浙江璜山造山型金矿的确认及其意义

造山型金矿是一种重要的金矿类型,在我国主要造山带都有分布,但在华南地区的江南造山带却少有人研究.通过与典型造山型金矿进行对比,认为浙江璜山金矿在成矿构造环境、赋矿地体变质特征、成矿时间与构造变形、峰期变质时间的关系、成矿元素富集特点以及成矿流体特征上,均与造山型金矿类似,所以确认璜山金矿为典型造山型金矿.璜山造山型金矿的确认对江南造山带区域找矿、璜山金矿深部找矿均具有十分重要的启发和借鉴意义,而且对江南造山带构造演化提供了约束.     

A scale-integrated exploration model for orogenic gold deposits based on a mineral system approach

Concept-based orogenic gold exploration requires a scale-integrated approach using a robust mineral system model.Most genetic hypotheses for orogenic gold deposits that involve near-surface or magmatic-hydrothermal fluids are now negated in terms of a global mineral system model.Plausible models involve metamorphic fluids,but the fluid source has been equivocal.Crustal metamorphic-fluid models are most widely-accepted but there are serious problems for Archean deposits,and numerous Chinese provinces,including Jiaodong,where the only feasible fluid source is sub-crustal.If all orogenic gold deposits define a coherent mineral system,there are only two realistic sources of fluid and gold,based on their syn-mineralization geodynamic settings.These are from devolatilization of a subducted oceanic slab with its overlying gold-bearing sulfide-rich sedimentary package,or release from mantle lithosphere that was metasomatized and fertilized during a subduction event,particularly adjacent to craton margins.In this model,CO_2 is generated during decarbonation and S and ore-related elements released from transformation of pyrite to pyrrhotite at about 500 ℃.This orogenic gold mineral system can be applied to conceptual exploration by first identifying the required settings at geodynamic to deposit scales.Within these settings,it is then possible to define the critical gold mineralization processes in the system:fertility,architecture,and preservation.The geological parameters that define these processes,and the geological,geophysical and geochemical proxies and responses for these critical parameters can then be identified.At the geodynamic to province scales,critical processes include a tectonic thermal engine and deep,effective,fluid plumbing system driven by seismic swarms up lithosphere-scale faults in an oblique-slip regime during uplift late in the orogenic cycle of a convergent margin.At the district to deposit scale,the important processes are fluid focussing into regions of complex structural geometry adjacent to crustal-scale plumbing systems,with gold deposition in trap sites involving complex conjugations of competent and/or reactive rock sequences and structural or lithological fluid caps.Critical indirect responses to defined parameters change from those generated by geophysics to those generated by geochemistry with reduction in scale of the mineral system-driven conceptual exploration.     

青藏高原碰撞造山背景造山型金矿床:构造背景、地质及地球化学特征

青藏高原碰撞造山背景下形成了雅鲁藏布江缝合带及哀牢山造山带两条造山型金矿带。雅鲁藏布江缝合带包含马攸木、念扎、邦布及折木朗金矿等;该矿带形成于拉萨地块及特提斯喜马拉雅地层序列地壳初始缩短加厚的背景(59~44Ma),与林子宗火山岩和高压变质岩同期形成。控矿构造主要以EW向展布。金以自然金形式赋存在石英硫化物脉及石英脉两侧以绿片岩相变质为主的千枚岩及板岩中。哀牢山造山带包含镇沅、金厂、大坪及长安金矿等,主要形成于35~26Ma,成矿背景为区域发生大规模走滑剪切,矿区内分布有成矿前期的煌斑岩及富碱斑岩。控矿构造主要以NW-SE向展布,围岩变质级低于雅鲁藏布江缝合带。C-S-H-O-Pb同位素变化较大,整体雅鲁藏布江缝合带及哀牢山造山带造山型金矿成矿流体主要来源于深部地幔流体、围岩地层的变质流体及岩浆流体,成矿围岩的差异性也会导致同位素的变化性。     

鄂东南地区赋存于沉积岩中金矿床的勘查进展和研究现状

赋存于沉积岩中的金矿床包括了绝大部分卡林型、少数造山型和部分斑岩成矿系统外围浸染型金矿床.鄂东南地区是长江中下游七个重要矿集区之一,发育一系列与岩浆岩有关的矽卡岩型、斑岩型矿床,以往的勘探和研究也主要围绕着岩体及接触带附近的斑岩、矽卡岩型矿床展开.对于岩浆岩外围赋存于沉积岩中的金矿床虽然也有发现,但并未引起足够重视.近...     

大坪金矿构造矿体空间分布特征与构造控矿规律

大坪金矿是哀牢山造山型金矿的典型代表。矿床明显受到了红河—哀牢山断裂、小新街断裂以及小新街断裂的次级断裂的控制。研究断裂构造与矿体的空间分布特征以及新生代(58 Ma)以来研究区内发生的多次构造动力机制的转变对成矿的影响具有重要的理论价值和找矿意义。新生代以来,印度板块与欧亚板块发生汇聚碰撞,形成NW向的三级断裂构造系统;汇聚过程中,印度板块发生四次旋转方向的转变引发区内构造动力机制的四次转换,构造动力机制的转换与哀牢山造山带的大规模成矿作用具有重要关系,成矿物质主要来源于下地壳或上地幔,受壳—幔相互作用影响。红河—哀牢山断裂控制了区内造山型金矿的分布,小新街断裂是大坪金矿的导矿构造,次级断裂带构成了大坪金矿的容矿构造,断裂带中构造应力引张部位为金矿的矿化富集带。研究成果为大坪金矿成矿机制研究和深部找矿预测提供了重要的依据,对区内其他造山型金矿的研究也具有重要的参考意义。     

秦岭Au- Pb- Zn成矿带成矿地质特征及潜力分析

地质大调查开展以来,秦岭地区地质调查和找矿勘探取得了重要进展,已成为我国重要的找矿远景区之一。为了更好地部署下一步找矿工作,开展了区域成矿规律总结研究、成矿远景区划分和找矿工作部署。本文重新划定了(修定)秦岭Au-Pb-Zn成矿带的边界。建立了秦岭成矿带的成矿系列组合,其中印支期是金铅锌大规模成矿的爆发期,区内矿床主要发育有卡林型金矿、造山型金矿、海底喷流-沉积-改造型铅锌矿、VMS型铜多金属矿、低温热液脉状汞锑矿、岩浆期后热液型铜金多金属矿等类型,带内仍具有极大的找矿潜力。结合区域找矿进展和潜力评价的最新成果,在该带内圈定了20处找矿远景区,其中8处为重点远景区,12处为一般远景区,建议下一步找矿勘查部署的主攻矿种为Au、Pb、Zn、Cu,主攻矿床类型为卡林型金矿、造山型金矿、海底喷流-沉积-改造型铅锌矿和岩浆期后热液型铜金多金属矿。该项成果对指导本成矿带下一步矿产勘查部署具有重要的意义。     

http://www.sciencedirect.com/science/article/pii/S1674987115000808

It is quite evident that it is not anomalous metal transport,nor unique depositional conditions,nor any single factor at the deposit scale,that dictates whether a mineral deposit becomes a giant or not.A hierarchical approach thus is required to progressively examine controlling parameters at successively decreasing scales in the total mineral system to understand the location of giant gold deposits in non-arc environments.For giant orogenic,intrusion-related gold systems(IRGS) and Carlin-type gold deposits and iron oxide-copper-gold(IOCG) deposits,there are common factors among all of these at the lithospheric to crustal scale.All are sited in giant gold provinces controlled by complex fundamental fault or shear zones that follow craton margins or,in the case of most Phanerozoic orogenic giants,define the primary suture zones between tectonic terranes.Giant provinces of IRGS,IOCG,and Carlin-type deposits require melting of metasomatized lithosphere beneath craton margins with ascent of hybrid lamprophyric to granitic magmas and associated heat flux to generate the giant province.The IRGS and IOCG deposits require direct exsolution of volatile-rich magmatic-hydrothermal fluids,whereas the association of such melts with Carlin-type ores is more indirect and enigmatic.Giant orogenic gold provinces show no direct relationship to such magmatism.forming from metamorphic fluids,but show an indirect relationship to lamprophyres that reflect the mantle connectivity of controlling first-order structures.In contrast to their province scale similarities,the different giant gold deposit styles show contrasting critical controls at the district to deposit scale.For orogenic gold deposits,the giants appear to have formed by conjunction of a greater number of parameters to those that control smaller deposits,with resultant geometrical and lithostratigraphic complexity as a guide to their location.There are few giant IRGS due to their inferior fluid-flux systems relative to orogenic gold deposits,and those few giants are essentially preservational exceptions.Many Carlin-type deposits are giants due to the exceptional conjunction of both structural and lithological parameters that caused reactive and permeable rocks,enriched in syngenetic gold,to be located below an impermeable cap along antiformal "trends".Hydrocarbons probably played an important role in concentrating metal.The supergiant Post-Betze deposit has additional ore zones in strain heterogeneities surrounding the pre-gold Goldstrike stock.All unequivocal IOCG deposits are giant or near-giant deposits in terms of gold-equivalent resources,partly due to economic factors for this relatively poorly understood,low Cu-Au grade deposit type.The supergiant Olympic Dam deposit,the most shallowly formed deposit among the larger IOCGs,probably owes its origin to eruption of volatile-rich hybrid magma at surface,with formation of a large maar and intense and widespread brecciation,alteration and Cu-Au-U deposition in a huge rock volume.     

Yangshan Gold Deposit:The Largest Carlin and Carlin-like Type Gold Deposit in China

Gold Headquarter of the CAPF has discovered the Yangshan super large-scale gold deposit in Gansu Province, which is a great breakthrough of gold exploration and prospecting in Western Qinling Mountains of China. The gold resources of this deposit achieved 308 tons with increasing potentials. Preliminary geological investigations indicate that the Yangshan gold deposit is located in the intra-continental collision orogenic belt; and the deposit was formed during the continent-continent collision orogenic processes. The geological characteristics of the deposit are similar to that of the typical Carlin-type gold deposits, while differences still exist. The ore-forming background is notably different from the Carlin gold deposit province in the United States; and the ore-forming fluids are similar with that of the orogenic-type gold deposit. Accordingly, the Yangshan gold deposit is a transitional type between the Carlin-type and the orogenic type gold deposits. At present, the Yangshan gold deposit is the largest Carlin and Carlin-like type gold deposit that is ever discovered in China. Researches on metallogeny, metallogenic model and ore-enrichment regularities of the Yangshan gold deposit are crucial to meet the pressing needs of the current geological investigation and ore exploration of the deposit.     

现代金矿成矿理论的若干进展

近十余年来，现代金矿成矿理论研究取得了长足进展，总结这些进展有助于开阔金矿研究和勘查思路。深入地研究了地球动力学背景对金矿成矿的控制，建立了区域成矿学的基本理论，提出了造山带型金矿的概念。岩浆热液和变质热液成矿理论获得了新的证据，在金矿成矿作用过程中岩浆流体较普遍存在，变质去挥发分作用所产生的大量热液是金矿成矿所需的低盐度流体。全球超大型金矿以中温热液型、浅成火山热液型金矿及砂金矿最为多见。从成矿系列理论发展到成矿系统理论，强调了金与其他矿产资源之间的相互联系，提出了铁氧化物型铜一金矿床和钨一锡成矿省内与侵入体有关的2种新类型金矿床。提出金的宇宙来源及撞击成矿理论。     

The giant Jiaodong gold province: The key to a unified model for orogenic gold deposits?

Although the term orogenic gold deposit has been widely accepted for all gold-only lode-gold deposits,with the exception of Carlin-type deposits and rare intrusion-related gold systems,there has been continuing debate on their genesis.Early syngenetic models and hydrothermal models dominated by meteoric fluids are now clearly unacceptable.Magmatic-hydrothermal models fail to explain the genesis of orogenic gold deposits because of the lack of consistent spatially- associated granitic intrusions and inconsistent temporal relationships.The most plausible,and widely accepted,models involve metamorphic fluids,but the source of these fluids is hotly debated.Sources within deeper segments of the supracrustal successions hosting the deposits,the underlying continental crust,and subducted oceanic lithosphere and its overlying sediment wedge all have their proponents.The orogenic gold deposits of the giant Jiaodong gold province of China,in the delaminated North China Craton,contain ca.120 Ma gold deposits in Precambrian crust that was metamorphosed over 2000 million years prior to gold mineralization.The only realistic source of fluid and gold is a subducted oceanic slab with its overlying sulfide-rich sedimentary package,or the associated mantle wedge.This could be viewed as an exception to a general metamorphic model where orogenic gold has been derived during greenschist- to amphibolite-facies metamorphism of supracrustal rocks:basaltic rocks in the Precambrian and sedimentary rocks in the Phanerozoic.Alternatively,if a holistic view is taken,Jiaodong can be considered the key orogenic gold province for a unified model in which gold is derived from late-orogenic metamorphic devolatilization of stalled subduction slabs and oceanic sediments throughout Earth history.The latter model satisfies all geological,geochronological,isotopic and geochemical constraints but the precise mechanisms of auriferous fluid release,like many other subduction-related processes,are model-driven and remain uncertain.     

熊耳山—外方山矿集区中生代Au-Mo成矿系统

熊耳山—外方山矿集区位于秦岭造山带之华北板块南缘,经历了复杂的碰撞造山过程,成矿时间跨度大,成矿强度高,成矿作用多样。复合造山过程和相应的成矿作用已被深入研究,但成矿系统的划分和叠加成矿作用尚需研究。本文将熊耳山—外方山矿集区发育的Au-Mo矿床划分为造山型Mo矿床、斑岩型Mo矿床、岩浆热液脉型Mo矿床、造山型Au矿床和岩浆热液型Au矿床5个类型,对应5种成矿系统：(1)造山型Mo矿床形成于250~227 Ma的同碰撞环境和227~194 Ma的后碰撞环境,为变质热液萃取壳源Mo成矿;(2)斑岩型Mo矿床形成于163~135 Ma的洋陆俯冲环境和135~116 Ma的岩石圈减薄环境,为岩浆热液携带幔源或壳源Mo成矿;(3)岩浆热液脉型Mo矿床形成于227~194 Ma的后碰撞环境,为岩浆热液携带幔源Mo成矿;(4)造山型Au矿床在三叠纪发生了预富集作用,主要形成于163~135 Ma的洋陆俯冲环境和135~103 Ma的岩石圈减薄环境,为变质热液萃取壳源Au成矿;(5)岩浆热液型Au矿床仅形成于135~103 Ma的岩石圈减薄环境,为岩浆热液携带壳源Au成矿。矿集区主要存在两种叠加成矿作用,即不同构造背景下多种成矿系统的叠加和同一构造背景下不同成矿系统的叠加。     

造山型金矿研究进展:兼论中国造山型金成矿作用

造山型金矿指与大洋板块俯冲和陆块拼贴有关、产在汇聚板块边界变质地体内部或者边缘受韧-脆性断裂构造控制的,成矿流体以低盐度H2O-CO2-CH4为主要特征的,成矿深度(2~20 km)和温度(200~650℃)及其相应的蚀变矿化组合有较大变化的系列金矿床.造山型金矿形成与超大陆聚合时限具有一致性.由于围岩类型和控矿构造多样性、地球化学特征具有多解性、金属源区和演化的不确定性以及成矿就位和物质起源的空间差距,造山型金矿成因模式有以下两个主要观点.第一种为大陆地壳变质流体成因模式,认为造山型金矿形成于造山作用同变质阶段,并随岩石圈演化矿床的物质来源发生变化;富金流体的释放由上地壳岩石绿片岩相到角闪岩相的进变质作用导致,该过程中的黄铁矿向磁黄铁矿转变释放了大量的金,这种模式被广泛运用于赋存在绿片岩相中的显生宙造山型金矿.然而越来越多的实例证实造山型金矿主要形成于峰期变质的退变质阶段或者与区域变质没有任何关系,变质流体成因模式受到了强烈质疑;与大陆地壳变质模式相对立的是幔源流体模式,其认为流体起源于俯冲洋壳脱水或富集地幔再活化,不同时代和地区的成矿流体具有一致性;尽管该模式不符合传统的平衡条件下的相变原理,但是基于幔源流体的存在及其浅部运移的大量观测,初步认为成矿流体是在超临界和非平衡条件下完成了金属的幔→壳迁移.中国造山型金矿分布于江南造山带志留纪、天山-阿尔泰二叠纪、华北克拉通北缘三叠-侏罗纪、特提斯造山带二叠-侏罗纪、华南板块晚三叠世-侏罗纪、华北克拉通东南缘白垩纪、青藏高原及周缘古近纪等七大成矿带,主要受到了显生宙不同时代造山作用的控制,成矿时代晚于变质峰期,重要成矿带大型矿集区(胶东、哀牢山、扬子西缘)的实例解剖均支持幔源流体成因模式.     

Exploration targeting for orogenic gold deposits in the Granites-Tanami Orogen: Mineral system analysis,targeting model and prospectivity analysis

A major challenge for mineral exploration geologists is the development of a transparent and reproducible approach to targeting exploration efforts, particularly at the regional to camp scales, in terranes under difficult cover where exploration and opportunity costs are high. In this study, a three-pronged approach is used for identifying the most prospective ground for orogenic gold deposits in the Paleoproterozoic Granite-Tanami Orogen (GTO) in Western Australia.A key input to the analyses is the recent development of a 4D model of the GTO architectural evolution that provides new insights on the spatio-temporal controls over orogenic gold occurrences in the area; in particular, on the role of pre-mineralization (pre-1795 Ma) D_GTOE–D_GTO1–D_GTO2 architecture in localization of gold deposits and the spatial distribution of rock types in 3D. This information is used to build up a model of orogenic gold minerals system in the area, which is then integrated into the three mutually independent but complementary mineral prospectivity maps namely, a concept-driven “manual” and “fuzzy” analysis; and a data-driven “automated” analysis.The manual analysis involved: (1) generation of a process-based gold mineral systems template to aid target selection; (2) manual delineation of targets; (3) manual estimation of the probability of occurrence of each critical mineralization process based on the available information; and (4) combining the above probabilities to derive the relative probability of occurrence of orogenic gold deposits in each of the targets. The knowledge-based Geological Information System (GIS) analysis attempts to replicate the expert knowledge used in the manual approach, but queried in a more systematic format to eliminate human heuristic bias. This involves representing the critical mineralization processes in the form of spatial predictor maps and systematically querying them through the use of a fuzzy logic model to integrate the predictor maps and to derive the western GTO orogenic gold prospectivity map. The data-driven ‘empirical’ GIS analysis uses no expert knowledge. Instead it employs statistical measures to evaluate the spatial associations between known deposits and predictor maps to establish weights for each predictor layer then combines these layers into a predictive map using a Weights of Evidence (WofE) approach.Application of a mineral systems approach in the manual analysis and the fuzzy analysis is critical: potential high value targets identified by these approaches in the western GTO lie largely under cover, whereas traditional manual targeting is biased to areas of outcrop or sub-crop amenable to direct detection technology such as exploration geochemistry, and therefore towards areas that are data rich.The results show the power of combining the three approaches to prioritize areas for exploration. While the manual analysis identifies and employs human intuition and can see through incomplete datasets, it is difficult to filter out human bias and to systematically apply to a large region. The fuzzy method is more systematic, and highlights areas that the manual analysis has undervalued, but lacks the intuitive power of the human mind that refines the target by seeing through incomplete datasets. The empirical WoE method highlights correlations with favorable host stratigraphy and highlights the control of an early set of structures potentially undervalued in the knowledge driven approaches, yet is biased due to the incomplete nature of exploration datasets and lack of abundant gold deposits due to the extensive cover.The results indicate that the most prospective areas for orogenic gold in western GTO are located in the central part of the study area, largely in areas blind to previous exploration efforts. According to our study, the procedure to follow should be to undertake the analyses in the following order: manual prospectivity analysis, followed by the conceptual fuzzy approach, followed by the empirical GIS-based method. Undertaking the manual analysis first is important to prevent explorationists from being biased by the automated GIS-based outputs. It is however emphasized that all of the prospectivity outputs from these three methods are possible, and they should not be treated as ‘treasure maps’, but instead, as decision-support aids. Therefore, a final manual prospectivity analysis redefined by the mutual consideration of output from all of the methods is required.The strategy employed in this study constitutes a new template for best-practice in terrane- to camp-scale exploration targeting that can be applied to different terranes and deposit types, particularly in terranes under cover, and provides a step forward in managing uncertainty in the exploration targeting process.     

Metallogeny of accretionary orogens — The connection between lithospheric processes and metal endowment

Accretionary orogens throughout space and time represent extremely fertile settings for the formation and preservation of a wide variety of mineral deposit types. These range from those within active magmatic arcs, either in continental margin or intra-oceanic settings, to those that develop in a variety of arc-flanking environments, such as fore-arcs and back-arcs during deformation and exhumation of the continental margin. Deposit types also include those that form in more distal, far back-arc and foreland basin settings. The metallogenic signature and endowment of individual accretionary orogens are, at a fundamental level, controlled by the nature, composition and age of the sub-continental lithosphere, and a complex interplay between formational processes and preservational forces in an evolving Earth. Some deposit types, such as orogenic gold and volcanic massive sulfide (VMS) deposits, have temporal patterns that mimic the major accretionary and crustal growth events in Earth history, whereas others, such as porphyry Cu–Au–Mo and epithermal Au–Ag deposits, have largely preservational patterns. The presence at c. 3.4 Ga of (rare) orogenic gold deposits, whose formation necessitates some form of subduction–accretion, provides strong evidence that accretionary processes operated then at the margins of continental nuclei, while the widespread distribution of orogenic gold and VMS deposits at c. 2.7–2.6 Ga reflects the global distribution of accretionary orogens by this time.     

苏里南共和国金矿类型及主要地质特征

苏里南金矿主要位于圭亚那地盾古元古代花岗岩-绿岩带上,沿大型剪切带或断层带分布。通过实地调查、综合研究及结合前人资料的基础上初步认为当地主要有冲洪积型、残坡积型、剪切带(造山)型金矿等类型。剪切带型金矿与剪切构造活动同期或晚于构造变形期,与泛亚马逊造山期后钙碱性火山作用和深成侵入作用同期。根据罗斯贝尔金矿等典型矿床研究,苏里南金矿与圭亚那地盾其它造山型金矿成矿时代相近(2.023~1.955Ga),泛亚马逊主期的构造对金矿起到了导矿和容矿作用,同时提出苏里南金矿的主要找矿方向。     

Yangshan Gold Deposit: The Largest Carlin and Carlin-like Type Gold Deposit in China

Gold Headquarter of the CAPF has discovered the Yangshan super large-scale gold depositin Gansu Province, which is a great breakthrough of gold exploration and prospecting in WesternQiniing Mountains of China. The gold resources of this deposit achieved 308 tons with increasingpotentials. Preliminary geological investigations indicate that the Yangshan gold deposit is located inthe intra-continental collision orogenic belt; and the deposit was formed during the continent-continentcollision orogenic processes. The geological characteristics of the deposit are similar to that of thetypical Carlin-type gold deposits, while differences still exist. The ore-forming background is notablydifferent from the Carlin gold deposit province in the United States; and the ore-forming fluids aresimilar with that of the orogenic-type gold deposit. Accordingly, the Yangshan gold deposit is atransitional type between the Carlin-type and the orogenic type gold deposits. At present, the Yangshangold deposit is the largest Carlin and Carlin-like type gold deposit that is ever discovered in China.Researches on metaliogeny, metaliogenic model and ore-enrichment regularities of the Yangshan golddeposit are crucial to meet the pressing needs of the current geological investigation and oreexploration of the deposit.     

Metallogeny of accretionary orogens — The connection between lithospheric processes and metal endowment

Accretionary orogens throughout space and time represent extremely fertile settings for the formation and preservation of a wide variety of mineral deposit types. These range from those within active magmatic arcs, either in continental margin or intra-oceanic settings, to those that develop in a variety of arc-flanking environments, such as fore-arcs and back-arcs during deformation and exhumation of the continental margin. Deposit types also include those that form in more distal, far back-arc and foreland basin settings. The metallogenic signature and endowment of individual accretionary orogens are, at a fundamental level, controlled by the nature, composition and age of the sub-continental lithosphere, and a complex interplay between formational processes and preservational forces in an evolving Earth. Some deposit types, such as orogenic gold and volcanic massive sulfide (VMS) deposits, have temporal patterns that mimic the major accretionary and crustal growth events in Earth history, whereas others, such as porphyry Cu–Au–Mo and epithermal Au–Ag deposits, have largely preservational patterns. The presence at c. 3.4 Ga of (rare) orogenic gold deposits, whose formation necessitates some form of subduction–accretion, provides strong evidence that accretionary processes operated then at the margins of continental nuclei, while the widespread distribution of orogenic gold and VMS deposits at c. 2.7–2.6 Ga reflects the global distribution of accretionary orogens by this time.     

甘肃李坝金矿围岩蚀变与金成矿关系

西秦岭地区是目前国内造山型和卡林型金矿找矿的热点地区之一,已发现的甘肃李坝造山型金矿为超大型规模。以李坝金矿6号矿带为例,系统地研究了其蚀变矿物组合、近矿围岩蚀变分带及相应的金矿化特征,总结了矿床(带)的蚀变分带模式。该模式具典型的中心式环带结构,可分为3个蚀变带,由中心向外依次为黄铁绢英岩化带、绢云母化带和绿泥石化带。蚀变矿物组合分别为黄铁矿+绢云母+石英±毒砂±白云母±电气石±方解石、绢云母+绿泥石+石英+黄铁矿±黑云母及绿泥石+黑云母±绢云母±黄铁矿;与这3个蚀变带相对应的是金的富集带、矿化带和无矿带。蚀变岩石物质组分迁移分析表明,围岩蚀变及其分带是热水流体/岩石反应时岩石化学组分发生迁移的结果,矿化伴随着蚀变发生,且金矿化与黄铁矿化和浸染状硅化关系最为密切。     

非造山带型金矿--胶东型金矿的陆内成矿作用

综合了全球有关金矿床的资料 ,Goldfarb和Groves等发表了著名的造山带金矿的论述 ,提出了与造山带有关的金矿在全球范围和从中太古代到整个显生宙的地质时期有广泛的分布和周期性。该类金矿的特点是与变形和变质的中地壳岩块共生 ,特别是在空间上与相应的地壳构造一致。金矿出现在造山带的不同构造部位 ,与不同的金属共生或伴生成矿。胶东作为一个重要的金矿矿集区 ,以不到中国领土面积的 0 .2 % ,而金矿产量占全国的 1 /4。国内一些地质学家也将胶东型金矿划归为造山带型金矿。最近的研究表明 ,胶东矿集区的东界与华北克拉通的东界吻合 ,金矿以华北克拉通变质岩及其有关的侵入岩为控矿围岩。主成矿期成矿时代为 (1 2 0± 1 0 )Ma ,约在不到 1 0Ma的短时限内。成矿物质具有多元性 ,既来自于控矿围岩———花岗片麻岩和变质岩 ,又来自于幔源的岩浆岩 ,特别是与中基性脉岩、偏碱的钙碱性花岗岩的侵入关系密切。除胶东金矿集区之外 ,华北克拉通的边缘和内部普遍含有金矿 ,而且金矿的物质来源、成矿方式、矿产类型、成矿围岩和成矿年龄都是一致的。这种大规模、短时限、高强度的成矿 ,被中国地质学家所重视并称为中生代成矿大爆发或金属异常巨量堆积。深部结构和成分的研究表明 ,华北东部的岩石圈在中生代急     

Developing the tools for geological shape analysis,with regional‐ to local‐scale examples from the Kalgoorlie Terrane of Western Australia

Geological map data are often underused in mineral‐exploration programs, which rely increasingly on regolith geochemistry and geophysical and other remotely sensed data to generate exploration targets. However, solid geology maps, which are progressively being upgraded due to improved interpretations of superior, remotely sensed images and airborne geophysical data, can be useful in targeting specific types of mineral deposits, which formed late in the evolutionary history of the host terrane. In such terranes, the present map geometry is essentially the same as that at the time of deposit formation. This is the case for orogenic lode‐gold deposits, which commonly show predictable structural controls and/or structural geometry. Thus, the shape of a rock body, or combinations of structures and rock bodies, may provide an important guide to the exploration potential for orogenic lode‐gold deposits. However, until recently, there has been a dearth of techniques to quantify the various properties of shape, and hence test the potential of the two‐dimensional shape of geological bodies in map view as an exploration tool. Integrating techniques from the field of pattern recognition with a modern Geographical Information System (GIS) can provide the shape‐analysis tools required to investigate the geometries of geological shapes. Two‐dimensional shape analysis is now possible through the calculation of several shape metrics including, but not restricted to, aspect ratio, blockiness, elongation, compactness, complexity, roundness, spreadness and squareness. Methods are developed for describing the geometries of rock units about mineral deposits, or any geological features, at any scale, which for the first time makes it possible to compare shapes. These shape‐analysis techniques are tested using orogenic lode‐gold deposits, particularly those in the Kalgoorlie Terrane of the highly auriferous Late Archaean Norseman‐Wiluna Belt of Western Australia. On a global scale, shape analysis indicates that those greenstone belts whose volcanic rock sequences have high elongation and relative low roundness, complexity and aspect ratio (e.g. Kalgoorlie Terrane) are likely to be the most richly endowed in gold. On a more local scale, characteristics of the shape of geological features around the Golden Mile deposit are calculated and used to test the likelihood of occurrence of gold deposits with similar geometry elsewhere in the Kalgoorlie Terrane. The area with the most closely matching shape, on the basis of a 2 km clipping‐circle radius, chosen on the basis of available proximity‐analysis data, corresponds to the recently discovered Ghost Crab deposit, illustrating the potential of the shape analysis methodology in mineral exploration. Shape analysis is, at least in part, scale dependent, due to the inherent problem of being able to define rock boundaries more precisely in units that have strong geophysical signatures than those with weak signatures in poorly exposed terranes. Overcoming this problem is a challenge to the application of this methodology.