金川铜镍硫化物矿床中铂族矿物的主要类型和产出特征: 热液蚀变过程中铂族元素的富集机理

金川铜镍硫化物矿床是我国最主要的铂族元素（PGE）资源产地,其矿石受热液蚀变作用影响明显,并产出多种铂族矿物（PGM）。岩浆演化和热液蚀变过程中PGE的迁移富集机制和PGM的成因,一直是研究PGE地球化学行为非常关注的问题。本文对金川铜镍硫化物矿床中PGM的研究发现,其主要类型包括含PGE的硫砷化物（硫砷铱矿）和砷化物（砷铂矿）,Pd的铋化物、碲化物和硒化物,以及少量其他铂族矿物。其中,硫砷铱矿可包裹于各种贱金属硫化物（镍黄铁矿、磁黄铁矿和黄铜矿）中,表明硫砷铱矿可能结晶于早期的含As硫化物熔体,随后被包裹于硫化物熔体冷凝分异产生的单硫化物固溶体（MSS）和中间硫化物固溶体（ISS）中。硫化物熔体中的As可能主要通过地壳混染作用加入幔源岩浆。大量铋钯矿（PdBi）呈微细乳滴状包裹于黄铜矿中,为晚期ISS冷凝形成黄铜矿过程中出溶的产物。少量铋钯矿（PdBi₂）呈不规则状充填于矿物裂隙,与次生磁铁矿脉紧密共生,并随矿石的蚀变程度增加,铋钯矿的化学成分由PdBi逐渐向PdBi₂转变,表明这部分铋钯矿为后期热液蚀变产物。铋碲钯矿和钯的硒化物则主要产出于镍黄铁矿裂隙且与次生磁铁矿紧密共生,指示明显的热液成因。钯的硒化物的出现表明,岩浆期后酸性、高盐度、高氧逸度的富Cl^-流体对金川铜镍硫化物矿床中Pd的迁移和富集起到了关键控制作用。

     

Controls on variations of platinum-group element concentrations in the sulfide ores of the Jinchuan Ni-Cu deposit, western China

Ongoing underground exploration in the giant Jinchuan Ni-Cu sulfide deposit in western China is beginning to emphasize the potential for Cu-, Pt-, and Pd-rich sulfide ores that may have formed by sulfide liquid fractionation. The success of such an effort relies on whether or not fractional crystallization of sulfide occurred in the Jinchuan system. In this paper, we used available PGE data to evaluate such a process. We found that about two thirds of the 126 samples analyzed to date exhibit significant decoupling not only between Pt and Pd but also between Ru, Rh, and Ir. The best explanation for the decoupling is postmagmatic hydrothermal alteration, which affected not only silicates but also sulfides. The effects of postmagmatic alteration must be considered when using metal and isotopic ratios to evaluate primary mineralization. PGE variations in the remaining one third of the samples with Ir/(Ir + Ru) = 0.3–0.7, Ir/(Ir + Rh) = 0.4–0.8, and Pt/(Pt + Pd) = 0.3–0.7 indicate variable R-factors within individual ore bodies as well as the entire deposit, consistent with the interpretation that multiple sulfide-bearing magmas from depth were involved in the formation of the Jinchuan deposit. The mantle-normalized PGE patterns of the least-altered samples from the Jinchuan deposit are similar to the picrite-related Pechenga Ni-Cu sulfide deposit in Russia. PGE variations that can be related to sulfide liquid fractionation are observed in orebody-1 and orebody-24 but not in orebody-2 at Jinchuan. Exploration for Cu-, Pt-, and Pd-rich sulfide ores that may have been expelled into fractures in the footwalls of orebody-1 and orebody-24 appears to be justified.     

布什维尔德铂族元素矿床:铂族矿物赋存状态及其成因

总结南非布什维尔德杂岩体中Merensky Reef(简称MR矿层)和Platreef(简称PR接触带)两类铂族元素矿床的矿床地质、矿化特征以及铂族元素的赋存状态。MR矿床是典型的层状铂族元素(PGE)矿床,在杂岩体东部和西部发育,PGE总含量稳定,赋存在堆晶间隙硫化物中,常以PGE硫化物的形式产出。PR接触带型矿化集中在杂岩体北段,整体上不连续,各个矿床的具体特征由于底盘岩性的多变而不同,PGE主要赋存在碲化物和砷化物等半金属化合物中,可以脱离硫化物产在硅酸盐矿物中。相关的实验研究显示,PGE在岩浆结晶过程中发生分异,Pd/Ir比值体现了硫化物的分异程度;Pd比Pt更容易被氧化以及在热液中迁移,Pt/Pd比值体现了混染和热液的作用,这些因素造成了PR接触带与MR矿层中PGE赋存状态的差异。岩浆可能在侵入之前已经达到了硫饱和,岩浆房的压力变化和岩浆通道对于PGE的富集有重要意义,热液流体可以对已经形成的PGE矿化进行改造。     

Siderophile and chalcophile elemental constraints on the origin of the Jinchuan Ni-Cu-(PGE) sulfide deposit, NW China

The Jinchuan deposit, NW China, is one of the world’s most important Ni-Cu-(PGE) sulfide deposits related to a magma conduit system and is hosted in an ultramafic intrusion. The intrusion is composed of lherzolite and dunite with the two largest sulfide ore bodies (named as ore body 1 and 2) in its middle portion. The sulfide ores may be disseminated, net-textured, or massive. The disseminated and net-textured sulfide ores are characterized by variable but generally low PGE concentrations: 10-3200 ppb Pt, 240-9800 ppb Pd, 17-800 ppb Ir, 25-1500 ppb Ru, and 15-400 ppb Rh in 100% sulfides. The massive sulfide ores are extremely low in Pt (<30 ppb) on a 100% sulfides and have very high Cu/Pd ratios, ranging from 10⁴ to 4.5 × 10⁵. The low PGE contents suggest that the sulfide ores formed from the silicate magmas that had already experienced prior-sulfide separation.Our calculations indicate that if the first stage basaltic magmas had contained 6.3 ppb Pt, 6.2 ppb Pd, and 0.1 ppb Ir, 0.008% sulfide removal would result in PGE-depletion in the residual magma with 0.57 ppb Pt, 0.25 ppb Pd, and 0.009 ppb Ir. The Jinchuan sulfides were formed by a second stage of sulfide segregation from a PGE-depleted magma under silicate/sulfide liquid ratios (R-factor) ranging from 10³ to 10⁴ in a deep-seated staging chamber. The massive sulfide ores and some of the net-textured sulfide ores exhibit strong negative Pt-anomalies that cannot be explained by sulfide segregation under variable R-factors. Instead, the sulfide melts that formed the massive ores were segregated from magmas experienced prior fractionation of Pt-Fe alloy. Alternatively, the Pt may have been selectively leached by hydrothermal fluids during remobilization of the sulfide melts that produced the massive sulfides, which occur in cross-cutting veins. We propose that the Jinchuan intrusion and ore bodies were formed by injections of sulfide-free and sulfide-bearing olivine mushes from a deep-seated staging chamber.     

陕西太白金矿含金角砾岩中铂族元素特征

采用硫镍火法试金(NiS-FA)结合电感耦合等离子质谱(ICP-MS)分析了太白金矿硫化物和含金角砾岩中铂族元素的含量,结果显示,与秦岭地区八卦庙相比铂族元素含量较高,而低于原始地幔,其中铂(Pt)、钯(Pd)、钌(Ru)富集,并结合前人研究资料对铂族元素的来源和迁移机制进行探讨。铂族元素可能受深源的影响,IPGE(Ir、Os、Ru)可能主要以硫化物形式存在而PPGE(Rh、Pt、Pd)可能主要以单质存在。     

金川岩浆铜镍（铂）硫化物矿床铂族金属富集过程及富集机制

金川岩浆铜镍（铂）硫化物矿床是我国最主要的铂族等战略性关键金属宝库。金川矿床中铂族金属的富集过程和富集机制还存在很多争论。本文通过详细的矿物学及矿床学研究,厘定了金川矿床成矿阶段。成矿阶段可划分为硫化物矿浆结晶阶段、挥发分流体作用阶段及热液改造阶段。其中硫化物矿浆结晶阶段的主要矿物组合为镍黄铁矿（Pn- a）- 磁黄铁矿（Po- a）- 黄铜矿（Ccp- a）;挥发分流体作用阶段的主要矿物组合为镍黄铁矿（Pn- b）- 磁黄铁矿（Po- b）- 黄铜矿（Ccp- b）- 黄铁矿（Py- Ⅰ）- 磁铁矿（Mag- Ⅰ）- 菱铁矿- 叶蛇纹石- 磷灰石- 铬铁矿- 白云石- 方解石（Cal- Ⅰ）- 金云母。热液改造阶段的矿物组合为透闪石- 绿泥石- 蛇纹石- 方解石（Cal- Ⅱ）- 磁铁矿（Mag- Ⅱ）。高倍电子探针镜下发现,金川矿床铂族矿物与磁铁矿（Mag- Ⅰ）、黄铁矿（Py- Ⅰ）、铬铁矿、磷灰石、黄铜矿、磁黄铁矿、镍黄铁矿及菱铁矿等共生。金川铜镍硫化物矿床中铂族元素(PGM)矿物主要包括硫砷铱矿（IrAsS）、钯的铋化物、碲化物和硒化物、钯的金属互化物（PdAu2）、砷铂矿（PtAs2）、铂单质以及铂的金属合金（Pt- Fe）。其中大量的PGM分布于镍黄铁矿的裂隙中,或产于镍黄铁矿、磁黄铁矿及蛇纹石裂隙中。与磁铁矿、菱铁矿、铬铁矿、黄铜矿、磷灰石以及叶蛇纹石等矿物共生,指示PGE富集与氧化性流体加入密切相关。金川矿石镍黄铁矿（Pn- b）、磁黄铁矿（Po- b）、黄铜矿（Ccp- b）、黄铁矿（Py- Ⅰ）、磁铁矿（Mag- Ⅰ）以及菱铁矿中高Co含量,表明流体在Co的超常富集过程中也起到了决定性作用。金川矿石中大量碳酸盐矿物、叶蛇纹石、金云母、磁铁矿、黄铁矿、铬铁矿以及富Cl磷灰石的出现;S、Mg元素呈网脉状分布于蚀变橄榄石和硫化物中,推测流体组分可能是一种富C富Cl的富含挥发分的高氧逸度流体。金川铬铁矿、磁铁矿（Ⅰ）、菱铁矿等矿物中高Ti、高Nb含量和高Nb/Ta比值,暗示此流体可能是一种高温的超临界流体。以上特征综合表明该特征流体对金川铜镍硫化物矿床中铂族元素等关键金属的超常富集起到了关键控制作用。当挥发分流体与残余硫化物矿浆相互作用及改造先存硫化物及橄榄石时,不仅会促使Os、Ir、Ru、Rh、Pt、Pd进一步活化、富集,还会导致流体中PGE强烈富集,使得流体中的Pd、Se、Te、Bi、Pt含量不断提高,最终形成大量的PGM。综上所述,本文认为在岩浆演化晚期可能存在一种高氧逸度的富Cl富C的深源流体注入岩浆房,该深源挥发分流体对PGE及Co的迁移和超常富集起到了关键控制作用。     

金川Cu、Ni(PGE)岩浆硫化物矿床成矿时代研究

金川Cu、Ni(PGE)岩浆硫化物矿床是世界最著名的矿床之一,其中超镁铁岩和矿床的形成时代一直备受关注,不同研究者采用不同的方法获得了大量的年龄数据,但均未获得公认一致的结果。文中通过对不同测试方法的适用性与局限性分析,结合金川岩体、矿体地质分异特点,对前人的和文中测得的同位素年龄数据进行分析研究,认为新元古代时期的成矿年龄(800 Ma左右)为后期构造变质叠加事件年龄,中元古代时期的成岩、成矿年龄(1 408~1 508 Ma)更接近实际的成岩、成矿事件年龄。这一成矿年龄的进一步厘定,说明了华北古陆边缘中元古代成岩成矿事件的重要性。     

Typomorphism of pyrite of the Sukhoi Log deposit (East Siberia)

The typomorphic features of pyrite of the Sukhoi Log deposit were studied by a set of volumetric and surface methods: electron probe microanalysis, scanning electron and probe microscopy, powder X-ray diffraction, X-ray photoelectron and Auger electron spectroscopy, atomic-absorption spectrometry in the SSADSC (method of statistical sample of analytical data for single crystals) version, and atomic-emission spectrometry. Pyrite from the Sukhoi Log deposit has the following distinctive features: permanent presence of sulfite ion, which often dominates over other surface sulfur anions; weakly determined size dependence of the content of uniformly distributed Au owing to the presence of an internal concentrator of gold—dispersed carbonaceous material—in pyrite from ore zones; cell sculptures of the crystal faces, which appeared owing to the nanofragmentation of the growth surface; micro- and nanoinclusions of carbonaceous phases within crystals, associated with defects in their structure; and thin films enriched in O and C on the surface of and within the crystals. It has been shown that gold-sulfide mineralization at the Sukhoi Log deposit formed in a single ore-generating hydrothermal system, in which gold, sulfur, and carbon belonged to a microparagenesis. Some features (composition of surface, characteristics of submicroscopic structure, and elemental composition) evidence that the conditions of crystallization of pyrite in inter-ore space were different from the conditions of its genesis in the ore zones, which suggests the presence of at least two genetic types of pyrite. Carbonaceous micro- and nanoparticles and O- and C-containing films can favor an increase in the adsorption of gold from cyanide solutions on pyrite. To reduce this effect during gold recovery, a technique for surface modification should be elaborated. The ways for solving the most complicated problems dealt with the source of noble metals (NM) and the ore specialization of the deposit have been outlined. For this purpose, a detailed analysis of the main ore minerals for trace-element speciation is required. In the case of the magmatic source of NM, correlation between the contents of Au and PGE structural forms should exist. On the other hand, there is no correlation between the structural forms of Au or Pt and elements whose contents in fluid are determined by the host rock rather than the magmatic source.     

Chalcophile elemental compositions and origin of the Tuwu porphyry Cu deposit,NW China

The Tuwu porphyry Cu deposit in the eastern Tianshan Orogenic Belt of southern Central Oceanic Orogen Belt contains 557 Mt ores at an average grade of 0.58 wt.% Cu and 0.2 g/t Au, being the largest porphyry Cu deposit in NW China. The deposit is genetically related to dioritic and plagiogranitic porphyries that intruded the Carboniferous Qieshan Group. Ore minerals are dominantly chalcopyrite, pyrite and enargite. Porphyric diorites have Sr/Y and La/Yb_N ratios lower but Y and Yb contents higher than plagiogranites. Diorites have highly variable Cu but nearly constant PGE contents (most Pd = 0.50–1.98 ppb) with Cu/Pd ratios ranging from 10,900 to 8,900,000. Plagiogranites have PGEs that are positively correlated with Cu and have nearly uniform Cu/Pd ratios (5,100,000 to 7,800,000). Diorites have concentrations of Re (0.73–15.18 ppb), and ¹⁸⁷Re/¹⁸⁸Os and ¹⁸⁷Os/¹⁸⁸Os ratios lower but common Os contents (0.006–0.097 ppb) higher than plagiogranites. However, both the diorites and plagiogranites have similar normalized patterns of rare earth elements (REE), trace element and platinum-group elements (PGEs). All the samples are characterized by the enrichments of LREE relative to HREE and display positive anomalies of Pb and Sr but negative anomalies of Nb and Ta in primitive-mantle normalized patterns. In the primitive mantle-normalized siderophile element diagrams, they are similarly depleted in all PGEs but slightly enriched in Au relative to Cu.Our new dataset suggests that both the diorite and plagiogranite porphyries were likely evolved from magmas derived from partial melting of a wet mantle wedge. Their parental magmas may have had different water contents and redox states, possibly due to different retaining time in staging magma chambers at the depth, and thus different histories of magma differentiation. Parental magmas of the diorite porphyries are relatively reduced with less water contents so that they have experienced sulfide saturation before fractional crystallization of silicate minerals, whereas the relatively more oxidized parental magmas with higher water contents of the plagiogranite porphyries did not reach sulfide saturation until the magmatic-hydrothermal stage. Our PGE data also indicates that the Cu mineralization in the Tuwu deposit involved an early stage with the enrichments of Au, Mo and Re and a late stage with the enrichment of As but depletion of Au–Mo. After the formation of the Cu mineralization, meteoric water heated by magmas penetrated into and interacted with porphyritic rocks at Tuwu, which was responsible for leaching Re from hosting rocks.     

河南周庵铂族-铜镍矿床的稀土和铂族元素地球化学特征: 热液成矿的证据

河南周庵超基性岩体蕴含大型Ni-Cu-(PGE)硫化物矿床,矿化带位于超基性岩体边缘与围岩的接触带.周庵超基性岩体轻稀土富集,其La/Sm_N比值为1.3～4.7,Sm/Yb_N比值为1.9～4.4,显示一定程度的LREE/HREE分异.原始地幔标准化的微量元素配分型显示弱的负Nb异常.岩体的M含量为70×10~(-60～2120×10~(-6),Cu含量为15×10~(-6)～1056×10~(-6);矿石的Ni含量为2592×10~(-6)～6549×10~(-6),Cu含量为1147×10~(-6)～3239×10`(-6).矿石的Ni/Cu比值(2.0～2.3)低于岩石样品(5-83).强蚀变矿化样品的PGE元素含量高于弱蚀变样品约一个数量级,所有样品的Pd/Ir和Pt/Ir比值高,Pd/Ir=1.4～21,Pt/Ir=2.4～22,表明PPGE相对IPGE富集.上述特征显示周庵岩体是构造侵位的地幔岩,岩体与围岩发生了较强烈的物质交换,含水流体交代作用导致了岩体-围岩物质交换和岩体边缘矿化.     

甘肃黑山铜镍硫化物含矿岩体的地质特征及橄榄石成因探讨

黑山铜镍硫化物含矿岩体位于中亚造山带南缘北山褶皱带东部,对该岩体的研究有助于正确理解造山带型铜镍硫化物的成矿作用。详细的野外基础地质特征表明黑山矿区仅出露单一的新元古代青白口系地层,无寒武纪地层出露。黑山含矿岩体由早期的方辉橄榄岩、二辉橄榄岩和橄榄辉长苏长岩,以及稍晚期的辉长岩脉组成。黑山岩体位于黑山背斜南翼,其初始产状应为一水平或近水平的岩床状岩体,因后期褶皱作用,岩体发生了倾斜形成现今的产状。黑山岩体中橄榄石Fo值为80.5~87.0,其Ni含量为1070×10^-6~3461×10^-6。借助"MELTS"软件,我们进一步厘定了黑山母岩浆为高镁玄武岩浆 (12.81% MgO, 10.84% FeO, 430×10^-6 Ni)。研究表明,黑山橄榄石的主要控制因素为:1)母岩浆的成分;2)后续新鲜岩浆的补充混合作用;3)硫化物熔离作用;4)晶间硅酸盐熔浆作用;5)橄榄石与硫化物之间发生的Fe-Ni交换。模拟计算表明,硫化物熔离与橄榄石结晶几乎同时发生,橄榄石与硫化物的最小质量比约为20:1。1号矿体及矿化体的橄榄石比4号矿体更富Mg和Ni,并且还呈现非常好的负相关关系,表明这些橄榄石与硫化物发生了不同程度的Fe-Ni交换,而与其发生Fe-Ni交换的硫化物更富Ni以及共生的岩浆更为原始。这很可能是因为黑山岩体形成于开放的岩浆通道系统,早期融离的硫化物与后续的新鲜的硫不饱和岩浆发生反应,使得该类硫化物含量减少但硫化物中的金属元素含量增高从而形成1号矿体及矿化体。     

Chemical composition of platinum-group minerals from the Bor-Uryakh massif (Maimecha-Kotui Province,Russia)

This contribution firstly presents particularities of mineral chemistry of platinum-group elements (PGE) mineralization from placer deposits linked to the Bor-Uryakh massif of the Maimecha-Kotui Province, northern part of the Siberian Craton. The chemical composition of PGE mineralization has been studied by electron microprobe analysis. At Bor-Uryakh, main platinum-group minerals (PGM) comprise Os-Ir and Pt-Fe alloys represented by individual crystals, and polyphase PGM assemblages. The majority (e.g., 12 out of 19) of the Os-rich nuggets are iridian osmium, with subordinate amounts of native osmium (Os) and chengdeite (Ir₃Fe). Pt-Fe alloys have a stoichiometric composition close to Pt₂Fe. According to the nomen-clature by L. Cabri and C. Feather [1975] these minerals correspond to ferroan platinum. Based on geological position and geochemical features of investigated PGE mineralization the particular rock sources have been established. This study has demonstrated the similarity of chemical characteristics of Os-Ir and Pt-Fe alloys of the Bor-Uryakh massif to those of PGM from the Guli massif (Maimecha-Kotui Province), platiniferous zoned-type ultramafic massifs (e.g., Kondyor, Inagli and Chad) of the Aldan Province and Platinum belt of the Urals (Nizhny Tagil, Kytlym, etc.).     

青海东昆仑阿斯哈金矿床含金黄铁矿微量元素地球化学特征及其地质意义

阿斯哈金矿床是青海东昆仑造山带东段金矿床的典型代表.金矿体主要赋存于闪长岩和花岗闪长岩体的构造破碎带内,受NNE向和NNW向-NW向断裂构造控制.与金矿化密切相关的蚀变类型为黄铁矿化、硅化、绢云母化和黄铜矿化.矿石矿物主要为黄铁矿,其次是黄铜矿、方铅矿、毒砂、自然金和银金矿.据矿脉穿插关系、矿石矿物共生组合和结构构造特...     

Platinum-group minerals in fluid inclusions from the Marathon deposit,Coldwell Complex,Canada

Summary Platinum-group minerals (PGM) project into fluid inclusions that occur in chalcopyrite and cubanite from the Marathon deposit, Two Duck Lake gabbro, Coldwell Complex, Ontario. Semi-quantitative analyses of the micron-sized PGM were made by SEM-EDS; they reveal Ag-bearing intermetallic compounds of Pd₃Sn-Pd₃Pb-Pd₃Te (i.e., atokitezvyagintsevite-keithconnite) and telargpalite (Pd₂AgTe) on broken, irregular surfaces of the Cu-Fe-S minerals. Halite daughter minerals, and quenched brine occur in and around some opened fluid inclusions. These data confirm the hypothesis based on petrography and mineral compositions that saline fluids remobilized PGE, Cu, and other elements and precipitated them well after crystallization of sulfide and silicate magmas in the Marathon deposit.

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Platin-Gruppenminerale in Flüssigkeitseinschlüssen aus der Marathon Lagerstdtte, Coldwall Komplex, Kanada

Zusammenfassung Platin-Gruppenminerale (PGM) ragen in Flüzssigkeiteinschliisse, die im Kupferkies und Cubanit der Marathon Lagerstätte, Two Duke Lake Gabbro, Coldwell Komplex, Ontario, vorkommen, hinein. Semiqantitative Analysen der mikrongroßen PGM wurden mit einem SEM-EDS durchgeführt. Sie ergaben Ag-führende, intermetallische Verbindungen von Pd₃Sn-Pd₃Pb-Pd₃Te (Atokit-Zvyagintsevit-Keithconnit) und Telargpalit (Pd₂AgTe) auf zerbrochenen, irregulären Oberflächen der Cu-Fe-SMinerale. Steinsalz-Tochterkristalle und abgeschreckte Salzlösungen treten innerhalb und in der unmittelbaren Umgebung geöffneter Flüssigkeitseinschlüsse auf. Diese Daten bestätigen die Hypothese, basierend auf der Petrographie und der Mineralzusammensetzung, daß saline Fluida PGE, Cu und andere Elemente remobilisieren können, und daß d iese nach der Kristallisation der Sulfide und des Silikatmagmas in der Marathon Lagerstätte zur Ablagerung gekommen sind.

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With 3 Figures     

Sulfur isotope and trace element data from ore sulfides in the Noranda district (Abitibi,Canada): implications for volcanogenic massive sulfide deposit genesis

We examine models for volcanogenic massive sulfide (VMS) mineralization in the ~2.7-Ga Noranda camp, Abitibi subprovince, Superior Province, Canada, using a combination of multiple sulfur isotope and trace element data from ore sulfide minerals. The Noranda camp is a well-preserved, VMS deposit-rich area that is thought to represent a collapsed volcanic caldera. Due to its economic value, the camp has been studied extensively, providing a robust geological framework within which to assess the new data presented in this study. We explore previously proposed controls on mineralization within the Noranda camp and, in particular, the exceptional Au-rich Horne and Quemont deposits. We present multiple sulfur isotope and trace element compositional data for sulfide separates representing 25 different VMS deposits and “showings” within the Noranda camp. Multiple sulfur isotope data for this study have δ³⁴S_V-CDT values of between ?1.9 and +2.5?‰, and Δ³³S_V-CDT values of between ?0.59 and ?0.03?‰. We interpret the negative Δ³³S values to be due to a contribution of sulfur that originated as seawater sulfate to form the ore sulfides of the Noranda camp VMS deposits. The contribution of seawater sulfate increased with the collapse and subsequent evolution of the Noranda caldera, an inference supported by select trace and major element analyses. In particular, higher concentrations of Se occur in samples with Δ³³S values closer to 0?‰, as well as lower Fe/Zn ratios in sphalerite, suggesting lower pressures and temperatures of formation. We also report a relationship between average Au grade and Δ³³S values within Au-rich VMS deposits of the Noranda camp, whereby higher gold grades are associated with near-zero Δ³³S values. From this, we infer a dominance of igneous sulfur in the gold-rich deposits, either leached from the volcanic pile and/or directly degassed from an associated intrusion.     

Gold contents of sulfide minerals in granitoids from southwestern New Brunswick,Canada

The abundance of gold and selected trace elements in magmatic sulfide and rock-forming minerals from Silurian–Devonian granitoids in southwestern New Brunswick were quantitatively analyzed by laser-ablation inductively coupled plasma mass-spectrometry. Gold is mainly hosted in sulfide minerals (i.e., chalcopyrite, pyrrhotite, and pyrite), in some cases perhaps as submicron inclusions (nanonuggets). Gold is below detection (<0.02 ppm) in major rock-forming minerals (i.e., plagioclase, K-feldspar, biotite, hornblende, and muscovite) and oxides (i.e., magnetite, and ilmenite). Gold distribution coefficients between sulfide and granitoid melt are calculated empirically as: . This result suggests that gold behavior in the granitoid systems is controlled by the conditions of sulfur saturation during magmatic evolution; the threshold of physiochemical conditions for sulfur saturation in the melts is a key factor affecting gold activity. Gold behaves incompatibly prior to the formation of sulfide liquids or minerals, but it becomes compatible at their appearance. Gold would be enriched in sulfur-undersaturated granitoid magmas during fractionation, partitioning into evolved magmatic fluids and favoring the formation of intrusion-related gold deposits. However, gold becomes depleted in residual melts if these melts become sulfur-saturated during differentiation, leading to gold precipitation in the early sulfide phases of a granitoid suite. Late-stage Cl-bearing magmatic–hydrothermal fluids with low pH and relatively high oxidation state derived from either progressively cooling magmas at depth or convective circulation of meteoric water buffered by reduced carbon-bearing sediments, may scavenge gold from early sulfide minerals. If a significant amount of gold produced in this manner is concentrated in a suitable geological environment (e.g., shear zones or fracture systems), intrusion-related gold deposits may also be generated. Exploration for intrusion-related gold systems should focus on the areas around evolved phases of granitoid suites that remained sulfur-undersaturated. For sulfur-saturated granitoid suites, the less differentiated phase and associated structures are the most prospective targets.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Assemblages and genesis of platinum-group minerals in low-sulfide ores of the monchetundra deposit,Kola Peninsula,Russia

New data on the composition, assemblages, and formation conditions of platinum-group minerals (PGM) identified in platinum-group element (PGE) occurrences of the Monchetundra intrusion (2495 +- 13 to 2435 ± 11 Ma) are described. This intrusion is a part of the Paleoproterozoic pluton of the Monche-Chuna-Volch’i and Losevy tundras located in the Pechenga-Imandra-Varzuga Rift System. The rhythmically layered host rocks comprise multiple megarhythms juxtaposed to mylonite zones and magmatic breccia and injected by younger intrusive rocks in the process of intense and long magmatic and fluid activity in the Monchetundra Fault Zone. The primary PGM and later assemblages that formed as a result of replacement of the former have been identified in low-sulfide PGE occurrences. More than 50 minerals and unnamed PGE phases including alloys, Pt and Pd sulfides and bismuthotellurides, PGE sulfarsenides, and minerals of the Pd-As-Sb, Pd-Ni-As, and Pd-Ag-Te systems have been established. The unnamed PGE phases—Ni₆Pd₂As₃, Pd₆AgTe₄, Cu₃Pt, Pd₂NiTe₂, and (Pd, Cu)₉Pb(Te, S)₄—are described. The primary PGM were altered due to the effect of several mineral-forming processes that resulted in the formation of micro- and nanograins of Pt and Pd alloys, sulfides, and oxides, as well as in the complex distribution of PGE, Au, and Ag mineral assemblages. New types of complex Pt and Pd oxides with variable Cu and Fe contents were identified in the altered ores. Pt and Pd oxides as products of replacement of secondary Pt-Pd-Cu-Fe alloys occur as zonal and fibrous nanoscale Pt-Pd-Cu-Fe-(±S)-O aggregates.     

夏塞银多金属矿床中硫化物和硫盐系列矿物特征及其意义

夏塞矿主档是大型的热液脉型银多金属矿床,通过对大量矿石光（薄）片观察和电子探针分析表明,除主要（方铅矿、富铁闪锌矿）和次要（黄铁矿、毒砂、磁黄铁矿、黄铜矿等）硫化物外,硫盐毓硫物十分发育,主要有Ｃｕ－Ｓｂ－Ａｇ硫盐（黝铜矿、含银黝铜矿和银黝铜矿）、Ｓｂ－Ａｇ硫盐（深红银矿、辉锑银矿）、Ｐｂ－Ｓｂ硫盐（脆硫锑铅矿、硫锑铅矿）和Ｂｉ－Ｐｂ硫盐（斜方辉饿铅矿）。此外,尚有少（微）量黄锡矿、锡石、自然饿和银金矿等。银的硫盐硫物和硫化物（辉银矿）乃是获得银的主要工业矿物,这些硫盐毓矿物常与硫化物伴生,多沿方铅矿、富铁闪锌矿、黄铁矿等的解理、裂隙或粒间产出,这些研究结果不仅有助于了解矿化作用过程,而且为矿床评价,组分综合利用和选冶提供重要依据。     

Sudbury Breccia (Canada): a product of the 1850 Ma Sudbury Event and host to footwall Cu–Ni–PGE deposits

The Sudbury Structure, formed by meteorite impact at 1850 Ma, consists of three major components: (1) the Sudbury Basin; (2) the Sudbury Igneous Complex, which surrounds the basin as an elliptical collar; and (3) breccia bodies in the footwall known as Sudbury Breccia. In general, the breccia consists of subrounded fragments set in a dark, fine-grained to aphanitic matrix. A comparison of the chemical composition of host rocks, clasts and matrices indicates that brecciation was essentially an in-situ process. Sudbury Breccia forms irregular-shaped bodies or dikes that range in size from mm to km scale. Contacts with the host rocks are commonly sharp. The aspect ratio of most clasts is approximately 2 with the long axes parallel to dike walls. The fractal dimension (Dr)=1.55. Although there appears to be some concentration of brecciation within concentric zones, small Sudbury Breccia bodies within and outside these zones have more or less random strikes and steep dips. Sudbury Breccia bodies near an embayment structure tend to be subparallel to the base of the Sudbury Igneous Complex. Sudbury Breccia occurs as much as 80 km from the outer margin of the Sudbury Igneous Complex. In an inner zone, 5 to 15 km wide, breccia comprises 5% of exposed bedrock with an increase in brecciation intensity in embayment structures. Sudbury Breccia may be classified into three types based on the nature of the matrix: clastic, pseudotachylite and microcrystalline. Clastic Sudbury Breccia, the dominant type in the Southern Province, is characterized by flow-surface structures. Possibly, a sudden rise in pore pressure caused explosive dilation and fragmentation, followed by fluidization and flowage into extension fractures. Pseudotachylite Sudbury Breccia, mainly confined to Archean rocks, apparently formed by comminution and frictional melting. Microcrystalline Sudbury Breccia formed as a result of the thermal metamorphism, of the North Range footwall, by the Sudbury Igneous Complex. This produced a zone, approximately 1.2 km wide, wherein the matrix of the breccia either recrystallized or, locally, melted. An overprint of regional metamorphism obliterated contact effects in the South Range footwall. The Ni–Cu–PGE magmatic sulphide deposits may be classified into four types based on structural setting: Sudbury Igneous Complex–footwall contact, footwall, offset, and sheared deposits. Sudbury Breccia is the main host for footwall deposits (e.g., McCreedy East, Victor, Lindsley). Sudbury Breccia locally hosts mineralization in radial (e.g., Parkin and Copper Cliff) and concentric (e.g., Frood–Stobie) offset dikes.