Mineralization of the Liwu large-scale stratiform copper deposits in Sichuan Province,China: Constraints from fluid inclusions

The Liwu stratiform copper deposit is located in the northwestern Jianglang dome, western China. Current studies mainly focus on the genetic type and mineralization of this deposit. Detailed fluid inclusion characteristics of metallogenic period quartz veins were studied to reveal the ore-forming fluid features. Laser Raman analysis indicates that the ore-forming fluids is a H₂O-NaCl-CH₄ (-CO₂) system. Fluid inclusions microthermometry shows a homogenization temperature of 181–375°C and a salinity of 5.26%–16.99% for the disseminated-banded Cu-Zn mineralization; but a homogenization temperature of 142–343°C and a salinity of 5.41%–21.19% for the massive-veined Cu-Zn mineralization. These features suggest a medium-high temperature and a medium salinity for the ore-forming fluids. H-O isotopic data indicates that the ore-forming fluids were mainly from the metamorphic and magmatic water, plus minor formation water. And sulfur isotopic data indicates that sulfur was mainly derived from the formation and magmatic rocks. Metallogenesis of the disseminated-banded mineralization was mainly correlated with fluid mixing and water-rock reaction; whereas that of the massive-veined mineralization was mainly correlated with fluid boiling. The genetic type of the deposit is a medium-high temperature hydrothermal deposit related to magmatism and controlled by shear zones. This study is beneficial to understand the stratiform copper deposit.©2023 China Geology Editorial Office.     

阿尔金造山带东段地质构造演化概论

阿尔金造山带曾是一个早古生代拗拉槽,其两侧地质体具有极为相似的地质构造特征。该区构造演化可以概括为:晚太古代至早元古代处于底侵造壳阶段,经吕梁旋回发生克拉通化,出现中元古代稳定型盖层沉积。加里东旋回中叶,经过短暂的拗拉、裂陷,分裂的塔柴板块又重新聚合。华力西旋回该区以剥蚀夷平作用为主,仅在山间断陷或山前凹陷的局部地段沉积有上泥盆统磨拉石建造。石炭纪发生短暂小规模海侵。侏罗纪全区进入陆相发育阶段。区内岩浆活动频繁,燕山旋回为最高潮。在喜山旋回,随着印度板块与欧亚板块的碰撞,该区也被卷入青藏高原总体的巨大演变之中。早期由边缘断陷转化为大型断陷盆地,至上新世湖水淹没了大部地区;晚期,随着阿尔金迅速崛起,塔里木—柴达木板块再度分裂,南盘抬升,北盘下降。文章最后探讨了阿尔金左行斜滑地震断裂带的控震作用。     

宽甸北部早元古宙铅锌矿地质特征及成因讨论

辽宁宽甸北部早元古宙铅锌矿位于辽东青城子—吉林荒沟山—朝鲜检德铅锌矿带上。赋存于辽东优、冒地槽的过渡带,靠近优地槽一侧的碳酸盐岩建造中。矿体受岩相、岩性控制明显,属层控矿床。吕梁构造旋回的变质变形作用对矿带的改造不明显。矿带的同位素特征表明,张家堡子铅锌矿形成于封闭盆地环境,矿质来源于大陆边缘深部液态矿源层;而高丽墓子铅锌矿带则形成于正常海洋环境,表现了明显的原始沉积矿床的特点。     

Late Proterozoic High-pressure granulite facies meta-morphism in the north-east Ox inlier, north-west Ireland

Abstract High-pressure granulite-facies gneisses in the NE Ox inlier in NW Ireland have undergone extensive Caledonian retrogression. In the local area of Slishwood, however, reworking was negligible and the gneisses (psammites, semipelites, pelites, metabasites and ultramafites) preserve evidence of P–T changes at high grade which mainly post-date pre-Caledonian polyphase deformation. Temperatures reached 850–900°C (based on garnet-clinopyroxene geothermometry and the presence of mesoperthite) during and after decompression from earlier eclogite-facies conditions (inferred from textural evidence of plagioclase release in sieve-textured augite). Subsequent cooling at high pressure is inferred from the unequivocal replacement of sillimanite by kyanite.
A Sm–Nd mineral isochron (gt–cpx–plag–WR) of 605 ± 37 Ma is taken to date a point on the cooling path, and confirms the hitherto suspected pre-Caledonian age of the high-grade metamorphism. Geochemical and Sm–Nd isotopic data indicate that the protoliths were probably late Proterozoic arkosic sediments and tholeiites. Following metamorphism they apparently came to reside near the base of the crust where they slowly cooled. The eventual exhumation of these gneisses is attributed to Caledonian crustal imbrication, followed by rapid isostatic recovery.     

Stable isotope constraints on the Al2SiO5'triple-point' rocks from the Proterozoic Priest pluton contact aureole, New Mexico, USA

The Priest pluton contact aureole in the Manzano Mountains, central New Mexico preserves evidence for upper amphibolite contact metamorphism and localized retrograde hydrothermal alteration associated with intrusion of the 1.42 Ga Priest pluton. Quartz–garnet and quartz–sillimanite oxygen isotope fractionations in pelitic schist document an increase in the temperatures of metamorphism from 540 °C, at a distance of 1 km from the pluton, to 690 °C at the contact with the pluton. Comparison of calculated temperature estimates with one‐dimensional thermal modelling suggests that background temperatures between 300 and 350 °C existed at the time of intrusion of the Priest pluton. Fibrolite is found within 300 m of the Priest pluton in pelitic and aluminous schist metamorphosed at temperatures >580 °C. Coexisting fibrolite and garnet in pelitic schist are in oxygen isotope equilibrium, suggesting these minerals were stable reaction products during peak metamorphism. The fibrolite‐in isograd is coincident with the staurolite‐out isograd in pelitic schist, and K‐feldspar is not observed with the first occurrence of fibrolite. This suggests that the breakdown of staurolite and not the second sillimanite reaction controls fibrolite growth in staurolite‐bearing pelitic schist. Muscovite‐rich aluminous schist locally preserves the Al₂SiO₅ polymorph triple‐point assemblage – kyanite, andalusite and fibrolite. Andalusite and fibrolite, but not kyanite, are in isotopic equilibrium in the aluminous schist. Co‐nucleation of fibrolite and andalusite at 580 °C in the presence of muscovite and absence of K‐feldspar suggests that univariant growth of andalusite and fibrolite occurred. Kyanite growth occurred during an earlier regional metamorphic event at a temperature nearly 80 °C lower than andalusite and fibrolite growth. Quartz–muscovite fractionations in hydrothermally altered pelitic schist and quartzite are small or negative, suggesting that late isotopic exchange between externally derived fluids and muscovite, but not quartz, occurred after peak contact metamorphism and that hydrothermal alteration in pelitic schist and quartzite occurred below the closure temperature of oxygen self diffusion in quartz (<500 °C).     

The Proterozoic,albitite-hosted,Valhalla uranium deposit,Queensland, Australia: a description of the alteration assemblage associated with uranium mineralisation in diamond drill hole V39

The Valhalla uranium deposit, located 40 km north of Mount Isa, Queensland, Australia, is an albitite-hosted, Mesoproterozoic U deposit similar to albitite-hosted uranium deposits in the Ukraine, Sweden, Brazil and Guyana. Uranium mineralisation is hosted by a thick package of interbedded fine-grained sandstones, arkoses and gritty siltstones that are bound by metabasalts belonging to the ca. 1,780 Ma Eastern Creek Volcanics in the Western Succession of the Mount Isa basin. Alteration associated with U mineralisation can be divided into an early, main and late stage. The early stage is dominated by laminated and intensely altered rock comprising albite, reibeckite, calcite, (titano)magnetite ± brannerite. The main stage of mineralisation is dominated by brecciated and intensely altered rocks that comprise laminated and intensely altered rock cemented by brannerite, apatite, (uranoan)-zircon, uraninite, anatase, albite, reibeckite, calcite and hematite. The late stage of mineralisation comprises uraninite, red hematite, dolomite, calcite, chlorite, quartz and Pb-, Fe-, Cu-sulfides. Brannerite has U–Pb and Pb–Pb ages that indicate formation between 1,555 and 1,510 Ma, with significant Pb loss evident at ca. 1,200 Ma, coincident with the assemblage of Rodinia. The oldest ages of the brannerite overlap with ⁴⁰Ar/³⁹Ar ages of 1,533 ± 9 Ma and 1,551 ± 7 Ma from early and main-stage reibeckite and are interpreted to represent the timing of formation of the deposit. These ages coincide with the timing of peak metamorphism in the Mount Isa area during the Isan Orogeny. Lithogeochemical assessment of whole rock data that includes mineralised and unmineralised samples from the greater Mount Isa district reveals that mineralisation involved the removal of K, Ba and Si and the addition of Na, Ca, U, V, Zr, P, Sr, F and Y. U/Th ratios indicate that the ore-forming fluid was oxidised, whereas the crystal chemistry of apatite and reibeckite within the ore zone suggests that F⁻ and were important ore-transporting complexes. δ¹⁸O values of co-existing calcite and reibeckite indicate that mineralisation occurred between 340 and 380°C and involved a fluid having δ¹⁸O_fluid values between 6.5 and 8.6‰. Reibeckite δD values reveal that the ore fluid had a δD_fluid value between −98 and −54‰. The mineral assemblages associated with early and main stages of alteration, plus δ¹⁸O_fluid and δD_fluid values, and timing of the U mineralisation are all very similar to those associated with Na–Ca alteration in the Eastern Succession of the Mount Isa basin, where a magmatic fluid is favoured for this style of alteration. However, isotopic data from Valhalla is also consistent with that from the nearby Mount Isa Cu deposit where a basinal brine is proposed for the transport of metals to the deposit. Based on the evidence to hand, the source fluids could have been derived from either or both the metasediments that underlie the Eastern Creek Volcanics or magmatism that is manifest in the Mount Isa area as small pegmatite dykes that intruded during the Isan Orogeny.     

Physical properties and petrologic description of rock samples from an IOCG mineralized area in the northern Fennoscandian Shield, Sweden

The Tjårrojåkka Fe–Cu-prospect in northern Sweden is considered an example of a Fe-oxide Cu–Au (IOCG) deposit and is hosted in metamorphosed Paleoproterozoic volcanic and intrusive rocks. Rock samples from 24 outcrops were collected for petrophysical analysis (magnetic susceptibility, remanent magnetization, variation of magnetic susceptibility with temperature, Curie temperature and density). The major Cu-prospect in the area has been studied by magnetic and electron microprobe analyses of four selected rock samples. The samples are from an exploration well that intersects the main Cu-mineralized body.The magnetic analyses show that magnetite is the dominant magnetic mineral, while hematite and other Fe-minerals are present in minor amounts. The electron microprobe observations confirm the presence of magnetite and further indicate that hematite is an alteration product of magnetite. Moreover, microprobe observations indicate that Fe-sulfides are present in negligible amounts in the samples from the Tjårrojåkka area. The strong spatial relationship of Cu-minerals (e.g., chalcopyrite) and the oxidation of magnetite to hematite suggest that the presence of rocks with low magnetic susceptibility in areas dominated by high susceptibility rocks may be a signal of related Cu-prospects.     

龙王(石童)A型花岗岩地球化学特征及其地球动力学意义

龙王花岗岩岩体产于华北克拉通南缘,岩石类型主要为黑云母钾长花岗岩,局部见有霓辉石花岗岩。岩体高硅(SiO2=72.17%～76.82%)、富碱(K2O+Na2O=8.28%～10.22%,K2O/Na2O>1),碱性指数AI(agpaitic index)=0.84～0.95,分异指数DI=95～97,铝指数ASI(aluminium saturation index)=0.96～1.13。含铁指数高(FeO/(FeO+Mg)=0.90～0.99),岩石为准铝质至弱过铝质、碱性—碱钙性、铁质A型花岗岩。岩石富集大离子亲石元素,稀土元素含量很高(854～1572μg/g);高场强元素(Nb、Ta、Zr、Hf)的富集程度明显低于大离子亲石元素,因此在微量元素蛛网图上呈相对亏损特征;岩石显著亏损Ba、Sr、Ti、Pb;εNd(t)=-4.5～-7.2,Nd模式年龄为2.3～2.5Ga。εHf(t)=-1.11～-5.26,模式年龄tHf1=2.1～2.3Ga,tHf2=2.4～2.6Ga。黑云母钾长花岗岩中的锆石主要为无色透明柱状晶体,CL图像多数显示清晰的岩浆成因的韵律环带结构,锆石LA-ICPMSU-Pb年龄为...     

扬子地台西南缘朱家坝辉绿岩地球化学特征及其地质意义

近年来在扬子西缘大量的早—中元古代岩浆岩证据显示扬子地台内形成的断陷盆地及早中元古代岩浆岩与全球性的Columbia超大陆裂解事件有着密不可分的联系。这种联系主要表现在区内早中元古代的岩浆岩地球化学特征上。为了探讨武定裂陷槽朱家坝辉绿岩的地球化学特征及其意义,以12块朱家坝辉绿岩的地球化学分析数据为基础,在分析了其主微量和稀土元素的特征之后发现朱家坝辉绿岩w(SiO_2)为44.16%～48.08%,w(K_2O+Na_2O)为3.54%～4.26%,在化学成分上属于钙碱性岩石;其稀土元素的总量为183.1×10^-6～206.91×10^-6,LREE/HREE=1.44～1.96,表明在其形成过程中发生了明显的地壳混然或者是岩浆分异作用,其化学成分基本可以反映出岩浆源区的化学组成特征。基于此,对朱家坝辉绿岩进行了源区性质、构造环境和可能的成因机制探讨,认为朱家坝辉绿岩形成于拉张环境之中,很有可能是在昆阳裂谷形成初期形成,其岩浆来源于较富集的地幔源区,形成过程中几乎没有地壳物质参与。