Association of IOCG and Kiruna-type Orebodies at the Dahongshan Fe-Cu Deposits, SW China: Implications for Ore Genesis of IOCG Deposits

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拉拉IOCG矿床萤石的微量元素地球化学特征及其指示意义

康滇地区元古宙拉拉IOCG矿床中有与铜、钼矿化密切相关的萤石产出,其中,变质期有萤石(I)和萤石(II)2个世代萤石产出,前者与鳞片状辉钼矿共生,后者与条带状辉钼矿共生;热液期萤石(III)呈脉状穿插含变质期萤石的矿石;萤石的微量元素记录了成矿流体来源方面的重要信息。通过ICP-MS方法分析矿床中2期萤石样品的微量元素组成,运用微量元素含量、比值及蛛网图探讨微量元素特征、成矿流体来源及性质。结果表明:变质期萤石中各微量元素含量有一定的变化范围,热液期中各微量元素含量比较稳定,元素在萤石中的含量主要由元素在原始流体中的含量及元素本身性质所决定。结论认为:1变质期萤石(I)和萤石(II)为同源流体不同阶段演化产物,成矿流体来自于围岩,为具有高F-,Cu,Mo和Y含量的低p H值海水相流体,活动范围有限,没有发生大规模流动或迁移;2热液期萤石(III)与变质期萤石不同源,成矿流体由大气降水或地下水渗透淋滤围岩形成,为具有低F-含量的高p H值大陆淡水相流体,可能发生较远距离的渗入性流体流动或迁移。     

New ages from the Mauritanides Belt: recognition of Archean IOCG mineralization at Guelb Moghrein,Mauritania

The Guelb Moghrein Fe oxide–Cu–Au–Co (IOCG) deposit is located in the northern part of the Mauritanides chain at the western edge of the West African Craton. It is commonly held that the orogenic belt has experienced a polyphase tectonothermal evolution, including two Panafrican and one Variscan event. Dating of two distinct morphological types of hydrothermal monazite and xenotime from Guelb Moghrein yielded in situ U–Pb ages of 2492 ± 9 and 1742 ± 12 Myr respectively. Such ages have not been reported previously from the region which is conspicuous by the widespread occurrence of banded iron formations, more akin to Proterozoic or Archean than to Paleozoic settings. The supracrustal rocks are thought, therefore, to represent a greenstone terrane that was mineralized by hydrothermal fluids during the late Archean and reactivated by middle Proterozoic fluid flow. Final emplacement at the current position on the West African Craton was at ～300 Ma during Gondwana–Laurentia collision.     

Mineralogy of Tourmaline in Dahongshan Deposit, SW China: Implications for the Origin and Evolution of Hydrothermal IOCG System

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四川拉拉IOCG矿床气成-热液成矿期磁铁矿地球化学特征及其成矿意义

四川省拉拉铁氧化物-铜-金(IOCG)矿床位于扬子地块西南缘,磁铁矿是矿床中重要的矿石矿物及Fe质的主要载体之一.结合矿相学及电子探针研究方法,探讨矿床中气成-热液成矿期磁铁矿的成因特征及Fe质来源.矿相学研究表明,气成-热液成矿期磁铁矿呈自形晶,与黄铜矿共伴生产出.电子探针分析表明,气成-热液成矿期粗粒自形晶磁铁矿主...     

中国白垩纪大陆成矿体系的初步研究及找矿前景浅析

中国白垩纪大陆成矿体系,是指在白垩纪时期发生于大陆环境(包括大陆边缘)的成矿作用及其成矿地质要素构成的整体。由分布在东北、古阴山-燕山、华北地台、古秦岭-大别、扬子地台和东南沿海等大型、超大型矿集区的12个主要矿床成矿系列,可大致构筑起中国白垩纪的大陆成矿体系。而西北和西南地区已知的白垩纪矿产资源尚少,找矿潜力很大。即使是东部地区,研究程度虽高,但只要开拓思路,深入研究,仍然可以取得找矿新突破,如到盆地区找金属矿床,到非金属矿集区找金属矿床,到“山下去找山上的金属矿床”等等。     

基于逻辑规范的水系连通定义及分类

水系连通的定义决定其科学技术和工程技术层次,如何科学概括现有科学研究和工程实践,研究水系连通的定义及分类具有重要的理论和生产应用价值。应用形式逻辑学的相关方法和规范,结合水利行业现有名词定义的主要问题分析,论述给名词下定义的意义和重大作用,系统论证应用"水系连通"替代"河湖水系连通"的必要性和科学性,评析现有多种水系连通定义存在的主要问题,给出水系连通的定义"研究相连水系连接通道的形成、水系的演化、水体转移的影响的科学技术",以及水系连通工程的定义"利用水工程、河流及湖泊等构成水系之间水体转移通道的工程",并论述了2个定义的内涵及其分类。该定义不仅比现行各种定义更科学、更简洁合理,而且能科学地处理概念定义适应性与分类完整性的关系。     

Testing the apatite-magnetite geochronometer: U-Pb and Ar/Ar geochronology of plutonic rocks, massive magnetite-apatite tabular bodies, and IOCG mineralization in Northern Chile

Detailed zircon and apatite U-Pb dating and ⁴⁰Ar/³⁹Ar dating of actinolite have been carried out on the Carmen-Sierra Aspera Kiruna type magnetite-apatite and iron oxide Cu-Au (IOCG) district in the Coastal Cordillera of northern Chile (∼26°S). They define a precise succession of magmatic and hydrothermal events associated with early Cretaceous Andean magmatism. Apatite and magnetite from a magnetite-apatite tabular body with intergrowth texture in the Carmen deposit yield a total Pb-U isochron age of 131.0 ± 1.0 Ma. This result is the first direct dating of magnetite-apatite mineralization in an early Andean deposit, and the age coincides with zircon ages of a quartz diorite stock that partially hosts mineralization (130.6 ± 0.3 Ma). Magnetite from the studied tabular body contains only small amounts of radiogenic Pb and serves to constrain the initial common Pb isotopic composition. The high degree of correlation suggests that both minerals closed for Pb diffusion at essentially the same time and at a relatively high temperature (close to that of zircon), making the apatite-magnetite pair a reliable geochronometer for igneous or hydrothermal crystallization. Zircon from the Sierra Aspera composite pluton yields ages between 131.3 ± 0.3 Ma and 127.4 ± 0.1 Ma, clearly resolving the timing of intrusion of discrete intrusive phases. Actinolite ⁴⁰Ar/³⁹Ar ages partially overlap the ages of plutonic phases of the Sierra Aspera pluton, but are younger than the magnetite-apatite tabular body. The initial Pb isotopic composition of the melts and/or fluids from which the magnetite-apatite tabular bodies crystallized is very similar to the primitive Pb isotopic composition of granitic magmas associated with early Cretaceous plutons measured in K-feldspar. The Pb isotopic correspondence, combined with the temporal and spatial association between magnetite-apatite mineralization and the dioritic-quartz dioritic magmatism, strongly suggests a genetic relationship between early Cretaceous continental arc magmatism, massive magnetite-apatite deposits, and IOCG mineralization.     

A new scenario for related IOCG and Ni–(Cu) mineralization: the relationship with giant mid-crustal mafic sills, Variscan Iberian Massif

Both magmatic Ni–(Cu) and hydrothermal iron oxide–copper–gold mineralization coexist in ancient belts but their relationship remains poorly known. Geochronology and field geology evidence show that in SW Iberia both styles of mineralization were coeval with widespread metaluminous to peraluminous Variscan magmatism (350–330 Ma). We propose that mineralization was probably related to a hidden large layered mafic–ultramafic layered complex, recently inferred from geophysics, that was emplaced in a mid-crustal decollement zone. Contamination of a primitive mantle-derived magma with continental crust in the layered complex led to fractional crystallization accompanied by high-T–low-P metamorphism and the incorporation of volatiles into the melt. Hot hypersaline CO₂–CH₄-bearing brines were subsequently released and focused along major thrusts and strike-slip faults to produce the IOCG mineralization. Assimilation of continental crust also led to the formation of sulphide magmas that were tectonically injected high into the crust, leading to the formation of pipe-like breccia-hosted Ni–(Cu) ore bodies. All these processes took probably place as a consequence of oblique ridge– and/or continent–continent collision.     

REE Geochemistry of Fluorite from the Lala IOCG Deposit and Its Geological Implications, Kangdian Region, SW China

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鄂东南铜山口铜(钼)矿床黑云母矿物化学特征及其对岩石成因与成矿的指示

在鄂东南铜山口铜(钼)矿床存在着3种产状的黑云母,分别是赋存于花岗闪长斑岩矿物颗粒间的黑云母、钾长石斑晶内的黑云母以及蚀变带内的黑云母。本文运用电子探针(EMPA)和激光剥蚀-等离子体质谱(LA-ICP-MS)技术,对这3种不同产状的黑云母进行了原位成分分析。结果表明,3种产状的黑云母Ti的含量介于0.38～0.45之间,且Mg/(Mg+Fe)介于0.53～0.72之间,类似于岩浆成因黑云母的成分特征。3种产状的黑云母MgO和FeOT值差别较大,但Al2O3、TiO2、SiO2、Na2O和K2O值差别不明显。作为花岗闪长斑岩质熔体中Rb、Ba、Nb、Ta等不相容元素及Sc、V、Co、Ni、Cr等相容元素的主要载体,黑云母的U、Th、Pb、Sr、Zr、Hf、Y等元素含量显著低于主岩,而且高场强元素Nb、Ta受后期岩浆热液作用的影响较弱。黑云母并不是影响全岩稀土特征的主要矿物相。铜山口花岗闪长斑岩的形成与幔源岩浆作用关系密切,并可能与板块俯冲作用相关。黑云母含Cu量的高低并不是衡量侵入体是否成矿的有效指标,但体系中高的氧逸度(logfO2NiNiO+1),有利于斑岩铜矿的形成。与Cu成矿有关的黑云母具有高镁低铁的特征,与Sn成矿有关的黑云母则具有高铁低镁的特征。     

湖南金鸡岭花岗岩和伟晶岩中黑云母矿物化学及其对成岩成矿的启示

湖南晚侏罗世金鸡岭花岗岩体是南岭地区典型W—Sn成矿岩体之一,内部发育黑云母花岗质伟晶岩团块和文象花岗质条带状伟晶岩脉。金鸡岭花岗岩和黑云花岗伟晶岩中的黑云母具有相似的地球化学特征,均表现出高的FeO、TiO2、Al2O3含量和低的MgO、CaO、Na2O、MnO含量,以及富集成矿元素Nb、Ta、W、Sn,亏损Sr、Ce、Eu等微量元素特征,从花岗岩体到黑云花岗伟晶岩,岩浆的形成温度和氧逸度降低,云母中Al2O3、Li2O*含量升高,TiO2、MgO含量降低,黑云母由铁叶云母演变为黑鳞云母。结合前人资料,金鸡岭花岗岩与黑云花岗伟晶岩均源于元古宙地壳的深熔作用,伟晶岩为花岗岩浆在晚期分异演化的产物,形成于岩浆—热液转化阶段。伟晶岩阶段是稀有金属元素显著富集,乃至进一步成矿的重要阶段。     

湖南金鸡岭花岗岩和伟晶岩中黑云母矿物化学及其对成岩成矿的启示

湖南晚侏罗世金鸡岭花岗岩体是南岭地区典型W—Sn成矿岩体之一,内部发育黑云母花岗质伟晶岩团块和文象花岗质条带状伟晶岩脉。金鸡岭花岗岩和黑云花岗伟晶岩中的黑云母具有相似的地球化学特征,均表现出高的FeO、TiO₂、Al₂O₃含量和低的MgO、CaO、Na₂O、MnO含量,以及富集成矿元素Nb、Ta、W、Sn,亏损Sr、Ce、Eu等微量元素特征,从花岗岩体到黑云花岗伟晶岩,岩浆的形成温度和氧逸度降低,云母中Al₂O₃、Li₂O^*含量升高,TiO₂、MgO含量降低,黑云母由铁叶云母演变为黑鳞云母。结合前人资料,金鸡岭花岗岩与黑云花岗伟晶岩均源于元古宙地壳的深熔作用,伟晶岩为花岗岩浆在晚期分异演化的产物,形成于岩浆—热液转化阶段。伟晶岩阶段是稀有金属元素显著富集,乃至进一步成矿的重要阶段。     

铜陵地区中生代侵入岩LA-ICP-MS锆石U-Pb年代学及Cu-Au成矿指示意义

安徽铜陵地区是我国著名的Cu-Au多金属产地之一,金属成矿与燕山期岩浆作用关系密切.本次对铜陵地区石英(二长)闪长岩和花岗闪长岩系统地进行了LA-ICP-MS锆石年代学研究.高质量锆石U-Pb同位素206Pb/238U加权平均年龄结果表明铜陵地区中酸性侵入岩的成岩序列可能为花岗闪长岩(141Ma)→辉石(二长)闪长岩(139Ma)→石英(二长)闪长岩(135Ms,136Ma,137Ms).对比已有的高精度锆石U-Pb同位素年龄,我们认为铜陵地区岩体侵入后可能有个快速冷却的过程.铜陵地区与Cu-Au矿床有关的最主要侵入岩LA-ICP-MS锆石数据给出两组年龄:130～132Ma和138～140Ma.据高精度锆石U-Pb数据和一些矿床的Re-Os年龄,结合锆石元素地球化学资料,本文得出铜陵地区主要表现出两次成矿事件:早期成矿事件是与高Ce异常流体密切相关的铜金成矿事件(辉钼矿Re-Os年龄138～140Ma);晚期成矿事件可能与低Ce异常流体密切相关的铁硫成矿事件(黄铁矿Re-Os年龄约126Ma).     

Multivariate screening of training sets for classification and the definition of geochemical background

A combination of R-mode factor residual, factor score, and univariate screening methods is more successful than univariate screening (based on cumulative frequency curves) alone in identifying outliers and sharpening definition of background populations. The factor models for the screened data sets are more easy to interpret than those for the original data sets, and are used to check the background nature of the screened populations. The resulting data sets can be used either for statistical evaluation of single-element data, or as training sets for multivariate classification. The screening method is illustrated with stream-sediment data from South Greenland.     

Alteration of the Damiao anorthosite complex in the northern North China Craton: Implications for high-grade iron mineralization

The Damiao type iron deposit is hosted in a typical Proterozoic anorthosite complex in the northern North China Craton. The types of ores in Damiao mainly comprise massive Fe ores, massive Fe–P ores, and disseminated Fe and Fe–P ores. The disseminated Fe and Fe–P ores formed by fractional crystallization are generally hosted in oxide-apatite gabbronorite and account for 70% of the proven reserve of the Damiao type iron ore. The massive Fe and Fe–P ores account for 30% of the proven reserve of the Damiao type deposit iron ore and generally occur as irregular dykes or veins filling vertical fractures of the previously consolidated anorthosite, showing typical features of hydrothermal mineralization. The contact between the massive orebodies and wall rocks is sharp and straight. The anorthosite comprises white and dark varieties, with the former resulted by the alteration of the latter that occurs as relicts. Petrographic observation and electron microprobe analyses show abundant Fe–Ti oxide inclusions in plagioclase which impart the dark color to the rock. The similar spider diagram patterns between fresh and altered plagioclase and between dark- and white-colored anorthosite imply a genetic relationship between the dark and white types. During the alteration of anorthosite, CaO and MgO were slightly decreased, the SiO₂, Al₂O₃ and Na₂O were significantly increased, and the TFe₂O₃ and TiO₂ were significantly decreased. The TFe₂O₃ and TiO₂ in the dark-colored anorthosite have a range of 4.86–12.18 wt.% and 0.37–1.65 wt.%, respectively. However, The TFe₂O₃ and TiO₂ in the white-colored anorthosite have a range of 1.67–3.1 wt.% and 0.14–0.31 wt.%, respectively. These features suggest that the alteration of the anorthosite led the Fe element by leaching from the dark-colored anorthosite at highly oxidized condition, and then precipitated within the fractures of the anorthosite, thus forming the massive Fe and Fe–P orebodies. Because the estimated amount of transported Fe is much more abundant than the proven ore reserve, we infer that there should be huge potential for prospecting Damiao type iron ores.     

Geochemical studies of Sr-Nd-Pb-Hf isotopes on the Guojialing granite suite: Implications to region Au mineralization in the Jiaodong ore-cluster region

Based on the systematic elemental and isotope geochemical study on the Guojialing granite that is closely related to the gold mineralization in the Jiaodong ore-cluster region, further understandings have been made regarding its genetic mechanism, source material and gold mineralization conditions of the Guojialing granites. The (⁸⁷Sr/⁸⁶Sr)_i values of Guojialing granite range from 0.7106 to 0.7120, and the εNd(t) from −18.1 to −13.2, respectively, which are similar to the initial SrNd isotopic compositions of those Late Jurassic-Early Cretaceous granites widely distributed in the Sulu orogenic belt, indicating similar sources of these intrusions in both Jiaodong and Su-Lu regions. The values of (²⁰⁶Pb/²⁰⁴Pb)_i and(²⁰⁷Pb/²⁰⁴Pb)_i of Guojialing granite are from 17.158–17.316, 15.453–15.478, respectively, indicating that the source of granites could be originated from mantle mixed with orogenic belt. The zircon Hf isotope of the Guojialing granite is decoupled from the Nd isotope of the whole rock, it has a zircon Hf model age(1979–3202 Ma) older than the full-rock Nd model age (1928 Ma). Compared to the full-rock Nd model age, the zircon Hf model age provides a more reliable age of crust-mantle differentiation and crust formation, suggesting that there is extensive crust deep-melting in the source area before the granitic magma activity, which was accompanied by strong Sm/Nd differentiation. Guojialing granite has similar characteristics to adakite, indicating that garnet is an important residual phase during magma formation. The formation of the Guojialing granite magma may be the partial melting of lithospheric mantle and thickened lower crust under eclogite facies, mixed with significant Neoarchaean crust or even Linglong granites when the magma upwelling. The Guojialing granite has high zircon Ce⁴⁺/Ce³⁺ ratios with the average values of 1151.7 and 811.4 respectively, indicating that the Guojialing granite was formed in a high oxygen fugacity environment, where sulfur is mainly present in the form of SO or SO₂, which prevents the immiscibility of sulfides in the magma and avoids the removal of the sulfide metal elements. With crystallization differentiation, high oxygen fugitive magma will become a magma-hydrothermal fluid which is rich in sulfide metal elements, providing favorable material and environmental conditions for gold mineralization, thus favorably formed such giant gold deposit.     

High-resolution δC intratooth profiles in bovine enamel: Implications for mineralization pattern and isotopic attenuation

We present the first high-resolution carbon isotope and carbonate content profiles generated through the thickness of enamel from a steer fed C₃- then C₄-dominant food. Carbonate contents decrease by ∼2 wt% from the enamel surface to the innermost enamel layer, and each carbon isotope profile shows a mixture of enamel portions mineralized over several months. Downward and outward increasing contribution of C₄ food to the enamel δ¹³C values reveal two components of the mineralization gradient: a vertical component from the tip of the tooth crown to the neck, and a horizontal component from the enamel-dentine junction to the outer enamel. We use our results to infer mineralization parameters for bovines and to calculate expected isotopic attenuations for an array of environmental inputs and microsampling strategies, using the model developed by Passey and Cerling [Geochim. Cosmochim. Acta. 66 (2002) 3225-3234]. Although it seems unlikely that any strategy will perfectly isolate discrete time slices, sampling the innermost enamel layer might offer the advantage of significantly reducing the isotope damping that would become independent of the structure of the input signal.     

湘南宝山矿床花岗闪长斑岩中黑云母的矿物学特征及其指示意义

湖南宝山矿床处于坪宝矿带的北端,是湘南地区最大的铜多金属矿床。为了进一步探讨矿区内花岗质岩石的形成条件及成矿潜力,文章在详细的野外地质和岩相学观察的基础上,对与成矿密切相关的花岗闪长斑岩中的黑云母进行了详细的矿物化学分析。电子探针分析结果表明:宝山花岗闪长斑岩中的黑云母为铁质黑云母和镁质黑云母,其中,Ti介于0.18~0.30,且Mg/(Mg+Fe2+)值介于0.42~0.58,属于典型的岩浆成因黑云母;黑云母的氧化系数为0.16~0.26,w(Mg O)为8.17%~11.72%,平均9.3%,MF值范围为0.38~0.50,指示其岩体属于壳幔混源型的I型花岗岩;岩体中以黑云母的全铝含量计算的结晶压力为97~174 MPa,相应的结晶深度为3.67~6.57 km,平均深度为5.12 km。其log f(O2)变化范围为-14.5~-12.8,表明黑云母是在较高氧逸度条件下结晶形成的,有利于铜矿的形成。