Problems of Siderite Formation and Iron Ore Epochs: Communication 1. Types of Siderite-Bearing Iron Ore Deposits

It is shown that siderite is unstable during sedimentation, diagenesis, and metamorphism of sedimentary and volcanosedimentary rocks. Regularities in the distribution of siderite in Precambrian jaspilites (iron formations), metasomatic ores of the Bakal type, continental–marine coaliferous formations, and oolitic iron ores are discussed. The genesis of the Precambrian iron formations and Riphean–Lower Paleozoic elisional–hydrothermal deposits is considered. The genetic relation of nodular siderites from coaliferous formations and oolitic iron ores with lowmoor coal-forming peat deposits is noted.     

Debate about ironstone: has solute supply been surficial weathering,hydrothermal convection,or exhalation of deep fluids?

Ironstone is any chemical sedimentary rock with > 15% Fe. An iron formation is a stratigraphic unit which is composed largely of ironstone. The solutes which have precipitated to become ironstone have dissolved from the Earth's surface, from the upper crust, e.g. the basaltic layer of oceanic crust, or from deeper within the Earth. Genetic modellers generally choose between surficial weathering, e.g. soil formation, and hydrothermal fluids which have convected through the upper kilometre of oceanic crust. Most genetic modellers attribute cherty laminated iron formations to hydrothermal convection and noncherty oolitic iron formations to surficial weathering. However, both types of iron formations are attributable to the exhalation of fluids from a source region too deep for convection of seawater. Evidence for a deep source of ferriferous fluids comes from a comparison of ancient ironstone with modern ferriferous sediment in coastal Venezuela. A deep-source origin for ironstone has wide-ranging implications for the origins of other chemical sedimentary ores, e.g. phosphorite, manganostone, bedded magnesite, sedimentary uranium ore, various karst-filling ores, and even petroleum. Preliminary study of a modern oolitic iron deposit described herein suggests that the source of iron and silica to iron formations may have been even deeper than envisioned within most hydrothermal convection models.     

Precambrian Weathering Crust of the Crystalline Basement in the Kaliningrad District

The weathering crust developed after the Precambrian crystalline basement in the Kaliningrad district is characterized on the basis of detailed mineralogical, geochemical, and isotopic investigations of the core material from deep wells. The Late Proterozoic age and zoned structure of the weathering crust is substantiated. The weathering crust is divided into the structural eluvium, hydromicaceous, and kaolinitic zones. After the replacement of a humid climate by the hot arid climate in the terminal Late Proterozoic, the kaolinitic weathering crust was dolomitized under the influence of mineralized waters. In the Early Cambrian, the Precambrian crust was partly eroded and its products (quartz sandstones with kaolinitic matrix, kaolinitic argillites, and oolitic iron ores) were redeposited in Lower and Middle Cambrian sediments of the Kaliningrad district.     

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.     

Siderite formation and evolution of sedimentary iron ore deposition in the Earth’s history

The role of siderite in Phanerozoic and Precambrian iron formations is discussed. Various types of iron formations are characterized, and their place in the evolution of sedimentary iron ore deposition is outlined. In Precambrian iron ore deposition, siderite is a primary mineral, whereas in Phanerozoic iron formations it becomes a secondary mineral and is commonly related to diagenetic and catagenetic processes.     

铜陵新桥层状菱铁矿成因的矿物学证据及成矿意义

安徽铜陵新桥矿区二叠系栖霞组底部和石炭系黄龙组—船山组之间产出层状、似层状菱铁矿矿层。开展菱铁矿矿层成因研究对于深入剖析区域层控矽卡岩型铜铁矿床成矿机制具有重要意义。本文利用粉晶X射线衍射（XRD）、扫描电镜（SEM）对菱铁矿矿石进行矿物学研究,结果发现菱铁矿矿石主要由菱铁矿、石英、伊利石和有机质等组成,菱铁矿颗粒粒径较小,表面具有成岩自生的自形石英硬模的微结构,SEM原位微区成分分析显示菱铁矿中除了主量元素铁,还含有大量的锰、锌和钙。矿石中存在两种微结构和不同成因的石英：表面具菱铁矿硬模和次生加大结构的碎屑石英;具六方双锥、单锥以及生物成因球形的自生石英。菱铁矿矿石的组成和矿物表面微结构表明其为沉积成因,非岩浆热液起源。富有机质和亚铁的沉积菱铁矿层和沉积胶状黄铁矿层协同作用,可能是铜陵地区乃至长江中下游成矿带层状铜铁矿床层控性重要制约因素,以及可能作为燕山期中酸岩浆演化的氧化性含铜成矿流体卸载成矿的地球化学还原障。

     

我国显生宙鲕铁石

我国显生宙鲕铁石主要分布在我国中南、西南,其次为华东地区,主要产于中奥陶世,中、晚泥盆世,早、中侏罗世地层中,以晚泥盆世最为重要,其矿石储量占70.5％,沉积条件最好,为接近封闭的浅海泻湖中。奥陶纪及泥盆纪海水中沉积的鲕粒直径分别为0.7—2mm,0.2—0.8mm。侏罗纪湖水沉积的鲕铁石直径为0.15—0.66mm。鲕粒环带的形成,与水体波动能量使铁质围绕碎屑矿物,或围绕先已形成的自形晶微粒铁矿物旋转有关。静水沉积时能量小,无环带形成,多为无核心的铁质团粒。鲕粒环带,杂基多为自形晶铁矿物或碳酸盐物,鲕核有的为石英碎屑,右的为自形晶铁矿物或碎屑铁矿物。     

Organic and inorganic geochemistry of Ljubija siderite deposits,NW Bosnia and Herzegovina

The Ljubija siderite deposits, hosted by a Carboniferous sedimentary complex within the Inner Dinarides, occur as stratabound replacement-type ore bodies in limestone blocks and as siderite–sulfides veins in shale. Three principal types of ore textures have been recognized including massive dark siderite and ankerite, siderite with zebra texture, and siderite veins. The ore and host rocks have been investigated by a combination of inorganic (major, trace, and rare earth element concentrations), organic (characterization of hydrocarbons including biomarkers), and stable isotope geochemical methods (isotope ratios of carbonates, sulfides, sulfates, kerogen, and individual hydrocarbons). New results indicate a marine origin of the host carbonates and a hydrothermal–metasomatic origin of the Fe mineralization. The differences in ore textures (e.g., massive siderite, zebra siderite) are attributed to physicochemical variations (e.g., changes in acidity, temperature, and/or salinity) of the mineralizing fluids and to the succession and intensity of replacement of host limestone. Vein siderite was formed by precipitation from hydrothermal fluids in the late stage of mineralization. The equilibrium fractionation of stable isotopes reveals higher formation temperatures for zebra siderites (around 245°C) then for siderite vein (around 185°C). Sulfur isotope ratios suggest Permian seawater or Permian evaporites as the main sulfur source. Fluid inclusion composition confirms a contribution of the Permian seawater to the mineralizing fluids and accord with a Permian mineralization age. Organic geochemistry data reflect mixing of hydrocarbons at the ore site and support the hydrothermal–metasomatic origin of the Ljubija iron deposits.     

繁昌桃冲铁矿成因探讨

The problems of the formation conditions for stratiform skarns and the genesis of the Taochong iron deposits are dealt with in this paper. Following is a summary of this discussion: 1. Stratiform skarns in this area occur in carbonate rocks of the Upper and Middle Carboniferous Period and the lower part of the Permian Qixia Group. No outcropping or concealed igneous bodies have ever been found, let alone any indications of an igneous contact zone or a corresponding zonality from "dry" skarn to "wet" skarn. The mineral facies and zonation of the skarns depend predominantly on the properties of the initial host rocks, and the development of skarns seems to have had much to do with chemical potential of silicon in these host rocks. As a result of the reaction of iron-bearing carbonates with siliceous materials in the rocks, iron-bearing silicates were formed, which in turn were transformed by pneumato-hydrothermal processes of the later stage. The stratiform skarns of this area, therefore, probably fall into the category of stratabound skarns subjected to transformation of thermometamorphism. 2. The iron deposits bear undisputable stratabound characteristics. The positions of ore-bearing beds and the petrological features as well as the mineral associations all point to a sedimentary ore-forming process of iron-carbonate (siderite). The presumption of siderite ore source is supported by the following facts: (l) Remnants of sedimentary siderite which survived the metamorphism have recently been observed in magnetite ore from neighbouring Xinqiao mining area. Siderite can have as many as 12.07% Fe⁺⁺ and, after corrosion, shows oolitic texture. (2) The ore is mainly of calcite/ dolomite- magnetite type. Mineral associations are quite simple and sulfides are rarely seen. (3) A comparison of the analytical data suggests that the content of organic carbon in iron ore decreases due to oxidation caused by metamorphism but is still higher than that in magnetite of contact- metasomatic skarn. (4) The paleogeographic reconstruction shows that this area was once an ancient underwater uplift favorable for the precipitation of iron carbonates. After its formation, the siderate bed underwent thermodynamic metamorphism and was hence decomposed into magnetite, which was then subjected to the superimposed transformation by subsequent hydrothermal fluids, leading to the partial activation and migration of iron matter and thus the formation of such ore as hematite (specularite) at shallow depth of the Changlongshan mining area. In brief, this deposit has a complex genesis: it experienced sedimentation, thermal metamorphism and transformation by hydrothermal fluids.     

繁昌桃冲铁矿成因探讨

桃冲铁矿,开采历史悠久,由于其品位富,以平炉富矿为主要矿石类型,受到了重视。有关矿床的成因也一直被人们所注意。自三十年代提出火成接触变质——热液成因的观点以来(谢家荣、程裕淇1935),人们习惯于将矿床划归于矽卡岩型。作者通过野外调查和初步研究之后,对本区铁矿的成因产生了疑问。本文就现有资料的分析,对层状矽卡岩的形成条件和铁矿的成因,做如下讨论。     

A geochemical investigation of pressure solution and the formation of veins in a deformed greywacke

Pressure solution and vein formation often occur simultaneously in shear zones during the deformation of sedimentary rocks. The mineralogical and chemical variations around a typical example of an en echelon zone of quartz veins from north Cornwall are discussed in detail. Solution of quartz is confined to the shear zone and occurs along discrete surfaces. Accumulation of insoluble minerals along these surfaces gives rise to spaced pressure solution cleavage. Petrographic data show that during pressure solution the breakdown of felspar and epidote results in the crystallisation of clay mineral, quartz and siderite. Redistribution of silica within the shear zone by pressure solution does not account for all the quartz in the veins, or for the observed increased concentration of iron and calcium. It is concluded that material was introduced from an external source into the shear zone.     

Zur Diagenese fluviatiler Sandsteine

Are cement minerals that form during the first stages of diagenesis indicative of the environment of deposition? Discussions of fluvial, marine, and evaporitic sandstones of Triassic and Upper Carboniferous age (fig. 1) indicate that kaolinite, sudoite, and potassium feldspar cements can be regarded as characteristic of freshwater sandstones, whereas (early) chlorite, analcime and albite cements are found in marine and evaporitic sandstones mainly, provided that influences of meteoric water during diagenesis can be excluded. Humid climate favors kaolinite, arid favors potassium feldspar. Early diagenetic siderite concretions develop in coal swamps. Reddish biotites are not resistant during synsedimentary weathering in humid alluvial plains. As a consequence of increasing pH, temperature, and salinity of the interstitial fluids with increasing burial depth, common sequences of cementation include (1) silicates + quartz, (2) carbonates, (3) sulphates, (4) halite (fig. 3). The formation of quartz — the most important cement — is mainly governed by modifications of the micro-environment (e.g. pressure solution). In the Lower Triassic Buntsandstein, lithification due to quartz cementation occurred at a burial depth of about 1000–1200 m in alluvial as well as in brackisch to marine sandstones. Cementation by potassium feldspar (in the alluvial sandstones) and by analcime transforming into albite (in the brackish to evaporitic sandstones) occurred earlier. This was shown by investigations of minus-cement-porosity and contact strength (fig. 2).     

Isotope composition of neodymium in neo-Archean banded iron formations of Karelia and Kola Peninsula

Studies of three deposits of neo-Archean banded iron formations from the West Karelian domain (the Kostomuksha deposit) and from the Central Kola block (the Olenegorsk and Kirovogorsk deposits) showed a pronounced difference in the isotope compositions of Nd from quartz and magnetite–hematite interlayers. The less radiogenic Nd of iron-containing layers compared to that of the quartz component may be considered as an indication of the formation mechanism of the treated banded iron formations. Thus, silicon-containing layers are related to submarine volcanism and iron was supplied to the sedimentation zone from other sources.     

Banded iron formation to high-grade iron ore: a critical review of supergene enrichment models

All the major worldwide direct-shipping iron ore deposits associated with banded iron formations (BIF) are characteristically deeply weathered. They extend to considerable depths below the water table and show well-preserved primary structures and textures, but characteristically most deposits contain no evidence of chert bands being present prior to weathering. Recent studies have found evidence of hydrothermal and/ or metamorphic influences in the development of certain ore deposits and new genesis models such as the supergene-modified hypogene model have been postulated for major high-grade iron ore deposits. Nevertheless, there are many high-grade deposits that show no evidence of hypogene alteration and for which a hypogene or metamorphic genesis is unreasonable that are automatically ascribed to supergene enrichment, commonly erroneously attributed to lateritic weathering in tropical environments. Laterite (sensu lato) is a soil formation in which primary textures are destroyed and is underlain by a pallid zone showing the preservation of chert and the depletion, not enrichment, of iron oxides and thus is totally incompatible with the formation of the high-grade ore deposits. Various theories and models that purported to explain the conditions under which such a uniquely BIF-related dissolution of quartz and residual accumulation of hematite could occur by supergene processes typically conflict with current understanding of groundwater hydrology, chemistry, weathering processes and soil formation.Supergene enrichment of ore is universal in the leaching of gangue minerals such as iron silicates, carbonates and apatite and supergene enrichment of BIF to low-grade ore is common in near surface environments above the water table such as ferrugenised BIF outcrops, detrital ore deposits, and some shallow ore deposits that have been subjected to prolonged exposure to fresh meteoric water. In all cases of supergene enrichment traces of the chert bands are visible and the dissolution or replacement processes for the removal of quartz are clear, in direct contrast to the most important deep saprolite ore deposits that show no trace of chert bands.The widespread acceptance of an inappropriate and untenable supergene enrichment model inhibits search for the true origin of the ore and our ability to predict and find concealed high-grade ore deposits.     

A Sr isotope study on fluorite and siderite from post-orogenic mineral veins in the eastern Harz Mountains,Germany

Rb–Sr isotope data for siderite and fluorite from sediment-hosted epithermal mineral veins in the eastern Harz Mountains (Germany) are presented. Several fluorite and siderite-bearing paragenetic stages have been proposed for these veins, with the most important mineralization being related to a quartz–sulfide and a subsequent calcite–fluorite–quartz stage, which occurred at 226±1 and 209±2 Ma, respectively. Our Rb–Sr data do not permit the identification of distinct generations of siderite and fluorite, but rather reveal straight internal mixing relations, reflecting mixing of fluids or differential fluid–rock interaction processes. This indicates merely two significant phases of mineral deposition related to the quartz–sulfide and calcite–fluorite–quartz stages. It is shown that the Paleozoic sedimentary host rocks of the veins are the most likely source for the siderite Sr, whereas fluorite displays a two-component mixture between sedimentary Sr and radiogenic Sr derived from locally occurring Permian metavolcanic rocks. Editorial handling: B. Lehmann     

Sodic metasomatism in a dacite weathering profile in Pinxiang, Guangxi, China

The Pinxiang weathering profile is well developed on Early Triassic dacite lavas of the Baisi Formation. At the top of the profile is developed a red clay zone which is characterized mineralogically by kaolinite, iron oxide minerals, quartz, and a small amount of illite, montmorillonite and vermiculite. In going downwards the red clay zone gives way to a saprolite zone in which plagioclase pseudomorphs have been well preserved although replaced by kaolinite. Beneath the saprolite zone is the saprock zone characterized by less weathering for dacite. At the bottom of the weathering profile is the parent material, dacite, which is composed mainly of plagioclase, quartz, K-feldspar and biotite which have been largely altered into chlorite owing to submarine extrusion of dacite lavas. Some layers in the weathering profile show obvious sodium enrichment and potassium depletion relative to others. In the Al2O3-(CaO* Na2O)-K2O triangular diagram, the weathering trends of these layers in the middle stage are remarkably deviated from normal ones. Both mineralogy and micro-morphology of these layers indicate such deviation resulted from sodic metasomatism of orthoclase.     

Geology of the Early Devonian oolitic iron ore of the Gara Djebilet Field, Saharan Platform, Algeria

The oolitic iron ore of the Gara Djebilet field occurs within the Early Devonian sediments of the Tindouf Basin (Algerian Sahara), particularly in the Upper Djebilet Formation of Pragian age. Three large lenses form three individual deposits, extending E-W for about 60 km, namely Gara West, Gara Center and Gara East.The mineralization is interbedded with argillaceous to sandy sediments and it can be related to a barrier island palaeoenvironment, bordered by an inner lagoon or shallow embayment and an epicontinental sea. Trapped by Palaeozoic shoals, the oolitic sediments show a mineralogy marked mainly by magnetite, hematite, goethite, maghemite, chamosite (bavalite), siderite, apatite and quartz. Three paragenetic associations present a vertical distribution with a Lower non-magnetitic ore, a magnetitic ore and an Upper non-magnetitic ore.Three petrographical facies types have been defined: a cemented facies (FOC); a detrital facies (FOD); and a non-detrital facies (FOND).Chemical data for the whole field show a difference between the Lower non-magnetitic ore (Fe=54.6%), the Magnetitic ore (Fe=57.8%) and the Upper non-magnetitic ore (Fe=53%). The Magnetitic ore, which corresponds mainly to the workable ore (cutoff grade at 57%), has the following composition: SiO₂=4.9%, Al₂O₃=4.2%, Fe₂O₃=61.43%, FeO=19.2%, and P₂O₅=1.8%. The corresponding calculated economical ore reserves are 985×10⁶t, with 57.8% Fe.Regarding the genesis of the oolitic iron ore, a southern source is suggested for the iron, with deposition taking place in a quiet environment. There, the ooids developed by an intrasedimentary accretion mechanism around detrital grain within an iron-rich mud.The Gara Djebilet field is an important occurrence of the “North African Palaeozoic Ironstone Belt” extending from the Zemmour to Libya which also includes ironstones of Ordovician, Silurian and Devonian age.     

冀西北宣龙地区菱铁矿的成因

本文以中晚元古代宣龙式铁岩中的菱铁矿为例,讨论碎屑岩中菱铁矿的成因。 宣龙式铁岩产于中晚元古代串岭沟组。成层状,层位稳定,分布较广,西起怀安龙泉寺,东至承德小平台一线均有出露,其中尤以宣龙地区发育最好。 宣龙地区的菱铁矿矿层薄,数量少,往往与赤铁矿构成混合矿体。该区菱铁矿分布规律性明显。横向上,由西往东逐渐增多;纵向上,由下至上由分散状变成层状,与赤铁矿间互产出。     

北山造山带古生代浊积岩构造环境探讨及其大地构造意义

北山造山带是研究中亚造山带增生造山的关键地区之一,浊积岩是增生造山带的重要组成部分。北山古生代浊积岩主要出露于营毛沱、柳园和黑山口地区。营毛沱浊积岩发育于下奥陶统,古水流方向由南向北,内部砂岩具中高等风化程度的长英质源区,构造背景为被动陆缘。早二叠世柳园浊积岩内部砂岩具低到中等风化程度的中基性源区,构造背景为大洋岛弧。早二叠世黑山口浊积岩中的砂岩源区具中等风化程度,环境相对柳园砂岩较为稳定,和长英质源区的沉积岩具相似性,构造环境可能为活动陆缘弧。对北山古生代浊积岩的解剖揭示北山古生代经历了复杂的俯冲增生过程。早古生代花牛山-火石山一带发育向北的俯冲,火石山南部被动陆缘形成营毛沱浊积岩,之后的俯冲带局部后撤形成泥盆纪墩墩山岛弧。柳园地区晚古生代洋壳向花牛山和石板山岛弧带俯冲分别形成了柳园和黑山口浊积岩。本研究支持北山增生时间持续到早二叠世的观点,对认识天山、索伦缝合带的衔接对比研究具有重要的意义。     

Late Palaeozoic arc flank and fore‐arc basin sequence of the New England fold belt in the stanage bay region,central Queensland

Devonian and Carboniferous (Yarrol terrane) rocks, Early Permian strata, and Permian‐(?)Triassic plutons outcrop in the Stanage Bay region of the northern New England Fold Belt. The Early‐(?)Middle Devonian Mt Holly Formation consists mainly of coarse volcaniclastic rocks of intermediate‐silicic provenance, and mafic, intermediate and silicic volcanics. Limestone is abundant in the Duke Island, along with a significant component of quartz sandstone on Hunter Island. Most Carboniferous rocks can be placed in two units, the late Tournaisian‐Namurian Campwyn Volcanics, composed of coarse volcaniclastic sedimentary rocks, silicic ash flow tuff and widespread oolitic limestone, and the conformably overlying Neerkol Formation dominated by volcaniclastic sandstone and siltstone with uncommon pebble conglomerate and scattered silicic ash fall tuff. Strata of uncertain stratigraphic affinity are mapped as ‘undifferentiated Carboniferous’. The Early Permian Youlambie Conglomerate unconformably overlies Carboniferous rocks. It consists of mudstone, sandstone and conglomerate, the last containing clasts of Carboniferous sedimentary rocks, diverse volcanics and rare granitic rocks. Intrusive bodies include the altered and variably strained Tynemouth Diorite of possible Devonian age, and a quartz monzonite mass of likely Late Permian or Triassic age.

The rocks of the Yarrol terrane accumulated in shallow (Mt Holly, Campwyn) and deeper (Neerkol) marine conditions proximal to an active magmatic arc which was probably of continental margin type. The Youlambie Conglomerate was deposited unconformably above the Yarrol terrane in a rift basin. Late Permian regional deformation, which involved east‐west horizontal shortening achieved by folding, cleavage formation and east‐over‐west thrusting, increases in intensity towards the east.