Geodynamic modelling of the Century deposit,Mt Isa Province,Queensland

This paper is concerned with an example of quantitative modelling of orebody formation as a guide to reducing the risk for future mineral exploration. Specifically, the paper presents a detailed 3–D numerical model for the formation of the Century zinc deposit in northern Queensland. The model couples fluid flow with deformation, thermal transport and chemical reactions. The emphasis of the study is a systems approach where the holistic mineralising system is considered rather than concentrating solely on the mineral deposit. In so doing the complete plumbing system for mineralisation is considered with a view to specifying the critical conditions responsible for the ore deposit occurring where it does and having the size and metal grades that are observed. The numerical model is based on detailed geological, tectonic, isotopic and mineralogical data collected over the past 20 years. The conclusions are that the Century zinc deposit is located where it is because of the following factors: (i) a thermal anomaly is associated with the Termite Range Fault due to advection of heat from depth by fluid flow up the Termite Range Fault; (ii) bedding‐plane fissility in the shale rocks hosting the Century zinc deposit has controlled the wavelength and nature of D₁ folding in the vicinity of the deposit and has also controlled increases in permeability due to hydrofracture of the shales; such hydrofracture is also associated with the production of hydrocarbons as these shales passed through the ‘oil‐window’; (iii) Pb–Zn leached from crustal rocks in the stratigraphic column migrated up along faults normal to the Termite Range Fault driven by topographic relief associated with inversion at the end of the Isan Orogeny; these fluids mixed with H₂S derived at depth moving up the Termite Range Fault to mix with the crustal fluids to precipitate Pb–Zn in a plume downstream from the point of mixing. Critical factors to be used as exploration guides are high temperatures, carbonaceous fissile shales now folded into relatively tight D₁ folds, fault‐controlled plumbing systems that enable fluid mixing, depletion of metals upstream of the deposit and,in particular,a very wide Fe‐depletion halo upstream of the deposit.     

Deformation Characters of the Maowen Fault Belt in Longmenshan, Western Sichuan

1. Introduction The Longmenshan orogenic belt is a typical intercontinental orogenic belt (Fig. 1), from NW to SE composed of Paleozoic epimetamorphic rock systems, Protozoic intermediate-acid intrusions and metamorphic rocks (called Pengguan Complex), Upper Triassic sandshales, and Paleozoic glided nappe as well as Jurassic-Tertiary molass formation,. The Maowen fault belt is a boundary fault belt between the Longmenshan orogenic belt and Songpan-Garze fold belt. It starts from Shenx…     

构造变形对煤化作用进程的影响—以大别造山带北麓地区石炭纪含煤岩系为例

以大别造山带楚地区石炭纪含煤岩系为研究对象,利用显微及超微分析手段,将构造煤划分为脆性变形和韧性变形两大类,结合X衍射分析方法研究结果认为,脆性变形不引起煤级的变化,而韧性变形可以促进煤的变质;温度是引起煤级升高的主导因素,定向压力是煤化作用进程的“催化剂”。     

新疆包古图地区金矿床矿化类型和与围岩关系研究

西准噶尔包古图地区是新疆北部重要的金铜产地,已发现中型金矿床1处,金矿点20余处,大型斑岩铜（金、钼）矿床1处。金矿床按矿化类型可分为石英脉-蚀变岩型、蚀变岩型、辉锑矿-石英脉型、富硫化物型以及产于斑岩型铜矿中的伴生金。石英脉-蚀变岩型是最主要的矿石类型,构成包古图地区最主要的经济矿体。蚀变岩型是包古图地区近年来发现的新矿化类型,矿体由就位于NW向断裂中的蚀变凝灰质细砂岩和蚀变凝灰岩组成。辉锑矿-石英脉型矿石中含自然砷、自然锑、Paakkonenite、方锑金矿和硫锑金银矿等罕见矿物,这些矿物都与金矿化直接相关。富硫化物型矿石中,自然铋和辉铋矿与金矿化紧密相关。这些金矿化在空间上与中酸性岩体和岩体附近的岩脉关系紧密,成因上金矿化与岩体密切相关,而与岩脉关系不大。成矿元素在岩体中含量最高,其次为岩体附近的火山碎屑沉积岩,同一区域内岩脉的成矿元素含量最低,离岩体越远,成矿元素含量越低。Au与As、Sb、Bi之间具有不同程度的正相关性,As、Sb、Bi异常是该区找金的重要化探标志。中酸性岩体是最重要的找矿标志,岩体附近的断裂系统是金矿最有利的就位空间。     

An indirect lead isotope age determination of gold mineralization at the Corinthia mine,Yilgarn Block,Western Australia

The Corinthia lode‐gold deposit in amphibolite‐facies greenstone belt rocks in the Southern Cross Province of the Archaean Yilgarn Block contains a largely undeformed pegmatite dyke emplaced during the last phases of movement along the Fraser's‐Corinthia shear zone. Gold mineralization and shear zone development were synchronous, and a Pb‐Pb isochron age of 2620 ±6 Ma for pegmatite emplacement either indirectly dates mineralization, or places a minimum age constraint on the timing of mineralization. This age is in accord with a broadly synchronous dominant episode of Archaean lode‐gold mineralization throughout the Yilgarn Block.     

湖南苗儿山韧性剪切带与金矿化

湖南雪峰弧形构造带中的苗儿山韧性剪切带存在糜棱岩和片理化岩石两大构造岩类,各具不同的变形特征,根据金矿的产出规律,认为该地区金矿化受韧性剪切带,老地层,后期脆性断裂等多重因素控制,发育于老地层中的片理化带提供了成矿流体的运移通道和容矿空间,加强片理化带的研究对于在雪峰弧形构造带上找金具有重要意义。     

再论东天山白山铼钼矿区成岩成矿时代

东天山白山铼钼矿区的成岩成矿时代尚存在海西期和印支期之争。最新的同位素年代学研究表明,矿区南部斜长花岗斑岩的锆石U-Pb年龄为235～245Ma,矿区东部黑云母斜长花岗岩的锆石SHRIMPU-Pb年龄为239Ma±8Ma,矿石中辉钼矿的Re-Os等时线年龄为229Ma±2Ma。结合笔者已报道的燕山期岩浆侵位与成矿的年代学证据,首次提出白山铼钼矿区具有印支期和燕山期2期成岩成矿作用,早期成岩成矿作用发生于中三叠世,晚期成岩成矿作用发生于早侏罗世。     

两广云开大山地区开合旋回转换与金成矿作用的关系

开合构造是总结地壳或岩石圈水平扩张和压缩运动规律的一种大地构造观点,开合构造旋回代表了地壳或岩石圈的汇聚、离散和平移等宏观构造运动形式,以及由此引发的壳幔物质相互作用、沉积作用、变形与变质作用、熔融或重熔的岩浆活动、构造流体运移的过程。因此,开合构造运动促使地球表层成矿物质活化、迁移、聚集和成矿。对于多数内生金属矿床而言,特别是贵金属矿床,其主成矿期发生在开合构造由压缩向扩张快速过渡转变的时期,油气等非金属矿产则形成于扩张时期。成矿与容矿主断层多数都属于压性或压扭性向张性转换的复杂断层。云开地区自新元古代以来经历了多旋回的开合构造运动,产生了一系列不同期次、不同类型的金银矿床。     

东天山秋格明塔什-黄山韧性剪切带特征与成矿综述

东天山"秋格明塔什-黄山韧性剪切带"是一条多期活动且持续时间很长的韧性剪切变形变质带,介于北部的康古尔塔格-黄山断裂和南部的雅满苏-苦水断裂之间。在研究其空间展布特征、变形组构、演化序列、力学性质、剪切位移量以及变形时代的基础上,对其与成矿的关系进行了初步探讨。     

Geochronology Constraints on Transformation Age from Ductile to Brittle Deformation of the Shangma Fault and Its Tectonic Significance, Dabieshan, Central China

By a detailed investigation of geometry and kinematics of the Shangma (商麻) fault in Dabieshan (大别山),three different crust levels of extension movement have been recognized in sequence from the deep to the shallow:① low-angle ductile detachment shearing with top to the NW; ② low-angle normal fault with top to the NW or NWW in brittle or brittle-ductile transition domain; ③high-angle brittle normal fault with top to the W or NWW. Two samples were chosen for zircon U-Pb age dating to constrain the activity age of the Shangma fault. A bedding intrusive granitoid pegmatite vein that is parallel to the foliation of the low-angle ductile detachment shear zone of the country rock exhibits a lotus-joint type of boudinage deformation,showing syn-tectonic emplacing at the end of the ductile deformation period and deformation in the brittle-ductile transition domain. The zircon U-Pb dating of this granitoid pegmatite vein gives an age of (125.9±4.2) Ma,which expresses the extension in the brittle-ductile transition domain of the Shangma fault. The other sample,which is collected from a granite pluton cutting the foliation of the low-angle ductile detachment shear zone, gives a zircon U-Pb age of (118.8±4.1) Ma,constraining the end of the ductile detachment shearing. Then the transformation age from ductile to brittle deformation can be constrained between 126-119 Ma.Combined with the previous researches,the formation of the Luotian (罗田) dome,which is located to the east of the Shangma fault,can beconstrained during 150-126 Ma. This study gives a new time constraint to the evolution of the Dabie orogenic belt.     

Structural geology of the Dugald River Zn---Pb---Ag deposit, Mount Isa Inlier, Australia

The sediment-hosted Zn---Pb---Ag deposit at Dugald River is situated 87 km northeast of Mount Isa, NW Queensland. It is a mid-scale base metal accumulation restricted to a black slate sequence of low metamorphic grade. The orebody is tabular and consists of fine- to medium-grained sulphides with a dominant mineralogy of sphalerite, pyrrhotite, pyrite, galena, quartz and muscovite. Three different ore types have been recognized based on mineralization textures; laminated, banded and brecciated. The present reserve stands at 38 million tons of ore averaging 13.0% Zn, 2.1% Pb and 42 g/t Ag. A structural investigation has revealed that six stages of deformation have affected the metasediments in the Dugald River area. The first four (D₁, D₂, D₃ and D₄) are characterized by the extensive development of folds and associated axial plane cleavage. They were all generated in a ductile regime and are of considerable significance for the structural evolution of this region as well as for the emplacement and localization of the sulphide mineralization. D₅ provides a transition towards brittle deformation developing strong kink folds with subhorizontal axial planes. D₆ was a brittle event, producing E-W-trending open folds and major NE and NW strike-slip faults crosscutting all the pre-existing structural elements plus segmenting the orebody. Correlation between the development of deformation and the formation of mineralization can be observed from macro- to microscales. Relationships of mineralization with folds and cleavage indicate a post-D₂ (dominant deformation event) and probably syn-D₄ deformation timing for the Zn---Pb---Ag mineralization at Dugald River, as suggested by the ubiquitous truncations of D₂ fabrics by ore mineral assemblages throughout the deposit.     

The transition from brittle to ductile deformation in the Sambagawa metamorphic belt, Japan

The dominant deformation mechanism during the Sambagawa metamorphism changes from brittle to ductile with increasing metamorphic temperature. The magnitude of plastic strains inferred from the shapes of deformed radiolaria in metachert increases sharply across the boundary between the epidote-pumpellyite-actinolite zone and the epidote-actinolite zone. The synmetamorphic crack density of metachert is an indicator of the contemporaneous brittle strain of rocks, and it decreases sharply as the grade reaches the epidote-actinolite zone. Hence, the ratio of the ductile strain to the brittle strain of metachert decreases rapidly across the transition to the epidote-actinolite zone of the Sambagawa metamorphic belt.
The sharp change of the ductile strain magnitude also takes place at the epidote-actinolite grade in the Shimanto metamorphic belt of Japan, an example of the intermediate pressure facies series of metamorphism. It is concluded that the transition from brittle to ductile deformation takes place at about 300-400°C. and is independent of pressure of metamorphism.     

新疆东天山康古尔塔格金矿带成矿作用的构造制约

康古尔塔格金矿带呈东西向展布于新疆东天山晚古生代造山带的中部，发育在秋格明塔什-黄山韧性剪切带的南缘，阿奇山-雅满苏火山岩带的北缘，形成的金矿床可划分为三种主要端元类型，即浅成低温热液型（热泉型）、剪切带交代蚀变岩型、与中浅成花岗岩类有关的石英脉型。金的成矿作用主要受控于二叠纪后碰撞阶段秋格明塔什-黄山大型韧性剪切带形成的右行走滑剪切系统，在剪切系统的不同构造部位由于应力应变状态的不同、岩石渗透率的不同、构造层次（深度）的不同等，导致成矿流体和成矿物质在组成比例上的差异，从而形成不同类型的金矿床。所有类型的金矿资源是在同一构造环境下相同区域成矿事件的产物，在不同构造部位产出的金矿床类型可以组成一个连续的金矿化系列。区域一级剪切构造带控制金矿带成矿物质和成矿流体的主要来源，二级剪切构造控制金矿床的发育，三级剪切裂隙系统控制金矿体（脉）的产出，从而构成三级构造控矿系统。     

Deformation history of the Naraku Batholith,Mt Isa Inlier,Australia: Implications for pluton ages and geometries from structural study of the Dipvale Granodiorite and Levian Granite

Plutons of the Naraku Batholith were emplaced into Proterozoic metasediments of the northern portion of the Eastern Fold Belt of the Mt Isa Inlier during two intrusive episodes approximately 200 million years apart. Structural relationships and geochronological data suggest that the older plutons (ca 1750 Ma) are contemporaneous with granites of the Wonga Batholith to the west. The Dipvale Granodiorite and the Levian Granite represent these older intrusive phases of the Naraku Batholith, and both contain an intense tectonic foliation, S₁, which is interpreted to have formed during the north‐south shortening associated with D₁ of the Isan Orogeny. The geometry of S₁ form surfaces at the southern end of the Dipvale Granodiorite, and of the previously unrecognised sheeted contact, defines a macroscopic, steeply south‐southwest‐plunging antiform, which was produced by the regional D₂ of the Isan Orogeny. S₁ form surfaces in the Levian Granite define open F₂ folds with wavelengths of several hundred metres. The structural age of emplacement of the Dipvale Granodiorite and the Levian Granite is interpreted to be pre‐ or syn‐ the regional D₁. An intense foliation present in some of the younger (ca 1505 Ma) granites that comprise the bulk of the Naraku Batholith is interpreted to represent S₃ of the Isan Orogeny. Foliations commonly have similar styles and orientations in both the pre‐D₁ and younger plutons. This emphasises the simplicity with which regional fabrics can be, and probably have been, miscorrelated in the Eastern Fold Belt, and that the classification of granites in general on the basis of structural and geometric criteria alone is fraught with danger.     

大别山商麻断裂韧-脆性变形转换的时间约束及其构造意义

通过对商麻断裂的几何学和运动学的详细构造解析, 鉴别出呈先后依次发育层次由深到浅的3种不同构造层次的伸展性断裂构造活动, 从早到晚分别为: ①低角度向北西西方向滑脱的韧性剪切; ②西倾的低角度脆性、脆-韧性滑脱正断层; ③西倾的高角度脆性正断层.在构造年代学的基础上, 选择①末期与围岩同构造并顺围岩面理侵入结晶的花岗质伟晶岩脉和后期的花岗岩侵入体进行了锆石U-Pb年龄测试, 花岗质伟晶岩脉中13颗岩浆锆石给出了125.9±4.2Ma的年龄数据, 花岗岩中10颗岩浆锆石给出了118.8±4.1Ma年龄数据, 从而可以将商麻断裂带从伸展滑脱型韧性变形向脆性滑脱断层转换的时间很好的约束在126~119Ma之间.通过与前人研究结果的对比, 笔者将罗田穹窿形成的时间限定在了150~126Ma之间, 为研究整个大别山构造演化提供了新的年代学约束.      

黔西北五指山地区叠加构造变形特征对铅锌矿成矿的控制

五指山铅锌矿区位于贵州省普定县与织金县交界区域,大地构造位于扬子板块中部、江南造山带西缘。野外构造研究表明,受早古生代加里东构造运动的控制与影响,矿区内震旦系—下古生界构造变形与上古生界—中生界的构造变形明显不同。震旦系—下古生界构造线近东西向,发育近东西向平缓褶皱、南倾或北倾劈理,显示近南北向的挤压收缩变形。震旦系—下古生界区内发育两组南北、北西向陡倾断层,断层明显受限制而不穿越晚古生代之后的地层。发育在震旦系—下古生界内的层间滑动与断层活动控制着铅锌矿的分布。晚古生代之后区域构造应力场发生转变,由早期近南北向的挤压收缩转为早燕山期SEE向NWW挤压逆冲,由此对震旦纪—早古生代变形进行叠加与改造,宏观上形成以NE走向为特征的区域构造格局。后期形成的褶皱轴面主要向SEE倾斜,断层向NWW逆冲,与早期变形呈斜跨式叠加。燕山期断层活动促进了铅锌矿的迁移与聚集。     

内蒙古正蓝旗丹金地区赋矿火山岩年代学、地球化学特征及铀成矿时代

内蒙古锡林郭勒盟正蓝旗丹金地区近年来取得了较好的铀矿找矿成果,但赋矿火山岩与铀成矿时间关系及成岩成矿背景尚不明确。本文开展了成岩成矿年代学和岩石地球化学研究,表明赋矿围岩流纹质晶屑熔结凝灰岩和流纹斑岩分别形成于143.8±0.5Ma(MSWD=0.61)和141.5±0.5Ma(MSWD=0.40),属于早白垩世早期;铀矿石的铀铅等时线年龄分别为113.0±1.0Ma(MSWD=0.10)和80.6±2.6Ma(MSWD=1.60),分别属于早白垩世晚期和晚白垩中期;赋矿岩石属于过铝质亚碱性系列流纹岩类,来源于陆壳部分熔融,属A型流纹岩。两个铀成矿年龄与赋矿岩石存在约30Ma和63Ma的时差,成矿作用可能与对应同时期火山活动有关。该火山岩是重要的铀源体,同时充足的成岩成矿时差、构造叠加及流纹斑岩等共同控制着该区的铀成矿。     

桂西天峨—凤山地区碳酸盐岩台地韧性剪切变形带

桂西天峨—凤山地区泥盆纪至二叠纪碳酸盐岩台地相地层均不同程度地发生过韧性剪切变形变质作用。在碳酸盐岩台地边缘,主要沿石炭系、二叠系的一定层位,形成了一套浅变质强变形、面型展布的钙质韧性剪切变形带,剪切变形带由强、弱变形亚带及两者之间过渡亚带组成。显微镜下观察发现:强变形带内变质变形岩石具糜棱结构,韧性剪切变形构造发育,属糜棱岩系列。研究表明,区内钙质韧性剪切变形带属浅层次逆冲型,主要是弧—陆碰撞挤压构造环境下变形分解作用的产物。     

Deformation history of the Hampden Synform in the Eastern Fold Belt of the Mt Isa terrane

The moderately metamorphosed and deformed rocks exposed in the Hampden Synform, Eastern Fold Belt, in the Mt Isa terrane, underwent complex multiple deformations during the early Mesoproterozoic Isan Orogeny (ca 1590–1500 Ma). The earliest deformation elements preserved in the Hampden Synform are first‐generation tight to isoclinal folds and an associated axial‐planar slaty cleavage. Preservation of recumbent first‐generation folds in the hinge zones of second‐generation folds, and the approximately northeast‐southwest orientation of restored L¹ ₀ intersection lineation suggest recumbent folding occurred during east‐west to northwest‐southeast shortening. First‐generation folds are refolded by north‐south‐oriented upright non‐cylindrical tight to isoclinal second‐generation folds. A differentiated axial‐planar cleavage to the second‐generation fold is the dominant fabric in the study area. This fabric crenulates an earlier fabric in the hinge zones of second‐generation folds, but forms a composite cleavage on the fold limbs. Two weakly developed steeply dipping crenulation cleavages overprint the dominant composite cleavage at a relatively high angle (>45°). These deformations appear to have had little regional effect. The composite cleavage is also overprinted by a subhorizontal crenulation cleavage inferred to have developed during vertical shortening associated with late‐orogenic pluton emplacement. We interpret the sequence of deformation events in the Hampden Synform to reflect the progression from thin‐skinned crustal shortening during the development of first‐generation structures to thick‐skinned crustal shortening during subsequent events. The Hampden Synform is interpreted to occur within a progressively deformed thrust slice located in the hangingwall of the Overhang Shear.     

江西省饶家山地区银多金属矿化特征及找矿远景

饶家山地区紧邻金溪县城以东,二十世纪70年代初,有关单位在该区开展过大量的地质找矿及科研工作,并未发现成型的工业矿体,但积累了大量地质成果。近两年通过对资料的二次开发、验证,在该区发现有较好的银铅锌矿化。笔者在总结前人成果资料的基础上,从成矿地质背景、矿化特征入手,结合堆积始于唐朝的大量古炉渣分析,表明本区具备形成大型银多金属矿的成矿条件,具有较大的找矿远景。