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1.
Abstract: The Mamut deposit of Sabah, East Malaysia, is a porphyry type Cu‐Au deposit genetically related to a quartz monzonite (“adamellite”) porphyry stock associated with upper Miocene Mount Kinabalu plutonism. The genesis of the Mamut deposit is discussed based on petrology of the intrusives in the Mount Kinabalu area combined with ore– and alteration–petrography, fluid inclusion and sulfur isotope studies. Groundmass of the adamellite porphyry at Mamut is rich in K which suggests vapor transport of alkaline elements during the mineralizing magmatic process, while the groundmass of the post‐ore “granodiorite” porphyry at Mamut contains small amounts of normative corundum suggesting depletion in alkaline elements at the root zone of the magma column. Sub‐dendritic tremolitic amphibole rims on hornblende phenocrysts in the Mamut adamellite porphyry suggest interaction between the mineralizing magma and the exsolved fluids. Occurrences of clinopyroxene microphenocrysts and pseudomor‐phic aggregates of shredded biotite and clinopyroxene after hornblende phenocrysts in the barren intrusives imply lower water fugacity and decreasing in water fugacity, respectively. Compositional gap between the core of hornblende phenocrysts and the tremolitic amphibole rims and those in the groundmass of the Mamut adamellite porphyry suggests a decrease in pressure. Higher XMg (=Mg/(Mg+Fe) atomic ratio) in the tremolitic amphibole rims in the Mamut adamellite porphyry compared to those of the barren intrusions suggests high oxygen fugacity. High halogen contents of igneous hydrous minerals such as amphiboles, biotite and apatite in the Mamut adamellite porphyry suggest the existence of highly saline fluids during the intrusion and solidification of the mineralizing magma. Fluid inclusions found in quartz veinlet stockworks are characterized by abundant hypersaline polyphase inclusions associated with subordinate amounts of immiscible gaseous vapor. Both Cu and Au are dispersed in disseminated and quartz stockwork ores. Chalcopyrite and pyrrhotite as well as magnetite are the principal ore minerals in the biotitized disseminated ores. Primary assemblage of intermediate solid solution (iss) and pyrrhotite converted to the present assemblage of chalcopyrite and pyrrhotite during cooling. Subsequent to biotitization, quartz veinlet stockworks formed associated with retrograde chlorite alteration. The Cu‐Fe sul–fides associated with stockwork quartz veinlet are chalcopyrite and pyrite. Overlapping Pb and Zn and subsequent Sb mineralizations were spatially controlled by NNE‐trending fractures accompanying the phyllic and advanced argillic alteration envelope. Sulfur isotopic composition of ore sulfides are homogeneous (about +2%) throughout the mineralization stages. These are identical to those of the magmatic sulfides of Mount Kinabalu adamellitic rocks.  相似文献   

2.
Dealt with in this paper are some geochemical characteristics of porphyry copper mineralization, especially those observed in intrusive bodies, wall rocks, alteration zones, ores and pyrites. Ore bearing bodies have been correlated with barren ones from such aspects as major and trace elements, copper contents of biotite and pyrite, and distribution pattern of copper. In the mineralized rocks, trace elements show apparent zoning surrounding ore bodies; major and trace elements seem to show some regularities with respect to their variations in the process of alteration, and as a result each alteration zone displays its own peculiar element association. Trace elements in ores can provide information on the genetic types of ore deposits, thus of great help in distinguishing ore types, while those in pyrites may be indicative of the main mineralizing stage, providing clues for distinguishing ore-bearing from barren rocks, and of the extent of denudation of ore bodies.  相似文献   

3.
The concentrations of platinum-group elements (PGE) have been analyzed in primary magmatic magnetite samples from the Zhireken,Shakhtama and Aksug porphyry Cu-Mo deposits (Siberia,Russia) by laser abla...  相似文献   

4.
Chemical analyses are given for actinolitic hornblendes of tonalitic rocks from the Hercynian belt of Northern Portugal. The distribution of elements between amphibole and co-existing biotite is studied. The composition of the amphiboles is analysed in the light of experimental data on amphiboles and the physical conditions of crystallization inferred from the study of the biotite and rock series. The data on the biotites lead to the definition of a temperature of 800°C for the crystallization of actinolitic hornblendes with Mg/(Mg + Fe) ratios of 0·72-0·61 at pressures of about 3 Kb and fO2 defined by FMQ.  相似文献   

5.
Summary At Climax, comagmatic igneous intrusions can be subdivided into two groups, mineralizing stocks which are parent intrusions for Mo orebodies and barren stocks. Magmatic biotites in mineralizing stocks are similar to hydrothermal biotites in that they contain a greater proportion of Si-enriched and Ti-depleted compositional domains than do magmatic biotites in barren stocks. A similar trend of Si-enrichment correlated with Ti-depletion is also recorded in biotites from the Bingham porphyry copper deposit. Such trends are attributed to vapour exsolution associated with mineralization. Mo concentrations of magmatic biotites, as determined by ion-probe analysis, from mineralizing stocks (av. 40 gg/g) and barren stocks (av. 33 /g) at Climax are similar, being in the same order of magnitude as magmatic biotite Cu concentrations in mineralizing and barren (type A) intrusions in North American porphyry copper deposits (Hendry et al., 1985). These Cu and Mo values are more than a factor of 10 lower than Cu concentrations commonly recorded in magmatic mafic phases in barren (type B) South West Pacific and Australian granitic systems that are temporally distinct from mineralizing events, and are consistent with the magmatic-hydrothermal origin for the Climax deposits proposed by White et al. (1981).
Chemische Charakteristika von Mineralen aus erzführenden und erzfreien Intrusionen im Bereich der Molybdänlagerstätte Climax, Colorado
Zusammenfassung Zwei Gruppen komagmatischer Intrusivkörper können im Bereich der Molybdän-Lagerstätte Climax, Colorado, unterschieden werden: Mineralisierende Intrusiva, die Stammagmen für Molybdän-Erzkörper darstellen, und erzfreie Intrusiva. Magmatische Biotite in mineralisierenden Intrusiva sind hydrothermalen Biotiten insofern ähnlich, als sie einen größeren Anteil von Si-angereicherten und Ti-verarmten Bereichen enthalten als magmatische Biotite in erzfreien Intrusiva. Ein ähnlicher Trend von Si-Anreicherung, die mit Ti-Verarmung korreliert werden kann, ist auch in Biotiten aus der Porphyry-copper-Lagerstätte Bingham bekannt geworden. Derartige Trends werden auf Entmischung von Dampfphasen in Zusammenhang mit der Mineralisation zurückgeführt.Molybdän-Konzentrationen von magmatischen Biotiten in Climax wurden mit der Ionensonde bestimmt und zeigen in mineralisierenden und erzfreien Intrusiva ähnliche Werte, i.e., 40 p/g bzw. 33 gg/g. Diese Werte liegen in derselben Größenordnung wie Kupferkonzentrationen in magmatischen Biotiten aus vererzten und erzfreien (Typ A) Intrusionen im nordamerikanischen Porphyry-copper-Lagerstätten (Hendry et al., 1985). Diese Kupfer- und Molybdänwerte sind um den Faktor 10 niedriger als Kupferkonzentrationen, die man gewöhnlich in magmatischen mafischen Phasen in erzfreien (Typ B) Granitsystemen im südwestlichen Pazifik und Australien nachgewiesen hat. Diese sind zeitlich einer anderen Entstehungsperiode zuzuordnen als die erzbildenden Vorgänge, und dies stimmt wiederum mit der magmatisch hydrothermalen Entstehung der Lagerstätten von Climax überein, wie sie vonWhite et al. (1981) vorgeschlagen worden ist.

With 4 Figures  相似文献   

6.
A detailed study of apatite and biotite compositions in multiple intrusive phases from five composite plutons in the northern Canadian Cordillera was undertaken with the aim of determining the composition of magmatic fluids relative to F:Cl:OH for several plutons―both barren and mineralizing―and for specific intrusive phases from each pluton that may be related to nearby tungsten skarns. Magmatic apatite and biotite compositions are consistent with a crustal source of magma, either derived from predominantly supracrustal rocks, and (or) derived from predominantly infracrustal rocks and fractionated to felsic compositions. Increasing MnO (± FeO and XF:XCl) with decreasing CaO in apatite broadly correlates with an increasing degree of magmatic differentiation, although Fe# vs. total aluminum in biotite is a better indicator of inter- and intra-plutonic differentiation. Anomalously iron-rich biotites occur in highly fractionated and (or) wallrock-contaminated phases of plutons associated with tungsten skarns.Estimates of magmatic fluid composition―calculated as the activity ratios log[aHCl / aHF] and log[aHOH / aHF] from apatite and biotite compositions―show several trends with respect to magmatic differentiation. Two barren plutons demonstrate that fluids in silicic magmas become HF enriched relative to HCl with increasing differentiation, although re-equilibration with late-stage sub-solidus or hydrothermal fluids may obscure this trend. The three intrusions with associated tungsten skarn mineralization, including the world-class Cantung deposit, also become HF-enriched with magmatic evolution. However, magmatic apatite and biotite in individual intrusive phases that are the most closely associated with mineralization have equilibrated with compositionally distinct fluids. In these particular intrusive phases, apatite appears to have equilibrated with an earlier HCl- and H2O-rich magmatic fluid, and biotite appears to have equilibrated with a later HCl- and (a particularly) H2O-rich magmatic fluid. The fluid in these magmas apparently evolved to a H2O-rich (or less saline) composition as the temperature of the magma decreased. None of the other intrusive phases, from either the barren or tungsten-associated plutons, have apatite and biotite activity ratios that are suggestive of equilibration with such an HCl/HF- and H2O/HF-rich fluid. Instead, the activity ratios calculated from apatite and biotite in intrusive phases that are not as closely associated with mineralization are well-coupled and unremarkable (although small variations are common), which would suggest that both minerals equilibrated with similar fluids. These intrusive phases do not appear to have produced a large quantity of saline hydrous fluid capable of seggregating and transporting tungsten. The identification of intrusive phases that did produce magmatic fluids that were anomalously enriched in HCl and H2O could, therefore, be a predictor of nearby tungsten skarn mineralization.  相似文献   

7.
The Koloula Igneous Complex comprises 26 different intrusive phases that have been divided into two major magmatic episodes — cycle 1 intrusions (4.5 Ma) and cycle 2 intrusions (2.4 to 1.5 Ma). The cycle 2 intrusions are further divided into the Inamumu Zoned Pluton (IZP) which is composed of 6 concentrically disposed quartz diorite and tonalite units; and several satellite intrusions. The IZP is host to porphyry-copper mineralization, whereas the cycle 1, and cycle 2 satellite intrusions are barren. Presently exposed mineralization in the IZP (A system) represents the deeply eroded core of a porphyry copper system, where widely-spaced veinlet alteration envelopes ( 1 mm thick) are separated by large volumes of unaltered rock.Compositional trends in biotites and amphiboles from both individual grains and throughout the differentiation series of the IZP, indicate fluctuating but generally increasing existed through the sequence from early magmatic late magmatic early hydrothermal conditions. In amphiboles, compositional domains (Mg-rich) that are indicative of high are correlated with episodes of fluid exsolution, independent evidence of which is provided by multiple generations of fluid inclusions in quartz phenocrysts. These high domains in amphiboles have higher Si, Mn, and Ca contents, but are depleted in Fe, Ti, Na, K, and Cl relative to the less oxidizing domains. The latter elements are those that are known from veinlet alteration assemblages and fluid-inclusion evidence to have been preferentially partitioned into the co-existing fluid phase (late magmatic hydrothermal solution).By contrast, amphiboles from barren rock types that are slightly older than, and of the same age as the IZP, exhibit restricted compositional ranges, and are more Fe-rich. Some individual grains and two cycle 2 satellite intrusions indicate Fe-enrichment during progressive crystallization. Siliceous deuteric amphiboles are commonly as Mg-rich as the high amphibole domains from the IZP, but are easily distinguished from them by their lack of smooth compositional trends versus Si, and by their highly variable Mg and Fe contents.Biotites from the IZP also indicate progressive oxidation, whereas biotites from the barren rock types show either little compositional variation or progressive Fe-enrichment. Biotites from the barren intrusions are richer in Cl, Li and Rb and poorer in Ba than those of the mineralizing intrusions. fHF was very low ( 0.003 bars) in both barren and mineralizing intrusions. During progressive differentiation, Rb content decreased and Ba content increased in IZP biotites, which is atypical, yet explicable owing to the former presence of a competing fluid phase during biotite crystallization.Because is a function of degree of fluid exsolution, then in igneous systems with sufficient Cu, Cl, and ultimately S, progressively higher should potentially lead to more mineralized intrusions. Higher is reflected by steeper Fe versus Si gradients in amphibole domains. Indeed, such a graph for amphiboles from 5 igneous complexes, indicates that two economically mineralized units produced steeper FeSi than those from weakly mineralized intrusions. Steep FeSi trends that do not continue to amphibole domains more siliceous than Si=7.3 (atoms per 23 oxygens) are unlikely to have resulted from subsolidus crystallization and these intrusions are unlikely to be strongly mineralized.  相似文献   

8.
龚林  陈华勇  王云峰  赵联党  肖兵 《地球科学》2018,43(9):2929-2942
黑云母的化学成分对于揭示结晶条件、岩石成因、成矿演化以及含矿性评价等具有重要的指示意义.利用电子探针（EPMA）对新疆玉海和三岔口铜矿中的黑云母进行成分分析,结果表明与成矿相关岩体的黑云母具有富镁贫铁的特征,而无矿化岩体中的黑云母则呈现富铁贫镁的特征.分析结果显示矿化岩体中黑云母为再平衡镁质黑云母,而无矿化岩体中黑云母为原生铁质黑云母;它们的寄主岩石均属于I型花岗岩,形成于与俯冲相关的构造背景,但是与矿化相关岩体的岩浆源区为壳幔混合来源,而无矿岩体的源区为地壳来源,形成过程中有新生地壳组分的混染;两类黑云母的结晶温度为529~677 ℃,寄主岩体的固结压力为1.1~2.8 kbar,均形成于高氧逸度条件;此外,黑云母的Mg/Fe和Fe2+/（Fe2++Mg2+）还可以区分斑岩型铜矿的含矿性.   相似文献   

9.
大别山典型燕山期侵入体中矿物成分特征及其地质意义   总被引：4，自引：0，他引：4  
分析了大别造山带核部典型燕山期侵入体中的斜长石、黑云母和角闪石的化学成分和成因特点,并从矿物平衡角度讨论了典型侵入体岩石成因。结果表明：（１）石鼓尖侵入岩中,斜长石成分较稳定,共生角闪石和黑云母为岩浆平衡结晶的矿物;（２）天堂寨和九资河侵入岩中,部分斜长石和黑云母可能为深蚀残留矿物,角闪石属于火成岩区的新生矿物,可能为斜长石和黑云母发生融反应所形成;（３）三个侵入体的岩石均为岩浆成因。  相似文献   

10.
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。  相似文献   

11.
安徽铜陵凤凰山岩体若干特征及成矿关系   总被引：1，自引：0，他引：1  
<正> 安徽铜陵凤凰山岩体,出露面积约9km2,呈似岩株状,总体成分属正常的钙碱系列的花岗闪长岩,副矿物为磁铁矿、榍石、磷灰石型,主要侵入于中三叠纪扁担山组灰岩中。岩体接触带北部向北陡倾,东部向东中等倾斜,南部向南倾较缓,西部超覆于围岩之上而产状较复杂。  相似文献   

12.
The Southwest prospect is located at the southwestern periphery of the Sto. Tomas II porphyry copper–gold deposit in the Baguio District, northwestern Luzon, Philippines. The Southwest prospect hosts a copper‐gold mineralization related to a complex of porphyry intrusions, breccia facies, and overlapping porphyry‐type veinlets emplaced within the basement Pugo metavolcanics rocks and conglomerates of the Zigzag Formation. The occurrences of porphyry‐type veinlets and potassic alteration hosted in the complex are thought to be indications of the presence of blind porphyry deposits within the Sto. Tomas II vicinity. The complex is composed of at least four broadly mineralogically similar dioritic intrusive rocks that vary in texture and alteration type and intensity. These intrusions were accompanied with at least five breccia facies that were formed by the explosive brecciation, induced by the magmatic–hydrothermal processes and phreatomagmatic activities during the emplacement of the various intrusions. Hydrothermal alteration assemblages consisting of potassic, chlorite–magnetite, propylitic and sericite–chlorite alteration, and contemporaneous veinlet types were developed on the host rocks. Elevated copper and gold grades correspond to (a) chalcopyrite–bornite assemblage in the potassic alteration in the syn‐mineralization early‐mineralization diorite (EMD) and contemporaneous veinlets and (b) chalcopyrite‐rich mineralization associated with the chalcopyrite–magnetite–chlorite–actinolite±sericite veinlets contemporaneous with the chlorite–magnetite alteration. Erratic remarkable concentrations of gold were also present in the late‐mineralization Late Diorite (LD). High XMg of calcic amphiboles (>0.60) in the intrusive rocks indicate that the magmas have been oxidizing since the early stages of crystallization, while a gap in the composition of Al between the rim and the cores of the calcic amphiboles in the EMD and LD indicate decompression at some point during the crystallization of these intrusive rocks. Fluid inclusion microthermometry suggests the trapping of immiscible fluids that formed the potassic alteration, associated ore mineralization, and sheeted quartz veinlets. The corresponding formation conditions of the shallower and deeper quartz veinlets were estimated at pressures of 50 and 30 MPa and temperatures of 554 and 436°C at depths of 1.9 and 1.1 km. Temperature data from the chlorite indicate that the chalcopyrite‐rich mineralization associated with the chlorite–magnetite alteration was formed at a much lower temperature (ca. 290°C) than the potassic alteration. Evidence from the vein offsetting matrix suggests multiple intrusions within the EMD, despite the K‐Ar ages of the potassic alteration in EMD and hornblende in the LD of about the same age at 3.5 ± 0.3 Ma. The K‐Ar age of the potassic alteration was likely to be thermally reset as a result of the overprinting hydrothermal alteration. The constrained K‐Ar ages also indicate earlier formed intrusive rocks in the Southwest prospect, possibly coeval to the earliest “dark diorite” intrusion in the Sto. Tomas II deposit. In addition, the range of δ34S of sulfide minerals from +1.8‰ to +5.1‰ in the Southwest prospect closely overlaps with the rest of the porphyry copper and epithermal deposits in the Sto. Tomas II deposit and its vicinity. This indicates that the sulfides may have formed from a homogeneous source of the porphyry copper deposits and epithermal deposits in the Sto. Tomas II orebody and its vicinity. The evidence presented in this work proves that the porphyry copper‐type veinlets and the adjacent potassic alteration in the Southwest prospect are formed earlier and at a shallower level in contrast with the other porphyry deposits in the Baguio District.  相似文献   

13.
Whole rock and mineral stable isotope and microprobe analyses are presented from granitoids of the North Chilean Precordillera. The Cretaceous to Tertiary plutonic rocks contain important ore deposits and frequently display compositional and textural evidence of hydrothermal alteration even in barren rocks. Deuteric alteration includes replacement of biotite and amphibole by chlorite and epidote, sericitization and saussuritization of feldspars, and uralitization of clinopyroxene and/or amphibole. While whole rock compositions are not significantly affected, compositional variations in amphiboles suggest two types of hydrothermal alteration. Hornblende with actinolitic patches and rims and tight compositional trends from hornblende to Mg-rich actinolite indicate increasing oxygen fugacity from magmatic to hydrothermal conditions. Uralitic amphiboles exhibiting irregular Mg-Fe distribution and variable Al content are interpreted as reflecting subsolidus hydration reactions at low temperatures. The δD values of hydrous silicates vary from −63 to −105‰. Most δ18O values of whole rocks are in the range of 5.7 to 7.7‰ and are considered normal for igneous rocks in the Andes. These δ18O values also coincide well with the oxygen isotope composition of geochemically similar recent volcanics from the Central Andean Volcanic Zone (δ18O = 7.0–7.4‰). Only one sample in this study (δ18O = 3.0‰) appears to be depleted by isotope exchange with light meteoric water at high temperatures. The formation of secondary minerals in all other intrusions is mainly the product of deuteric alteration. This also holds true for the sample from El Abra, the only pluton associated with mineralization. This indicates the dominant role of a magmatic rather than a meteoric fluid in the alteration of the Cretaceous and Tertiary granitoids in northern Chile. Received: 8 July 1998 / Accepted: 15 April 1999  相似文献   

14.
金坑Sn-Cu矿床是粤东地区新发现的典型Sn-Cu共生矿床.矿区发育花岗闪长斑岩、中粗粒黑云母花岗岩和细粒花岗岩等多种侵入岩以及高基坪组火山岩,而这些岩石的年代学格架,及其与成矿过程关系还不清楚.因此,本文以粤东地区新发现的金坑铜锡矿床为研究对象,系统开展不同岩性侵入岩锆石和矿石锡石的U-Pb年龄测定,旨在浅析Sn-C...  相似文献   

15.
冯钟燕 《现代地质》1998,12(4):467-476
摘 要　 太行山南段是我国著名的矽卡岩铁矿成矿区域。区内有很多岩体‚有的有矿‚有的 无矿。选择了一些有代表性的岩体‚进行系统的岩石学研究工作‚总结了有矿、无矿两类岩 体的判别标志‚并对一些现象产生的原因进行了初步讨论。  相似文献   

16.
尾亚—天湖地区位于新疆中亚造山带东南部的中天山地块内,晚古生代—中生代岩浆活动强烈,产出了战略性关键矿产尾亚钒铁磁铁矿.在详细岩相学观察的基础上,对尾亚、天湖和沙泉子南岩体中的角闪石和黑云母进行了电子探针(EMPA)测试分析,限定了 3个岩体结晶的温压条件、氧逸度、含水量和含铁指数等要素,为解析中天山地块的岩浆-成矿物...  相似文献   

17.
The Taihe, Baima, Hongge, Panzhihua and Anyi intrusions of the Emeishan Large Igneous Province (ELIP), SW China, contain large magmatic Fe–Ti–(V) oxide ore deposits. Magnetites from these intrusions have extensive trellis or sandwich exsolution lamellae of ilmenite and spinel. Regular electron microprobe analyses are insufficient to obtain the primary compositions of such magnetites. Instead, laser ablation ICP-MS uses large spot sizes (~ 40 μm) and can produce reliable data for magnetites with exsolution lamellae. Although magnetites from these deposits have variable trace element contents, they have similar multi-element variation patterns. Primary controls of trace element variations of magnetite in these deposits include crystallography in terms of the affinity of the ionic radius and the overall charge balance, oxygen fugacity, magma composition and coexisting minerals. Early deposition of chromite or Cr-magnetite can greatly deplete magmas in Cr and thus Cr-poor magnetite crystallized from such magmas. Co-crystallizing minerals, olivine, pyroxenes, plagioclase and apatite, have little influence on trace element contents of magnetite because elements compatible in magnetite are incompatible in these silicate and phosphate minerals. Low contents and bi-modal distribution of the highly compatible trace elements such as V and Cr in magnetite from Fe–Ti oxide ores of the ELIP suggest that magnetite may not form from fractional crystallization, but from relatively homogeneous Fe-rich melts. QUILF equilibrium modeling further indicates that the parental magmas of the Panzhihua and Baima intrusions had high oxygen fugacities and thus crystallized massive and/or net-textured Fe–Ti oxide ores at the bottom of the intrusive bodies. Magnetite of the Taihe, Hongge and Anyi intrusions, on the other hand, crystallized under relatively low oxygen fugacities and, therefore, formed net-textured and/or disseminated Fe–Ti oxides after a lengthy period of silicate fractionation. Plots of Ge vs. Ga + Co can be used as a discrimination diagram to differentiate magnetite of Fe–Ti–(V) oxide-bearing layered intrusions in the ELIP from that of massif anorthosites and magmatic Cu–Ni sulfide deposits. Variable amounts of trace elements of magmatic magnetites from Fe–Ti–(P) oxide ores of the Damiao anorthosite massif (North China) and from Cu–Ni sulfide deposits of Sudbury (Canada) and Huangshandong (northwest China) demonstrate the primary control of magma compositions on major and trace element contents of magnetite.  相似文献   

18.
The Duolong district in central Tibet hosts a number of porphyry as well as high sulfidation epithermal copper–gold deposits and prospects, associated with voluminous calc-alkaline volcanism and plutonism. In this study, we present new geochronological, geochemical, isotopic and mineralogical data for both economically mineralized and barren porphyritic intrusions from the Duobuza and Naruo porphyry Cu–Au deposits. Zircon U–Pb analyses suggest the emplacement of economically mineralized granodiorite porphyry and barren granodiorite porphyry at Naruo deposit took place at 119.8 ± 1.4 Ma and 117.2 ± 0.5 Ma, respectively. Four molybdenite samples from the Naruo deposit yield an isochron Re–Os age of 119.5 ± 3.2 Ma, indicating mineralization occurred synchronously with the emplacement of the early granodiorite porphyry. At Duobuza deposit, the barren quartz diorite porphyry intruded at 119.5 ± 0.7 Ma, and two economically mineralized intrusions intruded at 118.5 ± 1.2 Ma (granodiorite porphyry) and 117.5 ± 1.2 Ma (quartz diorite porphyry), respectively. Petrographic investigations and geochemical data indicate that all of the porphyritic intrusions were oxidized, water rich, and subduction-related calc-alkaline magmas. Zircons from the porphyritic intrusions have a wide range in the εHf (0–11.1) indicating that they were sourced from mixing of mantle-derived mafic, and crust-derived felsic melts. Moreover, the variation of trace element content of plagioclase phenocrysts indicates that the magma chambers were recharged by mafic magmas.Comparison of the composition of amphibole phenocrysts indicates the porphyry copper–gold mineralization at Duolong was generated in magma chambers at low crystallization temperatures and pressures (754° to 791 °C, 59 M to 73 MPa, n = 8), and under highly oxidizing conditions (ΔNNO 2.2 to 2.7, n = 8). In contrast, barren intrusions were sourced from the magma chambers with higher crystallization temperatures and pressures (816° to 892 °C, 111 to 232 MPa, n = 22) that were less oxidizing (ΔNNO 0.6 to 1.6, n = 22). The requirement for a thermal contrast is supported by the declining of Ti content in magnetite crystals in barren intrusions (12,550 to 34,200 ppm) versus those from economically mineralized intrusions (600 to 3400 ppm). Moreover, the V content in magnetite crystals from economically mineralized intrusions (990 to 2510 ppm) is lower than those recorded from barren intrusions (2610 to 3510 ppm), which might reflect the variation in oxidation state of the magma. The calculated water solubility of the magma forming the economically mineralized intrusions (3.2–3.7 wt%) is lower than that of magma forming the barren intrusions (4.6–6.4 wt%). Based on the chemical–physical characteristics of economically mineralized magma, our study suggests that the development of porphyry Cu–Au mineralization at Duolong was initiated by shallow-level emplacement of a magma that crystallized at lower temperatures and pressures. Experimental studies show that copper and water solubilities in silicate melts decrease with falling temperatures and pressures, indicating metals and ore-forming fluids are more likely to be released from a magma reservoir emplaced at shallow crustal levels. We propose the magnetite might be a convenient exploration tool in the search for porphyry copper mineralization because the variations in Ti and V content of mineral concentrates and rock samples are indicative of barren versus mineralized intrusions.  相似文献   

19.
The chemical compositions of rock-forming minerals have been determined for both altered and least-altered igneous rocks spatially associated with numerous mineralized zones (Nucleus Au–Bi–Cu–As deposit, Revenue Au ± Cu and Stoddart Cu–Mo ± W mineral occurrences, and Laforma Au–Ag deposit) across the Freegold Mountain area, Yukon, Canada. Within the study area, K-feldspar has a narrow compositional range (89.4–91% Or), whereas plagioclase spans a wide range (4.4–70.07% An). In all of the investigated samples, T Ab = T An = T Or, suggesting that magmatic equilibrium between the coexisting plagioclase and K-feldspar was maintained. Igneous amphibole phenocrysts from hypabyssal dikes are typically calcic, whereas the Stoddart Cu–Mo ± W, Laforma Au–Ag, and Goldy Au mineralization are associated with Mg-enriched primary amphibole of edenite composition, and Au–Bi–Cu–As mineralization from Nucleus is related to Al-enriched primary amphibole of ferropargasite composition. Primary biotite phenocrysts across the Freegold Mountain area re-equilibrated with oxidized magma (f(O2) values between 10–13 and 10–11.5 bars, lying between the Ni/NiO and the magnetite/haematite buffers). However, biotite and amphibole phenocrysts from Stoddart, Goldy, Laforma, and the Highway zones crystallized from a more oxidized magma, as indicated by their elevated X Mg up to 0.65, relative to biotite and hornblende from Nucleus and Revenue characterized by a lower X Mg (typically < 0.50). This suggests that various sources and (or) rapid emplacement were involved in magma genesis, as further supported by the considerable variation of pressure (1.8–7.3 kb) of amphibole crystallization and of the total Al content in least-altered biotite (2.6–2.9 afu) within the Freegold Mountain area. Biotite and apatite equilibrated within the T range of 520–780°C, consistent with temperatures of equilibration between ilmenite and magnetite, and their compositions indicate that they formed from an oxidized I-type magma. Magma differentiated by fractional crystallization (indicated by the presence of normally zoned plagioclase with Ca-rich cores and Na-enriched outer rims) and multiple magma mixing (supported by the presence of reversed zoned plagioclase and coexistence of normally and reversely zoned plagioclase). Lower X Mg biotite associated with the mineralized (Cu–Mo ± W) potassic alteration incorporated more F and Cl relative to least-altered biotite with higher X Mg. In both Nucleus and Revenue Au–Cu mineralizations, secondary biotite composition varies with respect to the associated alteration mineral assemblages. Although secondary biotite in the skarn re-equilibrated with F-poor fluids, secondary biotite from the pervasive biotitization is related to F- and Cl-enriched fluids, and secondary biotite from the phyllitic zone is related to F-, Cl-, and Mg-depleted fluids, thus consistent with a change in mineralizing fluid composition during mineralization.  相似文献   

20.
Two types of mafic rocks from the central Sanin district, and their mafic minerals, were studied chemically and microscopically. They are classified into pyroxene‐containing gabbroid and hornblende–biotite quartz diorite. The gabbroid had higher color index but lower magnetite content; while the quartz diorite had lower color index, but higher magnetite content. The magnetite contents are also related to the amounts of hydrous mafic silicates. The gabbroic magma having pyroxene–amphibole assemblage, originated in the upper mantle, was considered essentially anhydrous, but became partly hydrous on the way to the site of solidification in the continental crust, and crystallized some magnetites with hypersthene and amphibole. The quartz dioritic magma was formed by partial melting of possibly subducting ocean‐floor basalts, once exposed to the sea‐floor then altered; thus the magmas became hydrous and oxidized originally, and precipitated abundant magnetite and hydrous mafic silicates from the early crystallization stage onward. Their weathered parts provided the most placer magnetite ores in the history.  相似文献   

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