Alteration patterns and structural controls of the El Espino IOCG mining district,Chile

The El Espino IOCG mining district is characterized by several mineralized bodies the largest of which is the El Espino deposit, which has an estimated geologic resource of 123 Mt at 0.66 % Cu and 0.24 g/t Au. Mineralized bodies are distributed in a 7?×?10 km² area throughout a 1,000-m vertical section. They range from single veins to stockworks and breccias to manto-type deposits. The ore bodies are hosted primarily by volcanic, volcaniclastic, and sedimentary rocks of the Early Cretaceous Arqueros and Quebrada Marquesa formations, with a few mineralized zones within Late Cretaceous dioritic intrusions. The fault and vein architecture shows that El Espino IOCG system was localized within a dilatational jog along a major transtensional dextral fault system. Sodic alteration (albite) is the most extensive style of alteration in the district, and it is bounded by major NS–NNE trending faults. Sodic–calcic (epidote–albite) alteration occurs at deep to medium elevations (1,000–500 m) and grades inward into calcic alteration. Calcic alteration surrounds dioritic intrusions of the Llahuin plutonic suite. Significant iron oxides are associated with later calcic alteration associations (actinolite–epidote–hematite). The upper portions of the alteration system (0–500 m) display hydrolytic alteration associations with abundant hematite. Hydrolytic veins are feeders to zones of manto-type alteration and mineralization within favorable volcano-sedimentary lithologies that formed El Espino deposit. Sulfides are largely confined to calcic and hydrolytic alteration associations. Hydrothermal fluids responsible for hematite and sulfide mineralization had salinities between 32 and 34 wt% NaCl_eq and temperature of approximately 425 °C at an estimated depth of 3–4 km. Geochronological U–Pb and ⁴⁰Ar/³⁹Ar data indicate that hydrothermal alteration was coeval with magmatic intrusive activity. One particular dioritic intrusion (88.5 Ma) preceded the calcic stage (88.4 Ma), which was accompanied by iron oxide copper and gold mineralization. Hydrolytic alteration, related to economic iron oxide copper and gold mineralization, came immediately after at 87.9 Ma.     

新疆西天山智博铁矿床火山岩和侵入岩岩石地球化学

新疆西天山阿吾拉勒山集中产出多个大、中型海相火山岩型富铁矿床,引起人们的广泛关注。这些铁矿的成因被认为与火山作用有关,但对其成岩成矿的大地构造背景尚不清楚。文章研究了智博铁矿区出露的火山岩和侵入岩的岩石学、岩石地球化学,尝试探讨该问题。智博铁矿体赋矿围岩为早石炭世大哈拉军山组玄武岩和安山岩,侵入岩有晚石炭世花岗岩、花岗岩脉和闪长岩脉。玄武岩和安山岩在构造环境判别图解中投影于火山弧范围内,在花岗岩类构造环境判别图解中,320 Ma的花岗岩脉和319 Ma的石英闪长岩投影于岛弧环境,304 Ma的花岗闪长岩则投影于同碰撞环境。结合前人研究成果,认为智博地区在早石炭世为岛弧环境,晚石炭世可能经历了岛弧俯冲向同碰撞环境的转变。玄武岩亏损Ta、Nb,相对亏损Th,富集Rb、U、Pb;安山岩亏损Ta、Nb,富集轻稀土元素和Rb、U、Th、Pb,结合Sr/Th-Th/Ce和Th-Ba/Th图解判别,推测智博铁矿床玄武岩和安山岩岩浆源区为受到了俯冲带流体交代的楔形地幔。     

河南省安林矽卡岩型铁矿的成岩时代和成矿物质来源探讨

位于华北克拉通中部的河南省安林铁矿是典型的邯邢式矽卡岩型铁矿,矿体产于闪长质岩石和中奥陶统灰岩的接触带。LA-ICPMS锆石U-Pb定年结果表明安林闪长岩体的侵位年龄为123.38±0.81Ma,略晚于华北克拉通东部地区的含矿岩体,形成于岩石圈大规模减薄伸展时期。但其中含有古老的锆石说明岩浆经历了地壳的混染。闪长质岩石具有相对低SiO2、高Mg#、高碱,富集Ba、Sr和LREE大离子亲石元素,亏损Nb、Ti、Ta等高场强元素的特点,暗示了其形成于岩石圈地幔。岩相学特征以及Harker图解指示了岩浆经历了较强的分离结晶作用,因此推断安林闪长岩可能是软流圈地幔上涌导致富集的岩石圈地幔发生部分熔融形成原始的辉长质岩浆在上升过程中或岩浆房中发生了以铁镁矿物为主的分离结晶作用,同时受到地壳物质的混染的结果。安林地区矿石具有和闪长岩体相似的稀土元素地球化学特征,反映铁的成矿作用与岩浆作用密切相关。矿床中闪长岩体、矽卡岩、矿石和碳酸盐围岩的主量元素对比研究表明钠交代作用引起Na、K、Fe、Si等元素在各岩类间的迁移,其中迁移出的铁为成矿提供了物质基础。安林地区初始岩浆富含水,分离结晶作用使残留岩浆水饱和而发生出溶;且岩浆在演化过程中受到区内膏盐层和碳酸盐地层的混染,促进了岩浆中流体的出溶并使出溶的流体富含Cl-,为有利于铁质活化的富Cl-岩浆流体的形成创造了条件。     

青海省兴海县赛什塘铜矿床矽卡岩矿物学特征及地质意义

赛什塘铜矿位于东昆仑造山带东端的鄂拉山地区,是中国西部重要的矽卡岩型铜矿之一。矽卡岩形成于印支期石英闪长岩与中—下三叠统地层Tb2 1-2岩性段的接触带,矿体主要呈似层状、透镜状产于外接触带矽卡岩中。Tb2 1-2岩性段由中性火山岩、大理岩及变质粉砂岩构成,其中变安山质凝灰岩及安山岩与铜矿化有着密切的空间关系。岩相学研究表明,含铜矽卡岩的形成经历了矽卡岩阶段、退化蚀变阶段、石英-硫化物阶段及石英-碳酸盐阶段。矽卡岩阶段形成石榴子石、辉石及硅灰石,退化蚀变阶段则形成绿帘石、角闪石及磁铁矿,石英-硫化物阶段大量金属硫化物发生沉淀。电子探针分析表明,石榴子石与辉石矿物组分分别为Gro0.00~91.00And7.02~100.00(Pyr+Alm+Spe)0.00~4.27与Di12.80~98.08Hd2.41~79.80(Jo+Jd+Opx)0.00~13.47,表明其属于典型的钙矽卡岩类。空间上,靠近石英闪长岩与安山岩接触带处,钙铝榴石和绿帘石更富集,而向大理岩的一侧以钙铁榴石为主,并常见硅灰石及含Mn的钙铁辉石。矿物学特征及矿物成分的变化显示:从矽卡岩阶段到石英-硫化物阶段,流体性质呈幕式的变化,成矿流体至少经历了2次氧化还原性质的转变,这种变化可能与成矿流体中大气降水的不断加入有关。赛什塘铜矿属于矽卡岩型矿床,以石英闪长岩为主的岩浆活动携带了大量的热量及流体,侵入到中—下三叠统地层中,与围岩地层发生物质交换的同时,引起了大理岩、变质粉砂岩与中性火山岩之间的双交代作用,是导致矽卡岩和矿体形成的重要机制。     

Triassic arc mafic magmatism in North Qiangtang: Implications for tectonic reconstruction and mineral exploration

The North Qiangtang continental block in central Tibet is a critical piece of the Pangea puzzle. This paper uses integrated geochronological and geochemical data for selected mafic dykes and dioritic enclaves in this block to evaluate its tectonic evolution in the Triassic. Zircons from two mafic dykes and the dioritic enclaves of a large arc granodiorite pluton in eastern North Qiangtang yield indistinguishable U-Pb ages from 248 ± 2 to 251 ± 3 Ma, contemporaneous with widespread arc basaltic andesites and crust-derived rhyolites in the region. The mafic dykes and coeval arc basaltic andesites have almost identical Sr-Nd isotopes (initial ⁸⁷Sr/⁸⁶Sr = 0.707 to 0.708, ε_Nd = −4.4 to −3.6), and are all characterized by light REE enrichments and pronounced negative Nb-Ta anomalies. The dioritic enclaves and the hosts have indistinguishable zircon U-Pb ages, almost identical Sr-Nd isotopes (initial ⁸⁷Sr/⁸⁶Sr = 0.709 to 0.711, ε_Nd = −7.4 to −5.9), and similar zircon ε_Hf (−13.7 to −5.7), but contrasting chondrite-normalized REE patterns due to hornblende fractionation. The Sr-Nd isotope data indicate that the dioritic enclaves formed from the hybrid melts produced by mixing at depth between the arc basaltic andesites and the crust-derived rhyolites. We propose that the Early Triassic arc igneous suites are related to the northward subduction of the southern Paleo-Tethys beneath the North Qiangtang block from Early to Middle Triassic. The occurrence of several Late Triassic porphyry Cu deposits plus a VMS Ag-Pb-Zn deposit in the Yidun arc, which is the product of the southward subduction of the northern Paleo-Tethys beneath the North Qiangtang block in the Late Triassic, indicates that the arc magmas generated during the subduction of the Paleo-Tethys are fertile in ore metals. Therefore, exploration for Early–Middle Triassic porphyry Cu and VMS deposits in the southern part of the North Qiangtang block is warranted.     

岩浆矽卡岩及其矿床

岩浆矽卡岩是由钙硅酸盐熔（流）体或钙矽卡岩质岩浆贯入结晶或／和隐爆团结（结晶）形成的。主要呈脉状体，少数呈角砾岩筒（带），受断裂、裂隙构造控制，可产于各类不同岩石（层）中。岩浆矽卡岩与富碱中基－中酸性侵入岩密切共生，两者在主化学成分上具共轭、互补关系，组成特征的岩浆矽卡岩　－富碱（中基－中酸）侵入岩对。它们是深部高位岩浆房受钙质强烈混染的富碱闪长质岩浆发生不混溶分　离所衍生的两种不同性质的熔（流）体或岩浆的产物。与岩浆矽卡岩有关的各类矿床，主要是含同生铁氧　化物／硫化物液体的钙矽卡岩（矿）浆，伴随其成岩演变的产物，并构成了一个特殊的（岩）浆矽卡岩矿床系列。     

Geological Features and Formation Processes of the Makeng Fe Deposit,China

Recent studies have revealed that the Makeng Fe deposit is a skarn type deposit. However, the skarns in Makeng, occurring primarily between limestone and sandstone, are not typically associated with limestone and plutons. Different periods of intrusions, e.7. Hercynian mafic intrusions and Yanshanian (i.e. early Cretaceous) Dayang–Juzhou granitic intrusion, occurred in the Makeng deposit district. In this study, the formation processes of the skarns and Fe mineralization are constrained by detailed fieldwork, petrology, geochronology, and geochemistry. Skarns and Fe mineralization intersecting the Hercynian mafic intrusions are observed in consecutive specimens from the 106# tunnel. They suggest that the skarn formation and Fe mineralization occurred after the Hercynian mafic intrusions and are related to the later Yanshanian Dayang–Juzhou granitic intrusion. The geochronological characteristics of weakly skarn‐altered diabases, the decreasing nature of Fe contents in altered diabase, and the major element compositions of pyroxenes and garnets also support that Hercynian mafic intrusions are strongly reformed by Yanshanian granitic magmas and the Fe migrated from mafic intrusion was responsible for formation of iron ore.     

http://www.sciencedirect.com/science/article/pii/S1674987115000924

The Oyu Tolgoi cluster of seven porphyry Cu-Au-Mo deposits in southern Mongolia,define a narrow,linear,12 km long,almost continuously mineralised trend,which contains in excess of 42 Mt of Cu and1850 t of Au,and is among the largest high grade porphyry Cu-Au deposits in the world.These deposits lie within the Gurvansayhan island-arc terrane,a fault bounded segment of the broader Silurian to Carboniferous Kazakh-Mongol arc,located towards the southern margin of the Central Asian Orogenic Belt,a collage of magmatic arcs that were periodically active from the late Neoproterozoic to PermoTriassic,extending from the Urals Mountains to the Pacific Ocean.Mineralisation at Oyu Tolgoi is associated with multiple,overlapping,intrusions of late Devonian(~372 to 370 Ma) quartzmonzodiorite intruding Devonian(or older) juvenile,probably intra-oceanic arc-related,basaltic lavas and lesser volcaniclastic rocks,unconformably overlain by late Devonian(~370 Ma) basaltic to dacitic pyroclastic and volcano sedimentary rocks.These quartz-monzodiorite intrusions range from earlymineral porphyritic dykes,to larger,linear,syn-,late- and post-mineral dykes and stocks.Ore was deposited within syn-mineral quartz-monzodiorites,but is dominantly hosted by augite basalts and to a lesser degree by overlying dacitic pyroclastic rocks.Following ore deposition,an allochthonous plate of older Devonian(or pre-Devonian) rocks was overthrust and a post-ore biotite granodiorite intruded at~365 Ma.Mineralisation is characterised by varying,telescoped stages of intrusion and alteration.Early A-type quartz veined dykes were followed by Cu-Au mineralisation associated with potassic alteration,mainly K-feldspar in quartz-monzodiorite and biotite-magnetite in basaltic hosts.Downward reflux of cooled,late-magmatic hydrothermal fluid resulted in intense quartz-sericite retrograde alteration in the upper parts of the main syn-mineral intrusions,and an equivalent chlorite-muscovite/illite-hematite assemblage in basaltic host rocks.Uplift,facilitated by syn-mineral longitudinal faulting,brought sections of the porphyry deposit to shallower depths,to be overprinted and upgraded by late stage,shallower,advanced argillic alteration and high sulphidation mineralisation.Key controls on the location,size and grade of the deposit cluster include(i) a long-lived,narrow faulted corridor;(ii) multiple pulses of overlapping intrusion within the same structure;and(iii) enclosing reactive,mafic dominated wall rocks,focussing ore.     

Petrogenesis of granitoids in the Dewulu skarn copper deposit: implications for the evolution of the Paleotethys ocean and mineralization in Western Qinling,China

The Tethyan tectonic domain hosts numerous world-class mineral deposits. Among these, the Dewulu skarn copper deposit in Western Qinling, China belongs to the Paleotethys ore belt. The skarn and orebodies here occur as stratoids or lenses at the contact between the Triassic Dewulu intrusive complex and Permian marine clastic and carbonates. Alteration minerals include prograde skarns (garnet, diopside, wollastonite), plagioclase, hornblende, actinolite, tremolite, epidote, chlorite, calcite, quartz and sericite. The main ore types include early disseminated skarn-type replacement orebodies and late-stage quartz-sulfide veins. Chalcopyrite is the major ore mineral, along with pyrite, bornite and sphalerite. The Dewulu intrusive complex comprises quartz diorite, quartz diorite porphyry and dioritic mafic microgranular enclaves (MME). The MMEs are spheroidal in shape, and have igneous mineral assemblages, acicular apatites, complex oscillatory zoned plagioclase and quartz megacrysts surrounded by mafic minerals. The MMEs are metaluminous and calc-alkaline to high-K calc-alkaline, and possess relatively high Ni, Cr and MgO contents and Mg^# values. They display sub-parallel patterns in trace element spider diagrams and rare earth element (REE) plots. They are also characterized by the enrichment of Rb, U and Th, depletion of Ba, Sr, Nb and Ta and negative Eu anomaly. Zircon LA-ICP-MS U–Pb dating of the dioritic MME yields an age of 247.0 ± 2.2 Ma, coeval with the host quartz diorite, quartz diorite porphyry and ore-related sericite ⁴⁰Ar/³⁹Ar plateau ages within analytical uncertainties. Oxygen fugacity estimated from trace element compositions of zircons from the dioritic MME shows FMQ ± 3.3. The zircons have negative ε_Hf(t) values in a range of − 8.0 to − 3.3, corresponding to two-stage model ages ranging from 1.48 to 1.78 Ga. The integrated data from petrology, geochronology and bulk geochemistry suggest that the Early Triassic granitoids associated with Cu skarn mineralization at Dewulu were products of arc magmatism and involved magma mixing in an active continental margin setting. The magma was sourced through partial melting of enriched sub-continental lithospheric mantle that had been previously modified by slab-derived melt during the continuous northward subduction of the Paleotethys oceanic slab.     

云南北衙金矿床地质特征及成因研究

云南北衙金矿床是滇西北地区与喜山期富碱岩类有关的典型代表之一，矿床成矿与区内富碱岩体（脉）形成与分布具有空间上形影相随，时间上相近或稍晚，成因上密切相关的联系，研究表明，北衙金矿化类型多样，特别是于近期发现的具有特大远景的红土型矿化体，更成为该矿区的一大特色，矿石中金属矿物复杂，蚀变强烈且分带明显，对矿床和相关的富碱岩体（脉）开展的金丰度值，同位素和稀土元素研究表明，富碱岩体本身并不是矿质的源地，成矿流体和主要矿质均源于地球深部，文章初步讨论了岩浆成岩与流体成矿之间的关系，指出岩浆的形成，演化与侵位过程实际上是深部流体上升的载体以及矿质在流体中得以集中并成矿的热机。     

An intrusion-related origin for Cu–Au mineralization in iron oxide–copper–gold (IOCG) provinces

Major Cu–Au deposits of iron oxide–copper–gold (IOCG) style are temporally associated with oxidized, potassic granitoids similar to those linked to major porphyry Cu–Au deposits. Stable and radiogenic isotope evidence indicates fluids and ore components were likely sourced from the intrusions. IOCG deposits form over a range of crustal levels because CO₂-rich fluids separate from the magmas at higher pressures than in CO₂-poor systems, thereby, promoting partitioning of H₂O, Cl and metals to the fluid phase. At deep levels, the magma–fluid system cannot generate sufficient mechanical energy to fracture the host rocks as in porphyry systems and the IOCG deposits therefore form in a variety of fault-related structural traps where the magmatic fluids may mix with other fluids to promote ore formation. At shallow levels, the IOCG deposits form breccia and fracture-hosted mineralization styles similar to the hydrothermal intrusive breccias and sulphide vein systems that characterize many porphyry Cu–Au deposits. The fluids associated with IOCG deposits are typically H₂O–CO₂–salt fluids that evolve by unmixing of the carbonic phase and by mixing with fluids from other sources. In contrast, fluids in porphyry systems typically evolve by boiling of moderate salinity fluid to produce high salinity brine and a vapor phase commonly with input of externally derived fluids. These different fluid compositions and mechanisms of evolution lead to different alteration types and parageneses in porphyry and IOCG deposits. Porphyry Cu–Au deposits typically evolve through potassic, sericitic and (intermediate and/or advanced) argillic stages, while IOCG deposits typically evolve through sodic(–calcic), potassic and carbonate-rich stages, and at deeper levels, generally lack sericitic and argillic alteration. The common association of porphyry and IOCG Cu–Au deposits with potassic, oxidized intermediate to felsic granitoids, together with their contrasting fluid compositions, alteration styles and parageneses suggest that they should be considered as part of the broad family of intrusion-related systems but that they are typically not directly related to each other.     

新疆乔夏哈拉铁铜金矿床与国内外IOCG矿床的对比研究

随着IOCG矿床不断取得巨大的勘探成果,IOCG矿床在国内外都日益受到关注。新疆乔夏哈拉铁铜金矿床在构造环境、元素组合、蚀变特征等方面与国外典型的IOCG矿床有相似之处,乔夏哈拉铁铜金矿床处于大陆边缘拉张环境,具有Fe-Cu-Au(-REE)多元素组合,蚀变以绿帘石矽卡岩化为主,垂直分带不明显;在成矿时代方面又区别于多数产在元古代的IOCG矿床,而是在古生代;乔夏哈拉西矿区切割铁矿层的闪长岩脉角闪石的Ar-Ar坪年龄为378.1±3.6Ma,故铁的成矿年龄应在泥盆纪。本文认为乔夏哈拉铁铜金矿床不仅与IOCG矿床有较多相似之处,与国内内蒙古白云鄂博铁稀土铌矿床、云南迤纳厂铁铜稀土矿床、云南拉拉铜铁金钴钼稀土矿床和云南稀矿山铁铜矿床等也有相似之处,因此,在中国寻找IOCG矿床尤其是大型矿床,是有可能的。     

The U–Pb SHRIMP age of zircons from diorites of the Tomino–Bereznyaki ore field (South Urals,Russia): evolution of porphyry Cu–epithermal Au–Ag system

The Tomino–Bereznyaki ore field lies in the western part of the East Urals volcanic megazone (20–30 km southwest of Chelyabinsk). The commercial Tomino porphyry (Mo, Au)–Cu deposit is localized in the east of the field, within a small mesoabyssal intrusion of quartz–diorite composition. The epithermal Au–Ag Bereznyaki deposit is confined to subvolcanic dioritic porphyrites in the west of the field. The western and eastern parts of the ore field have a tectonic boundary. Granitoids belong to a single volcanoplutonic complex of K–Na-quartz–diorite composition. The U–Pb concordant age of zircons from the ore-bearing dioritic porphyrite of the Tomino and Bereznyaki deposits is 428 ± 3 Ma (MSWD = 0.9) and 427 ± 6 Ma (MSWD = 1.1), respectively. A Silurian absolute age has been established for the Urals porphyry Cu ore-magmatic system for the first time. The diorites and acid metasomatites of both deposits contain a unique three-mica assemblage (Mu, Pa, and Mu0.36Pa0.64). The metasomatized diorites are of similar isotope-petrogeochemical compositions; they have close total REE contents (24–52 ppm) and REE patterns. Their Zr–Hf, Nb–Ta, and La–Ce diagrams show similar trends. The obtained data indicate the close time of formation of the porphyry and epithermal deposits and their probable genetic unity. The vertical evolution of the porphyry Cu column from meso- and hypabyssal to subvolcanic level includes the isotope (Sr, S, and O) crust–mantle interaction. The deposits formed at different depths expose on the modern surface as a result of the block tectonic processes in the ore field.     

福建马坑铁（钼）矿床矽卡岩矿物学特征及分带研究

马坑大型铁(钼)矿赋存于莒舟-大洋花岗岩体外接触带黄龙组(C2h)灰岩和林地组(C1l)碎屑岩层间构造破碎带中,铁矿与矽卡岩密切共生,但矿床成因尚存在争议。本文就马坑铁矿矽卡岩进行了矿物学特征研究。电子探针分析结果表明:该矿矽卡岩矿物组合主要为辉石、石榴子石和钙蔷薇辉石,退化蚀变岩矿物组合为角闪石、绿帘石、绿泥石、石英等。单斜辉石以透辉石和钙铁辉石为主,仅存在少量锰钙辉石;似辉石为钙蔷薇辉石和蔷薇辉石;石榴子石端元成分以钙铁榴石为主,钙铝榴石少量;角闪石属于钙角闪石,矿物学特征表明它们形成于相对较氧化的条件下。马坑铁矿的矽卡岩是由热流体沿灰岩与碎屑岩之间层间构造破碎带交代形成的,铁矿石大部分产于矽卡岩内,磁铁矿多稍晚于矽卡岩,不仅广泛交代矽卡岩,而且还直接交代灰岩、砂岩等围岩,呈交代结构;主矿体下盘常出现厚层石英岩,碎屑岩也出现了明显的交代,矽卡岩分带现象普遍,与典型矽卡岩矿床特征一致。结合矿床地质特征,马坑铁矿矿床类型应为层控矽卡岩型矿床。     

Subduction-related mafic to felsic magmatism in the Malayer–Boroujerd plutonic complex,western Iran

The Malayer–Boroujerd plutonic complex (MBPC) in western Iran, consists of a portion of a magmatic arc built by the northeast verging subduction of the Neo-Tethys plate beneath the Central Iranian Microcontinent (CIMC). Middle Jurassic-aged felsic magmatic activity in MBPC is manifested by I-type and S-type granites. The mafic rocks include gabbroic intrusions and dykes and intermediate rocks are dioritic dykes and minor intrusions, as well as mafic microgranular enclaves (MMEs). MBPC Jurassic-aged rocks exhibit arc-like geochemical signatures, as they are LILE- and LREE-enriched and HFSE- and HREE-depleted and display negative Nb–Ta anomalies. The gabbro dykes and intrusions originated from metasomatically enriched garnet-spinel lherzolite [Degree of melting (f_mel) ~ 15%] and exhibit negative Nd and positive to slightly negative ε_Hf(T) (+ 3.0 to ? 1.6). The data reveal that evolution of Middle Jurassic magmatism occurred in two stages: (1) deep mantle-crust interplay zone and (2) the shallow level upper crustal magma chamber. The geochemical and isotopic data, as well as trace element modeling, indicate the parent magma for the MBPC S-type granites are products of upper crustal greywacke (f_mel: 0.2), while I-type granites formed by partial melting of amphibolitic lower crust (f_mel: 0.25) and mixing with upper crustal greywacke melt in a shallow level magma chamber [Degree of mixing (f_mix): 0.3]. Mixing between andesitic melt leaving behind a refractory dense cumulates during partial crystallization of mantle-derived magma and lower crustal partial melt most likely produced MMEs (f_mix: 0.2). However, enriched and moderately variable ε_Nd(T) (? 3.21 to ? 4.33) and high (⁸⁷Sr/⁸⁶Sr)_i (0.7085–0.7092) in dioritic intrusions indicate that these magmas are likely experienced assimilation of upper crustal materials. The interpretations of magmatic activity in the MBPC is consistent with the role considered for mantle-derived magma as heat and mass supplier for initiation and evolution of magmatism in continental arc setting, elsewhere.     

Calcic skarns and transversal zoning in the Banat mountains, Romania: indicators of an Andean-type setting

Calcic skarn deposits related to Upper Cretaceous – Paleocene banatitic intrusions are widely developed in the Banat Mountains (southwestern Romanian Carpathians). There is a spatial distribution of banatitic igneous rocks and associated ore deposits in parallel zones, due to subduction beneath the southwest Carpathians. As a result three distinct petro-metallogenetic units developed, i.e. marginal unit: Moldova Nouă– Sasca; median unit: Ciclova – Oravita; and the inner unit: Dognecea – Ocna de Fier. The magmatism changed inland from monzonite and diorite → granodiorite occurrences to granodiorite → granite plutons. The related mineralization shifted simultaneously from Cu (Mo) to Cu-Mo (W) and eventually Fe(Cu)/Pb-Zn. The distribution of both magmatism and related ore deposits in parallel petro-metallogenetic zones is considered similar to that in the Andes. In particular, calcic skarns and related ore deposits that occur in these units show a transversal zonal variation represented by compositional features of pyroxene and granat, sequence of mineralization and metallogenetic environment. Such zonal characteristics represent an additional but nonetheless significant indicator for an Andean-type subduction-related setting. Received: 3 June 1996 / Accepted: 10 January 1997     

徐宿弧安徽北段地区矽卡岩型Au-Fe-Cu矿床以及有关的中酸性侵入岩年代学研究

徐宿弧安徽北段地区中酸性岩体由多期次岩浆活动形成,部分岩体中发育一系列矽卡岩型（Fe）-Au-Cu-（Mo）和Fe矿床。对该区域内王场矽卡岩型铁矿床成矿岩体（闪长玢岩）和区内最大的矽卡岩型金矿床（杨桥孜Au-Cu矿床）中的辉钼矿进行了测年研究,获得王场闪长玢岩锆石LA-ICP-MS U-Pb加权平均年龄为132.1±1.9 Ma,杨桥孜矿床辉钼矿Re-Os等时线年龄为130.0±3.2 Ma。系统分析了区内成岩年代、矿化类型及成矿规律,认为区内的岩浆岩可分为4期,矿床分为4种类型,具体为：第1期岩浆岩为新元古代早期的浅成基性侵入岩（辉绿岩）,与原生金刚石矿床有关;第2期岩浆岩为侏罗纪早期的中酸性侵入岩;第3期岩浆岩为早白垩世早期的中酸性侵入岩,与矽卡岩型Fe矿床和矽卡岩型（Fe）-Au-Cu-（Mo）矿床有关;第4期为早白垩世晚期的酸性侵入岩。研究区还发现了与深成基性侵入岩有关的岩浆熔离型Cu-Ni矿床,但尚无年代学研究报道。矿化以与中酸性侵入岩有关的Fe、Au-Cu矿化为主,与基性侵入岩有关的Cu-Ni及金刚石矿化较少。研究区各期次岩浆岩都形成于华北克拉通伸展的构造环境,但受不同的地质事件控制。区内大规模的成岩成矿时代集中分布在早白垩世,可能与同时期华北克拉通岩石圈破坏有关。成岩成矿年代学与地球化学数据表明,徐宿弧地区深部可能存在与胶东地区相类似的热液金多金属矿床,为该区今后的找矿方向提供了参考。     

西藏墨竹工卡地区甲玛铜多金属矿床矽卡岩矿物学特征及其地质意义

为研究西藏甲玛铜多金属矿床中矽卡岩的矿物学特征,进一步确定矿床成因类型,利用电子探针测试和镜下鉴定手段对矽卡岩矿物中的石榴子石、辉石、硅灰石等矿物成分进行了分析。测试结果表明,矽卡岩中石榴子石以钙铁榴石-钙铝榴石为主,辉石以透辉石为主,甲玛矿床矽卡岩属于交代矽卡岩中典型的钙矽卡岩。结合前人对矿区矽卡岩、围岩和花岗岩类的岩石地球化学、矿床成矿年代学等的研究,进一步证实甲玛铜多金属矿床系矿区花岗岩类岩浆交代大理岩形成的典型矽卡岩型矿床。     

Gushan magnetite–apatite deposit in the Ningwu basin, Lower Yangtze River Valley, SE China: Hydrothermal or Kiruna-type?

The Gushan deposit is one of the typical magnetite–apatite deposits associated with dioritic porphyries in the Lower Yangtze River Valley belt of the eastern Yangtze craton. The origin of this deposit is still uncertain and remains a controversial issue. Divergent opinions are centered on whether the iron deposits are magmatic or hydrothermal in origin. However, our field observations and mineralogical studies, combined with previous published petrological and geochemical features strongly suggest that the main ore bodies in the Gushan magnetite–apatite deposit are magmatic. Specific evidence includes the existence of gas bubbles, tubes, and miarolitic and amygdaloidal structures, melt flow banding structure and the presence of “ore breccia”. New electron microprobe analyses of the pyroxene phenocrysts of the dioritic porphyry genetically associated with the Gushan magnetite–apatite deposit show that the Fe contents in the evolving magma dramatically decrease, and then gradually increase. Because there is no evidence of mafic magma recharge, this scenario (decreasing Fe) could be plausibly interpreted by Fe-rich melts separated from Fe-poor silicate melts, i.e., liquid immiscibility was triggered by minor addition of phosphorus by crustal contamination. The occurrence of massive iron ore bodies can be satisfactorily explained by the immiscible Fe-rich melt with enormous volatile contents was driven to the top of the magma chamber due to the low density. The hot and volatile-rich iron ore magma was injected along fractures and spaces between the dioritic intrusions and wall-rocks, and led to an explosion near the surface, resulting in the immediate fragmentation of the roof of the intrusion and wall-rocks, forming brecciated ores. Moreover, other types of ores can be considered as a result of post-magmatic hydrothermal activities. Our proposed metallogenic model involving the Kiruna-type mineralization is consistent with the observed phenomenon in the Gushan deposit.     

Geochemistry of Precambrian ophiolites from Bou Azzer,Morocco

The Upper Proterozoic ophiolite complex of Bou Azzer, Morocco, includes ultramafic rocks, cumulate gabbros, sheeted dykes, pillow lavas and diorite-quartz diorite intrusions and an overlying volcano-sedimentary sequence. The gabbroic cumulates, basaltic flows and dykes have compositions similar to recent ocean-floor rocks (N- and/or T-type). Among other features, they have comparable light REE-depleted patterns and relations of Ti-Zr and La-Nb. Although fractional crystallization played an important role in the evolution of these rocks, the large variations in their chemical compositions require generation from a heterogeneous upper mantle source and/or by a dynamic partial melting process. Diorites, quartz diorites and the volcanic rocks of the overlying sequence are calc-alkaline, genetically unrelated to the tholeiitic suite and indicative of an island arc setting. A possible tectonic model for the ophiolite complex is a marginal basin just behind a still active island arc.