Mineral Geochemistry of Apatite in the Jiama PorphyrySkarn Deposit,Tibet and its Geological Significance

The Jiama deposit,a significant porphyry-skarn-type copper polymetallic deposit located within the Gangdese metallogenic belt in Tibet,China,exemplifies a typical porphyry metallogenic system.However,the mineral chemistry of its accessory minerals remains under-examined,posing challenges for resource assessment and ore prospecting.Utilizing electron microprobe analysis and LA-ICP-MS analysis,this study investigated the geochemical characteristics of apatite in ore-bearing granite and monzogranite porphyries,as well as granodiorite,quartz diorite,and dark diorite porphyries in the deposit.It also delved into the diagenetic and metallogenic information from these geochemical signatures.Key findings include:(1)The SiO_(2) content,rare earth element(REE)contents,and REE partition coefficients of apatite indicate that the dark diorite porphyry possibly does not share a cogenetic magma source with the other four types of porphyries;(2)the volatile F and Cl contents in apatite,along with their ratio,indicate the Jiama deposit,formed in a collisional setting,demonstrates lower Cl/F ratios in apatite than the same type of deposits formed in a subduction environment;(3)compared to non-ore-bearing rock bodies in other deposits formed in a collisional setting,apatite in the Jiama deposit exhibits lower Ce and Ga contents.This might indicate that rock bodies in the Jiama deposit have higher oxygen fugacity.Nevertheless,the marginal variation in oxygen fugacity between ore-bearing and non-ore-bearing rock bodies within the deposit suggests oxygen fugacity may not serve as the decisive factor in the ore-hosting potential of rock bodies in the Jiama deposit.

Correction:Gardaneh Salavat porphyry copper system:Is it about metal endowment or fertility of the porphyritic intrusion?

Correction to:Acta Geochim(2022)41(3):496-514 https://doi.org/10.1007/s11631-022-00535-0 In the original publication of the article,under the section“4.1 Proposed hypothesis for Gardaneh Salavat porphyry system”,on page 509,the following sentence“Du and Audétat(2020)believed that early sulfide saturation is not necessarily detrimental to deposit formation or fertility of porphyritic intrusions.Further proving this fact”was included incorrectly.

Gardaneh Salavat porphyry copper system: Is it about metal endowment or fertility of the porphyritic intrusion?

Gardaneh Salavat porphyry copper system is located in the northwest of Iran. It comprises a quartz diorite to diorite porphyritic intrusion that created extensive alteration haloes in the host rocks. Despite all technical considerations, the exploration activities did not yield to ore discovery. As the matter of fact, all of the geological,geophysical, and geochemical characteristics of a porphyry Cu-Au deposit exist but there is no economic mineralization. Detailed examinations suggest that the only reasonable explanation can be related to the infertility or low metal endowment of the porphyritic intrusion. The reasons include(1) anomalous ranges of Cu, Au, and Mo rather than economic ore grades,(2) weakly development of potassic alteration,(3) probably sulfur saturation of magma that occurred before intrusion emplacement in the host rocks, and(4) probably low metal endowment in the regional scale and the lack of known porphyry copper deposits in close neighborhoods. It is tried to test the proposed hypothesis with the introduced fertility indicators based on major and trace element geochemistry. However,current fertility indicators could not prove or reject the proposed hypothesis for Gardaneh Salavat porphyritic intrusion because of the high-K calc-alkaline to shoshonitic nature of the intrusive rocks together with the unavailability of relatively fresh/unaltered samples. This case study is notable to examine because(1) it shows that characterization of fertile from barren intrusions seems to be as important as vectoring towards concealed porphyry copper deposits, especially while dealing with deep exploration targets that are associated with high financial risks, and(2) it highlights the inefficiencies and uncertainties in introduced magma fertility indicators for porphyry copper intrusions. As a result, it is of high importance to conduct an overarching investigation on other possible fertility indicators as a fundamental need for the future of the exploration industry.

Textural and compositional variation of mica from the Dexing porphyry Cu deposit:constraints on the behavior of halogens in porphyry systems

The Dexing porphyry deposit is the largest porphyry Cu–Mo–Au deposit in South China.Biotite composition can record the physicochemical conditions and evolution history of magmatic-hydrothermal system.Biotite from the Dexing porphyry deposit could be divided to three types:primary magmatic biotite(Bi-M),hydrothermal altered magmatic biotite(Bi-A)and hydrothermal biotite(Bi-H).The temperature of Bi-M and Bi-H range from 719 to 767℃ and 690 to 727℃,respectively.Both magmatic and hydrothermal biotite have high Fe^(3+)/Fe^(2+)ratios(from 0.18 to 0.24)and XMgvalues(from 0.57 to 0.66),indicating a high oxygen fugacity.BiM has F lower than Bi-A and Bi-H(up to 0.26 wt%),but has Cl(Cl=0.18–0.30 wt%)similar to Bi-A and Bi-H(Cl=0.21–0.35 wt%),suggesting that high Cl/F ratios of early hydrothermal fluid may result from the exsolution from high Cl magma.From potassic alteration zone to phyllic and propylitic alteration zones,Cl decreases with increasing Cu,whereas F increases roughly.Therefore,Cl mostly originate from magma,but enrichment of F possibly results from reaction of fluids and Neoproterozoic strata.Negative correlation between Cl and Cu indicates that Cl might act as an important catalyst during Cu mineralization process.Biotite from Dexing has similar halogen compositions to other porphyry Cu-/Mo deposits in the world.Chlorine contents of hydrothermal fluid may be critical for Cu transportation and enrichment,while consumption of Cl would promote Cu deposition.

Petrogenesis and Physicochemical Conditions of Fertile Porphyry in Non-arc Porphyry Mineralization:A Case from Habo Porphyry Cu-Mo Deposits,SW China

The Habo deposit is a typical porphyry Cu-Mo deposit in the Ailaoshan–Red River metallogenic belt.Ore minerals in the Habo deposit typically occur as veins in the monzonite porphyry.Zircon U-Pb dating suggests that the monzonite porphyry formed at 35.07±0.38 Ma.The monzonite porphyry is characterized by high SiO_(2),Al_(2)O_(3),K_(2)O and Na_(2)O contents,with A/CNK ratios ranging from 0.97 to 1.02.All samples exhibit fractionated REE patterns,characterized by high(La/Yb)N ratios(9.4–13.6,average of 11.2).They show adakite-like geochemical features,high Sr concentrations(627–751 ppm,average of 700 ppm),low Y concentrations(15.13–16.86 ppm,average of 15.81 ppm)and high Sr/Y values(39.5–47.4,average of 44.3).These samples have high initial^(87)Sr/^(86)Sr ratios(0.7074–0.7076)and negativeεNd(t)values(-5.1 to-3.7),whereas the zirconεHf(t)values range from-2.2 to+0.4,suggesting that the monzonite porphyry was derived from the partial melting of a thickened juvenile lower crust.The oxygen fugacity,calculated on the basis of the chemical composition of the amphiboles,shows?NNO values ranging from+1.65 to+2.16(average of 1.94)and lg(fO_(2))ranging from-12.72 to-11.99(average of-12.25),indicating that the monzonite porphyry has high oxygen fugacity.Zircons have high Ce^(4+)/Ce^(3+)ratios(29.29–164.24,average of 84.92),with high?FMQ values ranging from+0.50 to+1.51(average of 0.87)and high lg(fO_(2))values ranging from-14.72 to-12.85(average of-14.07),which also indicates that the oxygen fugacity of the magma was high.The dissolved water content of the Habo monzonite porphyry is 9.5–11.5 wt%,according to the geochemical characteristics,zircon-saturation thermometry(692–794°C)and the mineral phases(amphibole,no plagioclase)in the deep magma chamber.Combined with previous studies,we propose that the high oxygen fugacity and high water content of magma played key roles in controlling the formation of the Habo and other Cu-Mo-Au deposits in the Ailaoshan–Red River metallogenic belt.

Geochronology,Geochemistry and Petrogenesis of the Bangbule Quartz Porphyry:Implications for Metallogenesis

The Bangbule skarn lead-zinc(Pb-Zn)deposit(>1 Mt Zn+Pb)is located in the western Nyainqentanglha polymetallic metallogenetic belt,central Tibet.Lenticular orebodies are all hosted in skarn and developed in the contact zone between the quartz porphyry and carbonate strata of the mid Paleozoic Middle to Upper Chaguoluoma Formation as well as in carbonate and sandstone beds of the Upper Paleozoic Laga Formation.As a newly discovered skarn deposit,the geological background and metallogenesis of this deposit remain poorly understood.Detailed petrological,geochemical and geochronological data of the ore-related quartz porphyry,helps constrain the mineralization age and contributes to discussion on the ore genesis of the Bangbule deposit.Both endoskarn and exoskarn are identified in the Bangbule deposit.From quartz porphyry to carbonate formation,the exoskarn is zoned from proximal garnet skarn to distal pyroxene skarn.Zircon U-Pb dating results show that the quartz porphyry formed at 73.9±0.8 Ma.Geochemical analysis results show that the quartz porphyry has high contents of SiO_(2)(71.40–74.94 wt%)and K_(2)O+Na_(2)O(3.76–8.46 wt%)with A/CNK values of 0.69 to 1.06.Besides,the quartz porphyry is enriched in large ion lithophile elements(LILEs)and light rare earth elements(LREEs)and have lowεNd(t)(from-8.25 to-8.19)and high initial(^(87)Sr/^(86)Sr)i values(0.713611–0.714478).Major,trace elements and whole-rock F concentration analysis results from the endoskarn samples show higher TFe_(2)O_(3),MgO,CaO,Pb+Zn,W,Sn,Mo and F etc.,and lower alkalis(K_(2)O,Na_(2)O,Sr and Ba)than those of fresh quartz porphyry,indicating that the early ore-forming fluids were an Ca-Fe-F-enriched fluid.Massive ore in the proximal skarn might be related to the high F content in the magma,which lowered the solidus temperature of the quartz porphyry magma and caused a lower temperature of the ore-forming fluids,as well as facilitating the precipitation of sphalerite and galena.Based on the geochemical characteristics presented in this study,we propose that the ore-related quartz porphyry was formed by partial melting of crust materials with some juvenile crustal component input.The partial melting of the middle-upper crust after the initial enrichment of lead and zinc elements are important for the formation of Pb-Zn deposits.The case study of the Bangbule deposit has proven that there is still a crust-derived magmatic source region in the western segment of the central Lhasa terrane.Therefore,there is still great potential for Pb-Zn mineralization and Pb-Zn exploration.

Geology and mineralization of the Daheishan supergiant porphyry molybdenum deposit(1.65 Bt),Jilin,China:A review

The Daheishan supergiant porphyry molybdenum deposit(also referred to as the Daheishan deposit)is the second largest molybdenum deposit in Asia and ranks fifth among the top seven molybdenum deposits globally with total molybdenum reserves of 1.65 billion tons,an average molybdenum ore grade of 0.081%,and molybdenum resources of 1.09 million tons.The main ore body is housed in the granodiorite porphyry plutons and their surrounding inequigranular granodiorite plutons,with high-grade ores largely located in the ore-bearing granodiorite porphyries in the middle-upper part of the porphyry plutons.Specifically,it appears as an ore pipe with a large upper part and a small lower part,measuring about 1700 m in length and width,extending for about 500 m vertically,and covering an area of 2.3 km^(2).Mineralogically,the main ore body consists of molybdenite,chalcopyrite,and sphalerite horizontally from its center outward and exhibits molybdenite,azurite,and pyrite vertically from top to bottom.The primary ore minerals include pyrite and molybdenite,and the secondary ore minerals include sphalerite,chalcopyrite,tetrahedrite,and scheelite,with average grades of molybdenum,copper,sulfur,gallium,and rhenium being 0.081%,0.033%,1.67%,0.001%,and 0.0012%,respectively.The ore-forming fluids of the Daheishan deposit originated as the CO_(2)-H_(2)O-NaCl multiphase magmatic fluid system,rich in CO_(2)and bearing minor amounts of CH4,N2,and H2S,and later mixed with meteoric precipitation.In various mineralization stages,the ore-forming fluids had homogenization temperatures of>420℃‒400℃,360℃‒350℃,340℃‒230℃,220℃‒210℃,and 180℃‒160℃and salinities of>41.05%‒9.8%NaCleqv,38.16%‒4.48%NaCleqv,35.78%‒4.49%NaCleqv,7.43%NaCleqv,and 7.8%‒9.5%NaCleqv,respectively.The mineralization of the Daheishan deposit occurred at 186‒167 Ma.The granites closely related to the mineralization include granodiorites(granodiorite porphyries)and monzogranites(monzogranite porphyries),which were mineralized after magmatic evolution(189‒167 Ma).Moreover,these mineralization-related granites exhibit low initial strontium content and high initial neodymium content,indicating that these granites underwent crust-mantle mixing.The Daheishan deposit formed during the Early-Middle Jurassic,during which basaltic magma underplating induced the lower-crust melting,leading to the formation of magma chambers.After the fractional crystallization of magmas,ore-bearing fluids formed.As the temperature and pressure decreased,the ore-bearing fluids boiled drops while ascending,leading to massive unloading of metal elements.Consequently,brecciated and veinlet-disseminated ore bodies formed.

Geology and mineralization of the Duobaoshan supergiant porphyry Cu-Au-Mo-Ag deposit(2.36 Mt)in Heilongjiang Province,China:A review

The reserves of the Duobaoshan porphyry Cu-Au-Mo-Ag deposit(also referred to as the Duobaoshan porphyry Cu deposit)ranks first among the copper deposits in China and 33rd among the porphyry copper deposits in the world.It has proven resources of copper(Cu),molybdenum(Mo),gold(Au),and silver(Ag)of 2.28×10^(6)t,80×10^(3)t,73 t,and 1046 t,respectively.The major characteristics of the Duobaoshan porphyry Cu deposit are as follows.It is located in a zone sandwiched by the Siberian,North China,and paleo-Pacific plates in an island arc tectonic setting and was formed by the Paleozoic mineralization and the Mesozoic mineralization induced by superposition and transformation.The metallogenic porphyries are the Middle Hercynian granodiorite porphyries.The alterations of surrounding rocks are distributed in a ring form.With silicified porphyries at the center,the alteration zones of K-feldspar,biotite,sericite,and propylite occur from inside to outside.This deposit is composed of 215 ore bodies(including 14 major ore bodies)in four mineralized zones.Ore body No.X in the No.3 mineralized zone has the largest resource reserves,accounting for more than 78%of the total reserves of the deposit.Major ore components include Cu,Mo,Au,Ag,Se,and Ga,which have an average content of 0.46%,0.015%,0.16 g/t,1.22 g/t,0.0003%,and 0.001%-0.003%,respectively.The ore minerals of this deposit primarily include pyrite,chalcopyrite,bornite,and molybdenite,followed by magnetite,hematite,rutile,gelenite,and sphalerite.The ore-forming fluids of this deposit were magmatic water in the early metallogenic stage and then the mixture of meteoric water and magmatic water at the late metallogenic stage.The ore-forming fluids experienced three stages.The ore-forming fluids of stageⅠhad a hydrochemical type of H_(2)O-CO_(2)-Na Cl,an ore-forming temperature of 375-650℃,and ore-forming pressure of 110-160 MPa.The ore-forming fluids of stageⅡhad a hydrochemical type of H_(2)O-CO_(2)-Na Cl,an ore-forming temperature of 310-350℃,and ore-forming pressure of 58-80 MPa.The ore-forming fluids of stageⅢhad a hydrochemical type of Na Cl-H_(2)O,an ore-forming temperature of 210-290℃,and ore-forming pressure of 5-12 MPa.The CuAu-Mo-Ag mineralization mainly occurred at stagesⅠandⅡ,with the ore-forming materials having a mixed crust-mantle source.The Duobaoshan porphyry Cu deposit was formed in the initial subduction environment of the Paleo-Asian Ocean Plate during the Early Ordovician.Then,due to the closure of the Mongol-Okhotsk Ocean and the subduction and compression of the Paleo-Pacific Ocean,a composite orogenic metallogenic model of the deposit was formed.In other words,it is a porphyry-epithermal copper-gold polymetallic mineralization system of composite orogeny consisting of Paleozoic island arcs and Mesozoic orogeny and extension.

Geology, geochronology, and exploration of the Jiama giant porphyry copper deposit (11 Mt), Tibet, China: A review

Jiama,with more than 11 Mt of copper metal,is the largest porphyry-skarn copper system in the Gangdese metallogenic belt,Tibet,China,creating ideal conditions for deciphering the origin of porphyry ores in a collision setting.Despite massive studies of the geology,chronology,petrogenesis,and ore-related fluids and their sources in Jiama,there is a lack of systematic summaries and reviews of this system.In contrast to traditional porphyry copper systems in a subduction setting,recent studies and exploration suggest that the Jiama deposit includes porphyry-type Mo-Cu,skarn-type Cu polymetallic,vein-type Au and manto orebodies.This paper reviews the latest studies on the geology,chronology,petrogenesis,fluid inclusions,and isotopic geochemistry(hydrogen,oxygen,sulfur,and lead)of the Jiama deposit.Accordingly,a multi-center complex mineralization model was constructed,indicating that multi-phase intrusions from the same magma reservoir can form multiple hydrothermal centers.These centers are mutually independent and form various orebodies or are superimposed on each other and form thick,high-grade orebodies.Finally,a new comprehensive exploration model was established for the Jiama porphyry copper system.Both models established in this study help to refine the theories on continental-collision metallogeny and porphyry copper systems.

Application of tensor CSAMT with high-power orthogonal signal sources in Jiama porphyry copper deposit,South Tibet

The Jiama porphyry copper deposit in Tibet is one of the proven supergiant copper deposits in the Qinghai-Tibet Plateau at present,with the reserves of geological resources equivalent to nearly 20×10^(6) t.However,it features wavy and steep terrain,leading to extremely difficult field operation and heavy interference.This study attempts to determine the effects of the tensor controlled-source audiomagnetotellurics(CSAMT)with high-power orthogonal signal sources(also referred to as the high-power tensor CSAMT)when it is applied to the deep geophysical exploration in plateaus with complex terrain and mining areas with strong interference.The test results show that the high current provided by the highpower tensor CSAMT not only greatly improved the signal-to-noise ratio but also guaranteed that effective signals were received in the case of a long transmitter-receiver distance.Meanwhile,the tensor data better described the anisotropy of deep geologic bodies.In addition,the tests also show that when the transmitting current reaches 60 A,it is still guaranteed that strong enough signals can be received in the case of the transmitter-receiver distance of about 25 km,sounding curves show no near field effect,and effective exploration depth can reach 3 km.The 2D inversion results are roughly consistent with drilling results,indicating that the high-power tensor CSAMT can be used to achieve nearly actual characteristics of underground electrical structures.Therefore,this method has great potential for application in deep geophysical exploration in plateaus and mining areas with complex terrain and strong interference,respectively.This study not only serves as important guidance on the prospecting in the Qinghai-Tibet Plateau but also can be used as positive references for deep mineral exploration in other areas.

巴基斯坦新特提斯构造–岩浆演化与重要金属成矿作用

巴基斯坦在大地构造位置上处于印度、欧亚和阿拉伯三大板块的汇聚带,正同时发生着大陆碰撞和大洋俯冲作用,是研究地球系统深部圈层相互作用与成矿效应的绝佳天然实验室。但是,目前对于巴基斯坦构造演化与成矿作用的研究还不系统,对于巴基斯坦的大型–超大型矿床形成的背景和机制仍不清楚。笔者针对巴基斯坦不同类型的优势矿种开展了深入解剖和对比研究,系统梳理最新研究进展,围绕巴基斯坦新特提斯构造–岩浆演化与成矿作用响应的关键科学问题,分析铜矿、铬铁矿、铅锌矿以及碳酸岩有关的稀土矿床等重要金属成矿类型形成的构造环境以及与区域重大地质事件的耦合关系,总结巴基斯坦区域成矿规律,为资源潜力分析和境内外找矿勘查提供依据。

赣南铁山垅钨矿田花岗斑岩地球化学特征、锆石U-Pb年龄及Hf同位素特征

赣南铁山垅钨矿田位于南岭钨锡多金属成矿带东段,已探获黑钨矿资源量超10万吨。铁山垅复式岩体包括主体似斑状黑云母花岗岩和补体细粒二云母花岗岩两部分,花岗斑岩呈脉状分布。矿田内花岗岩具有相似的地球化学特征,都属过铝质高钾钙碱性花岗岩类,表现出高硅、富铝、富碱、高钾、富成矿元素(W、Sn、Cu、Mo)和亏损Ba、Sr、Ti、P、REE、Eu,稀土配分曲线呈典型的“海鸥式”分布和M型四分组效应等特征。利用LA-ICP-MS锆石U-Pb定年方法获得花岗斑岩^(206)Pb/^(238)U年龄为146.7±0.5 Ma(MSDW=0.5),成岩时代属晚侏罗世。锆石的n(^(176)Lu)/n(^(177)Hf)=0.000973~0.001989,f_(Lu/Hf)=-0.97~-0.94,ε_(Hf)(t)=-17.9~-10.3,二阶段模式年龄(TDM2)为1.86~2.33 Ga,显示原岩为古元古代地壳。综合分析认为,铁山垅矿田岩浆活动可划分为170~155 Ma、155~150 Ma、150~145 Ma三个阶段,钨锡矿成矿主要集中在第二阶段,且第三阶段花岗斑岩与铜多金属矿成矿关系密切,推测铜岭矿区深部具有较大的找矿前景。

河北省涿鹿县杏园矿区矿床成因及找矿标志

本研究通过系统的地质、地球化学及地球物理分析,深入探讨了河北省涿鹿县杏园矿区的成矿背景、矿床特征及其找矿指标。利用先进的地质勘查技术,首次明确揭示了矿区内斑岩型与热液脉型矿床的共生关系及其空间分布规律,提出了新的成矿模型和勘查方向。研究结果不仅深化了对杏园矿区成矿规律的理解,而且对指导未来的地质勘查工作,推动矿产资源的合理开发与利用具有重要意义。

安徽庐枞矿集区沙溪斑岩型铜金矿床中硒、碲的赋存状态及富集规律研究

硒和碲是重要的战略性关键金属,在现代工业和国防建设中有着广泛的应用。硒和碲通常很难形成独立矿床,目前全球大部分硒和碲来自斑岩型铜金矿床。长江中下游成矿带是我国东部重要的斑岩-矽卡岩型铜金矿床成矿带之一,前人虽然对成矿带内矽卡岩型矿床中伴生关键金属已开展了相关研究,但对成矿带内斑岩矿床中关键金属的赋存状态、分布和富集规律尚关注较少。本次工作以成矿带内沙溪斑岩型铜金矿床为研究对象,系统采集了矿床不同深度、不同类型的岩矿石样品,通过扫描电子显微镜、全岩化学分析、TIMA及矿物原位LA-ICP-MS微量成分测试等分析技术方法对矿床中硒和碲等关键金属开展了系统的研究。结果表明,沙溪矿床中硒和碲元素发生显著富集,与主成矿元素铜具有明显的正相关关系。估算矿床中伴生硒资源量约为1196t、碲资源量约为96.6t,其中硒达到大型规模,具有潜在利用价值。与成矿带内其他典型矽卡岩矿床(包括斑岩-矽卡岩矿床)相比,沙溪斑岩型矿床中硒和碲的含量明显偏低,这可能是深部成矿岩浆演化过程的差异导致的。矿床中有91.64%的硒、87.48%的碲是以独立矿物形式存在。沙溪矿床硒、碲与主成矿元素铜和金的富集规律一致,流体混合过程中氧逸度的变化可能是硒和碲的主要的沉淀机制。

遥感技术在阿根廷西北部米纳皮基塔斯地区斑岩型铜金矿找矿调查中的应用

阿根廷西北部的铜金多金属成矿带是南美安第斯成矿带的主要组成部分。该成矿带主要发育斑岩型铜金矿,是阿根廷最主要的铜金多金属矿产资源分布区,但该区交通差、地形地质构造复杂、岩性多样,极大地影响了地质找矿的进展。以阿根廷西北部胡胡伊省的米纳皮基塔斯地区为研究区,以ETM+卫星影像为数据源,进行环形构造、菱形构造、深大断裂和破碎带的遥感解译;基于Aster遥感影像数据开展了成像光谱法和主成分分析法矿化蚀变异常信息提取分析。结果显示,铝羟基类蚀变矿物组合和铁染蚀变矿物异常区与主要控矿构造较一致,通过分析认为该区域成矿条件优越。在此基础上,结合斑岩型矿床成矿地质条件等资料,建立该地区遥感地质找矿模型,划分出了重要找矿远景区。该方法具有良好的找矿效果,对阿根廷西北部地区的找矿调查工作具有重要指导作用。

藏西北多龙矿集区拿若斑岩铜(金)矿床磷灰石矿物学特征及地质意义

拿若矿床目前是藏西北改则县多龙矿集区第三大斑岩型铜(金)矿床,前人开展了系统的成岩成矿年代学、成矿地质背景等研究,但空间蚀变分带和岩浆演化过程等方面研究较为薄弱。笔者等以拿若矿床磷灰石作为研究对象,在大量钻孔科研编录的基础上,开展了磷灰石矿物学和矿物化学研究,探讨拿若矿床磷灰石矿物彩色阴极发光特征与蚀变分带的耦合关系,揭示含矿岩浆演化期次及氧化还原状态。磷灰石彩色阴极发光特征显示,拿若矿床磷灰石彩色阴极发光(CL)特征主要表现为黄褐色、绿色—亮黄色和灰黑色,分别对应未蚀变、钾化蚀变和绢英岩化蚀变环境,磷灰石彩色CL特征与其所处蚀变环境的关系验证了笔者等重新厘定的拿若矿床斑岩系统“双钾化带”空间蚀变分带结构。磷灰石电子探针(EPMA)主量元素测试结果显示,磷灰石的CaO=53.5%~56.5%,P_(2)O_(5)=39.5%~42%,F=1.26%~3.24%,Cl=0.01%~1.99%,SO_(3)=0~1.28%,由此计算的X_(F)=0.68~1.76,XCl=0.001~0.58,X_(OH)=0.21~1.05。不同类型、阶段的磷灰石挥发分(F、Cl、OH)、SO_(3)等成分含量变化趋势反映了拿若矿床岩浆—热液演化过程发生了气体饱和→流体出溶→金属沉淀的过程,并揭示了成矿岩浆高氧逸度的性质。此外,环带状岩浆磷灰石反映了隐爆角砾岩系统发育了三期次岩浆作用,并指示了第I、III期岩浆活动具有更高氧逸度特征,与成矿关系更加密切。因此,笔者等认为在多期次岩浆热液叠加型斑岩铜矿床中,磷灰石在辅助厘定蚀变类型和反演岩浆—热液演化过程中具有重要的价值。

江西会昌锡坑迳斑岩型锡矿床成矿系统发育特征与找矿模型

锡坑迳矿田位于南岭成矿带东段与武夷山成矿带交会部位,以早白垩世连续的岩浆喷发-侵入活动与多类型锡多金属成矿作用为特色。矿田内围绕似斑状花岗岩和花岗斑岩发育了岩背斑岩型、淘锡坝和矿背隐爆层间裂隙带型、苦竹岽和凤凰岽云英岩-破碎带蚀变岩型等大中型锡矿床。这些矿床的矿化-蚀变特征可与玻利维亚锡矿带、银岩、维拉斯托和洋滨等国内外斑岩型锡矿床类比,又独具特色,是研究斑岩型锡成矿系统发育特征与找矿模型的理想区域。文章在详细的野外地质调查基础上,系统总结了锡坑迳矿田内各类锡多金属矿化组合特征和蚀变结构,并对岩背矿床和淘锡坝矿床锡石开展了电子探针和LA-ICP-MS原位微区分析。研究结果显示,所有锡石样品均具有La、Pr、Gd和Tb的正异常、Ce与Eu的负异常、明显的Zr/Hf分馏和不规则的稀土元素配分模式,指示成矿热液早期阶段及锡石沉淀阶段经历了流体不相容。岩背锡石较淘锡坝锡石具有高的Ti/Zr和Ti/Sc比值,指示其更为靠近矿化中心。笔者研究认为,锡坑迳斑岩型锡成矿系统矿化类型包括细脉状、浸染状和细网脉状,围岩蚀变由早到晚、由成矿中心向外依次发育黄玉石英带、绿泥石-黄玉石英岩化带、绿泥石-绢云母化带和黏土化-碳酸盐化带。与斑岩型铜钼成矿系统相比,其成矿岩浆岩不仅有花岗斑岩,还有似斑状黑云母花岗岩,矿体在斑岩、花岗岩及上覆火山岩中均有赋存。相较于玻利维亚斑岩型锡成矿带发育的大面积石英-电气石化,锡坑迳斑岩成矿系统更富F,蚀变矿物中出现了大量黄玉、萤石和白云母等。对比国内外典型锡矿床的矿化-蚀变结构和锡石矿物学特征,文章建立了锡坑迳式斑岩型锡成矿系统的找矿模型。

玉龙铜(钼)矿带多霞松多岩体成因:锆石U-Pb年代学和岩石地球化学约束

玉龙铜(钼)矿带的成因机制和动力学背景一直存在争议。本文选择目前研究程度较低的多霞松多岩体,对该岩体含矿斑岩开展岩相学、年代学、岩石地球化学及锆石Hf同位素分析。研究表明,多霞松多岩体主要由二长花岗斑岩和碱长花岗斑岩组成,其中,二长花岗斑岩的主要造岩矿物为钾长石、斜长石和石英,碱长花岗斑岩的主要造岩矿物为钾长石和石英。两种岩石属于高钾钙碱性—钾玄质侵入岩,具有富碱高钾的特征;亏损Nb、Ti等高场强元素,富集Rb、Th、U等大离子亲石元素和Pb;稀土元素含量较高(ΣREE=145.04×10^(-6)~290.91×10^(-6)),富集轻稀土(LREE/HREE=6~37)。铕表现为从二长花岗斑岩的弱负异常(Eu/Eu^(*)=0.66~0.84)到碱长花岗斑岩的中等负异常(Eu/Eu^(*)=0.35~0.39)。锆石U-Pb定年显示,二长花岗斑岩的成岩年龄为38.3±0.6 Ma,碱长花岗斑岩的成岩年龄为37.8±1.0 Ma,两者形成时代基本一致,均属于喜马拉雅期,表明在多霞松多地区始新世存在一期重要的岩浆热液Cu-Mo成矿事件。多霞松多含矿斑岩的锆石ε_(Hf)(t)范围在+1.3~+2.6之间。结合元素和同位素地球化学特征,指示多霞松多含矿斑岩可能来源于亏损地幔分异的新生玄武质下地壳,受控于印度板块与欧亚板块碰撞诱发的金沙江走滑断裂系统。

埃达克岩与热液成矿过程中钾镁同位素分馏及其指示意义:以驱龙斑岩铜矿床为例

为研究后碰撞埃达克质岩岩浆分异和热液过程中的钾镁同位素分馏行为及其对斑岩铜矿床岩石成因的指示意义,本文对藏南驱龙斑岩铜矿床的一套埃达克质岩石开展了钾镁同位素分析。该套岩石包括闪长质包体、花岗闪长岩和花岗斑岩,后者是超大型斑岩铜矿床的成矿母岩。已有研究结果证实,这3套岩石很可能是由同一来源的不同程度的部分熔融和分离结晶作用形成的。研究结果表明,闪长质包体、花岗闪长岩和花岗斑岩的δ^(41)K组成分别为-0.38‰~-0.22‰、-0.43‰~-0.34‰和-0.59‰~-0.36‰。尽管3类岩石各自变化范围较小,但整体上δ^(41)K与K 2O和SiO_(2)含量呈现明显负相关趋势,表明全岩钾元素迁移和钾同位素发生了解耦,钾同位素产生了分馏。在闪长质包体花岗闪长岩演化期间,δ^(41)K与Sc和Y含量呈明显正相关关系,这指示了在该演化期间可能主要是角闪石分离结晶导致了钾同位素分馏。相比之下,花岗斑岩中具有明显的钾同位素组成变化,在花岗斑岩演化期间,δ^(41)K与Eu/Eu*和Sr含量呈正相关关系,表明在岩石演化晚期钾同位素的分馏可能主要跟斜长石分离结晶有关。然而,通过瑞利分馏模拟表明仅矿物分离结晶难以实现如此大的钾同位素分馏,花岗斑岩中的钾同位素分馏是岩浆热液共同作用的结果。值得注意的是,闪长质包体具有比地幔更重的钾同位素组成,导致这种现象的原因可能是复杂多样的:一方面,下地壳可能具有比地幔更重的钾同位素组成,岩浆混合机制下导致源区具有重钾同位素组成;另一方面,驱龙斑岩铜矿床的岩浆源区受到俯冲板片来源的富重钾流体/熔体所交代,导致其源区的钾同位素组成偏重。相比之下,这3类岩石的镁同位素组成比较类似(闪长质包体:-0.36‰~-0.19‰;花岗闪长岩:-0.28‰~-0.13‰;花岗斑岩:-0.44‰~-0.13‰),并且落在了地幔和下地壳范围内。这3类岩石的δ^(26)Mg跟MgO和SiO_(2)含量之间不存在相关性,表明埃达克质岩浆分异过程中(角闪石和黑云母)也不产生镁同位素分馏,与前人对花岗岩中镁同位素分馏行为的结论相一致。作为典型的热液型矿床,藏南驱龙斑岩铜矿床和江西德兴斑岩铜矿床在热液蚀变过程中均产生了钾镁同位素分馏。德兴斑岩铜矿床大部分蚀变岩的钾镁同位素值都高于新鲜岩浆岩,具有显著的钾镁同位素组成变化;相比之下,驱龙斑岩铜矿床埃达克质岩岩石的钾镁同位素组成大部分位于岩浆岩基线值范围内,受热液蚀变作用影响不显著。此外,驱龙斑岩铜矿床花岗斑岩中铜大量富集,岩浆热液流体出溶是导致铜大量富集的主要原因,可能至少有两种不同性质(温度、盐度)的热液流体导致花岗斑岩中钾镁同位素组成局部波动变化,这些流体不仅改变了花岗岩斑岩的钾镁同位素组成,并且从高度演化的岩浆中提取金属元素,最终导致铜成矿。

太岳山17.9亿年英安斑岩的发现及其对华北克拉通南部裂谷系成因的约束

熊耳群火山岩系主要分布于华北克拉通南部地区,主体喷发时限是1.75~1.80Ga。作为华北克拉通早期板块构造调整阶段的首次大规模岩浆活动,该火山-侵入岩系的形成时限、时空分布规律和地球动力学背景尚有争议,制约了对华北克拉通中元古代构造演化的进一步认识。本次研究在华北中部太岳山地区识别出中元古代英安斑岩,与古元古代花岗质片麻岩围岩呈侵入关系,无明显变质变形。锆石U-Pb年龄分析结果表明,该英安斑岩形成于1.79Ga,属于熊耳期岩浆活动的产物。样品中约90%的锆石显示出~1.92Ga和~2.16Ga两期年龄峰值,推测其为围岩的捕获锆石。英安斑岩SiO_(2)含量为65.12%~66.11%,A/CNK=0.91~1.05,全碱(K_(2)O+Na_(2)O)含量为6.85%~7.28%,Na_(2)O/K_(2)O=0.48~0.54,属于钾玄岩系列。样品稀土元素含量较高,亏损Nb、Ta、Zr、Hf等高场强元素,富集Rb、Ba、La等大离子亲石元素,与华北克拉通南部地区熊耳期英安-流纹斑岩的地球化学特征完全一致,指示板内伸展环境。太岳山熊耳期英安斑岩的发现,贯通了中条山地区的熊耳群火山岩系、吕梁地区汉高山群和小两岭火山岩系,完善了熊耳三叉裂谷系北支的空间分布范围,是华北克拉通中部地区开启中元古代裂陷作用演化的重要岩浆记录。