Insights into the extreme PGE enrichment of the W Horizon,Marathon Cu-Pd deposit,Coldwell Alkaline Complex,Canada: Platinum-group mineralogy,compositions and genetic implications

The W Horizon, Marathon Cu-Pd deposit in the Mesoproterozoic Midcontinent rift is one of the highest grade PGE repositories in magmatic ore deposits world-wide. The textural relationships and compositions of diverse platinum-group mineral (PGM) and sulfide assemblages in the extremely enriched ores (>100 ppm Pd-Pt-Au over 2 m) of the W Horizon have been investigated in mineral concentrates with ∼10,000 PGM grains and in situ using scanning electron microprobe and microprobe analyses.Here we show, from ore samples with concentrations up to 23.1 Pd ppm, 8.9 Pt ppm, 1.4 Au ppm and 0.73 Rh ppm, the diversity of minerals (n = 52) including several significant unknown minerals and three new mineral species marathonite (Pd₂₅Ge₉; McDonald et al., 2016), palladogermanide (Pd₂Ge; IMA 2016-086, McDonald et al., 2017), kravtsovite (PdAg₂S, IMA No 2016-092, Vymazalová et al., 2017). The PGM are distributed as PG-, sulfides (52 vol%), -arsenides (34 vol%), -intermetallics of Au-Ag-Pd-Cu and Pd-Ge(10 vol%) and -bismuthides and tellurides (4 vol%). The discovery of abundant (>330 grains) large unknown sulfide minerals with Rh allows us to present analyses three significant potentially new minerals (WUK-1, WUK-2, WUK-3) that are all clearly enriched in Rh (averaging 4.2, 8.5 and 28.21 wt% Rh respectively). Several examples of paragenetic sequences and mineral chemical changes for enrichment of Cu, Pd and Rh with time are revealed in the PGM and base-metal sulfides. We suggest this enhanced metal enrichment formed in response to increasing fO₂ causing the oxidation of Fe²⁺ to Fe³⁺ and to a lesser extent, S.Phase relations in the Ag-Pd-S, Rh-Ni-Fe-S, Pd-Ge, Au-Pd-Cu-Ag, Pd-Ag-Te systems help constrain the crystallization temperatures of the majority of ore minerals in the W Horizon at ∼500 °C or moderate to high subsolidus temperatures (400–600 °C). Local transport by aqueous fluids becomes evident as minerals recrystallize down to <300 °C. The PGE-enriched W Horizon ores exhibit a complex post-magmatic history dominated by the effects of oxidation during cooling of a Cu-PGE enriched magma source from a deep reservoir.     

锍镍试金富集—等离子质谱法测定地质样品中的金铂钯铑铱钌

建立了锍镍试金富集—电感耦合等离子质谱法测定地质样品中金铂钯铑铱钌的方法。研究了富集时各种实验因素的影响,样品用琉试金富集,盐酸处理锍镍扣,碲共沉淀富集,过滤,沉淀用王水溶解,ICP-M S测定。方法检出限:A u为0.11、P t为0.050、Pd为0.028、R h为0.018、Ir为0.013、R u为0.02,相对标准偏差(n=12),A u为8.25%、P t为4.76%、P t为4.97%、R h为5.63%、Ir为5.38%、R u为6.81%。经国家一级地球化学标准物质验证,铂族元素和金的测定值与标准质相吻合。     

High Resolution Electrical Resistivity Tomography (ERT) in a Transition Zone Environment: Application for Detailed Internal Architecture and Infilling Processes Study of a Rhône River Paleo-channel

Electrical Resistivity Tomography (ERT) was applied in a sand-infilled paleo-channel located in the Rhône Delta, in Southern France. The detailed pattern and sedimentological evolution of the channel fill deposits – know from both historical and geological sources – made it the ideal site to test the ERT method. A geoelectrical survey was performed, using the ABEM SAS-4000 multi-electrode array system in March 2003. Very low electrical resistivity values were obtained, ranging from 0.3 to 10 Ohm m, consistent with the high salinity measured in situ (the pore water conductivity was found to range from 0.9 to 1.2 S/m at 25 °C). The electrical resistivity profiles reflect mainly salinity variations. Indeed, in this case, salinity is so high that surface conductivity associated with clay minerals can be safely neglected. ERT provided valuable high-resolution information that complemented other exiting data such as historical information, bathymetric, geological, and lithostratigraphic data, which allowed the architecture of the channel to be defined. The ERT was used to determine the infilling dynamics of the Pégoulier Channel, which opens new perspectives in terms of paleoenvironmental reconstruction and paleodynamic studies.     

PGE distribution in massive sulfides from the P<Emphasis Type="SmallCaps">ACMANUS</Emphasis> hydrothermal field,eastern Manus basin,Papua New Guinea: implications for PGE enrichment in some ancient volcanogenic massive sulfide deposits

The distribution of platinum group elements (PGE) in Cu- and Zn-rich samples from the Roman Ruins and Satanic Mills vent sites in the PACMANUS hydrothermal field (Papua New Guinea) was studied and compared to that from selected ancient volcanogenic massive sulfide (VMS) deposits. Samples from the Satanic Mills site are enriched in Pd and Rh when compared to samples from Roman Ruins and reach highest values in active and inactive Cu-rich black smoker chimneys and chalcopyrite-cemented dacite breccias (up to 356 ppb Pd and up to 145 ppb Rh). A significant positive correlation was established between Cu and Pd and Rh in samples from both vent sites. Comparisons of chondrite normalized patterns and values of Pd/Pt and Pd/Ir ratios in Cu-rich sulfides and probable source rocks (felsic volcanic rocks/MORB) along with the evidence for a magmatic component in the PACMANUS hydrothermal system indicate that leaching of back-arc volcanic rocks together with addition of magmatic volatiles to the convecting hydrothermal system was the most important factor for PGE enrichment at PACMANUS and likely at some PGE-enriched ancient VMS deposits.An erratum to this article can be found at Editorial handling: B. Lehmann     

Tracing sediment pathways by zircon fission track analysis: Oligocene marine connections in Central Europe

In this study, we use contrasting zircon fission track age signatures of Alpine detritus and detritus derived from the Variscan realm to trace sediment pathways in Central Europe. Our data show that the Molasse Basin was connected with the Rhine Graben Sea during the Mid-Oligocene, thus joining the North Sea to the Paratethys. Within the Rhine Graben Sea, fairly strong south–north directed currents existed, transporting sand-sized Alpine detritus nearly 300 km towards the north. A connection between the Rhône-Bresse Graben and the Rhine Graben and/or the French Molasse Basin and the Swiss Molasse Basin, by contrast, is not supported by the fission track data. This may be explained by the existence of submarine rises that hampered the transport of sand-sized sediment towards the north/northeast.     

小锍试金－无火焰原子吸收法测定地质样品中超痕量金铂铑钯

将锍试金改成小锍试金，用小锍扣捕集法把分解样品同富集贵金属与分离基体成份结合在一起进行，炼得的锍扣经酸处理除去贱金属硫化物，富集的贵金属采用无火焰原子吸收光谱测定。取一份样可以测定Ａｕ、Ｐｔ、Ｒｈ和Ｐｄ。测定方法的特征质量（ｇ）：Ａｕ１．１×１０￣（－１１），Ｐｔ１．３×１Ｏ￣（－１０），Ｐｄ１．３×１０￣（－１１），Ｒｈ１．２×１０￣（－１１）；线性范围（ｇ／ｍｌ）：Ａｕ０～０．０４０，Ｐｄ和Ｒｈ为０～０．０５０，Ｐｔ为０～０．５０。方法用于超基性岩标样的测定，结果与推荐值相符。