomerates, mudstones and arkosic sandstones with andesitic lavas, followed by siliciclastic rocks and carbonates that yielded Early Middle Cambrian fossils.

Based on the geochemical characteristics of the felsic rocks of Kestel Cayi Porphyroid Suite and the depositional features of the associated sediments it is suggested that the Sandikli Basement Complex is related to a post-collisional extension event in NW Gondwanaland. Similar occurrences elsewhere have been related to a transition from continental plate convergence to continental plate divergence along the Pan-African Belt.     

西双版纳国防铁矿控矿条件及矿体分布规律

铁矿体赋存于中元古界大勐龙群疆峰旋回第二、四段。含矿岩石为变中基性熔岩、角闪(阳起)斜长变粒岩、透辉钠长(斜长)变粒岩,分为上(Ⅰ)和下(Ⅱ)矿层。上矿层不稳定,下矿层由4个矿体组成复式矿。铁质就地运移、聚集、变质,典型的受变质火山汽液磁铁矿床。     

Strontium isotopic geochemistry of Tianqiao Pb-Zn deposit,Southwest China

Tianqiao carbonate-hosted Pb-Zn deposit, controlled by NW-trending F37 thrust fault and NW-trending Tianqiao anticline, is located in the eastern part of Sichuan-Yunnan-Guizhou （SYG） Pb-Zn metallogenic province, southwestern Yangtze Block, southwest China. Ore bodies in this deposit are hosted in the Devonian-Carboniferous carbonate rocks, and ore minerals include sphalerite, galena and pyrite, while the gangue minerals are dominated by calcite and dolomite. Using high-precision solid thermal ionization mass spectrometry （TIMS）, this paper reports the strontium isotopic compositions （0.7119 to 0.7167） of sulfide samples from the Tianqiao deposit in order to trace the origin of hydrothermal fluids. Compared with the country rocks, the calculated 87Sr/86Sr200 Ma values of sulfide range from 0.7118 to 0.7130, higher than those of the age-corrected Devonian to Permian sedimentary rocks （0.7073 to 0.7101） and the Middle Permian Emeishan flood basalts （0.7078 to 0.7039）, but lower than those of the age-corrected Proterozoic basement rocks （such as the Kunyang and Huili Groups, 87Sr/86Sr200 Ma=0.7243 to 0.7288）. This implies a mixed strontium source between the older basement rocks and the younger cover sequences. Together with geologic and previous isotopic evidences, we considered that the fluids＇ mixing is a possible mechanism for sulfide precipitation in the Tianqiao deposit.