Geochemical evolution of halogen-enriched granite magmas and mineralizing fluids of the Zinnwald tin-tungsten mining district,Erzgebirge, Germany

We remelted and analyzed crystallized silicate melt inclusions in quartz from a porphyritic albite-zinnwaldite microgranite dike to determine the composition of highly evolved, shallowly intruded, Li- and F-rich granitic magma and to investigate the role of crystal fractionation and aqueous fluid exsolution in causing the extreme extent of magma differentiation. This dike is intimately associated with tin- and tungsten-mineralized granites of Zinnwald, Erzgebirge, Germany. Prior research on Zinnwald granite geochemistry was limited by the effects of strong and pervasive greisenization and alkali-feldspar metasomatism of the rocks. These melt inclusions, however, provide important new constraints on magmatic and mineralizing processes in Zinnwald magmas.The mildly peraluminous granitic melt inclusions are strongly depleted in CAFEMIC constituents (e.g., CaO, FeO, MgO, TiO₂), highly enriched in lithophile trace elements, and highly but variably enriched in F and Cl. The melt inclusions contain up to several thousand ppm Cl and nearly 3 wt% F, on average; several inclusions contain more than 5 wt% F. The melt inclusions are geochemically similar to the corresponding whole-rock sample, except that the former contain much more F and less CaO, FeO, Zr, Nb, Sr, and Ba. The Sr and Ba abundances are very low implying the melt inclusions represent magma that was more evolved than that represented by the bulk rock. Relationships involving melt constituents reflect increasing lithophile-element and halogen abundances in residual melt with progressive magma differentiation. Modeling demonstrates that differentiation was dominated by crystal fractionation involving quartz and feldspar and significant quantities of topaz and F-rich zinnwaldite. The computed abundances of the latter phases greatly exceed their abundances in the rocks, suggesting that the residual melt was separated physically from phenocrysts during magma movement and evolution.Interactions of aqueous fluids with silicate melt were also critical to magma evolution. To better understand the role of halogen-charged, aqueous fluids in magmatic differentiation and in subsequent mineralization and metasomatism of the Zinnwald granites, Cl-partitioning experiments were conducted with a F-enriched silicate melt and aqueous fluids at 2,000 bar (200 MPa). The results of the experimentally determined partition coefficients for Cl and F, the compositions of fluid inclusions in quartz and other phenocrysts, and associated geochemical modeling point to an important role of magmatic-hydrothermal fluids in influencing magma geochemistry and evolution. The exsolution of halogen-charged fluids from the Li- and F-enriched Zinnwald granitic magma modified the Cl, alkali, and F contents of the residual melt, and may have also sequestered Li, Sn, and W from the melt. Many of these fluids contained strongly elevated F concentrations that were equivalent to or greater than their Cl abundances. The exsolution of F-, Cl-, Li-, ± W- and Sn-bearing hydrothermal fluids from Zinnwald granite magmas was important in effecting the greisenizing and alkali-feldspathizing metasomatism of the granites and the concomitant mineralization.Editorial Handling: B. Lehmann     

Garnetization as a ground preparation process for copper mineralization: evidence from the Mazraeh skarn deposit, Iran

The Mazraeh Cu–Fe skarn deposit, NW Iran is the result of the intrusion of an Oligocene–Miocene granitic pluton into Cretaceous calcareous rocks. The pluton ranges in composition from monzonite to quartz monzonite, monzogranite, tonalite and granodiorite with I-type, calc-alkaline, and weakly peraluminous characteristics. The Mazraeh pluton was emplaced in a volcanic arc setting in an active continental margin at a depth of ~8 km. Pyroxene skarn, garnet skarn, and epidote skarn zones were formed during the intrusive phase. The garnet skarn developed as exoskarn and endoskarn from the calcareous wall rocks and the pluton, respectively, prior to mineralization. Garnet skarn from the exoskarn zone is identified by relict layering inherited from the precursor calcareous lithologies. Mass balance calculation of garnet skarn in the endoskarn zone indicates that hydrothermal fluids originating from the cooling magma introduced Si, Fe, Mn, Ca, Mg, P, Ag, Cu, Zn, La, Pb, Cd, Mo, and Y. The main mass loss in the garnet skarn was due to destruction of feldspars in the Mazraeh plutonic rocks and leaching of K₂O and Na₂O. Released Ca has been fixed in the andraditic garnet. Garnetization of the Mazraeh pluton was accompanied by mass and volume increase. The magnitude of these changes depends mainly on the degree of alteration and composition of the precursor. The brittle behavior of the endoskarn zone was increased due to formation of massive garnet which subsequently fractured. These fractures not only facilitated movement of hydrothermal fluids but also provided new locations for Cu mineralization. Therefore locating strongly garnetized zones may be a vector to ore in skarn deposits.     

磁铁矿显微结构及化学成分对铜绿山矽卡岩型铜铁矿床成矿过程的指示

铜绿山矽卡岩型铜铁多金属矿床是长江中下游鄂东南矿集区的一个典型矿床,矿体产于铜绿山岩体与三叠系碳酸盐岩地层的接触带.磁铁矿是铜绿山铜铁矿床中广泛发育的矿石矿物,选取内矽卡岩和外矽卡岩中的热液磁铁矿以及岩体中副矿物磁铁矿为研究对象,对其开展系统的显微结构观察和电子探针分析.热液磁铁矿中普遍发育有钛尖晶石出溶结构和富硅环带结构,且没有明显的后期热液交代改造现象.钛尖晶石出溶结构指示铜绿山矿床的早期热液磁铁矿具有较高的Ti含量,磁铁矿结晶后经历了降温和氧逸度降低过程导致钛尖晶石出溶.热液磁铁矿中还普遍含有较高含量的Si、Al、Cr、V、Mn、Mg、Co和Ni等元素,Si4+、Al3+、Mg2+、Mn2+等以类质同象方式进入磁铁矿晶格;但在不同产状的磁铁矿中,替代强度和机制略有不同,说明流体成分、温度、压力等物理化学条件影响元素替代强度和方式.外矽卡岩中磁铁矿的Al₂O₃/MgO比值小于4,内矽卡岩中磁铁矿的Al₂O₃/MgO比值为5~8,而副矿物磁铁矿的Al₂O₃/MgO比值约为13.岩体副矿物磁铁矿具有最高的V₂O₃含量（平均值为0.31%）,与岩体接触的内矽卡岩中的磁铁矿次之（平均值为0.14%）,外矽卡岩中磁铁矿的V₂O₃含量最低（平均值为0.01%~0.03%）.Al₂O₃/MgO比值和V₂O₃含量说明磁铁矿生长环境（熔体/热液）、围岩的成分及水-岩反应等对磁铁矿的化学组成均有影响.铜绿山矿床从岩体到内矽卡岩、再到外矽卡岩,磁铁矿的形成温度逐步下降,其成分的变化指示了磁铁矿可以作为矽卡岩矿床成矿过程的重要指示矿物.      

Rare Earth Elements as an Indicator to Origins of Skarn Deposits: Examples of the Kamioka Zn-Pb and Yoshiwara-Sannotake Cu(–Fe) Deposits in Japan

Abstract: Systematic data of rare earth elements (REEs) are presented in order to put some constraints on the origin of hydrothermal fluids responsible for two contrastive skarn deposits in Japan; the Kamioka Zn-Pb and Yoshiwara-Sannotake Cu(-Fe) deposits. Carbon and oxygen isotopic studies have demonstrated that the hydrothermal fluids responsible for the Kamioka Zn-Pb deposits are of meteoric water origin whereas those for the Yoshiwara-Sannotake Cu(-Fe) deposits are of magmatic water origin. The REE abundances of epidote skarn derived from aluminous rocks, garnet and clinopyroxene in calcic exoskarn derived from limestone, and interstitial calcite associated with sulfide minerals were determined for these contrastive skarn deposits by inductively-coupled plasma mass spectrometry (ICP-MS). A significant difference in the REE concentrations is not found between epidote skarn and aluminous original rock (plagioclase-clinopyroxene rock, called Inishi rock) from the Kamioka Zn-Pb deposits, indicating that the REEs are generally immobile during the formation of epidote skarn, and that the REE concentrations of the hydrothermal fluid are considerably low relative to the aluminous original rock. In contrast, the epidote skarn exhibits enrichment of Eu with increasing total REE concentrations relative to the aluminous original rock (quartz diorite) in the Yoshiwara-Sannotake Cu(-Fe) deposits, implying a contribution of magmatic fluid derived from granitoids during the skarn formation. Limestone generally has much lower REE concentrations related to surrounding aluminous rocks, and thus the REE concentrations of garnet and clinopyroxene in calcic exoskarn, originated from limestone, are variable due to the interaction with the hydrothermal fluids. The chondrite-normalized REE patterns of garnet, clinopyroxene, and interstitial calcite exactly provide useful information on origins of hydrothermal fluids. The REE patterns of these minerals from the Kamioka Zn-Pb deposits show lower (Pr/Yb)cn ratios, and negative Ce and Eu anomalies inherited from limestone with the decrease of This suggests that the hydrothermal fluids responsible for the Kamioka Zn-Pb deposits were depleted in REEs, and were not magmatic water in origin, but presumably meteoric one. In striking contrast, the REE patterns of exoskarn minerals and calcite from the Yoshiwara-Sannotake Cu(-Fe) deposits exhibit a positive Eu anomaly, and high (Pr/Yb)cn ratios with the considerable increase of σREE and the disappearance of negative Ce anomaly, implying that the fluids were dominantly of magmatic origin. The REE indices are very likely to be an excellent indicator to origins of the skarn deposits.     

滇西北红山铜矿床成矿流体地球化学特征及矿床成因

红山铜矿床为滇西北地区一大型斑岩-矽卡岩型铜多金属矿床,它产于印支期石英闪长玢岩及燕山期石英二长斑岩体内及其周边地层中,其形成经历了多期次热液叠加成矿作用过程.流体包裹体岩相学、显微测温及碳、氢、氧稳定同位素综合研究表明,矿区早期成矿流体为中高温、高盐度NaCl-H2O体系热液,主要来源于印支晚期岛弧型岩浆活动,对区内矽卡岩型矿化形成起了重要作用;晚期成矿流体为中高温、高盐度NaCl-CO2-H2O体系热液,主要来源于隐伏的燕山期后造山伸展型花岗质岩浆侵入体,形成了区内斑岩型Cu、Mo及相关的Pb、Zn多金属矿化.因此,红山铜矿床是两期岩浆热液叠加成矿作用结果.     

Origin and evolution of skarn fluids,Empire zinc skarns,Central Mining District,New Mexico,U.S.A.

Garnet-pyroxene-sphalerite skarns in the Empire Mine replace Paleozoic carbonates adjacent to the Tertiary Hanover-Fierro granodiorite. Skarn geometry suggests that fluids migrated up pre-ore dikes, faults and the igneous contact, and were deflected laterally into the permeable Tierra Blanca Limestone beneath the relatively impermeable Parting Shale.Silicates associated with propylitically altered pre-ore dikes are enriched in deuterium (D), and depleted in¹⁸O relative to the Hanover-Fierro pluton and post-ore igneous rocks. Early skarn silicates are also depleted in¹⁸O with respect to the pluton, while later skarn minerals are depleted in both D and¹⁸O. Variations in isotope composition of alteration and skarn minerals indicate isotope heterogeneities in mineralizing fluids, even at the small scale of centimeters. Isotope thermometry indicates that there is some degree of subsolidus re-equilibration of igneous and alteration minerals.Several possible fluid flow regimes may have operated to produce the fluids calculated to be in exchange equilibrium with the various rocks and minerals of the Empire skarn system, and mixing of end-member meteoric, formation and magmatic fluids in different proportions can produce observed δDδ¹⁸O trends. An end-member magmatic fluid could produce the D-enrichment observed for early skarn fluids, but this would require isolating magmatic fluids from external fluid sources during cooling of the system from magmatic temperatures of 700°C to skarn temperatures of the order of ≤ 400°C. The D-enrichment may also be explained by the mixing of magmatic and formation waters. Lower δD values, however, require that a large proportion of late-stage skarn fluids must be a D-depleted Tertiary meteoric water, and magmatic water is restricted to a relatively minor component.The end-member mixing approach indicates significant changes in fluid flow systematics over a relatively narrow range in temperature. Alternatively, observed trends in both δD and δ¹⁸O for skarn fluids can also be reproduced by interacting a D-depleted meteoric water with the Hanover-Fierro pluton at low and variable system water-rock ratios, and temperatures between 250 and 400°C. During migration along the long fluid flow paths implied by the low system water-rock ratios (≤0.1), the salinity of dilute meteoric waters could increase through interaction with minerals or leaking fluid inclusions in the country rock. Correlation of isotope depletions of the carbonate wallrocks with inferred fluid flow conduits, suggests significant amounts of fluid-rock exchange at relatively high local water-rock ratios during focusing of flow by critical structures. Although different C sources might require smaller values, it is clear that large (>1) local water-rock ratios are required to produce depletions observed in both¹⁸O and¹³C in hydrothermal calcites. Stable isotope evidence does not require the presence of a significant magmatic fluid component, and suggests that the bulk of the skarn fluids could instead be derived predominantly from a D-depleted meteoric water.     

A combined EMPA and LA-ICP-MS study of Li-bearing mica and Sn–Ti oxide minerals from the Qiguling topaz rhyolite (Qitianling District,China): The role of fluorine in origin of tin mineralization

The Sn-rich Qiguling topaz rhyolite dike intrudes the Qitianling biotite granite of the Nanling Range in southern China; the granite hosts the large Furong Sn deposit. The rhyolite dike is typically peraluminous, volatile-enriched, and highly evolved. Whole-rock F and Sn concentrations attain 1.9 wt.% and 2700 ppm, respectively. The rhyolite consists of a fine-grained matrix formed by quartz, feldspar, mica and topaz, enclosing phenocrysts of quartz, feldspar and mica; it is locally crosscut by quartz veinlets. Lithium-bearing micas in both phenocrysts and the groundmass can be classified as primary zinnwaldite, “Mus-Ann” (intermediate member between annite and muscovite), and secondary Fe-rich muscovite. Topaz is present in the groundmass only; common fluorite occurs in the groundmass and also in a specific cassiterite, rutile and fluorite (Sn–Ti–F) assemblage. Cassiterite and rutile are the only Sn and Ti minerals; both cassiterite and Nb-rich rutile are commonly included in the phenocrysts. The Sn–Ti–F assemblage is pervasive, and contains spongy cassiterite in some cases; cassiterite also occurs in quartz veinlets which cut the groundmass. Electron microprobe and LA-ICP-MS compositions were used to study the magmatic and hydrothermal processes and the role of F in Sn mineralization. The presence of zinnwaldite and “Mus-Ann”, which are respectively representative of early and late mica crystallization during magma differentiation, also suggests a significant decrease in f(HF)/f(H₂O) of the system. Cassiterite included in the zinnwaldite phenocrysts is suggested to have crystallized from the primary magma at high temperature. Within the Sn–Ti–F aggregates, rutile crystallized as the earliest mineral, followed by fluorite and cassiterite. Spongy cassiterite containing inclusions of the groundmass minerals indicate a low viscosity of the late fluid. The cassiterite in the quartz veinlets crystallized from low-temperature hydrothermal fluids, which possibly mixed with meteoric water. In general, cassiterite precipitated during both magmatic and hydrothermal stages, and over a range of temperatures. The original fluorine and tin enrichments, f(HF)/f(H₂O) change in the residual magma, formation of Ca,Sn,F-rich immiscible fluid, decrease of the f(HF) during groundmass crystallization, and mixing of magma-derived fluids with low-saline meteoric water during the late hydrothermal stage, are all factors independently or together responsible for the Sn mineralization in the Qiguling rhyolite.     

Characteristics of Pegmatite-Related Fluids and Significance to Ore-Forming Processes in the Zhaxikang Pb-Zn-Sb Polymetallic Deposit, Tibet, China

The Zhaxikang Pb-Zn-Sb polymetallic deposit is one of the most important deposits in the newly recognized southern Tibet antimony-gold metallogenic belt.Compared to the porphyry deposits in the Gangdese belt,much less researches have addressed these deposits,and the genesis of the Zhaxikang deposit is still controversial.Based on field investigation,petrographic,microthermometric,Laser Raman Microprobe（LRM） and SEM/EDS analyses of fluid,melt-fluid,melt and solid inclusions in quartz and beryl from pegmatite,this paper documents the characteristics and the evolution of primary magmatic fluid which was genetically related to greisenization,pegmatitization,and silification in the area.The results show that the primary magmatic fluids were derived from unmixing between melt and fluid and underwent a phase separation process soon after the exsolution.The primary magmatic fluids are of low salinity,high temperature,and can be approximated by the H₂O-NaCl-CO₂ system.The presence of Mn-Fe carbonate in melt-fluid inclusions and a Zn-bearing mineral（gahnite） trapped in beryl and in inclusions from pegmatite indicates high Mn,Fe,and Zn concentrations in the parent magma and magmatic fluids,and implies a genetic link between pegmatite and Pb-Zn-Sb mineralization.High B and F concentrations in the parent magma largely lower the solidus of the magma and lead to late fluid exsolution,thus the primary magmatic fluids related to pegmatite have much lower temperature than those in most porphyry systems.Boiling of the primary magmatic fluids leads to high-salinity and high-temperature fluids which have high capacity to transport Pb,Zn and Sb.The decrease in temperature and mixing with fluids from other sources may have caused the precipitation of Pb-Zn-Sn（Au） minerals in the distal fault systems surrounding the causative intrusion.     

安徽铜陵凤凰山燕山期中酸性侵入岩地球化学特征及其与金属成矿关系

安徽铜陵凤凰山铜矿是铜陵矿集区内最典型的矽卡岩型铜矿床之一,也是凤凰山矿田内规模最大的铜矿床。矿区内新屋里岩体属于高钾钙碱性系列,主要岩性为石英二长闪长岩和花岗闪长岩。岩石地球化学特征表明凤凰山中酸性侵入岩岩浆属于壳幔混合型,原始岩浆来源于上地幔碱性玄武岩区并有地壳物质混染,在岩浆不断演化过程中有外来物质的加入,成岩过程以混合作用为主。凤凰山铜矿体分布于岩体与大理岩的内矽卡岩带上,岩体中铜含量较高。铜矿体是岩浆期后热液交代碳酸盐地层形成的。矿体的空间分布受构造变形-岩浆侵入高温高压作用的双重控制。矿化经历了从高温矽卡岩阶段到中低温热液阶段的多期次复合成矿作用。     

青海祁漫塔格地区矽卡岩型矿床花岗质岩石矿物学及地质意义

青海祁漫塔格地区位于东昆仑造山带西段,是我国近些年来的重点找矿地区之一。本文对区内与虎头崖矿床I矿带(Fe)、野马泉矿床(Fe)、虎头崖矿床VI矿带(Zn)和卡而却卡矿床B区(Cu)有关的花岗质岩石开展了矿物学研究。结果显示,虎头崖矿床I矿带的斜长石以奥长石为主(An15.0-24.1);虎头崖矿床VI矿带的斜长石主要为钠长石和奥长石(An8.7-20.8);卡而却卡矿床B区的斜长石主要是中长石(An33.8-42.2);野马泉矿床的斜长石主要为奥长石和中长石(An26.2-48.4)。角闪石为典型的钙角闪石,其中,虎头崖矿床I矿带的角闪石属铁浅闪石;卡而却卡矿床B区的角闪石为镁角闪石和铁角闪石。各矿床(带)的黑云母普遍富Fe、Ti、F、Cl,属典型的铁黑云母。矿物学特征显示,各矿床(带)的黑云母结晶于相似的高氧逸度条件下,但在结晶温度和挥发份组成等方面存在差异。黑云母的结晶温度和氧逸度特征与各矿床类型之间未表现出明显的规律性特征。结合前人的研究成果可知,岩浆结晶的温度和氧逸度可能不是控制本区矽卡岩矿床成矿作用类型的主要因素。黑云母的挥发份组成与各成矿元素间表现出明显的规律性特征,其中,以Fe为主的虎头崖矿床I矿带和野马泉矿床的岩浆流体特征基本一致,表现出相对富Cl、贫H2O、F的特点;以Zn为主的虎头崖矿床VI矿带的岩浆流体相对富F贫H2O、Cl;以Cu为主的卡而却卡矿床B区的岩浆流体相对富Cl、H2O贫F,说明岩浆流体不同的挥发份组成可能与不同的矿床类型之间存在密切的联系。综合地质特征和矿物学特征可知,岩浆流体的挥发份组成可能是控制青海祁漫塔格地区矽卡岩矿床成矿作用类型多样性的重要因素之一。     

Fluid Inclusions and C,H, O,S, and Pb Isotopic Compositions of the Dabaoshan Cu Polymetallic Deposit,Northern Guangdong Province,South China

The Dabaoshan deposit in Northern Guangdong Province, South China, is a Cu–Mo–W–Pb–Zn polymetallic deposit, located in the southern part of the Qin–Hang porphyry–skarn Cu–Mo ore belt. The deposit mainly comprises porphyry Mo and stratiform skarn Cu ore deposits. The genesis of the Cu ore deposit has been ascribed to a typical skarn ore deposit formed by the metasomatism of Devonian carbonate rock layers or to a volcanic rock‐hosted massive sulfide deposit formed by marine exhalation. In this paper, we report on the homogenization temperatures and salinities of fluid inclusions and C, H, O, S, and Pb isotopic compositions of fluids and minerals in this deposit. Homogenization temperatures and salinities of fluid inclusions in garnet, diopside, quartz, and calcite provide information on the skarnification, mineralization, and postmineralization stages. The data show that ore‐forming fluids experienced a continuous transition from high temperatures and salinities to low temperatures and salinities over the entire period of mineralization. C, H, and O isotopic compositions indicate that ore‐forming fluids were derived mainly from magmatic water. O isotopic compositions indicate that ore‐forming fluids mingled with atmospheric water during the last stage of mineralization. Sulfur in the ore came mainly from deep magmatic sources. Pb isotopic compositions in the orebody show that almost all the lead in the ore was derived from magma with a crustal source. Combined geological, geophysical, and geochemical data were achieved before we proposed that the Dabaoshan porphyry–skarn Cu–Mo–W–Pb–Zn deposit, as one member of the Qin–Hang porphyry–skarn Cu–Mo ore belt, formed during the Jurassic subduction of the paleo‐Pacific plate beneath the Eurasian continent at quite low angle. NE‐ and EW‐trending structures controlled the emplacement of magmatic rocks in the South China region. In the mining area, the Xiangguanping Fault and its branches were the main conduits for magmatic crystallization and mineralization. The many subfaults, folds, and interlayer fracture zones on both sides of the main fault provided the requisite space for the ore and, together, were the controlling structures of the orebody.     

莱芜张家洼铁矿磁铁矿LA-ICP-MS微量元素特征及其对成矿过程的制约

莱芜张家洼铁矿位于华北克拉通东缘的鲁西地区,矿石成因类型为夕卡岩型铁矿。矿体赋存在早白垩世高镁闪长岩与奥陶系马家沟组灰岩及白云岩接触带附近。本文通过对莱芜岩浆和热液磁铁矿电子探针(EPMA)以及激光剥蚀电感耦合等离子体质谱(LA ICP MS)分析,探讨磁铁矿微量元素组成及变化规律对成岩和成矿作用的指示,为揭示张家洼铁矿的矿床成因及其成矿流体演化过程提供重要制约。分析结果表明,莱芜岩浆磁铁矿与热液磁铁矿相比明显富集Ti、V、Cr等亲铁元素,相对富集Nb、Ta、Zr、Hf等高场强元素以及Sn、Ga、Ge、Sc等中等相容元素,Mg、Al、Mn、Zn、Co显著富集于热液磁铁矿中。Ti、V、Cr以及Mg、Al、Mn、Zn在岩浆和热液中具有不同的地球化学行为,Ti、V、Cr从熔体中进入磁铁矿主要受温度、分配系数以及fO2控制。Mg、Al、Mn、Zn主要受控于水岩反应和后期绿泥石+碳酸盐脉的交代,这些元素通过类质同象替换富集于热液磁铁矿中。Co在热液磁铁矿中除了受水岩相互作用和后期流体交代的影响外,硫化物的出现会导致Co含量急剧降低。Si、Ca、Na及Sr、Ba在岩浆和热液磁铁矿中的地球化学行为非常一致。Ti Ni/Cr图能够用于区分岩浆和热液磁铁矿,莱芜岩浆磁铁矿中Ti含量较高且Ni/Cr比值≤1,热液磁铁矿Ti含量较低且绝大多数Ni/Cr比值≥1。张家洼热液磁铁矿可分为早、晚两个阶段：早期阶段包括(1)早期原生粒状磁铁矿和(2)早期次生磁铁矿;晚期阶段包括(3)晚期原生磁铁矿和(4)晚期次生磁铁矿。原生磁铁矿具有典型的三联点结构特征;次生磁铁矿受后期热液交代影响表现为多空隙,通常呈不规则状、树枝状、骸晶以及交代残余结构。磁铁矿微量元素生动记录了成矿流体演化过程,从早期到晚期、从原生到次生都显示Mg、Al、Mn、Zn包括Co含量持续升高,表明成矿流体可能朝着富集这些微量元素的方向演化。后期流体的交代导致绿泥石蚀变为磁铁矿,连续水岩相互作用和后期流体的交代以及绿泥石直接蚀变是导致热液磁铁矿富集Mg、Al、Mn、Zn等元素的主要原因。热液磁铁矿晚期孔隙较为发育,孔隙度的增加促使更多的流体和磁铁矿发生反应。热液磁铁矿的微量元素不仅能够反映矿床形成的物理化学条件,而且可以反映围岩性质以及水岩相互作用过程。     

Characteristic Features of Tin–iron–copper Mineralization in the Anle-Huanggangliang Mining Area, Inner Mongolia, China

Abstract: The Anle Sn‐Cu and Huanggangliang Fe‐Sn deposits have been exploited in the Linxi district, which is located 165 km northwest of Chifeng City in northern China. In this study the formation mechanisms of the tin deposits in the Anle and Huanggangliang mining area were investigated to understand the mechanisms of tin mineralization in northern China. The veins of the Anle deposit are divided into cassiterite–quartz–chlorite veins, chalcopyrite‐bearing quartz veins, cassi–terite–chalcopyrite–bearing quartz veins and sphalerite‐quartz veins. The sequence of mineralization is tin mineralization (stage I), copper mineralization (stage II), and lead‐zinc mineralization (stage III). The Huanggangliang tin deposit consists of magnetite skarn orebodies and many cassiterite‐bearing feldspar–fluorite veins and veinlets cutting the magnetite orebodies. The fluid inclusions in quartz and fluorite in ores from the Anle and Huanggangliang tin deposits are divided into two‐phase fluid inclusions, vapor‐rich fluid inclusions and poly‐phase fluid inclusions. The final homogenization temperatures of fluid inclusions of quartz in the ores of the Anle deposit and fluorite of tin‐bearing feldspar veins in the Huanggangliang tin deposit range from 195 to 425C and from 215 to 450C, respectively. The fluids responsible for the Anle and Huanggangliang tin deposits were of very high temperature and NaCl‐rich ones containing K, Ca, Al, Si, Ti, Fe and Cl in addition to ore metals such as Sn and Cu. The temperature and chemical composition of fluid in fluid inclusions of igneous rocks in the mining area are very similar to those of fluid in fluid inclusions in the ores of these deposits. The fluid for these ore deposits had a close relation with the fluid coexisting with melt of Late Jurassic granitic rocks in this mining area. Salinities of fluid inclusions from these ore deposits and granitic rocks in the mining area were estimated to range from 35 to 50 wt % NaCl equivalent. Based on arsenopy‐rite geothermometry and fluid inclusion studies, a fluid containing 40 wt% NaCl (eq.) could be formed by phase separation of fluid having 6 wt% NaCl (eq.) at a temperature of 420 to 500C and a pressure of 0.3 to 0.4 kb. The temperatures and pressures presented above indicate an NaCl‐rich magmatic fluid derived from granitic melt that had intruded into a shallow level of crust caused the Sn–Fe–Cu mineralization of the mining area. The geological relationship between these ore deposits and granitic bodies around the ore deposits, and the similarity of fluids forming these ore deposits and coexisting with granitic melt, suggest that these ore deposits were formed by the activity of fluid derived from granitic melt in Late Jurassic age.     

Genesis of the Mamut Porphyry Copper Deposit, Sabah, East Malaysia

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 X_Mg (=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.     

Fluid Inclusions and Hydrogen,Oxygen, Sulfur Isotopes of Nuri Cu‐W‐Mo Deposit in the Southern Gangdese,Tibet

The Nuri Cu‐W‐Mo deposit is located in the southern subzone of the Cenozoic Gangdese Cu‐Mo metallogenic belt. The intrusive rocks exposed in the Nuri ore district consist of quartz diorite, granodiorite, monzogranite, granite porphyry, quartz diorite porphyrite and granodiorite porphyry, all of which intrude in the Cretaceous strata of the Bima Group. Owing to the intense metasomatism and hydrothermal alteration, carbonate rocks of the Bima Group form stratiform skarn and hornfels. The mineralization at the Nuri deposit is dominated by skarn, quartz vein and porphyry type. Ore minerals are chalcopyrite, pyrite, molybdenite, scheelite, bornite and tetrahedrite, etc. The oxidized orebodies contain malachite and covellite on the surface. The mineralization of the Nuri deposit is divided into skarn stage, retrograde stage, oxide stage, quartz‐polymetallic sulfide stage and quartz‐carbonate stage. Detailed petrographic observation on the fluid inclusions in garnet, scheelite and quartz from the different stages shows that there are four types of primary fluid inclusions: two‐phase aqueous inclusions, daughter mineral‐bearing multiphase inclusions, CO₂‐rich inclusions and single‐phase inclusions. The homogenization temperature of the fluid inclusions are 280°C–386°C (skarn stage), 200°C–340°C (oxide stage), 140°C–375°C (quartz‐polymetallic sulfide stage) and 160°C–280°C (quartz‐carbonate stage), showing a temperature decreasing trend from the skarn stage to the quartz‐carbonate stage. The salinity of the corresponding stages are 2.9%–49.7 wt% (NaCl) equiv., 2.1%–7.2 wt% (NaCl) equiv._, 2.6%–55.8 wt% (NaCl) equiv. and 1.2%–15.3 wt% (NaCl) equiv., respectively. The analyses of CO₂‐rich inclusions suggest that the ore‐forming pressures are 22.1 M Pa–50.4 M Pa, corresponding to the depth of 0.9 km–2.2 km. The Laser Raman spectrum of the inclusions shows the fluid compositions are dominated in H₂O, with some CO₂ and very little CH₄, N₂, etc. δD values of garnet are between ?114.4‰ and ?108.7‰ and δ¹⁸O_H2O between 5.9‰ and 6.7‰; δD of scheelite range from ?103.2‰ to ?101.29‰ and δ¹⁸O_H2O values between 2.17‰ and 4.09‰; δD of quartz between ?110.2‰ and ?92.5‰ and δ¹⁸O_H2O between ?3.5‰ and 4.3‰. The results indicate that the fluid came from a deep magmatic hydrothermal system, and the proportion of meteoric water increased during the migration of original fluid. The δ³⁴S values of sulfides, concentrated in a rage between ?0.32‰ to 2.5‰, show that the sulfur has a homogeneous source with characteristics of magmatic sulfur. The characters of fluid inclusions, combined with hydrogen‐oxygen and sulfur isotopes data, show that the ore‐forming fluids of the Nuri deposit formed by a relatively high temperature, high salinity fluid originated from magma, which mixed with low temperature, low salinity meteoric water during the evolution. The fluid flow through wall carbonate rocks resulted in the formation of layered skarn and generated CO₂ or other gases. During the reaction, the ore‐forming fluid boiled and produced fractures when the pressure exceeded the overburden pressure. Themeteoric water mixed with the ore‐forming fluid along the fractures. The boiling changed the pressure and temperature, oxygen fugacity, physical and chemical conditions of the whole mineralization system. The escape of CO₂ from the fluid by boiling resulted in scheelite precipitation. The fluid mixing and boiling reduced the solubility of metal sulfides and led the precipitation of chalcopyrite, molybdenite, pyrite and other sulfide.     

Highly Oxidized Magma and Fluid Evolution of Miocene Qulong Giant Porphyry Cu‐Mo Deposit,Southern Tibet,China

The Miocene Qulong porphyry Cu‐Mo deposit, which is located at the Gangdese orogenic belt of Southern Tibet, is the largest porphyry‐type deposit in China, with confirmed Cu ～10 Mt and Mo ～0.5 Mt. It is spatially and temporally associated with multiphase granitic intrusions, which is accompanied by large‐scale hydrothermal alteration and mineralization zones, including abundant hydrothermal anhydrite. In addition to hydrothermal anhydrite, magmatic anhydrite is present as inclusions in plagioclase, interstitial minerals between plagioclase and quartz, and phenocrysts in unaltered granodiorite porphyry, usually in association with clusters of sulfur‐rich apatite in the Qulong deposit. These observations indicate that the Qulong magma‐hydrothermal system was highly oxidized and sulfur‐rich. Three main types of fluid inclusions are observed in the quartz phenocrysts and veins in the porphyry: (i) liquid‐rich; (ii) polyphase high‐salinity; and (iii) vapor‐rich inclusions. Homogenization temperatures and salinities of all type inclusions decrease from the quartz phenocrysts in the porphyry to hydrothermal veins (A, B, D veins). Microthermometric study suggests copper‐bearing sulfides precipitated at about 320–400°C in A and B veins. Fluid boiling is assumed for the early stage of mineralization, and these fluids may have been trapped at about 35–60 Mpa at 460–510°C and 28–42 Mpa at 400–450°C, corresponding to trapping depths of 1.4–2.4 km and 1.1–1.7 km, respectively.     

西藏甲玛铜多金属矿区成矿斑岩的岩浆混合作用:石英及长石斑晶新证据

西藏甲玛矿区斑岩内石英和长石斑晶的阴极发光(CL)特征及元素含量变化有效记录了岩浆演化、混合及补给事件.石英斑晶的显微生长结构表明,原始岩浆经历过2次铁镁质岩浆混合作用.根据石英斑晶中Ti含量的变化可知,在2次溶蚀前后,石英结晶温度分别增高了约110℃和80℃.此外,斜长石斑晶的反环带及其Ba、Sr、Fe等元素的浓度梯...     

安徽铜陵冬瓜山铜矿床的叠加改造成矿机制：来自矿石结构的证据

长江中、下游地区块状硫化物矿床普遍受到燕山期岩浆及其热液的改造与叠加.本文以铜陵冬瓜山矿床为例,探讨这类矿床的成矿机制.该矿床主要由层状硫化物矿体组成,伴有矽卡岩型和斑岩型矿体.野外地质观察及室内矿相学的研究表明,冬瓜山层状矿体中矿石遭受了强烈的热变质作用及热液交代作用.进变质过程中形成的结构主要为黄铁矿受燕山期岩浆侵...     

Genesis of massive sulfide deposits in the Verkhneural’sk ore district, the South Urals, Russia: Evidence for magmatic contribution of metals and fluids

Melt inclusions and aqueous fluid inclusions in quartz phenocrysts from host felsic volcanics, as well as fluid inclusions in minerals of ores and wall rocks were studied at the Cu-Zn massive sulfide deposits in the Verkhneural’sk ore district, the South Urals. The high-temperature (850–1210°C) magmatic melts of volcanic rocks are normal in alkalinity and correspond to rhyolites of the tholeiitic series. The groups of predominant K-Na-type (K₂O/Na₂O = 0.3–1.0), less abundant Na-type (K₂O/Na₂O = 0.15–0.3), and K-type (K₂O/Na₂O = 1.9–9.3) rhyolites are distinguished. The average concentrations (wt %) of volatile components in the melts are as follows: 2.9 H₂O (up to 6.5), 0.13 Cl (up to 0.28), and 0.09 F (up to 0.42). When quartz was crystallizing, the melt was heterogeneous, contained magnetite crystals and sulfide globules (pyrrhotite, pentlandite, chalcopyrite, bornite). High-density aqueous fluid inclusions, which were identified for the first time in quartz phenocrysts from felsic volcanics of the South Urals, provide evidence for real participation of magmatic water in hydrothermal ore formation. The fluids were homogenized at 124–245°C in the liquid phase; the salinity of the aqueous solution is 1.2–6.2 wt % NaCl equiv. The calculated fluid pressure is very high: 7.0–8.7 kbar at 850°C and 5.1–6.8 kbar at 700°C. The LA-ICP-MS analysis of melt and aqueous fluid inclusions in quartz phenocrysts shows a high saturation of primary magmatic fluid and melt with metals. This indicates ore potential of island-arc volcanic complexes spatially associated with massive sulfide deposits. The systematic study of fluid inclusions in minerals of ores and wall rocks at five massive sulfide deposits of the Verkhneural’sk district furnished evidence that ore-forming fluids had temperature of 375–115°C, pressure up to 1.0–0.5 kbar, chloride composition, and salinity of 0.8–11.2 (occasionally up to 22.8) wt % NaCl equiv. The H and O isotopic compositions of sericite from host metasomatic rocks suggest a substantial contribution of seawater to the composition of mineral-forming fluids. The role of magmatic water increases in the central zones of the feeding conduit and with depth. The dual nature of fluids with the prevalence of their magmatic source is supported by S, C, O, and Sr isotopic compositions. The TC parameters of the formation of massive sulfide deposits are consistent with the data on fluid inclusions from contemporary sulfide mounds on the oceanic bottom.